diff options
| -rw-r--r-- | .gitattributes | 3 | ||||
| -rw-r--r-- | 33483-0.txt | 4528 | ||||
| -rw-r--r-- | 33483-0.zip | bin | 0 -> 94695 bytes | |||
| -rw-r--r-- | 33483-8.txt | 4536 | ||||
| -rw-r--r-- | 33483-8.zip | bin | 0 -> 94660 bytes | |||
| -rw-r--r-- | 33483-h.zip | bin | 0 -> 676363 bytes | |||
| -rw-r--r-- | 33483-h/33483-h.htm | 4811 | ||||
| -rw-r--r-- | 33483-h/images/plate1.jpg | bin | 0 -> 65364 bytes | |||
| -rw-r--r-- | 33483-h/images/plate2.jpg | bin | 0 -> 70105 bytes | |||
| -rw-r--r-- | 33483-h/images/plate3.jpg | bin | 0 -> 60065 bytes | |||
| -rw-r--r-- | 33483-h/images/plate4.jpg | bin | 0 -> 35237 bytes | |||
| -rw-r--r-- | 33483-h/images/plate5.jpg | bin | 0 -> 62399 bytes | |||
| -rw-r--r-- | 33483-h/images/plate6.jpg | bin | 0 -> 33889 bytes | |||
| -rw-r--r-- | 33483-h/images/plate7.jpg | bin | 0 -> 32891 bytes | |||
| -rw-r--r-- | 33483-h/images/plate8.jpg | bin | 0 -> 149906 bytes | |||
| -rw-r--r-- | 33483-h/images/plate8_t.jpg | bin | 0 -> 71491 bytes | |||
| -rw-r--r-- | 33483.txt | 4537 | ||||
| -rw-r--r-- | 33483.zip | bin | 0 -> 94572 bytes | |||
| -rw-r--r-- | LICENSE.txt | 11 | ||||
| -rw-r--r-- | README.md | 2 |
20 files changed, 18428 insertions, 0 deletions
diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/33483-0.txt b/33483-0.txt new file mode 100644 index 0000000..2e5a7b9 --- /dev/null +++ b/33483-0.txt @@ -0,0 +1,4528 @@ +Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Eruption of Vesuvius in 1872 + +Author: Luigi Palmieri + +Translator: Robert Mallet + +Release Date: August 22, 2010 [EBook #33483] + +Language: English + +Character set encoding: UTF-8 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + + + + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + + + + + + + + +THE +ERUPTION OF VESUVIUS +IN 1872, + + +BY +PROFESSOR LUIGI PALMIERI, +_Of the University of Naples; Director of the Vesuvian Observatory._ + + +WITH NOTES, AND AN +_INTRODUCTORY SKETCH OF THE PRESENT STATE OF KNOWLEDGE_ +OF +TERRESTRIAL VULCANICITY, +_The Cosmical Nature and Relations of +Volcanoes and Earthquakes._ + + +BY +ROBERT MALLET, +_Mem. Inst. C.E., F.R.S., F.G.S., M.R.I.A., &c., &c._ + + +WITH ILLUSTRATIONS. + + +LONDON: + +_ASHER & CO._, +13, BEDFORD STREET, COVENT GARDEN, W.C. + +1873. + + +W. S. Johnson, Nassau Steam Press, 60, St. Martin's Lane, +Charing Cross, W.C. + + +"The Translator should look upon himself as a Merchant in the +Intellectual Exchange of the world, whose business it is to promote the +interchange of the produce of the mind." + + GŒTHE, "_Kunst und Alterthum_." + + + + +INTRODUCTORY SKETCH, &c. + + +The publishers of this little volume, in requesting me to undertake a +translation of the "Incendio Vesuviano," of Professor Palmieri, and to +accompany it with some introductory remarks, have felt justified by the +facts that Signor Palmieri's position as a physicist, the great +advantages which his long residence in Naples as a Professor of the +University, and for many years past Director of the Meteorological +Observatory--established upon Vesuvius itself, prior to the expulsion of +the late dynasty--have naturally caused much weight to attach to +anything emanating from his pen in reference to that volcano. + +Nearly forty memoirs on various branches of physics--chiefly +electricity, magnetism and meteorology--produced since 1842, are to be +found under Palmieri's name in the "Universal Catalogue of Scientific +Papers of the Royal Society," and of these nine refer to Vesuvius, the +earliest being entitled "Primi Studii Meteorologici fatti sul R. +Osservatorio Vesuviano," published in 1853. He was also author, in +conjunction with Professor A. Scacchi, of an elaborate report upon the +Volcanic Region of Monte Vulture, and on the Earthquake (commonly called +of Melfi) of 1851. These, however, by no means exhaust the stock of +Palmieri's labours. + +The following Memoir of Signor Palmieri on the eruption of Vesuvius in +April of this year (1872), brief as it is, embraces two distinct +subjects, viz., his narrative as an eye-witness of the actual events of +the eruption as they occurred upon the cone and slopes of the mountain, +and his observations as to pulses emanating from its interior, as +indicated by his Seismograph, and as to the electric conditions of the +overhanging cloud of smoke (so called) and ashes, as indicated by his +bifilar electrometer, both established at the Observatory. The two last +have but an indirect bearing upon Vulcanology. The narrative of the +events of the eruption is characterised by exactness of observation and +a sobriety of language--so widely different from the exaggerated style +of sensational writing that is found in almost all such accounts--that I +do the author no more than justice in thus expressing my view of its +merits. + +Nor should a special narration, such as this, become less important or +suffer even in popular estimation by the fact that so recently my +friend, Professor J. Phillips, has given to the world the best general +account of Vesuvius, in its historical and some of its scientific +aspects, which has yet appeared. That monograph--with its sparkling +style, and scholarly digressions, as well as for its more direct +merits--will, no doubt, become the manual for many a future visitor to +the volcanic region of Naples; but it, like the following Memoir of +Palmieri, and in common with almost every work that has appeared on the +subject of Volcanoes, contains a good deal which, however interesting, +and remotely related to Vulcanology, does not properly belong to the +body of that branch of cosmical science, as I understand its nature and +limits. + +It tends but little, for example, to clear our views, or enlarge our +knowledge of the vast mechanism in which the Volcano originates, and +that by which its visible mass is formed, that we should ascertain the +electric condition of the atmosphere above its eruptive cone, or into +what crystallographic classes the mineral species found about it may be +divided: it will help us but little to know Pliny's notions of how +Pompeii was overwhelmed, or to re-engrave pictures, assumed to give the +exact shape of the Vesuvian or other cone at different periods, or its +precise altitude, which are ever varying, above the sea. Even much more +time and labour may be spent upon analysing the vapours and gases of +fumaroles and salfatares than the results can now justify. + +Nothing, perhaps, tends more to the effective progress of any branch of +observational and inductive science, than that we should endeavour to +discern clearly the scope and boundary of our subject. + +To do so is but to accord with Bacon's maxim, "_Prudens questio dimidium +scientiæ_." That once shaped, the roads or methods of approach become +clearer; and every foothold attained upon these direct paths enables us +to look back upon such collateral or subordinate questions as at first +perplexed us, and find them so illuminated that they are already +probably solved, and, by solution, again prove to us that we _are_ in +the right paths. + +I believe, therefore, that I shall not do disservice to the grand +portion of cosmical physics to which volcanic phenomena belong, by +devoting the few pages accorded to me for this Introduction to sketching +what seems to me to be the present position of terrestrial +_Vulcanicity_, and tracing the outlines and relations of the two +branches of scientific investigation--_Vulcanology_ and _Seismology_--by +which its true nature and part in the Cosmos are chiefly to be +ascertained. + +The general term, _Vulcanicity_, properly comprehends all that we see or +know of actions taking place upon and modifying the surface of our +globe, which are referable not to forces of origin above the surface, +and acting superficially, but to causes that have been or are in +operation beneath it. It embraces all that Humboldt has somewhat vaguely +called "the reactions of the interior of a planet upon its exterior." + +These reactions show themselves principally and mainly in the marking +out and configuration of the great continents and ocean beds, in the +forcing up of mountain chains, and in the varied phenomena consequent +thereon, as seen in more or less adjacent formations. + +These constitute the mechanism which has moulded and fashioned the +surface of our globe from the period when it first became superficially +solid, and prepared it as the theatre for the action of all those +superficial actions--such as those of tides, waves, rain, rivers, solar +heat, frost, vitality, vegetable and animal (passing by many others less +obvious)--which perpetually modify, alter or renew the surface of our +world, and maintain the existing regimen of the great machine, and of +its inhabitants. These last are the domain of Geology, properly so +called. No geological system can be well founded, or can completely +explain the working of the world's system as we now see it, that does +not start from Vulcanicity as thus defined; and this is equally true, +whether, as do most geologists, we include within the term Geology +everything we can know about our world as a whole, exclusive of what +Astronomy teaches as to it, dividing Geology in general into Physical +Geology--the boundaries of which are very indistinct--and +Stratigraphical Geology, whose limits are equally so. + +It has been often said that Geology in this widest sense begins where +Astronomy or Cosmogony ends its information as to our globe, but this is +scarcely true. + +Vulcanicity--or Geology, if we choose to make it comprehend that--must +commence its survey of our world as a nebula upon which, for unknown +ages, thermic, gravitant and chemical forces were operative, and to the +final play of which, the form, density and volume, as well as order of +deposition of the different elements in the order of their chemical +combination and deposition was due, when first our globe became a liquid +or partly liquid spheroid, and which have equally determined the +chemical nature of the materials of the outward rind of the earth that +now is, and with these some of the primary conditions that have fixed +the characters, nature and interdependence of the vegetables and animals +that inhabit it. Physical Astronomy and Physical Geology, through +Vulcanicity, thus overlap each other; the first does not end where the +second begins; and in every sure attempt to bring Geology to that +pinnacle which is the proper ideal of its completed design--namely, the +interpretation of our world's machine, as part of the universal Cosmos +(so far as that can ever become known to our limited observation and +intelligence)--we must carry with us astronomic considerations, we must +keep in view events anterior to the "_status consistentior_" of +Leibnitz, nor lose sight of the fact that the chain of causation is one +endless and unbroken; that forces first set moving, we know not when or +how, the dim remoteness of which imagination tries to sound in shadowy +thought, like those of the grand old Eastern poem, "When the morning +stars first sang together," are, however changed in form, operative +still. The light and fragile butterfly, whose glorious garb irradiates +the summer zephyr in which it floats, has had its power of flight--which +is its power to live--determined by results of that same chain of causes +that lifted from the depths the mountain on whose sunny side he floats, +that has determined the seasons and the colour of the flower whose +nectar he sucks, and that discharges or dissipates the storm above, that +may crush the insect and the blossom in which it basked. And thus, as +has been said, it was not all a myth, that in older days affirmed that +in some mysterious way the actions and the lives of men were linked to +the stars in their courses. + +Whatever may have been the manifestations of Vulcanicity at former and +far remoter epochs of our planet, and to which I shall return, in the +existing state of regimen of and upon our globe it shows itself chiefly +in the phenomena of Volcanoes and of Earthquakes, which are the +subjects of Vulcanology and of Seismology respectively, and in principal +part, also, of this Introduction. + +The phenomena of hot springs, geysers, etc., which might be included +under the title of Thermopægology, have certain relations to both, but +more immediately to Vulcanology. + +Let us now glance at the history and progress of knowledge in these two +chief domains of Vulcanicity, preparatory to a sketch of its existing +stage as to both, and, by the way, attempt to extract a lesson as to the +methods by which such success as has attended our labours has been +achieved. + +It will be most convenient to treat of Seismology first in order. + +Aristotle--who devotes a larger space of his Fourth Book, Περἱ Κοσμου, +to Earthquakes--Seneca, Pliny, Strabo, in the so-called classic days, +and thence no end of writers down to about the end of the seventeenth +century--amongst whom Fromondi (1527) and Travagini (1679) are, perhaps, +the most important now--have filled volumes with records of facts, or +what they took to be such, of Earthquakes, as handed down to or observed +by themselves, and with plenty of hypotheses as to their nature and +origin, but sterile of much real knowledge. + +Hooke's "Discourses of Earthquakes," read before the Royal Society about +1690, afford a curious example of how abuse of words once given by +authority clings as a hindrance to progress. He had formed no distinct +idea of what he meant by an Earthquake, and so confusedly mixes up all +elevations or depressions of a permanent character with "subversions, +conversions and transpositions of parts of the earth," however sudden or +transitory, under the name of Earthquakes. + +A like confusion is far from uncommon amongst geological writers, even +at the present day, and examples might be quoted from very late writings +of even some of the great leaders of English Geology. + +From the seventeenth to the middle of the eighteenth century one finds +floods of hypotheses from Flamsteed, Höttinger, Amontons, Stukeley, +Beccaria, Percival, Priestly, and a crowd of others, in which +electricity, then attracting so much attention, is often called upon to +supply causation for a something of which no clear idea had been formed. +Count Bylandt's singular work, published in 1835, though showing a +curious _partial_ insight in point of advancement, might be put back +into that preceding period. + +In 1760 appeared the very remarkable Paper, in the fifty-first volume of +the "Philosophical Transactions," of the Rev. John Mitchell, of +Cambridge, in which he views an Earthquake as a sudden lifting up, by a +rapid evolution of steam or gas beneath, of a portion of the earth's +crust, and the lateral transfer of this gaseous bubble beneath the +earth's crust, bent to follow its shape and motion, or that of a wave of +liquid rock beneath, like a carpet shaken on air. Great as are certain +collateral merits of Mitchell's Paper, showing observation of various +sorts much in advance of his time, this notion of an Earthquake is such +as, had he applied to it even the imperfect knowledge of mechanics and +physics then possessed in a definite manner, he could scarcely have +failed to see its untenable nature. That the same notion, and in a far +more extravagant form, should have been reproduced in 1843 by Messrs. +Rogers, by whom the gigantic parallel anticlinals, flanks and valleys of +the whole Appalachian chain of mountains are taken for nothing more than +the indurated foldings and wrinkles of Mitchell's carpet, is one of the +most salient examples of the abuse of hypothesis untested by exact +science. + +Neither Humboldt nor Darwin, great as were the opportunities of +observation enjoyed by both, can be supposed to have formed any definite +idea of _what_ an Earthquake is; and the latter, who had observed well +the effects of great sea-waves rolling in-shore after the shock, did not +establish any clear relation between the two.[A] + +Hitherto no one appears to have formed any clear notion as to what an +Earthquake is--that is to say, any clear idea of what is the nature of +the movement constituting the shock, no matter what may be the nature or +origin of the movement itself. The first glimmering of such an idea, so +far as my reading has enabled me to ascertain, is due to the penetrating +genius of Dr. Thomas Young, who, in his "Lectures on Natural +Philosophy," published in 1807, casually suggests the probability that +earthquake motions are vibratory, and are analogous to those of +sound.[B] This was rendered somewhat more definite by Gay Lussac, who, +in an able paper "On the Chemical Theories of Volcanoes," in the +twenty-second volume of the "Annales de Chémie," in 1823, says: "En un +mot, les tremblements de terre ne sont que la propagation d'une +commotion à travers la masse de la terre, tellement indépendante des +cavités souterraines qu'elle s'entendrait, d'autant plus loin que la +terre serait plus homogène." + +These suggestions of Young and of Gay Lussac, as may be seen, only refer +to the movement in the more or less solid crust of the earth. But two, +if not three, other great movements were long known to frequently +accompany earthquake shocks--the recession of the sea from the shore +just about the moment of shock--the terrible sounds or subterraneous +growlings which sometimes preceded, sometimes accompanied, and sometimes +followed the shock--and the great sea-wave which rolls in-shore more or +less long after it, remained still unknown as to their nature. They had +been recognised only as concomitant but unconnected phenomena--the more +inexplicable, because sometimes present, sometimes absent, and wholly +without any known mutual bearing or community of cause. + +On the 9th February, 1846, I communicated to the Royal Irish Academy my +Paper, "On the Dynamics of Earthquakes," printed in Vol. XXI., Part I., +of the Transactions of that Academy, and published the same year in +which it was my good fortune to have been able to colligate the observed +facts, and bringing them together under the light of the known laws of +production and propagation of vibratory waves in elastic, solid, liquid +and gaseous bodies, and of the production and propagation of liquid +waves of translation in water varying in depth, to prove that all the +phenomena of earthquake shocks could be accounted for by a single +impulse given at a single centre. The definition given by me in that +Paper is that an earthquake is "_The transit of a wave or waves of +elastic compression in any direction, from vertically upwards to +horizontally, in any azimuth, through the crust and surface of the +earth, from any centre of impulse or from more than one, and which may +be attended with sound and tidal waves dependent upon the impulse and +upon circumstances of position as to sea and land_." + +Thus, for example, if the impulse (whatever may be its cause) be +delivered somewhere beneath the bed of the sea, all four classes of +earthquake waves may reach an observer on shore in succession. The +elastic wave of shock passing through the earth _generally_ reaches him +first: its velocity of propagation depending upon the specific +elasticity and the degree of continuity of the rocky or the incoherent +formations or materials through which it passes. + +Under conditions pointed out by me, this elastic wave may cause an +aqueous wave, producing recession of the sea, just as it reaches the +margin of sea and land. + +If the impulse be attended by fractures of the earth's crust, or other +sufficient causes for the impulse to be communicated to the air directly +or through the intervening sea, ordinary sound-waves will reach the +observer through the air, propagated at the rate of 1,140 feet per +second, or thereabouts; and may also reach him before or with or soon +after the shock itself, through the solid material of the earth; and +lastly, if the impulse be sufficient to disturb the sea-bottom above the +centre of impulse, or otherwise to generate an aqueous wave of +translation, that reaches the observer last, rolling in-shore as the +terrible "great sea-wave," which has ended so many of the great +earthquakes, its dimensions and its rate of propagation depending upon +the magnitude of the originating impulse and upon the variable depth of +the water. It is not my purpose, nor would it be possible within my +limits here, to give any complete account of the matter contained in +that Paper, which, in the words of the President of the Academy upon a +later occasion, "fixed upon an immutable basis the true theory of +Earthquakes."[C] I should state, however, that in it I proved the +fallacy of the notion of vorticose shocks, which had been held from the +days of Aristotle, and showed that the effects (such as the twisting on +their bases of the Calabrian Obelisks) which had been supposed due to +such, were but resolved motions, due to the transit rectilinearly of the +shock. + +This removed one apparent stumbling block to the true theory. + +Incidentally also it was shown that from the observed elements of the +movement of the elastic wave of shock at certain points--by suitable +instruments--the position and depth of the _focus_, or centre of +impulse, might be inferred. + +In the same volume ("Transactions of the Royal I. Academy," XXI.) I gave +account, with a design to scale, for the first self-registering and +recording seismometer ever, to my knowledge, proposed. In some respects +in principle it resembles that of Professor Palmieri, of which he has +made such extended use at the Vesuvian Observatory, though it differs +much from the latter in detail. In June, 1847, Mr. Hopkins, of +Cambridge, read his Report, "On the Geological Theories of Elevation and +Earthquakes," to the British Association--requested by that body the +year before--and printed in its Reports for that year. + +The chief features of this document are a digest of Mr. Hopkins's +previously published "Mathematical Papers" on the formations of +fissures, etc., by elevations and depressions, and those on the +thickness of the earth's crust, based on precession, etc., which he +discusses in some relations to volcanic action. + +This extends to forty-one pages, the remaining eighteen pages of the +Report being devoted to "Vibratory Motions of the Earth's Crust produced +by Subterranean Forces--Earthquakes." + +The latter consists mainly of a _résumé_ of the acknowledged laws, as +delivered principally by Poisson, of formation and propagation of +elastic waves and of liquid waves, by Webers, S. Russel and others--the +original matter in this Report is small--and as respects the latter +portion consists mainly in some problems for finding analytically the +position or depth of the centre of disturbance when certain elements of +the wave of shock are given, or have been supposed registered by +seismometric instruments, such as that described by myself, and above +referred to.[D] At the time my original Paper "On the Dynamics of +Earthquakes" was published, there was little or no _experimental_ +knowledge as to the actual velocity of transit of waves--analogous to +those of sound, but of greater amplitude--through elastic solids. The +velocity as deduced from theory, the solid being assumed quite +_homogeneous_ and _continuous_, was very great, and might be taken for +some of the harder and denser rock formations at 11,000 or 12,000 feet +per second. That these enormous velocities of wave transit would be +something near those of actual earthquake shock seemed probable to me, +and was so accepted by Hopkins. + +Thus, he says (Report, p. 88): "The velocity of the sea-wave, for any +probable depth of the sea, will be so small as compared with that of the +vibratory wave, that we may consider the time of the arrival of the +latter at the place of observation as coincident with that of the +departure of the sea-wave from the centre of divergence." + +In my original Paper (Dynamic, &c.), I had suggested, as an important +object, to ascertain by actual experiment what might be the wave's +transit rate in various rocky and incoherent formations; and having +proposed this in my first "Report upon the Facts of Earthquake" to the +British Association, I was enabled by its liberality to commence those +experiments, in which I was ably assisted by my eldest son, then quite a +lad--Dr. Jno. William Mallet, now Professor of Chemistry at the +University of Virginia, U.S.; and to give account of the results, in my +second Report ("Report, British Association for 1851") to that body. + +Those experiments were made by producing an impulse at one end of an +accurately measured base line, by the explosion of gunpowder in the +formation experimented upon, and noting the time the elastic wave +generated required to pass over that distance, upon a nearly level +surface. Special instruments were devised and employed, by which the +powder was fired and the time registered, by touching a lever which +completed certain galvanic contacts. The media or formations in which +these experiments were conducted were, damp sand--as likely to give the +minimum rate--and crystalline rock (granite), as likely to give the +maximum. The results were received, not with doubt, but with much +surprise, for it at once appeared that the actual velocity of transit +was vastly below what theory had indicated as derivable from the density +and modulus of elasticity of the material, taken as homogeneous, etc. +The actual velocities in feet per second found were: + + In sand 824·915 feet per second. + In discontinuous and + much shattered granite 1,306·425 " " + In more solid granite 1,664·574 " " + +This I at once attributed, and as it has since been proved correctly, to +the loss of _vis viva_, and consequently of speed, by the _discontinuity +of the materials_. + +And some indication of the general truth of the fact was derivable from +comparing the rude previous approximations to the transit rate of some +great Earthquakes. In the case of that of Lisbon, estimated by Mitchell +at 1,760 feet per second. It was still desirable to extend similar +experiments to the harder classes of stratified and of contorted rocks. +This I was enabled to carry into effect, at the great Quarries at +Holyhead (whence the slate and quartz rocks have been obtained for the +construction of the Asylum Harbour there), taking advantage of the +impulses generated at that period by the great mines of powder exploded +in these rocks. + +The results have been published in the "Philosophical Transactions for +1861 and 1862 (Appendix)." They show that the mean lowest rate of wave +transit in those rocks, through measured ranges of from 5,038 to 6,582 +feet, was 1,089 feet per second; and the mean highest, 1,352 feet per +second; and the general mean 1,320 feet per second. + +By a separate train of experiments on the compressibility of solid cubes +of these rocks, I obtained the mean modulus of elasticity of the +material when perfectly continuous and unshattered, with this +remarkable result--that in these rocks, as they exist at Holyhead, +_nearly seven-eighths of the full velocity of wave transmission due to +the material, if solid and continuous, is lost by reason of the +heterogeneity and discontinuity_ of the rocky masses as they are found +piled together in Nature. + +I also proved that the wave-transit period of the unshattered material +of these rocks was greatest in a direction _transverse_ to the bedding, +and least in line parallel with that; but the effect of this in the +rocky mass itself may be _more_ than counterbalanced by the +discontinuity and imperfect contact of the adjacent beds. + +These results indicate, therefore, that the superficial rate of +translation of the solitary sea-wave of earthquakes may, when over very +deep water, equal or even exceed the transit rate (in some cases) of the +elastic wave of shock itself. + +These results have since received general confirmation by the careful +determinations of the transit rates of actual earthquake waves, in the +rocks of the Rhine Country and in Hungary, by Nöggerath and Schmidt +respectively, and by those made since by myself in those of Southern +Italy, to which I shall again refer. In an elastic wave propagated from +a centre of impulse in an infinitely extended volume of a perfect gas, +normal vibrations are alone propagated--as is the case with sound in +air. + +In the case of like movements propagated in elastic and perfectly +homogeneous and isotropic solids, the wave possesses both normal and +transversal vibrations, and is, in so far, analogous to the case of +light. Mr. Hopkins, in his Report above referred to, has based certain +speculations upon the assumed necessary co-existence of both orders of +vibration in actual earthquake shocks in the materials of which our +earthy crust is actually composed. + +The existence of transversal vibration in those materials has not been +yet proved experimentally, though there is sufficient ground to preclude +our denying their probable existence. + +That if they do exist they play but a very subordinate part in the +observable phenomena of actual Earthquake is highly probable. This is +the view, supported not only by observations of the effects of such +shocks in Nature, but by the theoretic consideration of the effects of +discontinuity of formations in planes or beds more or less transverse to +the wave path (or line joining the centre of impulse with the mean +centre of wave disturbance at any point of its transit). If we suppose, +for illustration sake, such an elastic wave transmitted perpendicularly +through a mass of glass plates, each indefinitely thin, and all in +absolute contact with each other, but without adhesion or friction, more +or less of the transversal vibration of the wave would be cut off and +lost at each transit from plate to plate, as the elastic compression +can, by the conditions, be transmitted only normally or by direct push +perpendicularly from plate to plate. This must take place in Nature, and +to a very great extent, and the consideration, with others, enabled me +generally to apply the normal wave motion of shock alone to my +investigation as to the depth of the centre of impulse of the great +Neapolitan Earthquake of 1857, an account of which was published in +1862, and to be presently further referred to. + +Hitherto the multitudinous facts, or supposed facts, recorded in +numberless accounts of Earthquakes had remained almost wholly +unclassified, and so far as they had been discussed--in a very partial +manner, as incidental portions of geological treatises--with little +attempt to sift the fabulous from the real, or to connect the phenomena +admitted by reference to any general mechanical or physical causes. In +1850 my first "Report upon the Facts of Earthquakes," called for by the +British Association in 1847, was read and published in the Reports of +that body for that year. In this, for the first time, the many recorded +phenomena of Earthquakes are classified, and the important division of +the phenomena into primary and secondary effects of the shock was +established. Several facts or phenomena, previously held as marvellous +or inexplicable, were either, on sufficient grounds, rejected, or were, +for the first time, shown susceptible of explanation. Amongst the more +noticeable results were the pointing out that fissures and fractures of +rock or of incoherent formations were but secondary effects, and, in the +latter, were, in fact, generally of the nature of inceptive landslips. +This last was not accepted, I believe, by geologists at the time; but +the correctness of the views then propounded as to earth fissures--the +nature of the spouting from them of water or mud--the appearances taken +for smoke issuing from them, etc.--have since been fully confirmed, +first, by my own observations upon the effects of the Great Neapolitan +Earthquake of 1857, and more lately by those of Dr. Oldham upon the +Earthquake of Cachar (India), where he was enabled to observe fissures +of immense magnitude, the nature of the production of which he has well +described and explained in the "Proceedings, Geological Society, London, +1872." + +The relations between meteorological phenomena proper and Earthquakes +have always been a subject of popular belief and superstition. + +This was here carefully discussed, and with the result of disproving any +connection, or, if any, but of an indirect nature. I also, to some +extent, towards the end of this Report, discussed the question of the +possible nature of the _impulse itself_ which originates the shock; I +showed that it must be of the nature of a blow, and ventured to offer +_conjecturally_ five possible causes of the impulse: + + 1. Sudden fractures of rock, resulting from the steady and slow + increase of elevatory pressure. + + 2. Sudden evolution (under special conditions) of steam. + + 3. Sudden condensation of steam, also under special conditions. + + 4. Sudden dislocations in the rocky crust of the earth, through + pressure acting in any direction. + + 5. Occasionally through the recoil due to explosive effects at + volcanic foci (p. 79-80). + +The first and last of these I am, through subsequent light, disposed now +to withdraw or greatly to modify. + +The first, the supposed "_snap and jar_, occasioned by the sudden and +violent rupture of solid rock masses," to which Mr. Scrope, in his very +admirable work on Volcanoes, is disposed to refer the impulse of +earthquake shocks (Scrope, 2nd edit., p. 294), I believe may be proved +on acknowledged physical principles--when applied to the known +elasticities and extensibilities of rocks, and keeping in view the small +thicknesses fractured _at the same instant_--to be capable of only the +most insignificant impulsive effects; and if we also take into +consideration that strata, if so fractured, are necessarily not _free_, +but surrounded by others above and below, any such impulsive effect +emanating from fracture may be held as non-existent or impossible. In +the statement of his views which follows, and in objecting to my second +and third possible causes (p. 295-296, headed "Objections to Mallet's +Theory"), Mr. Scrope appears to me to have fallen into the error of +assuming that the nature of the _impulse_, or the cause producing it, +forms any part of "my theory of earthquake movement," or in anywise +affects it. I carefully guarded against this in the original Paper +("Transactions, Royal Irish Academy," Vol. XXI., p. 60, and again, p. +97), when I stated "it is quite immaterial to the truth of my theory of +earthquake motion what view be adopted, or what mechanism be assigned, +to account for the original impulse." + +As regards the fifth conjecture suggested by me, I am now, with better +knowledge and larger observation of volcanic phenomena, not prepared to +admit any single explosion at volcanic vents of a magnitude sufficient +to produce by its recoil an earthquake wave of any importance, or +extending to any great distance in the earth's crust. The rock of 200 +tons weight, said to have been projected nine miles from the crater of +Cotopaxi, which I quoted from Humboldt as an example,[E] I believe to be +as purely mythical as the rock (_bloc rejetté_) of perhaps one-sixth of +that weight which, previous to the late eruption, lay in the middle of +the Atria dell Cavallo, and which it was roundly affirmed had been +_blown_ out of the crater, but which in reality had at some time rolled +down from near the top of the cone, after having been dislodged from +some part of the upper lip of the crater walls, where, as its wonderful +hardness and texture and its enamel-like surface showed, it had been +roasted for years probably. + +Nor do I believe in the _sudden_ blowing away of one-half the crater and +cone of Vesuvius, or of any other volcano, at one effort, however +affirmed. + +Nothing more than conjecture as to the nature of the impulse producing +great or small Earthquakes can, I believe, as yet be produced. That +there is some one master mechanism productive of most of the impulses of +great shocks is highly probable, but that more causes than one may +produce these impulses, and that the causes operative in small and long +repeated shocks, like those of Visp-Comrie and East Haddam, differ much +from those producing great Earthquakes, is almost certain. + +We shall be better prepared to assign all of these when we have admitted +a true theory of volcanic action, and so are better able to see the +intimate relations in mechanism between seismic and volcanic actions. + +It is not difficult meanwhile to assign the very probable mechanism of +those comparatively petty repercussions which are experienced in close +proximity to volcanic vents when in eruption, and which, though +certainly seismic in their nature, and powerful enough, as upon the +flanks of Etna, to crack and fissure well-built church-towers, can +scarcely be termed Earthquakes. + +In my First Report I stated that almost nothing was known then of the +distribution of recorded Earthquakes in time or in space over our +globe's surface, and I proposed the formation and discussion of a +complete catalogue of all recorded Earthquakes, with this in view. + +This was approved by the Council of the British Association and at once +undertaken by me, with the zealous and efficient co-operation of my +eldest son, Dr. J. W. Mallet. Nearly the whole of the Second British +Association Report, of 1851, is occupied with the account of the +experiments as to the transit rate of artificially made shocks in sand +and granite, as already referred to. + +The Third Report, of 1852-1854, contains the whole of this, "The +Earthquake Catalogue of the British Association" (of which, through the +liberality of that body, more than one hundred copies were distributed +freely), in which are given, in columnar form, the following +particulars, from the earliest known dates to the end of 1842: + + 1. The date and time of day, as nearly as recorded. + + 2. The locality or place of occurrence. + + 3. The direction, duration, and number of shocks so far + recorded. + + 4. Phenomena connected with the sea--great sea-waves, tides, + etc. + + 5. Phenomena connected with the land--meteorological phenomena + preceding and succeeding. Secondary phenomena--all minor or + remarkable phenomena recorded. + + 6. The authority for the record. + +Though most materially assisted by the previous labours and partial +catalogues of Von Hoff, Cotte, Hoffman, Merrian, and, above all, of +Perrey, the preparation of this catalogue--which demanded visits to the +chief libraries of Europe, and the collating of some thousands of +authors in various languages and of all time--was a work of great and +sustained labour, which, except for my dear son's help, I should never +have found time and power to complete. Professor Perrey, formerly of the +Faculté des Sciences of Dijon, now _en retrait_, who has devoted a long +and useful life to assiduous labours in connection with Seismology, was +our great ally; and his catalogues are so large and complete for most +known parts of the world after 1842, that we were able to arrest our own +catalogue at that date, and take M. Perrey's as their continuation up to +1850. + +The whole British Association Catalogue thus embraces the long historic +period of from 1606 B.C. of vulgar chronology, when the first known +Earthquake is recorded, to A.D. 1850; and the base of induction which it +presents as to the facts recorded extends to between 6,000 and 7,000 +separate Earthquakes. My Fourth Report ("Reports, British Association, +1858,") is occupied principally with the discussion of this great +catalogue, and with that of several special catalogues produced by other +authors with limited areas or objects. + +The discussion of M. Perrey's local catalogues with those of others, in +reference to a supposed prevalent apparent horizontal direction of shock +in certain regions--as to distribution, as to season, months, time of +day or night, relation to state of tide--the bearings of the views of +Zantedeschi and others as to the probable existence of a terrane +tide--the supposed relations of the occurrence of Earthquakes upon the +age of the moon, as deduced by Perrey, viz.: that 1st, Earthquakes occur +most frequently at the syzygies; 2nd, that their frequency increases at +the perigee and diminishes at the apogee; 3rd, that they are more +frequent when the moon is on the meridian than when she is 90° away from +it--and the views of several authorities as to the distribution of +Earthquakes in time and in space--occupy the first 46 pages of this +Report. + +It then proceeds to discuss the distribution in time and in space as +deduced from the full base of the great catalogue. + +The results as to time are reduced to curves, and those as to space (or +distribution over our globe's surface) to the great seismic map +(Mercator's projection), upon which and in accordance with certain +principles and conventional laws, which admit of the indication of both +intensity and frequency, all recorded Earthquakes have been so laid down +as to present a real indication of the distribution of seismic energy +for the whole historic period and all over the world. + +The original of this map, which also shows the Volcano (size, about 7 +feet by 5 feet), remains for reference in the custody of the Royal +Society. A reduced copy was published with the Report, and to a still +more reduced scale has been reproduced in other places. It is impossible +here to do more than refer to a few of the more salient points. + +As regards distribution in time, durational seismic energy may be +considered as probably constant during historic time, though it is +probably a decaying energy viewed in reference to much longer periods. +It does not appear of the nature of a distinctly periodic force. + + 1. Whilst the minimum paroxysmal interval may be a year or two, + the average interval is from five to ten years of comparative + repose. + + 2. The shorter intervals are in connection with periods of + fewer Earthquakes, not always with those of least intensity, + but usually so. + + 3. The alternations of paroxysm and of repose appear to follow + no absolute law deducible from these causes. + + 4. Two marked periods of extreme paroxysm are observable in + each century (for the last three centuries), one greater than + the other--that of greatest number and intensity occurring + about the middle of each century, and the other towards the end + of each. + +As respects season, there appear distinct indications of a maximum about +the winter solstice, and equally so of a minimum rather before the +autumnal equinox. It is not improbable that there is a remote relation +between Earthquakes and the annual march of barometric pressure. + +We may expect, at present, one great Earthquake about every eight +months, and were we possessed of a sufficient report from all parts of +our globe, we should probably find scarcely a day pass without a very +sensible Earthquake occurring somewhere, whilst, as regards still +smaller tremors, it might almost be said that our globe, as a whole, is +scarcely ever free from them. + +As respects the distribution of seismic energy in space of our earth's +surface, it is that of bands of variable and of great breadth, with +sensible seismic influence extending to from 5° to 15° transversely, +which very generally follow: + + 1. The lines of elevated tracts which mark and divide the great + oceanic or terra-oceanic basins (or _saucers_, as I have called + them, from their shallowness in relation to surface, in this + discussion) of the earth's surface. + + 2. And in so far as these are frequently the lines of mountain + chains, and these latter those of volcanic vents, so the + seismic bands are found to follow these likewise. Isolated + Volcanoes are found in these bands also. + + 3. While sensible seismic influence is generally limited to + the average width of the band, paroxysmal efforts are + occasionally propagated to great distances transversely beyond + that. + + 4. The sensible width of the band depends upon the energy + developed at each point of the length, and upon the accidental + geologic and topographic conditions along the same. + + 5. Seismic energy _may_ become sensible at any point of the + earth's surface, its efforts being, however, greater and more + frequent as the great lines of elevation and of volcanic + activity are approached; yet not in the inverse ratio of + distance, for many of the most frequently and terribly shaken + regions of the earth, as the east shore of the Adriatic, Syria, + Asia Minor, Northern India, etc., are at great distances from + active Volcanoes. + + 6. The surfaces of minimum or of no known disturbance are the + central areas of great oceanic or of terra-oceanic basins or + saucers, and the greater islands existing in shallow seas. + +Space obliges me to pass unnoticed here many minor but not unimportant +deductions. The discussions as to distribution in time and space occupy +seventy-two pages of this fourth and last Report, the remainder of which +(thirty-one pages) embraces the description and mathematical discussion +as to seismometers, to which I may refer, as comprising the most +complete account of these instruments that has, I believe, been anywhere +given. + +The appendix to the Report comprises the entire bibliography of +Earthquakes collected during those researches, and a concluding chapter +on desiderata, and inquiries as to ill-understood phenomena supposed to +be connected with Earthquakes. + + * * * * * + +In 1849-50, I was honoured by the request to draw up the article +"Earthquake Phenomena," which has appeared in the first and subsequent +editions of the "Admiralty Manual of Scientific Inquiry." Originally the +subject was intended to have formed part of the article on Geology, +entrusted to Mr. Darwin, who consulted me upon the subject; and upon my +representing how much Earthquakes had, within a short time, become +matter for the mathematician and physicist, he, with a singleness of eye +to science which it is but just to place on record, took the necessary +steps with the Admiralty authorities that Earthquakes should form a +separate article, and advised its being placed, as it was, in my hands. +To record this will, I believe, be sufficient justification for my +reference to this article, in which a good deal of information as to +Seismometry is to be found. + + * * * * * + +By recurring to Mr. Hopkins's Report on Earthquake Theory, before +remarked upon ("Report of British Association, 1847"), it will be seen +that the solutions of the problems which he there gives for finding the +depth of focus of shock are founded upon the _velocity of propagation_ +of the wave in the interior of the mass, the _apparent horizontal +velocity_ and the _horizontal direction of propagation_ at any proposed +point being known (p. 82). + +By this it appears plainly that at that time Mr. Hopkins supposed that +it was the _velocity of translation_ of the wave of shock that did the +mischief, and not the _velocity of the wave particle_, or wave itself. +And, further, that the former might be obtained by reference simply to +the modulus of elasticity of the rock of any given formation, as, +indeed, was my own earliest view when I produced my "Dynamics of +Earthquake" in 1846. From the remarks already made as to the vast +difference between the actual transit velocity in more or less +discontinuous rocks--such as they occur in Nature--it will be equally +obvious that Mr. Hopkins's methods, as above mentioned, are +impracticable, even were there no confusion between the velocity of +translation of the wave and that of the wave particle or wave itself. + +This applies also to the demonstration and diagram (taken from Hopkins) +given by Professor Phillips ("Vesuvius," pp. 258-259). + +In December, 1857, occurred the great Neapolitan Earthquake, which +desolated a large portion of that kingdom; and an opportunity then arose +for practically applying to the problems of finding the directions of +earthquake shock at a given point through which it has passed, and +ultimately the position and depth of focus, other methods, which I had +seen, from soon after the date of publication of my original Paper +(1846), were easily practicable, and the details of which I had +gradually matured. + +Bearing in mind that, in the case of the normal vibration in any elastic +solid of indefinite dimensions, the direction of motion in space of the +_wave particle_ coincides in the first semiphase of the wave, and at the +instant of its _maximum velocity_ with the right line joining the +particle and the focus or centre of disturbance, it follows that, in the +case of earthquakes, the normal vibration of the wave of shock is always +in a vertical plane passing through the focus and any point on the +earth's surface through which the shock passes (assuming for the present +no disturbing causes after the impulse has been given), and that at such +a point the movement of the wave particle in the first semiphase of the +wave is in the same direction or sense as that of translation; and at +the moment of maximum velocity the direction in space of the motion of +the wave particle is that of the right line joining the point through +which the wave has passed with the focus or centre of impulse. + +If, therefore, we can determine the direction of motion of the wave +particle in the first semiphase, and its maximum velocity, we can +obtain, from any selected point, a line (that of emergence of the shock) +_somewhere in which_, if prolonged beneath the earth, the focus must +have been; and if we can obtain like results for two or more selected +points, we decide the position and the depth of the focus, which must be +in the intersection of the several lines of direction of the wave +particle motion at each point, when prolonged downwards. + +Now, as I have said, it is the _vibration of the wave itself_, _i.e._, +the motion of the wave particle that does the mischief--_not_ the +transit of the wave from place to place on the surface; just as in the +analogous (but _not_ similar) case of a tidal wave of translation +running up an estuary and passing a ship anchored there, it is not the +transit up the channel, but the wave form itself--_i.e._, the motion of +the wave particles--that lifts the ship, sends her a little way higher +up channel, drops her to her former level, and sends her down channel +again to the spot she lay in just before the arrival of the wave. + +Everything, therefore, that has been permanently disturbed by an +earthquake shock has been thus moved in the direction and with the +maximum velocity impressed upon it by the wave particle in the first +semiphase of the wave; and thus almost everything that has been so +disturbed may, by the application of established dynamical principles, +be made to give us more or less information as to the velocity of the +wave particle (or as we, for shortness, say, the velocity of shock), the +direction of its normal vibration, and the position and depth beneath +the earth's surface, from which came the generating impulse. We thus +arrive at these as simply and as surely as we can infer from the +position taken by a billiard ball, on which certain forces are known to +have acted, the forces themselves and their direction; or, from a broken +beam, the pressure or the blow which fractured it. + +It is obvious, then, that nearly every object disturbed, dislocated, +fractured or overthrown by an earthquake shock is a sort of natural +seismometer, and the best and surest of all seismometers, if we only +make a judicious choice of the objects which being found after such a +shock, we shall employ for our purpose. This was the principle which I +proposed to the Royal Society at once to apply to the effects of the +then quite recent great Neapolitan Earthquake of 1857, and which, +through the liberality and aid of that body, I was enabled to employ +with the result I had pretty confidently anticipated, namely, the +ascertainment of the approximate depth of the focus. + +_Every_ shock-disturbed object in an earthquake-shaken country is +capable of giving _some_ information as to the shock that acted upon it; +but it needs a careful choice, and some mechanical νους, to select +_proper_ and the best objects, so as to avoid the needless perplexity of +disturbing forces _not_ proper to the shock, or other complications. + +When properly chosen, these natural seismometers, or evidences fitted +for observation after the shock, are of two great classes, by which the +conditions of the earthquake motion are discoverable: + + 1. Fractures or dislocations (chiefly in the masonry of + buildings), which afford two principal sources and sorts of + information, namely: + + _a._ From the observed _directions of fractures or fissures_, + by which the _wave path_, and frequently the _angle of + emergence_, may be immediately inferred. + + _b._ Information from the preceding, united with known + conditions as to the strength of materials to resist + _fracture_, by which the _velocity_ of the fracturing impulse + may be calculated. + + 2. The overthrow or the projection, or both, of bodies large or + small, simple or complex. From these we are enabled to infer: + + _c._ By direct observation, the _direction in azimuth_ of the + wave path. + + _d._ By measurements of the horizontal and vertical distances + of overthrow or of projection, to infer either the _velocity_ + of projection, or _angle of emergence_. + +Fractures by shock present their planes always nearly in directions +transverse to the wave path. Projections or overthrow take place (unless +secondarily disturbed) in the line of the wave path, or in the vertical +plane passing through it: but the direction of fall or overthrow may be +either in the same direction as the wave transit (_i.e._, as the motion +of the wave particle in the first semiphase), or contrary to it. + +It is thus obvious that the principal phenomena presented by the effects +of earthquake shock upon the objects usually occurring upon the surface +of the inhabited parts of the earth, resolve themselves into problems of +three orders, and are all amenable to mechanical treatment, viz.: + + 1. Problems relating to the direction and amount of velocity + producing fracture or fissures. + + 2. Problems relating to the single or multiplied oscillations + of bodies, considered as compound pendulums. + + 3. Problems referable to the theory of projectiles. + +These three may combine in several cases, and on the part of the +observer must combine with measurements, angular and linear, and with +geodetic operations to be conducted in the shaken country. + +The methods of application in detail are described fully, as well as +their actual application and results, in my work published in 1862 (2 +vols.), entitled "The First Principles of Observational Seismology, as +developed in the Report to the Royal Society of London of the Expedition +made by Command of the Society into the Interior of the Kingdom of +Naples, to investigate the Circumstances of the Great Earthquake of +December, 1857," to the many illustrations of which the pecuniary grant, +in aid, of £300 was most liberally made to the publishers (Messrs. +Chapman and Hall) by the Society. + +It is not my intention here, nor would space allow, of my going into the +details of observation, nor of the deductions and conclusions I have +recorded in those volumes. I have referred to their contents as marking +the advent of a new method. I have ventured to call it a new _organon_ +in the investigation of Earthquakes, and, through them, of the deep +interior of our earth; and will only add that the method, on this its +very first trial, proved fertile and successful. The depth of focus for +this shock of December, 1857, was about seven to eight geographical +miles below sea level, roughly stated. It gives me great pleasure to add +that my friend, Dr. Oldham, Director-General of the Geological Survey of +India, has since applied these same methods to the phenomena of the +great Cachar Earthquake of the 10th January, 1869, and with success. The +pressure of official duties has, he informs me, as yet prevented his +fully working out his results, but they appear so far to indicate, as we +should expect, a depth of focus or origin considerably greater than in +the European case of 1857. Some account of Dr. Oldham's results were +this year communicated to the Geological Society of London through +myself, they are of great interest and importance. + +Such, briefly and imperfectly sketched, is the existing state of +Seismology. As a branch of exact science it is, as it were, an affair of +yesterday. It is with reluctance that I have been compelled, in this +review, to refer to my own work so prominently. The harvest has been and +still is plenteous, but in this field of intellectual work the labourers +are few. This must continue to be so as long as Geology shall continue +to be viewed in public estimation (in England at least) as a fashionable +toy, that everyone who has been to school is supposed capable of +handling; and until all who profess to be geologists shall have learnt +that, to make sound progress, they must first become mathematicians, +physicists and chemists. + +It is to the general imperfect knowledge of these sciences amongst +geologists that speculative errors show such vitality, and that Geology +makes such poor progress towards becoming the interpretation of the +world as a machine (_Erdkunde_). + +It is for the same reason that Seismology and Vulcanology make little +progress; the first cannot be pursued beyond its present boundaries, nor +can even its present position be understood or explained by anyone +unfamiliar with the laws of wave motion, of all classes of waves; and it +would be easy to show, by quoting from various British or foreign +text-books on Geology, how extremely imperfect is the grasp of some of +the authors upon the subject of earthquake-wave motion, even such as +they admit and endeavour to explain and apply: in fact, many geologists +appear never to have framed to themselves any clear idea of what _is_ a +wave of any sort, liquid or elastic. The general silence as to seismic +theory of French geological writers is remarkable, to whatever cause +attributable. It has been said that French philosophers show themselves +little disposed to acknowledge or to follow the lead of their foreign +compeers in any branch of science. If this be true, or in so far as it +may be so, it is unworthy of French science, which has such boundless +claims upon our homage. I am disposed to attribute the fact in this case +to other circumstances; and, amongst these, to the small extent to which +our language is known amongst French scientific men. + +Germany has shown more desire to cultivate this branch of science. +Although, as yet, the distinct enunciation of its fundamental principles +has but sparsely found its way into her text-books, several able +monographs, such as those of Schmidt and of Höttinger, prove how +completely some of her philosophers have mastered and how well applied +them. The men of science of Northern Italy, amongst whom so many +glorious names are to be found on the roll of discovery, have shown +themselves quite alive to the importance of Seismology; and I know of no +more clear, exact and popular exposition of its principles and +application, and of its cosmical relations, than is to be found in a +small volume by Professor Gerolamo Boccardo, published at Genoa in 1869, +entitled _Sismopirologia Terremoti, Vulcani e lente oscillazione del +suolo, saggio di una teoria di Geographia Fisica_. + +My object, so far, has been to mark the progress of ascertained +theoretic notions as to Seismology. I have, therefore, passed without +notice many speculative monographs, and the treatment upon Earthquakes, +whether speculative or historical, and however able, that constitutes a +prominent feature of nearly all systematic works on Geology. + +That which may be at present viewed as achieved and certainly +ascertained in theoretic Seismology is the clear conception of the +nature of earthquake motion; the relations to it of great sea or other +water wave commotions; the relations to it of sound waves--as to which, +however, more remains to be known; and the relations of all these to +secondary effects, tending in various ways to modify more or less the +topographic and other conditions of the land or sea bottom. And in +descriptive Seismology the present distribution of the earthquake bands +or regions of greatest seismic prevalence and activity are tolerably +ascertained, and their connection with volcanic lines and those of +elevation rendered more evident. Viewed alone, nothing can yet be said +to be absolutely ascertained as to the immediately antecedent cause or +causes of the impulse. The function of Earthquake, as part of the +cosmical machine, has become more clear, as the distinctive boundaries +between Earthquake and permanent elevation of the earth have been made +evident; and it has been seen that Earthquake, however contemporaneous +occasionally with permanent elevation, is not the cause, though it may +be one of the consequences of the same forces which produce elevation; +and thus, that an infinite number of Earthquakes, however violent, and +acting through however prolonged a time, can never act as an agent of +permanent elevation, unless, indeed, on that minute scale in which +surface elevation may arise from secondary effects, like that of the +Ullah Bund. + +Much remains to be done, and much may be expected even from the +continuation, if done in a systematic and organised manner, of the +statistic record of Earthquakes in connection with those other branches +of cosmical statistics, Climatology, Meteorology, Terrestrial Magnetism, +etc., the observation of which is already, to a certain extent, +organised over a large portion of the globe. + +And now let us look back for a moment to ask, How, by what mental path +of discovery, have we arrived at what we have passed in review? + +The facts of Earthquakes have been before men for unknown ages "open +secrets," as Nature's facts have been well called; "but eyes had they +and saw not." Facts viewed through the haze of superstition, or of +foregone notions of what Nature _ought_ to do, cease to be facts. When, +after the great Calabrian Earthquake of 1783, the Royal Academy of +Naples sent forth its commission of its learned members to examine into +the effects, they had spread around them in sad profusion all that was +necessary to have enabled them to arrive at a true notion of the nature +of the shock, and thence a sound explanation of the varied and great +secondary effects they witnessed, and of which they have left us the +records in their Report, and the engravings illustrative of it. But we +look in vain for any light; the things seen, often with distortion or +exaggeration, are heaped together as in the phantasmagoria of a wild +and terrible dream, from which neither order nor conclusion follow. + +Why was this? Why were these eminent _savants_ no more successful in +explaining what they saw than the ignorant peasants they found in the +Calabrian mountains? + +Because physical science itself was not sufficiently advanced, no doubt; +but also because they had no notion of applying such science as they +had, to the very central point itself of the main problem before them, +freed from all possible adventitious conditions, and so, as it were, +attacking it in the rear. How different might have been the result of +their labours, had they begun by asking themselves, What is an +earthquake? Can we not try to find out what it _is_ by observing and +_measuring_ what it has done? We see the converse mode of dealing with +Nature in Torricelli. "Nature abhors a vacuum," was told him, as the +wisdom of his day. Possibly: but her abhorrence is limited, for I find +it is _measured_ by the pressure of a column of water of thirty-four +feet in height. We need not pursue the story with Pascal, up to the top +of the Puy de Dôme. + +This lesson is instructive generally to all investigators, and +particularly here; for Vulcanology, to which we are about now to turn, +has occupied until almost to-day much the same position that Seismology +did in those of the Neapolitan Commissioners. + +Whole libraries have been written with respect to it dealing with +_quality_, but _measure_ and _quantity_ remain to be applied to it. + +To a very preponderant class in the civilised world no knowledge is of +much interest or value that does not point to what is called a +"practical result," one measurable into utility or coin. I do not stop +to remark as to the bad or as to certain good results of this tendency +of mind; but I may venture to point out to all, that the exact knowledge +of the nature of earthquake motion, even during the short time that it +has become known, has not been barren in results absolutely practical +and utilitarian. The minute investigation of the destruction of +buildings, etc., and the deductions that have been made as to the +relations between the form, height, materials, methods of building, +combination of timber and of masonry, and many other architectural or +constructive conditions, have made it certain now that earthquake-proof +houses and other edifices can be constructed with facility, and at no +great increase, if any at all, of cost. I can affirm that there is no +physical necessity why in frequently and violently shaken countries, +such as Southern Italy or the Oriental end generally of the +Mediterranean, victims should hereafter continue by thousands to be +sacrificed by the fall of their ill-designed and badly built houses. + +Were a "Building Act" properly framed, put in force by the Italian +Government in the Basilicatas and Capitanata, etc., so that new houses +or existing ones, when rebuilt, should be so in accordance with certain +simple rules, a not very distant time can be foreseen when Earthquakes, +passing through these rich and fertile but now frequently sorely +afflicted regions, should come and go, having left but little trace of +ruin or death behind. Some disasters there must always be, for we +cannot make the flanks of mountains, nor the beds of torrents, etc., +always secure; but the main mortality of all Earthquakes is in the +houses or other inhabited buildings. Make these proof, and the wholesale +slaughter is at an end. + +The principles we have established have been thus practically applied in +another direction. The Japanese Government, with the keen and rapid +perception of the powers inherent in European science which +characterises now that wonderful people, has commenced to illuminate its +coasts by lighthouses constructed after the best European models. But +Japan is greatly convulsed by earthquakes, and lighthouses, as being +lofty buildings, are peculiarly liable to be destroyed by them. + +The engineer of the Japanese Government for these lights, Mr. Thomas +Stevenson, C.E. (one of the engineers to the Commissioners of Northern +Lights), was instructed to have regard, in the design of those +lighthouses, to their exposure to shock. I was consulted by Mr. +Stevenson as to the general principles to be observed; and those +edifices have been constructed so that they are presumedly proof against +the most violent shocks likely to visit Japan; not, perhaps, upon the +best possible plan, but upon such as is truly based upon the principles +I have developed. Mr. Stevenson has published some account of their +construction. + +The earthquake regions of South America might with incalculable benefit +apply those ideas; and, indeed, they have been, to some extent, already +applied by my friend, Mr. William Lloyd, Member of the Institution of +Civil Engineers, to the New Custom Houses constructed from his designs +at Valparaiso. + +As one of these utilitarian views, and an important one, it will occur +to many to ask--Can the moment of the occurrence or the degree of +intensity of earthquake shock be predicted, or is it probable that at a +future day we may be able to predict them? At present, any prediction, +either of the one or the other, is impossible; and those few who have +professed themselves in possession of sufficient grounds for such +prediction are deceivers or deceived. Nor is it likely that, for very +many years to come, if ever, science shall have advanced so as to render +any such prediction possible; but it is neither impossible nor +improbable that the time shall arrive when, within certain, perhaps +wide, limits as to space, previous time, and instant of occurrence, such +forewarnings may be obtainable. + +Earthquakes, like storms and tempests, and nearly all changes of +weather, are not periodic phenomena, nor yet absolutely uncertain or, so +to say, accidental as to recurrence. + +They are quasi-periodic, that is to say, some of their conditions as to +causation rest upon a really periodic basis, as, for example, the +recurrence of storms upon the periodic march of the earth, and sun and +moon, etc., and the recurrence of Earthquakes upon the secular cooling +of our earth; but the conditions in both are so numerous and complicated +with particulars, that we cannot fully analyse them--hence, cannot +reduce the phenomena to law, and so cannot predict recurrence. Yet +storms and tempests--which were, along with pestilences and Earthquakes, +amongst the natural phenomena which Bishop Butler deemed in his own day +impossible of human prediction--have already, through the persistent and +systematised efforts of meteorological observers, become to a certain +extent foreseeable; and medical science assures us that it has rendered +that, though to a much less degree of probability, true of pestilences. + +We may, therefore, give the utilitarian some hope, that if he will help +us along--who value our accessions of knowledge primarily upon a +different standard to his--in our talk of discovery, our posterity, in a +century or two hence, may not improbably possess the advantage of being +able, in some degree, to predict their Earthquakes. I fear the +inducement will go but a small way with the utilitarian generation, +whose bent tends much towards asking, "What has posterity ever done for +them?" + +But though we cannot as yet predict the time when an Earthquake may take +place in any locality, we can, on mixed statistic and dynamic grounds, +in many cases state the limits of probable violence of the next that may +recur. For example, the three shafts of marble columns of the Temple of +Serapis, at Pozzuoli, each of about 41-1/2 feet in height, and 4 feet 10 +inches in diameter at the base, remain standing alone, since they were +uncovered, in the year 1750. + +Now, as we can calculate exactly what velocity of earthquake-wave motion +would be required to overset these, we are certain that, during the last +one hundred and twenty-two years, the site of the Temple, and we may +say Naples and the Phlegræan fields generally, have never experienced a +shock as great as the very moderate one that would overset these +columns. A shock whose wave particle had a horizontal velocity of only +about 3-1/2 feet (British) per second would overturn these columns; +which is only about one-fourth the velocity (within the meizoseismic +area) of the great shock of 1857, that produced wide-spread destruction +in the Basilicatas, and not enough to throw down any reasonably +well-built house of moderate height. + +Naples, so far as Earthquake is concerned, whether coming from the +throes of Vesuvius or elsewhere, has a pretty good chance of safety. She +may possibly (though not probably) be some day smothered in ashes; but +is in little danger of being shaken to the earth. During this time there +have been taking place, larger eruptions of Vesuvius and earthquake +shocks from other centres, together probably about the same number of +times as the numbers of those years, when those columns have been more +or less shaken. + +We may therefore affirm that the probability (on the basis of this +experience _only_) is, say 120 to 1, that the next shock, whether +derived from Vesuvius, or elsewhere, that may shake Pozzuoli, will be +one less in power than would be needed to overturn the shafts of the +Temple of Serapis there. + + * * * * * + +Let us now turn to the second branch of our subject--viz., +Vulcanology--upon which, as yet, we have secured less firm standing +ground than we have seen we possess in Seismology, for which reason we +took that first into consideration. + +It is the part of Vulcanology to co-ordinate and explain all the +phenomena of past or present times visible on our globe which are +evidences of the existence and action, whether local or general, of +temperatures within our globe greatly in excess of those of the surface, +and which reach the fusing points of various mineral compounds as found +arriving, heated or fused, at the surface. + +The stratigraphic geologist sees that such heated or fused masses have +come up from beneath, throughout every epoch that he can trace; but he +cannot fail to discern more or less a change in the order or character +of those outcomings, as he traces them from the lowest and oldest +formations to those of the present day. He sees immense outpourings of +granitoid or porphyrytic rocks that have welled up and overflowed the +oldest strata--huge dykes filling miles of fissures that had been +previously opened for the reception of the molten matter that has filled +them, and often passing through those masses of previously outpoured +rock; later he sees huge tables of basaltic rock poured forth over all. +One grand characteristic common to all these--commonly called plutonic +products--being that, whether they were poured forth over the surface or +injected into cavities in other rocks, the movements of the fused +material were, on the whole, hydrostatic and _not explosive_. + +At the present day, whatever other evidences we have of high temperature +below our globe's surface, that which primarily fixes the eye of the +geologist is the Volcano, whose characteristic, as we see it in +activity, _is explosive_. But though there is this great characteristic +difference between the plutonic and the volcanic actions and their +products, the two, when looked at largely, are seen so to inosculate, +that it is impossible not to refer them to an agency common to both, +however changed the modes of its action have been between the earliest +epochs of which traces are presented to us and the present day. + +To us little men, who, as Herschell has well said, in referring to the +methods of measuring the size of our globe, "can never see it all at +once, but must creep like mites about its surface," the Volcano, in the +stupendous grandeur of its effects, tends to fix itself in our minds in +exaggerated proportions to its true place in the cosmic machine; and, in +fact, nearly all who have sought to expound its nature and mode of +origination have occupied themselves far too exclusively with describing +and theorising upon the strange and varied phenomena which the volcanic +cone itself and its eruptions present, and too often, in the splendour +and variety of these, have very much lost sight of what ought to be the +centre-point of all such studies, namely, to arrive at some sound +knowledge of what is the _primum mobile_ of all these wonderful efforts. +Nor has the distinction been very clearly seen between the main +phenomena presented at and about volcanic active mouths, which can be +employed to elucidate the nature of the causation at work far below, and +those most varied and curious, and in other respects most pregnant and +instructive phenomena, mechanical and chemical, which are called into +action in and by the ejected matter of the volcanic cone after its +ejection. It can help us but little or very indirectly, in getting at a +true conception of the nature and source of the heat itself of the +Volcano, to examine, for example, all the curious circumstances that are +seen in the movements and changes in the lava that has already flowed +from its mouth; but it would be of great importance if we can ascertain, +by any form of observation around the cone, from what depth it has come, +or at what depth the igneous origin lies. + +The physician, endeavouring to ascertain the real nature of small-pox or +measles, will scarcely make much progress who, however curiously or +minutely, confines his attention to the pustules that he sees upon the +skin. + +Yet the Volcano, or rather all volcanic activity as now operative upon +our globe, is, as it were, an experiment of Nature's own perpetually +going on before us, the results of which, if well chosen--that is, as +Bacon says, by keeping to the main and neglecting the accidents--can, +when colligated and correctly reasoned upon, in relation to our planet +as a whole, give us the key to the enigma of terrestrial Vulcanicity in +its most general sense, and at every epoch of our world's geognostic +history, and show us its true place and use in the cosmical machine. Let +us glance at the history of past speculation on this subject, from which +so little real knowledge is to be derived, and then at the salient facts +of Vulcanology as now seen upon our earth, and finally see if we can +connect these with other great cosmical conditions, so as to arrive at +a consistent explanation in harmony with all. + +We gain nothing absolutely from the knowledge of the so-called +"ancients" as to Volcanoes in Europe at least, where alone historic +records likely to refer to them exist. The Volcanoes of Europe are few +and widely scattered. The Greeks saw but little of them, and the Romans +were all and at all times most singularly unobservant of natural +phenomena. + +Cæsar never mentions the existence in France of the Volcanoes of +Auvergne, so much like those he must have seen in Italy and Sicily; and +Roman writers pass in silence that great volcanic region, though +inhabited by them, and their language impressed upon the places, as +Volvic (_volcano-vicus_) seems with others to indicate; and though there +is some reason to believe that one or other of the Puys was in activity +within the first five hundred years of our epoch, the notices which +Humboldt and others have collected as from Plato, Pausanius, Pliny, +Ovid, etc., teach nothing. + +Whatever of mere speculation there may have been, volcanic theory, or +what has passed for such, there was none before 1700, when Léméry +brought forward a trivial experiment, the acceptance of which, even for +a moment, as a sufficient cause for volcanic heat (and it retarded other +or truer views for years), we can now only wonder at. Breislak's origin, +in the burning of subterranean petroleum or like combustibles, was +scarcely less absurd than Léméry's sulphur and iron filings. + +Davy, in the plenitude of his fame, and full of the intense chemical +activities of the metals of the alkalies which he had just isolated, +threw a new but transient verisimilitude upon the so-called chemical +theory of Volcanoes, by ascribing the source of heat to the oxidation of +those metals assumed to exist in vast, unproved and unindicated masses +in the interior of the earth. But Davy had too clear an intellect not to +see the baseless nature of his own hypothesis, which in his last work, +the "Consolations in Travel," he formally recanted; and it only survived +him in the long-continued though unconvincing advocacy of Dr. Daubeny. +So far, the origin of the heat had been sought always, in the crude +notion of some sort of _fuel consumed_, whether that were petroleum or +potassium and sodium; but as no fuel was to be found, nor any indicated +by the products, so far as known, of the volcanic heat, so what has been +called the mechanical theory, in a variety of shapes, took its place. + +This, in whatever form, takes its lava and other heated products of the +volcano ready made from a universal ocean of liquid material, which it +supposes constitutes the interior or nucleus of our globe, and which is +only skinned over by a thin, solid crust of cooled and consolidated +rock, which was variably estimated at from fourteen to perhaps fifty +miles in thickness. Here was a boundless supply of more than heat, of +hot lava ready made, the existence of which at these moderate depths the +then state of knowledge of hypogeal temperature, which was supposed to +go on increasing with depth at the rate of about 1° Fahrenheit, for +every thirty or forty feet, seemed quite to sustain. + +The difficulty remained, how was this fiery ocean brought to the +surface or far above it? To account for this two main notions prevailed, +and, indeed, have not ceased to prevail. Some unknown elastic gases or +vapour forced it up through fissures or rents pre-existent, or produced +by the tension of the elastic and liquid pressure below. + +The form in which this view took most consistency, and approaching most +nearly to truth, finds the elastic vapour in steam generated from water +passed down through fissures from the sea or from the land surface. But +to this the difficulty was started, that fissures that could let down +water would pass up steam. The objection, when all the conditions are +adequately considered, has really no weight; and it has been completely +disposed of, since within a few years it has been proved that capillary +infiltration goes on in all porous rocks to enormous depths, and that +the capillary passages in such media, though giving free vent to +water--and the more as the water is warmer--are, when once filled with +liquid, proof against the return through them of gases or vapours. So +that the deeply seated walls of the ducts leading to the crater, if of +such material, may be red hot and yet continue to pass water from every +pore (like the walls of a well in chalk), which is flushed off into +steam that cannot return by the way the water came down, and must reach +the surface again, if at all, by the duct and crater, overcoming in its +way whatever obstructions they may be filled with. + +And this remarkable property of capillarity sufficiently shows how the +lava--fused below or even at or above the level of infiltration--may +become interpenetrated throughout its mass by steam bubbles, as it +usually but not invariably is found to be. + +Nor is it difficult to see such a mechanism between volcanic ducts and +fissures conveying down water, as large and open pipes, for a large part +of their depth, as shall bring down water to foci of volcanic heat, +without the power of the water flowing back except as steam and through +the crater. + +Indeed, the facts known as to geysers, and those of half-drowned-out +Volcanoes such as Stromboli--whose action is intermittent just as much +as that of a geyser--show that this is not merely probable. There is, +therefore, no need for the hypothesis of those who have supposed all the +huge volumes of steam blown off from Volcanoes in eruption to come from +vesicular water pre-existent in the minute cavities of crystalline or +other rocks before their fusion into lava: a fact not proved for many +classes of rock, and for none in sufficient quantity to account for the +vast volume of steam required and for the irregularity of its issue. + +It is rather to anticipate, but I may state at once that, so far as the +admission of superficial waters to the interior, and to any depth to +which fissures or dislocation can extend, I believe no valid physical or +mechanical difficulties exist, taking into account _all_ the conditions +that may come into play together. + +Another set of views has been suggested and supported by various +writers, which proposes to account for the rise of lava on purely +hydrostatic principles. The solid crust, fractured into isolated +fragments by tensions due to its own contraction, is supposed to sink +into the sea of lava on which it floats; and much ingenuity has been +expended in imagining the mechanism by which, in places, the liquid +matter is supposed to rise _above_ the surface of the crust. + +I have no space for discussing these views further than to assert that, +in the existing state of our globe, and even admitting a solid crust of +only 60,000 metres thick, dislocation of the crust by _tension_ is not +possible. The solid crust of our globe, as I hope we shall see further +on, is not in a state of tension, and has not been so since it was +extremely thin, a mere pellicle as compared with the liquid nucleus, but +is, on the contrary, in a state of _tangential compression_. + +However tenable, in other respects, may be the volcanic theory which +rests upon the assumption of a very _thin_ crust and a universal ocean +of fused rock beneath, it fails wholly to explain many of the most +important circumstances observable as to the distribution and movements +of existing Volcanoes on our globe. + +It affords no adequate explanation of the configuration of the lines of +Volcanoes, nor of their occurrence in the ocean bed, nor of their +existence in high latitudes, near the Poles, where, no matter how or at +what rate our globe cooled from liquidity, the crust must be thickest; +nor of the independence of eruptive action of closely adjacent volcanic +vents; nor of the non-periodicity, the sudden awakening-up to activity, +the as sudden exhaustion, the long repose, the gradual decay of action +at particular vents, and of much more that might be stated and +sustained as difficulties left by that theory unexplained, or that are +of a nature even opposed to it. + +The researches of the last few years have, however, as it appears to me, +rendered any theory that demands as its postulates a _very thin crust_, +and a universal liquid nucleus beneath it, absolutely untenable. + +Without attaching any importance to the arguments of Mr. Hopkins, based +upon precession and nutation, it appears to me, on various other +grounds, some of which have been urged by Sir William Thompson, that the +earth's solid crust is not a thin one, at least not thin enough to +render it conceivable that water can ever gain admission to a fluid +nucleus, if any such still exist, situated at so great a depth; and +without such access we can have no Volcano. It is not necessary to go to +the extent of a crust of 800 or 1,000 miles thick: with one of half the +minor thickness, I believe it may be proved, on various grounds, +hydraulic amongst others, that neither water could reach the nucleus, +nor the liquid matter of the nucleus reach the surface. Mr. Hopkins +having proved to his own satisfaction an enormous thickness for the +crust, and seeing clearly the difficulties that this involved to the +generally accepted volcanic theory, and having no other to substitute +for it, fell back upon that most vague and weak notion of the existence +of isolated lakes of liquid rock, existing at comparatively small depths +beneath the earth's surface within the solid and relatively cold crust, +each supplying its own Volcano, or more than one, with ready-made lava. +What is to produce these lakes of fused matter in the midst of similar +solidified matter? what is perpetually to maintain their fluidity in the +midst of solid matter continually cooling? what has given them their +local position? why near or less near the surface? what should have +arranged them in directions stretching in some cases nearly from Pole to +Pole? + +Surely this creation of imaginary lakes, merely because it happens to +fit the vacant chink that seems needed to wedge up a falling theory, is +an instance of that abuse of hypothesis against which Newton so +vehemently declaims--"_Hypotheses non fingo._" + +Hypothesis, to be a philosophic scaffolding to knowledge, must, as +Whewell has said, "be close to the facts, and not merely connected with +them by arbitrary and untried facts." Yet this appears accepted by Lyell +(10th edition, Vol. II., p. 227, and elsewhere); by Phillips +("Vesuvius," pp. 331, 332); by Scrope, if, as I hope, I mistake him not +("Volcanoes," pp. 265, 307-8); though none of these excellent +authorities seem either quite clear or quite satisfied with the notion; +and in the very passage referred to, Lyell _may_ have possibly a much +more philosophic notion in view, where he says: "It is only necessary, +in order to explain the action of Volcanoes, to _discover some cause +which is capable of bringing about such a concentration of heat as may +melt one after the other certain portions of the solid crust_, so as to +form seas, lakes or oceans of subterraneous lava." (Vol. II, pp. 226, +227). If by this is meant, that all that is needed to complete a true +theory of volcanic action is to discover _an adequate cosmical cause for +the heat_--that is to say, a prime mover to which all its phenomena may +be traced back, which shall be at once reconcilable with the conditions +of our planet as a cooling mass in space and with facts of Vulcanology +as they are now seen upon it--then I entirely agree with it. + +It has been my own object to endeavour to discover and develope that +adequate cause in a Paper "On Volcanic Energy, an Attempt to develope +its True Nature and Cosmical Relations," read (in abstract) before the +Royal Society of London ("Proceedings, Royal Society," Vol. XX., May, +1872), and now (October, 1872) under consideration of Council with a +view to publication. + +I propose concluding this review of the progress of Vulcanology (in +which I have had to limit myself to reviewing merely the chief stages of +advance towards knowledge of the nature and origin of volcanic heat +itself, and have had to pass without notice the vast and important mass +of facts and reasonings collected by so many labourers as to its visible +phenomena and products, and the still greater mass of speculation, good +and bad, on every branch of the subject), by giving a necessarily very +brief and imperfect sketch of my own views as in that Paper in part +developed. It will first be necessary to retrace our steps a little, in +order to gain such a point as shall afford us a fuller view of the whole +problem before us. + +It is not necessary to dilate, even did space allow, upon the many +points which bind together Earthquakes and Volcanoes as belonging to the +play of like forces. These are generally admitted; and in various ways, +more or less obscure, geologists generally have supposed some relations +between these and the forces of elevation, which have raised up mountain +chains, etc. + +No one, however, that I am aware of, prior to myself, in the Paper just +alluded to, has attempted to show, still less to prove upon an +experimental basis, that all the phenomena of elevation, of volcanic +action, and of Earthquakes, are explicable as parts of one simple +machinery--namely, the play of forces resulting from the secular cooling +of our globe. We have seen that, on the whole, both Earthquakes and +Volcanoes follow along the great lines of elevation of our surface. Any +true solution of the play of forces which has produced any one of those +three classes of phenomena must connect itself with them all, and be +adequate to account for all. And this would have earlier been seen, had +geologists generally framed for themselves any correct notions of the +mechanism of elevation itself, and seen its real relation with the +secular cooling of our planet. But the play of forces resulting from +this secular cooling has never, until very recently, been adequately or +truly stated. The arbitrary assumption and neglect of several essential +conditions by La Place, in his celebrated Paper "On the Cooling of the +Earth," in the fifth volume of the "Mécanique Céleste," and the +arbitrary and unsustainable hypothesis of Poisson upon the same subject, +have tended to retard the progress of physical Geology as to the nature +of elevation: the first, by leaving the geologist in doubt as to whether +our globe were cooling at all; the second, by suggesting distorted +notions as to the mode of its cooling and consolidation. On the other +hand, neither geologists nor mathematicians generally have framed for +themselves any clear notions of the mechanism of elevation. Had a true +conception been formed of the forces and interior movements brought +necessarily into operation by the secular cooling of the globe, +geologists could scarcely have failed to see that their notion as to the +way and direction in which the forces producing elevation have actually +acted could not, if arising from refrigeration, be those which they have +almost universally supposed, namely--some force acting vertically +upwards, _i.e._, radially from the centre of the sphere. Had geologists +only looked at Nature with open eye, they must have seen that mountain +ranges, and elevations generally (exclusive of volcanic cones), +presented circumstances absolutely incompatible with their having been +thrust up by any force _primarily_ acting in the direction of a radius +to the spheroid. + +Yet this is the erroneous notion of the mechanism of elevation which to +the present hour prevails amongst geologists, so far as they in general +have framed to themselves any distinct idea of such mechanism at all. + +Thus, only to cite two examples from recent authors of justly high +reputation. Lyell says of the probable subterranean sources, whether of +upward or downward movement, when permanently uplifting a country, and +in reference to the crumpling of strata on mountain flanks by lateral +pressure, it would be rash to assume these able to resist a power of +such stupendous energy, "_if its direction, instead of being vertical_, +happened to be oblique or horizontal." This is somewhat vague--and I +trust I do not mistake or misrepresent the illustrious author--yet it +is the most explicit expression I can find in the "Principles of +Geology" as to his notion of the primary direction of elevatory force +(Edit. 10, Vol. I., p. 133). That Mr. Scrope's idea is that only of +primary radial or vertical direction of such forces, is apparent on +inspecting his Diagram No. 64 ("Volcanoes," p. 285), and in the use of +the words, "an axial wedge of granite," which, on the next page, we find +is "liquefied granite;" and if we read on to page 294, and refer also to +pages 50 and 51, I believe there can be no doubt that _vertical_ or +_direct up-thrust_ is the author's notion of the primary direction of +all forces of elevation. The true nature of these forces was, however, +clearly seen and most justly stated by Constant Prevost ("Compt. Rend.," +Tome XXXI., 1850, and "Bulletin de la Société Géolog. de France," Tome +II., 1840) as consisting, not in forces of some unknown origin acting +primarily in the vertical, but in _tangential pressures acting +horizontally, and resolved by mutual pressures at certain points into +vertical resultants_. These Prevost rightly attributed to the +contraction of the earth's solid crust. The same idea has been adopted +by Elie de Beaumont as the true mechanism of the elevation of mountain +ranges; and although De Beaumont's views as to the thinness he assigns +to the solid and contracting crust, and his strange deduction as to the +parallelism of contemporaneous mountain chains uplifted by its spasmodic +action along certain lines, may be untenable, his notion generally as to +the play of forces producing mountain elevation is much more nearly +correct. + +Mr. Hopkins's notion is simply that of the geologists. Anyone who reads +his well-known papers on elevation and the formation of fissures, etc., +must see that he views all elevatory forces as of liquids or +quasi-liquids forced up and acting primarily _vertically_ upon the +strata above them, and that these strata are not under tangential +compression, but under tension. Hence the mathematical deductions +contained in those papers as to the directions in which elevatory forces +act, and in which fissures are formed by them, are not in any way a +setting forth of such facts as occur in Nature, and, much attention as +they have attracted, can only now be viewed as exercises of mathematical +skill misapplied, because based upon data not to be found in Nature. In +fact, those papers do but misrepresent Nature, and, like many other +mathematical investigations based on untrue or insufficient data, have +tended to retard knowledge. + +The views which I have put forward in the Paper I have referred to, read +to the Royal Society, recapitulated in skeleton, so to say, are as +follows. Omitting those portions which treat of our globe from the +period of the first liquefaction out of a nebulous condition, and of the +earliest stages of the cooling by radiation into space, when the crust +was extremely thin, and of the deformation of the spheroid as one of the +first effects of its contraction, and through that the general shaping +out of continents and ocean beds; I have endeavoured to show that the +rate of contraction of the crust, while very thin, exceeded that of the +large fluid nucleus supporting it, and so gave rise to _tangential +tensions_ in the crust, and fracturing it into segments; next, that as +the crust thickened, these _tensions_ were gradually converted into +_tangential pressures_, the contraction of the nucleus now beginning to +exceed (for equal losses of heat) that of the crust through which it +cooled. At this stage these tangential pressures gave rise to the +_chief_ elevations of mountain chains--not by liquid matter by any +process being injected from beneath vertically, but by such pressures, +mutually reacting along certain lines, being resolved into the vertical, +and forcing upwards more or less of the crust itself. The great outlines +of the mountain ranges and the greater elevation of the land were +designated and formed during the long periods that elapsed in which the +continually increasing thickness of crust remained such that it was +still, as a whole, flexible enough, or opposed sufficiently little +resistance to crushing, to admit of this uprise of mountain chains by +resolved tangential pressures. I have shown that the simple mechanism of +such tangential pressures is competent to account for all the complex +phenomena both of the elevations and of the _depressions_ that we now +see on the earth's surface (other than continents and ocean beds), +including the production of gaping fissures (in directions generally +orthogonal to those of tangential pressure). And as our earth is still a +cooling body, and the crust, however now thicker and more rigid, is +still incapable of sustaining the tangential pressures to which it is +now exposed, so I by no means infer that slow and small (relatively) +movements of elevation and depression may not be still and now going on +upon the earth's surface; in fact all the phenomena of elevation and +depression, rending, etc., which at a much remoter epoch acted upon a +much grander and more effective scale. So that, for aught my views say +to the contrary, all the mountain chains in the world may be possibly +increasing in stature year by year, or at times; but in any case at a +rate almost infinitesimally small in its totality over the whole earth +to that with which their ridges were originally upreared. + +But the thickness of the earth's crust--thus constantly added to, by +accretion of solidifying matter from the still liquid or pasty nucleus, +as the whole mass has cooled--has now assumed such a thickness as to be +able to offer a too considerable resistance to the tangential pressures, +to admit of its giving way to any large extent by resolution upwards; +yet the cooling of the whole mass is going on, and contraction, though +unequal, both of thick crust and of hotter nucleus beneath also, whether +the latter be _now_ liquid or not. Were the contraction, lineal or +cubical, for equal decrements or losses of heat, or in equal +times--equal both in the material of the solidified crust and in that of +the hotter nucleus--there could be no such tangential pressures as are +here referred to, at any epoch of the earth's cooling. But in accordance +with the facts of experimental physics, we know that the co-efficient of +contraction for all bodies is greater as their actual temperature is +higher, and this both in their solid and liquid states. + +Hence for equal decrements of heat, or by the cooling in equal times, +the hotter nucleus contracts more than does its envelope of solid +matter. + +The result is now, as at all periods since the signs changed of the +tangential forces thus brought into play--_i.e._, since they became +tangential _pressures_--that the nucleus tends to shrink away as it +were from beneath the crust, and to leave the latter, unsupported or but +partially supported, as a spheroidal dome above it. + +Now what happens? If the hollow spheroidal shell were strong enough to +sustain, as a spheric dome, the tangential thrust of its own weight and +the attraction of the nucleus, the shell would be left behind altogether +by the nucleus, and the latter might be conceived as an independent +globe revolving, centrally or excentrically, within a shell outside of +it. This, however, is not what happens. + +The question then arises, Can the solid shell support the tangential +thrust to which it would be thus exposed? By the application to this +problem of an elegant theorem of Lagrange, I have proved that it cannot +possibly do so, no matter what may be its thickness nor what its +material, even were we to assume the latter not merely of the hardest +and most resistant rocks we know anything of, but even were it of +tempered cast-steel, the most resistant substance (unless possibly +iridio-osmium exceed it) that we know anything about. Lagrange has shown +that if P be the normal pressure upon any flexible plate curved in both +directions, the radii of these principal curvatures being ρ' and ρ'', +and T the tangential thrust at the point of application and due to the +force P, then: + + P = T (1/ρ' + 1/ρ'') + +When the surface is spherical, or may be viewed as such, ρ' = ρ'' and + + P = 2T/ρ or, T = P × ρ/2 + +In the present case P is for a unit square (taken relatively small and +so assumed as plane) of the shell, suppose a square mile, equal to the +effect of gravity upon that unit, ρ being the earth's radius, and if we +assume the unit square be also a unit in thickness, P is then the weight +of a cubic mile of its material; and if we take (roughly) the earth's +radius as 4,000 miles, the tangential pressure, T, is, on _each face_ of +the cubic mile, equal to + + (4000/2) P, + +or equal to the pressure of a column of the same material of 2,000 times +its weight. + +If the cubic mile that we have thus supposed cut out of the earth's +crust at the surface were of the hardest known granite or porphyry, it +would be exposed to a crushing tangential pressure equal to between 400 +and 500 times what it could withstand, and so must crush, even though +only left unsupported by the nucleus beneath, to the extent of 1/400 or +1/500 of its entire weight. And what is true here of a mile taken at the +surface, is true (neglecting some minute corrections for difference in +the co-efficient of gravity, etc.) if taken at any other depth within +the thick crust.[F] + +The crust of our earth, then, as it now is, must crush, to follow down +after the shrinking nucleus--if so be that the globe be still cooling, +and constituted as it is; even to the limited extent to which we know +anything of its nature--it must crush unequally, both regarded +superficially and as to depth; generally the crushing lines being +confined to the planes or places of greatest weakness; and the crushing +will not be absolutely constant and uniform anywhere, or at any time, or +at any of those places of weakness to which it will be principally +confined, but will be more or less irregular, quasi-periodic, or +paroxysmal: as is, indeed, the way in which all known material +substances (more or less rigid) give way to a slow and constantly +increasing, steady pressure. + +We have now to ask, _How much_ of this crushing is going on at present +year by year? And the answer to this depends upon what amount of heat +our world is losing into space year by year. + +Geologists who have taken on trust the statement, that La Place has +proved that the world has lost no sensible amount of heat for the last +10,000 years seem generally to suppose that to be a fact; but in reality +La Place has _proved_ nothing of the sort, as those geological teachers +who have echoed the conclusion should have known, had they deciphered +the mathematical argument upon which it has been supposed to rest. + +By application of Fourier's theorem (or definition) to the observed rate +of increment of heat in descending from the geothermal _couche_ of +invariable temperature, and the co-efficients of conductivity of the +rocks of our earth's crust, as given by the long-continued observations +made beneath the Observatories of Paris and of Edinburgh, it results +that the annual loss of heat into space of our globe at present is equal +to that which would liquefy into water, at 32° Fahr., about 777 cubic +miles of ice; and this is the measuring unit for the amount of +contraction of our globe now going on. The figures are not probably +exact, for the data are not on a basis sufficiently full or exactly +established as yet; but they are not very widely wrong, and their +precise exactness is not material here. Now, how is this annual loss of +heat (great or small, as we may please to view it) from the interior of +our globe disposed of? + +What does it _do_ in the interior? We have already seen that it is +primarily disposed of by conversion into work; into the work of +diminishing the earth's volume as a whole, and in so doing crushing +portions of the solid surrounding shell. + +But does the transformation of lost heat into the work of vertical +descent, and of the crush as it follows down after the shrinking +nucleus, end the cycle? No. A very large portion of the mechanical work +thus produced, and resolved, as we have seen, into tangential crushing +pressure, is retransformed into heat again in the very act of crushing +the solid material of the shell. If we see a cartload of granite +paving-stones shot out in the dark, we see fire and light produced by +their collision; if we rub two pieces of quartz together, and crush thus +their surfaces against each other, we find we heat the pieces and evolve +light. + +The machinery used for crushing by steam-power, hard rocks into road +metal, gets so hot that the surfaces cannot be touched. + +These are familiar instances of one result of what is now taking place +by the crushing of the rocky masses of our cooling and descending +earth's crust, every hour beneath our feet, only upon a vastly greater +scale. It is in this local transformation of work into heat that I find +the true origin of volcanic heat within our globe. But if we are to test +this, so as in the only way possible to decide is it a true solution of +this great problem, we must again ask the question, _How much?_ and to +answer this, we must determine _experimentally_ how much heat can be +developed by the crushing of a given volume, say a cubic mile, of such +rocky materials as we know must constitute the crust of our globe down +to the bottom of the known sedimentary strata, and extending to such +crystalloid rocks as we may presume underlie these. We must also obtain +at least approximately what are the co-efficients of _total contraction_ +between fusion and atmospheric temperature of such melted rocks, basic +and acid silicates, as may be deemed representative of that co-efficient +for the range of volcanic fused products, basalts, trachytes, etc., +which probably sufficiently nearly coincide with that of the whole +non-metallic mass of our globe. + +The first I have determined experimentally by two different methods, but +principally by the direct one of the _work_ expended in crushing prisms +of sixteen representative classes of rock; the specific gravities and +specific heats of which I have also determined. + +If H be the height of a prism of rock crushed to powder by a pressure, +P, applied to two opposite faces, which, when the prism has been +reduced to its volume in powder, has acted through a range of H - t, +then + + P × (H - t) / 772 + +is the heat corresponding to the work expended in the crushing, +expressed in British units of heat. The following were the rocks +experimented upon: Caen stone, Portland (both oolites), magnesian +limestone, sandstones of various sorts, carboniferous limestones +(marbles), the older slates (Cambrian and Silurian), basalts, various +granites and porphyries, thus ranging from the newest and least +resistant to the oldest and most resistant rocks. The results have been +tabulated, and are given in detail in my Paper, now in possession of the +Royal Society. The minimum obtained is 331 and the maximum 7,867 British +units of heat developed, by transformation of the work of crushing one +cubic foot of rock. If we apply the results to a thickness of solid +crust of 100 miles (British), of which the upper twenty-one miles +consist of neozoic, newer palæozoic, older palæozoic and azoic rocks in +nearly equal proportion as to thickness, and the remaining eighty miles +of crystalloid rocks (acid and basic magmas of Durocher) of physical +properties which we may assume not very different from those of our +known granites and porphyries--and which, in so far as they may differ, +would give a still _higher_ co-efficient of work transformed into heat +than I have attributed to them by ranging them as only equal to the +granites, etc.--then we obtain a mean co-efficient for the entire +thickness of crust of 100 miles of 6,472 British units of heat, +developable from each cubic foot of its material, if crushed to powder. +It results from this that each cubic mile of the mean material of such +a crust, when crushed to powder, developes sufficient heat to melt 0·876 +cubic miles of ice into water at 32°, or to raise 7·600 cubic miles of +water from 32° to 212° Fahr., or to boil off 1·124 cubic miles of water +at 32° into steam of one atmosphere, or, taking the average melting +point of rocky mixtures at 2,000° Fahr., to melt nearly three and a-half +cubic miles of such rock, if of the same specific heat. + +Of the heat annually lost by our globe and dissipated into space, +represented by 777 cubic miles of ice melted, as before stated, the +chief part is derived from the actual hypogeal source of a hotter though +not necessarily fused nucleus, and nearly, if not wholly, is quite +independent of the heat of Vulcanicity, which is developed as a +consequence of its loss or dissipation. But were we to take the extreme +case, and suppose it possible that all the heat the globe loses annually +resulted from the transformation of the work of internal crushing of its +shell, we shall find that the total volume of rock needed to be crushed +in order to produce the required amount of lost heat is perfectly +insignificant as compared with the volume of the globe itself, or that +of its shell. For, as 1·270 cubic miles of crushed rock developes heat +equivalent to that required to melt one cubic mile of ice to water at +32°, and if we assume the volume of our globe's _solid_ crust to equal +one-fourth of the total volume of the entire globe, 987 cubic miles of +rock crushed annually would supply the whole of the heat dissipated in +that time. But that is less than the _one sixty-five millionth_ of the +volume of the crust only. + +But a very small portion of the total heat annually lost by our globe +is sufficient to account for the whole of the volcanic energy of every +sort, including thermal waters, manifested annually upon our earth. In +the absence of complete data, we can only approximately calculate what +is the annual amount of present volcanic energy of our planet. This +energy shows itself to us in three ways: 1. The heating or fusing of the +ejected solid matters at volcanic vents. 2. The evolution of steam and +other heated elastic fluids by which these are carried. 3. The work of +raising through a certain height all the materials ejected. To which we +must add a large allowance for waste, or thermal mechanical and chemical +energy ineffectually dissipated in and above the vents. All these are +measurable into units of heat. + +I have applied this method of calculation to test the adequacy of the +source I have assigned for volcanic heat, in two ways, viz.: 1. To the +phenomena presented during the last two thousand years by Vesuvius, the +best known Volcano in the world; and 2. To the whole of the four hundred +and odd volcanic cones observed so far upon our globe, of which not more +than one-half have ever been known in activity. + +It is impossible here to refer to the details of the method or steps of +these calculations. The result however is, that making large allowances +for presumably defective data, _less than one-fourth_ of the total +telluric heat annually dissipated (as already stated in amount) is +sufficient to account for the annual volcanic energy at present expended +by our globe. + +It is thus represented by the transformation into heat of the work of +crushing about 247 cubic miles of (mean) rock, a quantity so perfectly +insignificant, as compared with the volume of the globe itself, as to be +absolutely inappreciable in any way but by calculation; and as its +mechanical result is only the vertical transposition transitorily of +material within or upon our globe, the proportion of the mass of which +to the whole is equally insignificant, so not likely in any way to +produce changes recognisable by the astronomer. + +Space here forbids my entering at all upon that branch of my +investigation which is based upon the experimental results, above +mentioned, of the total contraction of fused rocks: for these, the +original Paper can, I hope, be hereafter referred to. I am enabled, +however, to prove thus how enormously more than needful has been the +store of energy dissipated since our globe was wholly a melted mass, for +the production, through the contraction of its volume, of all the +phenomena of elevation and of Vulcanicity which its surface presents. +And how very small is the amount of that energy in a unit of time as now +operative, when compared with the same at very remote epochs in our +planet's history. + +I have said that if we can find a true cause in Nature for the +origination of volcanic _heat_, all the other known phenomena, at and +about volcanic vents, become simple. Lavas and all other solid ejecta of +Volcanoes, from all parts of the earth's surface, as well as basalts, +present in chemical and physical constitution close resemblance, and may +be all referred to the melting of more or less fusible mixtures of +siliceous crystalloid rocks with aluminous (slates, etc.) and calcareous +rocks. Their general chemical composition, and the higher or lower +temperatures of fusion resulting therefrom, together with the higher or +lower temperatures to which they have been submitted at the different +volcanic foci, determine their difference of flow (under like surface +conditions) and of mineral character after ejection and cooling. + +St. Clair de Ville and Fouqué have shown that the gaseous ejections, of +which steam forms probably 99 per cent., are such as arise from water +admitted to a _pre-existent focus of high temperature_. + +Whether sea or fresh water is not material, when we bear in mind that +the chemical constituents found in sea water and in natural fresh waters +that have penetrated the soil are, on the whole, alike in kind and only +differ in proportions. But I must pass almost without notice all the +varied and instructive phenomena which are presented by volcanic vents, +for to treat of these at all would be to more than double the size of +this sketch. + +In the source that has been pointed out as that from which volcanic heat +itself is derived, viz., the secular cooling of our globe, and the +effects of that upon its solid shell, we are enabled to point to that +which is the surest test of the truth of any theory--that it not only +enables us to account for all the phenomena, near or remote, but to +predict them. We see here linked together as parts of one grand play of +forces, those of contraction by cooling, producing by _direct_ +mechanical action the elevation of mountain chains, and by their +_indirect_ action, by transformation of mechanical work into heat, the +production of Volcanoes; and both by direct and by indirect action, of +Earthquakes, never previously shown to have thus the physical connection +of one common cause, but merely supposed, more or less, to be connected +by their distribution upon our earth's surface. + +We now discern thus the physical cause _why_ Volcanoes are distributed, +viewed largely, linearly, and follow the lines of elevation; we see +equally why their action is uncertain, non-periodic, fluctuating in +intensity, with longer or shorter periods of repose, shifting in +position, becoming extinct here, appearing in new activity or for the +first time there. We have an adequate solution of the before +inexplicable fact of their propinquity, and yet want of connection. We +have an adequate cause for the fusion of rock at local points without +resorting to the baseless hypothesis of perennial lakes of lava, etc. + +For the first time, too, we discern a true physical cause for earthquake +movement, where volcanic energy does not show itself. The crushing of +the world's solid shell, whether thick or thin, goes on _per saltum_ and +at ever-shifting places, however steadily the tangential pressures +producing it may act. Hence crushing _alone_ may be shown to develope +amply sufficient impulse to produce the most violent Earthquakes, +whether they be or be not at a given place or time connected with +volcanic outburst or possible injection, or with tangential pressures, +enough still, in some cases, to produce partial permanent elevation. + +When subterraneous crushing takes place, and the circumstances of the +site do not permit the access of water, there may be Earthquake, but can +be no Volcano; where water is admitted, there may be both. + +And thus we discern why there are comparatively few submarine +Volcanoes, the floor of the ocean being, on the whole, +water-tight--"puddled," as an engineer would say, by the huge deposit of +incoherent mud, etc., that covers most of it, and probably having a +thicker crust beneath it than beneath the land. + +We see, moreover, that the geological doctrine of absolute uniformity +cannot be true as to Vulcanicity, any more than it can for any other +energy in play in our world. Its development was greatest at its +earliest stages, when the great masses of the mountain chains were +elevated. It is even now--though as compared to men's experience, and +even to all historic time, apparently uniform and always the same--a +decaying energy. + +The regimen of our planet as part of the Cosmos, which seems to some +absolute (and presented to Playfair no trace of a beginning nor +indication of an end), is not absolute, and only seems to us to be so +because we see so little of it, and of its long perspective in time. +This the now established doctrine of the conservation of energy renders +certain. + +With this source for volcanic heat, too, in our possession, we can look +from our own world to others, and predict within certain limits, which +must widen as our knowledge of the facts of their substance and surface +becomes greater, what have been and what are the developments of +Vulcanicity which have taken place or are occurring in or upon them. +Looking to our own satellite, we see for the first time a sufficient +physical cause for the enormous display of volcanic energy there which +the telescope divulges to us; one which is not to be explained alone by +the commonly made statement of the small density of the moon, but by +the fact that as the rate of her cooling from a given temperature, as +compared with that of our earth (apart from questions of the chemical +nature of the two bodies, or of their specific heats, etc.), has been +inversely as their respective masses, and directly as their surfaces, so +has the rate of cooling of the moon been vastly greater than that of the +earth, and the energy due to contraction by cooling more intense and +rapidly developed in our satellite than upon our globe. + +We have thus traced, in meagre and broken outline only--because space +admitted no more--the progress of Science to its existing state as +respects Vulcanicity, in its two branches of Vulcanology and of +Seismology, and pointed out their more intimate relations and points of +connection, and been at length able to refer them, on the sure basis of +physical laws, to one common cause, and that one derived from no +hypothesis, but simply from the postulate of our world as a terr-aqueous +globe cooling in space. + +What I have here advanced with reference to volcanic energy, which +appertains to my own researches, I do not conceal from myself, nor from +the reader, has yet to await the reception generally and the award of +the true men of science of the world. + +That, like every new line of thought which has attempted or succeeded in +supplanting the old, it will meet with opposition, I make no doubt. + +My belief, however, is that in the end it will be found to have added a +fragment to the edifice of true knowledge. + +The interpretation which I have given of the nature and origin of +volcanic activity points at once to the function in the Cosmos which it +is its destiny to fulfil. It is the instrument provided for the purpose +of continually preserving the earth's solid shell in a state to follow +down after the descending nucleus. It does this by an apparatus or play +of mechanism whereby the material of the solid shell, locally or along +certain lines, is not only crushed, but the crushed material is blown +out as dust, or expelled as liquid rock from between the walls of the +shell, which are thus enabled to approach each other; and thus, by +relief of the tangential thrusts, to permit the shell to descend, which +it is obvious that crushing alone, unless it extended to the whole mass +of the shell, could not accomplish. + +It is a wonderful example of Nature's mechanism thus to see how simple +are the means by which this end is accomplished. The same inevitable +crush that dislocates the solid shell along certain lines, produces the +heat necessary to expel to the surface the material crushed. + +When attempted to be made the basis for philosophic discovery, "final +causes" are no doubt barren, as Bacon has said; but when we have +independently and by strict methods arrived at a result, we may justly +appeal, as a test of its truth, to its showing itself as plainly +fulfilling a needful end, and, by a distinctly discernible mechanism, +preserving that harmony and conservation which are the obvious law of +the universe. + +As has been said, if I mistake not by Daubeny, John Phillips, by +Herschell, and by myself, the function of the Earthquake and the +Volcano is not destructive but, preservative. But we now see that: that +the preservative scope of this function, as respects our earth, is far +wider than what has been previously attributed to it. The Volcano does +not merely throw up new fertile soil, and tend, in some small degree, to +restore to the dry land the waste for ever going on by rain and sea; it +fulfils a far weightier and more imperative task; it--by a mechanism the +power of which is exactly balanced to the variable calls demanded of it, +and which working almost imperceptibly, although in a manner however +terrible its surface-action may at times appear to us little +men[G]--prevents at longer intervals such sudden and unlooked-for +paroxysms in the mass of our subsiding earth's shell as would be +attended with wide-spread destruction to all that it inhabit. + +To the popular mind, Volcanoes and Earthquakes are only isolated items +of curiosity amongst "the wonders of the world:" few geologists even +appear to realise how great and important are the relations of +Vulcanicity to their science, viewed as a whole. Yet of Vulcanicity it +is not too much to say, that in proportion as its nature and doctrines +come to be known and understood as parts of the Cosmos, the nearer will +it be seen to lie at the basis of all Physical Geology. + + +[A] For a fuller account of the literature and history of advancement of +human knowledge as to Earthquakes, here merely glanced at, I must refer +to my First Report on the Facts of Earthquakes, "Reports, British +Association, 1850," and to the works of Daubeny, Lyell, Phillips and +others, its _complete_ history remaining yet to be written. + +[B] Yet how indistinctly formed were Young's ideas, and indistinct in +the same direction as those of Humboldt, becomes evident by a single +sentence: "When the agitation produced by an Earthquake extends further +than there is any reason to suspect a subterraneous communication, it is +probably propagated through the earth nearly in the same manner as a +noise is conveyed through the air."--_Lectures, Nat. Phil._, Vol. I. + +[C] The Right Rev. Charles Graves, F.R.S., etc., then Fellow of Trinity +College, Pres. R. I. Acad., and now Bishop of Limerick, on presentation +of the Academy's Cunningham Medal. + +[D] In this Report, though I have never before referred to it, and do so +now with reluctance, I have always felt that the Author did me some +injustice. The only reference made to my labours, published the +preceding year only, is in the following words: "Many persons have +regarded these phenomena (viz., Earthquakes) as due in a great measure +to vibrations ... and the subject has lately been brought under our +notice, in a Memoir by Mr. Mallet, 'On the Dynamics of Earthquakes,' in +which he has treated it in a more determinate manner, and in more +detail, than any preceding writer" (p. 74). If that Paper of mine be +collated with this Report, it will be, I believe, found that, as +respects the earthquake part, the latter tint parades, in a mathematical +dress, some portions of the general theory of earthquake movements, +previously published by me as above stated. So, also, in the chapter (p. +90) referring to Seismometry, and the important uses to Geology that +might be (and since have been, to some extent) made of it, no mention is +made of those instruments previously proposed by me, nor of my +anticipation of their important uses. This is but too mortifyingly +suggestive of the-- + + "Pereant qui mea ante mihi dixerunt." + +Having left this unnoticed for so many years, and during which the +Author has preceded me to that bourne where our errors to each other +must be forgotten, I should certainly not have now trespassed on the +good rule, _De mortuis nil nisi bonum_, had I not observed very recently +one amongst other results probably attributable to it. In Professor +Phillips's "Vesuvius," if any one will refer to the passage beginning +"The mechanism of earthquake movement has been investigated by competent +hands. The late eminent mathematician, Mr. Hopkins, explained these +tremors in the solid earth by the general theory of vibratory motion," +etc. (pages 257-259)--I think he must, in the absence of collateral +information, conclude that, not I, but Mr. Hopkins, was the discoverer +of the Theory of Earthquakes as explained by the general theory of +vibratory motion. + +Probably my friend, Professor Phillips, had not recently referred to +those Memoirs and Reports of twenty-four years back, and I am thoroughly +convinced that, if he has here perpetuated an injustice, he has done so +unintentionally and unwittingly. + +Still, the facts show how true it is that + + "The ill men do lives after them, + The good they do is oft interred with their bones." + +And I may venture to ask my friend, should his admirable book reach, as +I doubt not it will, another edition, to modify the passage. + +[E] Assuming the point of ejection of this block (the crater) to be +8,000 feet above where it landed, and allowing it as high a density as +admissible, and the angle of projection the best for large horizontal +range, it may be proved that this mass, to reach nine miles +horizontally, would require an initial velocity of projection of from +1,500 to 1,600 feet per second, one as great as that of a smooth-bore +cannon-shot at the muzzle, and perfectly inconceivable to be produced by +a volcano. + +[F] The Rev. O. Fisher, M.A., F.G.S., in a most interesting and valuable +Paper, "On the Elevation of Mountain Chains by Lateral Pressure, its +Cause, and the Amount of it, with a Speculation on the Origin of +Volcanic Action," read, April, 1868, and published in the Transactions +of the Cambridge Philosophical Society, Vol. XI., Part III., in 1869, +has deduced the necessary crushing of the earth's crust by a different +but closely analogous method. I had not seen this Paper until after my +own was in the hands of the Royal Society. The author's volcanic views +are wholly different from my own, and do not appear to me equally valid +with his notions as to elevation.--R. M. + +[G] "Magna ista quia parvi sumus"--SENECA, "Quæs. Nat." + + +END. + + + + +TRANSLATION +OF + +PROFESSOR PALMIERI'S + +_ACCOUNT OF_ +THE ERUPTION OF VESUVIUS +OF +_1871-1872_ + + + + +I. + +ACCOUNT OF THE ERUPTION. + + +The great and disastrous conflagration of Vesuvius, which took place on +the 26th of April, 1872, was, in my opinion, the last phase of an +eruption which commenced at the end of January, 1871, an account of +which I was unwilling to write, because I was convinced that it would +not really terminate without a more or less violent explosion, such as I +had often predicted. I shall now state the reasons upon which my +prediction was founded. + +When the central crater begins to heave, with slight eruptions, one may +always predict a series of slight convulsions of greater or less +duration, which are preparatory to the grand explosion, after which the +Volcano remains for the most part in repose. Thus, when I observed the +cone fissuring in November, 1868, and copious lava streams issuing from +it, and flowing over the beautiful and fertile plains of the Novelle, +through the Fossa della Vetrana, instead of announcing the beginning of +an eruption, I announced the termination of one which had been manifest +for upwards of a year by the constant flow of lava from the summit of +the cone. + +From the month of November, 1868, until the end of December, 1870, the +mountain remained quiet, except that the fumaroles at the head of the +fissure showed a degree of activity by which chlorides and sulphides of +copper, sulphide of potash and other products, were engendered. + +But in the beginning of 1871 the seismograph was disturbed,[1] and the +crater discharged, with a slight detonation, a few incandescent +projectiles. Then I announced that _a new eruption had commenced, which +might be of long duration, but with phases that could not possibly be +foreseen_; and on the 13th January, on the northern edge of the upper +plain of the Vesuvian cone, an aperture appeared, from which at first a +little lava issued, and then a small cone arose and threw out +incandescent projectiles, with much smoke of a reddish colour, whilst +the central crater continued to detonate more loudly and frequently. The +lava-flow continued to increase until the beginning of March, without +extending much beyond the base of the cone, although it had great +mobility. In March, this little cone appeared not only to subside, but +even partly to give way, as almost happens with eccentric cones when +their activity is at an end. Upon visiting it, I observed that four +prismatic or pillar-like masses remained standing, three of which were +formed of scoriæ which had fallen back again in a pasty condition, and +had become soldered together, the fourth consisting of a pyramidal block +of compact and lithoidal lava, which appeared to have been forced up by +impetus from the ground beneath. A little smoke issued from the small +crater, and a loud hissing from the interior was audible. By lying +along the edge, I could see a cavity of cylindrical form about ten +metres in depth, tapestried with stalactitic scoriæ covered with +sublimations of various colours. The bottom of this crater was level, +but in the centre a small cone of about two metres had formed, pointed +in such a manner that it possessed but a very narrow opening at the +apex, from which smoke issued with a hissing sound, and from which were +spurted a few very small incandescent scoriæ. This little cone increased +in size as well as activity until it filled the crater, and rose four or +five metres above the brim.[A] New and more abundant lavas appeared near +the base of this cone, and, pouring continually into the Atria del +Cavallo, rushed into the Fossa della Vetrana in the direction of the +Observatory and towards the Crocella, where they accumulated to such an +extent as to cover the hill-side for a distance of about 300 metres; +then turning below the Canteroni, they formed a hillock there without +spreading much farther. These very leucitic lavas are capable of great +extension, the pieces which are ejected forming for the most part very +fine filiform masses, which may be collected on the mountain in great +quantities, and specimens of which I presented to the Academy under the +name of _filiform lapilli_. These threads were often of a clear +yellowish colour, and, when observed under the microscope, were found to +consist of very minute crystals of leucite embedded in a homogeneous +paste. The crystals were still smaller as the diameter of the threads +was less, and never formed knots or swellings even in the most hair-like +threads. These observations led me to reject the opinion of those who +hold that crystals of leucite are pre-existent in the lava. The viscous +nature of these lavas prevented their being covered with fragmentary +scoriæ, but caused the formation at first of a skin, which, thickening, +became at last a more or less pliable shell, that, when more solidified, +allowed the still fluid part to run as in a tube formed of this solid +shell. For many months the lava descended thus from the cone and +traversed the Atria del Cavallo, always covered, appearing below the +Canteroni of a lively fluidity, until it could no longer be enveloped in +its skin, which was stretched by the addition of new lava, and finally +rent asunder to give room to the current until, owing to diminished +liquidity, it was constrained to stop. When the lava, having traversed +the covered channel it had made for itself from the top of the mountain +to below the Canteroni, made its appearance still running, it frequently +formed large bubbles on the surface, which mostly burst to give vent to +smoke, and then disappeared. + +In October, 1871, near the edge of the central crater, another small +crater was formed by falling in, which, after a few days, gave vent to +smoke and several jets of lava. The principal cone frequently opened in +some point of the slope to give egress to small currents of lava, which +quickly ceased. But towards the end of October the detonations +increased, the smoke from the central crater issued more densely and +mixed with ashes, and the seismograph and accompanying apparatus were +disturbed: for all these reasons, I said in one of my bulletins, _we +have either reached a new phase or the end of the eruption_, not knowing +whether the new phase would be the last. On the 3rd and 4th November +copious and splendid lava streams coursed down the principal cone on its +western side, but were soon exhausted. The cone of 1871 appeared again +at rest, and partly even fell in, but did not cease to emit smoke and to +show fire in the interior. + +In the beginning of January, 1872, the little cone again became active, +the crater of the preceding October resumed strength, with frequent +bellowings and projectiles, and soon after lavas of the same kind as +before reappeared. The cone of 1871, formed again by the lava ejected, +became so full that the lava poured from its summit in the most singular +and enchanting manner. So far only an eccentric or ephemeral cone had +risen close to the central crater, which, after exhaustion, regained +vigour and discharged lava from the apex instead of the base, as usually +happens. + +In the month of February matters were somewhat moderated; but in March, +with the full moon, the cone opened on the north-west side--the cleavage +being manifest by a line of fumaroles--and a lava stream issued from the +lowest part without any noise and with very little smoke, and poured +down into the Atria del Cavallo as far as the precipices of Monte di +Somma. This lava ceased flowing after a week, but the fumaroles pointed +out the cleft of the cone; and between the small re-made cone, which had +risen to the height of 35 metres, and the central crater, a new crater +of small dimensions and interrupted activity opened. + +On the 23rd April (another full moon) the Observatory instruments became +agitated, the activity of the craters increased, and on the evening of +the 24th splendid lavas descended the cone in various directions, +attracting on the same night the visits of a great many strangers. All +these lava streams were nearly exhausted on the morning of the 25th; +only one remained, which issued from the base of the cone, not far from +the spot whence that of the preceding month had issued. Numbers of +visitors, attracted by the splendour of the lava streams of the +preceding night, which they supposed still continued, soon arrived, but, +finding them exhausted, were for the most part conducted by their guides +to see the one still flowing. It was almost inaccessible, and to reach +it one had to walk over the rough inequalities of the scoriæ. It took me +two hours to get there from the Observatory, when I visited it that +morning, and therefore I endeavoured to dissuade those who wished to +visit it at night from the attempt, but set out myself from the +Observatory at 7 p.m., leaving my only assistant there. The instruments +were agitated. After midnight the Observatory was closed, and my +assistant retired to rest. Late and unlucky visitors passed unobserved +with an escort of inexperienced guides; at half-past 3 o'clock in the +morning of the 26th they were in the Atria del Cavallo, when the +Vesuvian cone became rent in a north-westerly direction, the fissure +commencing at the little cone which disappeared, and extending to the +Atria del Cavallo, whence a copious torrent of lava issued. Two large +craters formed at the summit of the mountain, discharging numerous +incandescent projectiles with white ashes, and glittering with particles +of mica, which frequently recurred. + +A cloud of smoke enveloped these unfortunates, who were under a hail of +burning projectiles and close to the lava torrent. Some were buried +beneath it[B] and disappeared for ever; two dead bodies were picked up, +and eleven grievously injured, one of whom died close to the +Observatory. He alone revealed his name, Antonio Giannone. I learned +afterwards that he was a fine young fellow, and Assistant-Professor in +one of the Universities. + +Assistant-Professors Signor Franco, who is a priest, and Signor +Francesco Cozzolino, a priest also, entrusted with the festive mass for +the Observatory, hastened to assist the dying. On my own return thither, +the sad spectacle of the dead and dying awaited me; the former were +conveyed, through the assistance of the municipal officer of Resina, to +the Cemetery, and the latter to the Hospital. But we must leave this +scene of grief and sorrow, and return to the eruption. + +The fissure of the cone on the north-west side was large and deep, and +extended into the Atria del Cavallo, about 300 metres. No mouth opened +along the cleft of the cone itself; all the lava issued from that part +which extended into the Atria. From previous experience I should have +expected to have seen the formation of adventitious cones along the +widest part of the fissure, which is never that most elevated, and these +discharging from their summits æriform matter frequently mixed with +projectiles, and from their base lava; but on this occasion no cone +appeared at the widest part of the fissure, but a long hillock was +formed like a little chain of mountains, one point of which was elevated +about fifty metres above the plain beneath, and bearing no resemblance +to a cone. + +Another fissure opened in the cone on the south side, which did not +extend to the base, and lava issued from this and flowed in the +direction of the Camaldoli. Streams of less importance furrowed the cone +in other directions, but the largest quantity of lava proceeded from the +fissure in the Atria del Cavallo, below the hillock or miniature chain +of collines just described. This lava stream was for some time +restrained within the Atria del Cavallo, among the holes and +inequalities of the lavas of 1871, but these being filled up and +overcome, it divided into two branches--the smaller one flowing through +a hollow which separated the lavas of 1867 from those of 1871, and made +its way over the lavas of 1858, threatening Resina, but stopped as soon +as it reached the first cultivated ground; the larger branch +precipitated itself into the Fossa della Vetrana, occupying the whole +width, about 800 metres; and traversing the entire length of 1,300 +metres in three hours. It dashed into the Fossa di Faraone; here it +again divided into two streams, one overlying the lava of 1868, on the +Plain of the Novelle, partially covering the cultivated ground and +country-houses; the other flowing on through the Fossa di Faraglione, +over the lava of 1855, reached the villages of Massa and St. Sebastiano, +covering a portion of the houses, and thence continued its course +through the bed of a foss or trench which, contrary to my advice, had +been excavated after the eruption of 1855, in the expectation of +diverting the course of that lava. I did not fail to observe that the +rains which previously descended through these steep channels, would in +future be kept back to filtrate through the scoriæ, without ever +reaching the new channel. + +The lava of this eruption, meeting with this said excavation, flowed +into it, instead of pursuing its road over the lava of 1855, and thus +invaded highly cultivated ground and towns of considerable value, +extending to the very walls of a country-house belonging to the +celebrated painter, Luca Giordano. This lava stream, having surmounted +the obstacles which the heaps of scoriæ in the Atria del Cavallo +presented to it, ran with great velocity (notwithstanding its being +greatly widened out in the Fossa del Vetrano), so that between 10 a.m. +and 11 p.m. it traversed about five kilometres of road, occupying a +surface of five to six square kilometres. If it had not greatly +slackened after midnight, from the failure of supply at its source, in +twenty-four hours more, by occupying Ponticelli, it would have reached +Naples, and flowed into the sea. + +Although I had often visited the two villages of Massa and St. +Sebastiano, previously greatly injured by the lava of 1855, yet I could +not well estimate, upon now seeing them again, the number of houses +which had disappeared. Massa seemed to me diminished by about one-third, +and St. Sebastiano by somewhat less than a fourth. But the way of escape +was open to the inhabitants of Massa; whilst a great river of lava +occupying the road leading to St. Giorgio a Cremano would have hindered +the flight of the inhabitants of St. Sebastiano, if they had been +dilatory. The lava stream now separating the two villages is little less +than a kilometre in width, and is about six metres in height. + +On the night of the 26th April, the Observatory lay between two torrents +of fire, which emitted an insufferable heat. The glass in the +window-frames, especially on the Vetrana side, was hot and cracking, and +a smell of scorching was perceptible in the rooms. The cone, besides +being furrowed by the lava streams just described, was traversed by +several others, which appeared and disappeared. It seemed completely +perforated, and the lava oozed as it were through its whole surface. I +cannot better express this phenomenon, than by saying that _Vesuvius +sweated fire_. In the day-time, the cone appeared momentarily covered +with white steam jets (fumaroles), which looked like flakes of cotton +against the dark mountain-side, appearing and disappearing at brief +intervals. + +Simultaneously with the grand fissure of the cone, two large craters +opened at the summit, discharging with a dreadful noise, audible at a +great distance, an immense cloud of smoke and ashes with bombs and +flakes, rising to the height of 1300 metres[C] above the brim of lava +(_sull' orlo de essi_). The white ashes, before described, although they +did not fall beyond the Crocella, were carried by the wind as far as +Cosenza, from whence they were sent to me by Dr. Conti. These ejections +were followed by dark sand, with lapilli and small fragments of scoriæ +of the same colour. The smoke, driven up with violence, assumed the +usual aspect of a pine tree, of so sad a colour that it reminded us of +the shadowy elm of Virgil's dreams ("_ulmus opaca ingens_"). From the +trunk and branches of the pine-tree cloud fell a rain of incandescent +material, which frequently covered all the cone. The lapilli and the +ashes were carried to greater distances. + +The victims of the morning of the 26th, the torrents of fire which +threatened Resina, Bosco and Torre Annunziata, and which devastated the +fertile country of the Novelle, of Massa, St. Sebastiano and Cercola, +the two partially buried villages, the continual and threatening +growlings of the craters, caused such terror that numbers fled from +their dwellings near the mountain into Naples, and several in Naples +went to Rome or to other places. Very many delayed from the knowledge +that I was in the Observatory, and held themselves in readiness for +flight whenever I should abandon it. + +The rapidity with which the vast torrent of fire assailed the houses +(_i.e._, in these villages), and the great heat which spread to a +distance, scarcely allowed the fugitives to carry away any of their +belongings; many were completely destitute. The authorities vied with +each other in zealous efforts to relieve the distress, and the +municipality of Naples sheltered and fed the wretched beings for many +days. + +The igneous period of the eruption was short, for on the morning of the +27th the lava stream, bearing down upon Resina, having covered a few +cultivated fields, stopped; the lava descending from the summit of the +mountain towards the Camaldoli also stopped; and the great lava torrent, +which passed the shoulders of the Observatory through the Fossa della +Vetrana, lowered the level of its surface below those of its two sides, +which appeared like two parallel ramparts above it. + +If these streams had continued on the 27th, flowing in the same manner +as they did on the night of the 26th, they would have reached the sea, +bringing destruction to the very walls of Naples. + +But before leaving the subject of these lavas I must narrate an +important fact to which I was witness, and which was thrice repeated, +near the banks of the great river of fire that ran close to the +Observatory. At three several points, and at different times, I observed +great balls of black smoke issue from the lava, driven up with continued +violence, as if from a crater; through the smoke I frequently observed +numerous projectiles thrown up into the air, but I could not say whether +with noise or in silence, for the noise of the central crater was +deafening. Each of these little eruptions, which I may call _external +eruptions_, lasted from fifteen to twenty minutes. The first took place +at the most elevated point of the Fossa della Vetrana, on the right bank +of the torrent; the second, under the hill of Apicella, where the lava +divided into the two branches, before described; and the third near to +the Observatory on the left bank of the lava stream. These singular +explosions terminated without leaving little cones or craters, the lava +in its impetuosity carrying every trace away. These eruptions were seen +from Naples, and the Observatory was justly believed to be in danger. +One has been clearly photographed, the one which was the best seen from +Naples, being the nearest and the least darkened by the smoke of the +lava. (Plate 4.) Is this the first time that the phenomenon has been +remarked? I believe that it is at least the first time it has been +authenticated. The authority of Julius Schmidt, quoted by Scrope, has no +weight with me, for I was also a witness of what happened at Vesuvius in +1855; and, although these cones were in the midst of the lava in the +Atria del Cavallo, they originated, according to the opinion of +everyone, from the fissure from which the other and much larger cones +proceeded. The same phenomenon was observed in the Atria del Cavallo in +1858, when I caused two of the little cones to be brought to the +Observatory; but these also might belong to the fissure along which the +other cones were arranged. The same may be said of the little craters +observed, after they had been exhausted, by Professor Scacchi in 1850. +But the discharging mouths now observed in the Fossa della Vetrana, +which existed for twenty minutes and then disappeared, and which were +not at all in a continuous line, and could not be supposed to correspond +with any fissure beneath, constitute a circumstance which, if not new, +is evident for the first time, and cause the recognition of a power in +the lava itself to form eruptive fumaroles.[2] + +The igneous period of the eruption having terminated on the evening of +the 27th, the ashes, lapilli, and projectiles became a little more +abundant, whilst the roaring noises of the craters apparently became +greater. The pine-tree cloud was of a darker colour, and was furrowed by +continual lightning, visible by daylight from the Observatory. Many +writers on the subject of Vesuvius affirm that the flashes which appear +through the smoke cloud were lightning unaccompanied with thunder, but +they studied the phenomena from Naples, or some place more or less +distant from the crater, where the report of the thunder was inaudible, +or could not be distinguished from the bellowing and detonation of the +mountain. The fact is that these flashes were constantly followed by +thunder, after an interval of about seven seconds.[D] When the flash was +very short, a simple noise like the report of a gun was heard, but if it +were long, a protracted sound like that from torn paper ensued. + +On the 28th the ashes and lapilli, continuing to fall abundantly, +darkened the air, yet without diminishing the terrible noise; at Resina, +Portici, St. Giorgio a Cremano, Naples, etc., terror was universal. + +On the 29th, with a strong wind blowing from the east, scoriæ of such a +size fell at the Observatory, that the glass of the windows unprotected +by external blinds was broken. The noise from the crater continued, but +the projectiles rose to a less height, indicating a diminution in the +dynamic power of the eruption. Towards midnight the noise of the craters +was no longer continuous, and recurred with less force and for shorter +intervals. Almost at the same hour a tempest burst over the Campania +with loud thunder and a little rain. The grass, the seeds, the vine +tendrils, the leaves and tops of the trees dried up immediately, and the +country was changed from spring to winter. The storm, although repeated +on the following days, passed away by degrees, and thus the floods, +which I strongly feared, did not occur. Almost always after great +eruptions of Vesuvius, storms of heavy rain have followed, and the +ground being covered with ashes, the water could not filtrate through +into the soil, but descended in muddy torrents over the adjacent +country, occasioning as much damage as the fire itself. + +On the 30th, the detonations were very few, and the smoke issued only at +intervals, and by the 1st May the eruption was completely over. + +When the smoke had cleared off the figure of the cone was seen to be +changed. (_Vide_ Plate 5a.) + +The ground was perpetually disturbed whilst the Volcano raged, so that +the Observatory oscillated continually. Some shocks were felt not only +in the adjacent territory, but at a greater distance, at Montovi and +elsewhere. The oscillations at the Observatory were chiefly undulatory, +from N.E. to S.W. They were observed for some days after the termination +of the eruption, but not continuously, although they maintained some +intensity. + +If we refer to January, 1871, we shall find that that eruption was +preceded by several earthquakes, among which were those of the months of +October, November and December, in the previous year, that wrought such +destruction in Calabria, and especially in the province of Cosenza; if +we consider that as only the last phase, we shall find that it was +preceded by great shocks of earthquake that devastated some regions of +Greece.[3] + +The great quantity of lapilli which fell buried the scoriæ with which +the Vesuvius cone was covered, so that it became somewhat more difficult +to ascend to the summit, and much less difficult to descend. Having +reached the top of the mountain, I found a large crater divided into two +parts by what seemed a cyclopean wall. The two abysses had vertical +sides, and revealed the internal structure of the cone. Their vertical +depth was 250 metres; and beyond that I observed a sort of tunnel +perforated in the rock, with a covering arch raised above the bottom of +the eastern abyss about 12 metres, judging by the eye. The interior +walls of the crater showed neither the usual stalactitic scoriæ nor +sublimations, nor fumaroles, but alternate beds of scoriæ and of compact +lava. The fumaroles and sublimations abounded, only about the brims of +the craters. Hydrochloric and sulphuric acid and sometimes sulphuretted +hydrogen affected respiration, and the temperature rose sometimes to 150 +degrees. Various fissures about the brim of the double crater indicated +prolongations downwards, which allowed me to descend with a rope, in +order to examine the interior of the tunnel to which I have just +alluded. The highest brim of the crater was fissured for a distance of +80 metres, and the greatest depth of fissure was at that place. + +By measurement with the barometer, we ascertained approximately (for +only one barometer was used) that the height of the Vesuvian cone was +somewhat diminished. + +Not only the Vesuvian cone, but the whole adjacent country appeared +white for many days, as if covered with snow, when exposed to sunlight. +This was due to the sea-salt contained in the ashes with which the +surface was strewn. + +A great quantity of coleoptera assembled on the flat roof of the +Observatory, where the ashes and lapilli were heaped up two decimetres +in height. I found the same species on the cone, where many insects were +observed on other occasions, such as the _Cuccinella septempunctata_; +the crysomela populi, etc., were wanting. This phenomenon of the +extraordinary concourse of insects on the top of Vesuvius, in order to +die in some of the fumaroles, especially noted previous to and after +great eruptions, is a circumstance for which I cannot account.[4] The +whole of the lava emitted in this eruption occupies a surface of about +five square kilometres; allowing an average thickness of four metres, we +obtain a mass of twenty millions of cubic metres. About three-fifths of +this lava did no injury, being deposited upon other pre-existing lava. +However, the lava in the Novelle, which was deposited upon the lava of +1858, covered quarries of the best stone which had been worked at the +time, covered many paths that had been cleared, and buried the new +Church of St. Michele, with some houses that surrounded it, which had +been rebuilt on the site of the former church, which was covered by the +lava of 1868. The destruction of land in occupation, of buildings and of +crops, exceeded three million francs in value. Many proposals for +relieving the sufferers have been received. Wishing to aid in this +benevolent work, I gave a public lecture, admission for each person +being one franc; and this lecture, from notes badly taken, was printed +by private speculation, and I was compelled to repudiate the report of +it through the public papers. + +The evolutions of carbonic acid (_mofette_), which usually appear at the +end of great Vesuvian eruptions at low-situated spots or hollows, with +very rare exceptions, were observed on this occasion a few days after +the eruption had completely ceased. They appeared in the direction of +Resina. I found the most elevated at Tironi, and the most numerous +between La Favorita and the Bosco Reale di Portici. + +The water in wells was on this occasion neither deficient nor scarce +previous to the eruption, but was very acid after the appearance of the +carbonic acid evolutions in those neighbourhoods in which they +abounded. Having stated that the disastrous conflagration of the 26th +April ought, in my opinion, to be regarded as the last phase of a long +period of eruption, which commenced at the beginning of 1871, I consider +it right to discuss the question at somewhat greater length. + +Not only from twenty years' personal observations, but from the +attentive study of accounts of previous eruptions, I have found that +when the central crater awakens with small eruptions after a certain +time of previous repose, these almost always have a long duration, and, +after various phases of increase and decrease, terminate in a great +eccentric eruption, that is to say, with the production of an aperture +from which a copious lava stream issues. The eruptions of 1858, 1861, +1868 and 1872, furnish the most recent examples of what I affirm. I +might cite many others of earlier date, but I shall content myself with +recording the greatest conflagration of this century, that of October, +1822. + +Before the erection of the Vesuvian Observatory, it was impossible to +obtain a consecutive account of all the phases which the Volcano +presented; but we generally obtained the description of the more +splendid phases of the eruption which arrested the attention of +everyone. Hence, notices of the small phenomena which preceded a great +eruption are frequently wanting. We cannot always ascertain whether the +fumaroles of the craters became active and at what periods, what was +their temperature and what the diverse nature of their emanations, etc.: +whether and when any change in the crater with slight eruptive +manifestations occurred; discharges which sometimes commenced in the +bottom of a crater becoming active, and so are invisible at Naples. + +But it may be asked whether the inverse proposition be equally true, +that is, whether all the great eruptions of our Volcano were preceded by +small fiery manifestations of long duration? There have undoubtedly been +great eruptions not preceded by small central eruptions, but these also +had their period of preparation or precursory signs. After the great +eruption of 1850, Vesuvius remained in apparent repose until the end of +May, 1855, when there was an eccentric eruption and a great flow of lava +lasting twenty-seven days. But for a year before the fumaroles on the +top of the mountain had acquired great activity, their temperature +increased, and hydrochloric and sulphuric acid became more abundant, and +generated the usual coloured products on the adjacent scoriæ. Finally, +in the month of January, a crater was formed by falling in of the +ground, and although it did not discharge fire, yet it poured forth +dense smoke. This was the beginning of the fissure manifested four +months afterwards. + +Ignazio Sorrentino, who spent a long life in the study of Vesuvius, and +frequently ascended it, considered the increase of those yellow +products--which are chiefly chlorides of iron, but were, at that time, +mistaken for sulphur--as the sign of an approaching eruption. + +The only grave objection that can be alleged is that of the memorable +eruption of 1631, which surprised the neighbouring population so +suddenly that many perished miserably, surrounded or covered with lava. +But that terrible conflagration occurred after centuries of repose, so +that trees had grown in the interior of the crater. No one suspected the +possibility of danger. It took place, too, at the end of autumn, when +the cone is usually covered with clouds, and, therefore, no one had an +opportunity of observing any precursory phenomena. + +When the Observatory was established, I was able--in the first instance, +at my own expense, and afterwards with some slight assistance from +Government--to undertake studies more assiduous than any previously +made. I had two instruments adjusted to indicate the internal efforts of +the Volcano, viz., M. Lamond's apparatus of variations, which, by means +of finely-balanced needles and methods of amplification proposed by +Gauss, indicates the slightest trepidation of the ground, and my own +electro-magnetic seismograph, a self-registering instrument of exquisite +delicacy. These instruments, when attentively observed, give the most +valuable information with respect to the activity of the adjacent +Volcano. + +If the very slightest eruption occurs, these instruments manifest slight +perturbation, increasing with the activity of the mountain. When the +Volcano attains a certain degree of activity, and the instruments are +proportionately disturbed, it is impossible to foresee a new phase of +increase without constantly watching the changes in the intensity of the +perturbations; and to effect this it is requisite to have upon the spot +a staff of assistants sufficiently numerous, scientific and intelligent. +If, therefore, on the night preceding the 26th of April the instruments +had been properly watched, they would have undoubtedly indicated the +great increase in the activity of the Volcano. The perturbations on the +23rd were steadily increasing, and on the evening of the 25th they were +much stronger than on the 24th, but on the morning of the 26th they had +become extraordinarily strong; they must, therefore, have increased +considerably during the night. + + + + +II. + +NATURE OF THE LAVAS. + + +When the observer is near the source of the lava, he sees matter in a +state of fusion, which, like a torrent of liquid fire, runs along, with +more or less impetuosity, between two banks formed by itself. But as +soon as the surface of the torrent cools to the point of congelation, it +loses the splendour of its first incandescence. The part which begins to +harden breaks readily in some lavas into fragments which float on the +viscous fluid beneath; these, increasing in number with distance from +the source, conceal the molten matter beneath and retard its progress, +and at last nothing is seen but the more or less red-hot scoriæ moving +along. These lavas I shall call "_Lavas with fragmentary scoriæ_." + +On other occasions, a skin forms on the surface of the lava, which, +gradually thickening, keeps flexible for some time, and then wrinkles or +swells or extends and breaks to give egress to the hot fluid within, +which, in its turn, skins over and repeats the same phenomena. This I +shall call "_Lavas with a united surface_." + +These, in their course, discharge less smoke than the first, draw out +more easily into threads, and, when cold, have a dark colour, something +like bitumen or pitch. _The lava with fragmentary scoriæ_, when +stretched, breaks easily, discharges smoke copiously, and, when +hardened, has a more bluish tint, like clods of upturned earth (_formato +di zolle_). It is noisy in its course, because the incoherent scoriæ +that it carries along strike and crunch against each other; the other +lava flows silently, except for a sort of crackling arising from the +actual fracturing up of the solid skin by distension from the liquid +matter within. If required to give the mineralogical characteristics of +this lava, I would say that it was rich in leucite and contained little +or no pyroxene; the fragmentary lava, on the contrary, is poor in +leucite and rich in pyroxene. The lavas of 1871 were of the "united +surface" character; those of 1872 were "fragmentary," with some +characteristics which I shall describe: + + 1. They were of the clearest tint I have ever seen, when + regarded superficially, but, when broken, the fracture was + darker than any other lava. + + 2. They had very little leucite and abounded in pyroxene and + olivine, and sometimes contained a few crystals of amphibole. + + 3. Their specific gravity varied with their porosity; the most + compact attained 2·75. + + 4. These lavas carried along in their course a quantity of + scoriæ which had long been subjected to the action of the acids + of the fumaroles close to the craters, and also a great many + bombs (_bombe_)--that is, round masses similar to those ejected + from craters. These varied in size, some having a diameter of + four to five meters. They frequently contained a large nucleus + of very leucitic lava, like that of 1871, with a larger or + smaller quantity of feroligiste (peroxide of iron). Others + contained lavas changed by the action of the acid vapours near + the craters. These bombs must have flowed out with the lava, + for they are found through its whole course, and they were + certainly not ejected from the crater; for not only are they + found on the lava exclusively, but masses so enormous were not + thrown up from the craters during the eruption; those lying on + the cone near the craters seldom exceed a decimetre in + diameter. + +As to the qualitative chemical analysis of the lavas, it always presents +the same elements, with the exception of small quantities of some +metals, lead for example, which have escaped the researches of good +chemists, but which I have constantly found in the sublimations of the +fumaroles of the lava. With respect to the quantitative analysis, two +specimens of the same lava appear indeed to have their constituents in +different proportions. To arrive at any conclusion a long and patient +investigation, requiring means and assistance which the Observatory does +not possess, would be necessary. + +Professor Fuchs, of Heidelberg, has devoted himself to this work for +years past, and if he continue it with well-selected and sufficiently +large specimens we may hope some day to obtain satisfactory results. + + 5. Every specimen of lava which I examined with a very + sensitive magnetoscope improved by myself, was invariably + magneto-polar, not excepting the pieces of the bombs, whether + rejected from the crater or carried along with the lava. + + + + +III. + +FUMAROLES OF THE LAVAS. + + +Smoke generally issues from all lava when it cools down to a certain +degree, hence it is more abundant at the edges of the fiery torrent, or +is liberated from the scoriæ that form on its surface. But when the lava +stops, the smoke issues only from certain vent-holes, through which we +can still see the fire, and at the edge of which different amorphous or +crystallized matters collect by sublimation. These centres of heat, of +more or less duration, are the fumaroles of the lavas. I believe I have +on other occasions shown that a fumarole is nothing but a communication +between the more or less cooled and hardened surface of the lava and the +interior, which is still incandescent. Some fumaroles last but a day, +others preserve their activity for weeks, months or years, according to +the depth of lava through which they penetrate; and when they cease to +be active, that is, when the sublimations are formed, or smoke or other +æriform matters issue from them, they still retain a rather elevated +temperature. In the lavas of 1858, in a place where they had a +transverse width of 150 metres, a vent-hole may still be found where the +thermometer registers 60° and the scoriæ are warm. Sometimes, while the +lava is in process of cooling, new fumaroles appear, in which the fire +is visible. This phenomenon, which appeared marvellous and inexplicable +when I first observed it in 1855, is now very easily understood; the +cooled and hardened crust of the lava fractures with noise and suddenly, +and so a new communication is opened with the incandescent lava below, +thus creating a new fumarole. + +As the smoke of the fluid lava is perfectly neutral, that is, neither +acid nor alkaline, so the fumaroles at the first period of their +existence with sublimations of sea-salt, mixed frequently with oxide of +copper either in black powder or in shining laminæ, ought also to be +neutral. But if the fumarole continues active, hydrochloric acid issues +with the smoke, and often some time after sulphuric acid. Then the +sublimations turn first yellow, then green, and more rarely azure. The +chemical reactions show that these sublimations are chlorides or +sulpho-chlorides, and sometimes sulphides, and they afford reactions, +indicative of soda, magnesia, copper, lead, and traces of other +substances, not excluding ammonia, which I must speak of separately. +This, I have observed, is the general law with the fumaroles of the +tranquil lavas, which occur with long and moderate eruptions--for +instance, the lavas of 1871, and even those of 1872, preceding the 26th +April. + +But in the great lavas of the great conflagrations of Vesuvius, chloride +of iron more or less in combination with all the other substances above +mentioned changes the appearance of the sublimations. The fumaroles in +the lava of the 26th April frequently indicated chloride of iron. +Sulphuretted hydrogen, by reaction of sulphurous acid, is decomposed, +and sulphur sublimed, having a particular aspect, collects on the +scoriæ. This is never found but in fumaroles of the smaller lavas; it +was therefore absent in those of 1871, but frequently occurred in those +of 1872. + +Although the sublimations are generally mixtures, yet sometimes distinct +and crystallized chemical or mineral species are found, such as sulphur, +sal ammoniac, _tenorite_, _cotunuite_, etc. Micaceous peroxide of iron +(feroligiste), so common near eruptive cones, is very scarce on lava; +any found in it has been carried down from the craters, and proofs of +this transport are very abundant and striking in the lavas of this last +eruption. Even the iron found in the bombs is evidently transported; +there is a fumarole on the ridge of the lava in the Fossa di Faraone +which contains micaceous peroxide of iron, and this, at first sight, +appears to oppose what I have affirmed; nevertheless, it gives +additional force to my statement. This fumarole is only a bomb or +rounded mass of enormous size, four or five metres in diameter. Smoke +and hydrochloric acid issued from the aperture in its envelope, and +being partly broken it was seen to contain lapilli and pieces of +antecedent lava, covered with micaceous peroxide of iron. The internal +temperature of this mass was very high; the hydrochloric acid which it +discharged had, in some places, covered the micaceous iron with a yellow +coating of chloride of iron. From small apertures, on the lower side of +the mass, white and green stalactites of chloride of calcium were +visible. In one spot only of lava I found a fumarole, with a small +quantity of micaceous peroxide of iron, evidently in a state of +formation; but this was the very spot where the lava became eruptive, +and whence issued the column of smoke which was so well +photographed--the place under the hill of Apicella. (See Plate 4a.) + +I have enumerated the products which are constantly collected in +fumaroles, although they are not all found at the same time or place, in +order to show that the sublimations follow a certain law in their +appearance. _Tenorite_, for instance, was formerly considered an +accidental product of certain eruptions, and I have always found it; but +if you visit the fumarole when the acids have had time to transform it, +you will no longer see it. I found the crystallized chloride of lead, or +"cotunuite," as it is called, for the first time in the lavas of 1855, +and thought it a singular circumstance; but from that time I recognised +it in all the lavas, though not always so beautiful and abundant; and +even when not found as a distinct substance, I observed it in +combination with chloride of copper. In the lavas of the 26th April +_cotunuite_ and _tenorite_[E] were not very abundant, because the +chloride of iron disturbed the greater number of the sublimations. I +found sal ammoniac very abundantly on the fumaroles of the lavas that +invaded the cultivated ground. Although chloride of ammonia, contrary to +opinion, was not wanting in the sublimations of the fumaroles of the +lavas deposited on other lavas, yet it was neither abundant nor +crystallized, but combined in small quantities with other substances. It +appeared in great abundance in all the fumaroles of lavas which covered +cultivated or woody ground. At first it was scarce enough, and mixed +with chloride of sodium; but when the rains came the sea-salt was washed +away, and sal ammoniac formed beautiful crystals, nearly free from +adventitious matters, as was the case with the fumaroles of the last +lava. Afterwards, when chloride of iron was produced, ferro-chloride of +ammonia was found. Crystals of sal ammoniac were sometimes found of a +beautiful amber yellow. This colour was, in the opinion of my colleague, +Professor Scacchi, produced by such small traces of chloride of iron +that neither Professor Guiscardi nor I, nor indeed any other chemists to +whom I submitted specimens for examination, could detect any. What I can +affirm with certainty is, that these limpid crystals of a yellow colour +were almost always attached to an amorphous substance, soluble in water, +composed of various chlorides, in which iron was often detected. + +From these remarks, it is evident that in the tranquil lavas the +sublimations appear with a certain order of succession, and in the +violent lavas, and those which flow most copiously, they are more +complicated, and render both chemical analysis and spectroscopic +researches more difficult. Notwithstanding, I observed traces of lithium +and thallium, which I had previously perceived in some sublimations of +1871. I purpose submitting many sublimations which I have collected to +more complete spectroscopic investigation, although I am persuaded that +the discovery of traces of certain bodies in the sublimations or in the +lavas is a matter of small importance to the science of volcanoes. I +must say, however, that calcium was discovered on this occasion in great +abundance, not only by the spectroscope, but also by chemical analysis. +Sulphate of lime has often been found in larger or smaller proportions, +but this was the first time I had observed chloride of calcium both +close to the craters, and also in the sublimations of the fumaroles upon +the lavas. The white stalactites which I collected beneath the great +mass or bomb above described were almost exclusively composed of +chloride of calcium, and only a few green drops manifested, with the +usual re-agents, the presence of iron. + +I did not fail to look often at the spectrum of the flowing lavas +covered with the smoke which issued from them, but I always had a +continuous spectrum. The spectroscope employed was Hoffmann's +construction, with direct vision; but I think it would be better on +other occasions to use a spectroscope combined with a telescope, like +those used by astronomers. + +But avoiding minute particulars of these sublimates, let us see what is +the general direction and the order of their appearance. Sublimations +are generally oxides, chlorides and sulphates, sometimes sulphides. +Among the oxides, we must enumerate in the first place "tenorite" and +_feroligiste_ or micaceous peroxide of iron. The first is almost always +found at the commencement of activity in the fumaroles, simultaneously +with the sublimation of chloride of sodium; the second--which is, +perhaps, never wanting in eruptive cones that are often found lined with +it inside--is seldom generated in the fumaroles of the lava, and +therefore it is not easy to define the moment of its appearance. +Sometimes one collects micaceous peroxide of iron on the lava, but it is +often transported there from the mouths of eruption, as happened on this +occasion. + +Trustworthy writers are of opinion that all the oxides are derived from +the decomposition of the chlorides, but I think I have clearly +demonstrated that, with regard to copper and lead, the opposite +statement may be affirmed; for the oxides are changed into chlorides, +and hydrochloric acid liberated. Oxide of copper forms sublimates at the +beginning, at the same time as the sea-salt; and if the fumarole be +anhydrous or, as Deville would say, _dry_, this oxide does not change +into either a chloride or a sulphate; but if the fumarole gives watery +vapour, after a little hydrochloric acid is formed, which changes the +oxide into a chloride, and if whilst this is going on oxide of lead be +developed, it is changed into the chloride of lead, so frequently found +in combination with chloride of copper. Then the sublimations change +from white to red or yellow, and specimens when carried away gradually +turn light blue, but when heated on platinum over a spirit lamp they +resume their yellow tint. Sometimes the yellow colour remains longer, +and in time changes to green; this also happens on the fumarole itself, +the green commencing at the zones furthest removed from the centre, +where the temperature is highest. When these sublimations are greenish, +they become far less soluble than at first. The yellow, so common at a +certain period on the fumaroles of the tranquil lavas, never attracted +attention before I first examined it, doubtless, because it was +considered chloride of iron, and yet in small eruptions this is only +found close to the discharging mouths, and never in the sublimations of +the fumaroles of the lava; but, on the other hand, it is the most +copious and common product on the lavas of the great eruptions. This +probably also accounts for the fact that lead, which is so obvious in +the fumaroles of the lavas, had never previously been observed. In 1855, +I noticed the crystallized chloride of lead in a fumarole in the Fossa +della Vetrana, and this induced me always to look for it on the +fumaroles of the later lavas; and I ascertained that, if it did not +always appear as a distinct mineral, it was easily discovered in +combination with other chlorides. The specimens which I have collected +are not the most beautiful, but the presence of lead in the sublimations +is not less common. + +Micaceous peroxide of iron, when found on the lava, has been mostly +conveyed from the eruptive mouths, as I have already stated, and perhaps +never so abundantly and evidently as on this occasion. The lava of the +26th of April carried along a large quantity of round masses or bombs, +varying in size, among which were found antecedent lava more or less +covered with micaceous iron, either collected in the cavities of the +lava, or incorporated with its mass. Sometimes the micaceous iron +appears like little veins in the paste of new lava enveloping the +exterior of these rounded masses, an exterior compact and lithoidal, and +not resembling scoriæ. Among these spherical masses I found one of +enormous size, four to five metres in diameter, which, having broken up +where the exterior envelope was thinnest, I found filled with a great +mass of lapilli and fragments of other lavas covered with micaceous +iron. This bomb still preserves (June 5th) an elevated temperature +within, and emits smoke and hydrochloric acid, which, meeting the +micaceous iron discovered by breaking the envelope with blows of a +hammer, transforms it superficially into chloride of iron, showing most +clearly how, on some occasions at least, chloride of iron is formed from +the oxide which precedes it. That those lapilli and the pieces of lava +were solid when enveloped in the paste of the new lava, we infer from +seeing the impressions on the inside of the said envelope. The chloride +of calcium, which I found in this spherical mass almost pure, caused me +to suspect that the sulphate of lime which is so often found on Vesuvius +is a transformation of the chloride produced by the contact of +sulphurous acid, which easily becomes transformed into sulphuric acid. +The hydrochloric acid which escapes from a fumarole coming into contact +with the scoriæ near its mouth, produces chloride of iron, which is, +therefore, not always obtained by sublimation, although, when the +temperature is very high, chloride of iron is conveyed from the interior +of the lava, and sublimes on the exterior and colder parts; for +instance, the chloride of iron which issues from the eruptive cones is +sometimes found sublimed on the rocks of Monte di Somma. When chloride +of iron has been produced by sublimation, we may collect it inside a +glass bell placed over the fumarole, or upon a piece of brick; but when +it is produced by the action of hydrochloric acid on the scoriæ, it will +only be found on the scoriæ themselves. + +If, therefore, the origin of micaceous peroxide of iron were due to the +decomposition of the sesqui-chloride of iron requiring a more elevated +temperature for its decomposition, it would follow that its genesis +would be easier near the discharging mouths, and more difficult on the +lavas, but there the fact was verified: for example, in the great bomb +on the fumarole, where we observed micaceous iron transformed into +chloride of iron. We may therefore consider it _proved_ that some +chlorides--for instance, chloride of sodium--issue from the lava itself, +either being there pre-existent, or being formed there; and that others +are derived from the oxides which precede them, as undoubtedly is the +case with chloride of copper; hence, the theory that derives the oxides +always from the chlorides cannot be considered true. Granting that this +theory might be applicable to the origin of micaceous iron, we should +still want to know how it is found with the paste of the new lava +itself, which forms the exterior coating of the bombs above described. + +Many of these rounded masses, which have been rolled along by the lava, +contain scoriæ partly decomposed by the long action of the acids found +on the fumaroles of the craters. They disintegrate easily, and have a +more or less yellowish tint. In the greater number of cases the interior +of these masses is formed of leucitic lava, with cavities lined with +micaceous iron. In short, their contents appeared to me quite similar to +the material of the cone of 1871 and 1872, which in all probability was +engulfed in the large crevasse or fissure that opened below it; and the +fragments having thus fallen down into the lava, were enveloped by it +and carried out by it after having been more or less rounded. The +external envelope of these spheres is not at all scoriaceous, but +compact and lithoidal, and sometimes composed of concentric folds or +plaits. + +As to the gaseous emanations of fumaroles, watery vapour with few +exceptions comes first; this conveys the material which first appears in +the sublimations, viz., sea-salt, and for the most part oxide of copper. +If the fumarole continue active, it passes from the neutral period to +the acid period, and first hydrochloric acid is produced, which, in +small lava streams, never conveys chloride of iron, and rarely attacks +the scoriæ to form that salt, but expends its force in changing the +sublimations already there. For this reason chloride of iron, though +completely absent in the lavas of 1871, was abundantly found in those of +the 26th April, 1872. Sulphurous acid follows hydrochloric at a later +period, and sulphuretted hydrogen occasionally succeeds. + +Having examined the gases of fumaroles by means of a graduated tube, and +the pyrogallate of potash, I always found that it contained less oxygen +than the surrounding atmosphere. + +For several years I wished to see whether the fumaroles of the lavas had +a period of evolution of carbonic acid, as sometimes happens with +fumaroles near the craters, but I have always obtained negative +results. I often found that the atmosphere on the lavas contained an +excess of carbonic acid, but as these lavas had burnt many trees, and it +was probable that carbonic acid springs had formed under the lava, I +never considered it safe to form any conclusion on the subject. + + + + +IV. + +BOMBS, LAPILLI AND ASHES. + + +The bombs ejected from the craters are like those carried down by the +lavas, but of smaller size, and they seldomer contain a nucleus similar +to those found in the latter. With the bombs properly so called, many +pieces of incandescent lava were thrown up, and in their fall went +beyond the base of the cone. A quantity of small scoriæ varying in size +accompanied these projectiles, and those fragments, which we call +_lapilli_, fell at a greater distance. With the lapilli, and sometimes +without them, the smoke carried a very minute dust or sand, which is +generally called ashes. These ashes, when washed with water, lose +soluble constituents which they have collected in the smoke--such as +chloride of sodium and other chlorides and often free acids. The +insoluble part originates in the detritus of lava, and with the +microscope we can detect abundant fragments of those crystals which most +frequently occur in the lava of the same eruption. + +The lavas of 1871, which were eminently leucitic, and almost entirely +deprived of pyroxene, resembled the ashes, which appeared to be +fragments of crystals of leucite, more or less enveloped in the paste of +the lava, so that having triturated the scoriæ of the lava, and looked +at the powder through the microscope, it was apparently quite the same +as the ashes. + +But at the beginning of the eruption of the 26th April, a white sand +fell in the Atria del Cavallo, close to the Crocella[5], which on the +dark scoriæ of 1871 looked like snow. Its fall had a limit so well +defined that one passed without any gradation from white to black. +Having collected some of this sand that very morning, I put it up in +white paper, for at that moment it was impossible for me to examine it. +Taking it out some days after, I found it had become reddish, and having +put it under the microscope, I observed that it was exclusively formed +of little pebbles more or less round, of a transparent vitreous matter, +partly covered with a red substance. Fragments of green crystals +occurred in this sand, upon which no red was perceptible. I consulted +our eminent crystallographer, Arcangelo Scacchi, whether these little +pebbles were leucite, as I suspected, and whether the green particles +were pyroxene: he confirmed my suspicion, and remarked that the red +colour was superficial only. We then washed a little of the sand in hot +water, and saw the pebbles become whitish; but having heated some on +platinum, we observed that they first turned black and then became +perfectly white, proving that the red was a deposit of organic matter. +To see these leucites, rounded like small pebbles transported by a +torrent, deprived of the soluble chlorides which generally accompany +Vesuvian ashes, is a matter worthy of attention. Whilst heating this +sand upon platinum, decrepitation was audible, which indicated the +cracking of some of the little pebbles. It is evident, therefore, that +crystals of leucite raised to a certain temperature may break, and thus +we can understand how almost all Vesuvian ashes contain fragments of +the said crystals enveloped in the paste of the lava. It is evident that +the soluble part of the ashes is obtained from the smoke through which +it passes. On this occasion the smoke from the craters did not +apparently contain much acids, for no bad smell was perceptible, and the +water in which I washed the ashes scarcely reddened litmus paper. Even +chloride of iron, which was so abundant in the lavas, was scarcely +perceptible in the smoke, which almost exclusively deposited sea-salt on +the surrounding rocks; I say sea-salt advisedly, and not chloride of +sodium, to show that I include all that sea-salt contains. The slight +disturbance it manifested with chloride of barium, and the small +precipitate with oxalate of ammonia, reveal sulphate of lime, without +excluding the possibility of the chloride. + +But how can these ashes do so much injury to the vegetation of the +ground they cover, especially at the first fall of rain? I think that +the damage is due partly to the sea-salt, and partly to the acids +contained either in the ashes or in the rain-water itself. Upon watering +the tender tops of some plants with a saturated solution of the salt +from Vesuvius itself, I noticed that they withered away after a few +hours. But very often the rain alone which traverses the smoke of +Vesuvius, or is produced by condensation from it, gives manifest acid +reactions, and destroys the grass and the tops of the trees. The +peasants believe that the rain is warm or of boiling water, from +observing that the tender parts of the plants are, by its deposit, all +burnt up. Vegetation is now recovering, but without flowers, and +consequently without fruit. + + + + +V. + +THE CRATERS AND THEIR FUMAROLES. + + +The greater part of the lava issued from the base of the great fissure +in the cone which I have described; and although two other lava streams +descended from the top of the mountain, neither proceeded from the +crater, but from apertures near it. The great crater, divided in two as +already described, opened wide on the morning of the 26th April, +destroying the brim of the antecedent crater, and remaking it in another +shape with ejected matter, except on the south-west side, where the brim +was split. (See Plate 5.) + +From this double crater, copious smoke, bombs and incandescent scoriæ, +with ashes and lapilli, issued with violence, and from the depths below +came dreadful detonations and bellowings, producing great terror. And +yet the lava poured out into the Atria del Cavallo without any noise, +and not even a column of smoke marked its origin of issue--namely, from +the fissure. + +When the eruption was over, the sight of the vertical walls of these +deep craters, of almost horizontal strata of scoriæ and lithoidal +masses, with a fracture fresh, and as if they had never undergone the +action of fire or of acid vapours, without recent scoriæ and without +fumaroles, was to me a marvellous spectacle. The fumaroles were almost +all on the brims of the craters, with emanations of hydrochloric and +sulphurous acid. In a few that were more removed from the brim, +sulphuretted hydrogen was perceptible. In the sublimations, chloride of +iron was most abundant, in combination with other chlorides, for +example, of sodium, magnesium and calcium. This last chloride was +frequent even among the sublimations of the fumaroles of the lavas, and +it was the first time it was ever remarked, but I do not think it was +the first time that it was ever produced: being in combination with +chloride of iron, and very deliquescent, it did not attract attention +from anyone. In a hollow fragment of scoriæ I observed a yellowish +substance, which looked like sulphur in a viscid state, and which boiled +at a temperature of 120°, and evolved hydrochloric acid. Having +collected this substance and poured it into a glass phial, it quickly +coagulated into an amorphous mass of the same colour; but before I +reached the Observatory, I found that it had become liquid by +deliquescence. It consisted of a mixture of the aforesaid chlorides, +according to an analysis made by Professor Silvestro Zinno and myself. +In some fumaroles, where I perceived the smell of sulphuretted hydrogen, +I found sublimed sulphur under the scoriæ. + +At the source of the lava stream that flowed towards the Camaldoli, on +the seaward flank of Vesuvius, I observed large fumaroles of steam only, +pure aqueous vapour. + +There was no trace of carbonic acid in these fumaroles, but that fact +does not imply that there was none at a later period, for, since the +first investigations of Deville, it is known that carbonic acid is found +under certain conditions on the very summit of Vesuvius. + + + + +VI. + +THE ELECTRICITY OF THE SMOKE AND ASHES. + + +Our ancestors could judge that a great amount of electricity was +occasionally evolved in the smoke, from their observation of the +lightning flashes that darted through the Vesuvian pine tree; but they +had no proper instruments for ascertaining whether this evolution of +electricity was constant or accidental, or what laws regulated its +manifestations. My _apparatus, with movable conductor_, by which +comparative observations of electric meteorology can be made, and the +errors arising from dispersion corrected, supplied me with an easy +method of studying the electricity evolved during eruptions. + +I must begin by describing the bifilar electrometer, in order to explain +the apparatus which I have named as above, "_Apparechio a conduttore +mobile_." + +_A A_ (Plate VIa, Fig. 1) is a glass cylinder, the lower edge of which +is ground, well varnished with gum lac, and let into a wooden base, B, +furnished with three levelling screws. Through a sufficiently wide glass +tube, _a a_, runs a copper rod covered with insulating mastic, having a +little plate or cylindrical cavity of gilded brass at the top (Figs. 2 +and 3), with two arms _d d_, _d' d_. In the plate a disc of aluminium, +_m_, is suspended by means of two silk fibres, and to the disc a very +fine aluminium wire is attached, _f f'_, bent a little at the ends, as +are the arms, _d d_, _d' d_. The disc has about three millimetres less +diameter than the plate. The diameter of the plate may vary within +certain limits, but I have found it convenient to make it eighteen +millimetres. The glass tube, _a a_ (Fig. 1), should descend below the +base as much as it rises above it, that is three to four centimetres. +The length of the index is about one decimetre. + +The upper ends of the two silk fibres, by which the disc and index are +suspended, are attached to the top of the glass tube, _C_, by a +contrivance which permits a change in the distance between the two +points of suspension, and a screw, _p_, is provided to raise and lower +the disc with the index. At _n_, at the lower part of the tube, _C_, +there is a kind of torsion micrometer, arranged so as to bring the index +to the zero of the scale engraved on the graduated ring, _B_, which is +formed of a strip of good paper pasted on the rim of a glass disc. The +index must be placed at the zero of the scale, and must be some distance +from the ends of the arms of the plate with which it is parallel. The +plate is about three millimetres deep. + +Having levelled the instrument, so as to render the disc concentric with +the plate, and placed the index at zero, it is obvious that if an +electric charge through the wire, _h_, reach the plate with the arms, it +will electrify the disc and index: the disc will have the opposite +electricity, and the extremities of the index will take the same +electricity as the arms, and consequently the index will describe an arc +more or less great. The motion of the index is sufficiently slow to +allow the eye conveniently to follow it. Having traversed the first arc, +which I call the _impulsive_ one, the index returns, and, after only two +oscillations, comes to rest at what I shall call the _definite_ arc. + +When the electric charges are of very brief duration, the impulsive arcs +are within certain limits proportional to the tensions, and the ratio +between the impulsive and definite arcs is expressed by the following +equation: + + α(β - α) / β = tang. (1/2) α + +In which β is the impulsive arc and α the definite arc, showing that α +comes out nearly equal to 1/2 β. In dry weather all goes perfectly +within the limits of proportion, and I can tell whether, during the time +in which the index traversed the impulsive arc, there were any +_dispersions_ and of what nature; for if the definite arc is not close +to the limit of the impulsive arc, it is a sign of _dispersions_ having +taken place during the motions of the index. Every degree less in the +definite arc denotes two degrees of loss for the impulsive arc; but as +the index employs double the time traversing the definite as it does the +impulsive arc, we may consider the loss of one equal to the loss of the +other. + +In excessively damp weather the index gives no definite arc, and it is +necessary to resort to artificial heat in order to dry the insulators. +The most simple means I know of is to hold the instrument over some +hollow vessel, which, for the time, is converted into a stove by the +introduction of a spirit lamp. + +From Gauss's formula for the bifilar system of instruments of this +class, we learn that the maximum sensitiveness of such instruments is +given when the length of the suspending fibres is greatest, and the +distance between them is smallest, with the weight of the movable or +rotating member a minimum; and these elements being the same, the +sensitiveness of the instruments is invariable. + +To some electrometers, in order to avoid errors of parallax, a small +telescope, with a micrometer wire, has been added; but, with a little +practice, we can read accurately without this refinement. In order to +obtain comparative measurements, it is necessary to select some given +unit of tension. I have observed that by making a galvanic pile of +copper, zinc and distilled water, and insulating it well, each pole has +a tension which remains the same for many days, if the conditions of +temperature and the moisture of the surrounding atmosphere are not very +different. With thirty pairs of this pile, each element having +twenty-five square centimetres of surface, I have on the electrometer a +definite arc of 15°, with the temperature of the atmosphere at 20° C., +and with the difference of 4° to 5° C. between the thermometers of the +psychrometer of August's construction. The first observation was made +twenty-four hours after mounting the pile. For unit of tension I took +that which corresponded to a single pair, that is, the thirtieth part of +the total tension. Other electrometers may be compared with one already +properly adjusted, without always having recourse to the pile. + +This done, let us see the arrangement of all the apparatus: + +_H H_ (Plate VIIa, Fig. 1) is the ceiling of a well-situated lofty +room, with an opening, _o o_, at the upper part. + +_M M_, a bracket or table fastened against the wall, about a metre +distant from the ceiling, _H H_. + +_N N_, a wooden platform for the observer. + +_A_, the bifilar electrometer. + +_B_, Bohnenberger's electroscope. + +_a a_, a movable conductor formed of a brass rod 15 to 18 millimetres in +diameter, insulated below by means of a glass rod, well varnished with +gum lac, having a suspending pulley, _c_, and a wooden guide-rod +underneath it, _l_, within the guiding tube, _k_. At the upper part of +this conductor, _a a_, there is a sliding roof, _b_, which can be +adjusted so as to prevent rain entering at the opening, _o o_. The +conductor terminates in a disc made of a sheet of thin brass, _d_, 24 +centimetres in diameter. Upon this disc, or even in place of it, we may +use metallic points. + +As a support to the conductor at the upper part, I have made use of a +triangular ring, _x_, drawn at its full size in Fig. 2. The conductor +passes between three springs, and the triangular ring is held in place +by three silk cords, _m m m_. Their material should not be mixed with +any cotton, and it may be advisable to saturate them with an alcoholic +solution of gum lac. + +_f f f_ is a hempen cord, which is used to raise and lower the +conductor. + +_i_ is a copper wire covered with silk, by means of which the triangular +ring, _x_, and through that and its springs the conductor communicates +with either the electrometer or the electroscope. + +Quickly raising the conductor by pulling the cord, _f_, the index of the +electrometer will describe a more or less large impulsive arc, and, +after two oscillations, will stop at the definite arc. Having thus +measured the electric tension of the air, and having lowered the +conductor, I next place the wire, _i_, in communication with the +electroscope, _B_, and by again raising the conductor, I ascertain +whether the electricity be positive or negative. It is scarcely +necessary to say that the conductor, when raised, gives electricity of +the same nature as that prevailing at the moment in the atmosphere; and +when lowered, manifests the opposite. In some conjunctures we must keep +the conductor raised and in communication with the electroscope, in +order to observe certain phenomena which I shall presently describe: +this method I call observation with a _fixed conductor_. + +I have also constructed a similar but portable apparatus for use on +eruptive cones, when required. + +Having given this description of the apparatus, it remains for me to +relate the results obtained, especially on the occasion of the last +eruption of Vesuvius. + +The Observatory is distant, in a direct line from the central crater of +Vesuvius, 2,380 metres, so that, when the smoke is copious, it is +properly situated for the study of electricity, particularly when the +wind inclines the pine-tree cloud in the direction of the Observatory, +as frequently happened on the last occasion. + +With smoke alone, without ashes, we obtained strong tensions of positive +electricity; with ashes only, which sometimes fell while the smoke +turned in the other direction, we had strong negative electricity; when +the smoke inclined towards the Observatory, accompanied with ashes and +lapilli, we had sometimes one kind of electricity, and sometimes the +other, just as the smoke or the ashes predominated; and often with a +"fixed conductor" we obtained negative electricity, and with a "movable +conductor" positive electricity. In Naples, too, at the Meteorological +Observatory attached to the University, my colleague, Professor Eugenio +Semmola, observed negative electricity of strong tension whilst ashes +were falling there in abundance. The tensions on this occasion were so +strong as to equal those obtained at changes of weather or during storms +(_temporali_), and, being beyond measure with a delicate electrometer, +we marked them with the symbol ∞: the same phenomena were observed when +lightnings flashed. + +When there is but little smoke, it is necessary to approach the eruptive +mouths with a portable apparatus, in order to observe those phenomena +which, in great eruptions, may be studied from the Observatory itself. + +The conditions under which (_folgori_) lightning flashes are seen from +the cloud of smoke are, that it is conveying great abundance of ashes. +In 1861, there were small flashes even from the line of eccentric mouths +above Torre del Greco, although the smoke was not very great; and when +these ceased to discharge, and the central crater became somewhat +active, with a moderate amount of smoke but a great deal of ashes, small +and frequent lightning flashes were observed in the twilight darting +through the smoke, which was dark in colour. In 1850 the eruption was +more vigorous, the smoke more abundant, and the ashes scarce, but the +flashes were very rare. In 1855, 1858, and 1868, with a scanty supply of +ashes and at intervals, no flashes were observed, and the electricity +remained constantly positive. But having regard to the facts of +antecedent eruptions, one sees that the flashes are always derived, from +the midst of smoke accompanied with ashes and lapilli, which separate +like rain from the rolling volumes of smoke, in the midst of which they +were ejected. + +But how can we account for the positive electricity of the smoke, and +the negative electricity of the falling ashes? Without denying the +probability that a part of the positive electricity depends upon the +elevation of the smoke, as in the case of every other conductor we raise +aloft, or with a jet of water sent from a vessel by compressed air, I +think that the greater part of the electricity proceeds from the rapid +condensation of vapours, which are changed from the gaseous condition +into dense clouds; for even when the smoke issues tranquilly and does +not rise, because carried away horizontally by the wind, it gives signs +of positive electricity. From all my studies of atmospheric electricity, +and from some experiments made specially, it follows that the +condensation of vapours is the origin of this development of positive +electricity. + +The negative electricity of the falling ashes certainly arises from the +fact itself of their fall; for if we place a metallic vessel full of +ashes upon an elevated and well-situated terrace, while the atmospheric +electricity is positive, and cause the ashes from the vessel to fall +gradually into an insulated metallic cup, communicating with +Bohnenberger's electroscope placed at three or four metres distance from +the vessel, the electroscope will manifest negative electricity. If the +upper vessel be insulated, and the ashes permitted to fall upon the +ground, we shall obtain, from the vessel, positive electricity. The +intensity of these electric manifestations depends (other things being +equal) upon that predominant at the moment in the air; so that if the +experiment be made while negative electricity prevails, the falling +ashes will manifest positive electricity, the upper vessel then showing +negative electricity. Now, as the ashes separate from the positively +electrified smoke in order to approach the ground, which is negatively +electrified, it follows that they must manifest negative electricity +upon touching the ground, leaving the positive electricity in the smoke +above. For this reason, the electric tension of the smoke is increased +by the descent of the ashes and lapilli, so that discharges between the +upper and lower part of the pine-tree cloud, or the surface of the +crater, are rendered possible. Hence it follows that the flashes of +lightning of Vesuvius play through the smoke, and with difficulty strike +bodies upon the earth; and from this circumstance our ancestors believed +the thunderbolts of Vesuvius to be harmless. However, if the smoke were +very great, and driven by the force of the wind to some distance from +the crater, with an abundant fall of ashes, it would be possible to have +lightning flashes proceed from the smoke to the earth. I possess some +documents which relate that, in 1631, thunderbolts fell upon the Church +of Santa Maria del Arco, and other places on the coast of Sorrento. + +After upwards of twenty years' study and observation of meteoric +electricity, I am enabled to prove that atmospheric electricity is never +manifested without rain, hail or snow, and that manifestations of light +are always accompanied by thunder--manifestations of light (_lampi_), +thunder and rain being most closely connected. We may have rain without +manifestations of light, but never the latter without rain or hail. I +cannot here repeat what I have demonstrated in other memoirs; I can only +say that the lightnings of Vesuvius, erroneously believed to be not +accompanied by thunder, are really not accompanied by rain, but are +induced by the descent of ashes and lapilli.[6] + + + + +GENERAL CONCLUSIONS. + + +We may conclude from what I have stated: + +1. That by the assiduous study of the central crater, and the +indications afforded by the "Apparatus of Variations" and the +"Electro-Magnetic Seismograph," we can obtain precursory signals of +eruptions; and that the other premonitory signs pointed out by our +ancestors, such as the drying up of wells, either only happen +occasionally or are mere coincidences, such as those of the coincidence +of a dry or a rainy season, the prevalence of certain winds, etc.[F] + +2. That the fumaroles of the lavas are communications between the +external surface of the lava, hardened and more or less cooled, and the +interior lava still pasty, or at least incandescent. + +3. That from the lava, while flowing, there is no escape of acid +vapours, neither from the fumaroles at the first period of their +existence, but these, if they last long enough, arrive at an acid +period. + +4. That hydrochloric is the first acid that appears, combined afterwards +with sulphurous acid, and, still later, with sulphuretted hydrogen. + +5. That vigorous lava streams may have eruptive fumaroles. (See +Translator's Note 2 to p. 94.) + +6. That the sublimations follow a certain order in their appearance. In +the neutral period we get sea-salt mixed with some metallic oxides, the +first of which is oxide of copper. But in the great lavas, chloride of +iron appears simultaneously with the acid period. Hydrochloric acid +transforms the oxides into chlorides, which, in their turn, change into +sulphurets or sulphates on the appearance of sulphurous acid. + +7. That the acids, by attacking the scoriæ, create new chlorides and +sulphates, which are thus not products merely of sublimation. + +8. That micaceous peroxide of iron--so common and abundant near the +eruptive mouths--is very scarce and rare on the lavas, unless conveyed +there from the craters. + +9. That chloride of iron--so manifest on the fumaroles of the great +lavas--is only found in small eruptions close to the discharging mouths. + +10. That the frequency of chloride of iron in the lavas of great +eruptions masks the order of transformation of the other products. + +11. The fumaroles at the summit of Vesuvius present even greater +gradations, for they often emit carbonic acid or pure watery vapour. + +12. Lead, which I first discovered in the fumaroles of the lavas of +1855, is a constant product of fumaroles which have a certain duration. +It is often obtained as a distinct and crystallized chloride, and often +is found in combination with other products. + +13. Oxide of copper is also a constant and primary (_primitivo_) product +of fumaroles. The chloride and sulphate of copper are formed from the +oxide, directly contrary to general belief. + +14. I do not think that the chloride of calcium, which I found on this +occasion in almost all the deliquescent sublimations, is a product +peculiar to this eruption only, in which alone, however, I found it. I +was, therefore, induced to look for it in other sublimates, in which I +might possibly have overlooked it, as, without doubt, my predecessors +have done, owing to the deliquescence of the chloride of iron with which +it was constantly combined. I think that this chloride, in accordance +with the general law, is transformed into a sulphate--a transformation +which readily occurs on Vesuvius. + +15. Copious and well-crystallized sal ammoniac is only found on the +fumaroles of those lavas which have covered cultivated or wooded ground. + +16. The scarcity of oxygen in the gases of fumaroles may possibly arise +from the formation of the oxides which precede the chlorides. + +17. Lavas give a continuous spectrum, although covered with smoke, when +looked at with Hoffmann's spectroscope with direct vision.[G] + +18. The smoke gives positive electricity, and the falling ashes negative +electricity. + + + + +REFERENCE TO THE PLATES. + + +PLATE + +Ia. The Cone of Vesuvius, in 1870, from a Photograph taken + near the Observatory. + + _a._ The Atria del Cavallo. + _b b._ Fossa della Vetrana. + _c._ Punta del Crocella. + _d._ Lava of 1858 and 1867. + _e._ Police Barrack near the Observatory. + _f._ Part of Monte Somma. + +IIa. Profile of Vesuvius, taken from a Photograph of the + Observatory in the month of September, 1871. + + 1. The Cone, on the 13th January, 1871. + 2, 2. Lava of 1871. + +IIIa. Profile of Vesuvius on the 16th April, 1872, about ten + days before the last Conflagration. + +IVa. Vesuvius, on the 26th April, 1872, from a Photograph taken + in the neighbourhood of Naples. + + 1. The Observatory. + 2. Fossa della Vetrana. + 3. Eruption of Smoke and Ashes, with Stones, from the + surface of the Lava. + 4. The Novelle, St. Sebastiano, and Massa. + 5. Lava which took the direction of Resina. + 6. Lava which, from the Crater, took the direction of the + Camaldoli. + 7. The Grain Stores, near Naples. + 8. Resina. + 9. Torre del Greco. + 10. The Camaldoli. + +Va. Profile of Vesuvius after the Eruption of the 26th April, + 1872, from a Photograph taken near the Observatory. + + 1, 1. The Fissures of the 26th of April. + 2, 3. Small Hill thrown up on the morning of the 26th of + April, from below which issued the great current of + Lava. +4, 4, 4. The Mouths out of which the Lava issued. + 5, 5. The larger Lava Stream, which passed near the Observatory + by the Fossa della Vetrana. + 6, 6. The other Lava Stream, which, after dividing from + the last, took the direction of Resina. + 7, 7. The Lava which ran down towards the Camaldoli. + 8 & 9. The two Craters on the summit of the Cone. + +VIa. The Bifilar Electrometer of Signor Palmieri. + (_Details._) + +VIIa. The assemblage of the Electroscopic Apparatus of Signor + Palmieri, as arranged at the Vesuvian Observatory. + +VIII. Professor Palmieri's Seismographic Apparatus. + + +[A] This small cone, as it appeared on the 1st April, is described and +drawn in a Memoir of Professor von Rath, of the University of Bonn, on +"Vesuvius on the 1st and 17th of April, 1871." + +[B] Eight young medical students perished beneath the lava, with others +unknown by name. They were all youths of good promise; their names will +be recorded on the marble monument to be erected near the Observatory. +They are: Girolamo Pausini, Antonio and Maurizio Fraggiacomo, Francesco +Binetti da Molfettu, Giuseppe Carbone da Bari, Francesco Spezzaferri da +Trani, and Giovanni Busco da Casamassima and Vitangelo Poli. + +[C] If this enormous height of projection really means, that above the +brim of the crater, it involves an initial velocity of projection of +above 600 feet (British) per second. + +Observations of the height of ascent of volcanic blocks are always +difficult and deceptive, and never free from error.--_Translator._ + +[D] Assuming these flashes to have emanated from somewhere within the +cloudy volume of steam and dust called "the head of the pine-tree," this +interval would indicate that the mean height of this cloudy volume +itself was not more than about four thousand feet above the top of the +cone; and, if so, that is not very far from the limit in height of +projection of the dust and lapilli.--_Translator._ + +[E] COTUNUITE, chloride of lead, in white, lustrous, acicular crystals, +of the trimetric system, easily scratched, Sp. gr., 5·238. + +TENORITE, peroxide of copper, in thin, hexagonal plates or scales, +translucent when very thin, dark steel gray, of the cubic system; hard +and lustrous. Sp. gr. about 5·950.--_Translator._ + +[F] Earthquakes, though in distant regions, usually precede eruptions. +The Earthquake of Melfi preceded the great Eruption of Etna in 1852; the +Earthquake of Basilicata of December, 1857, terminated with the Eruption +of 1858, which filled the Fossa Grande with lava; the Earthquakes of +Calabria of 1867 and 1870 were the precursors of the Vesuvian +conflagrations of 1868, 1871, 1872. A Volcano, also, in the Island of +Java had a great eruption in the month of April, some days before the +last conflagration of Vesuvius, as I learnt from a letter addressed to +Signor Herzel, Swiss Consul at Palermo, communicated to me[7] by the +astronomer, Signor Cacciatore.--_Palmieri._ + +[G] I have made a large collection of sublimates, which I purpose +examining with the spectroscope, and I shall be able to place some at +the disposal of experimentalists who may desire to pursue investigations +of this kind. + + + + +NOTES + +BY THE TRANSLATOR. + + +[1] (P. 82, text). Professor Palmieri has not given any description +in this Memoir of his seismograph--the instruments described being those +only which have relation to atmospheric electricity. The following brief +account of his seismograph will, therefore, form a not unsuitable +complement to his Memoir. The instrument, in general terms, is of that +class in which the wave movements are indicated by the displacement, +relative or absolute, of columns of mercury in glass tubes. It is a +self-recording instrument, composed of two distinct portions--one for +record of horizontal, or rather of what are called undulatory shocks; +the other for vertical shocks. In point of general principle, therefore, +it is very similar to that proposed by me ("Transactions, Royal Irish +Academy," in 1846), and in certain respects appears to me less +advantageous than the latter. Some account of the Palmieri instrument, +together with some critical remarks as to its action, may be found in my +"Fourth Report on Earthquakes" ("Reports, British Association, 1858," +pp. 75-81). The following description of the instrument is derived from +"The Engineer," of 7th June, 1872, and the publishers have to thank the +proprietors of that journal for permission to use the illustration, +Plate 8. + +In Fig. 1, _E_ is a helix of brass wire (gauge about one millimetre); +the helix consists of fourteen or fifteen turns, and has a diameter of +from twenty to twenty-five millimetres; it hangs from a fine metal +spring, and can be raised or lowered by a thumb screw. From the lower +end of the helix hangs a copper cone with a platinum point; the latter +is kept close to the surface of mercury in the iron basin, _f_, which +rests on an insulating column of wood or marble, _G_. The distance of +the point from the surface of the mercury remains constant, as the metal +pillar, _T_, is of such a length that its expansion or contraction by +change of temperature compensates that of the helix; the latter is in +connection (by _T_) with one pole of a Daniell's battery of two cells, +and the basin, _f_, is connected with the other pole. Any vertical +movement, however slight, makes the platinum point dip into the mercury, +and thus completes the circuit. In this circuit are included two +electro-magnets, _C_ and _D_; these, during the circulation of a +current, attract their armatures, which are connected with levers. The +action of _C's_ lever is to stop the clock, _A_, which thus records, to +a half-second, the time of the occurrence of the shock, at the same +instant that the clock strikes an alarm bell, which attracts the +attention of an observer. The lever, attached to the armature of _D_, at +the first instant of the current frees the pendulum of the clock, _B_, +which was before kept from swinging, in a position out of the vertical; +the clock then acts as a time-piece, and its motion unrolls a band of +paper, _k k k_, at a rate of three metres an hour. At the same time the +armature of _D_, while attracted, presses a pencil point against the +band of paper which passes over the roller, _m_, marking on it, while +the earthquake lasts, a series of points or strokes which occupy a +length of paper corresponding to its duration, and which record the work +of the shock. After it is over the paper continues to unroll from the +drum, _i_, and passing round the clock, rolls on to the drum, _l_. If a +fresh shock occur the pencil indicates it, as before, on the paper, and +the length of blank paper between the two sets of marks is a measure of +the interval of time between the shocks. By way of additional check, +several helices, _h h h_, are hung from a stand, with small permanent +magnets suspended from their ends; below and close to these latter are +small basins, holding iron filings; into these the points of the magnets +dip, when their helices oscillate vertically, and some filings remain +sticking to the magnets as a record of the shock. One of the magnets has +a shoulder on it which moves an index hand along a graduated arc, as +shown in Fig. 2, thus again registering the amount of the vertical +movement. Such are the arrangements intended for the record of the +undulatory or horizontal elements of the wave of shock. + +The following are the arrangements proposed for recording the horizontal +motions: On the stand, to the right of the clock, _A_, are set four +U-shaped glass tubes, open at their ends. One of each pair of vertical +branches must have a diameter at least double that of the other. These +pairs, with their supporting columns, are shown in plan, where one pair +lies N. and S., another E. and W., a third N.E. and S.W., and the other +N.W. and S.E. It will be observed that metallic bars pass from the +pillar, _P_, over the ends of all the long branches, and similar bars +pass from _R_, over the ends of the short branches; the pillars +themselves, as in the case of the other instruments, are each connected +with one pole of a Daniell's battery, the connections including the +electro-magnets, _C_ and _D_. The description of one U tube, _n_, will +apply to all the others; _n_ is partly filled with mercury, and an iron +or platinum wire, _o_, suspended from the bar above the short branch, +dips into the mercury therein, while another platinum wire hung from the +bar over the mouth of the longer branch, has its end very close to the +surface of the mercury in that branch. Any shock which is not +perpendicular in direction to the plane of the branches of the U will +cause the mercury to oscillate in the tubes, and more sensibly in that +with the smaller diameter; when it rises up in the latter, so as to +touch the platinum point, the connection between _P_ and _R_ is made and +the circuit completed, starting the action of the electro-magnets _C_ +and _D_, which record the shock, as already described. By having the +planes of the tubes set in the different azimuths, already mentioned, +one or more of the pairs is sure to be acted upon, and by observing in +which the oscillation takes place the direction of the shock is supposed +to be ascertained. Besides this, each long branch of the U, viz., that +of smaller diameter, has a small ivory pulley, _q_, fixed above it, over +which passes a single fibre of silk, with an iron float at one end, +resting on the surface of the mercury; at the other end of the fibre +hangs a counterpoise; fixed to the pulley is a fine index hand, capable +of moving along a graduated arc. When the shock takes place the mercury, +rising in the long branch, raises the float on its surface, the silk +fibre at the same time makes the pulley revolve with its index hand, +which afterwards remains stationary, as the counterpoise prevents the +float from sinking again with the mercury. The reading on the graduated +arc is thus a measure of the movements produced in the instrument by the +horizontal element of the shock, and is supposed to measure that shock. +It is assumed that in all these instruments shocks, however small, can +be recorded with certainty by adjusting the distance between the +platinum points and the mercury. + +The arrangement of Daniell's battery used for the seismograph is shown +in Fig. 4, where, for convenience of cleaning, the copper element is +made of wire (about No. 8 Birmingham wire gauge) coiled flat without the +spirals touching. Crystals of sulphate of copper are placed at the +bottom of the outer cell, into which water is poured; and the inner +cell, into which the zinc plate goes, is filled with siliceous sand. + +In addition to the above some instruments of a rougher description are +employed as checks. Thus, at the foot of the pillar, _G_, there is a +wooden trough with eight holes, facing as many equidistant points of the +compass (two of them shown in section) round its inner circumference; +mercury is poured into the basin until its level is nearly up to the +lips of the holes. The effect of a shock is to throw some of the mercury +into one or more of these holes, and the greater the oscillation the +more mercury is thrown into the cells through the holes. The screws +shown outside are for drawing off the mercury from the cells, when its +quantity can be measured. The direction of the shock is shown by seeing +which cells are filled with mercury. This is the old Cacciatore +seismometer which has been long employed in Italy. (See 4 "Report of +British Association, 1858," p. 73), and Daubeny's "Volcanoes," Appendix. +The following is another contrivance. From the arm of the pillar, _G_, a +fine metal wire hangs, with a metal ball at its end, which, by its +oscillation, thrusts out one or more light glass tubes, set horizontally +in a stand, as shown in Fig. 3. The two rings are of wood, and the glass +tubes pass through holes in them; small leather washers are placed +outside the outer rings; the displacement of one or more tubes is +assumed to measure the horizontal element of the shock. By means of this +apparatus the time of the first shock is recorded, as well as the +interval between the shocks, and the duration of each; their direction, +whether vertical or horizontal, is given, as also the maximum of +intensity. Professor Palmieri has the instruments examined three times a +day, and an assistant-observer is always at hand to attend to the bell, +and put back the apparatus to its normal position for fresh observation. + +It has been stated that this instrument is sensible to most of the +shocks which occur in the Mediterranean basin. + +It is not my intention here to offer any criticism as to the +construction or performances of this instrument, the rather as I must +confess I do not quite share the high opinion of its inventor as to the +certainty or exactitude of its indications. + +There can be no question as to the extreme importance to science of the +establishment and continued use of a seismographic instrument of +unexceptionable construction at the Observatory upon Vesuvius; and it +would be a valuable gift to science, were the Italian Government to +enable Signor Palmieri to establish such an one. Its great value and the +very first problem to set the instrument to solve should be, by _a rigid +determination of the direction of propagation of the wave of shock_, of +those slight or stronger pulsations which precede or accompany the +Vesuvian like all other eruptions, on arriving at the Observatory, _to +fix the depth, and the position vertically beneath the cone, whence +these pulses are derived_. This would be, in fact, to fix the depth and +position beneath the mountain at which the volcanic focus is situated +for the time, or, at least, where the volcanic activity is at the time +greatest. And the assured knowledge, even within moderate limits of +accuracy, of this depth, and even for this single mountain, would be an +immense accession to our positive knowledge, and a really new stage +gained for future advances. At present, we know but little as to the +actual depth below our globe's surface at which volcanic activity +occurs, or to which it is limited, either upwards or downwards. I have, +myself, established some data upon the flanks of Etna, not yet +published, which may enable me to afford some information on the subject +hereafter. Meanwhile, Professor Palmieri possesses unrivalled +opportunities for such observations; and I trust health, life and means +may be afforded him, to become the first who shall have made this great +addition to our positive knowledge of Vulcanology. + +So far, popularly at least, the alleged chief uses and value of these +seismographic instruments, at the Observatory of Vesuvius, have been +made to depend upon their being presumed to afford means for foretelling +eruptions, or affording precursory warnings of their probable progress +and destructive course. + +I feel compelled to express my own total disbelief in the possibility of +any such predictions in the present state of science, by the help of any +instruments whatsoever, of such a nature as to be of any _practical +value_, or any certainty beyond that which a certain amount of _mere +experience_ as to the _rôle commonly played_ by Vesuvius or other +Volcanoes in pretty habitual activity affords to the observer for a +lengthened period. And even this affords scarcely any guide as to what +may happen next. Monte Nuovo was thrown up in a night; Vesuvius _might_ +double its volume in a night, or might sink into a hollow like that of +the Val del Bove in a not much longer time. A small _fusillade_ may go +on for months, and yet, without an hour's notice, by any premonitory +sign, may waken up to a roar and darken the air with ashes and lapilli +such as those which overwhelmed Pompeii. One eruption may blow forth +little but dust and ashes (so called), another may pour out rivers of +lava and little else. + +The _main_ mischief of all eruptions is effected in two ways: by the +deposit of dust and ashes, lapilli, etc., to the injury or destruction +of fertile land, and by the streams of lava which overwhelm it, as well +as buildings, etc. But what information of any value can seismographic +observation afford as to the course that either of these may take in any +eruption? The volume of pulverulent material that may be ejected cannot +be foreseen; its distribution depends mainly upon its nature and upon +the direction and force of the wind at the time; or again, how shall +these warn us as to the course that the lava, if it appear, shall take, +when we cannot possibly foretell when, how, or by what mouth it may +issue. Even in this late eruption of 1872, with Palmieri stoutly at his +post upon the mountain, and the Observatory instruments in full +activity, they gave no forewarning of the sudden and unexpected belch +forth from the base of the cone, of that tremendous gush of liquid lava +which in a few minutes cut off from life the unhappy visitors whose +deaths he has recorded. + +[2] (P. 94). It can scarcely be supposed that these small +eruptive-looking belchings forth from the lava stream, _en route_, are +truly of an eruptive nature at all, _i.e._, in any way connected with +forces seated deeply beneath the bed of the lava stream, or in any way +connected with the volcanic ducts of the cone or beneath it. They are +most probably merely the bursting upwards of large bubbles; that is, of +cavities formed in the mass of the more or less liquid lava by intestine +movements, as its mass winds and rolls along, and by the aggregation of +smaller cavities--all being filled with steam and gases--together with +dust and volatile products which are ejected when the cavity opens up, +and its contents escape at the upper surface of the lava stream in +virtue of the continuation of the twistings and convolutions due to the +stream motion itself, and to the unbalanced hydrostatic pressures acting +upon the parietes of the bubble. Very large single bubbles of like +character rise in the fluid lava within craters in vigorous action, and +often so regularly that their recurrence causes a sort of rhythmical +rush and roar in the column of steam, etc., issuing above the mouth. +This was evident in the discharges issuing in 1857 from the highly +instructive minor _bocca_, then existing, examined by me, and referred +to ("Report, Naples, Earthquakes," etc. Vol. II., pp. 313, 314), as +presenting at the time great facilities for determining pyrometrically +the temperature of the lava within, and of the dry superheated steam +issuing with a rhythmic roar from it. M. Le Coq ("Époques Géologiques +d'Auvergne," Tome IV.) has recorded some examples of the formation and +opening-out of large bubble-like cavities in lava already ejected. +Perhaps that able and laborious vulcanologist, whose death a few months +ago science still deplores, attributes too much importance as well as +magnitude to them, when attributing the formation of what he has +denominated "craters of explosion," to the mechanism of the rise and +bursting of such bubbles upon a gigantic scale. Such blowings forth, +sudden or prolonged, from particular spots of lava streams, _en route_, +undoubtedly may also have their origin in damp places, or water or +air-filled cavities in or beneath the bed over which the lava rolls, +which, getting gradually heated, generate steam, or air or gases under +tension by expansion, etc., which thus at length blow through the liquid +or pasty lava flowing above, and which in bursting through delivers much +dust also, and so simulates a little eruptive crater. Examples of this, +upon a great and convincing scale, can be pointed to in the Val di +Calanna and elsewhere on Etna. + +[3] (P. 96). There are strong grounds for the gravest doubts that there +exists any real connection of a physical character between Volcanic +Eruptions, and Earthquakes more or less _approximately_ coincident only, +in time of occurrence; the respective sites being widely apart, and the +less the probability as the intervening distance is greater. The +discussions of the large number of records that are to be found of such +coincidences--mostly but partial, and in but _very_ few instances +complete coincidences--by Perrey, von Hoff, and others, as well as by +myself, do not tend to sustain the view that such imperfect +contemporaneity is based upon any causative connection. The seismic +region of Greece appears to have no _direct_ connection with that of +Southern Italy: the band of connection, if any, seems to lie between +Northern Italy, across the Northern Adriatic, by Ragusa, and thence +spreading into Asia Minor. + +[4] (P. 97). The abundance of coleoptera and of various other forms of +insect life about lava beds, both recent and old, is a very singular +fact, and one worthy of the careful observation of entomologists. In the +autumn of 1864, at mid-day, when sitting sketching upon the lava about +the middle of the Val del Bove (Etna), I found it almost impossible to +work, or even to remain for an instant still, in consequence of the +continual cloud of insects, large and small, that struck against me in +flight, endangered the eyes, and swarmed upon my clothes. It is quite +possible that this local superabundance of insect life may arise merely +from the general dryness and warmth of such places, and the plentiful +_nidus_ that the innumerable cavities in lava afford for the eggs and +earlier stages of insect life; still, this apparition of one form of +life may also be connected with other circumstances not unimportant to +discover. + +[5] (P. 120). The _Crocella_ is a small wooden cross, erected several +years ago, and which one passes to the right hand at the upper end of +the path along the ridge of tufa and volcanic conglomerate upon which +the Observatory stands, in ascending thence to the Atria del Cavallo. + +[6] (P. 134). That the causes assigned by Professor Palmieri for the +potent developments of electricity (positive or negative) which +characterise the ascent of the issuing columns of (chiefly if not +always) _dry_ steam, with a relatively small volume of various gases, +and throwing up, in their blast, volumes of small solid particles in +ashes and lapilli, etc., and the subsequent fall as a mineral or stony +hail-shower of the latter, through the partially condensing vapours and +the circumambient air, are the main causes of electrical development +evidencing itself in lightning flashes, is no doubt true. We must not, +however, lose sight of the many other and very effective agencies at +work here to produce electric excitement. The actual _bocca_ of the +volcanic vent whence the steam roars off constitute the cone a veritable +hydro-electric machine. Mechanical energy in various forms is +transformed into electric energy. Chemical action is going on both in +the solid and in the vapourous and gaseous emanations as they rush into +and remain in the air or descend from it, and chemical action is +transformed in part into electric energy. Percussion between ascending +and descending particles and fragments, fractures and breaking up of +more or less of these, thus and by sudden changes of temperature in +cooling, are likewise operative. In addition, great and violent +movements in the atmosphere itself result from the large local +accessions of temperature by the heated volume driven up into it, and +which in turn give rise to electric disturbance of the same character as +those produced in wind storms and whirlwinds, brought about by the +natural causes which every day effect disturbances in our atmosphere all +over the globe. + +[7] (P. 135). The views stated in note 3 (to page 96) may here again be +referred to as in point. How is it possible, in the present state of +science at least, to establish any physical connection between an +eruption in Java and one of Vesuvius, "with half the world between," +when not even having the solitary connecting link of complete +contemporaneity, and which, if it existed, yet might be nothing but +accidental? A list of shocks upon record, which have occurred more or +less nearly simultaneously at distant parts of the world, may be found +in my fourth Report, ("Facts of Earthquakes," "British Association +Reports, 1858") and the reasons are there given for rejecting the notion +of any direct physical connection between the origins of the respective +shocks. + +Shocks, emanating from the close neighbourhood of volcanic vents, or +simultaneity of eruption, in vents not far distant from each other, +stand upon a different footing. + + + + +Transcriber's Notes. + +Preserved the unusual, but consistent, spelling of "develope." + +Preserved the unusual, and inconsistent, references to the Plates. +Sometimes Arabic numerals are used, but usually Roman numerals. Most +have "A" attached to the name (which was changed to "a" to avoid +confusion in the Roman numerals), but not VIII, and sometimes not in the +references to them. + +Equations were converted to linear text, adding spacing and parentheses +as necessary. + +Changed "fumarolles" to "fumaroles" on page 3: "fumaroles and +salfatares." + +Changed "Lyall" to "Lyell" in footnote originally on page 9: "Daubeny, +Lyell, Phillips and others." + +Changed "throught" to "through" on page 35: "passing through it." + +Removed duplicated word "the" on page 40: "the great Calabrian +Earthquake." + +Page 89 refers to the "Fossa del Vetrano;" elsewhere there are +references to "Fossa della Vetrana," which may be what was intended. +However, I did not change this. + +Changed "hydrochloride" to "hydrochloric" on page 109: "the hydrochloric +acid which it discharged." + +Changed "disk" to "disc" on page 126: "the disc and index." + +Changed "azismuths" to "azimuths" on page 143: "the different azimuths." + +Changed "silicious" to "siliceous" on page 143: "filled with siliceous +sand." + + + + + +End of Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +*** END OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + +***** This file should be named 33483-0.txt or 33483-0.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/3/4/8/33483/ + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need are critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/33483-0.zip b/33483-0.zip Binary files differnew file mode 100644 index 0000000..2137dfa --- /dev/null +++ b/33483-0.zip diff --git a/33483-8.txt b/33483-8.txt new file mode 100644 index 0000000..166a812 --- /dev/null +++ b/33483-8.txt @@ -0,0 +1,4536 @@ +Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Eruption of Vesuvius in 1872 + +Author: Luigi Palmieri + +Translator: Robert Mallet + +Release Date: August 22, 2010 [EBook #33483] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + + + + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + + + + + + + + +THE +ERUPTION OF VESUVIUS +IN 1872, + + +BY +PROFESSOR LUIGI PALMIERI, +_Of the University of Naples; Director of the Vesuvian Observatory._ + + +WITH NOTES, AND AN +_INTRODUCTORY SKETCH OF THE PRESENT STATE OF KNOWLEDGE_ +OF +TERRESTRIAL VULCANICITY, +_The Cosmical Nature and Relations of +Volcanoes and Earthquakes._ + + +BY +ROBERT MALLET, +_Mem. Inst. C.E., F.R.S., F.G.S., M.R.I.A., &c., &c._ + + +WITH ILLUSTRATIONS. + + +LONDON: + +_ASHER & CO._, +13, BEDFORD STREET, COVENT GARDEN, W.C. + +1873. + + +W. S. Johnson, Nassau Steam Press, 60, St. Martin's Lane, +Charing Cross, W.C. + + +"The Translator should look upon himself as a Merchant in the +Intellectual Exchange of the world, whose business it is to promote the +interchange of the produce of the mind." + + GOETHE, "_Kunst und Alterthum_." + + + + +INTRODUCTORY SKETCH, &c. + + +The publishers of this little volume, in requesting me to undertake a +translation of the "Incendio Vesuviano," of Professor Palmieri, and to +accompany it with some introductory remarks, have felt justified by the +facts that Signor Palmieri's position as a physicist, the great +advantages which his long residence in Naples as a Professor of the +University, and for many years past Director of the Meteorological +Observatory--established upon Vesuvius itself, prior to the expulsion of +the late dynasty--have naturally caused much weight to attach to +anything emanating from his pen in reference to that volcano. + +Nearly forty memoirs on various branches of physics--chiefly +electricity, magnetism and meteorology--produced since 1842, are to be +found under Palmieri's name in the "Universal Catalogue of Scientific +Papers of the Royal Society," and of these nine refer to Vesuvius, the +earliest being entitled "Primi Studii Meteorologici fatti sul R. +Osservatorio Vesuviano," published in 1853. He was also author, in +conjunction with Professor A. Scacchi, of an elaborate report upon the +Volcanic Region of Monte Vulture, and on the Earthquake (commonly called +of Melfi) of 1851. These, however, by no means exhaust the stock of +Palmieri's labours. + +The following Memoir of Signor Palmieri on the eruption of Vesuvius in +April of this year (1872), brief as it is, embraces two distinct +subjects, viz., his narrative as an eye-witness of the actual events of +the eruption as they occurred upon the cone and slopes of the mountain, +and his observations as to pulses emanating from its interior, as +indicated by his Seismograph, and as to the electric conditions of the +overhanging cloud of smoke (so called) and ashes, as indicated by his +bifilar electrometer, both established at the Observatory. The two last +have but an indirect bearing upon Vulcanology. The narrative of the +events of the eruption is characterised by exactness of observation and +a sobriety of language--so widely different from the exaggerated style +of sensational writing that is found in almost all such accounts--that I +do the author no more than justice in thus expressing my view of its +merits. + +Nor should a special narration, such as this, become less important or +suffer even in popular estimation by the fact that so recently my +friend, Professor J. Phillips, has given to the world the best general +account of Vesuvius, in its historical and some of its scientific +aspects, which has yet appeared. That monograph--with its sparkling +style, and scholarly digressions, as well as for its more direct +merits--will, no doubt, become the manual for many a future visitor to +the volcanic region of Naples; but it, like the following Memoir of +Palmieri, and in common with almost every work that has appeared on the +subject of Volcanoes, contains a good deal which, however interesting, +and remotely related to Vulcanology, does not properly belong to the +body of that branch of cosmical science, as I understand its nature and +limits. + +It tends but little, for example, to clear our views, or enlarge our +knowledge of the vast mechanism in which the Volcano originates, and +that by which its visible mass is formed, that we should ascertain the +electric condition of the atmosphere above its eruptive cone, or into +what crystallographic classes the mineral species found about it may be +divided: it will help us but little to know Pliny's notions of how +Pompeii was overwhelmed, or to re-engrave pictures, assumed to give the +exact shape of the Vesuvian or other cone at different periods, or its +precise altitude, which are ever varying, above the sea. Even much more +time and labour may be spent upon analysing the vapours and gases of +fumaroles and salfatares than the results can now justify. + +Nothing, perhaps, tends more to the effective progress of any branch of +observational and inductive science, than that we should endeavour to +discern clearly the scope and boundary of our subject. + +To do so is but to accord with Bacon's maxim, "_Prudens questio dimidium +scienti_." That once shaped, the roads or methods of approach become +clearer; and every foothold attained upon these direct paths enables us +to look back upon such collateral or subordinate questions as at first +perplexed us, and find them so illuminated that they are already +probably solved, and, by solution, again prove to us that we _are_ in +the right paths. + +I believe, therefore, that I shall not do disservice to the grand +portion of cosmical physics to which volcanic phenomena belong, by +devoting the few pages accorded to me for this Introduction to sketching +what seems to me to be the present position of terrestrial +_Vulcanicity_, and tracing the outlines and relations of the two +branches of scientific investigation--_Vulcanology_ and _Seismology_--by +which its true nature and part in the Cosmos are chiefly to be +ascertained. + +The general term, _Vulcanicity_, properly comprehends all that we see or +know of actions taking place upon and modifying the surface of our +globe, which are referable not to forces of origin above the surface, +and acting superficially, but to causes that have been or are in +operation beneath it. It embraces all that Humboldt has somewhat vaguely +called "the reactions of the interior of a planet upon its exterior." + +These reactions show themselves principally and mainly in the marking +out and configuration of the great continents and ocean beds, in the +forcing up of mountain chains, and in the varied phenomena consequent +thereon, as seen in more or less adjacent formations. + +These constitute the mechanism which has moulded and fashioned the +surface of our globe from the period when it first became superficially +solid, and prepared it as the theatre for the action of all those +superficial actions--such as those of tides, waves, rain, rivers, solar +heat, frost, vitality, vegetable and animal (passing by many others less +obvious)--which perpetually modify, alter or renew the surface of our +world, and maintain the existing regimen of the great machine, and of +its inhabitants. These last are the domain of Geology, properly so +called. No geological system can be well founded, or can completely +explain the working of the world's system as we now see it, that does +not start from Vulcanicity as thus defined; and this is equally true, +whether, as do most geologists, we include within the term Geology +everything we can know about our world as a whole, exclusive of what +Astronomy teaches as to it, dividing Geology in general into Physical +Geology--the boundaries of which are very indistinct--and +Stratigraphical Geology, whose limits are equally so. + +It has been often said that Geology in this widest sense begins where +Astronomy or Cosmogony ends its information as to our globe, but this is +scarcely true. + +Vulcanicity--or Geology, if we choose to make it comprehend that--must +commence its survey of our world as a nebula upon which, for unknown +ages, thermic, gravitant and chemical forces were operative, and to the +final play of which, the form, density and volume, as well as order of +deposition of the different elements in the order of their chemical +combination and deposition was due, when first our globe became a liquid +or partly liquid spheroid, and which have equally determined the +chemical nature of the materials of the outward rind of the earth that +now is, and with these some of the primary conditions that have fixed +the characters, nature and interdependence of the vegetables and animals +that inhabit it. Physical Astronomy and Physical Geology, through +Vulcanicity, thus overlap each other; the first does not end where the +second begins; and in every sure attempt to bring Geology to that +pinnacle which is the proper ideal of its completed design--namely, the +interpretation of our world's machine, as part of the universal Cosmos +(so far as that can ever become known to our limited observation and +intelligence)--we must carry with us astronomic considerations, we must +keep in view events anterior to the "_status consistentior_" of +Leibnitz, nor lose sight of the fact that the chain of causation is one +endless and unbroken; that forces first set moving, we know not when or +how, the dim remoteness of which imagination tries to sound in shadowy +thought, like those of the grand old Eastern poem, "When the morning +stars first sang together," are, however changed in form, operative +still. The light and fragile butterfly, whose glorious garb irradiates +the summer zephyr in which it floats, has had its power of flight--which +is its power to live--determined by results of that same chain of causes +that lifted from the depths the mountain on whose sunny side he floats, +that has determined the seasons and the colour of the flower whose +nectar he sucks, and that discharges or dissipates the storm above, that +may crush the insect and the blossom in which it basked. And thus, as +has been said, it was not all a myth, that in older days affirmed that +in some mysterious way the actions and the lives of men were linked to +the stars in their courses. + +Whatever may have been the manifestations of Vulcanicity at former and +far remoter epochs of our planet, and to which I shall return, in the +existing state of regimen of and upon our globe it shows itself chiefly +in the phenomena of Volcanoes and of Earthquakes, which are the +subjects of Vulcanology and of Seismology respectively, and in principal +part, also, of this Introduction. + +The phenomena of hot springs, geysers, etc., which might be included +under the title of Thermopgology, have certain relations to both, but +more immediately to Vulcanology. + +Let us now glance at the history and progress of knowledge in these two +chief domains of Vulcanicity, preparatory to a sketch of its existing +stage as to both, and, by the way, attempt to extract a lesson as to the +methods by which such success as has attended our labours has been +achieved. + +It will be most convenient to treat of Seismology first in order. + +Aristotle--who devotes a larger space of his Fourth Book, [Greek: Peri +Kosmou], to Earthquakes--Seneca, Pliny, Strabo, in the so-called classic +days, and thence no end of writers down to about the end of the +seventeenth century--amongst whom Fromondi (1527) and Travagini (1679) +are, perhaps, the most important now--have filled volumes with records +of facts, or what they took to be such, of Earthquakes, as handed down +to or observed by themselves, and with plenty of hypotheses as to their +nature and origin, but sterile of much real knowledge. + +Hooke's "Discourses of Earthquakes," read before the Royal Society about +1690, afford a curious example of how abuse of words once given by +authority clings as a hindrance to progress. He had formed no distinct +idea of what he meant by an Earthquake, and so confusedly mixes up all +elevations or depressions of a permanent character with "subversions, +conversions and transpositions of parts of the earth," however sudden or +transitory, under the name of Earthquakes. + +A like confusion is far from uncommon amongst geological writers, even +at the present day, and examples might be quoted from very late writings +of even some of the great leaders of English Geology. + +From the seventeenth to the middle of the eighteenth century one finds +floods of hypotheses from Flamsteed, Httinger, Amontons, Stukeley, +Beccaria, Percival, Priestly, and a crowd of others, in which +electricity, then attracting so much attention, is often called upon to +supply causation for a something of which no clear idea had been formed. +Count Bylandt's singular work, published in 1835, though showing a +curious _partial_ insight in point of advancement, might be put back +into that preceding period. + +In 1760 appeared the very remarkable Paper, in the fifty-first volume of +the "Philosophical Transactions," of the Rev. John Mitchell, of +Cambridge, in which he views an Earthquake as a sudden lifting up, by a +rapid evolution of steam or gas beneath, of a portion of the earth's +crust, and the lateral transfer of this gaseous bubble beneath the +earth's crust, bent to follow its shape and motion, or that of a wave of +liquid rock beneath, like a carpet shaken on air. Great as are certain +collateral merits of Mitchell's Paper, showing observation of various +sorts much in advance of his time, this notion of an Earthquake is such +as, had he applied to it even the imperfect knowledge of mechanics and +physics then possessed in a definite manner, he could scarcely have +failed to see its untenable nature. That the same notion, and in a far +more extravagant form, should have been reproduced in 1843 by Messrs. +Rogers, by whom the gigantic parallel anticlinals, flanks and valleys of +the whole Appalachian chain of mountains are taken for nothing more than +the indurated foldings and wrinkles of Mitchell's carpet, is one of the +most salient examples of the abuse of hypothesis untested by exact +science. + +Neither Humboldt nor Darwin, great as were the opportunities of +observation enjoyed by both, can be supposed to have formed any definite +idea of _what_ an Earthquake is; and the latter, who had observed well +the effects of great sea-waves rolling in-shore after the shock, did not +establish any clear relation between the two.[A] + +Hitherto no one appears to have formed any clear notion as to what an +Earthquake is--that is to say, any clear idea of what is the nature of +the movement constituting the shock, no matter what may be the nature or +origin of the movement itself. The first glimmering of such an idea, so +far as my reading has enabled me to ascertain, is due to the penetrating +genius of Dr. Thomas Young, who, in his "Lectures on Natural +Philosophy," published in 1807, casually suggests the probability that +earthquake motions are vibratory, and are analogous to those of +sound.[B] This was rendered somewhat more definite by Gay Lussac, who, +in an able paper "On the Chemical Theories of Volcanoes," in the +twenty-second volume of the "Annales de Chmie," in 1823, says: "En un +mot, les tremblements de terre ne sont que la propagation d'une +commotion travers la masse de la terre, tellement indpendante des +cavits souterraines qu'elle s'entendrait, d'autant plus loin que la +terre serait plus homogne." + +These suggestions of Young and of Gay Lussac, as may be seen, only refer +to the movement in the more or less solid crust of the earth. But two, +if not three, other great movements were long known to frequently +accompany earthquake shocks--the recession of the sea from the shore +just about the moment of shock--the terrible sounds or subterraneous +growlings which sometimes preceded, sometimes accompanied, and sometimes +followed the shock--and the great sea-wave which rolls in-shore more or +less long after it, remained still unknown as to their nature. They had +been recognised only as concomitant but unconnected phenomena--the more +inexplicable, because sometimes present, sometimes absent, and wholly +without any known mutual bearing or community of cause. + +On the 9th February, 1846, I communicated to the Royal Irish Academy my +Paper, "On the Dynamics of Earthquakes," printed in Vol. XXI., Part I., +of the Transactions of that Academy, and published the same year in +which it was my good fortune to have been able to colligate the observed +facts, and bringing them together under the light of the known laws of +production and propagation of vibratory waves in elastic, solid, liquid +and gaseous bodies, and of the production and propagation of liquid +waves of translation in water varying in depth, to prove that all the +phenomena of earthquake shocks could be accounted for by a single +impulse given at a single centre. The definition given by me in that +Paper is that an earthquake is "_The transit of a wave or waves of +elastic compression in any direction, from vertically upwards to +horizontally, in any azimuth, through the crust and surface of the +earth, from any centre of impulse or from more than one, and which may +be attended with sound and tidal waves dependent upon the impulse and +upon circumstances of position as to sea and land_." + +Thus, for example, if the impulse (whatever may be its cause) be +delivered somewhere beneath the bed of the sea, all four classes of +earthquake waves may reach an observer on shore in succession. The +elastic wave of shock passing through the earth _generally_ reaches him +first: its velocity of propagation depending upon the specific +elasticity and the degree of continuity of the rocky or the incoherent +formations or materials through which it passes. + +Under conditions pointed out by me, this elastic wave may cause an +aqueous wave, producing recession of the sea, just as it reaches the +margin of sea and land. + +If the impulse be attended by fractures of the earth's crust, or other +sufficient causes for the impulse to be communicated to the air directly +or through the intervening sea, ordinary sound-waves will reach the +observer through the air, propagated at the rate of 1,140 feet per +second, or thereabouts; and may also reach him before or with or soon +after the shock itself, through the solid material of the earth; and +lastly, if the impulse be sufficient to disturb the sea-bottom above the +centre of impulse, or otherwise to generate an aqueous wave of +translation, that reaches the observer last, rolling in-shore as the +terrible "great sea-wave," which has ended so many of the great +earthquakes, its dimensions and its rate of propagation depending upon +the magnitude of the originating impulse and upon the variable depth of +the water. It is not my purpose, nor would it be possible within my +limits here, to give any complete account of the matter contained in +that Paper, which, in the words of the President of the Academy upon a +later occasion, "fixed upon an immutable basis the true theory of +Earthquakes."[C] I should state, however, that in it I proved the +fallacy of the notion of vorticose shocks, which had been held from the +days of Aristotle, and showed that the effects (such as the twisting on +their bases of the Calabrian Obelisks) which had been supposed due to +such, were but resolved motions, due to the transit rectilinearly of the +shock. + +This removed one apparent stumbling block to the true theory. + +Incidentally also it was shown that from the observed elements of the +movement of the elastic wave of shock at certain points--by suitable +instruments--the position and depth of the _focus_, or centre of +impulse, might be inferred. + +In the same volume ("Transactions of the Royal I. Academy," XXI.) I gave +account, with a design to scale, for the first self-registering and +recording seismometer ever, to my knowledge, proposed. In some respects +in principle it resembles that of Professor Palmieri, of which he has +made such extended use at the Vesuvian Observatory, though it differs +much from the latter in detail. In June, 1847, Mr. Hopkins, of +Cambridge, read his Report, "On the Geological Theories of Elevation and +Earthquakes," to the British Association--requested by that body the +year before--and printed in its Reports for that year. + +The chief features of this document are a digest of Mr. Hopkins's +previously published "Mathematical Papers" on the formations of +fissures, etc., by elevations and depressions, and those on the +thickness of the earth's crust, based on precession, etc., which he +discusses in some relations to volcanic action. + +This extends to forty-one pages, the remaining eighteen pages of the +Report being devoted to "Vibratory Motions of the Earth's Crust produced +by Subterranean Forces--Earthquakes." + +The latter consists mainly of a _rsum_ of the acknowledged laws, as +delivered principally by Poisson, of formation and propagation of +elastic waves and of liquid waves, by Webers, S. Russel and others--the +original matter in this Report is small--and as respects the latter +portion consists mainly in some problems for finding analytically the +position or depth of the centre of disturbance when certain elements of +the wave of shock are given, or have been supposed registered by +seismometric instruments, such as that described by myself, and above +referred to.[D] At the time my original Paper "On the Dynamics of +Earthquakes" was published, there was little or no _experimental_ +knowledge as to the actual velocity of transit of waves--analogous to +those of sound, but of greater amplitude--through elastic solids. The +velocity as deduced from theory, the solid being assumed quite +_homogeneous_ and _continuous_, was very great, and might be taken for +some of the harder and denser rock formations at 11,000 or 12,000 feet +per second. That these enormous velocities of wave transit would be +something near those of actual earthquake shock seemed probable to me, +and was so accepted by Hopkins. + +Thus, he says (Report, p. 88): "The velocity of the sea-wave, for any +probable depth of the sea, will be so small as compared with that of the +vibratory wave, that we may consider the time of the arrival of the +latter at the place of observation as coincident with that of the +departure of the sea-wave from the centre of divergence." + +In my original Paper (Dynamic, &c.), I had suggested, as an important +object, to ascertain by actual experiment what might be the wave's +transit rate in various rocky and incoherent formations; and having +proposed this in my first "Report upon the Facts of Earthquake" to the +British Association, I was enabled by its liberality to commence those +experiments, in which I was ably assisted by my eldest son, then quite a +lad--Dr. Jno. William Mallet, now Professor of Chemistry at the +University of Virginia, U.S.; and to give account of the results, in my +second Report ("Report, British Association for 1851") to that body. + +Those experiments were made by producing an impulse at one end of an +accurately measured base line, by the explosion of gunpowder in the +formation experimented upon, and noting the time the elastic wave +generated required to pass over that distance, upon a nearly level +surface. Special instruments were devised and employed, by which the +powder was fired and the time registered, by touching a lever which +completed certain galvanic contacts. The media or formations in which +these experiments were conducted were, damp sand--as likely to give the +minimum rate--and crystalline rock (granite), as likely to give the +maximum. The results were received, not with doubt, but with much +surprise, for it at once appeared that the actual velocity of transit +was vastly below what theory had indicated as derivable from the density +and modulus of elasticity of the material, taken as homogeneous, etc. +The actual velocities in feet per second found were: + + In sand 824915 feet per second. + In discontinuous and + much shattered granite 1,306425 " " + In more solid granite 1,664574 " " + +This I at once attributed, and as it has since been proved correctly, to +the loss of _vis viva_, and consequently of speed, by the _discontinuity +of the materials_. + +And some indication of the general truth of the fact was derivable from +comparing the rude previous approximations to the transit rate of some +great Earthquakes. In the case of that of Lisbon, estimated by Mitchell +at 1,760 feet per second. It was still desirable to extend similar +experiments to the harder classes of stratified and of contorted rocks. +This I was enabled to carry into effect, at the great Quarries at +Holyhead (whence the slate and quartz rocks have been obtained for the +construction of the Asylum Harbour there), taking advantage of the +impulses generated at that period by the great mines of powder exploded +in these rocks. + +The results have been published in the "Philosophical Transactions for +1861 and 1862 (Appendix)." They show that the mean lowest rate of wave +transit in those rocks, through measured ranges of from 5,038 to 6,582 +feet, was 1,089 feet per second; and the mean highest, 1,352 feet per +second; and the general mean 1,320 feet per second. + +By a separate train of experiments on the compressibility of solid cubes +of these rocks, I obtained the mean modulus of elasticity of the +material when perfectly continuous and unshattered, with this +remarkable result--that in these rocks, as they exist at Holyhead, +_nearly seven-eighths of the full velocity of wave transmission due to +the material, if solid and continuous, is lost by reason of the +heterogeneity and discontinuity_ of the rocky masses as they are found +piled together in Nature. + +I also proved that the wave-transit period of the unshattered material +of these rocks was greatest in a direction _transverse_ to the bedding, +and least in line parallel with that; but the effect of this in the +rocky mass itself may be _more_ than counterbalanced by the +discontinuity and imperfect contact of the adjacent beds. + +These results indicate, therefore, that the superficial rate of +translation of the solitary sea-wave of earthquakes may, when over very +deep water, equal or even exceed the transit rate (in some cases) of the +elastic wave of shock itself. + +These results have since received general confirmation by the careful +determinations of the transit rates of actual earthquake waves, in the +rocks of the Rhine Country and in Hungary, by Nggerath and Schmidt +respectively, and by those made since by myself in those of Southern +Italy, to which I shall again refer. In an elastic wave propagated from +a centre of impulse in an infinitely extended volume of a perfect gas, +normal vibrations are alone propagated--as is the case with sound in +air. + +In the case of like movements propagated in elastic and perfectly +homogeneous and isotropic solids, the wave possesses both normal and +transversal vibrations, and is, in so far, analogous to the case of +light. Mr. Hopkins, in his Report above referred to, has based certain +speculations upon the assumed necessary co-existence of both orders of +vibration in actual earthquake shocks in the materials of which our +earthy crust is actually composed. + +The existence of transversal vibration in those materials has not been +yet proved experimentally, though there is sufficient ground to preclude +our denying their probable existence. + +That if they do exist they play but a very subordinate part in the +observable phenomena of actual Earthquake is highly probable. This is +the view, supported not only by observations of the effects of such +shocks in Nature, but by the theoretic consideration of the effects of +discontinuity of formations in planes or beds more or less transverse to +the wave path (or line joining the centre of impulse with the mean +centre of wave disturbance at any point of its transit). If we suppose, +for illustration sake, such an elastic wave transmitted perpendicularly +through a mass of glass plates, each indefinitely thin, and all in +absolute contact with each other, but without adhesion or friction, more +or less of the transversal vibration of the wave would be cut off and +lost at each transit from plate to plate, as the elastic compression +can, by the conditions, be transmitted only normally or by direct push +perpendicularly from plate to plate. This must take place in Nature, and +to a very great extent, and the consideration, with others, enabled me +generally to apply the normal wave motion of shock alone to my +investigation as to the depth of the centre of impulse of the great +Neapolitan Earthquake of 1857, an account of which was published in +1862, and to be presently further referred to. + +Hitherto the multitudinous facts, or supposed facts, recorded in +numberless accounts of Earthquakes had remained almost wholly +unclassified, and so far as they had been discussed--in a very partial +manner, as incidental portions of geological treatises--with little +attempt to sift the fabulous from the real, or to connect the phenomena +admitted by reference to any general mechanical or physical causes. In +1850 my first "Report upon the Facts of Earthquakes," called for by the +British Association in 1847, was read and published in the Reports of +that body for that year. In this, for the first time, the many recorded +phenomena of Earthquakes are classified, and the important division of +the phenomena into primary and secondary effects of the shock was +established. Several facts or phenomena, previously held as marvellous +or inexplicable, were either, on sufficient grounds, rejected, or were, +for the first time, shown susceptible of explanation. Amongst the more +noticeable results were the pointing out that fissures and fractures of +rock or of incoherent formations were but secondary effects, and, in the +latter, were, in fact, generally of the nature of inceptive landslips. +This last was not accepted, I believe, by geologists at the time; but +the correctness of the views then propounded as to earth fissures--the +nature of the spouting from them of water or mud--the appearances taken +for smoke issuing from them, etc.--have since been fully confirmed, +first, by my own observations upon the effects of the Great Neapolitan +Earthquake of 1857, and more lately by those of Dr. Oldham upon the +Earthquake of Cachar (India), where he was enabled to observe fissures +of immense magnitude, the nature of the production of which he has well +described and explained in the "Proceedings, Geological Society, London, +1872." + +The relations between meteorological phenomena proper and Earthquakes +have always been a subject of popular belief and superstition. + +This was here carefully discussed, and with the result of disproving any +connection, or, if any, but of an indirect nature. I also, to some +extent, towards the end of this Report, discussed the question of the +possible nature of the _impulse itself_ which originates the shock; I +showed that it must be of the nature of a blow, and ventured to offer +_conjecturally_ five possible causes of the impulse: + + 1. Sudden fractures of rock, resulting from the steady and slow + increase of elevatory pressure. + + 2. Sudden evolution (under special conditions) of steam. + + 3. Sudden condensation of steam, also under special conditions. + + 4. Sudden dislocations in the rocky crust of the earth, through + pressure acting in any direction. + + 5. Occasionally through the recoil due to explosive effects at + volcanic foci (p. 79-80). + +The first and last of these I am, through subsequent light, disposed now +to withdraw or greatly to modify. + +The first, the supposed "_snap and jar_, occasioned by the sudden and +violent rupture of solid rock masses," to which Mr. Scrope, in his very +admirable work on Volcanoes, is disposed to refer the impulse of +earthquake shocks (Scrope, 2nd edit., p. 294), I believe may be proved +on acknowledged physical principles--when applied to the known +elasticities and extensibilities of rocks, and keeping in view the small +thicknesses fractured _at the same instant_--to be capable of only the +most insignificant impulsive effects; and if we also take into +consideration that strata, if so fractured, are necessarily not _free_, +but surrounded by others above and below, any such impulsive effect +emanating from fracture may be held as non-existent or impossible. In +the statement of his views which follows, and in objecting to my second +and third possible causes (p. 295-296, headed "Objections to Mallet's +Theory"), Mr. Scrope appears to me to have fallen into the error of +assuming that the nature of the _impulse_, or the cause producing it, +forms any part of "my theory of earthquake movement," or in anywise +affects it. I carefully guarded against this in the original Paper +("Transactions, Royal Irish Academy," Vol. XXI., p. 60, and again, p. +97), when I stated "it is quite immaterial to the truth of my theory of +earthquake motion what view be adopted, or what mechanism be assigned, +to account for the original impulse." + +As regards the fifth conjecture suggested by me, I am now, with better +knowledge and larger observation of volcanic phenomena, not prepared to +admit any single explosion at volcanic vents of a magnitude sufficient +to produce by its recoil an earthquake wave of any importance, or +extending to any great distance in the earth's crust. The rock of 200 +tons weight, said to have been projected nine miles from the crater of +Cotopaxi, which I quoted from Humboldt as an example,[E] I believe to be +as purely mythical as the rock (_bloc rejett_) of perhaps one-sixth of +that weight which, previous to the late eruption, lay in the middle of +the Atria dell Cavallo, and which it was roundly affirmed had been +_blown_ out of the crater, but which in reality had at some time rolled +down from near the top of the cone, after having been dislodged from +some part of the upper lip of the crater walls, where, as its wonderful +hardness and texture and its enamel-like surface showed, it had been +roasted for years probably. + +Nor do I believe in the _sudden_ blowing away of one-half the crater and +cone of Vesuvius, or of any other volcano, at one effort, however +affirmed. + +Nothing more than conjecture as to the nature of the impulse producing +great or small Earthquakes can, I believe, as yet be produced. That +there is some one master mechanism productive of most of the impulses of +great shocks is highly probable, but that more causes than one may +produce these impulses, and that the causes operative in small and long +repeated shocks, like those of Visp-Comrie and East Haddam, differ much +from those producing great Earthquakes, is almost certain. + +We shall be better prepared to assign all of these when we have admitted +a true theory of volcanic action, and so are better able to see the +intimate relations in mechanism between seismic and volcanic actions. + +It is not difficult meanwhile to assign the very probable mechanism of +those comparatively petty repercussions which are experienced in close +proximity to volcanic vents when in eruption, and which, though +certainly seismic in their nature, and powerful enough, as upon the +flanks of Etna, to crack and fissure well-built church-towers, can +scarcely be termed Earthquakes. + +In my First Report I stated that almost nothing was known then of the +distribution of recorded Earthquakes in time or in space over our +globe's surface, and I proposed the formation and discussion of a +complete catalogue of all recorded Earthquakes, with this in view. + +This was approved by the Council of the British Association and at once +undertaken by me, with the zealous and efficient co-operation of my +eldest son, Dr. J. W. Mallet. Nearly the whole of the Second British +Association Report, of 1851, is occupied with the account of the +experiments as to the transit rate of artificially made shocks in sand +and granite, as already referred to. + +The Third Report, of 1852-1854, contains the whole of this, "The +Earthquake Catalogue of the British Association" (of which, through the +liberality of that body, more than one hundred copies were distributed +freely), in which are given, in columnar form, the following +particulars, from the earliest known dates to the end of 1842: + + 1. The date and time of day, as nearly as recorded. + + 2. The locality or place of occurrence. + + 3. The direction, duration, and number of shocks so far + recorded. + + 4. Phenomena connected with the sea--great sea-waves, tides, + etc. + + 5. Phenomena connected with the land--meteorological phenomena + preceding and succeeding. Secondary phenomena--all minor or + remarkable phenomena recorded. + + 6. The authority for the record. + +Though most materially assisted by the previous labours and partial +catalogues of Von Hoff, Cotte, Hoffman, Merrian, and, above all, of +Perrey, the preparation of this catalogue--which demanded visits to the +chief libraries of Europe, and the collating of some thousands of +authors in various languages and of all time--was a work of great and +sustained labour, which, except for my dear son's help, I should never +have found time and power to complete. Professor Perrey, formerly of the +Facult des Sciences of Dijon, now _en retrait_, who has devoted a long +and useful life to assiduous labours in connection with Seismology, was +our great ally; and his catalogues are so large and complete for most +known parts of the world after 1842, that we were able to arrest our own +catalogue at that date, and take M. Perrey's as their continuation up to +1850. + +The whole British Association Catalogue thus embraces the long historic +period of from 1606 B.C. of vulgar chronology, when the first known +Earthquake is recorded, to A.D. 1850; and the base of induction which it +presents as to the facts recorded extends to between 6,000 and 7,000 +separate Earthquakes. My Fourth Report ("Reports, British Association, +1858,") is occupied principally with the discussion of this great +catalogue, and with that of several special catalogues produced by other +authors with limited areas or objects. + +The discussion of M. Perrey's local catalogues with those of others, in +reference to a supposed prevalent apparent horizontal direction of shock +in certain regions--as to distribution, as to season, months, time of +day or night, relation to state of tide--the bearings of the views of +Zantedeschi and others as to the probable existence of a terrane +tide--the supposed relations of the occurrence of Earthquakes upon the +age of the moon, as deduced by Perrey, viz.: that 1st, Earthquakes occur +most frequently at the syzygies; 2nd, that their frequency increases at +the perigee and diminishes at the apogee; 3rd, that they are more +frequent when the moon is on the meridian than when she is 90 away from +it--and the views of several authorities as to the distribution of +Earthquakes in time and in space--occupy the first 46 pages of this +Report. + +It then proceeds to discuss the distribution in time and in space as +deduced from the full base of the great catalogue. + +The results as to time are reduced to curves, and those as to space (or +distribution over our globe's surface) to the great seismic map +(Mercator's projection), upon which and in accordance with certain +principles and conventional laws, which admit of the indication of both +intensity and frequency, all recorded Earthquakes have been so laid down +as to present a real indication of the distribution of seismic energy +for the whole historic period and all over the world. + +The original of this map, which also shows the Volcano (size, about 7 +feet by 5 feet), remains for reference in the custody of the Royal +Society. A reduced copy was published with the Report, and to a still +more reduced scale has been reproduced in other places. It is impossible +here to do more than refer to a few of the more salient points. + +As regards distribution in time, durational seismic energy may be +considered as probably constant during historic time, though it is +probably a decaying energy viewed in reference to much longer periods. +It does not appear of the nature of a distinctly periodic force. + + 1. Whilst the minimum paroxysmal interval may be a year or two, + the average interval is from five to ten years of comparative + repose. + + 2. The shorter intervals are in connection with periods of + fewer Earthquakes, not always with those of least intensity, + but usually so. + + 3. The alternations of paroxysm and of repose appear to follow + no absolute law deducible from these causes. + + 4. Two marked periods of extreme paroxysm are observable in + each century (for the last three centuries), one greater than + the other--that of greatest number and intensity occurring + about the middle of each century, and the other towards the end + of each. + +As respects season, there appear distinct indications of a maximum about +the winter solstice, and equally so of a minimum rather before the +autumnal equinox. It is not improbable that there is a remote relation +between Earthquakes and the annual march of barometric pressure. + +We may expect, at present, one great Earthquake about every eight +months, and were we possessed of a sufficient report from all parts of +our globe, we should probably find scarcely a day pass without a very +sensible Earthquake occurring somewhere, whilst, as regards still +smaller tremors, it might almost be said that our globe, as a whole, is +scarcely ever free from them. + +As respects the distribution of seismic energy in space of our earth's +surface, it is that of bands of variable and of great breadth, with +sensible seismic influence extending to from 5 to 15 transversely, +which very generally follow: + + 1. The lines of elevated tracts which mark and divide the great + oceanic or terra-oceanic basins (or _saucers_, as I have called + them, from their shallowness in relation to surface, in this + discussion) of the earth's surface. + + 2. And in so far as these are frequently the lines of mountain + chains, and these latter those of volcanic vents, so the + seismic bands are found to follow these likewise. Isolated + Volcanoes are found in these bands also. + + 3. While sensible seismic influence is generally limited to + the average width of the band, paroxysmal efforts are + occasionally propagated to great distances transversely beyond + that. + + 4. The sensible width of the band depends upon the energy + developed at each point of the length, and upon the accidental + geologic and topographic conditions along the same. + + 5. Seismic energy _may_ become sensible at any point of the + earth's surface, its efforts being, however, greater and more + frequent as the great lines of elevation and of volcanic + activity are approached; yet not in the inverse ratio of + distance, for many of the most frequently and terribly shaken + regions of the earth, as the east shore of the Adriatic, Syria, + Asia Minor, Northern India, etc., are at great distances from + active Volcanoes. + + 6. The surfaces of minimum or of no known disturbance are the + central areas of great oceanic or of terra-oceanic basins or + saucers, and the greater islands existing in shallow seas. + +Space obliges me to pass unnoticed here many minor but not unimportant +deductions. The discussions as to distribution in time and space occupy +seventy-two pages of this fourth and last Report, the remainder of which +(thirty-one pages) embraces the description and mathematical discussion +as to seismometers, to which I may refer, as comprising the most +complete account of these instruments that has, I believe, been anywhere +given. + +The appendix to the Report comprises the entire bibliography of +Earthquakes collected during those researches, and a concluding chapter +on desiderata, and inquiries as to ill-understood phenomena supposed to +be connected with Earthquakes. + + * * * * * + +In 1849-50, I was honoured by the request to draw up the article +"Earthquake Phenomena," which has appeared in the first and subsequent +editions of the "Admiralty Manual of Scientific Inquiry." Originally the +subject was intended to have formed part of the article on Geology, +entrusted to Mr. Darwin, who consulted me upon the subject; and upon my +representing how much Earthquakes had, within a short time, become +matter for the mathematician and physicist, he, with a singleness of eye +to science which it is but just to place on record, took the necessary +steps with the Admiralty authorities that Earthquakes should form a +separate article, and advised its being placed, as it was, in my hands. +To record this will, I believe, be sufficient justification for my +reference to this article, in which a good deal of information as to +Seismometry is to be found. + + * * * * * + +By recurring to Mr. Hopkins's Report on Earthquake Theory, before +remarked upon ("Report of British Association, 1847"), it will be seen +that the solutions of the problems which he there gives for finding the +depth of focus of shock are founded upon the _velocity of propagation_ +of the wave in the interior of the mass, the _apparent horizontal +velocity_ and the _horizontal direction of propagation_ at any proposed +point being known (p. 82). + +By this it appears plainly that at that time Mr. Hopkins supposed that +it was the _velocity of translation_ of the wave of shock that did the +mischief, and not the _velocity of the wave particle_, or wave itself. +And, further, that the former might be obtained by reference simply to +the modulus of elasticity of the rock of any given formation, as, +indeed, was my own earliest view when I produced my "Dynamics of +Earthquake" in 1846. From the remarks already made as to the vast +difference between the actual transit velocity in more or less +discontinuous rocks--such as they occur in Nature--it will be equally +obvious that Mr. Hopkins's methods, as above mentioned, are +impracticable, even were there no confusion between the velocity of +translation of the wave and that of the wave particle or wave itself. + +This applies also to the demonstration and diagram (taken from Hopkins) +given by Professor Phillips ("Vesuvius," pp. 258-259). + +In December, 1857, occurred the great Neapolitan Earthquake, which +desolated a large portion of that kingdom; and an opportunity then arose +for practically applying to the problems of finding the directions of +earthquake shock at a given point through which it has passed, and +ultimately the position and depth of focus, other methods, which I had +seen, from soon after the date of publication of my original Paper +(1846), were easily practicable, and the details of which I had +gradually matured. + +Bearing in mind that, in the case of the normal vibration in any elastic +solid of indefinite dimensions, the direction of motion in space of the +_wave particle_ coincides in the first semiphase of the wave, and at the +instant of its _maximum velocity_ with the right line joining the +particle and the focus or centre of disturbance, it follows that, in the +case of earthquakes, the normal vibration of the wave of shock is always +in a vertical plane passing through the focus and any point on the +earth's surface through which the shock passes (assuming for the present +no disturbing causes after the impulse has been given), and that at such +a point the movement of the wave particle in the first semiphase of the +wave is in the same direction or sense as that of translation; and at +the moment of maximum velocity the direction in space of the motion of +the wave particle is that of the right line joining the point through +which the wave has passed with the focus or centre of impulse. + +If, therefore, we can determine the direction of motion of the wave +particle in the first semiphase, and its maximum velocity, we can +obtain, from any selected point, a line (that of emergence of the shock) +_somewhere in which_, if prolonged beneath the earth, the focus must +have been; and if we can obtain like results for two or more selected +points, we decide the position and the depth of the focus, which must be +in the intersection of the several lines of direction of the wave +particle motion at each point, when prolonged downwards. + +Now, as I have said, it is the _vibration of the wave itself_, _i.e._, +the motion of the wave particle that does the mischief--_not_ the +transit of the wave from place to place on the surface; just as in the +analogous (but _not_ similar) case of a tidal wave of translation +running up an estuary and passing a ship anchored there, it is not the +transit up the channel, but the wave form itself--_i.e._, the motion of +the wave particles--that lifts the ship, sends her a little way higher +up channel, drops her to her former level, and sends her down channel +again to the spot she lay in just before the arrival of the wave. + +Everything, therefore, that has been permanently disturbed by an +earthquake shock has been thus moved in the direction and with the +maximum velocity impressed upon it by the wave particle in the first +semiphase of the wave; and thus almost everything that has been so +disturbed may, by the application of established dynamical principles, +be made to give us more or less information as to the velocity of the +wave particle (or as we, for shortness, say, the velocity of shock), the +direction of its normal vibration, and the position and depth beneath +the earth's surface, from which came the generating impulse. We thus +arrive at these as simply and as surely as we can infer from the +position taken by a billiard ball, on which certain forces are known to +have acted, the forces themselves and their direction; or, from a broken +beam, the pressure or the blow which fractured it. + +It is obvious, then, that nearly every object disturbed, dislocated, +fractured or overthrown by an earthquake shock is a sort of natural +seismometer, and the best and surest of all seismometers, if we only +make a judicious choice of the objects which being found after such a +shock, we shall employ for our purpose. This was the principle which I +proposed to the Royal Society at once to apply to the effects of the +then quite recent great Neapolitan Earthquake of 1857, and which, +through the liberality and aid of that body, I was enabled to employ +with the result I had pretty confidently anticipated, namely, the +ascertainment of the approximate depth of the focus. + +_Every_ shock-disturbed object in an earthquake-shaken country is +capable of giving _some_ information as to the shock that acted upon it; +but it needs a careful choice, and some mechanical [Greek: nous], to +select _proper_ and the best objects, so as to avoid the needless +perplexity of disturbing forces _not_ proper to the shock, or other +complications. + +When properly chosen, these natural seismometers, or evidences fitted +for observation after the shock, are of two great classes, by which the +conditions of the earthquake motion are discoverable: + + 1. Fractures or dislocations (chiefly in the masonry of + buildings), which afford two principal sources and sorts of + information, namely: + + _a._ From the observed _directions of fractures or fissures_, + by which the _wave path_, and frequently the _angle of + emergence_, may be immediately inferred. + + _b._ Information from the preceding, united with known + conditions as to the strength of materials to resist + _fracture_, by which the _velocity_ of the fracturing impulse + may be calculated. + + 2. The overthrow or the projection, or both, of bodies large or + small, simple or complex. From these we are enabled to infer: + + _c._ By direct observation, the _direction in azimuth_ of the + wave path. + + _d._ By measurements of the horizontal and vertical distances + of overthrow or of projection, to infer either the _velocity_ + of projection, or _angle of emergence_. + +Fractures by shock present their planes always nearly in directions +transverse to the wave path. Projections or overthrow take place (unless +secondarily disturbed) in the line of the wave path, or in the vertical +plane passing through it: but the direction of fall or overthrow may be +either in the same direction as the wave transit (_i.e._, as the motion +of the wave particle in the first semiphase), or contrary to it. + +It is thus obvious that the principal phenomena presented by the effects +of earthquake shock upon the objects usually occurring upon the surface +of the inhabited parts of the earth, resolve themselves into problems of +three orders, and are all amenable to mechanical treatment, viz.: + + 1. Problems relating to the direction and amount of velocity + producing fracture or fissures. + + 2. Problems relating to the single or multiplied oscillations + of bodies, considered as compound pendulums. + + 3. Problems referable to the theory of projectiles. + +These three may combine in several cases, and on the part of the +observer must combine with measurements, angular and linear, and with +geodetic operations to be conducted in the shaken country. + +The methods of application in detail are described fully, as well as +their actual application and results, in my work published in 1862 (2 +vols.), entitled "The First Principles of Observational Seismology, as +developed in the Report to the Royal Society of London of the Expedition +made by Command of the Society into the Interior of the Kingdom of +Naples, to investigate the Circumstances of the Great Earthquake of +December, 1857," to the many illustrations of which the pecuniary grant, +in aid, of 300 was most liberally made to the publishers (Messrs. +Chapman and Hall) by the Society. + +It is not my intention here, nor would space allow, of my going into the +details of observation, nor of the deductions and conclusions I have +recorded in those volumes. I have referred to their contents as marking +the advent of a new method. I have ventured to call it a new _organon_ +in the investigation of Earthquakes, and, through them, of the deep +interior of our earth; and will only add that the method, on this its +very first trial, proved fertile and successful. The depth of focus for +this shock of December, 1857, was about seven to eight geographical +miles below sea level, roughly stated. It gives me great pleasure to add +that my friend, Dr. Oldham, Director-General of the Geological Survey of +India, has since applied these same methods to the phenomena of the +great Cachar Earthquake of the 10th January, 1869, and with success. The +pressure of official duties has, he informs me, as yet prevented his +fully working out his results, but they appear so far to indicate, as we +should expect, a depth of focus or origin considerably greater than in +the European case of 1857. Some account of Dr. Oldham's results were +this year communicated to the Geological Society of London through +myself, they are of great interest and importance. + +Such, briefly and imperfectly sketched, is the existing state of +Seismology. As a branch of exact science it is, as it were, an affair of +yesterday. It is with reluctance that I have been compelled, in this +review, to refer to my own work so prominently. The harvest has been and +still is plenteous, but in this field of intellectual work the labourers +are few. This must continue to be so as long as Geology shall continue +to be viewed in public estimation (in England at least) as a fashionable +toy, that everyone who has been to school is supposed capable of +handling; and until all who profess to be geologists shall have learnt +that, to make sound progress, they must first become mathematicians, +physicists and chemists. + +It is to the general imperfect knowledge of these sciences amongst +geologists that speculative errors show such vitality, and that Geology +makes such poor progress towards becoming the interpretation of the +world as a machine (_Erdkunde_). + +It is for the same reason that Seismology and Vulcanology make little +progress; the first cannot be pursued beyond its present boundaries, nor +can even its present position be understood or explained by anyone +unfamiliar with the laws of wave motion, of all classes of waves; and it +would be easy to show, by quoting from various British or foreign +text-books on Geology, how extremely imperfect is the grasp of some of +the authors upon the subject of earthquake-wave motion, even such as +they admit and endeavour to explain and apply: in fact, many geologists +appear never to have framed to themselves any clear idea of what _is_ a +wave of any sort, liquid or elastic. The general silence as to seismic +theory of French geological writers is remarkable, to whatever cause +attributable. It has been said that French philosophers show themselves +little disposed to acknowledge or to follow the lead of their foreign +compeers in any branch of science. If this be true, or in so far as it +may be so, it is unworthy of French science, which has such boundless +claims upon our homage. I am disposed to attribute the fact in this case +to other circumstances; and, amongst these, to the small extent to which +our language is known amongst French scientific men. + +Germany has shown more desire to cultivate this branch of science. +Although, as yet, the distinct enunciation of its fundamental principles +has but sparsely found its way into her text-books, several able +monographs, such as those of Schmidt and of Httinger, prove how +completely some of her philosophers have mastered and how well applied +them. The men of science of Northern Italy, amongst whom so many +glorious names are to be found on the roll of discovery, have shown +themselves quite alive to the importance of Seismology; and I know of no +more clear, exact and popular exposition of its principles and +application, and of its cosmical relations, than is to be found in a +small volume by Professor Gerolamo Boccardo, published at Genoa in 1869, +entitled _Sismopirologia Terremoti, Vulcani e lente oscillazione del +suolo, saggio di una teoria di Geographia Fisica_. + +My object, so far, has been to mark the progress of ascertained +theoretic notions as to Seismology. I have, therefore, passed without +notice many speculative monographs, and the treatment upon Earthquakes, +whether speculative or historical, and however able, that constitutes a +prominent feature of nearly all systematic works on Geology. + +That which may be at present viewed as achieved and certainly +ascertained in theoretic Seismology is the clear conception of the +nature of earthquake motion; the relations to it of great sea or other +water wave commotions; the relations to it of sound waves--as to which, +however, more remains to be known; and the relations of all these to +secondary effects, tending in various ways to modify more or less the +topographic and other conditions of the land or sea bottom. And in +descriptive Seismology the present distribution of the earthquake bands +or regions of greatest seismic prevalence and activity are tolerably +ascertained, and their connection with volcanic lines and those of +elevation rendered more evident. Viewed alone, nothing can yet be said +to be absolutely ascertained as to the immediately antecedent cause or +causes of the impulse. The function of Earthquake, as part of the +cosmical machine, has become more clear, as the distinctive boundaries +between Earthquake and permanent elevation of the earth have been made +evident; and it has been seen that Earthquake, however contemporaneous +occasionally with permanent elevation, is not the cause, though it may +be one of the consequences of the same forces which produce elevation; +and thus, that an infinite number of Earthquakes, however violent, and +acting through however prolonged a time, can never act as an agent of +permanent elevation, unless, indeed, on that minute scale in which +surface elevation may arise from secondary effects, like that of the +Ullah Bund. + +Much remains to be done, and much may be expected even from the +continuation, if done in a systematic and organised manner, of the +statistic record of Earthquakes in connection with those other branches +of cosmical statistics, Climatology, Meteorology, Terrestrial Magnetism, +etc., the observation of which is already, to a certain extent, +organised over a large portion of the globe. + +And now let us look back for a moment to ask, How, by what mental path +of discovery, have we arrived at what we have passed in review? + +The facts of Earthquakes have been before men for unknown ages "open +secrets," as Nature's facts have been well called; "but eyes had they +and saw not." Facts viewed through the haze of superstition, or of +foregone notions of what Nature _ought_ to do, cease to be facts. When, +after the great Calabrian Earthquake of 1783, the Royal Academy of +Naples sent forth its commission of its learned members to examine into +the effects, they had spread around them in sad profusion all that was +necessary to have enabled them to arrive at a true notion of the nature +of the shock, and thence a sound explanation of the varied and great +secondary effects they witnessed, and of which they have left us the +records in their Report, and the engravings illustrative of it. But we +look in vain for any light; the things seen, often with distortion or +exaggeration, are heaped together as in the phantasmagoria of a wild +and terrible dream, from which neither order nor conclusion follow. + +Why was this? Why were these eminent _savants_ no more successful in +explaining what they saw than the ignorant peasants they found in the +Calabrian mountains? + +Because physical science itself was not sufficiently advanced, no doubt; +but also because they had no notion of applying such science as they +had, to the very central point itself of the main problem before them, +freed from all possible adventitious conditions, and so, as it were, +attacking it in the rear. How different might have been the result of +their labours, had they begun by asking themselves, What is an +earthquake? Can we not try to find out what it _is_ by observing and +_measuring_ what it has done? We see the converse mode of dealing with +Nature in Torricelli. "Nature abhors a vacuum," was told him, as the +wisdom of his day. Possibly: but her abhorrence is limited, for I find +it is _measured_ by the pressure of a column of water of thirty-four +feet in height. We need not pursue the story with Pascal, up to the top +of the Puy de Dme. + +This lesson is instructive generally to all investigators, and +particularly here; for Vulcanology, to which we are about now to turn, +has occupied until almost to-day much the same position that Seismology +did in those of the Neapolitan Commissioners. + +Whole libraries have been written with respect to it dealing with +_quality_, but _measure_ and _quantity_ remain to be applied to it. + +To a very preponderant class in the civilised world no knowledge is of +much interest or value that does not point to what is called a +"practical result," one measurable into utility or coin. I do not stop +to remark as to the bad or as to certain good results of this tendency +of mind; but I may venture to point out to all, that the exact knowledge +of the nature of earthquake motion, even during the short time that it +has become known, has not been barren in results absolutely practical +and utilitarian. The minute investigation of the destruction of +buildings, etc., and the deductions that have been made as to the +relations between the form, height, materials, methods of building, +combination of timber and of masonry, and many other architectural or +constructive conditions, have made it certain now that earthquake-proof +houses and other edifices can be constructed with facility, and at no +great increase, if any at all, of cost. I can affirm that there is no +physical necessity why in frequently and violently shaken countries, +such as Southern Italy or the Oriental end generally of the +Mediterranean, victims should hereafter continue by thousands to be +sacrificed by the fall of their ill-designed and badly built houses. + +Were a "Building Act" properly framed, put in force by the Italian +Government in the Basilicatas and Capitanata, etc., so that new houses +or existing ones, when rebuilt, should be so in accordance with certain +simple rules, a not very distant time can be foreseen when Earthquakes, +passing through these rich and fertile but now frequently sorely +afflicted regions, should come and go, having left but little trace of +ruin or death behind. Some disasters there must always be, for we +cannot make the flanks of mountains, nor the beds of torrents, etc., +always secure; but the main mortality of all Earthquakes is in the +houses or other inhabited buildings. Make these proof, and the wholesale +slaughter is at an end. + +The principles we have established have been thus practically applied in +another direction. The Japanese Government, with the keen and rapid +perception of the powers inherent in European science which +characterises now that wonderful people, has commenced to illuminate its +coasts by lighthouses constructed after the best European models. But +Japan is greatly convulsed by earthquakes, and lighthouses, as being +lofty buildings, are peculiarly liable to be destroyed by them. + +The engineer of the Japanese Government for these lights, Mr. Thomas +Stevenson, C.E. (one of the engineers to the Commissioners of Northern +Lights), was instructed to have regard, in the design of those +lighthouses, to their exposure to shock. I was consulted by Mr. +Stevenson as to the general principles to be observed; and those +edifices have been constructed so that they are presumedly proof against +the most violent shocks likely to visit Japan; not, perhaps, upon the +best possible plan, but upon such as is truly based upon the principles +I have developed. Mr. Stevenson has published some account of their +construction. + +The earthquake regions of South America might with incalculable benefit +apply those ideas; and, indeed, they have been, to some extent, already +applied by my friend, Mr. William Lloyd, Member of the Institution of +Civil Engineers, to the New Custom Houses constructed from his designs +at Valparaiso. + +As one of these utilitarian views, and an important one, it will occur +to many to ask--Can the moment of the occurrence or the degree of +intensity of earthquake shock be predicted, or is it probable that at a +future day we may be able to predict them? At present, any prediction, +either of the one or the other, is impossible; and those few who have +professed themselves in possession of sufficient grounds for such +prediction are deceivers or deceived. Nor is it likely that, for very +many years to come, if ever, science shall have advanced so as to render +any such prediction possible; but it is neither impossible nor +improbable that the time shall arrive when, within certain, perhaps +wide, limits as to space, previous time, and instant of occurrence, such +forewarnings may be obtainable. + +Earthquakes, like storms and tempests, and nearly all changes of +weather, are not periodic phenomena, nor yet absolutely uncertain or, so +to say, accidental as to recurrence. + +They are quasi-periodic, that is to say, some of their conditions as to +causation rest upon a really periodic basis, as, for example, the +recurrence of storms upon the periodic march of the earth, and sun and +moon, etc., and the recurrence of Earthquakes upon the secular cooling +of our earth; but the conditions in both are so numerous and complicated +with particulars, that we cannot fully analyse them--hence, cannot +reduce the phenomena to law, and so cannot predict recurrence. Yet +storms and tempests--which were, along with pestilences and Earthquakes, +amongst the natural phenomena which Bishop Butler deemed in his own day +impossible of human prediction--have already, through the persistent and +systematised efforts of meteorological observers, become to a certain +extent foreseeable; and medical science assures us that it has rendered +that, though to a much less degree of probability, true of pestilences. + +We may, therefore, give the utilitarian some hope, that if he will help +us along--who value our accessions of knowledge primarily upon a +different standard to his--in our talk of discovery, our posterity, in a +century or two hence, may not improbably possess the advantage of being +able, in some degree, to predict their Earthquakes. I fear the +inducement will go but a small way with the utilitarian generation, +whose bent tends much towards asking, "What has posterity ever done for +them?" + +But though we cannot as yet predict the time when an Earthquake may take +place in any locality, we can, on mixed statistic and dynamic grounds, +in many cases state the limits of probable violence of the next that may +recur. For example, the three shafts of marble columns of the Temple of +Serapis, at Pozzuoli, each of about 41-1/2 feet in height, and 4 feet 10 +inches in diameter at the base, remain standing alone, since they were +uncovered, in the year 1750. + +Now, as we can calculate exactly what velocity of earthquake-wave motion +would be required to overset these, we are certain that, during the last +one hundred and twenty-two years, the site of the Temple, and we may +say Naples and the Phlegran fields generally, have never experienced a +shock as great as the very moderate one that would overset these +columns. A shock whose wave particle had a horizontal velocity of only +about 3-1/2 feet (British) per second would overturn these columns; +which is only about one-fourth the velocity (within the meizoseismic +area) of the great shock of 1857, that produced wide-spread destruction +in the Basilicatas, and not enough to throw down any reasonably +well-built house of moderate height. + +Naples, so far as Earthquake is concerned, whether coming from the +throes of Vesuvius or elsewhere, has a pretty good chance of safety. She +may possibly (though not probably) be some day smothered in ashes; but +is in little danger of being shaken to the earth. During this time there +have been taking place, larger eruptions of Vesuvius and earthquake +shocks from other centres, together probably about the same number of +times as the numbers of those years, when those columns have been more +or less shaken. + +We may therefore affirm that the probability (on the basis of this +experience _only_) is, say 120 to 1, that the next shock, whether +derived from Vesuvius, or elsewhere, that may shake Pozzuoli, will be +one less in power than would be needed to overturn the shafts of the +Temple of Serapis there. + + * * * * * + +Let us now turn to the second branch of our subject--viz., +Vulcanology--upon which, as yet, we have secured less firm standing +ground than we have seen we possess in Seismology, for which reason we +took that first into consideration. + +It is the part of Vulcanology to co-ordinate and explain all the +phenomena of past or present times visible on our globe which are +evidences of the existence and action, whether local or general, of +temperatures within our globe greatly in excess of those of the surface, +and which reach the fusing points of various mineral compounds as found +arriving, heated or fused, at the surface. + +The stratigraphic geologist sees that such heated or fused masses have +come up from beneath, throughout every epoch that he can trace; but he +cannot fail to discern more or less a change in the order or character +of those outcomings, as he traces them from the lowest and oldest +formations to those of the present day. He sees immense outpourings of +granitoid or porphyrytic rocks that have welled up and overflowed the +oldest strata--huge dykes filling miles of fissures that had been +previously opened for the reception of the molten matter that has filled +them, and often passing through those masses of previously outpoured +rock; later he sees huge tables of basaltic rock poured forth over all. +One grand characteristic common to all these--commonly called plutonic +products--being that, whether they were poured forth over the surface or +injected into cavities in other rocks, the movements of the fused +material were, on the whole, hydrostatic and _not explosive_. + +At the present day, whatever other evidences we have of high temperature +below our globe's surface, that which primarily fixes the eye of the +geologist is the Volcano, whose characteristic, as we see it in +activity, _is explosive_. But though there is this great characteristic +difference between the plutonic and the volcanic actions and their +products, the two, when looked at largely, are seen so to inosculate, +that it is impossible not to refer them to an agency common to both, +however changed the modes of its action have been between the earliest +epochs of which traces are presented to us and the present day. + +To us little men, who, as Herschell has well said, in referring to the +methods of measuring the size of our globe, "can never see it all at +once, but must creep like mites about its surface," the Volcano, in the +stupendous grandeur of its effects, tends to fix itself in our minds in +exaggerated proportions to its true place in the cosmic machine; and, in +fact, nearly all who have sought to expound its nature and mode of +origination have occupied themselves far too exclusively with describing +and theorising upon the strange and varied phenomena which the volcanic +cone itself and its eruptions present, and too often, in the splendour +and variety of these, have very much lost sight of what ought to be the +centre-point of all such studies, namely, to arrive at some sound +knowledge of what is the _primum mobile_ of all these wonderful efforts. +Nor has the distinction been very clearly seen between the main +phenomena presented at and about volcanic active mouths, which can be +employed to elucidate the nature of the causation at work far below, and +those most varied and curious, and in other respects most pregnant and +instructive phenomena, mechanical and chemical, which are called into +action in and by the ejected matter of the volcanic cone after its +ejection. It can help us but little or very indirectly, in getting at a +true conception of the nature and source of the heat itself of the +Volcano, to examine, for example, all the curious circumstances that are +seen in the movements and changes in the lava that has already flowed +from its mouth; but it would be of great importance if we can ascertain, +by any form of observation around the cone, from what depth it has come, +or at what depth the igneous origin lies. + +The physician, endeavouring to ascertain the real nature of small-pox or +measles, will scarcely make much progress who, however curiously or +minutely, confines his attention to the pustules that he sees upon the +skin. + +Yet the Volcano, or rather all volcanic activity as now operative upon +our globe, is, as it were, an experiment of Nature's own perpetually +going on before us, the results of which, if well chosen--that is, as +Bacon says, by keeping to the main and neglecting the accidents--can, +when colligated and correctly reasoned upon, in relation to our planet +as a whole, give us the key to the enigma of terrestrial Vulcanicity in +its most general sense, and at every epoch of our world's geognostic +history, and show us its true place and use in the cosmical machine. Let +us glance at the history of past speculation on this subject, from which +so little real knowledge is to be derived, and then at the salient facts +of Vulcanology as now seen upon our earth, and finally see if we can +connect these with other great cosmical conditions, so as to arrive at +a consistent explanation in harmony with all. + +We gain nothing absolutely from the knowledge of the so-called +"ancients" as to Volcanoes in Europe at least, where alone historic +records likely to refer to them exist. The Volcanoes of Europe are few +and widely scattered. The Greeks saw but little of them, and the Romans +were all and at all times most singularly unobservant of natural +phenomena. + +Csar never mentions the existence in France of the Volcanoes of +Auvergne, so much like those he must have seen in Italy and Sicily; and +Roman writers pass in silence that great volcanic region, though +inhabited by them, and their language impressed upon the places, as +Volvic (_volcano-vicus_) seems with others to indicate; and though there +is some reason to believe that one or other of the Puys was in activity +within the first five hundred years of our epoch, the notices which +Humboldt and others have collected as from Plato, Pausanius, Pliny, +Ovid, etc., teach nothing. + +Whatever of mere speculation there may have been, volcanic theory, or +what has passed for such, there was none before 1700, when Lmry +brought forward a trivial experiment, the acceptance of which, even for +a moment, as a sufficient cause for volcanic heat (and it retarded other +or truer views for years), we can now only wonder at. Breislak's origin, +in the burning of subterranean petroleum or like combustibles, was +scarcely less absurd than Lmry's sulphur and iron filings. + +Davy, in the plenitude of his fame, and full of the intense chemical +activities of the metals of the alkalies which he had just isolated, +threw a new but transient verisimilitude upon the so-called chemical +theory of Volcanoes, by ascribing the source of heat to the oxidation of +those metals assumed to exist in vast, unproved and unindicated masses +in the interior of the earth. But Davy had too clear an intellect not to +see the baseless nature of his own hypothesis, which in his last work, +the "Consolations in Travel," he formally recanted; and it only survived +him in the long-continued though unconvincing advocacy of Dr. Daubeny. +So far, the origin of the heat had been sought always, in the crude +notion of some sort of _fuel consumed_, whether that were petroleum or +potassium and sodium; but as no fuel was to be found, nor any indicated +by the products, so far as known, of the volcanic heat, so what has been +called the mechanical theory, in a variety of shapes, took its place. + +This, in whatever form, takes its lava and other heated products of the +volcano ready made from a universal ocean of liquid material, which it +supposes constitutes the interior or nucleus of our globe, and which is +only skinned over by a thin, solid crust of cooled and consolidated +rock, which was variably estimated at from fourteen to perhaps fifty +miles in thickness. Here was a boundless supply of more than heat, of +hot lava ready made, the existence of which at these moderate depths the +then state of knowledge of hypogeal temperature, which was supposed to +go on increasing with depth at the rate of about 1 Fahrenheit, for +every thirty or forty feet, seemed quite to sustain. + +The difficulty remained, how was this fiery ocean brought to the +surface or far above it? To account for this two main notions prevailed, +and, indeed, have not ceased to prevail. Some unknown elastic gases or +vapour forced it up through fissures or rents pre-existent, or produced +by the tension of the elastic and liquid pressure below. + +The form in which this view took most consistency, and approaching most +nearly to truth, finds the elastic vapour in steam generated from water +passed down through fissures from the sea or from the land surface. But +to this the difficulty was started, that fissures that could let down +water would pass up steam. The objection, when all the conditions are +adequately considered, has really no weight; and it has been completely +disposed of, since within a few years it has been proved that capillary +infiltration goes on in all porous rocks to enormous depths, and that +the capillary passages in such media, though giving free vent to +water--and the more as the water is warmer--are, when once filled with +liquid, proof against the return through them of gases or vapours. So +that the deeply seated walls of the ducts leading to the crater, if of +such material, may be red hot and yet continue to pass water from every +pore (like the walls of a well in chalk), which is flushed off into +steam that cannot return by the way the water came down, and must reach +the surface again, if at all, by the duct and crater, overcoming in its +way whatever obstructions they may be filled with. + +And this remarkable property of capillarity sufficiently shows how the +lava--fused below or even at or above the level of infiltration--may +become interpenetrated throughout its mass by steam bubbles, as it +usually but not invariably is found to be. + +Nor is it difficult to see such a mechanism between volcanic ducts and +fissures conveying down water, as large and open pipes, for a large part +of their depth, as shall bring down water to foci of volcanic heat, +without the power of the water flowing back except as steam and through +the crater. + +Indeed, the facts known as to geysers, and those of half-drowned-out +Volcanoes such as Stromboli--whose action is intermittent just as much +as that of a geyser--show that this is not merely probable. There is, +therefore, no need for the hypothesis of those who have supposed all the +huge volumes of steam blown off from Volcanoes in eruption to come from +vesicular water pre-existent in the minute cavities of crystalline or +other rocks before their fusion into lava: a fact not proved for many +classes of rock, and for none in sufficient quantity to account for the +vast volume of steam required and for the irregularity of its issue. + +It is rather to anticipate, but I may state at once that, so far as the +admission of superficial waters to the interior, and to any depth to +which fissures or dislocation can extend, I believe no valid physical or +mechanical difficulties exist, taking into account _all_ the conditions +that may come into play together. + +Another set of views has been suggested and supported by various +writers, which proposes to account for the rise of lava on purely +hydrostatic principles. The solid crust, fractured into isolated +fragments by tensions due to its own contraction, is supposed to sink +into the sea of lava on which it floats; and much ingenuity has been +expended in imagining the mechanism by which, in places, the liquid +matter is supposed to rise _above_ the surface of the crust. + +I have no space for discussing these views further than to assert that, +in the existing state of our globe, and even admitting a solid crust of +only 60,000 metres thick, dislocation of the crust by _tension_ is not +possible. The solid crust of our globe, as I hope we shall see further +on, is not in a state of tension, and has not been so since it was +extremely thin, a mere pellicle as compared with the liquid nucleus, but +is, on the contrary, in a state of _tangential compression_. + +However tenable, in other respects, may be the volcanic theory which +rests upon the assumption of a very _thin_ crust and a universal ocean +of fused rock beneath, it fails wholly to explain many of the most +important circumstances observable as to the distribution and movements +of existing Volcanoes on our globe. + +It affords no adequate explanation of the configuration of the lines of +Volcanoes, nor of their occurrence in the ocean bed, nor of their +existence in high latitudes, near the Poles, where, no matter how or at +what rate our globe cooled from liquidity, the crust must be thickest; +nor of the independence of eruptive action of closely adjacent volcanic +vents; nor of the non-periodicity, the sudden awakening-up to activity, +the as sudden exhaustion, the long repose, the gradual decay of action +at particular vents, and of much more that might be stated and +sustained as difficulties left by that theory unexplained, or that are +of a nature even opposed to it. + +The researches of the last few years have, however, as it appears to me, +rendered any theory that demands as its postulates a _very thin crust_, +and a universal liquid nucleus beneath it, absolutely untenable. + +Without attaching any importance to the arguments of Mr. Hopkins, based +upon precession and nutation, it appears to me, on various other +grounds, some of which have been urged by Sir William Thompson, that the +earth's solid crust is not a thin one, at least not thin enough to +render it conceivable that water can ever gain admission to a fluid +nucleus, if any such still exist, situated at so great a depth; and +without such access we can have no Volcano. It is not necessary to go to +the extent of a crust of 800 or 1,000 miles thick: with one of half the +minor thickness, I believe it may be proved, on various grounds, +hydraulic amongst others, that neither water could reach the nucleus, +nor the liquid matter of the nucleus reach the surface. Mr. Hopkins +having proved to his own satisfaction an enormous thickness for the +crust, and seeing clearly the difficulties that this involved to the +generally accepted volcanic theory, and having no other to substitute +for it, fell back upon that most vague and weak notion of the existence +of isolated lakes of liquid rock, existing at comparatively small depths +beneath the earth's surface within the solid and relatively cold crust, +each supplying its own Volcano, or more than one, with ready-made lava. +What is to produce these lakes of fused matter in the midst of similar +solidified matter? what is perpetually to maintain their fluidity in the +midst of solid matter continually cooling? what has given them their +local position? why near or less near the surface? what should have +arranged them in directions stretching in some cases nearly from Pole to +Pole? + +Surely this creation of imaginary lakes, merely because it happens to +fit the vacant chink that seems needed to wedge up a falling theory, is +an instance of that abuse of hypothesis against which Newton so +vehemently declaims--"_Hypotheses non fingo._" + +Hypothesis, to be a philosophic scaffolding to knowledge, must, as +Whewell has said, "be close to the facts, and not merely connected with +them by arbitrary and untried facts." Yet this appears accepted by Lyell +(10th edition, Vol. II., p. 227, and elsewhere); by Phillips +("Vesuvius," pp. 331, 332); by Scrope, if, as I hope, I mistake him not +("Volcanoes," pp. 265, 307-8); though none of these excellent +authorities seem either quite clear or quite satisfied with the notion; +and in the very passage referred to, Lyell _may_ have possibly a much +more philosophic notion in view, where he says: "It is only necessary, +in order to explain the action of Volcanoes, to _discover some cause +which is capable of bringing about such a concentration of heat as may +melt one after the other certain portions of the solid crust_, so as to +form seas, lakes or oceans of subterraneous lava." (Vol. II, pp. 226, +227). If by this is meant, that all that is needed to complete a true +theory of volcanic action is to discover _an adequate cosmical cause for +the heat_--that is to say, a prime mover to which all its phenomena may +be traced back, which shall be at once reconcilable with the conditions +of our planet as a cooling mass in space and with facts of Vulcanology +as they are now seen upon it--then I entirely agree with it. + +It has been my own object to endeavour to discover and develope that +adequate cause in a Paper "On Volcanic Energy, an Attempt to develope +its True Nature and Cosmical Relations," read (in abstract) before the +Royal Society of London ("Proceedings, Royal Society," Vol. XX., May, +1872), and now (October, 1872) under consideration of Council with a +view to publication. + +I propose concluding this review of the progress of Vulcanology (in +which I have had to limit myself to reviewing merely the chief stages of +advance towards knowledge of the nature and origin of volcanic heat +itself, and have had to pass without notice the vast and important mass +of facts and reasonings collected by so many labourers as to its visible +phenomena and products, and the still greater mass of speculation, good +and bad, on every branch of the subject), by giving a necessarily very +brief and imperfect sketch of my own views as in that Paper in part +developed. It will first be necessary to retrace our steps a little, in +order to gain such a point as shall afford us a fuller view of the whole +problem before us. + +It is not necessary to dilate, even did space allow, upon the many +points which bind together Earthquakes and Volcanoes as belonging to the +play of like forces. These are generally admitted; and in various ways, +more or less obscure, geologists generally have supposed some relations +between these and the forces of elevation, which have raised up mountain +chains, etc. + +No one, however, that I am aware of, prior to myself, in the Paper just +alluded to, has attempted to show, still less to prove upon an +experimental basis, that all the phenomena of elevation, of volcanic +action, and of Earthquakes, are explicable as parts of one simple +machinery--namely, the play of forces resulting from the secular cooling +of our globe. We have seen that, on the whole, both Earthquakes and +Volcanoes follow along the great lines of elevation of our surface. Any +true solution of the play of forces which has produced any one of those +three classes of phenomena must connect itself with them all, and be +adequate to account for all. And this would have earlier been seen, had +geologists generally framed for themselves any correct notions of the +mechanism of elevation itself, and seen its real relation with the +secular cooling of our planet. But the play of forces resulting from +this secular cooling has never, until very recently, been adequately or +truly stated. The arbitrary assumption and neglect of several essential +conditions by La Place, in his celebrated Paper "On the Cooling of the +Earth," in the fifth volume of the "Mcanique Cleste," and the +arbitrary and unsustainable hypothesis of Poisson upon the same subject, +have tended to retard the progress of physical Geology as to the nature +of elevation: the first, by leaving the geologist in doubt as to whether +our globe were cooling at all; the second, by suggesting distorted +notions as to the mode of its cooling and consolidation. On the other +hand, neither geologists nor mathematicians generally have framed for +themselves any clear notions of the mechanism of elevation. Had a true +conception been formed of the forces and interior movements brought +necessarily into operation by the secular cooling of the globe, +geologists could scarcely have failed to see that their notion as to the +way and direction in which the forces producing elevation have actually +acted could not, if arising from refrigeration, be those which they have +almost universally supposed, namely--some force acting vertically +upwards, _i.e._, radially from the centre of the sphere. Had geologists +only looked at Nature with open eye, they must have seen that mountain +ranges, and elevations generally (exclusive of volcanic cones), +presented circumstances absolutely incompatible with their having been +thrust up by any force _primarily_ acting in the direction of a radius +to the spheroid. + +Yet this is the erroneous notion of the mechanism of elevation which to +the present hour prevails amongst geologists, so far as they in general +have framed to themselves any distinct idea of such mechanism at all. + +Thus, only to cite two examples from recent authors of justly high +reputation. Lyell says of the probable subterranean sources, whether of +upward or downward movement, when permanently uplifting a country, and +in reference to the crumpling of strata on mountain flanks by lateral +pressure, it would be rash to assume these able to resist a power of +such stupendous energy, "_if its direction, instead of being vertical_, +happened to be oblique or horizontal." This is somewhat vague--and I +trust I do not mistake or misrepresent the illustrious author--yet it +is the most explicit expression I can find in the "Principles of +Geology" as to his notion of the primary direction of elevatory force +(Edit. 10, Vol. I., p. 133). That Mr. Scrope's idea is that only of +primary radial or vertical direction of such forces, is apparent on +inspecting his Diagram No. 64 ("Volcanoes," p. 285), and in the use of +the words, "an axial wedge of granite," which, on the next page, we find +is "liquefied granite;" and if we read on to page 294, and refer also to +pages 50 and 51, I believe there can be no doubt that _vertical_ or +_direct up-thrust_ is the author's notion of the primary direction of +all forces of elevation. The true nature of these forces was, however, +clearly seen and most justly stated by Constant Prevost ("Compt. Rend.," +Tome XXXI., 1850, and "Bulletin de la Socit Golog. de France," Tome +II., 1840) as consisting, not in forces of some unknown origin acting +primarily in the vertical, but in _tangential pressures acting +horizontally, and resolved by mutual pressures at certain points into +vertical resultants_. These Prevost rightly attributed to the +contraction of the earth's solid crust. The same idea has been adopted +by Elie de Beaumont as the true mechanism of the elevation of mountain +ranges; and although De Beaumont's views as to the thinness he assigns +to the solid and contracting crust, and his strange deduction as to the +parallelism of contemporaneous mountain chains uplifted by its spasmodic +action along certain lines, may be untenable, his notion generally as to +the play of forces producing mountain elevation is much more nearly +correct. + +Mr. Hopkins's notion is simply that of the geologists. Anyone who reads +his well-known papers on elevation and the formation of fissures, etc., +must see that he views all elevatory forces as of liquids or +quasi-liquids forced up and acting primarily _vertically_ upon the +strata above them, and that these strata are not under tangential +compression, but under tension. Hence the mathematical deductions +contained in those papers as to the directions in which elevatory forces +act, and in which fissures are formed by them, are not in any way a +setting forth of such facts as occur in Nature, and, much attention as +they have attracted, can only now be viewed as exercises of mathematical +skill misapplied, because based upon data not to be found in Nature. In +fact, those papers do but misrepresent Nature, and, like many other +mathematical investigations based on untrue or insufficient data, have +tended to retard knowledge. + +The views which I have put forward in the Paper I have referred to, read +to the Royal Society, recapitulated in skeleton, so to say, are as +follows. Omitting those portions which treat of our globe from the +period of the first liquefaction out of a nebulous condition, and of the +earliest stages of the cooling by radiation into space, when the crust +was extremely thin, and of the deformation of the spheroid as one of the +first effects of its contraction, and through that the general shaping +out of continents and ocean beds; I have endeavoured to show that the +rate of contraction of the crust, while very thin, exceeded that of the +large fluid nucleus supporting it, and so gave rise to _tangential +tensions_ in the crust, and fracturing it into segments; next, that as +the crust thickened, these _tensions_ were gradually converted into +_tangential pressures_, the contraction of the nucleus now beginning to +exceed (for equal losses of heat) that of the crust through which it +cooled. At this stage these tangential pressures gave rise to the +_chief_ elevations of mountain chains--not by liquid matter by any +process being injected from beneath vertically, but by such pressures, +mutually reacting along certain lines, being resolved into the vertical, +and forcing upwards more or less of the crust itself. The great outlines +of the mountain ranges and the greater elevation of the land were +designated and formed during the long periods that elapsed in which the +continually increasing thickness of crust remained such that it was +still, as a whole, flexible enough, or opposed sufficiently little +resistance to crushing, to admit of this uprise of mountain chains by +resolved tangential pressures. I have shown that the simple mechanism of +such tangential pressures is competent to account for all the complex +phenomena both of the elevations and of the _depressions_ that we now +see on the earth's surface (other than continents and ocean beds), +including the production of gaping fissures (in directions generally +orthogonal to those of tangential pressure). And as our earth is still a +cooling body, and the crust, however now thicker and more rigid, is +still incapable of sustaining the tangential pressures to which it is +now exposed, so I by no means infer that slow and small (relatively) +movements of elevation and depression may not be still and now going on +upon the earth's surface; in fact all the phenomena of elevation and +depression, rending, etc., which at a much remoter epoch acted upon a +much grander and more effective scale. So that, for aught my views say +to the contrary, all the mountain chains in the world may be possibly +increasing in stature year by year, or at times; but in any case at a +rate almost infinitesimally small in its totality over the whole earth +to that with which their ridges were originally upreared. + +But the thickness of the earth's crust--thus constantly added to, by +accretion of solidifying matter from the still liquid or pasty nucleus, +as the whole mass has cooled--has now assumed such a thickness as to be +able to offer a too considerable resistance to the tangential pressures, +to admit of its giving way to any large extent by resolution upwards; +yet the cooling of the whole mass is going on, and contraction, though +unequal, both of thick crust and of hotter nucleus beneath also, whether +the latter be _now_ liquid or not. Were the contraction, lineal or +cubical, for equal decrements or losses of heat, or in equal +times--equal both in the material of the solidified crust and in that of +the hotter nucleus--there could be no such tangential pressures as are +here referred to, at any epoch of the earth's cooling. But in accordance +with the facts of experimental physics, we know that the co-efficient of +contraction for all bodies is greater as their actual temperature is +higher, and this both in their solid and liquid states. + +Hence for equal decrements of heat, or by the cooling in equal times, +the hotter nucleus contracts more than does its envelope of solid +matter. + +The result is now, as at all periods since the signs changed of the +tangential forces thus brought into play--_i.e._, since they became +tangential _pressures_--that the nucleus tends to shrink away as it +were from beneath the crust, and to leave the latter, unsupported or but +partially supported, as a spheroidal dome above it. + +Now what happens? If the hollow spheroidal shell were strong enough to +sustain, as a spheric dome, the tangential thrust of its own weight and +the attraction of the nucleus, the shell would be left behind altogether +by the nucleus, and the latter might be conceived as an independent +globe revolving, centrally or excentrically, within a shell outside of +it. This, however, is not what happens. + +The question then arises, Can the solid shell support the tangential +thrust to which it would be thus exposed? By the application to this +problem of an elegant theorem of Lagrange, I have proved that it cannot +possibly do so, no matter what may be its thickness nor what its +material, even were we to assume the latter not merely of the hardest +and most resistant rocks we know anything of, but even were it of +tempered cast-steel, the most resistant substance (unless possibly +iridio-osmium exceed it) that we know anything about. Lagrange has shown +that if P be the normal pressure upon any flexible plate curved in both +directions, the radii of these principal curvatures being r' and r'', +and T the tangential thrust at the point of application and due to the +force P, then: + + P = T (1/r' + 1/r'') + +When the surface is spherical, or may be viewed as such, r' = r'' and + + P = 2T/r or, T = P r/2 + +In the present case P is for a unit square (taken relatively small and +so assumed as plane) of the shell, suppose a square mile, equal to the +effect of gravity upon that unit, r being the earth's radius, and if we +assume the unit square be also a unit in thickness, P is then the weight +of a cubic mile of its material; and if we take (roughly) the earth's +radius as 4,000 miles, the tangential pressure, T, is, on _each face_ of +the cubic mile, equal to + + (4000/2) P, + +or equal to the pressure of a column of the same material of 2,000 times +its weight. + +If the cubic mile that we have thus supposed cut out of the earth's +crust at the surface were of the hardest known granite or porphyry, it +would be exposed to a crushing tangential pressure equal to between 400 +and 500 times what it could withstand, and so must crush, even though +only left unsupported by the nucleus beneath, to the extent of 1/400 or +1/500 of its entire weight. And what is true here of a mile taken at the +surface, is true (neglecting some minute corrections for difference in +the co-efficient of gravity, etc.) if taken at any other depth within +the thick crust.[F] + +The crust of our earth, then, as it now is, must crush, to follow down +after the shrinking nucleus--if so be that the globe be still cooling, +and constituted as it is; even to the limited extent to which we know +anything of its nature--it must crush unequally, both regarded +superficially and as to depth; generally the crushing lines being +confined to the planes or places of greatest weakness; and the crushing +will not be absolutely constant and uniform anywhere, or at any time, or +at any of those places of weakness to which it will be principally +confined, but will be more or less irregular, quasi-periodic, or +paroxysmal: as is, indeed, the way in which all known material +substances (more or less rigid) give way to a slow and constantly +increasing, steady pressure. + +We have now to ask, _How much_ of this crushing is going on at present +year by year? And the answer to this depends upon what amount of heat +our world is losing into space year by year. + +Geologists who have taken on trust the statement, that La Place has +proved that the world has lost no sensible amount of heat for the last +10,000 years seem generally to suppose that to be a fact; but in reality +La Place has _proved_ nothing of the sort, as those geological teachers +who have echoed the conclusion should have known, had they deciphered +the mathematical argument upon which it has been supposed to rest. + +By application of Fourier's theorem (or definition) to the observed rate +of increment of heat in descending from the geothermal _couche_ of +invariable temperature, and the co-efficients of conductivity of the +rocks of our earth's crust, as given by the long-continued observations +made beneath the Observatories of Paris and of Edinburgh, it results +that the annual loss of heat into space of our globe at present is equal +to that which would liquefy into water, at 32 Fahr., about 777 cubic +miles of ice; and this is the measuring unit for the amount of +contraction of our globe now going on. The figures are not probably +exact, for the data are not on a basis sufficiently full or exactly +established as yet; but they are not very widely wrong, and their +precise exactness is not material here. Now, how is this annual loss of +heat (great or small, as we may please to view it) from the interior of +our globe disposed of? + +What does it _do_ in the interior? We have already seen that it is +primarily disposed of by conversion into work; into the work of +diminishing the earth's volume as a whole, and in so doing crushing +portions of the solid surrounding shell. + +But does the transformation of lost heat into the work of vertical +descent, and of the crush as it follows down after the shrinking +nucleus, end the cycle? No. A very large portion of the mechanical work +thus produced, and resolved, as we have seen, into tangential crushing +pressure, is retransformed into heat again in the very act of crushing +the solid material of the shell. If we see a cartload of granite +paving-stones shot out in the dark, we see fire and light produced by +their collision; if we rub two pieces of quartz together, and crush thus +their surfaces against each other, we find we heat the pieces and evolve +light. + +The machinery used for crushing by steam-power, hard rocks into road +metal, gets so hot that the surfaces cannot be touched. + +These are familiar instances of one result of what is now taking place +by the crushing of the rocky masses of our cooling and descending +earth's crust, every hour beneath our feet, only upon a vastly greater +scale. It is in this local transformation of work into heat that I find +the true origin of volcanic heat within our globe. But if we are to test +this, so as in the only way possible to decide is it a true solution of +this great problem, we must again ask the question, _How much?_ and to +answer this, we must determine _experimentally_ how much heat can be +developed by the crushing of a given volume, say a cubic mile, of such +rocky materials as we know must constitute the crust of our globe down +to the bottom of the known sedimentary strata, and extending to such +crystalloid rocks as we may presume underlie these. We must also obtain +at least approximately what are the co-efficients of _total contraction_ +between fusion and atmospheric temperature of such melted rocks, basic +and acid silicates, as may be deemed representative of that co-efficient +for the range of volcanic fused products, basalts, trachytes, etc., +which probably sufficiently nearly coincide with that of the whole +non-metallic mass of our globe. + +The first I have determined experimentally by two different methods, but +principally by the direct one of the _work_ expended in crushing prisms +of sixteen representative classes of rock; the specific gravities and +specific heats of which I have also determined. + +If H be the height of a prism of rock crushed to powder by a pressure, +P, applied to two opposite faces, which, when the prism has been +reduced to its volume in powder, has acted through a range of H - t, +then + + P (H - t) / 772 + +is the heat corresponding to the work expended in the crushing, +expressed in British units of heat. The following were the rocks +experimented upon: Caen stone, Portland (both oolites), magnesian +limestone, sandstones of various sorts, carboniferous limestones +(marbles), the older slates (Cambrian and Silurian), basalts, various +granites and porphyries, thus ranging from the newest and least +resistant to the oldest and most resistant rocks. The results have been +tabulated, and are given in detail in my Paper, now in possession of the +Royal Society. The minimum obtained is 331 and the maximum 7,867 British +units of heat developed, by transformation of the work of crushing one +cubic foot of rock. If we apply the results to a thickness of solid +crust of 100 miles (British), of which the upper twenty-one miles +consist of neozoic, newer palozoic, older palozoic and azoic rocks in +nearly equal proportion as to thickness, and the remaining eighty miles +of crystalloid rocks (acid and basic magmas of Durocher) of physical +properties which we may assume not very different from those of our +known granites and porphyries--and which, in so far as they may differ, +would give a still _higher_ co-efficient of work transformed into heat +than I have attributed to them by ranging them as only equal to the +granites, etc.--then we obtain a mean co-efficient for the entire +thickness of crust of 100 miles of 6,472 British units of heat, +developable from each cubic foot of its material, if crushed to powder. +It results from this that each cubic mile of the mean material of such +a crust, when crushed to powder, developes sufficient heat to melt 0876 +cubic miles of ice into water at 32, or to raise 7600 cubic miles of +water from 32 to 212 Fahr., or to boil off 1124 cubic miles of water +at 32 into steam of one atmosphere, or, taking the average melting +point of rocky mixtures at 2,000 Fahr., to melt nearly three and a-half +cubic miles of such rock, if of the same specific heat. + +Of the heat annually lost by our globe and dissipated into space, +represented by 777 cubic miles of ice melted, as before stated, the +chief part is derived from the actual hypogeal source of a hotter though +not necessarily fused nucleus, and nearly, if not wholly, is quite +independent of the heat of Vulcanicity, which is developed as a +consequence of its loss or dissipation. But were we to take the extreme +case, and suppose it possible that all the heat the globe loses annually +resulted from the transformation of the work of internal crushing of its +shell, we shall find that the total volume of rock needed to be crushed +in order to produce the required amount of lost heat is perfectly +insignificant as compared with the volume of the globe itself, or that +of its shell. For, as 1270 cubic miles of crushed rock developes heat +equivalent to that required to melt one cubic mile of ice to water at +32, and if we assume the volume of our globe's _solid_ crust to equal +one-fourth of the total volume of the entire globe, 987 cubic miles of +rock crushed annually would supply the whole of the heat dissipated in +that time. But that is less than the _one sixty-five millionth_ of the +volume of the crust only. + +But a very small portion of the total heat annually lost by our globe +is sufficient to account for the whole of the volcanic energy of every +sort, including thermal waters, manifested annually upon our earth. In +the absence of complete data, we can only approximately calculate what +is the annual amount of present volcanic energy of our planet. This +energy shows itself to us in three ways: 1. The heating or fusing of the +ejected solid matters at volcanic vents. 2. The evolution of steam and +other heated elastic fluids by which these are carried. 3. The work of +raising through a certain height all the materials ejected. To which we +must add a large allowance for waste, or thermal mechanical and chemical +energy ineffectually dissipated in and above the vents. All these are +measurable into units of heat. + +I have applied this method of calculation to test the adequacy of the +source I have assigned for volcanic heat, in two ways, viz.: 1. To the +phenomena presented during the last two thousand years by Vesuvius, the +best known Volcano in the world; and 2. To the whole of the four hundred +and odd volcanic cones observed so far upon our globe, of which not more +than one-half have ever been known in activity. + +It is impossible here to refer to the details of the method or steps of +these calculations. The result however is, that making large allowances +for presumably defective data, _less than one-fourth_ of the total +telluric heat annually dissipated (as already stated in amount) is +sufficient to account for the annual volcanic energy at present expended +by our globe. + +It is thus represented by the transformation into heat of the work of +crushing about 247 cubic miles of (mean) rock, a quantity so perfectly +insignificant, as compared with the volume of the globe itself, as to be +absolutely inappreciable in any way but by calculation; and as its +mechanical result is only the vertical transposition transitorily of +material within or upon our globe, the proportion of the mass of which +to the whole is equally insignificant, so not likely in any way to +produce changes recognisable by the astronomer. + +Space here forbids my entering at all upon that branch of my +investigation which is based upon the experimental results, above +mentioned, of the total contraction of fused rocks: for these, the +original Paper can, I hope, be hereafter referred to. I am enabled, +however, to prove thus how enormously more than needful has been the +store of energy dissipated since our globe was wholly a melted mass, for +the production, through the contraction of its volume, of all the +phenomena of elevation and of Vulcanicity which its surface presents. +And how very small is the amount of that energy in a unit of time as now +operative, when compared with the same at very remote epochs in our +planet's history. + +I have said that if we can find a true cause in Nature for the +origination of volcanic _heat_, all the other known phenomena, at and +about volcanic vents, become simple. Lavas and all other solid ejecta of +Volcanoes, from all parts of the earth's surface, as well as basalts, +present in chemical and physical constitution close resemblance, and may +be all referred to the melting of more or less fusible mixtures of +siliceous crystalloid rocks with aluminous (slates, etc.) and calcareous +rocks. Their general chemical composition, and the higher or lower +temperatures of fusion resulting therefrom, together with the higher or +lower temperatures to which they have been submitted at the different +volcanic foci, determine their difference of flow (under like surface +conditions) and of mineral character after ejection and cooling. + +St. Clair de Ville and Fouqu have shown that the gaseous ejections, of +which steam forms probably 99 per cent., are such as arise from water +admitted to a _pre-existent focus of high temperature_. + +Whether sea or fresh water is not material, when we bear in mind that +the chemical constituents found in sea water and in natural fresh waters +that have penetrated the soil are, on the whole, alike in kind and only +differ in proportions. But I must pass almost without notice all the +varied and instructive phenomena which are presented by volcanic vents, +for to treat of these at all would be to more than double the size of +this sketch. + +In the source that has been pointed out as that from which volcanic heat +itself is derived, viz., the secular cooling of our globe, and the +effects of that upon its solid shell, we are enabled to point to that +which is the surest test of the truth of any theory--that it not only +enables us to account for all the phenomena, near or remote, but to +predict them. We see here linked together as parts of one grand play of +forces, those of contraction by cooling, producing by _direct_ +mechanical action the elevation of mountain chains, and by their +_indirect_ action, by transformation of mechanical work into heat, the +production of Volcanoes; and both by direct and by indirect action, of +Earthquakes, never previously shown to have thus the physical connection +of one common cause, but merely supposed, more or less, to be connected +by their distribution upon our earth's surface. + +We now discern thus the physical cause _why_ Volcanoes are distributed, +viewed largely, linearly, and follow the lines of elevation; we see +equally why their action is uncertain, non-periodic, fluctuating in +intensity, with longer or shorter periods of repose, shifting in +position, becoming extinct here, appearing in new activity or for the +first time there. We have an adequate solution of the before +inexplicable fact of their propinquity, and yet want of connection. We +have an adequate cause for the fusion of rock at local points without +resorting to the baseless hypothesis of perennial lakes of lava, etc. + +For the first time, too, we discern a true physical cause for earthquake +movement, where volcanic energy does not show itself. The crushing of +the world's solid shell, whether thick or thin, goes on _per saltum_ and +at ever-shifting places, however steadily the tangential pressures +producing it may act. Hence crushing _alone_ may be shown to develope +amply sufficient impulse to produce the most violent Earthquakes, +whether they be or be not at a given place or time connected with +volcanic outburst or possible injection, or with tangential pressures, +enough still, in some cases, to produce partial permanent elevation. + +When subterraneous crushing takes place, and the circumstances of the +site do not permit the access of water, there may be Earthquake, but can +be no Volcano; where water is admitted, there may be both. + +And thus we discern why there are comparatively few submarine +Volcanoes, the floor of the ocean being, on the whole, +water-tight--"puddled," as an engineer would say, by the huge deposit of +incoherent mud, etc., that covers most of it, and probably having a +thicker crust beneath it than beneath the land. + +We see, moreover, that the geological doctrine of absolute uniformity +cannot be true as to Vulcanicity, any more than it can for any other +energy in play in our world. Its development was greatest at its +earliest stages, when the great masses of the mountain chains were +elevated. It is even now--though as compared to men's experience, and +even to all historic time, apparently uniform and always the same--a +decaying energy. + +The regimen of our planet as part of the Cosmos, which seems to some +absolute (and presented to Playfair no trace of a beginning nor +indication of an end), is not absolute, and only seems to us to be so +because we see so little of it, and of its long perspective in time. +This the now established doctrine of the conservation of energy renders +certain. + +With this source for volcanic heat, too, in our possession, we can look +from our own world to others, and predict within certain limits, which +must widen as our knowledge of the facts of their substance and surface +becomes greater, what have been and what are the developments of +Vulcanicity which have taken place or are occurring in or upon them. +Looking to our own satellite, we see for the first time a sufficient +physical cause for the enormous display of volcanic energy there which +the telescope divulges to us; one which is not to be explained alone by +the commonly made statement of the small density of the moon, but by +the fact that as the rate of her cooling from a given temperature, as +compared with that of our earth (apart from questions of the chemical +nature of the two bodies, or of their specific heats, etc.), has been +inversely as their respective masses, and directly as their surfaces, so +has the rate of cooling of the moon been vastly greater than that of the +earth, and the energy due to contraction by cooling more intense and +rapidly developed in our satellite than upon our globe. + +We have thus traced, in meagre and broken outline only--because space +admitted no more--the progress of Science to its existing state as +respects Vulcanicity, in its two branches of Vulcanology and of +Seismology, and pointed out their more intimate relations and points of +connection, and been at length able to refer them, on the sure basis of +physical laws, to one common cause, and that one derived from no +hypothesis, but simply from the postulate of our world as a terr-aqueous +globe cooling in space. + +What I have here advanced with reference to volcanic energy, which +appertains to my own researches, I do not conceal from myself, nor from +the reader, has yet to await the reception generally and the award of +the true men of science of the world. + +That, like every new line of thought which has attempted or succeeded in +supplanting the old, it will meet with opposition, I make no doubt. + +My belief, however, is that in the end it will be found to have added a +fragment to the edifice of true knowledge. + +The interpretation which I have given of the nature and origin of +volcanic activity points at once to the function in the Cosmos which it +is its destiny to fulfil. It is the instrument provided for the purpose +of continually preserving the earth's solid shell in a state to follow +down after the descending nucleus. It does this by an apparatus or play +of mechanism whereby the material of the solid shell, locally or along +certain lines, is not only crushed, but the crushed material is blown +out as dust, or expelled as liquid rock from between the walls of the +shell, which are thus enabled to approach each other; and thus, by +relief of the tangential thrusts, to permit the shell to descend, which +it is obvious that crushing alone, unless it extended to the whole mass +of the shell, could not accomplish. + +It is a wonderful example of Nature's mechanism thus to see how simple +are the means by which this end is accomplished. The same inevitable +crush that dislocates the solid shell along certain lines, produces the +heat necessary to expel to the surface the material crushed. + +When attempted to be made the basis for philosophic discovery, "final +causes" are no doubt barren, as Bacon has said; but when we have +independently and by strict methods arrived at a result, we may justly +appeal, as a test of its truth, to its showing itself as plainly +fulfilling a needful end, and, by a distinctly discernible mechanism, +preserving that harmony and conservation which are the obvious law of +the universe. + +As has been said, if I mistake not by Daubeny, John Phillips, by +Herschell, and by myself, the function of the Earthquake and the +Volcano is not destructive but, preservative. But we now see that: that +the preservative scope of this function, as respects our earth, is far +wider than what has been previously attributed to it. The Volcano does +not merely throw up new fertile soil, and tend, in some small degree, to +restore to the dry land the waste for ever going on by rain and sea; it +fulfils a far weightier and more imperative task; it--by a mechanism the +power of which is exactly balanced to the variable calls demanded of it, +and which working almost imperceptibly, although in a manner however +terrible its surface-action may at times appear to us little +men[G]--prevents at longer intervals such sudden and unlooked-for +paroxysms in the mass of our subsiding earth's shell as would be +attended with wide-spread destruction to all that it inhabit. + +To the popular mind, Volcanoes and Earthquakes are only isolated items +of curiosity amongst "the wonders of the world:" few geologists even +appear to realise how great and important are the relations of +Vulcanicity to their science, viewed as a whole. Yet of Vulcanicity it +is not too much to say, that in proportion as its nature and doctrines +come to be known and understood as parts of the Cosmos, the nearer will +it be seen to lie at the basis of all Physical Geology. + + +[A] For a fuller account of the literature and history of advancement of +human knowledge as to Earthquakes, here merely glanced at, I must refer +to my First Report on the Facts of Earthquakes, "Reports, British +Association, 1850," and to the works of Daubeny, Lyell, Phillips and +others, its _complete_ history remaining yet to be written. + +[B] Yet how indistinctly formed were Young's ideas, and indistinct in +the same direction as those of Humboldt, becomes evident by a single +sentence: "When the agitation produced by an Earthquake extends further +than there is any reason to suspect a subterraneous communication, it is +probably propagated through the earth nearly in the same manner as a +noise is conveyed through the air."--_Lectures, Nat. Phil._, Vol. I. + +[C] The Right Rev. Charles Graves, F.R.S., etc., then Fellow of Trinity +College, Pres. R. I. Acad., and now Bishop of Limerick, on presentation +of the Academy's Cunningham Medal. + +[D] In this Report, though I have never before referred to it, and do so +now with reluctance, I have always felt that the Author did me some +injustice. The only reference made to my labours, published the +preceding year only, is in the following words: "Many persons have +regarded these phenomena (viz., Earthquakes) as due in a great measure +to vibrations ... and the subject has lately been brought under our +notice, in a Memoir by Mr. Mallet, 'On the Dynamics of Earthquakes,' in +which he has treated it in a more determinate manner, and in more +detail, than any preceding writer" (p. 74). If that Paper of mine be +collated with this Report, it will be, I believe, found that, as +respects the earthquake part, the latter tint parades, in a mathematical +dress, some portions of the general theory of earthquake movements, +previously published by me as above stated. So, also, in the chapter (p. +90) referring to Seismometry, and the important uses to Geology that +might be (and since have been, to some extent) made of it, no mention is +made of those instruments previously proposed by me, nor of my +anticipation of their important uses. This is but too mortifyingly +suggestive of the-- + + "Pereant qui mea ante mihi dixerunt." + +Having left this unnoticed for so many years, and during which the +Author has preceded me to that bourne where our errors to each other +must be forgotten, I should certainly not have now trespassed on the +good rule, _De mortuis nil nisi bonum_, had I not observed very recently +one amongst other results probably attributable to it. In Professor +Phillips's "Vesuvius," if any one will refer to the passage beginning +"The mechanism of earthquake movement has been investigated by competent +hands. The late eminent mathematician, Mr. Hopkins, explained these +tremors in the solid earth by the general theory of vibratory motion," +etc. (pages 257-259)--I think he must, in the absence of collateral +information, conclude that, not I, but Mr. Hopkins, was the discoverer +of the Theory of Earthquakes as explained by the general theory of +vibratory motion. + +Probably my friend, Professor Phillips, had not recently referred to +those Memoirs and Reports of twenty-four years back, and I am thoroughly +convinced that, if he has here perpetuated an injustice, he has done so +unintentionally and unwittingly. + +Still, the facts show how true it is that + + "The ill men do lives after them, + The good they do is oft interred with their bones." + +And I may venture to ask my friend, should his admirable book reach, as +I doubt not it will, another edition, to modify the passage. + +[E] Assuming the point of ejection of this block (the crater) to be +8,000 feet above where it landed, and allowing it as high a density as +admissible, and the angle of projection the best for large horizontal +range, it may be proved that this mass, to reach nine miles +horizontally, would require an initial velocity of projection of from +1,500 to 1,600 feet per second, one as great as that of a smooth-bore +cannon-shot at the muzzle, and perfectly inconceivable to be produced by +a volcano. + +[F] The Rev. O. Fisher, M.A., F.G.S., in a most interesting and valuable +Paper, "On the Elevation of Mountain Chains by Lateral Pressure, its +Cause, and the Amount of it, with a Speculation on the Origin of +Volcanic Action," read, April, 1868, and published in the Transactions +of the Cambridge Philosophical Society, Vol. XI., Part III., in 1869, +has deduced the necessary crushing of the earth's crust by a different +but closely analogous method. I had not seen this Paper until after my +own was in the hands of the Royal Society. The author's volcanic views +are wholly different from my own, and do not appear to me equally valid +with his notions as to elevation.--R. M. + +[G] "Magna ista quia parvi sumus"--SENECA, "Qus. Nat." + + +END. + + + + +TRANSLATION +OF + +PROFESSOR PALMIERI'S + +_ACCOUNT OF_ +THE ERUPTION OF VESUVIUS +OF +_1871-1872_ + + + + +I. + +ACCOUNT OF THE ERUPTION. + + +The great and disastrous conflagration of Vesuvius, which took place on +the 26th of April, 1872, was, in my opinion, the last phase of an +eruption which commenced at the end of January, 1871, an account of +which I was unwilling to write, because I was convinced that it would +not really terminate without a more or less violent explosion, such as I +had often predicted. I shall now state the reasons upon which my +prediction was founded. + +When the central crater begins to heave, with slight eruptions, one may +always predict a series of slight convulsions of greater or less +duration, which are preparatory to the grand explosion, after which the +Volcano remains for the most part in repose. Thus, when I observed the +cone fissuring in November, 1868, and copious lava streams issuing from +it, and flowing over the beautiful and fertile plains of the Novelle, +through the Fossa della Vetrana, instead of announcing the beginning of +an eruption, I announced the termination of one which had been manifest +for upwards of a year by the constant flow of lava from the summit of +the cone. + +From the month of November, 1868, until the end of December, 1870, the +mountain remained quiet, except that the fumaroles at the head of the +fissure showed a degree of activity by which chlorides and sulphides of +copper, sulphide of potash and other products, were engendered. + +But in the beginning of 1871 the seismograph was disturbed,[1] and the +crater discharged, with a slight detonation, a few incandescent +projectiles. Then I announced that _a new eruption had commenced, which +might be of long duration, but with phases that could not possibly be +foreseen_; and on the 13th January, on the northern edge of the upper +plain of the Vesuvian cone, an aperture appeared, from which at first a +little lava issued, and then a small cone arose and threw out +incandescent projectiles, with much smoke of a reddish colour, whilst +the central crater continued to detonate more loudly and frequently. The +lava-flow continued to increase until the beginning of March, without +extending much beyond the base of the cone, although it had great +mobility. In March, this little cone appeared not only to subside, but +even partly to give way, as almost happens with eccentric cones when +their activity is at an end. Upon visiting it, I observed that four +prismatic or pillar-like masses remained standing, three of which were +formed of scori which had fallen back again in a pasty condition, and +had become soldered together, the fourth consisting of a pyramidal block +of compact and lithoidal lava, which appeared to have been forced up by +impetus from the ground beneath. A little smoke issued from the small +crater, and a loud hissing from the interior was audible. By lying +along the edge, I could see a cavity of cylindrical form about ten +metres in depth, tapestried with stalactitic scori covered with +sublimations of various colours. The bottom of this crater was level, +but in the centre a small cone of about two metres had formed, pointed +in such a manner that it possessed but a very narrow opening at the +apex, from which smoke issued with a hissing sound, and from which were +spurted a few very small incandescent scori. This little cone increased +in size as well as activity until it filled the crater, and rose four or +five metres above the brim.[A] New and more abundant lavas appeared near +the base of this cone, and, pouring continually into the Atria del +Cavallo, rushed into the Fossa della Vetrana in the direction of the +Observatory and towards the Crocella, where they accumulated to such an +extent as to cover the hill-side for a distance of about 300 metres; +then turning below the Canteroni, they formed a hillock there without +spreading much farther. These very leucitic lavas are capable of great +extension, the pieces which are ejected forming for the most part very +fine filiform masses, which may be collected on the mountain in great +quantities, and specimens of which I presented to the Academy under the +name of _filiform lapilli_. These threads were often of a clear +yellowish colour, and, when observed under the microscope, were found to +consist of very minute crystals of leucite embedded in a homogeneous +paste. The crystals were still smaller as the diameter of the threads +was less, and never formed knots or swellings even in the most hair-like +threads. These observations led me to reject the opinion of those who +hold that crystals of leucite are pre-existent in the lava. The viscous +nature of these lavas prevented their being covered with fragmentary +scori, but caused the formation at first of a skin, which, thickening, +became at last a more or less pliable shell, that, when more solidified, +allowed the still fluid part to run as in a tube formed of this solid +shell. For many months the lava descended thus from the cone and +traversed the Atria del Cavallo, always covered, appearing below the +Canteroni of a lively fluidity, until it could no longer be enveloped in +its skin, which was stretched by the addition of new lava, and finally +rent asunder to give room to the current until, owing to diminished +liquidity, it was constrained to stop. When the lava, having traversed +the covered channel it had made for itself from the top of the mountain +to below the Canteroni, made its appearance still running, it frequently +formed large bubbles on the surface, which mostly burst to give vent to +smoke, and then disappeared. + +In October, 1871, near the edge of the central crater, another small +crater was formed by falling in, which, after a few days, gave vent to +smoke and several jets of lava. The principal cone frequently opened in +some point of the slope to give egress to small currents of lava, which +quickly ceased. But towards the end of October the detonations +increased, the smoke from the central crater issued more densely and +mixed with ashes, and the seismograph and accompanying apparatus were +disturbed: for all these reasons, I said in one of my bulletins, _we +have either reached a new phase or the end of the eruption_, not knowing +whether the new phase would be the last. On the 3rd and 4th November +copious and splendid lava streams coursed down the principal cone on its +western side, but were soon exhausted. The cone of 1871 appeared again +at rest, and partly even fell in, but did not cease to emit smoke and to +show fire in the interior. + +In the beginning of January, 1872, the little cone again became active, +the crater of the preceding October resumed strength, with frequent +bellowings and projectiles, and soon after lavas of the same kind as +before reappeared. The cone of 1871, formed again by the lava ejected, +became so full that the lava poured from its summit in the most singular +and enchanting manner. So far only an eccentric or ephemeral cone had +risen close to the central crater, which, after exhaustion, regained +vigour and discharged lava from the apex instead of the base, as usually +happens. + +In the month of February matters were somewhat moderated; but in March, +with the full moon, the cone opened on the north-west side--the cleavage +being manifest by a line of fumaroles--and a lava stream issued from the +lowest part without any noise and with very little smoke, and poured +down into the Atria del Cavallo as far as the precipices of Monte di +Somma. This lava ceased flowing after a week, but the fumaroles pointed +out the cleft of the cone; and between the small re-made cone, which had +risen to the height of 35 metres, and the central crater, a new crater +of small dimensions and interrupted activity opened. + +On the 23rd April (another full moon) the Observatory instruments became +agitated, the activity of the craters increased, and on the evening of +the 24th splendid lavas descended the cone in various directions, +attracting on the same night the visits of a great many strangers. All +these lava streams were nearly exhausted on the morning of the 25th; +only one remained, which issued from the base of the cone, not far from +the spot whence that of the preceding month had issued. Numbers of +visitors, attracted by the splendour of the lava streams of the +preceding night, which they supposed still continued, soon arrived, but, +finding them exhausted, were for the most part conducted by their guides +to see the one still flowing. It was almost inaccessible, and to reach +it one had to walk over the rough inequalities of the scori. It took me +two hours to get there from the Observatory, when I visited it that +morning, and therefore I endeavoured to dissuade those who wished to +visit it at night from the attempt, but set out myself from the +Observatory at 7 p.m., leaving my only assistant there. The instruments +were agitated. After midnight the Observatory was closed, and my +assistant retired to rest. Late and unlucky visitors passed unobserved +with an escort of inexperienced guides; at half-past 3 o'clock in the +morning of the 26th they were in the Atria del Cavallo, when the +Vesuvian cone became rent in a north-westerly direction, the fissure +commencing at the little cone which disappeared, and extending to the +Atria del Cavallo, whence a copious torrent of lava issued. Two large +craters formed at the summit of the mountain, discharging numerous +incandescent projectiles with white ashes, and glittering with particles +of mica, which frequently recurred. + +A cloud of smoke enveloped these unfortunates, who were under a hail of +burning projectiles and close to the lava torrent. Some were buried +beneath it[B] and disappeared for ever; two dead bodies were picked up, +and eleven grievously injured, one of whom died close to the +Observatory. He alone revealed his name, Antonio Giannone. I learned +afterwards that he was a fine young fellow, and Assistant-Professor in +one of the Universities. + +Assistant-Professors Signor Franco, who is a priest, and Signor +Francesco Cozzolino, a priest also, entrusted with the festive mass for +the Observatory, hastened to assist the dying. On my own return thither, +the sad spectacle of the dead and dying awaited me; the former were +conveyed, through the assistance of the municipal officer of Resina, to +the Cemetery, and the latter to the Hospital. But we must leave this +scene of grief and sorrow, and return to the eruption. + +The fissure of the cone on the north-west side was large and deep, and +extended into the Atria del Cavallo, about 300 metres. No mouth opened +along the cleft of the cone itself; all the lava issued from that part +which extended into the Atria. From previous experience I should have +expected to have seen the formation of adventitious cones along the +widest part of the fissure, which is never that most elevated, and these +discharging from their summits riform matter frequently mixed with +projectiles, and from their base lava; but on this occasion no cone +appeared at the widest part of the fissure, but a long hillock was +formed like a little chain of mountains, one point of which was elevated +about fifty metres above the plain beneath, and bearing no resemblance +to a cone. + +Another fissure opened in the cone on the south side, which did not +extend to the base, and lava issued from this and flowed in the +direction of the Camaldoli. Streams of less importance furrowed the cone +in other directions, but the largest quantity of lava proceeded from the +fissure in the Atria del Cavallo, below the hillock or miniature chain +of collines just described. This lava stream was for some time +restrained within the Atria del Cavallo, among the holes and +inequalities of the lavas of 1871, but these being filled up and +overcome, it divided into two branches--the smaller one flowing through +a hollow which separated the lavas of 1867 from those of 1871, and made +its way over the lavas of 1858, threatening Resina, but stopped as soon +as it reached the first cultivated ground; the larger branch +precipitated itself into the Fossa della Vetrana, occupying the whole +width, about 800 metres; and traversing the entire length of 1,300 +metres in three hours. It dashed into the Fossa di Faraone; here it +again divided into two streams, one overlying the lava of 1868, on the +Plain of the Novelle, partially covering the cultivated ground and +country-houses; the other flowing on through the Fossa di Faraglione, +over the lava of 1855, reached the villages of Massa and St. Sebastiano, +covering a portion of the houses, and thence continued its course +through the bed of a foss or trench which, contrary to my advice, had +been excavated after the eruption of 1855, in the expectation of +diverting the course of that lava. I did not fail to observe that the +rains which previously descended through these steep channels, would in +future be kept back to filtrate through the scori, without ever +reaching the new channel. + +The lava of this eruption, meeting with this said excavation, flowed +into it, instead of pursuing its road over the lava of 1855, and thus +invaded highly cultivated ground and towns of considerable value, +extending to the very walls of a country-house belonging to the +celebrated painter, Luca Giordano. This lava stream, having surmounted +the obstacles which the heaps of scori in the Atria del Cavallo +presented to it, ran with great velocity (notwithstanding its being +greatly widened out in the Fossa del Vetrano), so that between 10 a.m. +and 11 p.m. it traversed about five kilometres of road, occupying a +surface of five to six square kilometres. If it had not greatly +slackened after midnight, from the failure of supply at its source, in +twenty-four hours more, by occupying Ponticelli, it would have reached +Naples, and flowed into the sea. + +Although I had often visited the two villages of Massa and St. +Sebastiano, previously greatly injured by the lava of 1855, yet I could +not well estimate, upon now seeing them again, the number of houses +which had disappeared. Massa seemed to me diminished by about one-third, +and St. Sebastiano by somewhat less than a fourth. But the way of escape +was open to the inhabitants of Massa; whilst a great river of lava +occupying the road leading to St. Giorgio a Cremano would have hindered +the flight of the inhabitants of St. Sebastiano, if they had been +dilatory. The lava stream now separating the two villages is little less +than a kilometre in width, and is about six metres in height. + +On the night of the 26th April, the Observatory lay between two torrents +of fire, which emitted an insufferable heat. The glass in the +window-frames, especially on the Vetrana side, was hot and cracking, and +a smell of scorching was perceptible in the rooms. The cone, besides +being furrowed by the lava streams just described, was traversed by +several others, which appeared and disappeared. It seemed completely +perforated, and the lava oozed as it were through its whole surface. I +cannot better express this phenomenon, than by saying that _Vesuvius +sweated fire_. In the day-time, the cone appeared momentarily covered +with white steam jets (fumaroles), which looked like flakes of cotton +against the dark mountain-side, appearing and disappearing at brief +intervals. + +Simultaneously with the grand fissure of the cone, two large craters +opened at the summit, discharging with a dreadful noise, audible at a +great distance, an immense cloud of smoke and ashes with bombs and +flakes, rising to the height of 1300 metres[C] above the brim of lava +(_sull' orlo de essi_). The white ashes, before described, although they +did not fall beyond the Crocella, were carried by the wind as far as +Cosenza, from whence they were sent to me by Dr. Conti. These ejections +were followed by dark sand, with lapilli and small fragments of scori +of the same colour. The smoke, driven up with violence, assumed the +usual aspect of a pine tree, of so sad a colour that it reminded us of +the shadowy elm of Virgil's dreams ("_ulmus opaca ingens_"). From the +trunk and branches of the pine-tree cloud fell a rain of incandescent +material, which frequently covered all the cone. The lapilli and the +ashes were carried to greater distances. + +The victims of the morning of the 26th, the torrents of fire which +threatened Resina, Bosco and Torre Annunziata, and which devastated the +fertile country of the Novelle, of Massa, St. Sebastiano and Cercola, +the two partially buried villages, the continual and threatening +growlings of the craters, caused such terror that numbers fled from +their dwellings near the mountain into Naples, and several in Naples +went to Rome or to other places. Very many delayed from the knowledge +that I was in the Observatory, and held themselves in readiness for +flight whenever I should abandon it. + +The rapidity with which the vast torrent of fire assailed the houses +(_i.e._, in these villages), and the great heat which spread to a +distance, scarcely allowed the fugitives to carry away any of their +belongings; many were completely destitute. The authorities vied with +each other in zealous efforts to relieve the distress, and the +municipality of Naples sheltered and fed the wretched beings for many +days. + +The igneous period of the eruption was short, for on the morning of the +27th the lava stream, bearing down upon Resina, having covered a few +cultivated fields, stopped; the lava descending from the summit of the +mountain towards the Camaldoli also stopped; and the great lava torrent, +which passed the shoulders of the Observatory through the Fossa della +Vetrana, lowered the level of its surface below those of its two sides, +which appeared like two parallel ramparts above it. + +If these streams had continued on the 27th, flowing in the same manner +as they did on the night of the 26th, they would have reached the sea, +bringing destruction to the very walls of Naples. + +But before leaving the subject of these lavas I must narrate an +important fact to which I was witness, and which was thrice repeated, +near the banks of the great river of fire that ran close to the +Observatory. At three several points, and at different times, I observed +great balls of black smoke issue from the lava, driven up with continued +violence, as if from a crater; through the smoke I frequently observed +numerous projectiles thrown up into the air, but I could not say whether +with noise or in silence, for the noise of the central crater was +deafening. Each of these little eruptions, which I may call _external +eruptions_, lasted from fifteen to twenty minutes. The first took place +at the most elevated point of the Fossa della Vetrana, on the right bank +of the torrent; the second, under the hill of Apicella, where the lava +divided into the two branches, before described; and the third near to +the Observatory on the left bank of the lava stream. These singular +explosions terminated without leaving little cones or craters, the lava +in its impetuosity carrying every trace away. These eruptions were seen +from Naples, and the Observatory was justly believed to be in danger. +One has been clearly photographed, the one which was the best seen from +Naples, being the nearest and the least darkened by the smoke of the +lava. (Plate 4.) Is this the first time that the phenomenon has been +remarked? I believe that it is at least the first time it has been +authenticated. The authority of Julius Schmidt, quoted by Scrope, has no +weight with me, for I was also a witness of what happened at Vesuvius in +1855; and, although these cones were in the midst of the lava in the +Atria del Cavallo, they originated, according to the opinion of +everyone, from the fissure from which the other and much larger cones +proceeded. The same phenomenon was observed in the Atria del Cavallo in +1858, when I caused two of the little cones to be brought to the +Observatory; but these also might belong to the fissure along which the +other cones were arranged. The same may be said of the little craters +observed, after they had been exhausted, by Professor Scacchi in 1850. +But the discharging mouths now observed in the Fossa della Vetrana, +which existed for twenty minutes and then disappeared, and which were +not at all in a continuous line, and could not be supposed to correspond +with any fissure beneath, constitute a circumstance which, if not new, +is evident for the first time, and cause the recognition of a power in +the lava itself to form eruptive fumaroles.[2] + +The igneous period of the eruption having terminated on the evening of +the 27th, the ashes, lapilli, and projectiles became a little more +abundant, whilst the roaring noises of the craters apparently became +greater. The pine-tree cloud was of a darker colour, and was furrowed by +continual lightning, visible by daylight from the Observatory. Many +writers on the subject of Vesuvius affirm that the flashes which appear +through the smoke cloud were lightning unaccompanied with thunder, but +they studied the phenomena from Naples, or some place more or less +distant from the crater, where the report of the thunder was inaudible, +or could not be distinguished from the bellowing and detonation of the +mountain. The fact is that these flashes were constantly followed by +thunder, after an interval of about seven seconds.[D] When the flash was +very short, a simple noise like the report of a gun was heard, but if it +were long, a protracted sound like that from torn paper ensued. + +On the 28th the ashes and lapilli, continuing to fall abundantly, +darkened the air, yet without diminishing the terrible noise; at Resina, +Portici, St. Giorgio a Cremano, Naples, etc., terror was universal. + +On the 29th, with a strong wind blowing from the east, scori of such a +size fell at the Observatory, that the glass of the windows unprotected +by external blinds was broken. The noise from the crater continued, but +the projectiles rose to a less height, indicating a diminution in the +dynamic power of the eruption. Towards midnight the noise of the craters +was no longer continuous, and recurred with less force and for shorter +intervals. Almost at the same hour a tempest burst over the Campania +with loud thunder and a little rain. The grass, the seeds, the vine +tendrils, the leaves and tops of the trees dried up immediately, and the +country was changed from spring to winter. The storm, although repeated +on the following days, passed away by degrees, and thus the floods, +which I strongly feared, did not occur. Almost always after great +eruptions of Vesuvius, storms of heavy rain have followed, and the +ground being covered with ashes, the water could not filtrate through +into the soil, but descended in muddy torrents over the adjacent +country, occasioning as much damage as the fire itself. + +On the 30th, the detonations were very few, and the smoke issued only at +intervals, and by the 1st May the eruption was completely over. + +When the smoke had cleared off the figure of the cone was seen to be +changed. (_Vide_ Plate 5a.) + +The ground was perpetually disturbed whilst the Volcano raged, so that +the Observatory oscillated continually. Some shocks were felt not only +in the adjacent territory, but at a greater distance, at Montovi and +elsewhere. The oscillations at the Observatory were chiefly undulatory, +from N.E. to S.W. They were observed for some days after the termination +of the eruption, but not continuously, although they maintained some +intensity. + +If we refer to January, 1871, we shall find that that eruption was +preceded by several earthquakes, among which were those of the months of +October, November and December, in the previous year, that wrought such +destruction in Calabria, and especially in the province of Cosenza; if +we consider that as only the last phase, we shall find that it was +preceded by great shocks of earthquake that devastated some regions of +Greece.[3] + +The great quantity of lapilli which fell buried the scori with which +the Vesuvius cone was covered, so that it became somewhat more difficult +to ascend to the summit, and much less difficult to descend. Having +reached the top of the mountain, I found a large crater divided into two +parts by what seemed a cyclopean wall. The two abysses had vertical +sides, and revealed the internal structure of the cone. Their vertical +depth was 250 metres; and beyond that I observed a sort of tunnel +perforated in the rock, with a covering arch raised above the bottom of +the eastern abyss about 12 metres, judging by the eye. The interior +walls of the crater showed neither the usual stalactitic scori nor +sublimations, nor fumaroles, but alternate beds of scori and of compact +lava. The fumaroles and sublimations abounded, only about the brims of +the craters. Hydrochloric and sulphuric acid and sometimes sulphuretted +hydrogen affected respiration, and the temperature rose sometimes to 150 +degrees. Various fissures about the brim of the double crater indicated +prolongations downwards, which allowed me to descend with a rope, in +order to examine the interior of the tunnel to which I have just +alluded. The highest brim of the crater was fissured for a distance of +80 metres, and the greatest depth of fissure was at that place. + +By measurement with the barometer, we ascertained approximately (for +only one barometer was used) that the height of the Vesuvian cone was +somewhat diminished. + +Not only the Vesuvian cone, but the whole adjacent country appeared +white for many days, as if covered with snow, when exposed to sunlight. +This was due to the sea-salt contained in the ashes with which the +surface was strewn. + +A great quantity of coleoptera assembled on the flat roof of the +Observatory, where the ashes and lapilli were heaped up two decimetres +in height. I found the same species on the cone, where many insects were +observed on other occasions, such as the _Cuccinella septempunctata_; +the crysomela populi, etc., were wanting. This phenomenon of the +extraordinary concourse of insects on the top of Vesuvius, in order to +die in some of the fumaroles, especially noted previous to and after +great eruptions, is a circumstance for which I cannot account.[4] The +whole of the lava emitted in this eruption occupies a surface of about +five square kilometres; allowing an average thickness of four metres, we +obtain a mass of twenty millions of cubic metres. About three-fifths of +this lava did no injury, being deposited upon other pre-existing lava. +However, the lava in the Novelle, which was deposited upon the lava of +1858, covered quarries of the best stone which had been worked at the +time, covered many paths that had been cleared, and buried the new +Church of St. Michele, with some houses that surrounded it, which had +been rebuilt on the site of the former church, which was covered by the +lava of 1868. The destruction of land in occupation, of buildings and of +crops, exceeded three million francs in value. Many proposals for +relieving the sufferers have been received. Wishing to aid in this +benevolent work, I gave a public lecture, admission for each person +being one franc; and this lecture, from notes badly taken, was printed +by private speculation, and I was compelled to repudiate the report of +it through the public papers. + +The evolutions of carbonic acid (_mofette_), which usually appear at the +end of great Vesuvian eruptions at low-situated spots or hollows, with +very rare exceptions, were observed on this occasion a few days after +the eruption had completely ceased. They appeared in the direction of +Resina. I found the most elevated at Tironi, and the most numerous +between La Favorita and the Bosco Reale di Portici. + +The water in wells was on this occasion neither deficient nor scarce +previous to the eruption, but was very acid after the appearance of the +carbonic acid evolutions in those neighbourhoods in which they +abounded. Having stated that the disastrous conflagration of the 26th +April ought, in my opinion, to be regarded as the last phase of a long +period of eruption, which commenced at the beginning of 1871, I consider +it right to discuss the question at somewhat greater length. + +Not only from twenty years' personal observations, but from the +attentive study of accounts of previous eruptions, I have found that +when the central crater awakens with small eruptions after a certain +time of previous repose, these almost always have a long duration, and, +after various phases of increase and decrease, terminate in a great +eccentric eruption, that is to say, with the production of an aperture +from which a copious lava stream issues. The eruptions of 1858, 1861, +1868 and 1872, furnish the most recent examples of what I affirm. I +might cite many others of earlier date, but I shall content myself with +recording the greatest conflagration of this century, that of October, +1822. + +Before the erection of the Vesuvian Observatory, it was impossible to +obtain a consecutive account of all the phases which the Volcano +presented; but we generally obtained the description of the more +splendid phases of the eruption which arrested the attention of +everyone. Hence, notices of the small phenomena which preceded a great +eruption are frequently wanting. We cannot always ascertain whether the +fumaroles of the craters became active and at what periods, what was +their temperature and what the diverse nature of their emanations, etc.: +whether and when any change in the crater with slight eruptive +manifestations occurred; discharges which sometimes commenced in the +bottom of a crater becoming active, and so are invisible at Naples. + +But it may be asked whether the inverse proposition be equally true, +that is, whether all the great eruptions of our Volcano were preceded by +small fiery manifestations of long duration? There have undoubtedly been +great eruptions not preceded by small central eruptions, but these also +had their period of preparation or precursory signs. After the great +eruption of 1850, Vesuvius remained in apparent repose until the end of +May, 1855, when there was an eccentric eruption and a great flow of lava +lasting twenty-seven days. But for a year before the fumaroles on the +top of the mountain had acquired great activity, their temperature +increased, and hydrochloric and sulphuric acid became more abundant, and +generated the usual coloured products on the adjacent scori. Finally, +in the month of January, a crater was formed by falling in of the +ground, and although it did not discharge fire, yet it poured forth +dense smoke. This was the beginning of the fissure manifested four +months afterwards. + +Ignazio Sorrentino, who spent a long life in the study of Vesuvius, and +frequently ascended it, considered the increase of those yellow +products--which are chiefly chlorides of iron, but were, at that time, +mistaken for sulphur--as the sign of an approaching eruption. + +The only grave objection that can be alleged is that of the memorable +eruption of 1631, which surprised the neighbouring population so +suddenly that many perished miserably, surrounded or covered with lava. +But that terrible conflagration occurred after centuries of repose, so +that trees had grown in the interior of the crater. No one suspected the +possibility of danger. It took place, too, at the end of autumn, when +the cone is usually covered with clouds, and, therefore, no one had an +opportunity of observing any precursory phenomena. + +When the Observatory was established, I was able--in the first instance, +at my own expense, and afterwards with some slight assistance from +Government--to undertake studies more assiduous than any previously +made. I had two instruments adjusted to indicate the internal efforts of +the Volcano, viz., M. Lamond's apparatus of variations, which, by means +of finely-balanced needles and methods of amplification proposed by +Gauss, indicates the slightest trepidation of the ground, and my own +electro-magnetic seismograph, a self-registering instrument of exquisite +delicacy. These instruments, when attentively observed, give the most +valuable information with respect to the activity of the adjacent +Volcano. + +If the very slightest eruption occurs, these instruments manifest slight +perturbation, increasing with the activity of the mountain. When the +Volcano attains a certain degree of activity, and the instruments are +proportionately disturbed, it is impossible to foresee a new phase of +increase without constantly watching the changes in the intensity of the +perturbations; and to effect this it is requisite to have upon the spot +a staff of assistants sufficiently numerous, scientific and intelligent. +If, therefore, on the night preceding the 26th of April the instruments +had been properly watched, they would have undoubtedly indicated the +great increase in the activity of the Volcano. The perturbations on the +23rd were steadily increasing, and on the evening of the 25th they were +much stronger than on the 24th, but on the morning of the 26th they had +become extraordinarily strong; they must, therefore, have increased +considerably during the night. + + + + +II. + +NATURE OF THE LAVAS. + + +When the observer is near the source of the lava, he sees matter in a +state of fusion, which, like a torrent of liquid fire, runs along, with +more or less impetuosity, between two banks formed by itself. But as +soon as the surface of the torrent cools to the point of congelation, it +loses the splendour of its first incandescence. The part which begins to +harden breaks readily in some lavas into fragments which float on the +viscous fluid beneath; these, increasing in number with distance from +the source, conceal the molten matter beneath and retard its progress, +and at last nothing is seen but the more or less red-hot scori moving +along. These lavas I shall call "_Lavas with fragmentary scori_." + +On other occasions, a skin forms on the surface of the lava, which, +gradually thickening, keeps flexible for some time, and then wrinkles or +swells or extends and breaks to give egress to the hot fluid within, +which, in its turn, skins over and repeats the same phenomena. This I +shall call "_Lavas with a united surface_." + +These, in their course, discharge less smoke than the first, draw out +more easily into threads, and, when cold, have a dark colour, something +like bitumen or pitch. _The lava with fragmentary scori_, when +stretched, breaks easily, discharges smoke copiously, and, when +hardened, has a more bluish tint, like clods of upturned earth (_formato +di zolle_). It is noisy in its course, because the incoherent scori +that it carries along strike and crunch against each other; the other +lava flows silently, except for a sort of crackling arising from the +actual fracturing up of the solid skin by distension from the liquid +matter within. If required to give the mineralogical characteristics of +this lava, I would say that it was rich in leucite and contained little +or no pyroxene; the fragmentary lava, on the contrary, is poor in +leucite and rich in pyroxene. The lavas of 1871 were of the "united +surface" character; those of 1872 were "fragmentary," with some +characteristics which I shall describe: + + 1. They were of the clearest tint I have ever seen, when + regarded superficially, but, when broken, the fracture was + darker than any other lava. + + 2. They had very little leucite and abounded in pyroxene and + olivine, and sometimes contained a few crystals of amphibole. + + 3. Their specific gravity varied with their porosity; the most + compact attained 275. + + 4. These lavas carried along in their course a quantity of + scori which had long been subjected to the action of the acids + of the fumaroles close to the craters, and also a great many + bombs (_bombe_)--that is, round masses similar to those ejected + from craters. These varied in size, some having a diameter of + four to five meters. They frequently contained a large nucleus + of very leucitic lava, like that of 1871, with a larger or + smaller quantity of feroligiste (peroxide of iron). Others + contained lavas changed by the action of the acid vapours near + the craters. These bombs must have flowed out with the lava, + for they are found through its whole course, and they were + certainly not ejected from the crater; for not only are they + found on the lava exclusively, but masses so enormous were not + thrown up from the craters during the eruption; those lying on + the cone near the craters seldom exceed a decimetre in + diameter. + +As to the qualitative chemical analysis of the lavas, it always presents +the same elements, with the exception of small quantities of some +metals, lead for example, which have escaped the researches of good +chemists, but which I have constantly found in the sublimations of the +fumaroles of the lava. With respect to the quantitative analysis, two +specimens of the same lava appear indeed to have their constituents in +different proportions. To arrive at any conclusion a long and patient +investigation, requiring means and assistance which the Observatory does +not possess, would be necessary. + +Professor Fuchs, of Heidelberg, has devoted himself to this work for +years past, and if he continue it with well-selected and sufficiently +large specimens we may hope some day to obtain satisfactory results. + + 5. Every specimen of lava which I examined with a very + sensitive magnetoscope improved by myself, was invariably + magneto-polar, not excepting the pieces of the bombs, whether + rejected from the crater or carried along with the lava. + + + + +III. + +FUMAROLES OF THE LAVAS. + + +Smoke generally issues from all lava when it cools down to a certain +degree, hence it is more abundant at the edges of the fiery torrent, or +is liberated from the scori that form on its surface. But when the lava +stops, the smoke issues only from certain vent-holes, through which we +can still see the fire, and at the edge of which different amorphous or +crystallized matters collect by sublimation. These centres of heat, of +more or less duration, are the fumaroles of the lavas. I believe I have +on other occasions shown that a fumarole is nothing but a communication +between the more or less cooled and hardened surface of the lava and the +interior, which is still incandescent. Some fumaroles last but a day, +others preserve their activity for weeks, months or years, according to +the depth of lava through which they penetrate; and when they cease to +be active, that is, when the sublimations are formed, or smoke or other +riform matters issue from them, they still retain a rather elevated +temperature. In the lavas of 1858, in a place where they had a +transverse width of 150 metres, a vent-hole may still be found where the +thermometer registers 60 and the scori are warm. Sometimes, while the +lava is in process of cooling, new fumaroles appear, in which the fire +is visible. This phenomenon, which appeared marvellous and inexplicable +when I first observed it in 1855, is now very easily understood; the +cooled and hardened crust of the lava fractures with noise and suddenly, +and so a new communication is opened with the incandescent lava below, +thus creating a new fumarole. + +As the smoke of the fluid lava is perfectly neutral, that is, neither +acid nor alkaline, so the fumaroles at the first period of their +existence with sublimations of sea-salt, mixed frequently with oxide of +copper either in black powder or in shining lamin, ought also to be +neutral. But if the fumarole continues active, hydrochloric acid issues +with the smoke, and often some time after sulphuric acid. Then the +sublimations turn first yellow, then green, and more rarely azure. The +chemical reactions show that these sublimations are chlorides or +sulpho-chlorides, and sometimes sulphides, and they afford reactions, +indicative of soda, magnesia, copper, lead, and traces of other +substances, not excluding ammonia, which I must speak of separately. +This, I have observed, is the general law with the fumaroles of the +tranquil lavas, which occur with long and moderate eruptions--for +instance, the lavas of 1871, and even those of 1872, preceding the 26th +April. + +But in the great lavas of the great conflagrations of Vesuvius, chloride +of iron more or less in combination with all the other substances above +mentioned changes the appearance of the sublimations. The fumaroles in +the lava of the 26th April frequently indicated chloride of iron. +Sulphuretted hydrogen, by reaction of sulphurous acid, is decomposed, +and sulphur sublimed, having a particular aspect, collects on the +scori. This is never found but in fumaroles of the smaller lavas; it +was therefore absent in those of 1871, but frequently occurred in those +of 1872. + +Although the sublimations are generally mixtures, yet sometimes distinct +and crystallized chemical or mineral species are found, such as sulphur, +sal ammoniac, _tenorite_, _cotunuite_, etc. Micaceous peroxide of iron +(feroligiste), so common near eruptive cones, is very scarce on lava; +any found in it has been carried down from the craters, and proofs of +this transport are very abundant and striking in the lavas of this last +eruption. Even the iron found in the bombs is evidently transported; +there is a fumarole on the ridge of the lava in the Fossa di Faraone +which contains micaceous peroxide of iron, and this, at first sight, +appears to oppose what I have affirmed; nevertheless, it gives +additional force to my statement. This fumarole is only a bomb or +rounded mass of enormous size, four or five metres in diameter. Smoke +and hydrochloric acid issued from the aperture in its envelope, and +being partly broken it was seen to contain lapilli and pieces of +antecedent lava, covered with micaceous peroxide of iron. The internal +temperature of this mass was very high; the hydrochloric acid which it +discharged had, in some places, covered the micaceous iron with a yellow +coating of chloride of iron. From small apertures, on the lower side of +the mass, white and green stalactites of chloride of calcium were +visible. In one spot only of lava I found a fumarole, with a small +quantity of micaceous peroxide of iron, evidently in a state of +formation; but this was the very spot where the lava became eruptive, +and whence issued the column of smoke which was so well +photographed--the place under the hill of Apicella. (See Plate 4a.) + +I have enumerated the products which are constantly collected in +fumaroles, although they are not all found at the same time or place, in +order to show that the sublimations follow a certain law in their +appearance. _Tenorite_, for instance, was formerly considered an +accidental product of certain eruptions, and I have always found it; but +if you visit the fumarole when the acids have had time to transform it, +you will no longer see it. I found the crystallized chloride of lead, or +"cotunuite," as it is called, for the first time in the lavas of 1855, +and thought it a singular circumstance; but from that time I recognised +it in all the lavas, though not always so beautiful and abundant; and +even when not found as a distinct substance, I observed it in +combination with chloride of copper. In the lavas of the 26th April +_cotunuite_ and _tenorite_[E] were not very abundant, because the +chloride of iron disturbed the greater number of the sublimations. I +found sal ammoniac very abundantly on the fumaroles of the lavas that +invaded the cultivated ground. Although chloride of ammonia, contrary to +opinion, was not wanting in the sublimations of the fumaroles of the +lavas deposited on other lavas, yet it was neither abundant nor +crystallized, but combined in small quantities with other substances. It +appeared in great abundance in all the fumaroles of lavas which covered +cultivated or woody ground. At first it was scarce enough, and mixed +with chloride of sodium; but when the rains came the sea-salt was washed +away, and sal ammoniac formed beautiful crystals, nearly free from +adventitious matters, as was the case with the fumaroles of the last +lava. Afterwards, when chloride of iron was produced, ferro-chloride of +ammonia was found. Crystals of sal ammoniac were sometimes found of a +beautiful amber yellow. This colour was, in the opinion of my colleague, +Professor Scacchi, produced by such small traces of chloride of iron +that neither Professor Guiscardi nor I, nor indeed any other chemists to +whom I submitted specimens for examination, could detect any. What I can +affirm with certainty is, that these limpid crystals of a yellow colour +were almost always attached to an amorphous substance, soluble in water, +composed of various chlorides, in which iron was often detected. + +From these remarks, it is evident that in the tranquil lavas the +sublimations appear with a certain order of succession, and in the +violent lavas, and those which flow most copiously, they are more +complicated, and render both chemical analysis and spectroscopic +researches more difficult. Notwithstanding, I observed traces of lithium +and thallium, which I had previously perceived in some sublimations of +1871. I purpose submitting many sublimations which I have collected to +more complete spectroscopic investigation, although I am persuaded that +the discovery of traces of certain bodies in the sublimations or in the +lavas is a matter of small importance to the science of volcanoes. I +must say, however, that calcium was discovered on this occasion in great +abundance, not only by the spectroscope, but also by chemical analysis. +Sulphate of lime has often been found in larger or smaller proportions, +but this was the first time I had observed chloride of calcium both +close to the craters, and also in the sublimations of the fumaroles upon +the lavas. The white stalactites which I collected beneath the great +mass or bomb above described were almost exclusively composed of +chloride of calcium, and only a few green drops manifested, with the +usual re-agents, the presence of iron. + +I did not fail to look often at the spectrum of the flowing lavas +covered with the smoke which issued from them, but I always had a +continuous spectrum. The spectroscope employed was Hoffmann's +construction, with direct vision; but I think it would be better on +other occasions to use a spectroscope combined with a telescope, like +those used by astronomers. + +But avoiding minute particulars of these sublimates, let us see what is +the general direction and the order of their appearance. Sublimations +are generally oxides, chlorides and sulphates, sometimes sulphides. +Among the oxides, we must enumerate in the first place "tenorite" and +_feroligiste_ or micaceous peroxide of iron. The first is almost always +found at the commencement of activity in the fumaroles, simultaneously +with the sublimation of chloride of sodium; the second--which is, +perhaps, never wanting in eruptive cones that are often found lined with +it inside--is seldom generated in the fumaroles of the lava, and +therefore it is not easy to define the moment of its appearance. +Sometimes one collects micaceous peroxide of iron on the lava, but it is +often transported there from the mouths of eruption, as happened on this +occasion. + +Trustworthy writers are of opinion that all the oxides are derived from +the decomposition of the chlorides, but I think I have clearly +demonstrated that, with regard to copper and lead, the opposite +statement may be affirmed; for the oxides are changed into chlorides, +and hydrochloric acid liberated. Oxide of copper forms sublimates at the +beginning, at the same time as the sea-salt; and if the fumarole be +anhydrous or, as Deville would say, _dry_, this oxide does not change +into either a chloride or a sulphate; but if the fumarole gives watery +vapour, after a little hydrochloric acid is formed, which changes the +oxide into a chloride, and if whilst this is going on oxide of lead be +developed, it is changed into the chloride of lead, so frequently found +in combination with chloride of copper. Then the sublimations change +from white to red or yellow, and specimens when carried away gradually +turn light blue, but when heated on platinum over a spirit lamp they +resume their yellow tint. Sometimes the yellow colour remains longer, +and in time changes to green; this also happens on the fumarole itself, +the green commencing at the zones furthest removed from the centre, +where the temperature is highest. When these sublimations are greenish, +they become far less soluble than at first. The yellow, so common at a +certain period on the fumaroles of the tranquil lavas, never attracted +attention before I first examined it, doubtless, because it was +considered chloride of iron, and yet in small eruptions this is only +found close to the discharging mouths, and never in the sublimations of +the fumaroles of the lava; but, on the other hand, it is the most +copious and common product on the lavas of the great eruptions. This +probably also accounts for the fact that lead, which is so obvious in +the fumaroles of the lavas, had never previously been observed. In 1855, +I noticed the crystallized chloride of lead in a fumarole in the Fossa +della Vetrana, and this induced me always to look for it on the +fumaroles of the later lavas; and I ascertained that, if it did not +always appear as a distinct mineral, it was easily discovered in +combination with other chlorides. The specimens which I have collected +are not the most beautiful, but the presence of lead in the sublimations +is not less common. + +Micaceous peroxide of iron, when found on the lava, has been mostly +conveyed from the eruptive mouths, as I have already stated, and perhaps +never so abundantly and evidently as on this occasion. The lava of the +26th of April carried along a large quantity of round masses or bombs, +varying in size, among which were found antecedent lava more or less +covered with micaceous iron, either collected in the cavities of the +lava, or incorporated with its mass. Sometimes the micaceous iron +appears like little veins in the paste of new lava enveloping the +exterior of these rounded masses, an exterior compact and lithoidal, and +not resembling scori. Among these spherical masses I found one of +enormous size, four to five metres in diameter, which, having broken up +where the exterior envelope was thinnest, I found filled with a great +mass of lapilli and fragments of other lavas covered with micaceous +iron. This bomb still preserves (June 5th) an elevated temperature +within, and emits smoke and hydrochloric acid, which, meeting the +micaceous iron discovered by breaking the envelope with blows of a +hammer, transforms it superficially into chloride of iron, showing most +clearly how, on some occasions at least, chloride of iron is formed from +the oxide which precedes it. That those lapilli and the pieces of lava +were solid when enveloped in the paste of the new lava, we infer from +seeing the impressions on the inside of the said envelope. The chloride +of calcium, which I found in this spherical mass almost pure, caused me +to suspect that the sulphate of lime which is so often found on Vesuvius +is a transformation of the chloride produced by the contact of +sulphurous acid, which easily becomes transformed into sulphuric acid. +The hydrochloric acid which escapes from a fumarole coming into contact +with the scori near its mouth, produces chloride of iron, which is, +therefore, not always obtained by sublimation, although, when the +temperature is very high, chloride of iron is conveyed from the interior +of the lava, and sublimes on the exterior and colder parts; for +instance, the chloride of iron which issues from the eruptive cones is +sometimes found sublimed on the rocks of Monte di Somma. When chloride +of iron has been produced by sublimation, we may collect it inside a +glass bell placed over the fumarole, or upon a piece of brick; but when +it is produced by the action of hydrochloric acid on the scori, it will +only be found on the scori themselves. + +If, therefore, the origin of micaceous peroxide of iron were due to the +decomposition of the sesqui-chloride of iron requiring a more elevated +temperature for its decomposition, it would follow that its genesis +would be easier near the discharging mouths, and more difficult on the +lavas, but there the fact was verified: for example, in the great bomb +on the fumarole, where we observed micaceous iron transformed into +chloride of iron. We may therefore consider it _proved_ that some +chlorides--for instance, chloride of sodium--issue from the lava itself, +either being there pre-existent, or being formed there; and that others +are derived from the oxides which precede them, as undoubtedly is the +case with chloride of copper; hence, the theory that derives the oxides +always from the chlorides cannot be considered true. Granting that this +theory might be applicable to the origin of micaceous iron, we should +still want to know how it is found with the paste of the new lava +itself, which forms the exterior coating of the bombs above described. + +Many of these rounded masses, which have been rolled along by the lava, +contain scori partly decomposed by the long action of the acids found +on the fumaroles of the craters. They disintegrate easily, and have a +more or less yellowish tint. In the greater number of cases the interior +of these masses is formed of leucitic lava, with cavities lined with +micaceous iron. In short, their contents appeared to me quite similar to +the material of the cone of 1871 and 1872, which in all probability was +engulfed in the large crevasse or fissure that opened below it; and the +fragments having thus fallen down into the lava, were enveloped by it +and carried out by it after having been more or less rounded. The +external envelope of these spheres is not at all scoriaceous, but +compact and lithoidal, and sometimes composed of concentric folds or +plaits. + +As to the gaseous emanations of fumaroles, watery vapour with few +exceptions comes first; this conveys the material which first appears in +the sublimations, viz., sea-salt, and for the most part oxide of copper. +If the fumarole continue active, it passes from the neutral period to +the acid period, and first hydrochloric acid is produced, which, in +small lava streams, never conveys chloride of iron, and rarely attacks +the scori to form that salt, but expends its force in changing the +sublimations already there. For this reason chloride of iron, though +completely absent in the lavas of 1871, was abundantly found in those of +the 26th April, 1872. Sulphurous acid follows hydrochloric at a later +period, and sulphuretted hydrogen occasionally succeeds. + +Having examined the gases of fumaroles by means of a graduated tube, and +the pyrogallate of potash, I always found that it contained less oxygen +than the surrounding atmosphere. + +For several years I wished to see whether the fumaroles of the lavas had +a period of evolution of carbonic acid, as sometimes happens with +fumaroles near the craters, but I have always obtained negative +results. I often found that the atmosphere on the lavas contained an +excess of carbonic acid, but as these lavas had burnt many trees, and it +was probable that carbonic acid springs had formed under the lava, I +never considered it safe to form any conclusion on the subject. + + + + +IV. + +BOMBS, LAPILLI AND ASHES. + + +The bombs ejected from the craters are like those carried down by the +lavas, but of smaller size, and they seldomer contain a nucleus similar +to those found in the latter. With the bombs properly so called, many +pieces of incandescent lava were thrown up, and in their fall went +beyond the base of the cone. A quantity of small scori varying in size +accompanied these projectiles, and those fragments, which we call +_lapilli_, fell at a greater distance. With the lapilli, and sometimes +without them, the smoke carried a very minute dust or sand, which is +generally called ashes. These ashes, when washed with water, lose +soluble constituents which they have collected in the smoke--such as +chloride of sodium and other chlorides and often free acids. The +insoluble part originates in the detritus of lava, and with the +microscope we can detect abundant fragments of those crystals which most +frequently occur in the lava of the same eruption. + +The lavas of 1871, which were eminently leucitic, and almost entirely +deprived of pyroxene, resembled the ashes, which appeared to be +fragments of crystals of leucite, more or less enveloped in the paste of +the lava, so that having triturated the scori of the lava, and looked +at the powder through the microscope, it was apparently quite the same +as the ashes. + +But at the beginning of the eruption of the 26th April, a white sand +fell in the Atria del Cavallo, close to the Crocella[5], which on the +dark scori of 1871 looked like snow. Its fall had a limit so well +defined that one passed without any gradation from white to black. +Having collected some of this sand that very morning, I put it up in +white paper, for at that moment it was impossible for me to examine it. +Taking it out some days after, I found it had become reddish, and having +put it under the microscope, I observed that it was exclusively formed +of little pebbles more or less round, of a transparent vitreous matter, +partly covered with a red substance. Fragments of green crystals +occurred in this sand, upon which no red was perceptible. I consulted +our eminent crystallographer, Arcangelo Scacchi, whether these little +pebbles were leucite, as I suspected, and whether the green particles +were pyroxene: he confirmed my suspicion, and remarked that the red +colour was superficial only. We then washed a little of the sand in hot +water, and saw the pebbles become whitish; but having heated some on +platinum, we observed that they first turned black and then became +perfectly white, proving that the red was a deposit of organic matter. +To see these leucites, rounded like small pebbles transported by a +torrent, deprived of the soluble chlorides which generally accompany +Vesuvian ashes, is a matter worthy of attention. Whilst heating this +sand upon platinum, decrepitation was audible, which indicated the +cracking of some of the little pebbles. It is evident, therefore, that +crystals of leucite raised to a certain temperature may break, and thus +we can understand how almost all Vesuvian ashes contain fragments of +the said crystals enveloped in the paste of the lava. It is evident that +the soluble part of the ashes is obtained from the smoke through which +it passes. On this occasion the smoke from the craters did not +apparently contain much acids, for no bad smell was perceptible, and the +water in which I washed the ashes scarcely reddened litmus paper. Even +chloride of iron, which was so abundant in the lavas, was scarcely +perceptible in the smoke, which almost exclusively deposited sea-salt on +the surrounding rocks; I say sea-salt advisedly, and not chloride of +sodium, to show that I include all that sea-salt contains. The slight +disturbance it manifested with chloride of barium, and the small +precipitate with oxalate of ammonia, reveal sulphate of lime, without +excluding the possibility of the chloride. + +But how can these ashes do so much injury to the vegetation of the +ground they cover, especially at the first fall of rain? I think that +the damage is due partly to the sea-salt, and partly to the acids +contained either in the ashes or in the rain-water itself. Upon watering +the tender tops of some plants with a saturated solution of the salt +from Vesuvius itself, I noticed that they withered away after a few +hours. But very often the rain alone which traverses the smoke of +Vesuvius, or is produced by condensation from it, gives manifest acid +reactions, and destroys the grass and the tops of the trees. The +peasants believe that the rain is warm or of boiling water, from +observing that the tender parts of the plants are, by its deposit, all +burnt up. Vegetation is now recovering, but without flowers, and +consequently without fruit. + + + + +V. + +THE CRATERS AND THEIR FUMAROLES. + + +The greater part of the lava issued from the base of the great fissure +in the cone which I have described; and although two other lava streams +descended from the top of the mountain, neither proceeded from the +crater, but from apertures near it. The great crater, divided in two as +already described, opened wide on the morning of the 26th April, +destroying the brim of the antecedent crater, and remaking it in another +shape with ejected matter, except on the south-west side, where the brim +was split. (See Plate 5.) + +From this double crater, copious smoke, bombs and incandescent scori, +with ashes and lapilli, issued with violence, and from the depths below +came dreadful detonations and bellowings, producing great terror. And +yet the lava poured out into the Atria del Cavallo without any noise, +and not even a column of smoke marked its origin of issue--namely, from +the fissure. + +When the eruption was over, the sight of the vertical walls of these +deep craters, of almost horizontal strata of scori and lithoidal +masses, with a fracture fresh, and as if they had never undergone the +action of fire or of acid vapours, without recent scori and without +fumaroles, was to me a marvellous spectacle. The fumaroles were almost +all on the brims of the craters, with emanations of hydrochloric and +sulphurous acid. In a few that were more removed from the brim, +sulphuretted hydrogen was perceptible. In the sublimations, chloride of +iron was most abundant, in combination with other chlorides, for +example, of sodium, magnesium and calcium. This last chloride was +frequent even among the sublimations of the fumaroles of the lavas, and +it was the first time it was ever remarked, but I do not think it was +the first time that it was ever produced: being in combination with +chloride of iron, and very deliquescent, it did not attract attention +from anyone. In a hollow fragment of scori I observed a yellowish +substance, which looked like sulphur in a viscid state, and which boiled +at a temperature of 120, and evolved hydrochloric acid. Having +collected this substance and poured it into a glass phial, it quickly +coagulated into an amorphous mass of the same colour; but before I +reached the Observatory, I found that it had become liquid by +deliquescence. It consisted of a mixture of the aforesaid chlorides, +according to an analysis made by Professor Silvestro Zinno and myself. +In some fumaroles, where I perceived the smell of sulphuretted hydrogen, +I found sublimed sulphur under the scori. + +At the source of the lava stream that flowed towards the Camaldoli, on +the seaward flank of Vesuvius, I observed large fumaroles of steam only, +pure aqueous vapour. + +There was no trace of carbonic acid in these fumaroles, but that fact +does not imply that there was none at a later period, for, since the +first investigations of Deville, it is known that carbonic acid is found +under certain conditions on the very summit of Vesuvius. + + + + +VI. + +THE ELECTRICITY OF THE SMOKE AND ASHES. + + +Our ancestors could judge that a great amount of electricity was +occasionally evolved in the smoke, from their observation of the +lightning flashes that darted through the Vesuvian pine tree; but they +had no proper instruments for ascertaining whether this evolution of +electricity was constant or accidental, or what laws regulated its +manifestations. My _apparatus, with movable conductor_, by which +comparative observations of electric meteorology can be made, and the +errors arising from dispersion corrected, supplied me with an easy +method of studying the electricity evolved during eruptions. + +I must begin by describing the bifilar electrometer, in order to explain +the apparatus which I have named as above, "_Apparechio a conduttore +mobile_." + +_A A_ (Plate VIa, Fig. 1) is a glass cylinder, the lower edge of which +is ground, well varnished with gum lac, and let into a wooden base, B, +furnished with three levelling screws. Through a sufficiently wide glass +tube, _a a_, runs a copper rod covered with insulating mastic, having a +little plate or cylindrical cavity of gilded brass at the top (Figs. 2 +and 3), with two arms _d d_, _d' d_. In the plate a disc of aluminium, +_m_, is suspended by means of two silk fibres, and to the disc a very +fine aluminium wire is attached, _f f'_, bent a little at the ends, as +are the arms, _d d_, _d' d_. The disc has about three millimetres less +diameter than the plate. The diameter of the plate may vary within +certain limits, but I have found it convenient to make it eighteen +millimetres. The glass tube, _a a_ (Fig. 1), should descend below the +base as much as it rises above it, that is three to four centimetres. +The length of the index is about one decimetre. + +The upper ends of the two silk fibres, by which the disc and index are +suspended, are attached to the top of the glass tube, _C_, by a +contrivance which permits a change in the distance between the two +points of suspension, and a screw, _p_, is provided to raise and lower +the disc with the index. At _n_, at the lower part of the tube, _C_, +there is a kind of torsion micrometer, arranged so as to bring the index +to the zero of the scale engraved on the graduated ring, _B_, which is +formed of a strip of good paper pasted on the rim of a glass disc. The +index must be placed at the zero of the scale, and must be some distance +from the ends of the arms of the plate with which it is parallel. The +plate is about three millimetres deep. + +Having levelled the instrument, so as to render the disc concentric with +the plate, and placed the index at zero, it is obvious that if an +electric charge through the wire, _h_, reach the plate with the arms, it +will electrify the disc and index: the disc will have the opposite +electricity, and the extremities of the index will take the same +electricity as the arms, and consequently the index will describe an arc +more or less great. The motion of the index is sufficiently slow to +allow the eye conveniently to follow it. Having traversed the first arc, +which I call the _impulsive_ one, the index returns, and, after only two +oscillations, comes to rest at what I shall call the _definite_ arc. + +When the electric charges are of very brief duration, the impulsive arcs +are within certain limits proportional to the tensions, and the ratio +between the impulsive and definite arcs is expressed by the following +equation: + + A (B - A) / B = tang. (1/2) A + +In which B is the impulsive arc and A the definite arc, showing that A +comes out nearly equal to 1/2 B. In dry weather all goes perfectly +within the limits of proportion, and I can tell whether, during the time +in which the index traversed the impulsive arc, there were any +_dispersions_ and of what nature; for if the definite arc is not close +to the limit of the impulsive arc, it is a sign of _dispersions_ having +taken place during the motions of the index. Every degree less in the +definite arc denotes two degrees of loss for the impulsive arc; but as +the index employs double the time traversing the definite as it does the +impulsive arc, we may consider the loss of one equal to the loss of the +other. + +In excessively damp weather the index gives no definite arc, and it is +necessary to resort to artificial heat in order to dry the insulators. +The most simple means I know of is to hold the instrument over some +hollow vessel, which, for the time, is converted into a stove by the +introduction of a spirit lamp. + +From Gauss's formula for the bifilar system of instruments of this +class, we learn that the maximum sensitiveness of such instruments is +given when the length of the suspending fibres is greatest, and the +distance between them is smallest, with the weight of the movable or +rotating member a minimum; and these elements being the same, the +sensitiveness of the instruments is invariable. + +To some electrometers, in order to avoid errors of parallax, a small +telescope, with a micrometer wire, has been added; but, with a little +practice, we can read accurately without this refinement. In order to +obtain comparative measurements, it is necessary to select some given +unit of tension. I have observed that by making a galvanic pile of +copper, zinc and distilled water, and insulating it well, each pole has +a tension which remains the same for many days, if the conditions of +temperature and the moisture of the surrounding atmosphere are not very +different. With thirty pairs of this pile, each element having +twenty-five square centimetres of surface, I have on the electrometer a +definite arc of 15, with the temperature of the atmosphere at 20 C., +and with the difference of 4 to 5 C. between the thermometers of the +psychrometer of August's construction. The first observation was made +twenty-four hours after mounting the pile. For unit of tension I took +that which corresponded to a single pair, that is, the thirtieth part of +the total tension. Other electrometers may be compared with one already +properly adjusted, without always having recourse to the pile. + +This done, let us see the arrangement of all the apparatus: + +_H H_ (Plate VIIa, Fig. 1) is the ceiling of a well-situated lofty +room, with an opening, _o o_, at the upper part. + +_M M_, a bracket or table fastened against the wall, about a metre +distant from the ceiling, _H H_. + +_N N_, a wooden platform for the observer. + +_A_, the bifilar electrometer. + +_B_, Bohnenberger's electroscope. + +_a a_, a movable conductor formed of a brass rod 15 to 18 millimetres in +diameter, insulated below by means of a glass rod, well varnished with +gum lac, having a suspending pulley, _c_, and a wooden guide-rod +underneath it, _l_, within the guiding tube, _k_. At the upper part of +this conductor, _a a_, there is a sliding roof, _b_, which can be +adjusted so as to prevent rain entering at the opening, _o o_. The +conductor terminates in a disc made of a sheet of thin brass, _d_, 24 +centimetres in diameter. Upon this disc, or even in place of it, we may +use metallic points. + +As a support to the conductor at the upper part, I have made use of a +triangular ring, _x_, drawn at its full size in Fig. 2. The conductor +passes between three springs, and the triangular ring is held in place +by three silk cords, _m m m_. Their material should not be mixed with +any cotton, and it may be advisable to saturate them with an alcoholic +solution of gum lac. + +_f f f_ is a hempen cord, which is used to raise and lower the +conductor. + +_i_ is a copper wire covered with silk, by means of which the triangular +ring, _x_, and through that and its springs the conductor communicates +with either the electrometer or the electroscope. + +Quickly raising the conductor by pulling the cord, _f_, the index of the +electrometer will describe a more or less large impulsive arc, and, +after two oscillations, will stop at the definite arc. Having thus +measured the electric tension of the air, and having lowered the +conductor, I next place the wire, _i_, in communication with the +electroscope, _B_, and by again raising the conductor, I ascertain +whether the electricity be positive or negative. It is scarcely +necessary to say that the conductor, when raised, gives electricity of +the same nature as that prevailing at the moment in the atmosphere; and +when lowered, manifests the opposite. In some conjunctures we must keep +the conductor raised and in communication with the electroscope, in +order to observe certain phenomena which I shall presently describe: +this method I call observation with a _fixed conductor_. + +I have also constructed a similar but portable apparatus for use on +eruptive cones, when required. + +Having given this description of the apparatus, it remains for me to +relate the results obtained, especially on the occasion of the last +eruption of Vesuvius. + +The Observatory is distant, in a direct line from the central crater of +Vesuvius, 2,380 metres, so that, when the smoke is copious, it is +properly situated for the study of electricity, particularly when the +wind inclines the pine-tree cloud in the direction of the Observatory, +as frequently happened on the last occasion. + +With smoke alone, without ashes, we obtained strong tensions of positive +electricity; with ashes only, which sometimes fell while the smoke +turned in the other direction, we had strong negative electricity; when +the smoke inclined towards the Observatory, accompanied with ashes and +lapilli, we had sometimes one kind of electricity, and sometimes the +other, just as the smoke or the ashes predominated; and often with a +"fixed conductor" we obtained negative electricity, and with a "movable +conductor" positive electricity. In Naples, too, at the Meteorological +Observatory attached to the University, my colleague, Professor Eugenio +Semmola, observed negative electricity of strong tension whilst ashes +were falling there in abundance. The tensions on this occasion were so +strong as to equal those obtained at changes of weather or during storms +(_temporali_), and, being beyond measure with a delicate electrometer, +we marked them with the symbol for infinity: the same phenomena were +observed when lightnings flashed. + +When there is but little smoke, it is necessary to approach the eruptive +mouths with a portable apparatus, in order to observe those phenomena +which, in great eruptions, may be studied from the Observatory itself. + +The conditions under which (_folgori_) lightning flashes are seen from +the cloud of smoke are, that it is conveying great abundance of ashes. +In 1861, there were small flashes even from the line of eccentric mouths +above Torre del Greco, although the smoke was not very great; and when +these ceased to discharge, and the central crater became somewhat +active, with a moderate amount of smoke but a great deal of ashes, small +and frequent lightning flashes were observed in the twilight darting +through the smoke, which was dark in colour. In 1850 the eruption was +more vigorous, the smoke more abundant, and the ashes scarce, but the +flashes were very rare. In 1855, 1858, and 1868, with a scanty supply of +ashes and at intervals, no flashes were observed, and the electricity +remained constantly positive. But having regard to the facts of +antecedent eruptions, one sees that the flashes are always derived, from +the midst of smoke accompanied with ashes and lapilli, which separate +like rain from the rolling volumes of smoke, in the midst of which they +were ejected. + +But how can we account for the positive electricity of the smoke, and +the negative electricity of the falling ashes? Without denying the +probability that a part of the positive electricity depends upon the +elevation of the smoke, as in the case of every other conductor we raise +aloft, or with a jet of water sent from a vessel by compressed air, I +think that the greater part of the electricity proceeds from the rapid +condensation of vapours, which are changed from the gaseous condition +into dense clouds; for even when the smoke issues tranquilly and does +not rise, because carried away horizontally by the wind, it gives signs +of positive electricity. From all my studies of atmospheric electricity, +and from some experiments made specially, it follows that the +condensation of vapours is the origin of this development of positive +electricity. + +The negative electricity of the falling ashes certainly arises from the +fact itself of their fall; for if we place a metallic vessel full of +ashes upon an elevated and well-situated terrace, while the atmospheric +electricity is positive, and cause the ashes from the vessel to fall +gradually into an insulated metallic cup, communicating with +Bohnenberger's electroscope placed at three or four metres distance from +the vessel, the electroscope will manifest negative electricity. If the +upper vessel be insulated, and the ashes permitted to fall upon the +ground, we shall obtain, from the vessel, positive electricity. The +intensity of these electric manifestations depends (other things being +equal) upon that predominant at the moment in the air; so that if the +experiment be made while negative electricity prevails, the falling +ashes will manifest positive electricity, the upper vessel then showing +negative electricity. Now, as the ashes separate from the positively +electrified smoke in order to approach the ground, which is negatively +electrified, it follows that they must manifest negative electricity +upon touching the ground, leaving the positive electricity in the smoke +above. For this reason, the electric tension of the smoke is increased +by the descent of the ashes and lapilli, so that discharges between the +upper and lower part of the pine-tree cloud, or the surface of the +crater, are rendered possible. Hence it follows that the flashes of +lightning of Vesuvius play through the smoke, and with difficulty strike +bodies upon the earth; and from this circumstance our ancestors believed +the thunderbolts of Vesuvius to be harmless. However, if the smoke were +very great, and driven by the force of the wind to some distance from +the crater, with an abundant fall of ashes, it would be possible to have +lightning flashes proceed from the smoke to the earth. I possess some +documents which relate that, in 1631, thunderbolts fell upon the Church +of Santa Maria del Arco, and other places on the coast of Sorrento. + +After upwards of twenty years' study and observation of meteoric +electricity, I am enabled to prove that atmospheric electricity is never +manifested without rain, hail or snow, and that manifestations of light +are always accompanied by thunder--manifestations of light (_lampi_), +thunder and rain being most closely connected. We may have rain without +manifestations of light, but never the latter without rain or hail. I +cannot here repeat what I have demonstrated in other memoirs; I can only +say that the lightnings of Vesuvius, erroneously believed to be not +accompanied by thunder, are really not accompanied by rain, but are +induced by the descent of ashes and lapilli.[6] + + + + +GENERAL CONCLUSIONS. + + +We may conclude from what I have stated: + +1. That by the assiduous study of the central crater, and the +indications afforded by the "Apparatus of Variations" and the +"Electro-Magnetic Seismograph," we can obtain precursory signals of +eruptions; and that the other premonitory signs pointed out by our +ancestors, such as the drying up of wells, either only happen +occasionally or are mere coincidences, such as those of the coincidence +of a dry or a rainy season, the prevalence of certain winds, etc.[F] + +2. That the fumaroles of the lavas are communications between the +external surface of the lava, hardened and more or less cooled, and the +interior lava still pasty, or at least incandescent. + +3. That from the lava, while flowing, there is no escape of acid +vapours, neither from the fumaroles at the first period of their +existence, but these, if they last long enough, arrive at an acid +period. + +4. That hydrochloric is the first acid that appears, combined afterwards +with sulphurous acid, and, still later, with sulphuretted hydrogen. + +5. That vigorous lava streams may have eruptive fumaroles. (See +Translator's Note 2 to p. 94.) + +6. That the sublimations follow a certain order in their appearance. In +the neutral period we get sea-salt mixed with some metallic oxides, the +first of which is oxide of copper. But in the great lavas, chloride of +iron appears simultaneously with the acid period. Hydrochloric acid +transforms the oxides into chlorides, which, in their turn, change into +sulphurets or sulphates on the appearance of sulphurous acid. + +7. That the acids, by attacking the scori, create new chlorides and +sulphates, which are thus not products merely of sublimation. + +8. That micaceous peroxide of iron--so common and abundant near the +eruptive mouths--is very scarce and rare on the lavas, unless conveyed +there from the craters. + +9. That chloride of iron--so manifest on the fumaroles of the great +lavas--is only found in small eruptions close to the discharging mouths. + +10. That the frequency of chloride of iron in the lavas of great +eruptions masks the order of transformation of the other products. + +11. The fumaroles at the summit of Vesuvius present even greater +gradations, for they often emit carbonic acid or pure watery vapour. + +12. Lead, which I first discovered in the fumaroles of the lavas of +1855, is a constant product of fumaroles which have a certain duration. +It is often obtained as a distinct and crystallized chloride, and often +is found in combination with other products. + +13. Oxide of copper is also a constant and primary (_primitivo_) product +of fumaroles. The chloride and sulphate of copper are formed from the +oxide, directly contrary to general belief. + +14. I do not think that the chloride of calcium, which I found on this +occasion in almost all the deliquescent sublimations, is a product +peculiar to this eruption only, in which alone, however, I found it. I +was, therefore, induced to look for it in other sublimates, in which I +might possibly have overlooked it, as, without doubt, my predecessors +have done, owing to the deliquescence of the chloride of iron with which +it was constantly combined. I think that this chloride, in accordance +with the general law, is transformed into a sulphate--a transformation +which readily occurs on Vesuvius. + +15. Copious and well-crystallized sal ammoniac is only found on the +fumaroles of those lavas which have covered cultivated or wooded ground. + +16. The scarcity of oxygen in the gases of fumaroles may possibly arise +from the formation of the oxides which precede the chlorides. + +17. Lavas give a continuous spectrum, although covered with smoke, when +looked at with Hoffmann's spectroscope with direct vision.[G] + +18. The smoke gives positive electricity, and the falling ashes negative +electricity. + + + + +REFERENCE TO THE PLATES. + + +PLATE + +Ia. The Cone of Vesuvius, in 1870, from a Photograph taken + near the Observatory. + + _a._ The Atria del Cavallo. + _b b._ Fossa della Vetrana. + _c._ Punta del Crocella. + _d._ Lava of 1858 and 1867. + _e._ Police Barrack near the Observatory. + _f._ Part of Monte Somma. + +IIa. Profile of Vesuvius, taken from a Photograph of the + Observatory in the month of September, 1871. + + 1. The Cone, on the 13th January, 1871. + 2, 2. Lava of 1871. + +IIIa. Profile of Vesuvius on the 16th April, 1872, about ten + days before the last Conflagration. + +IVa. Vesuvius, on the 26th April, 1872, from a Photograph taken + in the neighbourhood of Naples. + + 1. The Observatory. + 2. Fossa della Vetrana. + 3. Eruption of Smoke and Ashes, with Stones, from the + surface of the Lava. + 4. The Novelle, St. Sebastiano, and Massa. + 5. Lava which took the direction of Resina. + 6. Lava which, from the Crater, took the direction of the + Camaldoli. + 7. The Grain Stores, near Naples. + 8. Resina. + 9. Torre del Greco. + 10. The Camaldoli. + +Va. Profile of Vesuvius after the Eruption of the 26th April, + 1872, from a Photograph taken near the Observatory. + + 1, 1. The Fissures of the 26th of April. + 2, 3. Small Hill thrown up on the morning of the 26th of + April, from below which issued the great current of + Lava. +4, 4, 4. The Mouths out of which the Lava issued. + 5, 5. The larger Lava Stream, which passed near the Observatory + by the Fossa della Vetrana. + 6, 6. The other Lava Stream, which, after dividing from + the last, took the direction of Resina. + 7, 7. The Lava which ran down towards the Camaldoli. + 8 & 9. The two Craters on the summit of the Cone. + +VIa. The Bifilar Electrometer of Signor Palmieri. + (_Details._) + +VIIa. The assemblage of the Electroscopic Apparatus of Signor + Palmieri, as arranged at the Vesuvian Observatory. + +VIII. Professor Palmieri's Seismographic Apparatus. + + +[A] This small cone, as it appeared on the 1st April, is described and +drawn in a Memoir of Professor von Rath, of the University of Bonn, on +"Vesuvius on the 1st and 17th of April, 1871." + +[B] Eight young medical students perished beneath the lava, with others +unknown by name. They were all youths of good promise; their names will +be recorded on the marble monument to be erected near the Observatory. +They are: Girolamo Pausini, Antonio and Maurizio Fraggiacomo, Francesco +Binetti da Molfettu, Giuseppe Carbone da Bari, Francesco Spezzaferri da +Trani, and Giovanni Busco da Casamassima and Vitangelo Poli. + +[C] If this enormous height of projection really means, that above the +brim of the crater, it involves an initial velocity of projection of +above 600 feet (British) per second. + +Observations of the height of ascent of volcanic blocks are always +difficult and deceptive, and never free from error.--_Translator._ + +[D] Assuming these flashes to have emanated from somewhere within the +cloudy volume of steam and dust called "the head of the pine-tree," this +interval would indicate that the mean height of this cloudy volume +itself was not more than about four thousand feet above the top of the +cone; and, if so, that is not very far from the limit in height of +projection of the dust and lapilli.--_Translator._ + +[E] COTUNUITE, chloride of lead, in white, lustrous, acicular crystals, +of the trimetric system, easily scratched, Sp. gr., 5238. + +TENORITE, peroxide of copper, in thin, hexagonal plates or scales, +translucent when very thin, dark steel gray, of the cubic system; hard +and lustrous. Sp. gr. about 5950.--_Translator._ + +[F] Earthquakes, though in distant regions, usually precede eruptions. +The Earthquake of Melfi preceded the great Eruption of Etna in 1852; the +Earthquake of Basilicata of December, 1857, terminated with the Eruption +of 1858, which filled the Fossa Grande with lava; the Earthquakes of +Calabria of 1867 and 1870 were the precursors of the Vesuvian +conflagrations of 1868, 1871, 1872. A Volcano, also, in the Island of +Java had a great eruption in the month of April, some days before the +last conflagration of Vesuvius, as I learnt from a letter addressed to +Signor Herzel, Swiss Consul at Palermo, communicated to me[7] by the +astronomer, Signor Cacciatore.--_Palmieri._ + +[G] I have made a large collection of sublimates, which I purpose +examining with the spectroscope, and I shall be able to place some at +the disposal of experimentalists who may desire to pursue investigations +of this kind. + + + + +NOTES + +BY THE TRANSLATOR. + + +[1] (P. 82, text). Professor Palmieri has not given any description +in this Memoir of his seismograph--the instruments described being those +only which have relation to atmospheric electricity. The following brief +account of his seismograph will, therefore, form a not unsuitable +complement to his Memoir. The instrument, in general terms, is of that +class in which the wave movements are indicated by the displacement, +relative or absolute, of columns of mercury in glass tubes. It is a +self-recording instrument, composed of two distinct portions--one for +record of horizontal, or rather of what are called undulatory shocks; +the other for vertical shocks. In point of general principle, therefore, +it is very similar to that proposed by me ("Transactions, Royal Irish +Academy," in 1846), and in certain respects appears to me less +advantageous than the latter. Some account of the Palmieri instrument, +together with some critical remarks as to its action, may be found in my +"Fourth Report on Earthquakes" ("Reports, British Association, 1858," +pp. 75-81). The following description of the instrument is derived from +"The Engineer," of 7th June, 1872, and the publishers have to thank the +proprietors of that journal for permission to use the illustration, +Plate 8. + +In Fig. 1, _E_ is a helix of brass wire (gauge about one millimetre); +the helix consists of fourteen or fifteen turns, and has a diameter of +from twenty to twenty-five millimetres; it hangs from a fine metal +spring, and can be raised or lowered by a thumb screw. From the lower +end of the helix hangs a copper cone with a platinum point; the latter +is kept close to the surface of mercury in the iron basin, _f_, which +rests on an insulating column of wood or marble, _G_. The distance of +the point from the surface of the mercury remains constant, as the metal +pillar, _T_, is of such a length that its expansion or contraction by +change of temperature compensates that of the helix; the latter is in +connection (by _T_) with one pole of a Daniell's battery of two cells, +and the basin, _f_, is connected with the other pole. Any vertical +movement, however slight, makes the platinum point dip into the mercury, +and thus completes the circuit. In this circuit are included two +electro-magnets, _C_ and _D_; these, during the circulation of a +current, attract their armatures, which are connected with levers. The +action of _C's_ lever is to stop the clock, _A_, which thus records, to +a half-second, the time of the occurrence of the shock, at the same +instant that the clock strikes an alarm bell, which attracts the +attention of an observer. The lever, attached to the armature of _D_, at +the first instant of the current frees the pendulum of the clock, _B_, +which was before kept from swinging, in a position out of the vertical; +the clock then acts as a time-piece, and its motion unrolls a band of +paper, _k k k_, at a rate of three metres an hour. At the same time the +armature of _D_, while attracted, presses a pencil point against the +band of paper which passes over the roller, _m_, marking on it, while +the earthquake lasts, a series of points or strokes which occupy a +length of paper corresponding to its duration, and which record the work +of the shock. After it is over the paper continues to unroll from the +drum, _i_, and passing round the clock, rolls on to the drum, _l_. If a +fresh shock occur the pencil indicates it, as before, on the paper, and +the length of blank paper between the two sets of marks is a measure of +the interval of time between the shocks. By way of additional check, +several helices, _h h h_, are hung from a stand, with small permanent +magnets suspended from their ends; below and close to these latter are +small basins, holding iron filings; into these the points of the magnets +dip, when their helices oscillate vertically, and some filings remain +sticking to the magnets as a record of the shock. One of the magnets has +a shoulder on it which moves an index hand along a graduated arc, as +shown in Fig. 2, thus again registering the amount of the vertical +movement. Such are the arrangements intended for the record of the +undulatory or horizontal elements of the wave of shock. + +The following are the arrangements proposed for recording the horizontal +motions: On the stand, to the right of the clock, _A_, are set four +U-shaped glass tubes, open at their ends. One of each pair of vertical +branches must have a diameter at least double that of the other. These +pairs, with their supporting columns, are shown in plan, where one pair +lies N. and S., another E. and W., a third N.E. and S.W., and the other +N.W. and S.E. It will be observed that metallic bars pass from the +pillar, _P_, over the ends of all the long branches, and similar bars +pass from _R_, over the ends of the short branches; the pillars +themselves, as in the case of the other instruments, are each connected +with one pole of a Daniell's battery, the connections including the +electro-magnets, _C_ and _D_. The description of one U tube, _n_, will +apply to all the others; _n_ is partly filled with mercury, and an iron +or platinum wire, _o_, suspended from the bar above the short branch, +dips into the mercury therein, while another platinum wire hung from the +bar over the mouth of the longer branch, has its end very close to the +surface of the mercury in that branch. Any shock which is not +perpendicular in direction to the plane of the branches of the U will +cause the mercury to oscillate in the tubes, and more sensibly in that +with the smaller diameter; when it rises up in the latter, so as to +touch the platinum point, the connection between _P_ and _R_ is made and +the circuit completed, starting the action of the electro-magnets _C_ +and _D_, which record the shock, as already described. By having the +planes of the tubes set in the different azimuths, already mentioned, +one or more of the pairs is sure to be acted upon, and by observing in +which the oscillation takes place the direction of the shock is supposed +to be ascertained. Besides this, each long branch of the U, viz., that +of smaller diameter, has a small ivory pulley, _q_, fixed above it, over +which passes a single fibre of silk, with an iron float at one end, +resting on the surface of the mercury; at the other end of the fibre +hangs a counterpoise; fixed to the pulley is a fine index hand, capable +of moving along a graduated arc. When the shock takes place the mercury, +rising in the long branch, raises the float on its surface, the silk +fibre at the same time makes the pulley revolve with its index hand, +which afterwards remains stationary, as the counterpoise prevents the +float from sinking again with the mercury. The reading on the graduated +arc is thus a measure of the movements produced in the instrument by the +horizontal element of the shock, and is supposed to measure that shock. +It is assumed that in all these instruments shocks, however small, can +be recorded with certainty by adjusting the distance between the +platinum points and the mercury. + +The arrangement of Daniell's battery used for the seismograph is shown +in Fig. 4, where, for convenience of cleaning, the copper element is +made of wire (about No. 8 Birmingham wire gauge) coiled flat without the +spirals touching. Crystals of sulphate of copper are placed at the +bottom of the outer cell, into which water is poured; and the inner +cell, into which the zinc plate goes, is filled with siliceous sand. + +In addition to the above some instruments of a rougher description are +employed as checks. Thus, at the foot of the pillar, _G_, there is a +wooden trough with eight holes, facing as many equidistant points of the +compass (two of them shown in section) round its inner circumference; +mercury is poured into the basin until its level is nearly up to the +lips of the holes. The effect of a shock is to throw some of the mercury +into one or more of these holes, and the greater the oscillation the +more mercury is thrown into the cells through the holes. The screws +shown outside are for drawing off the mercury from the cells, when its +quantity can be measured. The direction of the shock is shown by seeing +which cells are filled with mercury. This is the old Cacciatore +seismometer which has been long employed in Italy. (See 4 "Report of +British Association, 1858," p. 73), and Daubeny's "Volcanoes," Appendix. +The following is another contrivance. From the arm of the pillar, _G_, a +fine metal wire hangs, with a metal ball at its end, which, by its +oscillation, thrusts out one or more light glass tubes, set horizontally +in a stand, as shown in Fig. 3. The two rings are of wood, and the glass +tubes pass through holes in them; small leather washers are placed +outside the outer rings; the displacement of one or more tubes is +assumed to measure the horizontal element of the shock. By means of this +apparatus the time of the first shock is recorded, as well as the +interval between the shocks, and the duration of each; their direction, +whether vertical or horizontal, is given, as also the maximum of +intensity. Professor Palmieri has the instruments examined three times a +day, and an assistant-observer is always at hand to attend to the bell, +and put back the apparatus to its normal position for fresh observation. + +It has been stated that this instrument is sensible to most of the +shocks which occur in the Mediterranean basin. + +It is not my intention here to offer any criticism as to the +construction or performances of this instrument, the rather as I must +confess I do not quite share the high opinion of its inventor as to the +certainty or exactitude of its indications. + +There can be no question as to the extreme importance to science of the +establishment and continued use of a seismographic instrument of +unexceptionable construction at the Observatory upon Vesuvius; and it +would be a valuable gift to science, were the Italian Government to +enable Signor Palmieri to establish such an one. Its great value and the +very first problem to set the instrument to solve should be, by _a rigid +determination of the direction of propagation of the wave of shock_, of +those slight or stronger pulsations which precede or accompany the +Vesuvian like all other eruptions, on arriving at the Observatory, _to +fix the depth, and the position vertically beneath the cone, whence +these pulses are derived_. This would be, in fact, to fix the depth and +position beneath the mountain at which the volcanic focus is situated +for the time, or, at least, where the volcanic activity is at the time +greatest. And the assured knowledge, even within moderate limits of +accuracy, of this depth, and even for this single mountain, would be an +immense accession to our positive knowledge, and a really new stage +gained for future advances. At present, we know but little as to the +actual depth below our globe's surface at which volcanic activity +occurs, or to which it is limited, either upwards or downwards. I have, +myself, established some data upon the flanks of Etna, not yet +published, which may enable me to afford some information on the subject +hereafter. Meanwhile, Professor Palmieri possesses unrivalled +opportunities for such observations; and I trust health, life and means +may be afforded him, to become the first who shall have made this great +addition to our positive knowledge of Vulcanology. + +So far, popularly at least, the alleged chief uses and value of these +seismographic instruments, at the Observatory of Vesuvius, have been +made to depend upon their being presumed to afford means for foretelling +eruptions, or affording precursory warnings of their probable progress +and destructive course. + +I feel compelled to express my own total disbelief in the possibility of +any such predictions in the present state of science, by the help of any +instruments whatsoever, of such a nature as to be of any _practical +value_, or any certainty beyond that which a certain amount of _mere +experience_ as to the _rle commonly played_ by Vesuvius or other +Volcanoes in pretty habitual activity affords to the observer for a +lengthened period. And even this affords scarcely any guide as to what +may happen next. Monte Nuovo was thrown up in a night; Vesuvius _might_ +double its volume in a night, or might sink into a hollow like that of +the Val del Bove in a not much longer time. A small _fusillade_ may go +on for months, and yet, without an hour's notice, by any premonitory +sign, may waken up to a roar and darken the air with ashes and lapilli +such as those which overwhelmed Pompeii. One eruption may blow forth +little but dust and ashes (so called), another may pour out rivers of +lava and little else. + +The _main_ mischief of all eruptions is effected in two ways: by the +deposit of dust and ashes, lapilli, etc., to the injury or destruction +of fertile land, and by the streams of lava which overwhelm it, as well +as buildings, etc. But what information of any value can seismographic +observation afford as to the course that either of these may take in any +eruption? The volume of pulverulent material that may be ejected cannot +be foreseen; its distribution depends mainly upon its nature and upon +the direction and force of the wind at the time; or again, how shall +these warn us as to the course that the lava, if it appear, shall take, +when we cannot possibly foretell when, how, or by what mouth it may +issue. Even in this late eruption of 1872, with Palmieri stoutly at his +post upon the mountain, and the Observatory instruments in full +activity, they gave no forewarning of the sudden and unexpected belch +forth from the base of the cone, of that tremendous gush of liquid lava +which in a few minutes cut off from life the unhappy visitors whose +deaths he has recorded. + +[2] (P. 94). It can scarcely be supposed that these small +eruptive-looking belchings forth from the lava stream, _en route_, are +truly of an eruptive nature at all, _i.e._, in any way connected with +forces seated deeply beneath the bed of the lava stream, or in any way +connected with the volcanic ducts of the cone or beneath it. They are +most probably merely the bursting upwards of large bubbles; that is, of +cavities formed in the mass of the more or less liquid lava by intestine +movements, as its mass winds and rolls along, and by the aggregation of +smaller cavities--all being filled with steam and gases--together with +dust and volatile products which are ejected when the cavity opens up, +and its contents escape at the upper surface of the lava stream in +virtue of the continuation of the twistings and convolutions due to the +stream motion itself, and to the unbalanced hydrostatic pressures acting +upon the parietes of the bubble. Very large single bubbles of like +character rise in the fluid lava within craters in vigorous action, and +often so regularly that their recurrence causes a sort of rhythmical +rush and roar in the column of steam, etc., issuing above the mouth. +This was evident in the discharges issuing in 1857 from the highly +instructive minor _bocca_, then existing, examined by me, and referred +to ("Report, Naples, Earthquakes," etc. Vol. II., pp. 313, 314), as +presenting at the time great facilities for determining pyrometrically +the temperature of the lava within, and of the dry superheated steam +issuing with a rhythmic roar from it. M. Le Coq ("poques Gologiques +d'Auvergne," Tome IV.) has recorded some examples of the formation and +opening-out of large bubble-like cavities in lava already ejected. +Perhaps that able and laborious vulcanologist, whose death a few months +ago science still deplores, attributes too much importance as well as +magnitude to them, when attributing the formation of what he has +denominated "craters of explosion," to the mechanism of the rise and +bursting of such bubbles upon a gigantic scale. Such blowings forth, +sudden or prolonged, from particular spots of lava streams, _en route_, +undoubtedly may also have their origin in damp places, or water or +air-filled cavities in or beneath the bed over which the lava rolls, +which, getting gradually heated, generate steam, or air or gases under +tension by expansion, etc., which thus at length blow through the liquid +or pasty lava flowing above, and which in bursting through delivers much +dust also, and so simulates a little eruptive crater. Examples of this, +upon a great and convincing scale, can be pointed to in the Val di +Calanna and elsewhere on Etna. + +[3] (P. 96). There are strong grounds for the gravest doubts that there +exists any real connection of a physical character between Volcanic +Eruptions, and Earthquakes more or less _approximately_ coincident only, +in time of occurrence; the respective sites being widely apart, and the +less the probability as the intervening distance is greater. The +discussions of the large number of records that are to be found of such +coincidences--mostly but partial, and in but _very_ few instances +complete coincidences--by Perrey, von Hoff, and others, as well as by +myself, do not tend to sustain the view that such imperfect +contemporaneity is based upon any causative connection. The seismic +region of Greece appears to have no _direct_ connection with that of +Southern Italy: the band of connection, if any, seems to lie between +Northern Italy, across the Northern Adriatic, by Ragusa, and thence +spreading into Asia Minor. + +[4] (P. 97). The abundance of coleoptera and of various other forms of +insect life about lava beds, both recent and old, is a very singular +fact, and one worthy of the careful observation of entomologists. In the +autumn of 1864, at mid-day, when sitting sketching upon the lava about +the middle of the Val del Bove (Etna), I found it almost impossible to +work, or even to remain for an instant still, in consequence of the +continual cloud of insects, large and small, that struck against me in +flight, endangered the eyes, and swarmed upon my clothes. It is quite +possible that this local superabundance of insect life may arise merely +from the general dryness and warmth of such places, and the plentiful +_nidus_ that the innumerable cavities in lava afford for the eggs and +earlier stages of insect life; still, this apparition of one form of +life may also be connected with other circumstances not unimportant to +discover. + +[5] (P. 120). The _Crocella_ is a small wooden cross, erected several +years ago, and which one passes to the right hand at the upper end of +the path along the ridge of tufa and volcanic conglomerate upon which +the Observatory stands, in ascending thence to the Atria del Cavallo. + +[6] (P. 134). That the causes assigned by Professor Palmieri for the +potent developments of electricity (positive or negative) which +characterise the ascent of the issuing columns of (chiefly if not +always) _dry_ steam, with a relatively small volume of various gases, +and throwing up, in their blast, volumes of small solid particles in +ashes and lapilli, etc., and the subsequent fall as a mineral or stony +hail-shower of the latter, through the partially condensing vapours and +the circumambient air, are the main causes of electrical development +evidencing itself in lightning flashes, is no doubt true. We must not, +however, lose sight of the many other and very effective agencies at +work here to produce electric excitement. The actual _bocca_ of the +volcanic vent whence the steam roars off constitute the cone a veritable +hydro-electric machine. Mechanical energy in various forms is +transformed into electric energy. Chemical action is going on both in +the solid and in the vapourous and gaseous emanations as they rush into +and remain in the air or descend from it, and chemical action is +transformed in part into electric energy. Percussion between ascending +and descending particles and fragments, fractures and breaking up of +more or less of these, thus and by sudden changes of temperature in +cooling, are likewise operative. In addition, great and violent +movements in the atmosphere itself result from the large local +accessions of temperature by the heated volume driven up into it, and +which in turn give rise to electric disturbance of the same character as +those produced in wind storms and whirlwinds, brought about by the +natural causes which every day effect disturbances in our atmosphere all +over the globe. + +[7] (P. 135). The views stated in note 3 (to page 96) may here again be +referred to as in point. How is it possible, in the present state of +science at least, to establish any physical connection between an +eruption in Java and one of Vesuvius, "with half the world between," +when not even having the solitary connecting link of complete +contemporaneity, and which, if it existed, yet might be nothing but +accidental? A list of shocks upon record, which have occurred more or +less nearly simultaneously at distant parts of the world, may be found +in my fourth Report, ("Facts of Earthquakes," "British Association +Reports, 1858") and the reasons are there given for rejecting the notion +of any direct physical connection between the origins of the respective +shocks. + +Shocks, emanating from the close neighbourhood of volcanic vents, or +simultaneity of eruption, in vents not far distant from each other, +stand upon a different footing. + + + + +Transcriber's Notes. + +Preserved the unusual, but consistent, spelling of "develope." + +Preserved the unusual, and inconsistent, references to the Plates. +Sometimes Arabic numerals are used, but usually Roman numerals. Most +have "A" attached to the name (which was changed to "a" to avoid +confusion in the Roman numerals), but not VIII, and sometimes not in the +references to them. + +Equations were converted to linear text, adding spacing and parentheses +as necessary. Greek characters were also replaced by Latin letters in +the Latin-1 version. + +Replaced the oe ligature with the two characters in "Goethe" in the +front material. + +Changed "fumarolles" to "fumaroles" on page 3: "fumaroles and +salfatares." + +Changed "Lyall" to "Lyell" in footnote originally on page 9: "Daubeny, +Lyell, Phillips and others." + +Changed "throught" to "through" on page 35: "passing through it." + +Removed duplicated word "the" on page 40: "the great Calabrian +Earthquake." + +Page 89 refers to the "Fossa del Vetrano;" elsewhere there are +references to "Fossa della Vetrana," which may be what was intended. +However, I did not change this. + +Changed "hydrochloride" to "hydrochloric" on page 109: "the hydrochloric +acid which it discharged." + +Changed "disk" to "disc" on page 126: "the disc and index." + +Replaced the infinity symbol on page 131 with "for infinity," in the +Latin-1 text version. + +Changed "azismuths" to "azimuths" on page 143: "the different azimuths." + +Changed "silicious" to "siliceous" on page 143: "filled with siliceous +sand." + + + + + +End of Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +*** END OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + +***** This file should be named 33483-8.txt or 33483-8.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/3/4/8/33483/ + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need are critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/33483-8.zip b/33483-8.zip Binary files differnew file mode 100644 index 0000000..5010dbf --- /dev/null +++ b/33483-8.zip diff --git a/33483-h.zip b/33483-h.zip Binary files differnew file mode 100644 index 0000000..84f207f --- /dev/null +++ b/33483-h.zip diff --git a/33483-h/33483-h.htm b/33483-h/33483-h.htm new file mode 100644 index 0000000..1360549 --- /dev/null +++ b/33483-h/33483-h.htm @@ -0,0 +1,4811 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<!-- $Id: header.txt 236 2009-12-07 18:57:00Z vlsimpson $ --> + +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" /> + <meta http-equiv="Content-Style-Type" content="text/css" /> + <title> + The Project Gutenberg eBook of The Eruption of Vesuvius in 1872, by Professor Luigi Palmieri. + </title> + <style type="text/css"> + +body { + margin-left: 10%; + margin-right: 10%; +} + + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; +} + +p { + margin-top: .75em; + text-align: justify; + margin-bottom: .75em; +} + +hr { + width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; +} +hr.tb { + width:45%; +} +hr.chap { + width:65%; +} +hr.full { + width:95%; +} + +table { + margin-left: auto; + margin-right: auto; +} + +.pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: smaller; + text-align: right; +} /* page numbers */ + +.linenum { + position: absolute; + top: auto; + left: 4%; +} /* poetry number */ + +.blockquot { + margin-left: 5%; + margin-right: 10%; +} + + +.bb {border-bottom: solid 2px;} + +.bl {border-left: solid 2px;} + +.bt {border-top: solid 2px;} + +.br {border-right: solid 2px;} + +.bbox {border: solid 2px;} + +.center {text-align: center;} + +.smcap {font-variant: small-caps;} + +.u {text-decoration: underline;} + +.caption {font-weight: bold;} + +/* Images */ +.figcenter { + margin: auto; + text-align: center; +} + +.figleft { + float: left; + clear: left; + margin-left: 0; + margin-bottom: 1em; + margin-top: 1em; + margin-right: 1em; + padding: 0; + text-align: center; +} + +.figright { + float: right; + clear: right; + margin-left: 1em; + margin-bottom: + 1em; + margin-top: 1em; + margin-right: 0; + padding: 0; + text-align: center; +} + +/* Non-headings that display like them */ +div.likeheading1 { + text-align:center; + margin-bottom: 2em; + font-weight: bold; + font-size:200%; +} + +div.likeheading2 { + text-align:center; + margin-bottom: 2em; + font-weight: bold; + font-size:150%; +} + +div.likeheading3 { + text-align:center; + margin-bottom: 2em; + font-weight: bold; + font-size:120%; +} + +.greek { + border-bottom: 1px dashed gray; +} + +.lsoff { + list-style-type:none; +} + +/* Footnotes */ +.footnotes {border: dashed 1px;} + +.footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + +.footnote .label {position: absolute; right: 84%; text-align: right;} + +.fnanchor { + vertical-align: super; + font-size: .8em; + text-decoration: + none; +} + +/* Classy fractions */ +.frac { + font-style: italic; } +.frac sup, .frac sub { + font-style: normal; + font-size: 65%; + position: relative; } +.frac sup { + top: 0.1em; + left: 0.05em; + vertical-align: text-top; } +.frac sub { + top: 0.1em; + left: -.1em; + vertical-align: text-bottom; } + + + </style> + </head> +<body> + + +<pre> + +Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Eruption of Vesuvius in 1872 + +Author: Luigi Palmieri + +Translator: Robert Mallet + +Release Date: August 22, 2010 [EBook #33483] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + + + + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + + + + + +</pre> + + + + + + + +<h1> +THE<br /> +ERUPTION OF VESUVIUS<br /> +IN 1872,</h1> + + +<div class="likeheading3">BY</div> +<div class="likeheading2">PROFESSOR LUIGI PALMIERI,</div> +<p class="center"><i>Of the University of Naples; Director of the Vesuvian Observatory.</i></p> + + +<div class="likeheading2" style="margin-top:3em;">WITH NOTES, AND AN<br /> +<i>INTRODUCTORY SKETCH OF THE PRESENT STATE OF KNOWLEDGE</i><br /> +OF +TERRESTRIAL VULCANICITY,</div> +<div class="likeheading3"><i>The Cosmical Nature and Relations of +Volcanoes and Earthquakes.</i></div> + + +<div class="likeheading3">BY</div> +<div class="likeheading2">ROBERT MALLET,</div> +<p class="center"><i>Mem. Inst. C.E., F.R.S., F.G.S., M.R.I.A., &c., &c.</i></p> + + +<p class="center" style="margin-top:3em;">WITH ILLUSTRATIONS.</p> + + +<p class="center">LONDON:</p> + +<p class="center"><i>ASHER & CO.</i>,<br /> +13, BEDFORD STREET, COVENT GARDEN, W.C.</p> + +<p class="center">1873. +</p> + + +<hr class="chap" /> +<p class="center">W. S. Johnson, Nassau Steam Press, 60, St. Martin's Lane, Charing +Cross, W.C.</p> + + +<hr class="chap" /> +<p>"The Translator should look upon himself as a Merchant in the +Intellectual Exchange of the world, whose business it is to promote the +interchange of the produce of the mind."</p> + +<p style="margin-left:15em;"><span class="smcap">Gœthe</span>, "<i>Kunst und Alterthum</i>." </p> + +<hr class="chap" /> +<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + +<h2><a name="INTRODUCTORY_SKETCH_c" id="INTRODUCTORY_SKETCH_c"></a>INTRODUCTORY SKETCH, &c.</h2> + + +<p>The publishers of this little volume, in requesting me to undertake a +translation of the "Incendio Vesuviano," of Professor Palmieri, and to +accompany it with some introductory remarks, have felt justified by the +facts that Signor Palmieri's position as a physicist, the great +advantages which his long residence in Naples as a Professor of the +University, and for many years past Director of the Meteorological +Observatory—established upon Vesuvius itself, prior to the expulsion of +the late dynasty—have naturally caused much weight to attach to +anything emanating from his pen in reference to that volcano.</p> + +<p>Nearly forty memoirs on various branches of physics—chiefly +electricity, magnetism and meteorology—produced since 1842, are to be +found under Palmieri's name in the "Universal Catalogue of Scientific +Papers of the Royal Society," and of these nine refer to Vesuvius, the +earliest being entitled "Primi Studii Meteorologici fatti sul R. +Osservatorio Vesuviano," published in 1853. He was also author, in +conjunction with Professor A. Scacchi, of an elaborate report upon the +Volcanic Region of Monte Vulture, and on the Earthquake (commonly called +of Melfi) of 1851. These, however, by no means exhaust the stock of +Palmieri's labours.</p> + +<p><span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span></p><p>The following Memoir of Signor Palmieri on the eruption of Vesuvius in +April of this year (1872), brief as it is, embraces two distinct +subjects, viz., his narrative as an eye-witness of the actual events of +the eruption as they occurred upon the cone and slopes of the mountain, +and his observations as to pulses emanating from its interior, as +indicated by his Seismograph, and as to the electric conditions of the +overhanging cloud of smoke (so called) and ashes, as indicated by his +bifilar electrometer, both established at the Observatory. The two last +have but an indirect bearing upon Vulcanology. The narrative of the +events of the eruption is characterised by exactness of observation and +a sobriety of language—so widely different from the exaggerated style +of sensational writing that is found in almost all such accounts—that I +do the author no more than justice in thus expressing my view of its +merits.</p> + +<p>Nor should a special narration, such as this, become less important or +suffer even in popular estimation by the fact that so recently my +friend, Professor J. Phillips, has given to the world the best general +account of Vesuvius, in its historical and some of its scientific +aspects, which has yet appeared. That monograph—with its sparkling +style, and scholarly digressions, as well as for its more direct +merits—will, no doubt, become the manual for many a future visitor to +the volcanic region of Naples; but it, like the following Memoir of +Palmieri, and in common with almost every work that has appeared on the +subject of Volcanoes, contains a good deal which, however interesting, +and remotely related to Vulcanology, does not properly belong to <span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span>the +body of that branch of cosmical science, as I understand its nature and +limits.</p> + +<p>It tends but little, for example, to clear our views, or enlarge our +knowledge of the vast mechanism in which the Volcano originates, and +that by which its visible mass is formed, that we should ascertain the +electric condition of the atmosphere above its eruptive cone, or into +what crystallographic classes the mineral species found about it may be +divided: it will help us but little to know Pliny's notions of how +Pompeii was overwhelmed, or to re-engrave pictures, assumed to give the +exact shape of the Vesuvian or other cone at different periods, or its +precise altitude, which are ever varying, above the sea. Even much more +time and labour may be spent upon analysing the vapours and gases of +fumaroles and salfatares than the results can now justify.</p> + +<p>Nothing, perhaps, tends more to the effective progress of any branch of +observational and inductive science, than that we should endeavour to +discern clearly the scope and boundary of our subject.</p> + +<p>To do so is but to accord with Bacon's maxim, "<i>Prudens questio dimidium +scienti</i>." That once shaped, the roads or methods of approach become +clearer; and every foothold attained upon these direct paths enables us +to look back upon such collateral or subordinate questions as at first +perplexed us, and find them so illuminated that they are already +probably solved, and, by solution, again prove to us that we <i>are</i> in +the right paths.</p> + +<p>I believe, therefore, that I shall not do disservice to <span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span>the grand +portion of cosmical physics to which volcanic phenomena belong, by +devoting the few pages accorded to me for this Introduction to sketching +what seems to me to be the present position of terrestrial +<i>Vulcanicity</i>, and tracing the outlines and relations of the two +branches of scientific investigation—<i>Vulcanology</i> and <i>Seismology</i>—by +which its true nature and part in the Cosmos are chiefly to be +ascertained.</p> + +<p>The general term, <i>Vulcanicity</i>, properly comprehends all that we see or +know of actions taking place upon and modifying the surface of our +globe, which are referable not to forces of origin above the surface, +and acting superficially, but to causes that have been or are in +operation beneath it. It embraces all that Humboldt has somewhat vaguely +called "the reactions of the interior of a planet upon its exterior."</p> + +<p>These reactions show themselves principally and mainly in the marking +out and configuration of the great continents and ocean beds, in the +forcing up of mountain chains, and in the varied phenomena consequent +thereon, as seen in more or less adjacent formations.</p> + +<p>These constitute the mechanism which has moulded and fashioned the +surface of our globe from the period when it first became superficially +solid, and prepared it as the theatre for the action of all those +superficial actions—such as those of tides, waves, rain, rivers, solar +heat, frost, vitality, vegetable and animal (passing by many others less +obvious)—which perpetually modify, alter or renew the surface of our +world, and maintain the existing regimen of the great machine, and of +its <span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span>inhabitants. These last are the domain of Geology, properly so +called. No geological system can be well founded, or can completely +explain the working of the world's system as we now see it, that does +not start from Vulcanicity as thus defined; and this is equally true, +whether, as do most geologists, we include within the term Geology +everything we can know about our world as a whole, exclusive of what +Astronomy teaches as to it, dividing Geology in general into Physical +Geology—the boundaries of which are very indistinct—and +Stratigraphical Geology, whose limits are equally so.</p> + +<p>It has been often said that Geology in this widest sense begins where +Astronomy or Cosmogony ends its information as to our globe, but this is +scarcely true.</p> + +<p>Vulcanicity—or Geology, if we choose to make it comprehend that—must +commence its survey of our world as a nebula upon which, for unknown +ages, thermic, gravitant and chemical forces were operative, and to the +final play of which, the form, density and volume, as well as order of +deposition of the different elements in the order of their chemical +combination and deposition was due, when first our globe became a liquid +or partly liquid spheroid, and which have equally determined the +chemical nature of the materials of the outward rind of the earth that +now is, and with these some of the primary conditions that have fixed +the characters, nature and interdependence of the vegetables and animals +that inhabit it. Physical Astronomy and Physical Geology, through +Vulcanicity, thus overlap each other; the first does not end where the +second begins; and in every sure attempt to bring Geology to <span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span>that +pinnacle which is the proper ideal of its completed design—namely, the +interpretation of our world's machine, as part of the universal Cosmos +(so far as that can ever become known to our limited observation and +intelligence)—we must carry with us astronomic considerations, we must +keep in view events anterior to the "<i>status consistentior</i>" of +Leibnitz, nor lose sight of the fact that the chain of causation is one +endless and unbroken; that forces first set moving, we know not when or +how, the dim remoteness of which imagination tries to sound in shadowy +thought, like those of the grand old Eastern poem, "When the morning +stars first sang together," are, however changed in form, operative +still. The light and fragile butterfly, whose glorious garb irradiates +the summer zephyr in which it floats, has had its power of flight—which +is its power to live—determined by results of that same chain of causes +that lifted from the depths the mountain on whose sunny side he floats, +that has determined the seasons and the colour of the flower whose +nectar he sucks, and that discharges or dissipates the storm above, that +may crush the insect and the blossom in which it basked. And thus, as +has been said, it was not all a myth, that in older days affirmed that +in some mysterious way the actions and the lives of men were linked to +the stars in their courses.</p> + +<p>Whatever may have been the manifestations of Vulcanicity at former and +far remoter epochs of our planet, and to which I shall return, in the +existing state of regimen of and upon our globe it shows itself chiefly +in the phenomena of Volcanoes and of Earthquakes, <span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span>which are the +subjects of Vulcanology and of Seismology respectively, and in principal +part, also, of this Introduction.</p> + +<p>The phenomena of hot springs, geysers, etc., which might be included +under the title of Thermopgology, have certain relations to both, but +more immediately to Vulcanology.</p> + +<p>Let us now glance at the history and progress of knowledge in these two +chief domains of Vulcanicity, preparatory to a sketch of its existing +stage as to both, and, by the way, attempt to extract a lesson as to the +methods by which such success as has attended our labours has been +achieved.</p> + +<p>It will be most convenient to treat of Seismology first in order.</p> + +<p>Aristotle—who devotes a larger space of his Fourth Book, <span class="greek" title="Greek: Peri +Kosmou">Περἱ Κοσμου</span>, to Earthquakes—Seneca, Pliny, Strabo, in the so-called classic +days, and thence no end of writers down to about the end of the +seventeenth century—amongst whom Fromondi (1527) and Travagini (1679) +are, perhaps, the most important now—have filled volumes with records +of facts, or what they took to be such, of Earthquakes, as handed down +to or observed by themselves, and with plenty of hypotheses as to their +nature and origin, but sterile of much real knowledge.</p> + +<p>Hooke's "Discourses of Earthquakes," read before the Royal Society about +1690, afford a curious example of how abuse of words once given by +authority clings as a hindrance to progress. He had formed no distinct +idea of what he meant by an Earthquake, and so confusedly mixes up all +elevations or depressions of a <span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>permanent character with "subversions, +conversions and transpositions of parts of the earth," however sudden or +transitory, under the name of Earthquakes.</p> + +<p>A like confusion is far from uncommon amongst geological writers, even +at the present day, and examples might be quoted from very late writings +of even some of the great leaders of English Geology.</p> + +<p>From the seventeenth to the middle of the eighteenth century one finds +floods of hypotheses from Flamsteed, Httinger, Amontons, Stukeley, +Beccaria, Percival, Priestly, and a crowd of others, in which +electricity, then attracting so much attention, is often called upon to +supply causation for a something of which no clear idea had been formed. +Count Bylandt's singular work, published in 1835, though showing a +curious <i>partial</i> insight in point of advancement, might be put back +into that preceding period.</p> + +<p>In 1760 appeared the very remarkable Paper, in the fifty-first volume of +the "Philosophical Transactions," of the Rev. John Mitchell, of +Cambridge, in which he views an Earthquake as a sudden lifting up, by a +rapid evolution of steam or gas beneath, of a portion of the earth's +crust, and the lateral transfer of this gaseous bubble beneath the +earth's crust, bent to follow its shape and motion, or that of a wave of +liquid rock beneath, like a carpet shaken on air. Great as are certain +collateral merits of Mitchell's Paper, showing observation of various +sorts much in advance of his time, this notion of an Earthquake is such +as, had he applied to it even the imperfect knowledge of mechanics and +physics then possessed in a definite manner, he could <span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span>scarcely have +failed to see its untenable nature. That the same notion, and in a far +more extravagant form, should have been reproduced in 1843 by Messrs. +Rogers, by whom the gigantic parallel anticlinals, flanks and valleys of +the whole Appalachian chain of mountains are taken for nothing more than +the indurated foldings and wrinkles of Mitchell's carpet, is one of the +most salient examples of the abuse of hypothesis untested by exact +science.</p> + +<p>Neither Humboldt nor Darwin, great as were the opportunities of +observation enjoyed by both, can be supposed to have formed any definite +idea of <i>what</i> an Earthquake is; and the latter, who had observed well +the effects of great sea-waves rolling in-shore after the shock, did not +establish any clear relation between the two.<a name="FNanchor_A_1" id="FNanchor_A_1"></a><a href="#Footnote_A_1" class="fnanchor">[A]</a></p> + +<p>Hitherto no one appears to have formed any clear notion as to what an +Earthquake is—that is to say, any clear idea of what is the nature of +the movement constituting the shock, no matter what may be the nature or +origin of the movement itself. The first glimmering of such an idea, so +far as my reading has enabled me to ascertain, is due to the penetrating +genius of Dr. Thomas Young, who, in his "Lectures on Natural +Philosophy," published in 1807, casually suggests the probability that +earthquake motions are vibratory, and <span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span>are analogous to those of +sound.<a name="FNanchor_B_2" id="FNanchor_B_2"></a><a href="#Footnote_B_2" class="fnanchor">[B]</a> This was rendered somewhat more definite by Gay Lussac, who, +in an able paper "On the Chemical Theories of Volcanoes," in the +twenty-second volume of the "Annales de Chmie," in 1823, says: "En un +mot, les tremblements de terre ne sont que la propagation d'une +commotion travers la masse de la terre, tellement indpendante des +cavits souterraines qu'elle s'entendrait, d'autant plus loin que la +terre serait plus homogne."</p> + +<p>These suggestions of Young and of Gay Lussac, as may be seen, only refer +to the movement in the more or less solid crust of the earth. But two, +if not three, other great movements were long known to frequently +accompany earthquake shocks—the recession of the sea from the shore +just about the moment of shock—the terrible sounds or subterraneous +growlings which sometimes preceded, sometimes accompanied, and sometimes +followed the shock—and the great sea-wave which rolls in-shore more or +less long after it, remained still unknown as to their nature. They had +been recognised only as concomitant but unconnected phenomena—the more +inexplicable, because sometimes present, sometimes absent, and wholly +without any known mutual bearing or community of cause.</p> + +<p>On the 9th February, 1846, I communicated to the <span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span>Royal Irish Academy my +Paper, "On the Dynamics of Earthquakes," printed in Vol. XXI., Part I., +of the Transactions of that Academy, and published the same year in +which it was my good fortune to have been able to colligate the observed +facts, and bringing them together under the light of the known laws of +production and propagation of vibratory waves in elastic, solid, liquid +and gaseous bodies, and of the production and propagation of liquid +waves of translation in water varying in depth, to prove that all the +phenomena of earthquake shocks could be accounted for by a single +impulse given at a single centre. The definition given by me in that +Paper is that an earthquake is "<i>The transit of a wave or waves of +elastic compression in any direction, from vertically upwards to +horizontally, in any azimuth, through the crust and surface of the +earth, from any centre of impulse or from more than one, and which may +be attended with sound and tidal waves dependent upon the impulse and +upon circumstances of position as to sea and land</i>."</p> + +<p>Thus, for example, if the impulse (whatever may be its cause) be +delivered somewhere beneath the bed of the sea, all four classes of +earthquake waves may reach an observer on shore in succession. The +elastic wave of shock passing through the earth <i>generally</i> reaches him +first: its velocity of propagation depending upon the specific +elasticity and the degree of continuity of the rocky or the incoherent +formations or materials through which it passes.</p> + +<p>Under conditions pointed out by me, this elastic wave may cause an +aqueous wave, producing recession <span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span>of the sea, just as it reaches the +margin of sea and land.</p> + +<p>If the impulse be attended by fractures of the earth's crust, or other +sufficient causes for the impulse to be communicated to the air directly +or through the intervening sea, ordinary sound-waves will reach the +observer through the air, propagated at the rate of 1,140 feet per +second, or thereabouts; and may also reach him before or with or soon +after the shock itself, through the solid material of the earth; and +lastly, if the impulse be sufficient to disturb the sea-bottom above the +centre of impulse, or otherwise to generate an aqueous wave of +translation, that reaches the observer last, rolling in-shore as the +terrible "great sea-wave," which has ended so many of the great +earthquakes, its dimensions and its rate of propagation depending upon +the magnitude of the originating impulse and upon the variable depth of +the water. It is not my purpose, nor would it be possible within my +limits here, to give any complete account of the matter contained in +that Paper, which, in the words of the President of the Academy upon a +later occasion, "fixed upon an immutable basis the true theory of +Earthquakes."<a name="FNanchor_C_3" id="FNanchor_C_3"></a><a href="#Footnote_C_3" class="fnanchor">[C]</a> I should state, however, that in it I proved the +fallacy of the notion of vorticose shocks, which had been held from the +days of Aristotle, and showed that the effects (such as the twisting on +their bases of the Calabrian Obelisks) which <span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span>had been supposed due to +such, were but resolved motions, due to the transit rectilinearly of the +shock.</p> + +<p>This removed one apparent stumbling block to the true theory.</p> + +<p>Incidentally also it was shown that from the observed elements of the +movement of the elastic wave of shock at certain points—by suitable +instruments—the position and depth of the <i>focus</i>, or centre of +impulse, might be inferred.</p> + +<p>In the same volume ("Transactions of the Royal I. Academy," XXI.) I gave +account, with a design to scale, for the first self-registering and +recording seismometer ever, to my knowledge, proposed. In some respects +in principle it resembles that of Professor Palmieri, of which he has +made such extended use at the Vesuvian Observatory, though it differs +much from the latter in detail. In June, 1847, Mr. Hopkins, of +Cambridge, read his Report, "On the Geological Theories of Elevation and +Earthquakes," to the British Association—requested by that body the +year before—and printed in its Reports for that year.</p> + +<p>The chief features of this document are a digest of Mr. Hopkins's +previously published "Mathematical Papers" on the formations of +fissures, etc., by elevations and depressions, and those on the +thickness of the earth's crust, based on precession, etc., which he +discusses in some relations to volcanic action.</p> + +<p>This extends to forty-one pages, the remaining eighteen pages of the +Report being devoted to "Vibratory Motions of the Earth's Crust produced +by Subterranean Forces—Earthquakes."</p> + +<p><span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span></p><p>The latter consists mainly of a <i>rsum</i> of the acknowledged laws, as +delivered principally by Poisson, of formation and propagation of +elastic waves and of liquid waves, by Webers, S. Russel and others—the +original matter in this Report is small—and as respects the latter +portion consists mainly in some problems for finding analytically the +position or depth of the centre of disturbance when certain elements of +the wave of shock are given, or have been supposed registered by +seismometric instruments, such as that described by myself, and above +referred to.<a name="FNanchor_D_4" id="FNanchor_D_4"></a><a href="#Footnote_D_4" class="fnanchor">[D]</a> At the time my original Paper "On the Dynamics of +Earthquakes" was published, there was little or no <i>experimental</i> +knowledge as to the actual velocity of transit of waves—analogous to +those of sound, but of greater amplitude—through <span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span>elastic solids. The +velocity as deduced from theory, the solid being assumed quite +<i>homogeneous</i> and <i>continuous</i>, was very great, and might be taken for +some of the harder and denser rock formations at 11,000 or 12,000 feet +per second. That these enormous velocities of wave transit would be +something near those of actual earthquake shock seemed probable to me, +and was so accepted by Hopkins.</p> + +<p>Thus, he says (Report, p. 88): "The velocity of the sea-wave, for any +probable depth of the sea, will be so small as compared with that of the +vibratory wave, that we may consider the time of the arrival of the +latter at the place of observation as coincident with that of the +departure of the sea-wave from the centre of divergence."</p> + +<p><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span></p><p>In my original Paper (Dynamic, &c.), I had suggested, as an important +object, to ascertain by actual experiment what might be the wave's +transit rate in various rocky and incoherent formations; and having +proposed this in my first "Report upon the Facts of Earthquake" to the +British Association, I was enabled by its liberality to commence those +experiments, in which I was ably assisted by my eldest son, then quite a +lad—Dr. Jno. William Mallet, now Professor of Chemistry at the +University of Virginia, U.S.; and to give account of the results, in my +second Report ("Report, British Association for 1851") to that body.</p> + +<p>Those experiments were made by producing an impulse at one end of an +accurately measured base line, by the explosion of gunpowder in the +formation experimented upon, and noting the time the elastic wave +generated required to pass over that distance, upon a nearly level +surface. Special instruments were devised and employed, by which the +powder was fired and the time registered, by touching a lever which +completed certain galvanic contacts. The media or formations in which +these experiments were conducted were, damp sand—as likely to give the +minimum rate—and crystalline rock (granite), as likely to give the +maximum. The results were received, not with doubt, but with much +surprise, for it at once appeared that the actual velocity of transit +was vastly below what theory had indicated as derivable from the density +and modulus of elasticity of the material, taken as homogeneous, etc. +The actual velocities in feet per second found were:</p> + +<p> +<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span></p> + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="left">In sand</td><td align="right">824915</td><td align="center">feet</td><td align="center">per second.</td></tr> +<tr><td align="left">In discontinuous and much shattered granite</td><td align="right">1,306425</td><td align="center">"</td><td align="center">"</td></tr> +<tr><td align="left">In more solid granite</td><td align="right">1,664574</td><td align="center">"</td><td align="center">"</td></tr> +</table></div> + +<p>This I at once attributed, and as it has since been proved correctly, to +the loss of <i>vis viva</i>, and consequently of speed, by the <i>discontinuity +of the materials</i>.</p> + +<p>And some indication of the general truth of the fact was derivable from +comparing the rude previous approximations to the transit rate of some +great Earthquakes. In the case of that of Lisbon, estimated by Mitchell +at 1,760 feet per second. It was still desirable to extend similar +experiments to the harder classes of stratified and of contorted rocks. +This I was enabled to carry into effect, at the great Quarries at +Holyhead (whence the slate and quartz rocks have been obtained for the +construction of the Asylum Harbour there), taking advantage of the +impulses generated at that period by the great mines of powder exploded +in these rocks.</p> + +<p>The results have been published in the "Philosophical Transactions for +1861 and 1862 (Appendix)." They show that the mean lowest rate of wave +transit in those rocks, through measured ranges of from 5,038 to 6,582 +feet, was 1,089 feet per second; and the mean highest, 1,352 feet per +second; and the general mean 1,320 feet per second.</p> + +<p>By a separate train of experiments on the compressibility of solid cubes +of these rocks, I obtained the mean modulus of elasticity of the +material when <span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span>perfectly continuous and unshattered, with this +remarkable result—that in these rocks, as they exist at Holyhead, +<i>nearly seven-eighths of the full velocity of wave transmission due to +the material, if solid and continuous, is lost by reason of the +heterogeneity and discontinuity</i> of the rocky masses as they are found +piled together in Nature.</p> + +<p>I also proved that the wave-transit period of the unshattered material +of these rocks was greatest in a direction <i>transverse</i> to the bedding, +and least in line parallel with that; but the effect of this in the +rocky mass itself may be <i>more</i> than counterbalanced by the +discontinuity and imperfect contact of the adjacent beds.</p> + +<p>These results indicate, therefore, that the superficial rate of +translation of the solitary sea-wave of earthquakes may, when over very +deep water, equal or even exceed the transit rate (in some cases) of the +elastic wave of shock itself.</p> + +<p>These results have since received general confirmation by the careful +determinations of the transit rates of actual earthquake waves, in the +rocks of the Rhine Country and in Hungary, by Nggerath and Schmidt +respectively, and by those made since by myself in those of Southern +Italy, to which I shall again refer. In an elastic wave propagated from +a centre of impulse in an infinitely extended volume of a perfect gas, +normal vibrations are alone propagated—as is the case with sound in +air.</p> + +<p>In the case of like movements propagated in elastic and perfectly +homogeneous and isotropic solids, the <span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span>wave possesses both normal and +transversal vibrations, and is, in so far, analogous to the case of +light. Mr. Hopkins, in his Report above referred to, has based certain +speculations upon the assumed necessary co-existence of both orders of +vibration in actual earthquake shocks in the materials of which our +earthy crust is actually composed.</p> + +<p>The existence of transversal vibration in those materials has not been +yet proved experimentally, though there is sufficient ground to preclude +our denying their probable existence.</p> + +<p>That if they do exist they play but a very subordinate part in the +observable phenomena of actual Earthquake is highly probable. This is +the view, supported not only by observations of the effects of such +shocks in Nature, but by the theoretic consideration of the effects of +discontinuity of formations in planes or beds more or less transverse to +the wave path (or line joining the centre of impulse with the mean +centre of wave disturbance at any point of its transit). If we suppose, +for illustration sake, such an elastic wave transmitted perpendicularly +through a mass of glass plates, each indefinitely thin, and all in +absolute contact with each other, but without adhesion or friction, more +or less of the transversal vibration of the wave would be cut off and +lost at each transit from plate to plate, as the elastic compression +can, by the conditions, be transmitted only normally or by direct push +perpendicularly from plate to plate. This must take place in Nature, and +to a very great extent, and the consideration, with others, enabled me +generally to apply the normal <span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span>wave motion of shock alone to my +investigation as to the depth of the centre of impulse of the great +Neapolitan Earthquake of 1857, an account of which was published in +1862, and to be presently further referred to.</p> + +<p>Hitherto the multitudinous facts, or supposed facts, recorded in +numberless accounts of Earthquakes had remained almost wholly +unclassified, and so far as they had been discussed—in a very partial +manner, as incidental portions of geological treatises—with little +attempt to sift the fabulous from the real, or to connect the phenomena +admitted by reference to any general mechanical or physical causes. In +1850 my first "Report upon the Facts of Earthquakes," called for by the +British Association in 1847, was read and published in the Reports of +that body for that year. In this, for the first time, the many recorded +phenomena of Earthquakes are classified, and the important division of +the phenomena into primary and secondary effects of the shock was +established. Several facts or phenomena, previously held as marvellous +or inexplicable, were either, on sufficient grounds, rejected, or were, +for the first time, shown susceptible of explanation. Amongst the more +noticeable results were the pointing out that fissures and fractures of +rock or of incoherent formations were but secondary effects, and, in the +latter, were, in fact, generally of the nature of inceptive landslips. +This last was not accepted, I believe, by geologists at the time; but +the correctness of the views then propounded as to earth fissures—the +nature of the spouting from them of water or mud—the appearances taken +<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span>for smoke issuing from them, etc.—have since been fully confirmed, +first, by my own observations upon the effects of the Great Neapolitan +Earthquake of 1857, and more lately by those of Dr. Oldham upon the +Earthquake of Cachar (India), where he was enabled to observe fissures +of immense magnitude, the nature of the production of which he has well +described and explained in the "Proceedings, Geological Society, London, +1872."</p> + +<p>The relations between meteorological phenomena proper and Earthquakes +have always been a subject of popular belief and superstition.</p> + +<p>This was here carefully discussed, and with the result of disproving any +connection, or, if any, but of an indirect nature. I also, to some +extent, towards the end of this Report, discussed the question of the +possible nature of the <i>impulse itself</i> which originates the shock; I +showed that it must be of the nature of a blow, and ventured to offer +<i>conjecturally</i> five possible causes of the impulse:</p> + +<ol> +<li>Sudden fractures of rock, resulting from the steady and slow +increase of elevatory pressure.</li> + +<li>Sudden evolution (under special conditions) of steam.</li> + +<li>Sudden condensation of steam, also under special conditions.</li> + +<li>Sudden dislocations in the rocky crust of the earth, through +pressure acting in any direction.</li> + +<li>Occasionally through the recoil due to explosive effects at +volcanic foci (p. 79-80). +</li> +</ol> + +<p>The first and last of these I am, through subsequent light, disposed now +to withdraw or greatly to modify.</p> + +<p><span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span></p><p>The first, the supposed "<i>snap and jar</i>, occasioned by the sudden and +violent rupture of solid rock masses," to which Mr. Scrope, in his very +admirable work on Volcanoes, is disposed to refer the impulse of +earthquake shocks (Scrope, 2nd edit., p. 294), I believe may be proved +on acknowledged physical principles—when applied to the known +elasticities and extensibilities of rocks, and keeping in view the small +thicknesses fractured <i>at the same instant</i>—to be capable of only the +most insignificant impulsive effects; and if we also take into +consideration that strata, if so fractured, are necessarily not <i>free</i>, +but surrounded by others above and below, any such impulsive effect +emanating from fracture may be held as non-existent or impossible. In +the statement of his views which follows, and in objecting to my second +and third possible causes (p. 295-296, headed "Objections to Mallet's +Theory"), Mr. Scrope appears to me to have fallen into the error of +assuming that the nature of the <i>impulse</i>, or the cause producing it, +forms any part of "my theory of earthquake movement," or in anywise +affects it. I carefully guarded against this in the original Paper +("Transactions, Royal Irish Academy," Vol. XXI., p. 60, and again, p. +97), when I stated "it is quite immaterial to the truth of my theory of +earthquake motion what view be adopted, or what mechanism be assigned, +to account for the original impulse."</p> + +<p>As regards the fifth conjecture suggested by me, I am now, with better +knowledge and larger observation of volcanic phenomena, not prepared to +admit any single explosion at volcanic vents of a magnitude sufficient +to produce by its recoil an earthquake wave of any importance, <span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span>or +extending to any great distance in the earth's crust. The rock of 200 +tons weight, said to have been projected nine miles from the crater of +Cotopaxi, which I quoted from Humboldt as an example,<a name="FNanchor_E_5" id="FNanchor_E_5"></a><a href="#Footnote_E_5" class="fnanchor">[E]</a> I believe to be +as purely mythical as the rock (<i>bloc rejett</i>) of perhaps one-sixth of +that weight which, previous to the late eruption, lay in the middle of +the Atria dell Cavallo, and which it was roundly affirmed had been +<i>blown</i> out of the crater, but which in reality had at some time rolled +down from near the top of the cone, after having been dislodged from +some part of the upper lip of the crater walls, where, as its wonderful +hardness and texture and its enamel-like surface showed, it had been +roasted for years probably.</p> + +<p>Nor do I believe in the <i>sudden</i> blowing away of one-half the crater and +cone of Vesuvius, or of any other volcano, at one effort, however +affirmed.</p> + +<p>Nothing more than conjecture as to the nature of the impulse producing +great or small Earthquakes can, I believe, as yet be produced. That +there is some one master mechanism productive of most of the impulses of +great shocks is highly probable, but that more causes than one may +produce these impulses, and that the causes operative in small and long +repeated shocks, like those of Visp-Comrie and East Haddam, differ <span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span>much +from those producing great Earthquakes, is almost certain.</p> + +<p>We shall be better prepared to assign all of these when we have admitted +a true theory of volcanic action, and so are better able to see the +intimate relations in mechanism between seismic and volcanic actions.</p> + +<p>It is not difficult meanwhile to assign the very probable mechanism of +those comparatively petty repercussions which are experienced in close +proximity to volcanic vents when in eruption, and which, though +certainly seismic in their nature, and powerful enough, as upon the +flanks of Etna, to crack and fissure well-built church-towers, can +scarcely be termed Earthquakes.</p> + +<p>In my First Report I stated that almost nothing was known then of the +distribution of recorded Earthquakes in time or in space over our +globe's surface, and I proposed the formation and discussion of a +complete catalogue of all recorded Earthquakes, with this in view.</p> + +<p>This was approved by the Council of the British Association and at once +undertaken by me, with the zealous and efficient co-operation of my +eldest son, Dr. J. W. Mallet. Nearly the whole of the Second British +Association Report, of 1851, is occupied with the account of the +experiments as to the transit rate of artificially made shocks in sand +and granite, as already referred to.</p> + +<p>The Third Report, of 1852-1854, contains the whole of this, "The +Earthquake Catalogue of the British Association" (of which, through the +liberality of that body, more than one hundred copies were distributed +<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span>freely), in which are given, in columnar form, the following +particulars, from the earliest known dates to the end of 1842:</p> + +<ol> +<li>The date and time of day, as nearly as recorded.</li> + +<li>The locality or place of occurrence.</li> + +<li>The direction, duration, and number of shocks so far +recorded.</li> + +<li>Phenomena connected with the sea—great sea-waves, tides, +etc.</li> + +<li>Phenomena connected with the land—meteorological phenomena +preceding and succeeding. Secondary phenomena—all minor or +remarkable phenomena recorded.</li> + +<li>The authority for the record. +</li> +</ol> + +<p>Though most materially assisted by the previous labours and partial +catalogues of Von Hoff, Cotte, Hoffman, Merrian, and, above all, of +Perrey, the preparation of this catalogue—which demanded visits to the +chief libraries of Europe, and the collating of some thousands of +authors in various languages and of all time—was a work of great and +sustained labour, which, except for my dear son's help, I should never +have found time and power to complete. Professor Perrey, formerly of the +Facult des Sciences of Dijon, now <i>en retrait</i>, who has devoted a long +and useful life to assiduous labours in connection with Seismology, was +our great ally; and his catalogues are so large and complete for most +known parts of the world after 1842, that we were able to arrest our own +catalogue at that date, and take M. Perrey's as their continuation up to +1850.</p> + +<p>The whole British Association Catalogue thus embraces <span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span>the long historic +period of from 1606 <span class="smcap">B.C.</span> of vulgar chronology, when the first known +Earthquake is recorded, to <span class="smcap">A.D.</span> 1850; and the base of induction which it +presents as to the facts recorded extends to between 6,000 and 7,000 +separate Earthquakes. My Fourth Report ("Reports, British Association, +1858,") is occupied principally with the discussion of this great +catalogue, and with that of several special catalogues produced by other +authors with limited areas or objects.</p> + +<p>The discussion of M. Perrey's local catalogues with those of others, in +reference to a supposed prevalent apparent horizontal direction of shock +in certain regions—as to distribution, as to season, months, time of +day or night, relation to state of tide—the bearings of the views of +Zantedeschi and others as to the probable existence of a terrane +tide—the supposed relations of the occurrence of Earthquakes upon the +age of the moon, as deduced by Perrey, viz.: that 1st, Earthquakes occur +most frequently at the syzygies; 2nd, that their frequency increases at +the perigee and diminishes at the apogee; 3rd, that they are more +frequent when the moon is on the meridian than when she is 90 away from +it—and the views of several authorities as to the distribution of +Earthquakes in time and in space—occupy the first 46 pages of this +Report.</p> + +<p>It then proceeds to discuss the distribution in time and in space as +deduced from the full base of the great catalogue.</p> + +<p>The results as to time are reduced to curves, and those as to space (or +distribution over our globe's surface) to the great seismic map +(Mercator's projection), <span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span>upon which and in accordance with certain +principles and conventional laws, which admit of the indication of both +intensity and frequency, all recorded Earthquakes have been so laid down +as to present a real indication of the distribution of seismic energy +for the whole historic period and all over the world.</p> + +<p>The original of this map, which also shows the Volcano (size, about 7 +feet by 5 feet), remains for reference in the custody of the Royal +Society. A reduced copy was published with the Report, and to a still +more reduced scale has been reproduced in other places. It is impossible +here to do more than refer to a few of the more salient points.</p> + +<p>As regards distribution in time, durational seismic energy may be +considered as probably constant during historic time, though it is +probably a decaying energy viewed in reference to much longer periods. +It does not appear of the nature of a distinctly periodic force.</p> + +<ol> +<li>Whilst the minimum paroxysmal interval may be a year or two, +the average interval is from five to ten years of comparative +repose.</li> + +<li>The shorter intervals are in connection with periods of +fewer Earthquakes, not always with those of least intensity, +but usually so.</li> + +<li>The alternations of paroxysm and of repose appear to follow +no absolute law deducible from these causes.</li> + +<li>Two marked periods of extreme paroxysm are observable in +each century (for the last three centuries), one greater than +the other—that of <span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span>greatest number and intensity occurring +about the middle of each century, and the other towards the end +of each. +</li> +</ol> + +<p>As respects season, there appear distinct indications of a maximum about +the winter solstice, and equally so of a minimum rather before the +autumnal equinox. It is not improbable that there is a remote relation +between Earthquakes and the annual march of barometric pressure.</p> + +<p>We may expect, at present, one great Earthquake about every eight +months, and were we possessed of a sufficient report from all parts of +our globe, we should probably find scarcely a day pass without a very +sensible Earthquake occurring somewhere, whilst, as regards still +smaller tremors, it might almost be said that our globe, as a whole, is +scarcely ever free from them.</p> + +<p>As respects the distribution of seismic energy in space of our earth's +surface, it is that of bands of variable and of great breadth, with +sensible seismic influence extending to from 5 to 15 transversely, +which very generally follow:</p> + +<ol> +<li>The lines of elevated tracts which mark and divide the great +oceanic or terra-oceanic basins (or <i>saucers</i>, as I have called +them, from their shallowness in relation to surface, in this +discussion) of the earth's surface.</li> + +<li>And in so far as these are frequently the lines of mountain +chains, and these latter those of volcanic vents, so the +seismic bands are found to follow these likewise. Isolated +Volcanoes are found in these bands also.</li> + +<li><span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span>While sensible seismic influence is generally limited to +the average width of the band, paroxysmal efforts are +occasionally propagated to great distances transversely beyond +that.</li> + +<li>The sensible width of the band depends upon the energy +developed at each point of the length, and upon the accidental +geologic and topographic conditions along the same.</li> + +<li>Seismic energy <i>may</i> become sensible at any point of the +earth's surface, its efforts being, however, greater and more +frequent as the great lines of elevation and of volcanic +activity are approached; yet not in the inverse ratio of +distance, for many of the most frequently and terribly shaken +regions of the earth, as the east shore of the Adriatic, Syria, +Asia Minor, Northern India, etc., are at great distances from +active Volcanoes.</li> + +<li>The surfaces of minimum or of no known disturbance are the +central areas of great oceanic or of terra-oceanic basins or +saucers, and the greater islands existing in shallow seas. +</li> +</ol> + +<p>Space obliges me to pass unnoticed here many minor but not unimportant +deductions. The discussions as to distribution in time and space occupy +seventy-two pages of this fourth and last Report, the remainder of which +(thirty-one pages) embraces the description and mathematical discussion +as to seismometers, to which I may refer, as comprising the most +complete account of these instruments that has, I believe, been anywhere +given.</p> + +<p>The appendix to the Report comprises the entire bibliography of +Earthquakes collected during those <span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span>researches, and a concluding chapter +on desiderata, and inquiries as to ill-understood phenomena supposed to +be connected with Earthquakes.</p> + +<hr class="tb" /> + +<p>In 1849-50, I was honoured by the request to draw up the article +"Earthquake Phenomena," which has appeared in the first and subsequent +editions of the "Admiralty Manual of Scientific Inquiry." Originally the +subject was intended to have formed part of the article on Geology, +entrusted to Mr. Darwin, who consulted me upon the subject; and upon my +representing how much Earthquakes had, within a short time, become +matter for the mathematician and physicist, he, with a singleness of eye +to science which it is but just to place on record, took the necessary +steps with the Admiralty authorities that Earthquakes should form a +separate article, and advised its being placed, as it was, in my hands. +To record this will, I believe, be sufficient justification for my +reference to this article, in which a good deal of information as to +Seismometry is to be found.</p> + +<hr class="tb" /> + +<p>By recurring to Mr. Hopkins's Report on Earthquake Theory, before +remarked upon ("Report of British Association, 1847"), it will be seen +that the solutions of the problems which he there gives for finding the +depth of focus of shock are founded upon the <i>velocity of propagation</i> +of the wave in the interior of the mass, the <i>apparent horizontal +velocity</i> and the <i>horizontal direction of propagation</i> at any proposed +point being known (p. 82).</p> + +<p>By this it appears plainly that at that time <span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span>Mr. Hopkins supposed that +it was the <i>velocity of translation</i> of the wave of shock that did the +mischief, and not the <i>velocity of the wave particle</i>, or wave itself. +And, further, that the former might be obtained by reference simply to +the modulus of elasticity of the rock of any given formation, as, +indeed, was my own earliest view when I produced my "Dynamics of +Earthquake" in 1846. From the remarks already made as to the vast +difference between the actual transit velocity in more or less +discontinuous rocks—such as they occur in Nature—it will be equally +obvious that Mr. Hopkins's methods, as above mentioned, are +impracticable, even were there no confusion between the velocity of +translation of the wave and that of the wave particle or wave itself.</p> + +<p>This applies also to the demonstration and diagram (taken from Hopkins) +given by Professor Phillips ("Vesuvius," pp. 258-259).</p> + +<p>In December, 1857, occurred the great Neapolitan Earthquake, which +desolated a large portion of that kingdom; and an opportunity then arose +for practically applying to the problems of finding the directions of +earthquake shock at a given point through which it has passed, and +ultimately the position and depth of focus, other methods, which I had +seen, from soon after the date of publication of my original Paper +(1846), were easily practicable, and the details of which I had +gradually matured.</p> + +<p>Bearing in mind that, in the case of the normal vibration in any elastic +solid of indefinite dimensions, the direction of motion in space of the +<i>wave particle</i> coincides in the first semiphase of the wave, and at the +<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span>instant of its <i>maximum velocity</i> with the right line joining the +particle and the focus or centre of disturbance, it follows that, in the +case of earthquakes, the normal vibration of the wave of shock is always +in a vertical plane passing through the focus and any point on the +earth's surface through which the shock passes (assuming for the present +no disturbing causes after the impulse has been given), and that at such +a point the movement of the wave particle in the first semiphase of the +wave is in the same direction or sense as that of translation; and at +the moment of maximum velocity the direction in space of the motion of +the wave particle is that of the right line joining the point through +which the wave has passed with the focus or centre of impulse.</p> + +<p>If, therefore, we can determine the direction of motion of the wave +particle in the first semiphase, and its maximum velocity, we can +obtain, from any selected point, a line (that of emergence of the shock) +<i>somewhere in which</i>, if prolonged beneath the earth, the focus must +have been; and if we can obtain like results for two or more selected +points, we decide the position and the depth of the focus, which must be +in the intersection of the several lines of direction of the wave +particle motion at each point, when prolonged downwards.</p> + +<p>Now, as I have said, it is the <i>vibration of the wave itself</i>, <i>i.e.</i>, +the motion of the wave particle that does the mischief—<i>not</i> the +transit of the wave from place to place on the surface; just as in the +analogous (but <i>not</i> similar) case of a tidal wave of translation +running up <span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span>an estuary and passing a ship anchored there, it is not the +transit up the channel, but the wave form itself—<i>i.e.</i>, the motion of +the wave particles—that lifts the ship, sends her a little way higher +up channel, drops her to her former level, and sends her down channel +again to the spot she lay in just before the arrival of the wave.</p> + +<p>Everything, therefore, that has been permanently disturbed by an +earthquake shock has been thus moved in the direction and with the +maximum velocity impressed upon it by the wave particle in the first +semiphase of the wave; and thus almost everything that has been so +disturbed may, by the application of established dynamical principles, +be made to give us more or less information as to the velocity of the +wave particle (or as we, for shortness, say, the velocity of shock), the +direction of its normal vibration, and the position and depth beneath +the earth's surface, from which came the generating impulse. We thus +arrive at these as simply and as surely as we can infer from the +position taken by a billiard ball, on which certain forces are known to +have acted, the forces themselves and their direction; or, from a broken +beam, the pressure or the blow which fractured it.</p> + +<p>It is obvious, then, that nearly every object disturbed, dislocated, +fractured or overthrown by an earthquake shock is a sort of natural +seismometer, and the best and surest of all seismometers, if we only +make a judicious choice of the objects which being found after such a +shock, we shall employ for our purpose. This was the principle which I +proposed to the Royal Society at once to apply to the effects of the +then quite recent great <span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span>Neapolitan Earthquake of 1857, and which, +through the liberality and aid of that body, I was enabled to employ +with the result I had pretty confidently anticipated, namely, the +ascertainment of the approximate depth of the focus.</p> + +<p><i>Every</i> shock-disturbed object in an earthquake-shaken country is +capable of giving <i>some</i> information as to the shock that acted upon it; +but it needs a careful choice, and some mechanical <span class="greek" title="Greek: nous">νους</span>, to +select <i>proper</i> and the best objects, so as to avoid the needless +perplexity of disturbing forces <i>not</i> proper to the shock, or other +complications.</p> + +<p>When properly chosen, these natural seismometers, or evidences fitted +for observation after the shock, are of two great classes, by which the +conditions of the earthquake motion are discoverable:</p> + +<ul class="lsoff"> +<li style="text-indent:-1em;">1. Fractures or dislocations (chiefly in the masonry of +buildings), which afford two principal sources and sorts of +information, namely: + +<ul class="lsoff"> +<li style="text-indent:-1em;"><i>a.</i> From the observed <i>directions of fractures or fissures</i>, +by which the <i>wave path</i>, and frequently the <i>angle of +emergence</i>, may be immediately inferred.</li> + +<li style="text-indent:-1em;"><i>b.</i> Information from the preceding, united with known +conditions as to the strength of materials to resist +<i>fracture</i>, by which the <i>velocity</i> of the fracturing impulse +may be calculated.</li> +</ul></li> + +<li style="text-indent:-1em;">2. The overthrow or the projection, or both, of bodies large or +small, simple or complex. From these we are enabled to infer: + +<ul class="lsoff"> +<li style="text-indent:-1em;"><i>c.</i> By direct observation, the <i>direction in azimuth</i> of the +wave path.</li> + +<li style="text-indent:-1em;"><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span><i>d.</i> By measurements of the horizontal and vertical distances +of overthrow or of projection, to infer either the <i>velocity</i> +of projection, or <i>angle of emergence</i>. +</li> +</ul></li> +</ul> + +<p>Fractures by shock present their planes always nearly in directions +transverse to the wave path. Projections or overthrow take place (unless +secondarily disturbed) in the line of the wave path, or in the vertical +plane passing through it: but the direction of fall or overthrow may be +either in the same direction as the wave transit (<i>i.e.</i>, as the motion +of the wave particle in the first semiphase), or contrary to it.</p> + +<p>It is thus obvious that the principal phenomena presented by the effects +of earthquake shock upon the objects usually occurring upon the surface +of the inhabited parts of the earth, resolve themselves into problems of +three orders, and are all amenable to mechanical treatment, viz.:</p> + +<ol> +<li>Problems relating to the direction and amount of velocity +producing fracture or fissures.</li> + +<li>Problems relating to the single or multiplied oscillations +of bodies, considered as compound pendulums.</li> + +<li>Problems referable to the theory of projectiles. +</li> +</ol> + +<p>These three may combine in several cases, and on the part of the +observer must combine with measurements, angular and linear, and with +geodetic operations to be conducted in the shaken country.</p> + +<p>The methods of application in detail are described fully, as well as +their actual application and results, in my work published in 1862 (2 +vols.), entitled "The <span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span>First Principles of Observational Seismology, as +developed in the Report to the Royal Society of London of the Expedition +made by Command of the Society into the Interior of the Kingdom of +Naples, to investigate the Circumstances of the Great Earthquake of +December, 1857," to the many illustrations of which the pecuniary grant, +in aid, of 300 was most liberally made to the publishers (Messrs. +Chapman and Hall) by the Society.</p> + +<p>It is not my intention here, nor would space allow, of my going into the +details of observation, nor of the deductions and conclusions I have +recorded in those volumes. I have referred to their contents as marking +the advent of a new method. I have ventured to call it a new <i>organon</i> +in the investigation of Earthquakes, and, through them, of the deep +interior of our earth; and will only add that the method, on this its +very first trial, proved fertile and successful. The depth of focus for +this shock of December, 1857, was about seven to eight geographical +miles below sea level, roughly stated. It gives me great pleasure to add +that my friend, Dr. Oldham, Director-General of the Geological Survey of +India, has since applied these same methods to the phenomena of the +great Cachar Earthquake of the 10th January, 1869, and with success. The +pressure of official duties has, he informs me, as yet prevented his +fully working out his results, but they appear so far to indicate, as we +should expect, a depth of focus or origin considerably greater than in +the European case of 1857. Some account of Dr. Oldham's results were +this year communicated to the Geological Society of <span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span>London through +myself, they are of great interest and importance.</p> + +<p>Such, briefly and imperfectly sketched, is the existing state of +Seismology. As a branch of exact science it is, as it were, an affair of +yesterday. It is with reluctance that I have been compelled, in this +review, to refer to my own work so prominently. The harvest has been and +still is plenteous, but in this field of intellectual work the labourers +are few. This must continue to be so as long as Geology shall continue +to be viewed in public estimation (in England at least) as a fashionable +toy, that everyone who has been to school is supposed capable of +handling; and until all who profess to be geologists shall have learnt +that, to make sound progress, they must first become mathematicians, +physicists and chemists.</p> + +<p>It is to the general imperfect knowledge of these sciences amongst +geologists that speculative errors show such vitality, and that Geology +makes such poor progress towards becoming the interpretation of the +world as a machine (<i>Erdkunde</i>).</p> + +<p>It is for the same reason that Seismology and Vulcanology make little +progress; the first cannot be pursued beyond its present boundaries, nor +can even its present position be understood or explained by anyone +unfamiliar with the laws of wave motion, of all classes of waves; and it +would be easy to show, by quoting from various British or foreign +text-books on Geology, how extremely imperfect is the grasp of some of +the authors upon the subject of earthquake-wave motion, even such as +they admit and endeavour to explain and <span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span>apply: in fact, many geologists +appear never to have framed to themselves any clear idea of what <i>is</i> a +wave of any sort, liquid or elastic. The general silence as to seismic +theory of French geological writers is remarkable, to whatever cause +attributable. It has been said that French philosophers show themselves +little disposed to acknowledge or to follow the lead of their foreign +compeers in any branch of science. If this be true, or in so far as it +may be so, it is unworthy of French science, which has such boundless +claims upon our homage. I am disposed to attribute the fact in this case +to other circumstances; and, amongst these, to the small extent to which +our language is known amongst French scientific men.</p> + +<p>Germany has shown more desire to cultivate this branch of science. +Although, as yet, the distinct enunciation of its fundamental principles +has but sparsely found its way into her text-books, several able +monographs, such as those of Schmidt and of Httinger, prove how +completely some of her philosophers have mastered and how well applied +them. The men of science of Northern Italy, amongst whom so many +glorious names are to be found on the roll of discovery, have shown +themselves quite alive to the importance of Seismology; and I know of no +more clear, exact and popular exposition of its principles and +application, and of its cosmical relations, than is to be found in a +small volume by Professor Gerolamo Boccardo, published at Genoa in 1869, +entitled <i>Sismopirologia Terremoti, Vulcani e lente oscillazione del +suolo, saggio di una teoria di Geographia Fisica</i>.</p> + +<p><span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span></p><p>My object, so far, has been to mark the progress of ascertained +theoretic notions as to Seismology. I have, therefore, passed without +notice many speculative monographs, and the treatment upon Earthquakes, +whether speculative or historical, and however able, that constitutes a +prominent feature of nearly all systematic works on Geology.</p> + +<p>That which may be at present viewed as achieved and certainly +ascertained in theoretic Seismology is the clear conception of the +nature of earthquake motion; the relations to it of great sea or other +water wave commotions; the relations to it of sound waves—as to which, +however, more remains to be known; and the relations of all these to +secondary effects, tending in various ways to modify more or less the +topographic and other conditions of the land or sea bottom. And in +descriptive Seismology the present distribution of the earthquake bands +or regions of greatest seismic prevalence and activity are tolerably +ascertained, and their connection with volcanic lines and those of +elevation rendered more evident. Viewed alone, nothing can yet be said +to be absolutely ascertained as to the immediately antecedent cause or +causes of the impulse. The function of Earthquake, as part of the +cosmical machine, has become more clear, as the distinctive boundaries +between Earthquake and permanent elevation of the earth have been made +evident; and it has been seen that Earthquake, however contemporaneous +occasionally with permanent elevation, is not the cause, though it may +be one of the consequences of the same forces which produce elevation; +and thus, that an infinite <span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span>number of Earthquakes, however violent, and +acting through however prolonged a time, can never act as an agent of +permanent elevation, unless, indeed, on that minute scale in which +surface elevation may arise from secondary effects, like that of the +Ullah Bund.</p> + +<p>Much remains to be done, and much may be expected even from the +continuation, if done in a systematic and organised manner, of the +statistic record of Earthquakes in connection with those other branches +of cosmical statistics, Climatology, Meteorology, Terrestrial Magnetism, +etc., the observation of which is already, to a certain extent, +organised over a large portion of the globe.</p> + +<p>And now let us look back for a moment to ask, How, by what mental path +of discovery, have we arrived at what we have passed in review?</p> + +<p>The facts of Earthquakes have been before men for unknown ages "open +secrets," as Nature's facts have been well called; "but eyes had they +and saw not." Facts viewed through the haze of superstition, or of +foregone notions of what Nature <i>ought</i> to do, cease to be facts. When, +after the great Calabrian Earthquake of 1783, the Royal Academy of +Naples sent forth its commission of its learned members to examine into +the effects, they had spread around them in sad profusion all that was +necessary to have enabled them to arrive at a true notion of the nature +of the shock, and thence a sound explanation of the varied and great +secondary effects they witnessed, and of which they have left us the +records in their Report, and the engravings illustrative of it. But we +look in vain for any light; the things seen, often with distortion or +exaggeration, are <span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span>heaped together as in the phantasmagoria of a wild +and terrible dream, from which neither order nor conclusion follow.</p> + +<p>Why was this? Why were these eminent <i>savants</i> no more successful in +explaining what they saw than the ignorant peasants they found in the +Calabrian mountains?</p> + +<p>Because physical science itself was not sufficiently advanced, no doubt; +but also because they had no notion of applying such science as they +had, to the very central point itself of the main problem before them, +freed from all possible adventitious conditions, and so, as it were, +attacking it in the rear. How different might have been the result of +their labours, had they begun by asking themselves, What is an +earthquake? Can we not try to find out what it <i>is</i> by observing and +<i>measuring</i> what it has done? We see the converse mode of dealing with +Nature in Torricelli. "Nature abhors a vacuum," was told him, as the +wisdom of his day. Possibly: but her abhorrence is limited, for I find +it is <i>measured</i> by the pressure of a column of water of thirty-four +feet in height. We need not pursue the story with Pascal, up to the top +of the Puy de Dme.</p> + +<p>This lesson is instructive generally to all investigators, and +particularly here; for Vulcanology, to which we are about now to turn, +has occupied until almost to-day much the same position that Seismology +did in those of the Neapolitan Commissioners.</p> + +<p>Whole libraries have been written with respect to it dealing with +<i>quality</i>, but <i>measure</i> and <i>quantity</i> remain to be applied to it.</p> + +<p><span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span></p><p>To a very preponderant class in the civilised world no knowledge is of +much interest or value that does not point to what is called a +"practical result," one measurable into utility or coin. I do not stop +to remark as to the bad or as to certain good results of this tendency +of mind; but I may venture to point out to all, that the exact knowledge +of the nature of earthquake motion, even during the short time that it +has become known, has not been barren in results absolutely practical +and utilitarian. The minute investigation of the destruction of +buildings, etc., and the deductions that have been made as to the +relations between the form, height, materials, methods of building, +combination of timber and of masonry, and many other architectural or +constructive conditions, have made it certain now that earthquake-proof +houses and other edifices can be constructed with facility, and at no +great increase, if any at all, of cost. I can affirm that there is no +physical necessity why in frequently and violently shaken countries, +such as Southern Italy or the Oriental end generally of the +Mediterranean, victims should hereafter continue by thousands to be +sacrificed by the fall of their ill-designed and badly built houses.</p> + +<p>Were a "Building Act" properly framed, put in force by the Italian +Government in the Basilicatas and Capitanata, etc., so that new houses +or existing ones, when rebuilt, should be so in accordance with certain +simple rules, a not very distant time can be foreseen when Earthquakes, +passing through these rich and fertile but now frequently sorely +afflicted regions, should come and go, having left but little trace of +ruin or <span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span>death behind. Some disasters there must always be, for we +cannot make the flanks of mountains, nor the beds of torrents, etc., +always secure; but the main mortality of all Earthquakes is in the +houses or other inhabited buildings. Make these proof, and the wholesale +slaughter is at an end.</p> + +<p>The principles we have established have been thus practically applied in +another direction. The Japanese Government, with the keen and rapid +perception of the powers inherent in European science which +characterises now that wonderful people, has commenced to illuminate its +coasts by lighthouses constructed after the best European models. But +Japan is greatly convulsed by earthquakes, and lighthouses, as being +lofty buildings, are peculiarly liable to be destroyed by them.</p> + +<p>The engineer of the Japanese Government for these lights, Mr. Thomas +Stevenson, C.E. (one of the engineers to the Commissioners of Northern +Lights), was instructed to have regard, in the design of those +lighthouses, to their exposure to shock. I was consulted by Mr. +Stevenson as to the general principles to be observed; and those +edifices have been constructed so that they are presumedly proof against +the most violent shocks likely to visit Japan; not, perhaps, upon the +best possible plan, but upon such as is truly based upon the principles +I have developed. Mr. Stevenson has published some account of their +construction.</p> + +<p>The earthquake regions of South America might with incalculable benefit +apply those ideas; and, indeed, they have been, to some extent, already +applied by my friend, Mr. William Lloyd, Member of the <span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span>Institution of +Civil Engineers, to the New Custom Houses constructed from his designs +at Valparaiso.</p> + +<p>As one of these utilitarian views, and an important one, it will occur +to many to ask—Can the moment of the occurrence or the degree of +intensity of earthquake shock be predicted, or is it probable that at a +future day we may be able to predict them? At present, any prediction, +either of the one or the other, is impossible; and those few who have +professed themselves in possession of sufficient grounds for such +prediction are deceivers or deceived. Nor is it likely that, for very +many years to come, if ever, science shall have advanced so as to render +any such prediction possible; but it is neither impossible nor +improbable that the time shall arrive when, within certain, perhaps +wide, limits as to space, previous time, and instant of occurrence, such +forewarnings may be obtainable.</p> + +<p>Earthquakes, like storms and tempests, and nearly all changes of +weather, are not periodic phenomena, nor yet absolutely uncertain or, so +to say, accidental as to recurrence.</p> + +<p>They are quasi-periodic, that is to say, some of their conditions as to +causation rest upon a really periodic basis, as, for example, the +recurrence of storms upon the periodic march of the earth, and sun and +moon, etc., and the recurrence of Earthquakes upon the secular cooling +of our earth; but the conditions in both are so numerous and complicated +with particulars, that we cannot fully analyse them—hence, cannot +reduce the phenomena to law, and so cannot predict recurrence. <span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span>Yet +storms and tempests—which were, along with pestilences and Earthquakes, +amongst the natural phenomena which Bishop Butler deemed in his own day +impossible of human prediction—have already, through the persistent and +systematised efforts of meteorological observers, become to a certain +extent foreseeable; and medical science assures us that it has rendered +that, though to a much less degree of probability, true of pestilences.</p> + +<p>We may, therefore, give the utilitarian some hope, that if he will help +us along—who value our accessions of knowledge primarily upon a +different standard to his—in our talk of discovery, our posterity, in a +century or two hence, may not improbably possess the advantage of being +able, in some degree, to predict their Earthquakes. I fear the +inducement will go but a small way with the utilitarian generation, +whose bent tends much towards asking, "What has posterity ever done for +them?"</p> + +<p>But though we cannot as yet predict the time when an Earthquake may take +place in any locality, we can, on mixed statistic and dynamic grounds, +in many cases state the limits of probable violence of the next that may +recur. For example, the three shafts of marble columns of the Temple of +Serapis, at Pozzuoli, each of about 41<span class="frac"><sup>1</sup>/<sub>2</sub></span> feet in height, and 4 feet 10 +inches in diameter at the base, remain standing alone, since they were +uncovered, in the year 1750.</p> + +<p>Now, as we can calculate exactly what velocity of earthquake-wave motion +would be required to overset these, we are certain that, during the last +one hundred and twenty-two years, the site of the Temple, and we <span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span>may +say Naples and the Phlegran fields generally, have never experienced a +shock as great as the very moderate one that would overset these +columns. A shock whose wave particle had a horizontal velocity of only +about 3<span class="frac"><sup>1</sup>/<sub>2</sub></span> feet (British) per second would overturn these columns; +which is only about one-fourth the velocity (within the meizoseismic +area) of the great shock of 1857, that produced wide-spread destruction +in the Basilicatas, and not enough to throw down any reasonably +well-built house of moderate height.</p> + +<p>Naples, so far as Earthquake is concerned, whether coming from the +throes of Vesuvius or elsewhere, has a pretty good chance of safety. She +may possibly (though not probably) be some day smothered in ashes; but +is in little danger of being shaken to the earth. During this time there +have been taking place, larger eruptions of Vesuvius and earthquake +shocks from other centres, together probably about the same number of +times as the numbers of those years, when those columns have been more +or less shaken.</p> + +<p>We may therefore affirm that the probability (on the basis of this +experience <i>only</i>) is, say 120 to 1, that the next shock, whether +derived from Vesuvius, or elsewhere, that may shake Pozzuoli, will be +one less in power than would be needed to overturn the shafts of the +Temple of Serapis there.</p> + +<hr class="tb" /> + +<p>Let us now turn to the second branch of our subject—viz., +Vulcanology—upon which, as yet, we have secured less firm standing +ground than we have seen we possess <span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span>in Seismology, for which reason we +took that first into consideration.</p> + +<p>It is the part of Vulcanology to co-ordinate and explain all the +phenomena of past or present times visible on our globe which are +evidences of the existence and action, whether local or general, of +temperatures within our globe greatly in excess of those of the surface, +and which reach the fusing points of various mineral compounds as found +arriving, heated or fused, at the surface.</p> + +<p>The stratigraphic geologist sees that such heated or fused masses have +come up from beneath, throughout every epoch that he can trace; but he +cannot fail to discern more or less a change in the order or character +of those outcomings, as he traces them from the lowest and oldest +formations to those of the present day. He sees immense outpourings of +granitoid or porphyrytic rocks that have welled up and overflowed the +oldest strata—huge dykes filling miles of fissures that had been +previously opened for the reception of the molten matter that has filled +them, and often passing through those masses of previously outpoured +rock; later he sees huge tables of basaltic rock poured forth over all. +One grand characteristic common to all these—commonly called plutonic +products—being that, whether they were poured forth over the surface or +injected into cavities in other rocks, the movements of the fused +material were, on the whole, hydrostatic and <i>not explosive</i>.</p> + +<p>At the present day, whatever other evidences we have of high temperature +below our globe's surface, that which primarily fixes the eye of the +geologist is the <span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span>Volcano, whose characteristic, as we see it in +activity, <i>is explosive</i>. But though there is this great characteristic +difference between the plutonic and the volcanic actions and their +products, the two, when looked at largely, are seen so to inosculate, +that it is impossible not to refer them to an agency common to both, +however changed the modes of its action have been between the earliest +epochs of which traces are presented to us and the present day.</p> + +<p>To us little men, who, as Herschell has well said, in referring to the +methods of measuring the size of our globe, "can never see it all at +once, but must creep like mites about its surface," the Volcano, in the +stupendous grandeur of its effects, tends to fix itself in our minds in +exaggerated proportions to its true place in the cosmic machine; and, in +fact, nearly all who have sought to expound its nature and mode of +origination have occupied themselves far too exclusively with describing +and theorising upon the strange and varied phenomena which the volcanic +cone itself and its eruptions present, and too often, in the splendour +and variety of these, have very much lost sight of what ought to be the +centre-point of all such studies, namely, to arrive at some sound +knowledge of what is the <i>primum mobile</i> of all these wonderful efforts. +Nor has the distinction been very clearly seen between the main +phenomena presented at and about volcanic active mouths, which can be +employed to elucidate the nature of the causation at work far below, and +those most varied and curious, and in other respects most pregnant and +instructive phenomena, mechanical and chemical, <span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span>which are called into +action in and by the ejected matter of the volcanic cone after its +ejection. It can help us but little or very indirectly, in getting at a +true conception of the nature and source of the heat itself of the +Volcano, to examine, for example, all the curious circumstances that are +seen in the movements and changes in the lava that has already flowed +from its mouth; but it would be of great importance if we can ascertain, +by any form of observation around the cone, from what depth it has come, +or at what depth the igneous origin lies.</p> + +<p>The physician, endeavouring to ascertain the real nature of small-pox or +measles, will scarcely make much progress who, however curiously or +minutely, confines his attention to the pustules that he sees upon the +skin.</p> + +<p>Yet the Volcano, or rather all volcanic activity as now operative upon +our globe, is, as it were, an experiment of Nature's own perpetually +going on before us, the results of which, if well chosen—that is, as +Bacon says, by keeping to the main and neglecting the accidents—can, +when colligated and correctly reasoned upon, in relation to our planet +as a whole, give us the key to the enigma of terrestrial Vulcanicity in +its most general sense, and at every epoch of our world's geognostic +history, and show us its true place and use in the cosmical machine. Let +us glance at the history of past speculation on this subject, from which +so little real knowledge is to be derived, and then at the salient facts +of Vulcanology as now seen upon our earth, and finally see if we can +connect these with other great cosmical <span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span>conditions, so as to arrive at +a consistent explanation in harmony with all.</p> + +<p>We gain nothing absolutely from the knowledge of the so-called +"ancients" as to Volcanoes in Europe at least, where alone historic +records likely to refer to them exist. The Volcanoes of Europe are few +and widely scattered. The Greeks saw but little of them, and the Romans +were all and at all times most singularly unobservant of natural +phenomena.</p> + +<p>Csar never mentions the existence in France of the Volcanoes of +Auvergne, so much like those he must have seen in Italy and Sicily; and +Roman writers pass in silence that great volcanic region, though +inhabited by them, and their language impressed upon the places, as +Volvic (<i>volcano-vicus</i>) seems with others to indicate; and though there +is some reason to believe that one or other of the Puys was in activity +within the first five hundred years of our epoch, the notices which +Humboldt and others have collected as from Plato, Pausanius, Pliny, +Ovid, etc., teach nothing.</p> + +<p>Whatever of mere speculation there may have been, volcanic theory, or +what has passed for such, there was none before 1700, when Lmry +brought forward a trivial experiment, the acceptance of which, even for +a moment, as a sufficient cause for volcanic heat (and it retarded other +or truer views for years), we can now only wonder at. Breislak's origin, +in the burning of subterranean petroleum or like combustibles, was +scarcely less absurd than Lmry's sulphur and iron filings.</p> + +<p>Davy, in the plenitude of his fame, and full of the <span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span>intense chemical +activities of the metals of the alkalies which he had just isolated, +threw a new but transient verisimilitude upon the so-called chemical +theory of Volcanoes, by ascribing the source of heat to the oxidation of +those metals assumed to exist in vast, unproved and unindicated masses +in the interior of the earth. But Davy had too clear an intellect not to +see the baseless nature of his own hypothesis, which in his last work, +the "Consolations in Travel," he formally recanted; and it only survived +him in the long-continued though unconvincing advocacy of Dr. Daubeny. +So far, the origin of the heat had been sought always, in the crude +notion of some sort of <i>fuel consumed</i>, whether that were petroleum or +potassium and sodium; but as no fuel was to be found, nor any indicated +by the products, so far as known, of the volcanic heat, so what has been +called the mechanical theory, in a variety of shapes, took its place.</p> + +<p>This, in whatever form, takes its lava and other heated products of the +volcano ready made from a universal ocean of liquid material, which it +supposes constitutes the interior or nucleus of our globe, and which is +only skinned over by a thin, solid crust of cooled and consolidated +rock, which was variably estimated at from fourteen to perhaps fifty +miles in thickness. Here was a boundless supply of more than heat, of +hot lava ready made, the existence of which at these moderate depths the +then state of knowledge of hypogeal temperature, which was supposed to +go on increasing with depth at the rate of about 1 Fahrenheit, for +every thirty or forty feet, seemed quite to sustain.</p> + +<p><span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span></p><p>The difficulty remained, how was this fiery ocean brought to the +surface or far above it? To account for this two main notions prevailed, +and, indeed, have not ceased to prevail. Some unknown elastic gases or +vapour forced it up through fissures or rents pre-existent, or produced +by the tension of the elastic and liquid pressure below.</p> + +<p>The form in which this view took most consistency, and approaching most +nearly to truth, finds the elastic vapour in steam generated from water +passed down through fissures from the sea or from the land surface. But +to this the difficulty was started, that fissures that could let down +water would pass up steam. The objection, when all the conditions are +adequately considered, has really no weight; and it has been completely +disposed of, since within a few years it has been proved that capillary +infiltration goes on in all porous rocks to enormous depths, and that +the capillary passages in such media, though giving free vent to +water—and the more as the water is warmer—are, when once filled with +liquid, proof against the return through them of gases or vapours. So +that the deeply seated walls of the ducts leading to the crater, if of +such material, may be red hot and yet continue to pass water from every +pore (like the walls of a well in chalk), which is flushed off into +steam that cannot return by the way the water came down, and must reach +the surface again, if at all, by the duct and crater, overcoming in its +way whatever obstructions they may be filled with.</p> + +<p>And this remarkable property of capillarity sufficiently <span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span>shows how the +lava—fused below or even at or above the level of infiltration—may +become interpenetrated throughout its mass by steam bubbles, as it +usually but not invariably is found to be.</p> + +<p>Nor is it difficult to see such a mechanism between volcanic ducts and +fissures conveying down water, as large and open pipes, for a large part +of their depth, as shall bring down water to foci of volcanic heat, +without the power of the water flowing back except as steam and through +the crater.</p> + +<p>Indeed, the facts known as to geysers, and those of half-drowned-out +Volcanoes such as Stromboli—whose action is intermittent just as much +as that of a geyser—show that this is not merely probable. There is, +therefore, no need for the hypothesis of those who have supposed all the +huge volumes of steam blown off from Volcanoes in eruption to come from +vesicular water pre-existent in the minute cavities of crystalline or +other rocks before their fusion into lava: a fact not proved for many +classes of rock, and for none in sufficient quantity to account for the +vast volume of steam required and for the irregularity of its issue.</p> + +<p>It is rather to anticipate, but I may state at once that, so far as the +admission of superficial waters to the interior, and to any depth to +which fissures or dislocation can extend, I believe no valid physical or +mechanical difficulties exist, taking into account <i>all</i> the conditions +that may come into play together.</p> + +<p>Another set of views has been suggested and supported by various +writers, which proposes to account for the rise of lava on purely +hydrostatic principles. The <span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span>solid crust, fractured into isolated +fragments by tensions due to its own contraction, is supposed to sink +into the sea of lava on which it floats; and much ingenuity has been +expended in imagining the mechanism by which, in places, the liquid +matter is supposed to rise <i>above</i> the surface of the crust.</p> + +<p>I have no space for discussing these views further than to assert that, +in the existing state of our globe, and even admitting a solid crust of +only 60,000 metres thick, dislocation of the crust by <i>tension</i> is not +possible. The solid crust of our globe, as I hope we shall see further +on, is not in a state of tension, and has not been so since it was +extremely thin, a mere pellicle as compared with the liquid nucleus, but +is, on the contrary, in a state of <i>tangential compression</i>.</p> + +<p>However tenable, in other respects, may be the volcanic theory which +rests upon the assumption of a very <i>thin</i> crust and a universal ocean +of fused rock beneath, it fails wholly to explain many of the most +important circumstances observable as to the distribution and movements +of existing Volcanoes on our globe.</p> + +<p>It affords no adequate explanation of the configuration of the lines of +Volcanoes, nor of their occurrence in the ocean bed, nor of their +existence in high latitudes, near the Poles, where, no matter how or at +what rate our globe cooled from liquidity, the crust must be thickest; +nor of the independence of eruptive action of closely adjacent volcanic +vents; nor of the non-periodicity, the sudden awakening-up to activity, +the as sudden exhaustion, the long repose, the gradual decay of action +<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span>at particular vents, and of much more that might be stated and +sustained as difficulties left by that theory unexplained, or that are +of a nature even opposed to it.</p> + +<p>The researches of the last few years have, however, as it appears to me, +rendered any theory that demands as its postulates a <i>very thin crust</i>, +and a universal liquid nucleus beneath it, absolutely untenable.</p> + +<p>Without attaching any importance to the arguments of Mr. Hopkins, based +upon precession and nutation, it appears to me, on various other +grounds, some of which have been urged by Sir William Thompson, that the +earth's solid crust is not a thin one, at least not thin enough to +render it conceivable that water can ever gain admission to a fluid +nucleus, if any such still exist, situated at so great a depth; and +without such access we can have no Volcano. It is not necessary to go to +the extent of a crust of 800 or 1,000 miles thick: with one of half the +minor thickness, I believe it may be proved, on various grounds, +hydraulic amongst others, that neither water could reach the nucleus, +nor the liquid matter of the nucleus reach the surface. Mr. Hopkins +having proved to his own satisfaction an enormous thickness for the +crust, and seeing clearly the difficulties that this involved to the +generally accepted volcanic theory, and having no other to substitute +for it, fell back upon that most vague and weak notion of the existence +of isolated lakes of liquid rock, existing at comparatively small depths +beneath the earth's surface within the solid and relatively cold crust, +each supplying its own Volcano, or more than one, with ready-made lava. +<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span>What is to produce these lakes of fused matter in the midst of similar +solidified matter? what is perpetually to maintain their fluidity in the +midst of solid matter continually cooling? what has given them their +local position? why near or less near the surface? what should have +arranged them in directions stretching in some cases nearly from Pole to +Pole?</p> + +<p>Surely this creation of imaginary lakes, merely because it happens to +fit the vacant chink that seems needed to wedge up a falling theory, is +an instance of that abuse of hypothesis against which Newton so +vehemently declaims—"<i>Hypotheses non fingo.</i>"</p> + +<p>Hypothesis, to be a philosophic scaffolding to knowledge, must, as +Whewell has said, "be close to the facts, and not merely connected with +them by arbitrary and untried facts." Yet this appears accepted by Lyell +(10th edition, Vol. II., p. 227, and elsewhere); by Phillips +("Vesuvius," pp. 331, 332); by Scrope, if, as I hope, I mistake him not +("Volcanoes," pp. 265, 307-8); though none of these excellent +authorities seem either quite clear or quite satisfied with the notion; +and in the very passage referred to, Lyell <i>may</i> have possibly a much +more philosophic notion in view, where he says: "It is only necessary, +in order to explain the action of Volcanoes, to <i>discover some cause +which is capable of bringing about such a concentration of heat as may +melt one after the other certain portions of the solid crust</i>, so as to +form seas, lakes or oceans of subterraneous lava." (Vol. II, pp. 226, +227). If by this is meant, that all that is needed to complete a true +theory of volcanic action is to discover <i>an adequate cosmical cause for +the heat</i>—that <span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span>is to say, a prime mover to which all its phenomena may +be traced back, which shall be at once reconcilable with the conditions +of our planet as a cooling mass in space and with facts of Vulcanology +as they are now seen upon it—then I entirely agree with it.</p> + +<p>It has been my own object to endeavour to discover and develope that +adequate cause in a Paper "On Volcanic Energy, an Attempt to develope +its True Nature and Cosmical Relations," read (in abstract) before the +Royal Society of London ("Proceedings, Royal Society," Vol. XX., May, +1872), and now (October, 1872) under consideration of Council with a +view to publication.</p> + +<p>I propose concluding this review of the progress of Vulcanology (in +which I have had to limit myself to reviewing merely the chief stages of +advance towards knowledge of the nature and origin of volcanic heat +itself, and have had to pass without notice the vast and important mass +of facts and reasonings collected by so many labourers as to its visible +phenomena and products, and the still greater mass of speculation, good +and bad, on every branch of the subject), by giving a necessarily very +brief and imperfect sketch of my own views as in that Paper in part +developed. It will first be necessary to retrace our steps a little, in +order to gain such a point as shall afford us a fuller view of the whole +problem before us.</p> + +<p>It is not necessary to dilate, even did space allow, upon the many +points which bind together Earthquakes and Volcanoes as belonging to the +play of like forces. These are generally admitted; and in various ways, +more <span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span>or less obscure, geologists generally have supposed some relations +between these and the forces of elevation, which have raised up mountain +chains, etc.</p> + +<p>No one, however, that I am aware of, prior to myself, in the Paper just +alluded to, has attempted to show, still less to prove upon an +experimental basis, that all the phenomena of elevation, of volcanic +action, and of Earthquakes, are explicable as parts of one simple +machinery—namely, the play of forces resulting from the secular cooling +of our globe. We have seen that, on the whole, both Earthquakes and +Volcanoes follow along the great lines of elevation of our surface. Any +true solution of the play of forces which has produced any one of those +three classes of phenomena must connect itself with them all, and be +adequate to account for all. And this would have earlier been seen, had +geologists generally framed for themselves any correct notions of the +mechanism of elevation itself, and seen its real relation with the +secular cooling of our planet. But the play of forces resulting from +this secular cooling has never, until very recently, been adequately or +truly stated. The arbitrary assumption and neglect of several essential +conditions by La Place, in his celebrated Paper "On the Cooling of the +Earth," in the fifth volume of the "Mcanique Cleste," and the +arbitrary and unsustainable hypothesis of Poisson upon the same subject, +have tended to retard the progress of physical Geology as to the nature +of elevation: the first, by leaving the geologist in doubt as to whether +our globe were cooling at all; the second, by suggesting distorted +notions as to the mode of its cooling and consolidation. On the other +hand, neither geologists <span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span>nor mathematicians generally have framed for +themselves any clear notions of the mechanism of elevation. Had a true +conception been formed of the forces and interior movements brought +necessarily into operation by the secular cooling of the globe, +geologists could scarcely have failed to see that their notion as to the +way and direction in which the forces producing elevation have actually +acted could not, if arising from refrigeration, be those which they have +almost universally supposed, namely—some force acting vertically +upwards, <i>i.e.</i>, radially from the centre of the sphere. Had geologists +only looked at Nature with open eye, they must have seen that mountain +ranges, and elevations generally (exclusive of volcanic cones), +presented circumstances absolutely incompatible with their having been +thrust up by any force <i>primarily</i> acting in the direction of a radius +to the spheroid.</p> + +<p>Yet this is the erroneous notion of the mechanism of elevation which to +the present hour prevails amongst geologists, so far as they in general +have framed to themselves any distinct idea of such mechanism at all.</p> + +<p>Thus, only to cite two examples from recent authors of justly high +reputation. Lyell says of the probable subterranean sources, whether of +upward or downward movement, when permanently uplifting a country, and +in reference to the crumpling of strata on mountain flanks by lateral +pressure, it would be rash to assume these able to resist a power of +such stupendous energy, "<i>if its direction, instead of being vertical</i>, +happened to be oblique or horizontal." This is somewhat vague—and I +trust I do not mistake or misrepresent the illustrious <span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span>author—yet it +is the most explicit expression I can find in the "Principles of +Geology" as to his notion of the primary direction of elevatory force +(Edit. 10, Vol. I., p. 133). That Mr. Scrope's idea is that only of +primary radial or vertical direction of such forces, is apparent on +inspecting his Diagram No. 64 ("Volcanoes," p. 285), and in the use of +the words, "an axial wedge of granite," which, on the next page, we find +is "liquefied granite;" and if we read on to page 294, and refer also to +pages 50 and 51, I believe there can be no doubt that <i>vertical</i> or +<i>direct up-thrust</i> is the author's notion of the primary direction of +all forces of elevation. The true nature of these forces was, however, +clearly seen and most justly stated by Constant Prevost ("Compt. Rend.," +Tome XXXI., 1850, and "Bulletin de la Socit Golog. de France," Tome +II., 1840) as consisting, not in forces of some unknown origin acting +primarily in the vertical, but in <i>tangential pressures acting +horizontally, and resolved by mutual pressures at certain points into +vertical resultants</i>. These Prevost rightly attributed to the +contraction of the earth's solid crust. The same idea has been adopted +by Elie de Beaumont as the true mechanism of the elevation of mountain +ranges; and although De Beaumont's views as to the thinness he assigns +to the solid and contracting crust, and his strange deduction as to the +parallelism of contemporaneous mountain chains uplifted by its spasmodic +action along certain lines, may be untenable, his notion generally as to +the play of forces producing mountain elevation is much more nearly +correct.</p> + +<p>Mr. Hopkins's notion is simply that of the geologists. <span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span>Anyone who reads +his well-known papers on elevation and the formation of fissures, etc., +must see that he views all elevatory forces as of liquids or +quasi-liquids forced up and acting primarily <i>vertically</i> upon the +strata above them, and that these strata are not under tangential +compression, but under tension. Hence the mathematical deductions +contained in those papers as to the directions in which elevatory forces +act, and in which fissures are formed by them, are not in any way a +setting forth of such facts as occur in Nature, and, much attention as +they have attracted, can only now be viewed as exercises of mathematical +skill misapplied, because based upon data not to be found in Nature. In +fact, those papers do but misrepresent Nature, and, like many other +mathematical investigations based on untrue or insufficient data, have +tended to retard knowledge.</p> + +<p>The views which I have put forward in the Paper I have referred to, read +to the Royal Society, recapitulated in skeleton, so to say, are as +follows. Omitting those portions which treat of our globe from the +period of the first liquefaction out of a nebulous condition, and of the +earliest stages of the cooling by radiation into space, when the crust +was extremely thin, and of the deformation of the spheroid as one of the +first effects of its contraction, and through that the general shaping +out of continents and ocean beds; I have endeavoured to show that the +rate of contraction of the crust, while very thin, exceeded that of the +large fluid nucleus supporting it, and so gave rise to <i>tangential +tensions</i> in the crust, and fracturing it into segments; next, that as +the crust thickened, these <i>tensions</i> were <span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span>gradually converted into +<i>tangential pressures</i>, the contraction of the nucleus now beginning to +exceed (for equal losses of heat) that of the crust through which it +cooled. At this stage these tangential pressures gave rise to the +<i>chief</i> elevations of mountain chains—not by liquid matter by any +process being injected from beneath vertically, but by such pressures, +mutually reacting along certain lines, being resolved into the vertical, +and forcing upwards more or less of the crust itself. The great outlines +of the mountain ranges and the greater elevation of the land were +designated and formed during the long periods that elapsed in which the +continually increasing thickness of crust remained such that it was +still, as a whole, flexible enough, or opposed sufficiently little +resistance to crushing, to admit of this uprise of mountain chains by +resolved tangential pressures. I have shown that the simple mechanism of +such tangential pressures is competent to account for all the complex +phenomena both of the elevations and of the <i>depressions</i> that we now +see on the earth's surface (other than continents and ocean beds), +including the production of gaping fissures (in directions generally +orthogonal to those of tangential pressure). And as our earth is still a +cooling body, and the crust, however now thicker and more rigid, is +still incapable of sustaining the tangential pressures to which it is +now exposed, so I by no means infer that slow and small (relatively) +movements of elevation and depression may not be still and now going on +upon the earth's surface; in fact all the phenomena of elevation and +depression, rending, etc., which at a much remoter epoch acted <span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span>upon a +much grander and more effective scale. So that, for aught my views say +to the contrary, all the mountain chains in the world may be possibly +increasing in stature year by year, or at times; but in any case at a +rate almost infinitesimally small in its totality over the whole earth +to that with which their ridges were originally upreared.</p> + +<p>But the thickness of the earth's crust—thus constantly added to, by +accretion of solidifying matter from the still liquid or pasty nucleus, +as the whole mass has cooled—has now assumed such a thickness as to be +able to offer a too considerable resistance to the tangential pressures, +to admit of its giving way to any large extent by resolution upwards; +yet the cooling of the whole mass is going on, and contraction, though +unequal, both of thick crust and of hotter nucleus beneath also, whether +the latter be <i>now</i> liquid or not. Were the contraction, lineal or +cubical, for equal decrements or losses of heat, or in equal +times—equal both in the material of the solidified crust and in that of +the hotter nucleus—there could be no such tangential pressures as are +here referred to, at any epoch of the earth's cooling. But in accordance +with the facts of experimental physics, we know that the co-efficient of +contraction for all bodies is greater as their actual temperature is +higher, and this both in their solid and liquid states.</p> + +<p>Hence for equal decrements of heat, or by the cooling in equal times, +the hotter nucleus contracts more than does its envelope of solid +matter.</p> + +<p>The result is now, as at all periods since the signs changed of the +tangential forces thus brought into play—<i>i.e.</i>, since they became +tangential <i>pressures</i>—that the <span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span>nucleus tends to shrink away as it +were from beneath the crust, and to leave the latter, unsupported or but +partially supported, as a spheroidal dome above it.</p> + +<p>Now what happens? If the hollow spheroidal shell were strong enough to +sustain, as a spheric dome, the tangential thrust of its own weight and +the attraction of the nucleus, the shell would be left behind altogether +by the nucleus, and the latter might be conceived as an independent +globe revolving, centrally or excentrically, within a shell outside of +it. This, however, is not what happens.</p> + +<p>The question then arises, Can the solid shell support the tangential +thrust to which it would be thus exposed? By the application to this +problem of an elegant theorem of Lagrange, I have proved that it cannot +possibly do so, no matter what may be its thickness nor what its +material, even were we to assume the latter not merely of the hardest +and most resistant rocks we know anything of, but even were it of +tempered cast-steel, the most resistant substance (unless possibly +iridio-osmium exceed it) that we know anything about. Lagrange has shown +that if P be the normal pressure upon any flexible plate curved in both +directions, the radii of these principal curvatures being ρ' +and ρ'', and T the tangential thrust at the point of +application and due to the force P, then:</p> + +<blockquote> +<p>P = T (1/ρ' + 1/ρ'')</p> +</blockquote> + +<p>When the surface is spherical, or may be viewed as such, ρ' = +ρ'' and</p> + +<blockquote> +<p>P = 2T / ρ or, T = P ρ/2</p> +</blockquote> + +<p><span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span></p><p>In the present case P is for a unit square (taken relatively small and +so assumed as plane) of the shell, suppose a square mile, equal to the +effect of gravity upon that unit, ρ being the earth's radius, +and if we assume the unit square be also a unit in thickness, P is then +the weight of a cubic mile of its material; and if we take (roughly) the +earth's radius as 4,000 miles, the tangential pressure, T, is, on <i>each +face</i> of the cubic mile, equal to</p> + +<blockquote> +<p>(4000/2) P,</p> +</blockquote> + +<p>or equal to the pressure of a column of the same material of 2,000 times +its weight.</p> + +<p>If the cubic mile that we have thus supposed cut out of the earth's +crust at the surface were of the hardest known granite or porphyry, it +would be exposed to a crushing tangential pressure equal to between 400 +and 500 times what it could withstand, and so must crush, even though +only left unsupported by the nucleus beneath, to the extent of <span class="frac"><sup>1</sup>/<sub>400</sub></span> or +<span class="frac"><sup>1</sup>/<sub>500</sub></span> of its entire weight. And what is true here of a mile taken at the +surface, is true (neglecting some minute corrections for difference in +the co-efficient of gravity, etc.) if taken at any other depth within +the thick crust.<a name="FNanchor_F_6" id="FNanchor_F_6"></a><a href="#Footnote_F_6" class="fnanchor">[F]</a></p> + +<p><span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span></p><p>The crust of our earth, then, as it now is, must crush, to follow down +after the shrinking nucleus—if so be that the globe be still cooling, +and constituted as it is; even to the limited extent to which we know +anything of its nature—it must crush unequally, both regarded +superficially and as to depth; generally the crushing lines being +confined to the planes or places of greatest weakness; and the crushing +will not be absolutely constant and uniform anywhere, or at any time, or +at any of those places of weakness to which it will be principally +confined, but will be more or less irregular, quasi-periodic, or +paroxysmal: as is, indeed, the way in which all known material +substances (more or less rigid) give way to a slow and constantly +increasing, steady pressure.</p> + +<p>We have now to ask, <i>How much</i> of this crushing is going on at present +year by year? And the answer to this depends upon what amount of heat +our world is losing into space year by year.</p> + +<p>Geologists who have taken on trust the statement, that La Place has +proved that the world has lost no sensible amount of heat for the last +10,000 years seem generally to suppose that to be a fact; but in reality +La Place has <i>proved</i> nothing of the sort, as those geological teachers +who have echoed the conclusion should have known, had they deciphered +the mathematical argument upon which it has been supposed to rest.</p> + +<p>By application of Fourier's theorem (or definition) to the observed rate +of increment of heat in descending from the geothermal <i>couche</i> of +invariable temperature, and the co-efficients of conductivity of the +rocks of our <span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span>earth's crust, as given by the long-continued observations +made beneath the Observatories of Paris and of Edinburgh, it results +that the annual loss of heat into space of our globe at present is equal +to that which would liquefy into water, at 32 Fahr., about 777 cubic +miles of ice; and this is the measuring unit for the amount of +contraction of our globe now going on. The figures are not probably +exact, for the data are not on a basis sufficiently full or exactly +established as yet; but they are not very widely wrong, and their +precise exactness is not material here. Now, how is this annual loss of +heat (great or small, as we may please to view it) from the interior of +our globe disposed of?</p> + +<p>What does it <i>do</i> in the interior? We have already seen that it is +primarily disposed of by conversion into work; into the work of +diminishing the earth's volume as a whole, and in so doing crushing +portions of the solid surrounding shell.</p> + +<p>But does the transformation of lost heat into the work of vertical +descent, and of the crush as it follows down after the shrinking +nucleus, end the cycle? No. A very large portion of the mechanical work +thus produced, and resolved, as we have seen, into tangential crushing +pressure, is retransformed into heat again in the very act of crushing +the solid material of the shell. If we see a cartload of granite +paving-stones shot out in the dark, we see fire and light produced by +their collision; if we rub two pieces of quartz together, and crush thus +their surfaces against each other, we find we heat the pieces and evolve +light.</p> + +<p>The machinery used for crushing by steam-power, <span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span>hard rocks into road +metal, gets so hot that the surfaces cannot be touched.</p> + +<p>These are familiar instances of one result of what is now taking place +by the crushing of the rocky masses of our cooling and descending +earth's crust, every hour beneath our feet, only upon a vastly greater +scale. It is in this local transformation of work into heat that I find +the true origin of volcanic heat within our globe. But if we are to test +this, so as in the only way possible to decide is it a true solution of +this great problem, we must again ask the question, <i>How much?</i> and to +answer this, we must determine <i>experimentally</i> how much heat can be +developed by the crushing of a given volume, say a cubic mile, of such +rocky materials as we know must constitute the crust of our globe down +to the bottom of the known sedimentary strata, and extending to such +crystalloid rocks as we may presume underlie these. We must also obtain +at least approximately what are the co-efficients of <i>total contraction</i> +between fusion and atmospheric temperature of such melted rocks, basic +and acid silicates, as may be deemed representative of that co-efficient +for the range of volcanic fused products, basalts, trachytes, etc., +which probably sufficiently nearly coincide with that of the whole +non-metallic mass of our globe.</p> + +<p>The first I have determined experimentally by two different methods, but +principally by the direct one of the <i>work</i> expended in crushing prisms +of sixteen representative classes of rock; the specific gravities and +specific heats of which I have also determined.</p> + +<p>If H be the height of a prism of rock crushed to powder by a pressure, +P, applied to two opposite faces, <span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span>which, when the prism has been +reduced to its volume in powder, has acted through a range of H - <i>t</i>, +then</p> + +<blockquote> +<p>P (H - <i>t</i>) / 772</p> +</blockquote> + +<p>is the heat corresponding to the work expended in the crushing, +expressed in British units of heat. The following were the rocks +experimented upon: Caen stone, Portland (both oolites), magnesian +limestone, sandstones of various sorts, carboniferous limestones +(marbles), the older slates (Cambrian and Silurian), basalts, various +granites and porphyries, thus ranging from the newest and least +resistant to the oldest and most resistant rocks. The results have been +tabulated, and are given in detail in my Paper, now in possession of the +Royal Society. The minimum obtained is 331 and the maximum 7,867 British +units of heat developed, by transformation of the work of crushing one +cubic foot of rock. If we apply the results to a thickness of solid +crust of 100 miles (British), of which the upper twenty-one miles +consist of neozoic, newer palozoic, older palozoic and azoic rocks in +nearly equal proportion as to thickness, and the remaining eighty miles +of crystalloid rocks (acid and basic magmas of Durocher) of physical +properties which we may assume not very different from those of our +known granites and porphyries—and which, in so far as they may differ, +would give a still <i>higher</i> co-efficient of work transformed into heat +than I have attributed to them by ranging them as only equal to the +granites, etc.—then we obtain a mean co-efficient for the entire +thickness of crust of 100 miles of 6,472 British units of heat, +developable from each cubic foot of its material, if crushed to powder. +It results from this <span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span>that each cubic mile of the mean material of such +a crust, when crushed to powder, developes sufficient heat to melt 0876 +cubic miles of ice into water at 32, or to raise 7600 cubic miles of +water from 32 to 212 Fahr., or to boil off 1124 cubic miles of water +at 32 into steam of one atmosphere, or, taking the average melting +point of rocky mixtures at 2,000 Fahr., to melt nearly three and a-half +cubic miles of such rock, if of the same specific heat.</p> + +<p>Of the heat annually lost by our globe and dissipated into space, +represented by 777 cubic miles of ice melted, as before stated, the +chief part is derived from the actual hypogeal source of a hotter though +not necessarily fused nucleus, and nearly, if not wholly, is quite +independent of the heat of Vulcanicity, which is developed as a +consequence of its loss or dissipation. But were we to take the extreme +case, and suppose it possible that all the heat the globe loses annually +resulted from the transformation of the work of internal crushing of its +shell, we shall find that the total volume of rock needed to be crushed +in order to produce the required amount of lost heat is perfectly +insignificant as compared with the volume of the globe itself, or that +of its shell. For, as 1270 cubic miles of crushed rock developes heat +equivalent to that required to melt one cubic mile of ice to water at +32, and if we assume the volume of our globe's <i>solid</i> crust to equal +one-fourth of the total volume of the entire globe, 987 cubic miles of +rock crushed annually would supply the whole of the heat dissipated in +that time. But that is less than the <i>one sixty-five millionth</i> of the +volume of the crust only.</p> + +<p>But a very small portion of the total heat annually <span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span>lost by our globe +is sufficient to account for the whole of the volcanic energy of every +sort, including thermal waters, manifested annually upon our earth. In +the absence of complete data, we can only approximately calculate what +is the annual amount of present volcanic energy of our planet. This +energy shows itself to us in three ways: 1. The heating or fusing of the +ejected solid matters at volcanic vents. 2. The evolution of steam and +other heated elastic fluids by which these are carried. 3. The work of +raising through a certain height all the materials ejected. To which we +must add a large allowance for waste, or thermal mechanical and chemical +energy ineffectually dissipated in and above the vents. All these are +measurable into units of heat.</p> + +<p>I have applied this method of calculation to test the adequacy of the +source I have assigned for volcanic heat, in two ways, viz.: 1. To the +phenomena presented during the last two thousand years by Vesuvius, the +best known Volcano in the world; and 2. To the whole of the four hundred +and odd volcanic cones observed so far upon our globe, of which not more +than one-half have ever been known in activity.</p> + +<p>It is impossible here to refer to the details of the method or steps of +these calculations. The result however is, that making large allowances +for presumably defective data, <i>less than one-fourth</i> of the total +telluric heat annually dissipated (as already stated in amount) is +sufficient to account for the annual volcanic energy at present expended +by our globe.</p> + +<p>It is thus represented by the transformation into heat of the work of +crushing about 247 cubic miles of (mean) <span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span>rock, a quantity so perfectly +insignificant, as compared with the volume of the globe itself, as to be +absolutely inappreciable in any way but by calculation; and as its +mechanical result is only the vertical transposition transitorily of +material within or upon our globe, the proportion of the mass of which +to the whole is equally insignificant, so not likely in any way to +produce changes recognisable by the astronomer.</p> + +<p>Space here forbids my entering at all upon that branch of my +investigation which is based upon the experimental results, above +mentioned, of the total contraction of fused rocks: for these, the +original Paper can, I hope, be hereafter referred to. I am enabled, +however, to prove thus how enormously more than needful has been the +store of energy dissipated since our globe was wholly a melted mass, for +the production, through the contraction of its volume, of all the +phenomena of elevation and of Vulcanicity which its surface presents. +And how very small is the amount of that energy in a unit of time as now +operative, when compared with the same at very remote epochs in our +planet's history.</p> + +<p>I have said that if we can find a true cause in Nature for the +origination of volcanic <i>heat</i>, all the other known phenomena, at and +about volcanic vents, become simple. Lavas and all other solid ejecta of +Volcanoes, from all parts of the earth's surface, as well as basalts, +present in chemical and physical constitution close resemblance, and may +be all referred to the melting of more or less fusible mixtures of +siliceous crystalloid rocks with aluminous (slates, etc.) and calcareous +rocks. Their general chemical composition, and the higher or lower +temperatures <span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span>of fusion resulting therefrom, together with the higher or +lower temperatures to which they have been submitted at the different +volcanic foci, determine their difference of flow (under like surface +conditions) and of mineral character after ejection and cooling.</p> + +<p>St. Clair de Ville and Fouqu have shown that the gaseous ejections, of +which steam forms probably 99 per cent., are such as arise from water +admitted to a <i>pre-existent focus of high temperature</i>.</p> + +<p>Whether sea or fresh water is not material, when we bear in mind that +the chemical constituents found in sea water and in natural fresh waters +that have penetrated the soil are, on the whole, alike in kind and only +differ in proportions. But I must pass almost without notice all the +varied and instructive phenomena which are presented by volcanic vents, +for to treat of these at all would be to more than double the size of +this sketch.</p> + +<p>In the source that has been pointed out as that from which volcanic heat +itself is derived, viz., the secular cooling of our globe, and the +effects of that upon its solid shell, we are enabled to point to that +which is the surest test of the truth of any theory—that it not only +enables us to account for all the phenomena, near or remote, but to +predict them. We see here linked together as parts of one grand play of +forces, those of contraction by cooling, producing by <i>direct</i> +mechanical action the elevation of mountain chains, and by their +<i>indirect</i> action, by transformation of mechanical work into heat, the +production of Volcanoes; and both by direct and by indirect action, of +Earthquakes, never previously shown to have thus the physical connection +of one common cause, <span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span>but merely supposed, more or less, to be connected +by their distribution upon our earth's surface.</p> + +<p>We now discern thus the physical cause <i>why</i> Volcanoes are distributed, +viewed largely, linearly, and follow the lines of elevation; we see +equally why their action is uncertain, non-periodic, fluctuating in +intensity, with longer or shorter periods of repose, shifting in +position, becoming extinct here, appearing in new activity or for the +first time there. We have an adequate solution of the before +inexplicable fact of their propinquity, and yet want of connection. We +have an adequate cause for the fusion of rock at local points without +resorting to the baseless hypothesis of perennial lakes of lava, etc.</p> + +<p>For the first time, too, we discern a true physical cause for earthquake +movement, where volcanic energy does not show itself. The crushing of +the world's solid shell, whether thick or thin, goes on <i>per saltum</i> and +at ever-shifting places, however steadily the tangential pressures +producing it may act. Hence crushing <i>alone</i> may be shown to develope +amply sufficient impulse to produce the most violent Earthquakes, +whether they be or be not at a given place or time connected with +volcanic outburst or possible injection, or with tangential pressures, +enough still, in some cases, to produce partial permanent elevation.</p> + +<p>When subterraneous crushing takes place, and the circumstances of the +site do not permit the access of water, there may be Earthquake, but can +be no Volcano; where water is admitted, there may be both.</p> + +<p>And thus we discern why there are comparatively few <span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span>submarine +Volcanoes, the floor of the ocean being, on the whole, +water-tight—"puddled," as an engineer would say, by the huge deposit of +incoherent mud, etc., that covers most of it, and probably having a +thicker crust beneath it than beneath the land.</p> + +<p>We see, moreover, that the geological doctrine of absolute uniformity +cannot be true as to Vulcanicity, any more than it can for any other +energy in play in our world. Its development was greatest at its +earliest stages, when the great masses of the mountain chains were +elevated. It is even now—though as compared to men's experience, and +even to all historic time, apparently uniform and always the same—a +decaying energy.</p> + +<p>The regimen of our planet as part of the Cosmos, which seems to some +absolute (and presented to Playfair no trace of a beginning nor +indication of an end), is not absolute, and only seems to us to be so +because we see so little of it, and of its long perspective in time. +This the now established doctrine of the conservation of energy renders +certain.</p> + +<p>With this source for volcanic heat, too, in our possession, we can look +from our own world to others, and predict within certain limits, which +must widen as our knowledge of the facts of their substance and surface +becomes greater, what have been and what are the developments of +Vulcanicity which have taken place or are occurring in or upon them. +Looking to our own satellite, we see for the first time a sufficient +physical cause for the enormous display of volcanic energy there which +the telescope divulges to us; one which is not to be explained alone by +the commonly made statement of <span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span>the small density of the moon, but by +the fact that as the rate of her cooling from a given temperature, as +compared with that of our earth (apart from questions of the chemical +nature of the two bodies, or of their specific heats, etc.), has been +inversely as their respective masses, and directly as their surfaces, so +has the rate of cooling of the moon been vastly greater than that of the +earth, and the energy due to contraction by cooling more intense and +rapidly developed in our satellite than upon our globe.</p> + +<p>We have thus traced, in meagre and broken outline only—because space +admitted no more—the progress of Science to its existing state as +respects Vulcanicity, in its two branches of Vulcanology and of +Seismology, and pointed out their more intimate relations and points of +connection, and been at length able to refer them, on the sure basis of +physical laws, to one common cause, and that one derived from no +hypothesis, but simply from the postulate of our world as a terr-aqueous +globe cooling in space.</p> + +<p>What I have here advanced with reference to volcanic energy, which +appertains to my own researches, I do not conceal from myself, nor from +the reader, has yet to await the reception generally and the award of +the true men of science of the world.</p> + +<p>That, like every new line of thought which has attempted or succeeded in +supplanting the old, it will meet with opposition, I make no doubt.</p> + +<p>My belief, however, is that in the end it will be found to have added a +fragment to the edifice of true knowledge.</p> + +<p><span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span></p><p>The interpretation which I have given of the nature and origin of +volcanic activity points at once to the function in the Cosmos which it +is its destiny to fulfil. It is the instrument provided for the purpose +of continually preserving the earth's solid shell in a state to follow +down after the descending nucleus. It does this by an apparatus or play +of mechanism whereby the material of the solid shell, locally or along +certain lines, is not only crushed, but the crushed material is blown +out as dust, or expelled as liquid rock from between the walls of the +shell, which are thus enabled to approach each other; and thus, by +relief of the tangential thrusts, to permit the shell to descend, which +it is obvious that crushing alone, unless it extended to the whole mass +of the shell, could not accomplish.</p> + +<p>It is a wonderful example of Nature's mechanism thus to see how simple +are the means by which this end is accomplished. The same inevitable +crush that dislocates the solid shell along certain lines, produces the +heat necessary to expel to the surface the material crushed.</p> + +<p>When attempted to be made the basis for philosophic discovery, "final +causes" are no doubt barren, as Bacon has said; but when we have +independently and by strict methods arrived at a result, we may justly +appeal, as a test of its truth, to its showing itself as plainly +fulfilling a needful end, and, by a distinctly discernible mechanism, +preserving that harmony and conservation which are the obvious law of +the universe.</p> + +<p>As has been said, if I mistake not by Daubeny, John Phillips, by +Herschell, and by myself, the function of the <span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span>Earthquake and the +Volcano is not destructive but, preservative. But we now see that: that +the preservative scope of this function, as respects our earth, is far +wider than what has been previously attributed to it. The Volcano does +not merely throw up new fertile soil, and tend, in some small degree, to +restore to the dry land the waste for ever going on by rain and sea; it +fulfils a far weightier and more imperative task; it—by a mechanism the +power of which is exactly balanced to the variable calls demanded of it, +and which working almost imperceptibly, although in a manner however +terrible its surface-action may at times appear to us little +men<a name="FNanchor_G_7" id="FNanchor_G_7"></a><a href="#Footnote_G_7" class="fnanchor">[G]</a>—prevents at longer intervals such sudden and unlooked-for +paroxysms in the mass of our subsiding earth's shell as would be +attended with wide-spread destruction to all that it inhabit.</p> + +<p>To the popular mind, Volcanoes and Earthquakes are only isolated items +of curiosity amongst "the wonders of the world:" few geologists even +appear to realise how great and important are the relations of +Vulcanicity to their science, viewed as a whole. Yet of Vulcanicity it +is not too much to say, that in proportion as its nature and doctrines +come to be known and understood as parts of the Cosmos, the nearer will +it be seen to lie at the basis of all Physical Geology.</p> + +<hr class="chap" /> +<div class="footnote"><p><a name="Footnote_A_1" id="Footnote_A_1"></a><a href="#FNanchor_A_1"><span class="label">[A]</span></a> For a fuller account of the literature and history of +advancement of human knowledge as to Earthquakes, here merely glanced +at, I must refer to my First Report on the Facts of Earthquakes, +"Reports, British Association, 1850," and to the works of Daubeny, +Lyell, Phillips and others, its <i>complete</i> history remaining yet to be +written.</p></div> + +<div class="footnote"><p><a name="Footnote_B_2" id="Footnote_B_2"></a><a href="#FNanchor_B_2"><span class="label">[B]</span></a> Yet how indistinctly formed were Young's ideas, and +indistinct in the same direction as those of Humboldt, becomes evident +by a single sentence: "When the agitation produced by an Earthquake +extends further than there is any reason to suspect a subterraneous +communication, it is probably propagated through the earth nearly in the +same manner as a noise is conveyed through the air."—<i>Lectures, Nat. +Phil.</i>, Vol. I.</p></div> + +<div class="footnote"><p><a name="Footnote_C_3" id="Footnote_C_3"></a><a href="#FNanchor_C_3"><span class="label">[C]</span></a> The Right Rev. Charles Graves, F.R.S., etc., then Fellow of +Trinity College, Pres. R. I. Acad., and now Bishop of Limerick, on +presentation of the Academy's Cunningham Medal.</p></div> + +<div class="footnote"><p><a name="Footnote_D_4" id="Footnote_D_4"></a><a href="#FNanchor_D_4"><span class="label">[D]</span></a> In this Report, though I have never before referred to it, +and do so now with reluctance, I have always felt that the Author did me +some injustice. The only reference made to my labours, published the +preceding year only, is in the following words: "Many persons have +regarded these phenomena (viz., Earthquakes) as due in a great measure +to vibrations ... and the subject has lately been brought under our +notice, in a Memoir by Mr. Mallet, 'On the Dynamics of Earthquakes,' in +which he has treated it in a more determinate manner, and in more +detail, than any preceding writer" (p. 74). If that Paper of mine be +collated with this Report, it will be, I believe, found that, as +respects the earthquake part, the latter tint parades, in a mathematical +dress, some portions of the general theory of earthquake movements, +previously published by me as above stated. So, also, in the chapter (p. +90) referring to Seismometry, and the important uses to Geology that +might be (and since have been, to some extent) made of it, no mention is +made of those instruments previously proposed by me, nor of my +anticipation of their important uses. This is but too mortifyingly +suggestive of the— +</p> +<blockquote><p>"Pereant qui mea ante mihi dixerunt." </p></blockquote> +<p> +Having left this unnoticed for so many years, and during which the +Author has preceded me to that bourne where our errors to each other +must be forgotten, I should certainly not have now trespassed on the +good rule, <i>De mortuis nil nisi bonum</i>, had I not observed very recently +one amongst other results probably attributable to it. In Professor +Phillips's "Vesuvius," if any one will refer to the passage beginning +"The mechanism of earthquake movement has been investigated by competent +hands. The late eminent mathematician, Mr. Hopkins, explained these +tremors in the solid earth by the general theory of vibratory motion," +etc. (pages 257-259)—I think he must, in the absence of collateral +information, conclude that, not I, but Mr. Hopkins, was the discoverer +of the Theory of Earthquakes as explained by the general theory of +vibratory motion. +</p><p> +Probably my friend, Professor Phillips, had not recently referred to +those Memoirs and Reports of twenty-four years back, and I am thoroughly +convinced that, if he has here perpetuated an injustice, he has done so +unintentionally and unwittingly. +</p><p> +Still, the facts show how true it is that +</p><p> +<span style="margin-left: 2.5em;">"The ill men do lives after them,</span><br /> +<span style="margin-left: 2.5em;">The good they do is oft interred with their bones."</span><br /> +</p> +<p> +And I may venture to ask my friend, should his admirable book reach, as +I doubt not it will, another edition, to modify the passage.</p></div> + +<div class="footnote"><p><a name="Footnote_E_5" id="Footnote_E_5"></a><a href="#FNanchor_E_5"><span class="label">[E]</span></a> Assuming the point of ejection of this block (the crater) +to be 8,000 feet above where it landed, and allowing it as high a +density as admissible, and the angle of projection the best for large +horizontal range, it may be proved that this mass, to reach nine miles +horizontally, would require an initial velocity of projection of from +1,500 to 1,600 feet per second, one as great as that of a smooth-bore +cannon-shot at the muzzle, and perfectly inconceivable to be produced by +a volcano.</p></div> + +<div class="footnote"><p><a name="Footnote_F_6" id="Footnote_F_6"></a><a href="#FNanchor_F_6"><span class="label">[F]</span></a> The Rev. O. Fisher, M.A., F.G.S., in a most interesting and +valuable Paper, "On the Elevation of Mountain Chains by Lateral +Pressure, its Cause, and the Amount of it, with a Speculation on the +Origin of Volcanic Action," read, April, 1868, and published in the +Transactions of the Cambridge Philosophical Society, Vol. XI., Part +III., in 1869, has deduced the necessary crushing of the earth's crust +by a different but closely analogous method. I had not seen this Paper +until after my own was in the hands of the Royal Society. The author's +volcanic views are wholly different from my own, and do not appear to me +equally valid with his notions as to elevation.—R. M.</p></div> + +<div class="footnote"><p><a name="Footnote_G_7" id="Footnote_G_7"></a><a href="#FNanchor_G_7"><span class="label">[G]</span></a> "Magna ista quia parvi sumus"—<span class="smcap">Seneca</span>, "Qus. Nat."</p></div> + + +<p class="center">END.</p> + + +<hr class="chap" /> + +<p><span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span></p> + +<div class="likeheading2">TRANSLATION</div> +<div class="likeheading3">OF</div> +<div class="likeheading2">PROFESSOR PALMIERI'S</div> + +<div class="likeheading3"><i>ACCOUNT OF</i></div> +<h2>THE ERUPTION OF VESUVIUS<br /> +OF<br /> +<i>1871-1872</i></h2> + + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span></p> +<h2><a name="I" id="I"></a>I.<br /> + +ACCOUNT OF THE ERUPTION.</h2> + + +<p>The great and disastrous conflagration of Vesuvius, which took place on +the 26th of April, 1872, was, in my opinion, the last phase of an +eruption which commenced at the end of January, 1871, an account of +which I was unwilling to write, because I was convinced that it would +not really terminate without a more or less violent explosion, such as I +had often predicted. I shall now state the reasons upon which my +prediction was founded.</p> + +<p>When the central crater begins to heave, with slight eruptions, one may +always predict a series of slight convulsions of greater or less +duration, which are preparatory to the grand explosion, after which the +Volcano remains for the most part in repose. Thus, when I observed the +cone fissuring in November, 1868, and copious lava streams issuing from +it, and flowing over the beautiful and fertile plains of the Novelle, +through the Fossa della Vetrana, instead of announcing the beginning of +an eruption, I announced the termination of one which had been manifest +for upwards of a year by the constant flow of lava from the summit of +the cone.</p> + +<p>From the month of November, 1868, until the end of <span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span>December, 1870, the +mountain remained quiet, except that the fumaroles at the head of the +fissure showed a degree of activity by which chlorides and sulphides of +copper, sulphide of potash and other products, were engendered.</p> + +<p>But in the beginning of 1871 the seismograph was disturbed,<a name="FNanchor_1_15" id="FNanchor_1_15"></a><a href="#Footnote_1_15" class="fnanchor">[1]</a> and the +crater discharged, with a slight detonation, a few incandescent +projectiles. Then I announced that <i>a new eruption had commenced, which +might be of long duration, but with phases that could not possibly be +foreseen</i>; and on the 13th January, on the northern edge of the upper +plain of the Vesuvian cone, an aperture appeared, from which at first a +little lava issued, and then a small cone arose and threw out +incandescent projectiles, with much smoke of a reddish colour, whilst +the central crater continued to detonate more loudly and frequently. The +lava-flow continued to increase until the beginning of March, without +extending much beyond the base of the cone, although it had great +mobility. In March, this little cone appeared not only to subside, but +even partly to give way, as almost happens with eccentric cones when +their activity is at an end. Upon visiting it, I observed that four +prismatic or pillar-like masses remained standing, three of which were +formed of scori which had fallen back again in a pasty condition, and +had become soldered together, the fourth consisting of a pyramidal block +of compact and lithoidal lava, which appeared to have been forced up by +impetus from the ground beneath. A little smoke issued from the small +crater, and a loud hissing from the interior was audible. <span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span>By lying +along the edge, I could see a cavity of cylindrical form about ten +metres in depth, tapestried with stalactitic scori covered with +sublimations of various colours. The bottom of this crater was level, +but in the centre a small cone of about two metres had formed, pointed +in such a manner that it possessed but a very narrow opening at the +apex, from which smoke issued with a hissing sound, and from which were +spurted a few very small incandescent scori. This little cone increased +in size as well as activity until it filled the crater, and rose four or +five metres above the brim.<a name="FNanchor_A_8" id="FNanchor_A_8"></a><a href="#Footnote_A_8" class="fnanchor">[A]</a> New and more abundant lavas appeared near +the base of this cone, and, pouring continually into the Atria del +Cavallo, rushed into the Fossa della Vetrana in the direction of the +Observatory and towards the Crocella, where they accumulated to such an +extent as to cover the hill-side for a distance of about 300 metres; +then turning below the Canteroni, they formed a hillock there without +spreading much farther. These very leucitic lavas are capable of great +extension, the pieces which are ejected forming for the most part very +fine filiform masses, which may be collected on the mountain in great +quantities, and specimens of which I presented to the Academy under the +name of <i>filiform lapilli</i>. These threads were often of a clear +yellowish colour, and, when observed under the microscope, were found to +consist of very minute crystals of leucite embedded in a homogeneous +paste. <span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span>The crystals were still smaller as the diameter of the threads +was less, and never formed knots or swellings even in the most hair-like +threads. These observations led me to reject the opinion of those who +hold that crystals of leucite are pre-existent in the lava. The viscous +nature of these lavas prevented their being covered with fragmentary +scori, but caused the formation at first of a skin, which, thickening, +became at last a more or less pliable shell, that, when more solidified, +allowed the still fluid part to run as in a tube formed of this solid +shell. For many months the lava descended thus from the cone and +traversed the Atria del Cavallo, always covered, appearing below the +Canteroni of a lively fluidity, until it could no longer be enveloped in +its skin, which was stretched by the addition of new lava, and finally +rent asunder to give room to the current until, owing to diminished +liquidity, it was constrained to stop. When the lava, having traversed +the covered channel it had made for itself from the top of the mountain +to below the Canteroni, made its appearance still running, it frequently +formed large bubbles on the surface, which mostly burst to give vent to +smoke, and then disappeared.</p> + +<p>In October, 1871, near the edge of the central crater, another small +crater was formed by falling in, which, after a few days, gave vent to +smoke and several jets of lava. The principal cone frequently opened in +some point of the slope to give egress to small currents of lava, which +quickly ceased. But towards the end of October the detonations +increased, the smoke from the central crater issued more densely and +mixed with <span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span>ashes, and the seismograph and accompanying apparatus were +disturbed: for all these reasons, I said in one of my bulletins, <i>we +have either reached a new phase or the end of the eruption</i>, not knowing +whether the new phase would be the last. On the 3rd and 4th November +copious and splendid lava streams coursed down the principal cone on its +western side, but were soon exhausted. The cone of 1871 appeared again +at rest, and partly even fell in, but did not cease to emit smoke and to +show fire in the interior.</p> + +<p>In the beginning of January, 1872, the little cone again became active, +the crater of the preceding October resumed strength, with frequent +bellowings and projectiles, and soon after lavas of the same kind as +before reappeared. The cone of 1871, formed again by the lava ejected, +became so full that the lava poured from its summit in the most singular +and enchanting manner. So far only an eccentric or ephemeral cone had +risen close to the central crater, which, after exhaustion, regained +vigour and discharged lava from the apex instead of the base, as usually +happens.</p> + +<p>In the month of February matters were somewhat moderated; but in March, +with the full moon, the cone opened on the north-west side—the cleavage +being manifest by a line of fumaroles—and a lava stream issued from the +lowest part without any noise and with very little smoke, and poured +down into the Atria del Cavallo as far as the precipices of Monte di +Somma. This lava ceased flowing after a week, but the fumaroles pointed +out the cleft of the cone; and between the small re-made cone, which had +risen to the height of <span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span>35 metres, and the central crater, a new crater +of small dimensions and interrupted activity opened.</p> + +<p>On the 23rd April (another full moon) the Observatory instruments became +agitated, the activity of the craters increased, and on the evening of +the 24th splendid lavas descended the cone in various directions, +attracting on the same night the visits of a great many strangers. All +these lava streams were nearly exhausted on the morning of the 25th; +only one remained, which issued from the base of the cone, not far from +the spot whence that of the preceding month had issued. Numbers of +visitors, attracted by the splendour of the lava streams of the +preceding night, which they supposed still continued, soon arrived, but, +finding them exhausted, were for the most part conducted by their guides +to see the one still flowing. It was almost inaccessible, and to reach +it one had to walk over the rough inequalities of the scori. It took me +two hours to get there from the Observatory, when I visited it that +morning, and therefore I endeavoured to dissuade those who wished to +visit it at night from the attempt, but set out myself from the +Observatory at 7 p.m., leaving my only assistant there. The instruments +were agitated. After midnight the Observatory was closed, and my +assistant retired to rest. Late and unlucky visitors passed unobserved +with an escort of inexperienced guides; at half-past 3 o'clock in the +morning of the 26th they were in the Atria del Cavallo, when the +Vesuvian cone became rent in a north-westerly direction, the fissure +commencing at the little cone which disappeared, and extending to the +Atria del Cavallo, whence a copious torrent of <span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span>lava issued. Two large +craters formed at the summit of the mountain, discharging numerous +incandescent projectiles with white ashes, and glittering with particles +of mica, which frequently recurred.</p> + +<p>A cloud of smoke enveloped these unfortunates, who were under a hail of +burning projectiles and close to the lava torrent. Some were buried +beneath it<a name="FNanchor_B_9" id="FNanchor_B_9"></a><a href="#Footnote_B_9" class="fnanchor">[B]</a> and disappeared for ever; two dead bodies were picked up, +and eleven grievously injured, one of whom died close to the +Observatory. He alone revealed his name, Antonio Giannone. I learned +afterwards that he was a fine young fellow, and Assistant-Professor in +one of the Universities.</p> + +<p>Assistant-Professors Signor Franco, who is a priest, and Signor +Francesco Cozzolino, a priest also, entrusted with the festive mass for +the Observatory, hastened to assist the dying. On my own return thither, +the sad spectacle of the dead and dying awaited me; the former were +conveyed, through the assistance of the municipal officer of Resina, to +the Cemetery, and the latter to the Hospital. But we must leave this +scene of grief and sorrow, and return to the eruption.</p> + +<p>The fissure of the cone on the north-west side was large and deep, and +extended into the Atria del Cavallo, about 300 metres. No mouth opened +along the cleft of <span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span>the cone itself; all the lava issued from that part +which extended into the Atria. From previous experience I should have +expected to have seen the formation of adventitious cones along the +widest part of the fissure, which is never that most elevated, and these +discharging from their summits riform matter frequently mixed with +projectiles, and from their base lava; but on this occasion no cone +appeared at the widest part of the fissure, but a long hillock was +formed like a little chain of mountains, one point of which was elevated +about fifty metres above the plain beneath, and bearing no resemblance +to a cone.</p> + +<p>Another fissure opened in the cone on the south side, which did not +extend to the base, and lava issued from this and flowed in the +direction of the Camaldoli. Streams of less importance furrowed the cone +in other directions, but the largest quantity of lava proceeded from the +fissure in the Atria del Cavallo, below the hillock or miniature chain +of collines just described. This lava stream was for some time +restrained within the Atria del Cavallo, among the holes and +inequalities of the lavas of 1871, but these being filled up and +overcome, it divided into two branches—the smaller one flowing through +a hollow which separated the lavas of 1867 from those of 1871, and made +its way over the lavas of 1858, threatening Resina, but stopped as soon +as it reached the first cultivated ground; the larger branch +precipitated itself into the Fossa della Vetrana, occupying the whole +width, about 800 metres; and traversing the entire length of 1,300 +metres in three hours. It dashed into the Fossa di Faraone; here it +again divided <span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span>into two streams, one overlying the lava of 1868, on the +Plain of the Novelle, partially covering the cultivated ground and +country-houses; the other flowing on through the Fossa di Faraglione, +over the lava of 1855, reached the villages of Massa and St. Sebastiano, +covering a portion of the houses, and thence continued its course +through the bed of a foss or trench which, contrary to my advice, had +been excavated after the eruption of 1855, in the expectation of +diverting the course of that lava. I did not fail to observe that the +rains which previously descended through these steep channels, would in +future be kept back to filtrate through the scori, without ever +reaching the new channel.</p> + +<p>The lava of this eruption, meeting with this said excavation, flowed +into it, instead of pursuing its road over the lava of 1855, and thus +invaded highly cultivated ground and towns of considerable value, +extending to the very walls of a country-house belonging to the +celebrated painter, Luca Giordano. This lava stream, having surmounted +the obstacles which the heaps of scori in the Atria del Cavallo +presented to it, ran with great velocity (notwithstanding its being +greatly widened out in the Fossa del Vetrano), so that between 10 a.m. +and 11 p.m. it traversed about five kilometres of road, occupying a +surface of five to six square kilometres. If it had not greatly +slackened after midnight, from the failure of supply at its source, in +twenty-four hours more, by occupying Ponticelli, it would have reached +Naples, and flowed into the sea.</p> + +<p>Although I had often visited the two villages of <span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span>Massa and St. +Sebastiano, previously greatly injured by the lava of 1855, yet I could +not well estimate, upon now seeing them again, the number of houses +which had disappeared. Massa seemed to me diminished by about one-third, +and St. Sebastiano by somewhat less than a fourth. But the way of escape +was open to the inhabitants of Massa; whilst a great river of lava +occupying the road leading to St. Giorgio a Cremano would have hindered +the flight of the inhabitants of St. Sebastiano, if they had been +dilatory. The lava stream now separating the two villages is little less +than a kilometre in width, and is about six metres in height.</p> + +<p>On the night of the 26th April, the Observatory lay between two torrents +of fire, which emitted an insufferable heat. The glass in the +window-frames, especially on the Vetrana side, was hot and cracking, and +a smell of scorching was perceptible in the rooms. The cone, besides +being furrowed by the lava streams just described, was traversed by +several others, which appeared and disappeared. It seemed completely +perforated, and the lava oozed as it were through its whole surface. I +cannot better express this phenomenon, than by saying that <i>Vesuvius +sweated fire</i>. In the day-time, the cone appeared momentarily covered +with white steam jets (fumaroles), which looked like flakes of cotton +against the dark mountain-side, appearing and disappearing at brief +intervals.</p> + +<p>Simultaneously with the grand fissure of the cone, two large craters +opened at the summit, discharging with a dreadful noise, audible at a +great distance, an immense <span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span>cloud of smoke and ashes with bombs and +flakes, rising to the height of 1300 metres<a name="FNanchor_C_10" id="FNanchor_C_10"></a><a href="#Footnote_C_10" class="fnanchor">[C]</a> above the brim of lava +(<i>sull' orlo de essi</i>). The white ashes, before described, although they +did not fall beyond the Crocella, were carried by the wind as far as +Cosenza, from whence they were sent to me by Dr. Conti. These ejections +were followed by dark sand, with lapilli and small fragments of scori +of the same colour. The smoke, driven up with violence, assumed the +usual aspect of a pine tree, of so sad a colour that it reminded us of +the shadowy elm of Virgil's dreams ("<i>ulmus opaca ingens</i>"). From the +trunk and branches of the pine-tree cloud fell a rain of incandescent +material, which frequently covered all the cone. The lapilli and the +ashes were carried to greater distances.</p> + +<p>The victims of the morning of the 26th, the torrents of fire which +threatened Resina, Bosco and Torre Annunziata, and which devastated the +fertile country of the Novelle, of Massa, St. Sebastiano and Cercola, +the two partially buried villages, the continual and threatening +growlings of the craters, caused such terror that numbers fled from +their dwellings near the mountain into Naples, and several in Naples +went to Rome or to other places. Very many delayed from the knowledge +that I was in the Observatory, and held themselves in readiness for +flight whenever I should abandon it.</p> + +<p><span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span></p><p>The rapidity with which the vast torrent of fire assailed the houses +(<i>i.e.</i>, in these villages), and the great heat which spread to a +distance, scarcely allowed the fugitives to carry away any of their +belongings; many were completely destitute. The authorities vied with +each other in zealous efforts to relieve the distress, and the +municipality of Naples sheltered and fed the wretched beings for many +days.</p> + +<p>The igneous period of the eruption was short, for on the morning of the +27th the lava stream, bearing down upon Resina, having covered a few +cultivated fields, stopped; the lava descending from the summit of the +mountain towards the Camaldoli also stopped; and the great lava torrent, +which passed the shoulders of the Observatory through the Fossa della +Vetrana, lowered the level of its surface below those of its two sides, +which appeared like two parallel ramparts above it.</p> + +<p>If these streams had continued on the 27th, flowing in the same manner +as they did on the night of the 26th, they would have reached the sea, +bringing destruction to the very walls of Naples.</p> + +<p>But before leaving the subject of these lavas I must narrate an +important fact to which I was witness, and which was thrice repeated, +near the banks of the great river of fire that ran close to the +Observatory. At three several points, and at different times, I observed +great balls of black smoke issue from the lava, driven up with continued +violence, as if from a crater; through the smoke I frequently observed +numerous projectiles thrown up into the air, but I could not say whether +with noise or in silence, for the noise of the central crater was +<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span>deafening. Each of these little eruptions, which I may call <i>external +eruptions</i>, lasted from fifteen to twenty minutes. The first took place +at the most elevated point of the Fossa della Vetrana, on the right bank +of the torrent; the second, under the hill of Apicella, where the lava +divided into the two branches, before described; and the third near to +the Observatory on the left bank of the lava stream. These singular +explosions terminated without leaving little cones or craters, the lava +in its impetuosity carrying every trace away. These eruptions were seen +from Naples, and the Observatory was justly believed to be in danger. +One has been clearly photographed, the one which was the best seen from +Naples, being the nearest and the least darkened by the smoke of the +lava. (<a href="#PLATE_4">Plate 4</a>.) Is this the first time that the phenomenon has been +remarked? I believe that it is at least the first time it has been +authenticated. The authority of Julius Schmidt, quoted by Scrope, has no +weight with me, for I was also a witness of what happened at Vesuvius in +1855; and, although these cones were in the midst of the lava in the +Atria del Cavallo, they originated, according to the opinion of +everyone, from the fissure from which the other and much larger cones +proceeded. The same phenomenon was observed in the Atria del Cavallo in +1858, when I caused two of the little cones to be brought to the +Observatory; but these also might belong to the fissure along which the +other cones were arranged. The same may be said of the little craters +observed, after they had been exhausted, by Professor Scacchi in 1850. +But the discharging mouths now observed <span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span>in the Fossa della Vetrana, +which existed for twenty minutes and then disappeared, and which were +not at all in a continuous line, and could not be supposed to correspond +with any fissure beneath, constitute a circumstance which, if not new, +is evident for the first time, and cause the recognition of a power in +the lava itself to form eruptive fumaroles.<a name="FNanchor_2_16" id="FNanchor_2_16"></a><a href="#Footnote_2_16" class="fnanchor">[2]</a></p> + +<p>The igneous period of the eruption having terminated on the evening of +the 27th, the ashes, lapilli, and projectiles became a little more +abundant, whilst the roaring noises of the craters apparently became +greater. The pine-tree cloud was of a darker colour, and was furrowed by +continual lightning, visible by daylight from the Observatory. Many +writers on the subject of Vesuvius affirm that the flashes which appear +through the smoke cloud were lightning unaccompanied with thunder, but +they studied the phenomena from Naples, or some place more or less +distant from the crater, where the report of the thunder was inaudible, +or could not be distinguished from the bellowing and detonation of the +mountain. The fact is that these flashes were constantly followed by +thunder, after an interval of about seven seconds.<a name="FNanchor_D_11" id="FNanchor_D_11"></a><a href="#Footnote_D_11" class="fnanchor">[D]</a> When the flash was +very short, a simple noise like the report of a gun was heard, but if it +were long, a protracted sound like that from torn paper ensued.</p> + +<p><span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span></p><p>On the 28th the ashes and lapilli, continuing to fall abundantly, +darkened the air, yet without diminishing the terrible noise; at Resina, +Portici, St. Giorgio a Cremano, Naples, etc., terror was universal.</p> + +<p>On the 29th, with a strong wind blowing from the east, scori of such a +size fell at the Observatory, that the glass of the windows unprotected +by external blinds was broken. The noise from the crater continued, but +the projectiles rose to a less height, indicating a diminution in the +dynamic power of the eruption. Towards midnight the noise of the craters +was no longer continuous, and recurred with less force and for shorter +intervals. Almost at the same hour a tempest burst over the Campania +with loud thunder and a little rain. The grass, the seeds, the vine +tendrils, the leaves and tops of the trees dried up immediately, and the +country was changed from spring to winter. The storm, although repeated +on the following days, passed away by degrees, and thus the floods, +which I strongly feared, did not occur. Almost always after great +eruptions of Vesuvius, storms of heavy rain have followed, and the +ground being covered with ashes, the water could not filtrate through +into the soil, but descended in muddy torrents over the adjacent +country, occasioning as much damage as the fire itself.</p> + +<p>On the 30th, the detonations were very few, and the smoke issued only at +intervals, and by the 1st May the eruption was completely over.</p> + +<p>When the smoke had cleared off the figure of the cone was seen to be +changed. (<i>Vide</i> <a href="#PLATE_5">Plate 5<span class="smcap">a</span></a>.)</p> + +<p>The ground was perpetually disturbed whilst the <span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span>Volcano raged, so that +the Observatory oscillated continually. Some shocks were felt not only +in the adjacent territory, but at a greater distance, at Montovi and +elsewhere. The oscillations at the Observatory were chiefly undulatory, +from N.E. to S.W. They were observed for some days after the termination +of the eruption, but not continuously, although they maintained some +intensity.</p> + +<p>If we refer to January, 1871, we shall find that that eruption was +preceded by several earthquakes, among which were those of the months of +October, November and December, in the previous year, that wrought such +destruction in Calabria, and especially in the province of Cosenza; if +we consider that as only the last phase, we shall find that it was +preceded by great shocks of earthquake that devastated some regions of +Greece.<a name="FNanchor_3_17" id="FNanchor_3_17"></a><a href="#Footnote_3_17" class="fnanchor">[3]</a></p> + +<p>The great quantity of lapilli which fell buried the scori with which +the Vesuvius cone was covered, so that it became somewhat more difficult +to ascend to the summit, and much less difficult to descend. Having +reached the top of the mountain, I found a large crater divided into two +parts by what seemed a cyclopean wall. The two abysses had vertical +sides, and revealed the internal structure of the cone. Their vertical +depth was 250 metres; and beyond that I observed a sort of tunnel +perforated in the rock, with a covering arch raised above the bottom of +the eastern abyss about 12 metres, judging by the eye. The interior +walls of the crater showed neither the usual stalactitic scori nor +sublimations, nor fumaroles, but alternate beds of scori and of compact +lava. The fumaroles and sublimations <span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span>abounded, only about the brims of +the craters. Hydrochloric and sulphuric acid and sometimes sulphuretted +hydrogen affected respiration, and the temperature rose sometimes to 150 +degrees. Various fissures about the brim of the double crater indicated +prolongations downwards, which allowed me to descend with a rope, in +order to examine the interior of the tunnel to which I have just +alluded. The highest brim of the crater was fissured for a distance of +80 metres, and the greatest depth of fissure was at that place.</p> + +<p>By measurement with the barometer, we ascertained approximately (for +only one barometer was used) that the height of the Vesuvian cone was +somewhat diminished.</p> + +<p>Not only the Vesuvian cone, but the whole adjacent country appeared +white for many days, as if covered with snow, when exposed to sunlight. +This was due to the sea-salt contained in the ashes with which the +surface was strewn.</p> + +<p>A great quantity of coleoptera assembled on the flat roof of the +Observatory, where the ashes and lapilli were heaped up two decimetres +in height. I found the same species on the cone, where many insects were +observed on other occasions, such as the <i>Cuccinella septempunctata</i>; +the crysomela populi, etc., were wanting. This phenomenon of the +extraordinary concourse of insects on the top of Vesuvius, in order to +die in some of the fumaroles, especially noted previous to and after +great eruptions, is a circumstance for which I cannot account.<a name="FNanchor_4_18" id="FNanchor_4_18"></a><a href="#Footnote_4_18" class="fnanchor">[4]</a> The +whole of the lava emitted in this <span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span>eruption occupies a surface of about +five square kilometres; allowing an average thickness of four metres, we +obtain a mass of twenty millions of cubic metres. About three-fifths of +this lava did no injury, being deposited upon other pre-existing lava. +However, the lava in the Novelle, which was deposited upon the lava of +1858, covered quarries of the best stone which had been worked at the +time, covered many paths that had been cleared, and buried the new +Church of St. Michele, with some houses that surrounded it, which had +been rebuilt on the site of the former church, which was covered by the +lava of 1868. The destruction of land in occupation, of buildings and of +crops, exceeded three million francs in value. Many proposals for +relieving the sufferers have been received. Wishing to aid in this +benevolent work, I gave a public lecture, admission for each person +being one franc; and this lecture, from notes badly taken, was printed +by private speculation, and I was compelled to repudiate the report of +it through the public papers.</p> + +<p>The evolutions of carbonic acid (<i>mofette</i>), which usually appear at the +end of great Vesuvian eruptions at low-situated spots or hollows, with +very rare exceptions, were observed on this occasion a few days after +the eruption had completely ceased. They appeared in the direction of +Resina. I found the most elevated at Tironi, and the most numerous +between La Favorita and the Bosco Reale di Portici.</p> + +<p>The water in wells was on this occasion neither deficient nor scarce +previous to the eruption, but was very acid after the appearance of the +carbonic acid evolutions <span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span>in those neighbourhoods in which they +abounded. Having stated that the disastrous conflagration of the 26th +April ought, in my opinion, to be regarded as the last phase of a long +period of eruption, which commenced at the beginning of 1871, I consider +it right to discuss the question at somewhat greater length.</p> + +<p>Not only from twenty years' personal observations, but from the +attentive study of accounts of previous eruptions, I have found that +when the central crater awakens with small eruptions after a certain +time of previous repose, these almost always have a long duration, and, +after various phases of increase and decrease, terminate in a great +eccentric eruption, that is to say, with the production of an aperture +from which a copious lava stream issues. The eruptions of 1858, 1861, +1868 and 1872, furnish the most recent examples of what I affirm. I +might cite many others of earlier date, but I shall content myself with +recording the greatest conflagration of this century, that of October, +1822.</p> + +<p>Before the erection of the Vesuvian Observatory, it was impossible to +obtain a consecutive account of all the phases which the Volcano +presented; but we generally obtained the description of the more +splendid phases of the eruption which arrested the attention of +everyone. Hence, notices of the small phenomena which preceded a great +eruption are frequently wanting. We cannot always ascertain whether the +fumaroles of the craters became active and at what periods, what was +their temperature and what the diverse nature of their emanations, etc.: +whether and when any change in the <span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span>crater with slight eruptive +manifestations occurred; discharges which sometimes commenced in the +bottom of a crater becoming active, and so are invisible at Naples.</p> + +<p>But it may be asked whether the inverse proposition be equally true, +that is, whether all the great eruptions of our Volcano were preceded by +small fiery manifestations of long duration? There have undoubtedly been +great eruptions not preceded by small central eruptions, but these also +had their period of preparation or precursory signs. After the great +eruption of 1850, Vesuvius remained in apparent repose until the end of +May, 1855, when there was an eccentric eruption and a great flow of lava +lasting twenty-seven days. But for a year before the fumaroles on the +top of the mountain had acquired great activity, their temperature +increased, and hydrochloric and sulphuric acid became more abundant, and +generated the usual coloured products on the adjacent scori. Finally, +in the month of January, a crater was formed by falling in of the +ground, and although it did not discharge fire, yet it poured forth +dense smoke. This was the beginning of the fissure manifested four +months afterwards.</p> + +<p>Ignazio Sorrentino, who spent a long life in the study of Vesuvius, and +frequently ascended it, considered the increase of those yellow +products—which are chiefly chlorides of iron, but were, at that time, +mistaken for sulphur—as the sign of an approaching eruption.</p> + +<p>The only grave objection that can be alleged is that of the memorable +eruption of 1631, which surprised the neighbouring population so +suddenly that many perished miserably, surrounded or covered with lava. +But that <span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span>terrible conflagration occurred after centuries of repose, so +that trees had grown in the interior of the crater. No one suspected the +possibility of danger. It took place, too, at the end of autumn, when +the cone is usually covered with clouds, and, therefore, no one had an +opportunity of observing any precursory phenomena.</p> + +<p>When the Observatory was established, I was able—in the first instance, +at my own expense, and afterwards with some slight assistance from +Government—to undertake studies more assiduous than any previously +made. I had two instruments adjusted to indicate the internal efforts of +the Volcano, viz., M. Lamond's apparatus of variations, which, by means +of finely-balanced needles and methods of amplification proposed by +Gauss, indicates the slightest trepidation of the ground, and my own +electro-magnetic seismograph, a self-registering instrument of exquisite +delicacy. These instruments, when attentively observed, give the most +valuable information with respect to the activity of the adjacent +Volcano.</p> + +<p>If the very slightest eruption occurs, these instruments manifest slight +perturbation, increasing with the activity of the mountain. When the +Volcano attains a certain degree of activity, and the instruments are +proportionately disturbed, it is impossible to foresee a new phase of +increase without constantly watching the changes in the intensity of the +perturbations; and to effect this it is requisite to have upon the spot +a staff of assistants sufficiently numerous, scientific and intelligent. +If, therefore, on the night preceding the 26th of April the instruments +had been properly <span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span>watched, they would have undoubtedly indicated the +great increase in the activity of the Volcano. The perturbations on the +23rd were steadily increasing, and on the evening of the 25th they were +much stronger than on the 24th, but on the morning of the 26th they had +become extraordinarily strong; they must, therefore, have increased +considerably during the night.</p> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span></p> +<h2><a name="II" id="II"></a>II.<br /> + +NATURE OF THE LAVAS.</h2> + + +<p>When the observer is near the source of the lava, he sees matter in a +state of fusion, which, like a torrent of liquid fire, runs along, with +more or less impetuosity, between two banks formed by itself. But as +soon as the surface of the torrent cools to the point of congelation, it +loses the splendour of its first incandescence. The part which begins to +harden breaks readily in some lavas into fragments which float on the +viscous fluid beneath; these, increasing in number with distance from +the source, conceal the molten matter beneath and retard its progress, +and at last nothing is seen but the more or less red-hot scori moving +along. These lavas I shall call "<i>Lavas with fragmentary scori</i>."</p> + +<p>On other occasions, a skin forms on the surface of the lava, which, +gradually thickening, keeps flexible for some time, and then wrinkles or +swells or extends and breaks to give egress to the hot fluid within, +which, in its turn, skins over and repeats the same phenomena. This I +shall call "<i>Lavas with a united surface</i>."</p> + +<p>These, in their course, discharge less smoke than the first, draw out +more easily into threads, and, when cold, have a dark colour, something +like bitumen or pitch. <span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span><i>The lava with fragmentary scori</i>, when +stretched, breaks easily, discharges smoke copiously, and, when +hardened, has a more bluish tint, like clods of upturned earth (<i>formato +di zolle</i>). It is noisy in its course, because the incoherent scori +that it carries along strike and crunch against each other; the other +lava flows silently, except for a sort of crackling arising from the +actual fracturing up of the solid skin by distension from the liquid +matter within. If required to give the mineralogical characteristics of +this lava, I would say that it was rich in leucite and contained little +or no pyroxene; the fragmentary lava, on the contrary, is poor in +leucite and rich in pyroxene. The lavas of 1871 were of the "united +surface" character; those of 1872 were "fragmentary," with some +characteristics which I shall describe:</p> + +<ul style="text-indent:-1em;list-style-type:none;"> +<li>1. They were of the clearest tint I have ever seen, when +regarded superficially, but, when broken, the fracture was +darker than any other lava.</li> + +<li>2. They had very little leucite and abounded in pyroxene and +olivine, and sometimes contained a few crystals of amphibole.</li> + +<li>3. Their specific gravity varied with their porosity; the most +compact attained 275.</li> + +<li>4. These lavas carried along in their course a quantity of +scori which had long been subjected to the action of the acids +of the fumaroles close to the craters, and also a great many +bombs (<i>bombe</i>)—that is, round masses similar to those ejected +from craters. These varied in <span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span>size, some having a diameter of +four to five meters. They frequently contained a large nucleus +of very leucitic lava, like that of 1871, with a larger or +smaller quantity of feroligiste (peroxide of iron). Others +contained lavas changed by the action of the acid vapours near +the craters. These bombs must have flowed out with the lava, +for they are found through its whole course, and they were +certainly not ejected from the crater; for not only are they +found on the lava exclusively, but masses so enormous were not +thrown up from the craters during the eruption; those lying on +the cone near the craters seldom exceed a decimetre in +diameter. +</li> +</ul> + +<p>As to the qualitative chemical analysis of the lavas, it always presents +the same elements, with the exception of small quantities of some +metals, lead for example, which have escaped the researches of good +chemists, but which I have constantly found in the sublimations of the +fumaroles of the lava. With respect to the quantitative analysis, two +specimens of the same lava appear indeed to have their constituents in +different proportions. To arrive at any conclusion a long and patient +investigation, requiring means and assistance which the Observatory does +not possess, would be necessary.</p> + +<p>Professor Fuchs, of Heidelberg, has devoted himself to this work for +years past, and if he continue it with well-selected and sufficiently +large specimens we may hope some day to obtain satisfactory results.</p> +<p><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span></p> + +<ul style="text-indent:-1em;list-style-type:none;"> +<li>5. Every specimen of lava which I examined with a very +sensitive magnetoscope improved by myself, was invariably +magneto-polar, not excepting the pieces of the bombs, whether +rejected from the crater or carried along with the lava.</li> +</ul> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span></p> +<h2><a name="III" id="III"></a>III.<br /> + +FUMAROLES OF THE LAVAS.</h2> + + +<p>Smoke generally issues from all lava when it cools down to a certain +degree, hence it is more abundant at the edges of the fiery torrent, or +is liberated from the scori that form on its surface. But when the lava +stops, the smoke issues only from certain vent-holes, through which we +can still see the fire, and at the edge of which different amorphous or +crystallized matters collect by sublimation. These centres of heat, of +more or less duration, are the fumaroles of the lavas. I believe I have +on other occasions shown that a fumarole is nothing but a communication +between the more or less cooled and hardened surface of the lava and the +interior, which is still incandescent. Some fumaroles last but a day, +others preserve their activity for weeks, months or years, according to +the depth of lava through which they penetrate; and when they cease to +be active, that is, when the sublimations are formed, or smoke or other +riform matters issue from them, they still retain a rather elevated +temperature. In the lavas of 1858, in a place where they had a +transverse width of 150 metres, a vent-hole may still be found where the +thermometer registers 60 and the scori are warm. Sometimes, <span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span>while the +lava is in process of cooling, new fumaroles appear, in which the fire +is visible. This phenomenon, which appeared marvellous and inexplicable +when I first observed it in 1855, is now very easily understood; the +cooled and hardened crust of the lava fractures with noise and suddenly, +and so a new communication is opened with the incandescent lava below, +thus creating a new fumarole.</p> + +<p>As the smoke of the fluid lava is perfectly neutral, that is, neither +acid nor alkaline, so the fumaroles at the first period of their +existence with sublimations of sea-salt, mixed frequently with oxide of +copper either in black powder or in shining lamin, ought also to be +neutral. But if the fumarole continues active, hydrochloric acid issues +with the smoke, and often some time after sulphuric acid. Then the +sublimations turn first yellow, then green, and more rarely azure. The +chemical reactions show that these sublimations are chlorides or +sulpho-chlorides, and sometimes sulphides, and they afford reactions, +indicative of soda, magnesia, copper, lead, and traces of other +substances, not excluding ammonia, which I must speak of separately. +This, I have observed, is the general law with the fumaroles of the +tranquil lavas, which occur with long and moderate eruptions—for +instance, the lavas of 1871, and even those of 1872, preceding the 26th +April.</p> + +<p>But in the great lavas of the great conflagrations of Vesuvius, chloride +of iron more or less in combination with all the other substances above +mentioned changes the appearance of the sublimations. The fumaroles in +the lava of the 26th April frequently indicated chloride <span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span>of iron. +Sulphuretted hydrogen, by reaction of sulphurous acid, is decomposed, +and sulphur sublimed, having a particular aspect, collects on the +scori. This is never found but in fumaroles of the smaller lavas; it +was therefore absent in those of 1871, but frequently occurred in those +of 1872.</p> + +<p>Although the sublimations are generally mixtures, yet sometimes distinct +and crystallized chemical or mineral species are found, such as sulphur, +sal ammoniac, <i>tenorite</i>, <i>cotunuite</i>, etc. Micaceous peroxide of iron +(feroligiste), so common near eruptive cones, is very scarce on lava; +any found in it has been carried down from the craters, and proofs of +this transport are very abundant and striking in the lavas of this last +eruption. Even the iron found in the bombs is evidently transported; +there is a fumarole on the ridge of the lava in the Fossa di Faraone +which contains micaceous peroxide of iron, and this, at first sight, +appears to oppose what I have affirmed; nevertheless, it gives +additional force to my statement. This fumarole is only a bomb or +rounded mass of enormous size, four or five metres in diameter. Smoke +and hydrochloric acid issued from the aperture in its envelope, and +being partly broken it was seen to contain lapilli and pieces of +antecedent lava, covered with micaceous peroxide of iron. The internal +temperature of this mass was very high; the hydrochloric acid which it +discharged had, in some places, covered the micaceous iron with a yellow +coating of chloride of iron. From small apertures, on the lower side of +the mass, white and green stalactites of chloride of calcium were +visible. In one spot only of lava I <span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span>found a fumarole, with a small +quantity of micaceous peroxide of iron, evidently in a state of +formation; but this was the very spot where the lava became eruptive, +and whence issued the column of smoke which was so well +photographed—the place under the hill of Apicella. (See <a href="#PLATE_4">Plate 4<span class="smcap">a</span></a>.)</p> + +<p>I have enumerated the products which are constantly collected in +fumaroles, although they are not all found at the same time or place, in +order to show that the sublimations follow a certain law in their +appearance. <i>Tenorite</i>, for instance, was formerly considered an +accidental product of certain eruptions, and I have always found it; but +if you visit the fumarole when the acids have had time to transform it, +you will no longer see it. I found the crystallized chloride of lead, or +"cotunuite," as it is called, for the first time in the lavas of 1855, +and thought it a singular circumstance; but from that time I recognised +it in all the lavas, though not always so beautiful and abundant; and +even when not found as a distinct substance, I observed it in +combination with chloride of copper. In the lavas of the 26th April +<i>cotunuite</i> and <i>tenorite</i><a name="FNanchor_E_12" id="FNanchor_E_12"></a><a href="#Footnote_E_12" class="fnanchor">[E]</a> were not very abundant, because the +chloride of iron disturbed the greater number of the sublimations. I +found sal ammoniac very abundantly on the fumaroles of the lavas that +invaded the cultivated ground. Although chloride of ammonia, contrary to +<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span>opinion, was not wanting in the sublimations of the fumaroles of the +lavas deposited on other lavas, yet it was neither abundant nor +crystallized, but combined in small quantities with other substances. It +appeared in great abundance in all the fumaroles of lavas which covered +cultivated or woody ground. At first it was scarce enough, and mixed +with chloride of sodium; but when the rains came the sea-salt was washed +away, and sal ammoniac formed beautiful crystals, nearly free from +adventitious matters, as was the case with the fumaroles of the last +lava. Afterwards, when chloride of iron was produced, ferro-chloride of +ammonia was found. Crystals of sal ammoniac were sometimes found of a +beautiful amber yellow. This colour was, in the opinion of my colleague, +Professor Scacchi, produced by such small traces of chloride of iron +that neither Professor Guiscardi nor I, nor indeed any other chemists to +whom I submitted specimens for examination, could detect any. What I can +affirm with certainty is, that these limpid crystals of a yellow colour +were almost always attached to an amorphous substance, soluble in water, +composed of various chlorides, in which iron was often detected.</p> + +<p>From these remarks, it is evident that in the tranquil lavas the +sublimations appear with a certain order of succession, and in the +violent lavas, and those which flow most copiously, they are more +complicated, and render both chemical analysis and spectroscopic +researches more difficult. Notwithstanding, I observed traces of lithium +and thallium, which I had previously perceived in some sublimations of +1871. I purpose <span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span>submitting many sublimations which I have collected to +more complete spectroscopic investigation, although I am persuaded that +the discovery of traces of certain bodies in the sublimations or in the +lavas is a matter of small importance to the science of volcanoes. I +must say, however, that calcium was discovered on this occasion in great +abundance, not only by the spectroscope, but also by chemical analysis. +Sulphate of lime has often been found in larger or smaller proportions, +but this was the first time I had observed chloride of calcium both +close to the craters, and also in the sublimations of the fumaroles upon +the lavas. The white stalactites which I collected beneath the great +mass or bomb above described were almost exclusively composed of +chloride of calcium, and only a few green drops manifested, with the +usual re-agents, the presence of iron.</p> + +<p>I did not fail to look often at the spectrum of the flowing lavas +covered with the smoke which issued from them, but I always had a +continuous spectrum. The spectroscope employed was Hoffmann's +construction, with direct vision; but I think it would be better on +other occasions to use a spectroscope combined with a telescope, like +those used by astronomers.</p> + +<p>But avoiding minute particulars of these sublimates, let us see what is +the general direction and the order of their appearance. Sublimations +are generally oxides, chlorides and sulphates, sometimes sulphides. +Among the oxides, we must enumerate in the first place "tenorite" and +<i>feroligiste</i> or micaceous peroxide of iron. The first is almost always +found at the commencement of <span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span>activity in the fumaroles, simultaneously +with the sublimation of chloride of sodium; the second—which is, +perhaps, never wanting in eruptive cones that are often found lined with +it inside—is seldom generated in the fumaroles of the lava, and +therefore it is not easy to define the moment of its appearance. +Sometimes one collects micaceous peroxide of iron on the lava, but it is +often transported there from the mouths of eruption, as happened on this +occasion.</p> + +<p>Trustworthy writers are of opinion that all the oxides are derived from +the decomposition of the chlorides, but I think I have clearly +demonstrated that, with regard to copper and lead, the opposite +statement may be affirmed; for the oxides are changed into chlorides, +and hydrochloric acid liberated. Oxide of copper forms sublimates at the +beginning, at the same time as the sea-salt; and if the fumarole be +anhydrous or, as Deville would say, <i>dry</i>, this oxide does not change +into either a chloride or a sulphate; but if the fumarole gives watery +vapour, after a little hydrochloric acid is formed, which changes the +oxide into a chloride, and if whilst this is going on oxide of lead be +developed, it is changed into the chloride of lead, so frequently found +in combination with chloride of copper. Then the sublimations change +from white to red or yellow, and specimens when carried away gradually +turn light blue, but when heated on platinum over a spirit lamp they +resume their yellow tint. Sometimes the yellow colour remains longer, +and in time changes to green; this also happens on the fumarole itself, +the green commencing at the zones furthest removed from the centre, +where the temperature is <span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span>highest. When these sublimations are greenish, +they become far less soluble than at first. The yellow, so common at a +certain period on the fumaroles of the tranquil lavas, never attracted +attention before I first examined it, doubtless, because it was +considered chloride of iron, and yet in small eruptions this is only +found close to the discharging mouths, and never in the sublimations of +the fumaroles of the lava; but, on the other hand, it is the most +copious and common product on the lavas of the great eruptions. This +probably also accounts for the fact that lead, which is so obvious in +the fumaroles of the lavas, had never previously been observed. In 1855, +I noticed the crystallized chloride of lead in a fumarole in the Fossa +della Vetrana, and this induced me always to look for it on the +fumaroles of the later lavas; and I ascertained that, if it did not +always appear as a distinct mineral, it was easily discovered in +combination with other chlorides. The specimens which I have collected +are not the most beautiful, but the presence of lead in the sublimations +is not less common.</p> + +<p>Micaceous peroxide of iron, when found on the lava, has been mostly +conveyed from the eruptive mouths, as I have already stated, and perhaps +never so abundantly and evidently as on this occasion. The lava of the +26th of April carried along a large quantity of round masses or bombs, +varying in size, among which were found antecedent lava more or less +covered with micaceous iron, either collected in the cavities of the +lava, or incorporated with its mass. Sometimes the micaceous iron +appears like little veins in the paste of new lava <span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span>enveloping the +exterior of these rounded masses, an exterior compact and lithoidal, and +not resembling scori. Among these spherical masses I found one of +enormous size, four to five metres in diameter, which, having broken up +where the exterior envelope was thinnest, I found filled with a great +mass of lapilli and fragments of other lavas covered with micaceous +iron. This bomb still preserves (June 5th) an elevated temperature +within, and emits smoke and hydrochloric acid, which, meeting the +micaceous iron discovered by breaking the envelope with blows of a +hammer, transforms it superficially into chloride of iron, showing most +clearly how, on some occasions at least, chloride of iron is formed from +the oxide which precedes it. That those lapilli and the pieces of lava +were solid when enveloped in the paste of the new lava, we infer from +seeing the impressions on the inside of the said envelope. The chloride +of calcium, which I found in this spherical mass almost pure, caused me +to suspect that the sulphate of lime which is so often found on Vesuvius +is a transformation of the chloride produced by the contact of +sulphurous acid, which easily becomes transformed into sulphuric acid. +The hydrochloric acid which escapes from a fumarole coming into contact +with the scori near its mouth, produces chloride of iron, which is, +therefore, not always obtained by sublimation, although, when the +temperature is very high, chloride of iron is conveyed from the interior +of the lava, and sublimes on the exterior and colder parts; for +instance, the chloride of iron which issues from the eruptive cones is +sometimes found sublimed on the rocks of Monte di <span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>Somma. When chloride +of iron has been produced by sublimation, we may collect it inside a +glass bell placed over the fumarole, or upon a piece of brick; but when +it is produced by the action of hydrochloric acid on the scori, it will +only be found on the scori themselves.</p> + +<p>If, therefore, the origin of micaceous peroxide of iron were due to the +decomposition of the sesqui-chloride of iron requiring a more elevated +temperature for its decomposition, it would follow that its genesis +would be easier near the discharging mouths, and more difficult on the +lavas, but there the fact was verified: for example, in the great bomb +on the fumarole, where we observed micaceous iron transformed into +chloride of iron. We may therefore consider it <i>proved</i> that some +chlorides—for instance, chloride of sodium—issue from the lava itself, +either being there pre-existent, or being formed there; and that others +are derived from the oxides which precede them, as undoubtedly is the +case with chloride of copper; hence, the theory that derives the oxides +always from the chlorides cannot be considered true. Granting that this +theory might be applicable to the origin of micaceous iron, we should +still want to know how it is found with the paste of the new lava +itself, which forms the exterior coating of the bombs above described.</p> + +<p>Many of these rounded masses, which have been rolled along by the lava, +contain scori partly decomposed by the long action of the acids found +on the fumaroles of the craters. They disintegrate easily, and have a +more or less yellowish tint. In the greater number of cases the interior +of these masses is formed <span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span>of leucitic lava, with cavities lined with +micaceous iron. In short, their contents appeared to me quite similar to +the material of the cone of 1871 and 1872, which in all probability was +engulfed in the large crevasse or fissure that opened below it; and the +fragments having thus fallen down into the lava, were enveloped by it +and carried out by it after having been more or less rounded. The +external envelope of these spheres is not at all scoriaceous, but +compact and lithoidal, and sometimes composed of concentric folds or +plaits.</p> + +<p>As to the gaseous emanations of fumaroles, watery vapour with few +exceptions comes first; this conveys the material which first appears in +the sublimations, viz., sea-salt, and for the most part oxide of copper. +If the fumarole continue active, it passes from the neutral period to +the acid period, and first hydrochloric acid is produced, which, in +small lava streams, never conveys chloride of iron, and rarely attacks +the scori to form that salt, but expends its force in changing the +sublimations already there. For this reason chloride of iron, though +completely absent in the lavas of 1871, was abundantly found in those of +the 26th April, 1872. Sulphurous acid follows hydrochloric at a later +period, and sulphuretted hydrogen occasionally succeeds.</p> + +<p>Having examined the gases of fumaroles by means of a graduated tube, and +the pyrogallate of potash, I always found that it contained less oxygen +than the surrounding atmosphere.</p> + +<p>For several years I wished to see whether the fumaroles of the lavas had +a period of evolution of carbonic acid, as sometimes happens with +fumaroles near the craters, but <span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span>I have always obtained negative +results. I often found that the atmosphere on the lavas contained an +excess of carbonic acid, but as these lavas had burnt many trees, and it +was probable that carbonic acid springs had formed under the lava, I +never considered it safe to form any conclusion on the subject.</p> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span></p> +<h2><a name="IV" id="IV"></a>IV.<br /> + +BOMBS, LAPILLI AND ASHES.</h2> + + +<p>The bombs ejected from the craters are like those carried down by the +lavas, but of smaller size, and they seldomer contain a nucleus similar +to those found in the latter. With the bombs properly so called, many +pieces of incandescent lava were thrown up, and in their fall went +beyond the base of the cone. A quantity of small scori varying in size +accompanied these projectiles, and those fragments, which we call +<i>lapilli</i>, fell at a greater distance. With the lapilli, and sometimes +without them, the smoke carried a very minute dust or sand, which is +generally called ashes. These ashes, when washed with water, lose +soluble constituents which they have collected in the smoke—such as +chloride of sodium and other chlorides and often free acids. The +insoluble part originates in the detritus of lava, and with the +microscope we can detect abundant fragments of those crystals which most +frequently occur in the lava of the same eruption.</p> + +<p>The lavas of 1871, which were eminently leucitic, and almost entirely +deprived of pyroxene, resembled the ashes, which appeared to be +fragments of crystals of leucite, more or less enveloped in the paste of +the lava, so that having triturated the scori of the lava, and looked +at the powder through the microscope, it was apparently quite the same +as the ashes.</p> + +<p><span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span></p><p>But at the beginning of the eruption of the 26th April, a white sand +fell in the Atria del Cavallo, close to the Crocella<a name="FNanchor_5_19" id="FNanchor_5_19"></a><a href="#Footnote_5_19" class="fnanchor">[5]</a>, which on the +dark scori of 1871 looked like snow. Its fall had a limit so well +defined that one passed without any gradation from white to black. +Having collected some of this sand that very morning, I put it up in +white paper, for at that moment it was impossible for me to examine it. +Taking it out some days after, I found it had become reddish, and having +put it under the microscope, I observed that it was exclusively formed +of little pebbles more or less round, of a transparent vitreous matter, +partly covered with a red substance. Fragments of green crystals +occurred in this sand, upon which no red was perceptible. I consulted +our eminent crystallographer, Arcangelo Scacchi, whether these little +pebbles were leucite, as I suspected, and whether the green particles +were pyroxene: he confirmed my suspicion, and remarked that the red +colour was superficial only. We then washed a little of the sand in hot +water, and saw the pebbles become whitish; but having heated some on +platinum, we observed that they first turned black and then became +perfectly white, proving that the red was a deposit of organic matter. +To see these leucites, rounded like small pebbles transported by a +torrent, deprived of the soluble chlorides which generally accompany +Vesuvian ashes, is a matter worthy of attention. Whilst heating this +sand upon platinum, decrepitation was audible, which indicated the +cracking of some of the little pebbles. It is evident, therefore, that +crystals of leucite raised to a certain temperature may break, and thus +we can understand how almost all Vesuvian ashes contain <span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span>fragments of +the said crystals enveloped in the paste of the lava. It is evident that +the soluble part of the ashes is obtained from the smoke through which +it passes. On this occasion the smoke from the craters did not +apparently contain much acids, for no bad smell was perceptible, and the +water in which I washed the ashes scarcely reddened litmus paper. Even +chloride of iron, which was so abundant in the lavas, was scarcely +perceptible in the smoke, which almost exclusively deposited sea-salt on +the surrounding rocks; I say sea-salt advisedly, and not chloride of +sodium, to show that I include all that sea-salt contains. The slight +disturbance it manifested with chloride of barium, and the small +precipitate with oxalate of ammonia, reveal sulphate of lime, without +excluding the possibility of the chloride.</p> + +<p>But how can these ashes do so much injury to the vegetation of the +ground they cover, especially at the first fall of rain? I think that +the damage is due partly to the sea-salt, and partly to the acids +contained either in the ashes or in the rain-water itself. Upon watering +the tender tops of some plants with a saturated solution of the salt +from Vesuvius itself, I noticed that they withered away after a few +hours. But very often the rain alone which traverses the smoke of +Vesuvius, or is produced by condensation from it, gives manifest acid +reactions, and destroys the grass and the tops of the trees. The +peasants believe that the rain is warm or of boiling water, from +observing that the tender parts of the plants are, by its deposit, all +burnt up. Vegetation is now recovering, but without flowers, and +consequently without fruit.</p> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span></p> +<h2><a name="V" id="V"></a>V.<br /> + +THE CRATERS AND THEIR FUMAROLES.</h2> + + +<p>The greater part of the lava issued from the base of the great fissure +in the cone which I have described; and although two other lava streams +descended from the top of the mountain, neither proceeded from the +crater, but from apertures near it. The great crater, divided in two as +already described, opened wide on the morning of the 26th April, +destroying the brim of the antecedent crater, and remaking it in another +shape with ejected matter, except on the south-west side, where the brim +was split. (See <a href="#PLATE_5">Plate 5</a>.)</p> + +<p>From this double crater, copious smoke, bombs and incandescent scori, +with ashes and lapilli, issued with violence, and from the depths below +came dreadful detonations and bellowings, producing great terror. And +yet the lava poured out into the Atria del Cavallo without any noise, +and not even a column of smoke marked its origin of issue—namely, from +the fissure.</p> + +<p>When the eruption was over, the sight of the vertical walls of these +deep craters, of almost horizontal strata of scori and lithoidal +masses, with a fracture fresh, and as if they had never undergone the +action of <span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span>fire or of acid vapours, without recent scori and without +fumaroles, was to me a marvellous spectacle. The fumaroles were almost +all on the brims of the craters, with emanations of hydrochloric and +sulphurous acid. In a few that were more removed from the brim, +sulphuretted hydrogen was perceptible. In the sublimations, chloride of +iron was most abundant, in combination with other chlorides, for +example, of sodium, magnesium and calcium. This last chloride was +frequent even among the sublimations of the fumaroles of the lavas, and +it was the first time it was ever remarked, but I do not think it was +the first time that it was ever produced: being in combination with +chloride of iron, and very deliquescent, it did not attract attention +from anyone. In a hollow fragment of scori I observed a yellowish +substance, which looked like sulphur in a viscid state, and which boiled +at a temperature of 120, and evolved hydrochloric acid. Having +collected this substance and poured it into a glass phial, it quickly +coagulated into an amorphous mass of the same colour; but before I +reached the Observatory, I found that it had become liquid by +deliquescence. It consisted of a mixture of the aforesaid chlorides, +according to an analysis made by Professor Silvestro Zinno and myself. +In some fumaroles, where I perceived the smell of sulphuretted hydrogen, +I found sublimed sulphur under the scori.</p> + +<p>At the source of the lava stream that flowed towards the Camaldoli, on +the seaward flank of Vesuvius, I observed large fumaroles of steam only, +pure aqueous vapour.</p> + +<p><span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span></p><p>There was no trace of carbonic acid in these fumaroles, but that fact +does not imply that there was none at a later period, for, since the +first investigations of Deville, it is known that carbonic acid is found +under certain conditions on the very summit of Vesuvius.</p> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span></p> +<h2><a name="VI" id="VI"></a>VI.<br /> + +THE ELECTRICITY OF THE SMOKE AND ASHES.</h2> + + +<p>Our ancestors could judge that a great amount of electricity was +occasionally evolved in the smoke, from their observation of the +lightning flashes that darted through the Vesuvian pine tree; but they +had no proper instruments for ascertaining whether this evolution of +electricity was constant or accidental, or what laws regulated its +manifestations. My <i>apparatus, with movable conductor</i>, by which +comparative observations of electric meteorology can be made, and the +errors arising from dispersion corrected, supplied me with an easy +method of studying the electricity evolved during eruptions.</p> + +<p>I must begin by describing the bifilar electrometer, in order to explain +the apparatus which I have named as above, "<i>Apparechio a conduttore +mobile</i>."</p> + +<p><i>A A</i> (<a href="#PLATE_6">Plate VI<span class="smcap">a</span></a>, Fig. 1) is a glass cylinder, the lower edge of which +is ground, well varnished with gum lac, and let into a wooden base, B, +furnished with three levelling screws. Through a sufficiently wide glass +tube, <i>a a</i>, runs a copper rod covered with insulating <span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span>mastic, having a +little plate or cylindrical cavity of gilded brass at the top (Figs. 2 +and 3), with two arms <i>d d</i>, <i>d' d</i>. In the plate a disc of aluminium, +<i>m</i>, is suspended by means of two silk fibres, and to the disc a very +fine aluminium wire is attached, <i>f f'</i>, bent a little at the ends, as +are the arms, <i>d d</i>, <i>d' d</i>. The disc has about three millimetres less +diameter than the plate. The diameter of the plate may vary within +certain limits, but I have found it convenient to make it eighteen +millimetres. The glass tube, <i>a a</i> (Fig. 1), should descend below the +base as much as it rises above it, that is three to four centimetres. +The length of the index is about one decimetre.</p> + +<p>The upper ends of the two silk fibres, by which the disc and index are +suspended, are attached to the top of the glass tube, <i>C</i>, by a +contrivance which permits a change in the distance between the two +points of suspension, and a screw, <i>p</i>, is provided to raise and lower +the disc with the index. At <i>n</i>, at the lower part of the tube, <i>C</i>, +there is a kind of torsion micrometer, arranged so as to bring the index +to the zero of the scale engraved on the graduated ring, <i>B</i>, which is +formed of a strip of good paper pasted on the rim of a glass disc. The +index must be placed at the zero of the scale, and must be some distance +from the ends of the arms of the plate with which it is parallel. The +plate is about three millimetres deep.</p> + +<p>Having levelled the instrument, so as to render the disc concentric with +the plate, and placed the index at zero, it is obvious that if an +electric charge through the wire, <i>h</i>, reach the plate with the arms, it +will electrify <span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span>the disc and index: the disc will have the opposite +electricity, and the extremities of the index will take the same +electricity as the arms, and consequently the index will describe an arc +more or less great. The motion of the index is sufficiently slow to +allow the eye conveniently to follow it. Having traversed the first arc, +which I call the <i>impulsive</i> one, the index returns, and, after only two +oscillations, comes to rest at what I shall call the <i>definite</i> arc.</p> + +<p>When the electric charges are of very brief duration, the impulsive arcs +are within certain limits proportional to the tensions, and the ratio +between the impulsive and definite arcs is expressed by the following +equation:</p> + +<blockquote> +<p>α(β - α) / β = tang. <span class="frac"><sup>1</sup>/<sub>2</sub></span> α</p> +</blockquote> + +<p>In which β is the impulsive arc and α the definite +arc, showing that α comes out nearly equal to <span class="frac"><sup>1</sup>/<sub>2</sub></span> β. +In dry weather all goes perfectly within the limits of proportion, and I +can tell whether, during the time in which the index traversed the +impulsive arc, there were any <i>dispersions</i> and of what nature; for if +the definite arc is not close to the limit of the impulsive arc, it is a +sign of <i>dispersions</i> having taken place during the motions of the +index. Every degree less in the definite arc denotes two degrees of loss +for the impulsive arc; but as the index employs double the time +traversing the definite as it does the impulsive arc, we may consider +the loss of one equal to the loss of the other.</p> + +<p>In excessively damp weather the index gives no definite arc, and it is +necessary to resort to artificial heat in order to dry the insulators. +The most simple means I <span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span>know of is to hold the instrument over some +hollow vessel, which, for the time, is converted into a stove by the +introduction of a spirit lamp.</p> + +<p>From Gauss's formula for the bifilar system of instruments of this +class, we learn that the maximum sensitiveness of such instruments is +given when the length of the suspending fibres is greatest, and the +distance between them is smallest, with the weight of the movable or +rotating member a minimum; and these elements being the same, the +sensitiveness of the instruments is invariable.</p> + +<p>To some electrometers, in order to avoid errors of parallax, a small +telescope, with a micrometer wire, has been added; but, with a little +practice, we can read accurately without this refinement. In order to +obtain comparative measurements, it is necessary to select some given +unit of tension. I have observed that by making a galvanic pile of +copper, zinc and distilled water, and insulating it well, each pole has +a tension which remains the same for many days, if the conditions of +temperature and the moisture of the surrounding atmosphere are not very +different. With thirty pairs of this pile, each element having +twenty-five square centimetres of surface, I have on the electrometer a +definite arc of 15, with the temperature of the atmosphere at 20 C., +and with the difference of 4 to 5 C. between the thermometers of the +psychrometer of August's construction. The first observation was made +twenty-four hours after mounting the pile. For unit of tension I took +that which corresponded to a single pair, that is, the thirtieth part of +the total tension. Other electrometers may be compared <span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span>with one already +properly adjusted, without always having recourse to the pile.</p> + +<p>This done, let us see the arrangement of all the apparatus:</p> + +<p><i>H H</i> (<a href="#PLATE_7">Plate VII<span class="smcap">a</span></a>, Fig. 1) is the ceiling of a well-situated lofty room, +with an opening, <i>o o</i>, at the upper part.</p> + +<p><i>M M</i>, a bracket or table fastened against the wall, about a metre +distant from the ceiling, <i>H H</i>.</p> + +<p><i>N N</i>, a wooden platform for the observer.</p> + +<p><i>A</i>, the bifilar electrometer.</p> + +<p><i>B</i>, Bohnenberger's electroscope.</p> + +<p><i>a a</i>, a movable conductor formed of a brass rod 15 to 18 millimetres in +diameter, insulated below by means of a glass rod, well varnished with +gum lac, having a suspending pulley, <i>c</i>, and a wooden guide-rod +underneath it, <i>l</i>, within the guiding tube, <i>k</i>. At the upper part of +this conductor, <i>a a</i>, there is a sliding roof, <i>b</i>, which can be +adjusted so as to prevent rain entering at the opening, <i>o o</i>. The +conductor terminates in a disc made of a sheet of thin brass, <i>d</i>, 24 +centimetres in diameter. Upon this disc, or even in place of it, we may +use metallic points.</p> + +<p>As a support to the conductor at the upper part, I have made use of a +triangular ring, <i>x</i>, drawn at its full size in Fig. 2. The conductor +passes between three springs, and the triangular ring is held in place +by three silk cords, <i>m m m</i>. Their material should not be mixed with +any cotton, and it may be advisable to saturate them with an alcoholic +solution of gum lac.</p> + +<p><span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span></p><p><i>f f f</i> is a hempen cord, which is used to raise and lower the +conductor.</p> + +<p><i>i</i> is a copper wire covered with silk, by means of which the triangular +ring, <i>x</i>, and through that and its springs the conductor communicates +with either the electrometer or the electroscope.</p> + +<p>Quickly raising the conductor by pulling the cord, <i>f</i>, the index of the +electrometer will describe a more or less large impulsive arc, and, +after two oscillations, will stop at the definite arc. Having thus +measured the electric tension of the air, and having lowered the +conductor, I next place the wire, <i>i</i>, in communication with the +electroscope, <i>B</i>, and by again raising the conductor, I ascertain +whether the electricity be positive or negative. It is scarcely +necessary to say that the conductor, when raised, gives electricity of +the same nature as that prevailing at the moment in the atmosphere; and +when lowered, manifests the opposite. In some conjunctures we must keep +the conductor raised and in communication with the electroscope, in +order to observe certain phenomena which I shall presently describe: +this method I call observation with a <i>fixed conductor</i>.</p> + +<p>I have also constructed a similar but portable apparatus for use on +eruptive cones, when required.</p> + +<p>Having given this description of the apparatus, it remains for me to +relate the results obtained, especially on the occasion of the last +eruption of Vesuvius.</p> + +<p>The Observatory is distant, in a direct line from the central crater of +Vesuvius, 2,380 metres, so that, when the smoke is copious, it is +properly situated for the <span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span>study of electricity, particularly when the +wind inclines the pine-tree cloud in the direction of the Observatory, +as frequently happened on the last occasion.</p> + +<p>With smoke alone, without ashes, we obtained strong tensions of positive +electricity; with ashes only, which sometimes fell while the smoke +turned in the other direction, we had strong negative electricity; when +the smoke inclined towards the Observatory, accompanied with ashes and +lapilli, we had sometimes one kind of electricity, and sometimes the +other, just as the smoke or the ashes predominated; and often with a +"fixed conductor" we obtained negative electricity, and with a "movable +conductor" positive electricity. In Naples, too, at the Meteorological +Observatory attached to the University, my colleague, Professor Eugenio +Semmola, observed negative electricity of strong tension whilst ashes +were falling there in abundance. The tensions on this occasion were so +strong as to equal those obtained at changes of weather or during storms +(<i>temporali</i>), and, being beyond measure with a delicate electrometer, +we marked them with the symbol ∞: the same +phenomena were observed when lightnings flashed.</p> + +<p>When there is but little smoke, it is necessary to approach the eruptive +mouths with a portable apparatus, in order to observe those phenomena +which, in great eruptions, may be studied from the Observatory itself.</p> + +<p>The conditions under which (<i>folgori</i>) lightning flashes are seen from +the cloud of smoke are, that it is conveying great abundance of ashes. +In 1861, there were small flashes even from the line of eccentric mouths +<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span>above Torre del Greco, although the smoke was not very great; and when +these ceased to discharge, and the central crater became somewhat +active, with a moderate amount of smoke but a great deal of ashes, small +and frequent lightning flashes were observed in the twilight darting +through the smoke, which was dark in colour. In 1850 the eruption was +more vigorous, the smoke more abundant, and the ashes scarce, but the +flashes were very rare. In 1855, 1858, and 1868, with a scanty supply of +ashes and at intervals, no flashes were observed, and the electricity +remained constantly positive. But having regard to the facts of +antecedent eruptions, one sees that the flashes are always derived, from +the midst of smoke accompanied with ashes and lapilli, which separate +like rain from the rolling volumes of smoke, in the midst of which they +were ejected.</p> + +<p>But how can we account for the positive electricity of the smoke, and +the negative electricity of the falling ashes? Without denying the +probability that a part of the positive electricity depends upon the +elevation of the smoke, as in the case of every other conductor we raise +aloft, or with a jet of water sent from a vessel by compressed air, I +think that the greater part of the electricity proceeds from the rapid +condensation of vapours, which are changed from the gaseous condition +into dense clouds; for even when the smoke issues tranquilly and does +not rise, because carried away horizontally by the wind, it gives signs +of positive electricity. From all my studies of atmospheric electricity, +and from some experiments made specially, it follows that the +<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span>condensation of vapours is the origin of this development of positive +electricity.</p> + +<p>The negative electricity of the falling ashes certainly arises from the +fact itself of their fall; for if we place a metallic vessel full of +ashes upon an elevated and well-situated terrace, while the atmospheric +electricity is positive, and cause the ashes from the vessel to fall +gradually into an insulated metallic cup, communicating with +Bohnenberger's electroscope placed at three or four metres distance from +the vessel, the electroscope will manifest negative electricity. If the +upper vessel be insulated, and the ashes permitted to fall upon the +ground, we shall obtain, from the vessel, positive electricity. The +intensity of these electric manifestations depends (other things being +equal) upon that predominant at the moment in the air; so that if the +experiment be made while negative electricity prevails, the falling +ashes will manifest positive electricity, the upper vessel then showing +negative electricity. Now, as the ashes separate from the positively +electrified smoke in order to approach the ground, which is negatively +electrified, it follows that they must manifest negative electricity +upon touching the ground, leaving the positive electricity in the smoke +above. For this reason, the electric tension of the smoke is increased +by the descent of the ashes and lapilli, so that discharges between the +upper and lower part of the pine-tree cloud, or the surface of the +crater, are rendered possible. Hence it follows that the flashes of +lightning of Vesuvius play through the smoke, and with difficulty strike +bodies upon the earth; and from this circumstance our ancestors believed +the <span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span>thunderbolts of Vesuvius to be harmless. However, if the smoke were +very great, and driven by the force of the wind to some distance from +the crater, with an abundant fall of ashes, it would be possible to have +lightning flashes proceed from the smoke to the earth. I possess some +documents which relate that, in 1631, thunderbolts fell upon the Church +of Santa Maria del Arco, and other places on the coast of Sorrento.</p> + +<p>After upwards of twenty years' study and observation of meteoric +electricity, I am enabled to prove that atmospheric electricity is never +manifested without rain, hail or snow, and that manifestations of light +are always accompanied by thunder—manifestations of light (<i>lampi</i>), +thunder and rain being most closely connected. We may have rain without +manifestations of light, but never the latter without rain or hail. I +cannot here repeat what I have demonstrated in other memoirs; I can only +say that the lightnings of Vesuvius, erroneously believed to be not +accompanied by thunder, are really not accompanied by rain, but are +induced by the descent of ashes and lapilli.<a name="FNanchor_6_20" id="FNanchor_6_20"></a><a href="#Footnote_6_20" class="fnanchor">[6]</a></p> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span></p> +<h2><a name="GENERAL_CONCLUSIONS" id="GENERAL_CONCLUSIONS"></a>GENERAL CONCLUSIONS.</h2> + + +<p>We may conclude from what I have stated:</p> + +<ol> +<li>That by the assiduous study of the central crater, and the +indications afforded by the "Apparatus of Variations" and the +"Electro-Magnetic Seismograph," we can obtain precursory signals of +eruptions; and that the other premonitory signs pointed out by our +ancestors, such as the drying up of wells, either only happen +occasionally or are mere coincidences, such as those of the coincidence +of a dry or a rainy season, the prevalence of certain winds, etc.<a name="FNanchor_F_13" id="FNanchor_F_13"></a><a href="#Footnote_F_13" class="fnanchor">[F]</a></li> + +<li>That the fumaroles of the lavas are communications between the +external surface of the lava, hardened and more or less cooled, and the +interior lava still pasty, or at least incandescent.</li> + +<li><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span>That from the lava, while flowing, there is no escape of acid +vapours, neither from the fumaroles at the first period of their +existence, but these, if they last long enough, arrive at an acid +period.</li> + +<li>That hydrochloric is the first acid that appears, combined afterwards +with sulphurous acid, and, still later, with sulphuretted hydrogen.</li> + +<li>That vigorous lava streams may have eruptive fumaroles. (See +<a href="#Footnote_2_16">Translator's Note 2</a> to p. 94.)</li> + +<li>That the sublimations follow a certain order in their appearance. In +the neutral period we get sea-salt mixed with some metallic oxides, the +first of which is oxide of copper. But in the great lavas, chloride of +iron appears simultaneously with the acid period. Hydrochloric acid +transforms the oxides into chlorides, which, in their turn, change into +sulphurets or sulphates on the appearance of sulphurous acid.</li> + +<li>That the acids, by attacking the scori, create new chlorides and +sulphates, which are thus not products merely of sublimation.</li> + +<li>That micaceous peroxide of iron—so common and abundant near the +eruptive mouths—is very scarce and rare on the lavas, unless conveyed +there from the craters.</li> + +<li>That chloride of iron—so manifest on the fumaroles of the great +lavas—is only found in small eruptions close to the discharging mouths.</li> + +<li>That the frequency of chloride of iron in the lavas of great +eruptions masks the order of transformation of the other products.</li> + +<li><span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span>The fumaroles at the summit of Vesuvius present even greater +gradations, for they often emit carbonic acid or pure watery vapour.</li> + +<li>Lead, which I first discovered in the fumaroles of the lavas of +1855, is a constant product of fumaroles which have a certain duration. +It is often obtained as a distinct and crystallized chloride, and often +is found in combination with other products.</li> + +<li>Oxide of copper is also a constant and primary (<i>primitivo</i>) product +of fumaroles. The chloride and sulphate of copper are formed from the +oxide, directly contrary to general belief.</li> + +<li>I do not think that the chloride of calcium, which I found on this +occasion in almost all the deliquescent sublimations, is a product +peculiar to this eruption only, in which alone, however, I found it. I +was, therefore, induced to look for it in other sublimates, in which I +might possibly have overlooked it, as, without doubt, my predecessors +have done, owing to the deliquescence of the chloride of iron with which +it was constantly combined. I think that this chloride, in accordance +with the general law, is transformed into a sulphate—a transformation +which readily occurs on Vesuvius.</li> + +<li>Copious and well-crystallized sal ammoniac is only found on the +fumaroles of those lavas which have covered cultivated or wooded ground.</li> + +<li>The scarcity of oxygen in the gases of fumaroles may possibly arise +from the formation of the oxides which precede the chlorides.</li> + +<li>Lavas give a continuous spectrum, although <span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span>covered with smoke, when +looked at with Hoffmann's spectroscope with direct vision.<a name="FNanchor_G_14" id="FNanchor_G_14"></a><a href="#Footnote_G_14" class="fnanchor">[G]</a></li> + +<li>The smoke gives positive electricity, and the falling ashes negative +electricity.</li> +</ol> + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span></p> +<h2><a name="REFERENCE_TO_THE_PLATES" id="REFERENCE_TO_THE_PLATES"></a>REFERENCE TO THE PLATES.</h2> + +<p class="center"><a name="PLATE_1"><img src="images/plate1.jpg" alt="" /></a><br /> +I<span class="smcap">a</span>. The Cone of Vesuvius, in 1870, from a Photograph taken +near the Observatory.</p> + +<table border="0" cellpadding="2" cellspacing="0" summary=""> +<tr><td align="right" valign="top" style="width:8em;"><i>a.</i></td><td>The Atria del Cavallo.</td></tr> +<tr><td align="right" valign="top"><i>b b.</i></td><td>Fossa della Vetrana.</td></tr> +<tr><td align="right" valign="top"><i>c.</i></td><td>Punta del Crocella.</td></tr> +<tr><td align="right" valign="top"><i>d.</i></td><td>Lava of 1858 and 1867.</td></tr> +<tr><td align="right" valign="top"><i>e.</i></td><td>Police Barrack near the Observatory.</td></tr> +<tr><td align="right" valign="top"><i>f.</i></td><td> Part of Monte Somma.</td></tr> +</table> + +<hr class="tb" /> +<p class="center"><a name="PLATE_2"><img src="images/plate2.jpg" alt="" /></a><br /> +II<span class="smcap">a</span>. Profile of Vesuvius, taken from a Photograph of the +Observatory in the month of September, 1871.</p> + +<table border="0" cellpadding="2" cellspacing="0" summary=""> +<tr><td align="right" valign="top" style="width:8em;">1.</td><td>The Cone, on the 13th January, 1871.</td></tr> +<tr><td align="right" valign="top">2, 2.</td><td>Lava of 1871.</td></tr> +</table> + +<hr class="tb" /> +<p class="center"><a name="PLATE_3"><img src="images/plate3.jpg" alt="" /></a><br /> +III<span class="smcap">a</span>. Profile of Vesuvius on the 16th April, 1872, about ten +days before the last Conflagration.</p> + +<hr class="tb" /> +<p class="center"><a name="PLATE_4"><img src="images/plate4.jpg" alt="" /></a><br /> +IV<span class="smcap">a</span>. Vesuvius, on the 26th April, 1872, from a Photograph taken +in the neighbourhood of Naples.</p> + +<table border="0" cellpadding="2" cellspacing="0" summary=""> +<tr><td align="right" valign="top" style="width:8em;">1.</td><td>The Observatory.</td></tr> +<tr><td align="right" valign="top">2.</td><td>Fossa della Vetrana.</td></tr> +<tr><td align="right" valign="top">3.</td><td>Eruption of Smoke and Ashes, with Stones, from the +surface of the Lava.</td></tr> +<tr><td align="right" valign="top">4.</td><td>The Novelle, St. Sebastiano, and Massa.</td></tr> +<tr><td align="right" valign="top">5.</td><td>Lava which took the direction of Resina.</td></tr> +<tr><td align="right" valign="top">6.</td><td>Lava which, from the Crater, took the direction of the +Camaldoli.</td></tr> +<tr><td align="right" valign="top">7.</td><td>The Grain Stores, near Naples.</td></tr> +<tr><td align="right" valign="top">8.</td><td>Resina.</td></tr> +<tr><td align="right" valign="top">9.</td><td>Torre del Greco.</td></tr> +<tr><td align="right" valign="top">10.</td><td>The Camaldoli.</td></tr> +</table> + +<hr class="tb" /> +<p class="center"><a name="PLATE_5"><img src="images/plate5.jpg" alt="" /></a><br /> +V<span class="smcap">a</span>. Profile of Vesuvius after the Eruption of the 26th April, +1872, from a Photograph taken near the Observatory.</p> + +<table border="0" cellpadding="2" cellspacing="0" summary=""> +<tr><td align="right" valign="top" style="width:8em;">1, 1.</td><td>The Fissures of the 26th of April.</td></tr> +<tr><td align="right" valign="top">2, 3.</td><td>Small Hill thrown up on the morning of the 26th of +April, from below which issued the great current of +Lava.</td></tr> +<tr><td align="right" valign="top">4, 4, 4.</td><td>The Mouths out of which the Lava issued.</td></tr> +<tr><td align="right" valign="top">5, 5.</td><td>The larger Lava Stream, which passed near the Observatory +by the Fossa della Vetrana.</td></tr> +<tr><td align="right" valign="top">6, 6.</td><td>The other Lava Stream, which, after dividing from +the last, took the direction of Resina.</td></tr> +<tr><td align="right" valign="top">7, 7.</td><td>The Lava which ran down towards the Camaldoli.</td></tr> +<tr><td align="right" valign="top">8 & 9.</td><td>The two Craters on the summit of the Cone.</td></tr> +</table> + +<hr class="tb" /> +<p class="center"><a name="PLATE_6"><img src="images/plate6.jpg" alt="" /></a><br /> +VI<span class="smcap">a</span>. The Bifilar Electrometer of Signor Palmieri. (<i>Details.</i>)</p> + +<hr class="tb" /> +<p class="center"><a name="PLATE_7"><img src="images/plate7.jpg" alt="" /></a><br /> +VII<span class="smcap">a</span>. The assemblage of the Electroscopic Apparatus of Signor Palmieri, as arranged at the Vesuvian Observatory.</p> + +<hr class="tb" /> +<p class="center"><a name="PLATE_8"></a><a href="images/plate8.jpg"><img src="images/plate8_t.jpg" alt="" /></a><br /> +VIII. Professor Palmieri's Seismographic Apparatus.</p> + + +<hr class="chap" /> +<div class="footnote"><p><a name="Footnote_A_8" id="Footnote_A_8"></a><a href="#FNanchor_A_8"><span class="label">[A]</span></a> This small cone, as it appeared on the 1st April, is +described and drawn in a Memoir of Professor von Rath, of the University +of Bonn, on "Vesuvius on the 1st and 17th of April, 1871."</p></div> + +<div class="footnote"><p><a name="Footnote_B_9" id="Footnote_B_9"></a><a href="#FNanchor_B_9"><span class="label">[B]</span></a> Eight young medical students perished beneath the lava, +with others unknown by name. They were all youths of good promise; their +names will be recorded on the marble monument to be erected near the +Observatory. They are: Girolamo Pausini, Antonio and Maurizio +Fraggiacomo, Francesco Binetti da Molfettu, Giuseppe Carbone da Bari, +Francesco Spezzaferri da Trani, and Giovanni Busco da Casamassima and +Vitangelo Poli.</p></div> + +<div class="footnote"><p><a name="Footnote_C_10" id="Footnote_C_10"></a><a href="#FNanchor_C_10"><span class="label">[C]</span></a> If this enormous height of projection really means, that +above the brim of the crater, it involves an initial velocity of +projection of above 600 feet (British) per second. +</p><p> +Observations of the height of ascent of volcanic blocks are always +difficult and deceptive, and never free from error.—<i>Translator.</i></p></div> + +<div class="footnote"><p><a name="Footnote_D_11" id="Footnote_D_11"></a><a href="#FNanchor_D_11"><span class="label">[D]</span></a> Assuming these flashes to have emanated from somewhere +within the cloudy volume of steam and dust called "the head of the +pine-tree," this interval would indicate that the mean height of this +cloudy volume itself was not more than about four thousand feet above +the top of the cone; and, if so, that is not very far from the limit in +height of projection of the dust and lapilli.—<i>Translator.</i></p></div> + +<div class="footnote"><p><a name="Footnote_E_12" id="Footnote_E_12"></a><a href="#FNanchor_E_12"><span class="label">[E]</span></a> <span class="smcap">Cotunuite</span>, chloride of lead, in white, lustrous, acicular +crystals, of the trimetric system, easily scratched, Sp. gr., 5238. +</p><p> +<span class="smcap">Tenorite</span>, peroxide of copper, in thin, hexagonal plates or scales, +translucent when very thin, dark steel gray, of the cubic system; hard +and lustrous. Sp. gr. about 5950.—<i>Translator.</i></p></div> + +<div class="footnote"><p><a name="Footnote_F_13" id="Footnote_F_13"></a><a href="#FNanchor_F_13"><span class="label">[F]</span></a> Earthquakes, though in distant regions, usually precede +eruptions. The Earthquake of Melfi preceded the great Eruption of Etna +in 1852; the Earthquake of Basilicata of December, 1857, terminated with +the Eruption of 1858, which filled the Fossa Grande with lava; the +Earthquakes of Calabria of 1867 and 1870 were the precursors of the +Vesuvian conflagrations of 1868, 1871, 1872. A Volcano, also, in the +Island of Java had a great eruption in the month of April, some days +before the last conflagration of Vesuvius, as I learnt from a letter +addressed to Signor Herzel, Swiss Consul at Palermo, communicated to +me<a name="FNanchor_7_21" id="FNanchor_7_21"></a><a href="#Footnote_7_21" class="fnanchor">[7]</a> by the astronomer, Signor Cacciatore.—<i>Palmieri.</i></p></div> + +<div class="footnote"><p><a name="Footnote_G_14" id="Footnote_G_14"></a><a href="#FNanchor_G_14"><span class="label">[G]</span></a> I have made a large collection of sublimates, which I +purpose examining with the spectroscope, and I shall be able to place +some at the disposal of experimentalists who may desire to pursue +investigations of this kind.</p></div> + + + +<hr class="chap" /><p><span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span></p> +<h2><a name="NOTES" id="NOTES"></a>NOTES<br /> + +BY THE TRANSLATOR.</h2> + + + +<div class="footnote"><p><a name="Footnote_1_15" id="Footnote_1_15"></a><a href="#FNanchor_1_15"><span class="label">[1]</span></a> (P. 82, text). Professor Palmieri has not given any +description in this Memoir of his seismograph—the instruments described +being those only which have relation to atmospheric electricity. The +following brief account of his seismograph will, therefore, form a not +unsuitable complement to his Memoir. The instrument, in general terms, +is of that class in which the wave movements are indicated by the +displacement, relative or absolute, of columns of mercury in glass +tubes. It is a self-recording instrument, composed of two distinct +portions—one for record of horizontal, or rather of what are called +undulatory shocks; the other for vertical shocks. In point of general +principle, therefore, it is very similar to that proposed by me +("Transactions, Royal Irish Academy," in 1846), and in certain respects +appears to me less advantageous than the latter. Some account of the +Palmieri instrument, together with some critical remarks as to its +action, may be found in my "Fourth Report on Earthquakes" ("Reports, +British Association, 1858," pp. 75-81). The following description of the +instrument is derived from "The Engineer," of 7th June, 1872, and the +publishers have to thank the proprietors of that journal for permission +to use the illustration, <a href="#PLATE_8">Plate 8</a>. +</p><p> +In Fig. 1, <i>E</i> is a helix of brass wire (gauge about one millimetre); +the helix consists of fourteen or fifteen turns, and has a diameter of +from twenty to twenty-five millimetres; it hangs from a fine metal +spring, and can be raised or lowered by a thumb screw. From the lower +end of the helix hangs a copper cone with a platinum point; the latter +is kept close to the surface of mercury in the iron basin, <i>f</i>, which +rests on an insulating column of wood or marble, <i>G</i>. The distance of +the point from the surface of the mercury remains constant, as the metal +pillar, <i>T</i>, is of such a length that its expansion or contraction by +change of temperature compensates that of the helix; the latter is in +connection (by <i>T</i>) with one pole of a Daniell's battery of two cells, +and the basin, <i>f</i>, is connected with the other pole. Any vertical +movement, however slight, makes the platinum point dip into the mercury, +and thus completes the circuit. In this circuit are included two +electro-magnets, <i>C</i> and <i>D</i>; these, during the circulation of a +current, <span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span>attract their armatures, which are connected with levers. The +action of <i>C's</i> lever is to stop the clock, <i>A</i>, which thus records, to +a half-second, the time of the occurrence of the shock, at the same +instant that the clock strikes an alarm bell, which attracts the +attention of an observer. The lever, attached to the armature of <i>D</i>, at +the first instant of the current frees the pendulum of the clock, <i>B</i>, +which was before kept from swinging, in a position out of the vertical; +the clock then acts as a time-piece, and its motion unrolls a band of +paper, <i>k k k</i>, at a rate of three metres an hour. At the same time the +armature of <i>D</i>, while attracted, presses a pencil point against the +band of paper which passes over the roller, <i>m</i>, marking on it, while +the earthquake lasts, a series of points or strokes which occupy a +length of paper corresponding to its duration, and which record the work +of the shock. After it is over the paper continues to unroll from the +drum, <i>i</i>, and passing round the clock, rolls on to the drum, <i>l</i>. If a +fresh shock occur the pencil indicates it, as before, on the paper, and +the length of blank paper between the two sets of marks is a measure of +the interval of time between the shocks. By way of additional check, +several helices, <i>h h h</i>, are hung from a stand, with small permanent +magnets suspended from their ends; below and close to these latter are +small basins, holding iron filings; into these the points of the magnets +dip, when their helices oscillate vertically, and some filings remain +sticking to the magnets as a record of the shock. One of the magnets has +a shoulder on it which moves an index hand along a graduated arc, as +shown in Fig. 2, thus again registering the amount of the vertical +movement. Such are the arrangements intended for the record of the +undulatory or horizontal elements of the wave of shock. +</p><p> +The following are the arrangements proposed for recording the horizontal +motions: On the stand, to the right of the clock, <i>A</i>, are set four +<b>U</b>-shaped glass tubes, open at their ends. One of each pair of vertical +branches must have a diameter at least double that of the other. These +pairs, with their supporting columns, are shown in plan, where one pair +lies N. and S., another E. and W., a third N.E. and S.W., and the other +N.W. and S.E. It will be observed that metallic bars pass from the +pillar, <i>P</i>, over the ends of all the long branches, and similar bars +pass from <i>R</i>, over the ends of the short branches; the pillars +themselves, as in the case of the other instruments, are each connected +with one pole of a Daniell's battery, the connections including the +electro-magnets, <i>C</i> and <i>D</i>. The description of one <b>U</b> tube, <i>n</i>, will +apply to all the others; <i>n</i> is partly filled with mercury, and an iron +or platinum wire, <i>o</i>, suspended from the bar above the short branch, +dips into the mercury therein, while another platinum wire hung from the +bar over the mouth of the longer branch, has its end very close to the +surface of the mercury in that branch. Any shock which is not +perpendicular in direction to the plane of the branches of the <b>U</b> will +cause the mercury to oscillate in the tubes, and more sensibly in that +with the smaller diameter; when it rises up in <span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span>the latter, so as to +touch the platinum point, the connection between <i>P</i> and <i>R</i> is made and +the circuit completed, starting the action of the electro-magnets <i>C</i> +and <i>D</i>, which record the shock, as already described. By having the +planes of the tubes set in the different azimuths, already mentioned, +one or more of the pairs is sure to be acted upon, and by observing in +which the oscillation takes place the direction of the shock is supposed +to be ascertained. Besides this, each long branch of the <b>U</b>, viz., that +of smaller diameter, has a small ivory pulley, <i>q</i>, fixed above it, over +which passes a single fibre of silk, with an iron float at one end, +resting on the surface of the mercury; at the other end of the fibre +hangs a counterpoise; fixed to the pulley is a fine index hand, capable +of moving along a graduated arc. When the shock takes place the mercury, +rising in the long branch, raises the float on its surface, the silk +fibre at the same time makes the pulley revolve with its index hand, +which afterwards remains stationary, as the counterpoise prevents the +float from sinking again with the mercury. The reading on the graduated +arc is thus a measure of the movements produced in the instrument by the +horizontal element of the shock, and is supposed to measure that shock. +It is assumed that in all these instruments shocks, however small, can +be recorded with certainty by adjusting the distance between the +platinum points and the mercury. +</p><p> +The arrangement of Daniell's battery used for the seismograph is shown +in Fig. 4, where, for convenience of cleaning, the copper element is +made of wire (about No. 8 Birmingham wire gauge) coiled flat without the +spirals touching. Crystals of sulphate of copper are placed at the +bottom of the outer cell, into which water is poured; and the inner +cell, into which the zinc plate goes, is filled with siliceous sand. +</p><p> +In addition to the above some instruments of a rougher description are +employed as checks. Thus, at the foot of the pillar, <i>G</i>, there is a +wooden trough with eight holes, facing as many equidistant points of the +compass (two of them shown in section) round its inner circumference; +mercury is poured into the basin until its level is nearly up to the +lips of the holes. The effect of a shock is to throw some of the mercury +into one or more of these holes, and the greater the oscillation the +more mercury is thrown into the cells through the holes. The screws +shown outside are for drawing off the mercury from the cells, when its +quantity can be measured. The direction of the shock is shown by seeing +which cells are filled with mercury. This is the old Cacciatore +seismometer which has been long employed in Italy. (See 4 "Report of +British Association, 1858," p. 73), and Daubeny's "Volcanoes," Appendix. +The following is another contrivance. From the arm of the pillar, <i>G</i>, a +fine metal wire hangs, with a metal ball at its end, which, by its +oscillation, thrusts out one or more light glass tubes, set horizontally +in a stand, as shown in Fig. 3. The two rings are of wood, and the glass +tubes pass through holes in them; small leather washers are placed +outside the outer rings; the displacement <span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span>of one or more tubes is +assumed to measure the horizontal element of the shock. By means of this +apparatus the time of the first shock is recorded, as well as the +interval between the shocks, and the duration of each; their direction, +whether vertical or horizontal, is given, as also the maximum of +intensity. Professor Palmieri has the instruments examined three times a +day, and an assistant-observer is always at hand to attend to the bell, +and put back the apparatus to its normal position for fresh observation. +</p><p> +It has been stated that this instrument is sensible to most of the +shocks which occur in the Mediterranean basin. +</p><p> +It is not my intention here to offer any criticism as to the +construction or performances of this instrument, the rather as I must +confess I do not quite share the high opinion of its inventor as to the +certainty or exactitude of its indications. +</p><p> +There can be no question as to the extreme importance to science of the +establishment and continued use of a seismographic instrument of +unexceptionable construction at the Observatory upon Vesuvius; and it +would be a valuable gift to science, were the Italian Government to +enable Signor Palmieri to establish such an one. Its great value and the +very first problem to set the instrument to solve should be, by <i>a rigid +determination of the direction of propagation of the wave of shock</i>, of +those slight or stronger pulsations which precede or accompany the +Vesuvian like all other eruptions, on arriving at the Observatory, <i>to +fix the depth, and the position vertically beneath the cone, whence +these pulses are derived</i>. This would be, in fact, to fix the depth and +position beneath the mountain at which the volcanic focus is situated +for the time, or, at least, where the volcanic activity is at the time +greatest. And the assured knowledge, even within moderate limits of +accuracy, of this depth, and even for this single mountain, would be an +immense accession to our positive knowledge, and a really new stage +gained for future advances. At present, we know but little as to the +actual depth below our globe's surface at which volcanic activity +occurs, or to which it is limited, either upwards or downwards. I have, +myself, established some data upon the flanks of Etna, not yet +published, which may enable me to afford some information on the subject +hereafter. Meanwhile, Professor Palmieri possesses unrivalled +opportunities for such observations; and I trust health, life and means +may be afforded him, to become the first who shall have made this great +addition to our positive knowledge of Vulcanology. +</p><p> +So far, popularly at least, the alleged chief uses and value of these +seismographic instruments, at the Observatory of Vesuvius, have been +made to depend upon their being presumed to afford means for foretelling +eruptions, or affording precursory warnings of their probable progress +and destructive course. +</p><p> +I feel compelled to express my own total disbelief in the possibility of +any such predictions in the present state of science, by the help of any +instruments whatsoever, of such a nature as to be of any <i>practical +value</i>, <span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span>or any certainty beyond that which a certain amount of <i>mere +experience</i> as to the <i>rle commonly played</i> by Vesuvius or other +Volcanoes in pretty habitual activity affords to the observer for a +lengthened period. And even this affords scarcely any guide as to what +may happen next. Monte Nuovo was thrown up in a night; Vesuvius <i>might</i> +double its volume in a night, or might sink into a hollow like that of +the Val del Bove in a not much longer time. A small <i>fusillade</i> may go +on for months, and yet, without an hour's notice, by any premonitory +sign, may waken up to a roar and darken the air with ashes and lapilli +such as those which overwhelmed Pompeii. One eruption may blow forth +little but dust and ashes (so called), another may pour out rivers of +lava and little else. +</p><p> +The <i>main</i> mischief of all eruptions is effected in two ways: by the +deposit of dust and ashes, lapilli, etc., to the injury or destruction +of fertile land, and by the streams of lava which overwhelm it, as well +as buildings, etc. But what information of any value can seismographic +observation afford as to the course that either of these may take in any +eruption? The volume of pulverulent material that may be ejected cannot +be foreseen; its distribution depends mainly upon its nature and upon +the direction and force of the wind at the time; or again, how shall +these warn us as to the course that the lava, if it appear, shall take, +when we cannot possibly foretell when, how, or by what mouth it may +issue. Even in this late eruption of 1872, with Palmieri stoutly at his +post upon the mountain, and the Observatory instruments in full +activity, they gave no forewarning of the sudden and unexpected belch +forth from the base of the cone, of that tremendous gush of liquid lava +which in a few minutes cut off from life the unhappy visitors whose +deaths he has recorded.</p></div> + +<div class="footnote"><p><a name="Footnote_2_16" id="Footnote_2_16"></a><a href="#FNanchor_2_16"><span class="label">[2]</span></a> (P. 94). It can scarcely be supposed that these small +eruptive-looking belchings forth from the lava stream, <i>en route</i>, are +truly of an eruptive nature at all, <i>i.e.</i>, in any way connected with +forces seated deeply beneath the bed of the lava stream, or in any way +connected with the volcanic ducts of the cone or beneath it. They are +most probably merely the bursting upwards of large bubbles; that is, of +cavities formed in the mass of the more or less liquid lava by intestine +movements, as its mass winds and rolls along, and by the aggregation of +smaller cavities—all being filled with steam and gases—together with +dust and volatile products which are ejected when the cavity opens up, +and its contents escape at the upper surface of the lava stream in +virtue of the continuation of the twistings and convolutions due to the +stream motion itself, and to the unbalanced hydrostatic pressures acting +upon the parietes of the bubble. Very large single bubbles of like +character rise in the fluid lava within craters in vigorous action, and +often so regularly that their recurrence causes a sort of rhythmical +rush and roar in the column of steam, etc., <span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span>issuing above the mouth. +This was evident in the discharges issuing in 1857 from the highly +instructive minor <i>bocca</i>, then existing, examined by me, and referred +to ("Report, Naples, Earthquakes," etc. Vol. II., pp. 313, 314), as +presenting at the time great facilities for determining pyrometrically +the temperature of the lava within, and of the dry superheated steam +issuing with a rhythmic roar from it. M. Le Coq ("poques Gologiques +d'Auvergne," Tome IV.) has recorded some examples of the formation and +opening-out of large bubble-like cavities in lava already ejected. +Perhaps that able and laborious vulcanologist, whose death a few months +ago science still deplores, attributes too much importance as well as +magnitude to them, when attributing the formation of what he has +denominated "craters of explosion," to the mechanism of the rise and +bursting of such bubbles upon a gigantic scale. Such blowings forth, +sudden or prolonged, from particular spots of lava streams, <i>en route</i>, +undoubtedly may also have their origin in damp places, or water or +air-filled cavities in or beneath the bed over which the lava rolls, +which, getting gradually heated, generate steam, or air or gases under +tension by expansion, etc., which thus at length blow through the liquid +or pasty lava flowing above, and which in bursting through delivers much +dust also, and so simulates a little eruptive crater. Examples of this, +upon a great and convincing scale, can be pointed to in the Val di +Calanna and elsewhere on Etna.</p></div> + +<div class="footnote"><p><a name="Footnote_3_17" id="Footnote_3_17"></a><a href="#FNanchor_3_17"><span class="label">[3]</span></a> (P. 96). There are strong grounds for the gravest doubts +that there exists any real connection of a physical character between +Volcanic Eruptions, and Earthquakes more or less <i>approximately</i> +coincident only, in time of occurrence; the respective sites being +widely apart, and the less the probability as the intervening distance +is greater. The discussions of the large number of records that are to +be found of such coincidences—mostly but partial, and in but <i>very</i> few +instances complete coincidences—by Perrey, von Hoff, and others, as +well as by myself, do not tend to sustain the view that such imperfect +contemporaneity is based upon any causative connection. The seismic +region of Greece appears to have no <i>direct</i> connection with that of +Southern Italy: the band of connection, if any, seems to lie between +Northern Italy, across the Northern Adriatic, by Ragusa, and thence +spreading into Asia Minor.</p></div> + +<div class="footnote"><p><a name="Footnote_4_18" id="Footnote_4_18"></a><a href="#FNanchor_4_18"><span class="label">[4]</span></a> (P. 97). The abundance of coleoptera and of various other +forms of insect life about lava beds, both recent and old, is a very +singular fact, and one worthy of the careful observation of +entomologists. In the autumn of 1864, at mid-day, when sitting sketching +upon the lava about the middle of the Val del Bove (Etna), I found it +almost impossible to work, or even to remain for an instant still, in +consequence of the continual cloud of insects, large and small, that +struck against me in flight, endangered the eyes, and swarmed upon <span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span>my +clothes. It is quite possible that this local superabundance of insect +life may arise merely from the general dryness and warmth of such +places, and the plentiful <i>nidus</i> that the innumerable cavities in lava +afford for the eggs and earlier stages of insect life; still, this +apparition of one form of life may also be connected with other +circumstances not unimportant to discover.</p></div> + +<div class="footnote"><p><a name="Footnote_5_19" id="Footnote_5_19"></a><a href="#FNanchor_5_19"><span class="label">[5]</span></a> (P. 120). The <i>Crocella</i> is a small wooden cross, erected +several years ago, and which one passes to the right hand at the upper +end of the path along the ridge of tufa and volcanic conglomerate upon +which the Observatory stands, in ascending thence to the Atria del +Cavallo.</p></div> + +<div class="footnote"><p><a name="Footnote_6_20" id="Footnote_6_20"></a><a href="#FNanchor_6_20"><span class="label">[6]</span></a> (P. 134). That the causes assigned by Professor Palmieri +for the potent developments of electricity (positive or negative) which +characterise the ascent of the issuing columns of (chiefly if not +always) <i>dry</i> steam, with a relatively small volume of various gases, +and throwing up, in their blast, volumes of small solid particles in +ashes and lapilli, etc., and the subsequent fall as a mineral or stony +hail-shower of the latter, through the partially condensing vapours and +the circumambient air, are the main causes of electrical development +evidencing itself in lightning flashes, is no doubt true. We must not, +however, lose sight of the many other and very effective agencies at +work here to produce electric excitement. The actual <i>bocca</i> of the +volcanic vent whence the steam roars off constitute the cone a veritable +hydro-electric machine. Mechanical energy in various forms is +transformed into electric energy. Chemical action is going on both in +the solid and in the vapourous and gaseous emanations as they rush into +and remain in the air or descend from it, and chemical action is +transformed in part into electric energy. Percussion between ascending +and descending particles and fragments, fractures and breaking up of +more or less of these, thus and by sudden changes of temperature in +cooling, are likewise operative. In addition, great and violent +movements in the atmosphere itself result from the large local +accessions of temperature by the heated volume driven up into it, and +which in turn give rise to electric disturbance of the same character as +those produced in wind storms and whirlwinds, brought about by the +natural causes which every day effect disturbances in our atmosphere all +over the globe.</p></div> + +<div class="footnote"><p><a name="Footnote_7_21" id="Footnote_7_21"></a><a href="#FNanchor_7_21"><span class="label">[7]</span></a> (P. 135). The views stated in <a href="#Footnote_3_17">note 3</a> (to page 96) may here +again be referred to as in point. How is it possible, in the present +state of science at least, to establish any physical connection between +an eruption in Java and one of Vesuvius, "with half the world between," +when not even having the solitary connecting link of complete +contemporaneity, <span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span>and which, if it existed, yet might be nothing but +accidental? A list of shocks upon record, which have occurred more or +less nearly simultaneously at distant parts of the world, may be found +in my fourth Report, ("Facts of Earthquakes," "British Association +Reports, 1858") and the reasons are there given for rejecting the notion +of any direct physical connection between the origins of the respective +shocks. +</p><p> +Shocks, emanating from the close neighbourhood of volcanic vents, or +simultaneity of eruption, in vents not far distant from each other, +stand upon a different footing.</p></div> + + + +<hr class="chap" /> +<h2><a name="Transcribers_Notes" id="Transcribers_Notes"></a>Transcriber's Notes.</h2> + +<p>Preserved the unusual, but consistent, spelling of "develope."</p> + +<p>Preserved the unusual, and inconsistent, references to the Plates. +Sometimes Arabic numerals are used, but usually Roman numerals. Most +have "<span class="smcap">a</span>" attached to the name, but not VIII, and sometimes not in the +references to them.</p> + +<p>Equations were converted to linear text, adding spacing and parentheses +as necessary.</p> + +<p>Changed "fumarolles" to "fumaroles" on page 3: "fumaroles and +salfatares."</p> + +<p>Changed "Lyall" to "Lyell" in footnote originally on page 9: "Daubeny, +Lyell, Phillips and others."</p> + +<p>Changed "throught" to "through" on page 35: "passing through it."</p> + +<p>Removed duplicated word "the" on page 40: "the great Calabrian +Earthquake."</p> + +<p>Page 89 refers to the "Fossa del Vetrano;" elsewhere there are +references to "Fossa della Vetrana," which may be what was intended. +However, I did not change this.</p> + +<p>Changed "hydrochloride" to "hydrochloric" on page 109: "the hydrochloric +acid which it discharged."</p> + +<p>Changed "disk" to "disc" on page 126: "the disc and index."</p> + +<p>Changed "azismuths" to "azimuths" on page 143: "the different azimuths."</p> + +<p>Changed "silicious" to "siliceous" on page 143: "filled with siliceous +sand."</p> + + + + + + + + +<pre> + + + + + +End of Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +*** END OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + +***** This file should be named 33483-h.htm or 33483-h.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/3/4/8/33483/ + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need are critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. + + +</pre> + +</body> +</html> diff --git a/33483-h/images/plate1.jpg b/33483-h/images/plate1.jpg Binary files differnew file mode 100644 index 0000000..cf344d8 --- /dev/null +++ b/33483-h/images/plate1.jpg diff --git a/33483-h/images/plate2.jpg b/33483-h/images/plate2.jpg Binary files differnew file mode 100644 index 0000000..34f9459 --- /dev/null +++ b/33483-h/images/plate2.jpg diff --git a/33483-h/images/plate3.jpg b/33483-h/images/plate3.jpg Binary files differnew file mode 100644 index 0000000..f5caa31 --- /dev/null +++ b/33483-h/images/plate3.jpg diff --git a/33483-h/images/plate4.jpg b/33483-h/images/plate4.jpg Binary files differnew file mode 100644 index 0000000..384b023 --- /dev/null +++ b/33483-h/images/plate4.jpg diff --git a/33483-h/images/plate5.jpg b/33483-h/images/plate5.jpg Binary files differnew file mode 100644 index 0000000..ffc2f64 --- /dev/null +++ b/33483-h/images/plate5.jpg diff --git a/33483-h/images/plate6.jpg b/33483-h/images/plate6.jpg Binary files differnew file mode 100644 index 0000000..6294f77 --- /dev/null +++ b/33483-h/images/plate6.jpg diff --git a/33483-h/images/plate7.jpg b/33483-h/images/plate7.jpg Binary files differnew file mode 100644 index 0000000..f6b8d46 --- /dev/null +++ b/33483-h/images/plate7.jpg diff --git a/33483-h/images/plate8.jpg b/33483-h/images/plate8.jpg Binary files differnew file mode 100644 index 0000000..e07bff7 --- /dev/null +++ b/33483-h/images/plate8.jpg diff --git a/33483-h/images/plate8_t.jpg b/33483-h/images/plate8_t.jpg Binary files differnew file mode 100644 index 0000000..2695d82 --- /dev/null +++ b/33483-h/images/plate8_t.jpg diff --git a/33483.txt b/33483.txt new file mode 100644 index 0000000..72988ae --- /dev/null +++ b/33483.txt @@ -0,0 +1,4537 @@ +Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Eruption of Vesuvius in 1872 + +Author: Luigi Palmieri + +Translator: Robert Mallet + +Release Date: August 22, 2010 [EBook #33483] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + + + + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + + + + + + + + +THE +ERUPTION OF VESUVIUS +IN 1872, + + +BY +PROFESSOR LUIGI PALMIERI, +_Of the University of Naples; Director of the Vesuvian Observatory._ + + +WITH NOTES, AND AN +_INTRODUCTORY SKETCH OF THE PRESENT STATE OF KNOWLEDGE_ +OF +TERRESTRIAL VULCANICITY, +_The Cosmical Nature and Relations of +Volcanoes and Earthquakes._ + + +BY +ROBERT MALLET, +_Mem. Inst. C.E., F.R.S., F.G.S., M.R.I.A., &c., &c._ + + +WITH ILLUSTRATIONS. + + +LONDON: + +_ASHER & CO._, +13, BEDFORD STREET, COVENT GARDEN, W.C. + +1873. + + +W. S. Johnson, Nassau Steam Press, 60, St. Martin's Lane, +Charing Cross, W.C. + + +"The Translator should look upon himself as a Merchant in the +Intellectual Exchange of the world, whose business it is to promote the +interchange of the produce of the mind." + + GOETHE, "_Kunst und Alterthum_." + + + + +INTRODUCTORY SKETCH, &c. + + +The publishers of this little volume, in requesting me to undertake a +translation of the "Incendio Vesuviano," of Professor Palmieri, and to +accompany it with some introductory remarks, have felt justified by the +facts that Signor Palmieri's position as a physicist, the great +advantages which his long residence in Naples as a Professor of the +University, and for many years past Director of the Meteorological +Observatory--established upon Vesuvius itself, prior to the expulsion of +the late dynasty--have naturally caused much weight to attach to +anything emanating from his pen in reference to that volcano. + +Nearly forty memoirs on various branches of physics--chiefly +electricity, magnetism and meteorology--produced since 1842, are to be +found under Palmieri's name in the "Universal Catalogue of Scientific +Papers of the Royal Society," and of these nine refer to Vesuvius, the +earliest being entitled "Primi Studii Meteorologici fatti sul R. +Osservatorio Vesuviano," published in 1853. He was also author, in +conjunction with Professor A. Scacchi, of an elaborate report upon the +Volcanic Region of Monte Vulture, and on the Earthquake (commonly called +of Melfi) of 1851. These, however, by no means exhaust the stock of +Palmieri's labours. + +The following Memoir of Signor Palmieri on the eruption of Vesuvius in +April of this year (1872), brief as it is, embraces two distinct +subjects, viz., his narrative as an eye-witness of the actual events of +the eruption as they occurred upon the cone and slopes of the mountain, +and his observations as to pulses emanating from its interior, as +indicated by his Seismograph, and as to the electric conditions of the +overhanging cloud of smoke (so called) and ashes, as indicated by his +bifilar electrometer, both established at the Observatory. The two last +have but an indirect bearing upon Vulcanology. The narrative of the +events of the eruption is characterised by exactness of observation and +a sobriety of language--so widely different from the exaggerated style +of sensational writing that is found in almost all such accounts--that I +do the author no more than justice in thus expressing my view of its +merits. + +Nor should a special narration, such as this, become less important or +suffer even in popular estimation by the fact that so recently my +friend, Professor J. Phillips, has given to the world the best general +account of Vesuvius, in its historical and some of its scientific +aspects, which has yet appeared. That monograph--with its sparkling +style, and scholarly digressions, as well as for its more direct +merits--will, no doubt, become the manual for many a future visitor to +the volcanic region of Naples; but it, like the following Memoir of +Palmieri, and in common with almost every work that has appeared on the +subject of Volcanoes, contains a good deal which, however interesting, +and remotely related to Vulcanology, does not properly belong to the +body of that branch of cosmical science, as I understand its nature and +limits. + +It tends but little, for example, to clear our views, or enlarge our +knowledge of the vast mechanism in which the Volcano originates, and +that by which its visible mass is formed, that we should ascertain the +electric condition of the atmosphere above its eruptive cone, or into +what crystallographic classes the mineral species found about it may be +divided: it will help us but little to know Pliny's notions of how +Pompeii was overwhelmed, or to re-engrave pictures, assumed to give the +exact shape of the Vesuvian or other cone at different periods, or its +precise altitude, which are ever varying, above the sea. Even much more +time and labour may be spent upon analysing the vapours and gases of +fumaroles and salfatares than the results can now justify. + +Nothing, perhaps, tends more to the effective progress of any branch of +observational and inductive science, than that we should endeavour to +discern clearly the scope and boundary of our subject. + +To do so is but to accord with Bacon's maxim, "_Prudens questio dimidium +scientiae_." That once shaped, the roads or methods of approach become +clearer; and every foothold attained upon these direct paths enables us +to look back upon such collateral or subordinate questions as at first +perplexed us, and find them so illuminated that they are already +probably solved, and, by solution, again prove to us that we _are_ in +the right paths. + +I believe, therefore, that I shall not do disservice to the grand +portion of cosmical physics to which volcanic phenomena belong, by +devoting the few pages accorded to me for this Introduction to sketching +what seems to me to be the present position of terrestrial +_Vulcanicity_, and tracing the outlines and relations of the two +branches of scientific investigation--_Vulcanology_ and _Seismology_--by +which its true nature and part in the Cosmos are chiefly to be +ascertained. + +The general term, _Vulcanicity_, properly comprehends all that we see or +know of actions taking place upon and modifying the surface of our +globe, which are referable not to forces of origin above the surface, +and acting superficially, but to causes that have been or are in +operation beneath it. It embraces all that Humboldt has somewhat vaguely +called "the reactions of the interior of a planet upon its exterior." + +These reactions show themselves principally and mainly in the marking +out and configuration of the great continents and ocean beds, in the +forcing up of mountain chains, and in the varied phenomena consequent +thereon, as seen in more or less adjacent formations. + +These constitute the mechanism which has moulded and fashioned the +surface of our globe from the period when it first became superficially +solid, and prepared it as the theatre for the action of all those +superficial actions--such as those of tides, waves, rain, rivers, solar +heat, frost, vitality, vegetable and animal (passing by many others less +obvious)--which perpetually modify, alter or renew the surface of our +world, and maintain the existing regimen of the great machine, and of +its inhabitants. These last are the domain of Geology, properly so +called. No geological system can be well founded, or can completely +explain the working of the world's system as we now see it, that does +not start from Vulcanicity as thus defined; and this is equally true, +whether, as do most geologists, we include within the term Geology +everything we can know about our world as a whole, exclusive of what +Astronomy teaches as to it, dividing Geology in general into Physical +Geology--the boundaries of which are very indistinct--and +Stratigraphical Geology, whose limits are equally so. + +It has been often said that Geology in this widest sense begins where +Astronomy or Cosmogony ends its information as to our globe, but this is +scarcely true. + +Vulcanicity--or Geology, if we choose to make it comprehend that--must +commence its survey of our world as a nebula upon which, for unknown +ages, thermic, gravitant and chemical forces were operative, and to the +final play of which, the form, density and volume, as well as order of +deposition of the different elements in the order of their chemical +combination and deposition was due, when first our globe became a liquid +or partly liquid spheroid, and which have equally determined the +chemical nature of the materials of the outward rind of the earth that +now is, and with these some of the primary conditions that have fixed +the characters, nature and interdependence of the vegetables and animals +that inhabit it. Physical Astronomy and Physical Geology, through +Vulcanicity, thus overlap each other; the first does not end where the +second begins; and in every sure attempt to bring Geology to that +pinnacle which is the proper ideal of its completed design--namely, the +interpretation of our world's machine, as part of the universal Cosmos +(so far as that can ever become known to our limited observation and +intelligence)--we must carry with us astronomic considerations, we must +keep in view events anterior to the "_status consistentior_" of +Leibnitz, nor lose sight of the fact that the chain of causation is one +endless and unbroken; that forces first set moving, we know not when or +how, the dim remoteness of which imagination tries to sound in shadowy +thought, like those of the grand old Eastern poem, "When the morning +stars first sang together," are, however changed in form, operative +still. The light and fragile butterfly, whose glorious garb irradiates +the summer zephyr in which it floats, has had its power of flight--which +is its power to live--determined by results of that same chain of causes +that lifted from the depths the mountain on whose sunny side he floats, +that has determined the seasons and the colour of the flower whose +nectar he sucks, and that discharges or dissipates the storm above, that +may crush the insect and the blossom in which it basked. And thus, as +has been said, it was not all a myth, that in older days affirmed that +in some mysterious way the actions and the lives of men were linked to +the stars in their courses. + +Whatever may have been the manifestations of Vulcanicity at former and +far remoter epochs of our planet, and to which I shall return, in the +existing state of regimen of and upon our globe it shows itself chiefly +in the phenomena of Volcanoes and of Earthquakes, which are the +subjects of Vulcanology and of Seismology respectively, and in principal +part, also, of this Introduction. + +The phenomena of hot springs, geysers, etc., which might be included +under the title of Thermopaegology, have certain relations to both, but +more immediately to Vulcanology. + +Let us now glance at the history and progress of knowledge in these two +chief domains of Vulcanicity, preparatory to a sketch of its existing +stage as to both, and, by the way, attempt to extract a lesson as to the +methods by which such success as has attended our labours has been +achieved. + +It will be most convenient to treat of Seismology first in order. + +Aristotle--who devotes a larger space of his Fourth Book, [Greek: Peri +Kosmou], to Earthquakes--Seneca, Pliny, Strabo, in the so-called classic +days, and thence no end of writers down to about the end of the +seventeenth century--amongst whom Fromondi (1527) and Travagini (1679) +are, perhaps, the most important now--have filled volumes with records +of facts, or what they took to be such, of Earthquakes, as handed down +to or observed by themselves, and with plenty of hypotheses as to their +nature and origin, but sterile of much real knowledge. + +Hooke's "Discourses of Earthquakes," read before the Royal Society about +1690, afford a curious example of how abuse of words once given by +authority clings as a hindrance to progress. He had formed no distinct +idea of what he meant by an Earthquake, and so confusedly mixes up all +elevations or depressions of a permanent character with "subversions, +conversions and transpositions of parts of the earth," however sudden or +transitory, under the name of Earthquakes. + +A like confusion is far from uncommon amongst geological writers, even +at the present day, and examples might be quoted from very late writings +of even some of the great leaders of English Geology. + +From the seventeenth to the middle of the eighteenth century one finds +floods of hypotheses from Flamsteed, Hoettinger, Amontons, Stukeley, +Beccaria, Percival, Priestly, and a crowd of others, in which +electricity, then attracting so much attention, is often called upon to +supply causation for a something of which no clear idea had been formed. +Count Bylandt's singular work, published in 1835, though showing a +curious _partial_ insight in point of advancement, might be put back +into that preceding period. + +In 1760 appeared the very remarkable Paper, in the fifty-first volume of +the "Philosophical Transactions," of the Rev. John Mitchell, of +Cambridge, in which he views an Earthquake as a sudden lifting up, by a +rapid evolution of steam or gas beneath, of a portion of the earth's +crust, and the lateral transfer of this gaseous bubble beneath the +earth's crust, bent to follow its shape and motion, or that of a wave of +liquid rock beneath, like a carpet shaken on air. Great as are certain +collateral merits of Mitchell's Paper, showing observation of various +sorts much in advance of his time, this notion of an Earthquake is such +as, had he applied to it even the imperfect knowledge of mechanics and +physics then possessed in a definite manner, he could scarcely have +failed to see its untenable nature. That the same notion, and in a far +more extravagant form, should have been reproduced in 1843 by Messrs. +Rogers, by whom the gigantic parallel anticlinals, flanks and valleys of +the whole Appalachian chain of mountains are taken for nothing more than +the indurated foldings and wrinkles of Mitchell's carpet, is one of the +most salient examples of the abuse of hypothesis untested by exact +science. + +Neither Humboldt nor Darwin, great as were the opportunities of +observation enjoyed by both, can be supposed to have formed any definite +idea of _what_ an Earthquake is; and the latter, who had observed well +the effects of great sea-waves rolling in-shore after the shock, did not +establish any clear relation between the two.[A] + +Hitherto no one appears to have formed any clear notion as to what an +Earthquake is--that is to say, any clear idea of what is the nature of +the movement constituting the shock, no matter what may be the nature or +origin of the movement itself. The first glimmering of such an idea, so +far as my reading has enabled me to ascertain, is due to the penetrating +genius of Dr. Thomas Young, who, in his "Lectures on Natural +Philosophy," published in 1807, casually suggests the probability that +earthquake motions are vibratory, and are analogous to those of +sound.[B] This was rendered somewhat more definite by Gay Lussac, who, +in an able paper "On the Chemical Theories of Volcanoes," in the +twenty-second volume of the "Annales de Chemie," in 1823, says: "En un +mot, les tremblements de terre ne sont que la propagation d'une +commotion a travers la masse de la terre, tellement independante des +cavites souterraines qu'elle s'entendrait, d'autant plus loin que la +terre serait plus homogene." + +These suggestions of Young and of Gay Lussac, as may be seen, only refer +to the movement in the more or less solid crust of the earth. But two, +if not three, other great movements were long known to frequently +accompany earthquake shocks--the recession of the sea from the shore +just about the moment of shock--the terrible sounds or subterraneous +growlings which sometimes preceded, sometimes accompanied, and sometimes +followed the shock--and the great sea-wave which rolls in-shore more or +less long after it, remained still unknown as to their nature. They had +been recognised only as concomitant but unconnected phenomena--the more +inexplicable, because sometimes present, sometimes absent, and wholly +without any known mutual bearing or community of cause. + +On the 9th February, 1846, I communicated to the Royal Irish Academy my +Paper, "On the Dynamics of Earthquakes," printed in Vol. XXI., Part I., +of the Transactions of that Academy, and published the same year in +which it was my good fortune to have been able to colligate the observed +facts, and bringing them together under the light of the known laws of +production and propagation of vibratory waves in elastic, solid, liquid +and gaseous bodies, and of the production and propagation of liquid +waves of translation in water varying in depth, to prove that all the +phenomena of earthquake shocks could be accounted for by a single +impulse given at a single centre. The definition given by me in that +Paper is that an earthquake is "_The transit of a wave or waves of +elastic compression in any direction, from vertically upwards to +horizontally, in any azimuth, through the crust and surface of the +earth, from any centre of impulse or from more than one, and which may +be attended with sound and tidal waves dependent upon the impulse and +upon circumstances of position as to sea and land_." + +Thus, for example, if the impulse (whatever may be its cause) be +delivered somewhere beneath the bed of the sea, all four classes of +earthquake waves may reach an observer on shore in succession. The +elastic wave of shock passing through the earth _generally_ reaches him +first: its velocity of propagation depending upon the specific +elasticity and the degree of continuity of the rocky or the incoherent +formations or materials through which it passes. + +Under conditions pointed out by me, this elastic wave may cause an +aqueous wave, producing recession of the sea, just as it reaches the +margin of sea and land. + +If the impulse be attended by fractures of the earth's crust, or other +sufficient causes for the impulse to be communicated to the air directly +or through the intervening sea, ordinary sound-waves will reach the +observer through the air, propagated at the rate of 1,140 feet per +second, or thereabouts; and may also reach him before or with or soon +after the shock itself, through the solid material of the earth; and +lastly, if the impulse be sufficient to disturb the sea-bottom above the +centre of impulse, or otherwise to generate an aqueous wave of +translation, that reaches the observer last, rolling in-shore as the +terrible "great sea-wave," which has ended so many of the great +earthquakes, its dimensions and its rate of propagation depending upon +the magnitude of the originating impulse and upon the variable depth of +the water. It is not my purpose, nor would it be possible within my +limits here, to give any complete account of the matter contained in +that Paper, which, in the words of the President of the Academy upon a +later occasion, "fixed upon an immutable basis the true theory of +Earthquakes."[C] I should state, however, that in it I proved the +fallacy of the notion of vorticose shocks, which had been held from the +days of Aristotle, and showed that the effects (such as the twisting on +their bases of the Calabrian Obelisks) which had been supposed due to +such, were but resolved motions, due to the transit rectilinearly of the +shock. + +This removed one apparent stumbling block to the true theory. + +Incidentally also it was shown that from the observed elements of the +movement of the elastic wave of shock at certain points--by suitable +instruments--the position and depth of the _focus_, or centre of +impulse, might be inferred. + +In the same volume ("Transactions of the Royal I. Academy," XXI.) I gave +account, with a design to scale, for the first self-registering and +recording seismometer ever, to my knowledge, proposed. In some respects +in principle it resembles that of Professor Palmieri, of which he has +made such extended use at the Vesuvian Observatory, though it differs +much from the latter in detail. In June, 1847, Mr. Hopkins, of +Cambridge, read his Report, "On the Geological Theories of Elevation and +Earthquakes," to the British Association--requested by that body the +year before--and printed in its Reports for that year. + +The chief features of this document are a digest of Mr. Hopkins's +previously published "Mathematical Papers" on the formations of +fissures, etc., by elevations and depressions, and those on the +thickness of the earth's crust, based on precession, etc., which he +discusses in some relations to volcanic action. + +This extends to forty-one pages, the remaining eighteen pages of the +Report being devoted to "Vibratory Motions of the Earth's Crust produced +by Subterranean Forces--Earthquakes." + +The latter consists mainly of a _resume_ of the acknowledged laws, as +delivered principally by Poisson, of formation and propagation of +elastic waves and of liquid waves, by Webers, S. Russel and others--the +original matter in this Report is small--and as respects the latter +portion consists mainly in some problems for finding analytically the +position or depth of the centre of disturbance when certain elements of +the wave of shock are given, or have been supposed registered by +seismometric instruments, such as that described by myself, and above +referred to.[D] At the time my original Paper "On the Dynamics of +Earthquakes" was published, there was little or no _experimental_ +knowledge as to the actual velocity of transit of waves--analogous to +those of sound, but of greater amplitude--through elastic solids. The +velocity as deduced from theory, the solid being assumed quite +_homogeneous_ and _continuous_, was very great, and might be taken for +some of the harder and denser rock formations at 11,000 or 12,000 feet +per second. That these enormous velocities of wave transit would be +something near those of actual earthquake shock seemed probable to me, +and was so accepted by Hopkins. + +Thus, he says (Report, p. 88): "The velocity of the sea-wave, for any +probable depth of the sea, will be so small as compared with that of the +vibratory wave, that we may consider the time of the arrival of the +latter at the place of observation as coincident with that of the +departure of the sea-wave from the centre of divergence." + +In my original Paper (Dynamic, &c.), I had suggested, as an important +object, to ascertain by actual experiment what might be the wave's +transit rate in various rocky and incoherent formations; and having +proposed this in my first "Report upon the Facts of Earthquake" to the +British Association, I was enabled by its liberality to commence those +experiments, in which I was ably assisted by my eldest son, then quite a +lad--Dr. Jno. William Mallet, now Professor of Chemistry at the +University of Virginia, U.S.; and to give account of the results, in my +second Report ("Report, British Association for 1851") to that body. + +Those experiments were made by producing an impulse at one end of an +accurately measured base line, by the explosion of gunpowder in the +formation experimented upon, and noting the time the elastic wave +generated required to pass over that distance, upon a nearly level +surface. Special instruments were devised and employed, by which the +powder was fired and the time registered, by touching a lever which +completed certain galvanic contacts. The media or formations in which +these experiments were conducted were, damp sand--as likely to give the +minimum rate--and crystalline rock (granite), as likely to give the +maximum. The results were received, not with doubt, but with much +surprise, for it at once appeared that the actual velocity of transit +was vastly below what theory had indicated as derivable from the density +and modulus of elasticity of the material, taken as homogeneous, etc. +The actual velocities in feet per second found were: + + In sand 824.915 feet per second. + In discontinuous and + much shattered granite 1,306.425 " " + In more solid granite 1,664.574 " " + +This I at once attributed, and as it has since been proved correctly, to +the loss of _vis viva_, and consequently of speed, by the _discontinuity +of the materials_. + +And some indication of the general truth of the fact was derivable from +comparing the rude previous approximations to the transit rate of some +great Earthquakes. In the case of that of Lisbon, estimated by Mitchell +at 1,760 feet per second. It was still desirable to extend similar +experiments to the harder classes of stratified and of contorted rocks. +This I was enabled to carry into effect, at the great Quarries at +Holyhead (whence the slate and quartz rocks have been obtained for the +construction of the Asylum Harbour there), taking advantage of the +impulses generated at that period by the great mines of powder exploded +in these rocks. + +The results have been published in the "Philosophical Transactions for +1861 and 1862 (Appendix)." They show that the mean lowest rate of wave +transit in those rocks, through measured ranges of from 5,038 to 6,582 +feet, was 1,089 feet per second; and the mean highest, 1,352 feet per +second; and the general mean 1,320 feet per second. + +By a separate train of experiments on the compressibility of solid cubes +of these rocks, I obtained the mean modulus of elasticity of the +material when perfectly continuous and unshattered, with this +remarkable result--that in these rocks, as they exist at Holyhead, +_nearly seven-eighths of the full velocity of wave transmission due to +the material, if solid and continuous, is lost by reason of the +heterogeneity and discontinuity_ of the rocky masses as they are found +piled together in Nature. + +I also proved that the wave-transit period of the unshattered material +of these rocks was greatest in a direction _transverse_ to the bedding, +and least in line parallel with that; but the effect of this in the +rocky mass itself may be _more_ than counterbalanced by the +discontinuity and imperfect contact of the adjacent beds. + +These results indicate, therefore, that the superficial rate of +translation of the solitary sea-wave of earthquakes may, when over very +deep water, equal or even exceed the transit rate (in some cases) of the +elastic wave of shock itself. + +These results have since received general confirmation by the careful +determinations of the transit rates of actual earthquake waves, in the +rocks of the Rhine Country and in Hungary, by Noeggerath and Schmidt +respectively, and by those made since by myself in those of Southern +Italy, to which I shall again refer. In an elastic wave propagated from +a centre of impulse in an infinitely extended volume of a perfect gas, +normal vibrations are alone propagated--as is the case with sound in +air. + +In the case of like movements propagated in elastic and perfectly +homogeneous and isotropic solids, the wave possesses both normal and +transversal vibrations, and is, in so far, analogous to the case of +light. Mr. Hopkins, in his Report above referred to, has based certain +speculations upon the assumed necessary co-existence of both orders of +vibration in actual earthquake shocks in the materials of which our +earthy crust is actually composed. + +The existence of transversal vibration in those materials has not been +yet proved experimentally, though there is sufficient ground to preclude +our denying their probable existence. + +That if they do exist they play but a very subordinate part in the +observable phenomena of actual Earthquake is highly probable. This is +the view, supported not only by observations of the effects of such +shocks in Nature, but by the theoretic consideration of the effects of +discontinuity of formations in planes or beds more or less transverse to +the wave path (or line joining the centre of impulse with the mean +centre of wave disturbance at any point of its transit). If we suppose, +for illustration sake, such an elastic wave transmitted perpendicularly +through a mass of glass plates, each indefinitely thin, and all in +absolute contact with each other, but without adhesion or friction, more +or less of the transversal vibration of the wave would be cut off and +lost at each transit from plate to plate, as the elastic compression +can, by the conditions, be transmitted only normally or by direct push +perpendicularly from plate to plate. This must take place in Nature, and +to a very great extent, and the consideration, with others, enabled me +generally to apply the normal wave motion of shock alone to my +investigation as to the depth of the centre of impulse of the great +Neapolitan Earthquake of 1857, an account of which was published in +1862, and to be presently further referred to. + +Hitherto the multitudinous facts, or supposed facts, recorded in +numberless accounts of Earthquakes had remained almost wholly +unclassified, and so far as they had been discussed--in a very partial +manner, as incidental portions of geological treatises--with little +attempt to sift the fabulous from the real, or to connect the phenomena +admitted by reference to any general mechanical or physical causes. In +1850 my first "Report upon the Facts of Earthquakes," called for by the +British Association in 1847, was read and published in the Reports of +that body for that year. In this, for the first time, the many recorded +phenomena of Earthquakes are classified, and the important division of +the phenomena into primary and secondary effects of the shock was +established. Several facts or phenomena, previously held as marvellous +or inexplicable, were either, on sufficient grounds, rejected, or were, +for the first time, shown susceptible of explanation. Amongst the more +noticeable results were the pointing out that fissures and fractures of +rock or of incoherent formations were but secondary effects, and, in the +latter, were, in fact, generally of the nature of inceptive landslips. +This last was not accepted, I believe, by geologists at the time; but +the correctness of the views then propounded as to earth fissures--the +nature of the spouting from them of water or mud--the appearances taken +for smoke issuing from them, etc.--have since been fully confirmed, +first, by my own observations upon the effects of the Great Neapolitan +Earthquake of 1857, and more lately by those of Dr. Oldham upon the +Earthquake of Cachar (India), where he was enabled to observe fissures +of immense magnitude, the nature of the production of which he has well +described and explained in the "Proceedings, Geological Society, London, +1872." + +The relations between meteorological phenomena proper and Earthquakes +have always been a subject of popular belief and superstition. + +This was here carefully discussed, and with the result of disproving any +connection, or, if any, but of an indirect nature. I also, to some +extent, towards the end of this Report, discussed the question of the +possible nature of the _impulse itself_ which originates the shock; I +showed that it must be of the nature of a blow, and ventured to offer +_conjecturally_ five possible causes of the impulse: + + 1. Sudden fractures of rock, resulting from the steady and slow + increase of elevatory pressure. + + 2. Sudden evolution (under special conditions) of steam. + + 3. Sudden condensation of steam, also under special conditions. + + 4. Sudden dislocations in the rocky crust of the earth, through + pressure acting in any direction. + + 5. Occasionally through the recoil due to explosive effects at + volcanic foci (p. 79-80). + +The first and last of these I am, through subsequent light, disposed now +to withdraw or greatly to modify. + +The first, the supposed "_snap and jar_, occasioned by the sudden and +violent rupture of solid rock masses," to which Mr. Scrope, in his very +admirable work on Volcanoes, is disposed to refer the impulse of +earthquake shocks (Scrope, 2nd edit., p. 294), I believe may be proved +on acknowledged physical principles--when applied to the known +elasticities and extensibilities of rocks, and keeping in view the small +thicknesses fractured _at the same instant_--to be capable of only the +most insignificant impulsive effects; and if we also take into +consideration that strata, if so fractured, are necessarily not _free_, +but surrounded by others above and below, any such impulsive effect +emanating from fracture may be held as non-existent or impossible. In +the statement of his views which follows, and in objecting to my second +and third possible causes (p. 295-296, headed "Objections to Mallet's +Theory"), Mr. Scrope appears to me to have fallen into the error of +assuming that the nature of the _impulse_, or the cause producing it, +forms any part of "my theory of earthquake movement," or in anywise +affects it. I carefully guarded against this in the original Paper +("Transactions, Royal Irish Academy," Vol. XXI., p. 60, and again, p. +97), when I stated "it is quite immaterial to the truth of my theory of +earthquake motion what view be adopted, or what mechanism be assigned, +to account for the original impulse." + +As regards the fifth conjecture suggested by me, I am now, with better +knowledge and larger observation of volcanic phenomena, not prepared to +admit any single explosion at volcanic vents of a magnitude sufficient +to produce by its recoil an earthquake wave of any importance, or +extending to any great distance in the earth's crust. The rock of 200 +tons weight, said to have been projected nine miles from the crater of +Cotopaxi, which I quoted from Humboldt as an example,[E] I believe to be +as purely mythical as the rock (_bloc rejette_) of perhaps one-sixth of +that weight which, previous to the late eruption, lay in the middle of +the Atria dell Cavallo, and which it was roundly affirmed had been +_blown_ out of the crater, but which in reality had at some time rolled +down from near the top of the cone, after having been dislodged from +some part of the upper lip of the crater walls, where, as its wonderful +hardness and texture and its enamel-like surface showed, it had been +roasted for years probably. + +Nor do I believe in the _sudden_ blowing away of one-half the crater and +cone of Vesuvius, or of any other volcano, at one effort, however +affirmed. + +Nothing more than conjecture as to the nature of the impulse producing +great or small Earthquakes can, I believe, as yet be produced. That +there is some one master mechanism productive of most of the impulses of +great shocks is highly probable, but that more causes than one may +produce these impulses, and that the causes operative in small and long +repeated shocks, like those of Visp-Comrie and East Haddam, differ much +from those producing great Earthquakes, is almost certain. + +We shall be better prepared to assign all of these when we have admitted +a true theory of volcanic action, and so are better able to see the +intimate relations in mechanism between seismic and volcanic actions. + +It is not difficult meanwhile to assign the very probable mechanism of +those comparatively petty repercussions which are experienced in close +proximity to volcanic vents when in eruption, and which, though +certainly seismic in their nature, and powerful enough, as upon the +flanks of Etna, to crack and fissure well-built church-towers, can +scarcely be termed Earthquakes. + +In my First Report I stated that almost nothing was known then of the +distribution of recorded Earthquakes in time or in space over our +globe's surface, and I proposed the formation and discussion of a +complete catalogue of all recorded Earthquakes, with this in view. + +This was approved by the Council of the British Association and at once +undertaken by me, with the zealous and efficient co-operation of my +eldest son, Dr. J. W. Mallet. Nearly the whole of the Second British +Association Report, of 1851, is occupied with the account of the +experiments as to the transit rate of artificially made shocks in sand +and granite, as already referred to. + +The Third Report, of 1852-1854, contains the whole of this, "The +Earthquake Catalogue of the British Association" (of which, through the +liberality of that body, more than one hundred copies were distributed +freely), in which are given, in columnar form, the following +particulars, from the earliest known dates to the end of 1842: + + 1. The date and time of day, as nearly as recorded. + + 2. The locality or place of occurrence. + + 3. The direction, duration, and number of shocks so far + recorded. + + 4. Phenomena connected with the sea--great sea-waves, tides, + etc. + + 5. Phenomena connected with the land--meteorological phenomena + preceding and succeeding. Secondary phenomena--all minor or + remarkable phenomena recorded. + + 6. The authority for the record. + +Though most materially assisted by the previous labours and partial +catalogues of Von Hoff, Cotte, Hoffman, Merrian, and, above all, of +Perrey, the preparation of this catalogue--which demanded visits to the +chief libraries of Europe, and the collating of some thousands of +authors in various languages and of all time--was a work of great and +sustained labour, which, except for my dear son's help, I should never +have found time and power to complete. Professor Perrey, formerly of the +Faculte des Sciences of Dijon, now _en retrait_, who has devoted a long +and useful life to assiduous labours in connection with Seismology, was +our great ally; and his catalogues are so large and complete for most +known parts of the world after 1842, that we were able to arrest our own +catalogue at that date, and take M. Perrey's as their continuation up to +1850. + +The whole British Association Catalogue thus embraces the long historic +period of from 1606 B.C. of vulgar chronology, when the first known +Earthquake is recorded, to A.D. 1850; and the base of induction which it +presents as to the facts recorded extends to between 6,000 and 7,000 +separate Earthquakes. My Fourth Report ("Reports, British Association, +1858,") is occupied principally with the discussion of this great +catalogue, and with that of several special catalogues produced by other +authors with limited areas or objects. + +The discussion of M. Perrey's local catalogues with those of others, in +reference to a supposed prevalent apparent horizontal direction of shock +in certain regions--as to distribution, as to season, months, time of +day or night, relation to state of tide--the bearings of the views of +Zantedeschi and others as to the probable existence of a terrane +tide--the supposed relations of the occurrence of Earthquakes upon the +age of the moon, as deduced by Perrey, viz.: that 1st, Earthquakes occur +most frequently at the syzygies; 2nd, that their frequency increases at +the perigee and diminishes at the apogee; 3rd, that they are more +frequent when the moon is on the meridian than when she is 90 deg. away +from it--and the views of several authorities as to the distribution of +Earthquakes in time and in space--occupy the first 46 pages of this +Report. + +It then proceeds to discuss the distribution in time and in space as +deduced from the full base of the great catalogue. + +The results as to time are reduced to curves, and those as to space (or +distribution over our globe's surface) to the great seismic map +(Mercator's projection), upon which and in accordance with certain +principles and conventional laws, which admit of the indication of both +intensity and frequency, all recorded Earthquakes have been so laid down +as to present a real indication of the distribution of seismic energy +for the whole historic period and all over the world. + +The original of this map, which also shows the Volcano (size, about 7 +feet by 5 feet), remains for reference in the custody of the Royal +Society. A reduced copy was published with the Report, and to a still +more reduced scale has been reproduced in other places. It is impossible +here to do more than refer to a few of the more salient points. + +As regards distribution in time, durational seismic energy may be +considered as probably constant during historic time, though it is +probably a decaying energy viewed in reference to much longer periods. +It does not appear of the nature of a distinctly periodic force. + + 1. Whilst the minimum paroxysmal interval may be a year or two, + the average interval is from five to ten years of comparative + repose. + + 2. The shorter intervals are in connection with periods of + fewer Earthquakes, not always with those of least intensity, + but usually so. + + 3. The alternations of paroxysm and of repose appear to follow + no absolute law deducible from these causes. + + 4. Two marked periods of extreme paroxysm are observable in + each century (for the last three centuries), one greater than + the other--that of greatest number and intensity occurring + about the middle of each century, and the other towards the end + of each. + +As respects season, there appear distinct indications of a maximum about +the winter solstice, and equally so of a minimum rather before the +autumnal equinox. It is not improbable that there is a remote relation +between Earthquakes and the annual march of barometric pressure. + +We may expect, at present, one great Earthquake about every eight +months, and were we possessed of a sufficient report from all parts of +our globe, we should probably find scarcely a day pass without a very +sensible Earthquake occurring somewhere, whilst, as regards still +smaller tremors, it might almost be said that our globe, as a whole, is +scarcely ever free from them. + +As respects the distribution of seismic energy in space of our earth's +surface, it is that of bands of variable and of great breadth, with +sensible seismic influence extending to from 5 deg. to 15 deg. +transversely, which very generally follow: + + 1. The lines of elevated tracts which mark and divide the great + oceanic or terra-oceanic basins (or _saucers_, as I have called + them, from their shallowness in relation to surface, in this + discussion) of the earth's surface. + + 2. And in so far as these are frequently the lines of mountain + chains, and these latter those of volcanic vents, so the + seismic bands are found to follow these likewise. Isolated + Volcanoes are found in these bands also. + + 3. While sensible seismic influence is generally limited to + the average width of the band, paroxysmal efforts are + occasionally propagated to great distances transversely beyond + that. + + 4. The sensible width of the band depends upon the energy + developed at each point of the length, and upon the accidental + geologic and topographic conditions along the same. + + 5. Seismic energy _may_ become sensible at any point of the + earth's surface, its efforts being, however, greater and more + frequent as the great lines of elevation and of volcanic + activity are approached; yet not in the inverse ratio of + distance, for many of the most frequently and terribly shaken + regions of the earth, as the east shore of the Adriatic, Syria, + Asia Minor, Northern India, etc., are at great distances from + active Volcanoes. + + 6. The surfaces of minimum or of no known disturbance are the + central areas of great oceanic or of terra-oceanic basins or + saucers, and the greater islands existing in shallow seas. + +Space obliges me to pass unnoticed here many minor but not unimportant +deductions. The discussions as to distribution in time and space occupy +seventy-two pages of this fourth and last Report, the remainder of which +(thirty-one pages) embraces the description and mathematical discussion +as to seismometers, to which I may refer, as comprising the most +complete account of these instruments that has, I believe, been anywhere +given. + +The appendix to the Report comprises the entire bibliography of +Earthquakes collected during those researches, and a concluding chapter +on desiderata, and inquiries as to ill-understood phenomena supposed to +be connected with Earthquakes. + + * * * * * + +In 1849-50, I was honoured by the request to draw up the article +"Earthquake Phenomena," which has appeared in the first and subsequent +editions of the "Admiralty Manual of Scientific Inquiry." Originally the +subject was intended to have formed part of the article on Geology, +entrusted to Mr. Darwin, who consulted me upon the subject; and upon my +representing how much Earthquakes had, within a short time, become +matter for the mathematician and physicist, he, with a singleness of eye +to science which it is but just to place on record, took the necessary +steps with the Admiralty authorities that Earthquakes should form a +separate article, and advised its being placed, as it was, in my hands. +To record this will, I believe, be sufficient justification for my +reference to this article, in which a good deal of information as to +Seismometry is to be found. + + * * * * * + +By recurring to Mr. Hopkins's Report on Earthquake Theory, before +remarked upon ("Report of British Association, 1847"), it will be seen +that the solutions of the problems which he there gives for finding the +depth of focus of shock are founded upon the _velocity of propagation_ +of the wave in the interior of the mass, the _apparent horizontal +velocity_ and the _horizontal direction of propagation_ at any proposed +point being known (p. 82). + +By this it appears plainly that at that time Mr. Hopkins supposed that +it was the _velocity of translation_ of the wave of shock that did the +mischief, and not the _velocity of the wave particle_, or wave itself. +And, further, that the former might be obtained by reference simply to +the modulus of elasticity of the rock of any given formation, as, +indeed, was my own earliest view when I produced my "Dynamics of +Earthquake" in 1846. From the remarks already made as to the vast +difference between the actual transit velocity in more or less +discontinuous rocks--such as they occur in Nature--it will be equally +obvious that Mr. Hopkins's methods, as above mentioned, are +impracticable, even were there no confusion between the velocity of +translation of the wave and that of the wave particle or wave itself. + +This applies also to the demonstration and diagram (taken from Hopkins) +given by Professor Phillips ("Vesuvius," pp. 258-259). + +In December, 1857, occurred the great Neapolitan Earthquake, which +desolated a large portion of that kingdom; and an opportunity then arose +for practically applying to the problems of finding the directions of +earthquake shock at a given point through which it has passed, and +ultimately the position and depth of focus, other methods, which I had +seen, from soon after the date of publication of my original Paper +(1846), were easily practicable, and the details of which I had +gradually matured. + +Bearing in mind that, in the case of the normal vibration in any elastic +solid of indefinite dimensions, the direction of motion in space of the +_wave particle_ coincides in the first semiphase of the wave, and at the +instant of its _maximum velocity_ with the right line joining the +particle and the focus or centre of disturbance, it follows that, in the +case of earthquakes, the normal vibration of the wave of shock is always +in a vertical plane passing through the focus and any point on the +earth's surface through which the shock passes (assuming for the present +no disturbing causes after the impulse has been given), and that at such +a point the movement of the wave particle in the first semiphase of the +wave is in the same direction or sense as that of translation; and at +the moment of maximum velocity the direction in space of the motion of +the wave particle is that of the right line joining the point through +which the wave has passed with the focus or centre of impulse. + +If, therefore, we can determine the direction of motion of the wave +particle in the first semiphase, and its maximum velocity, we can +obtain, from any selected point, a line (that of emergence of the shock) +_somewhere in which_, if prolonged beneath the earth, the focus must +have been; and if we can obtain like results for two or more selected +points, we decide the position and the depth of the focus, which must be +in the intersection of the several lines of direction of the wave +particle motion at each point, when prolonged downwards. + +Now, as I have said, it is the _vibration of the wave itself_, _i.e._, +the motion of the wave particle that does the mischief--_not_ the +transit of the wave from place to place on the surface; just as in the +analogous (but _not_ similar) case of a tidal wave of translation +running up an estuary and passing a ship anchored there, it is not the +transit up the channel, but the wave form itself--_i.e._, the motion of +the wave particles--that lifts the ship, sends her a little way higher +up channel, drops her to her former level, and sends her down channel +again to the spot she lay in just before the arrival of the wave. + +Everything, therefore, that has been permanently disturbed by an +earthquake shock has been thus moved in the direction and with the +maximum velocity impressed upon it by the wave particle in the first +semiphase of the wave; and thus almost everything that has been so +disturbed may, by the application of established dynamical principles, +be made to give us more or less information as to the velocity of the +wave particle (or as we, for shortness, say, the velocity of shock), the +direction of its normal vibration, and the position and depth beneath +the earth's surface, from which came the generating impulse. We thus +arrive at these as simply and as surely as we can infer from the +position taken by a billiard ball, on which certain forces are known to +have acted, the forces themselves and their direction; or, from a broken +beam, the pressure or the blow which fractured it. + +It is obvious, then, that nearly every object disturbed, dislocated, +fractured or overthrown by an earthquake shock is a sort of natural +seismometer, and the best and surest of all seismometers, if we only +make a judicious choice of the objects which being found after such a +shock, we shall employ for our purpose. This was the principle which I +proposed to the Royal Society at once to apply to the effects of the +then quite recent great Neapolitan Earthquake of 1857, and which, +through the liberality and aid of that body, I was enabled to employ +with the result I had pretty confidently anticipated, namely, the +ascertainment of the approximate depth of the focus. + +_Every_ shock-disturbed object in an earthquake-shaken country is +capable of giving _some_ information as to the shock that acted upon it; +but it needs a careful choice, and some mechanical [Greek: nous], to +select _proper_ and the best objects, so as to avoid the needless +perplexity of disturbing forces _not_ proper to the shock, or other +complications. + +When properly chosen, these natural seismometers, or evidences fitted +for observation after the shock, are of two great classes, by which the +conditions of the earthquake motion are discoverable: + + 1. Fractures or dislocations (chiefly in the masonry of + buildings), which afford two principal sources and sorts of + information, namely: + + _a._ From the observed _directions of fractures or fissures_, + by which the _wave path_, and frequently the _angle of + emergence_, may be immediately inferred. + + _b._ Information from the preceding, united with known + conditions as to the strength of materials to resist + _fracture_, by which the _velocity_ of the fracturing impulse + may be calculated. + + 2. The overthrow or the projection, or both, of bodies large or + small, simple or complex. From these we are enabled to infer: + + _c._ By direct observation, the _direction in azimuth_ of the + wave path. + + _d._ By measurements of the horizontal and vertical distances + of overthrow or of projection, to infer either the _velocity_ + of projection, or _angle of emergence_. + +Fractures by shock present their planes always nearly in directions +transverse to the wave path. Projections or overthrow take place (unless +secondarily disturbed) in the line of the wave path, or in the vertical +plane passing through it: but the direction of fall or overthrow may be +either in the same direction as the wave transit (_i.e._, as the motion +of the wave particle in the first semiphase), or contrary to it. + +It is thus obvious that the principal phenomena presented by the effects +of earthquake shock upon the objects usually occurring upon the surface +of the inhabited parts of the earth, resolve themselves into problems of +three orders, and are all amenable to mechanical treatment, viz.: + + 1. Problems relating to the direction and amount of velocity + producing fracture or fissures. + + 2. Problems relating to the single or multiplied oscillations + of bodies, considered as compound pendulums. + + 3. Problems referable to the theory of projectiles. + +These three may combine in several cases, and on the part of the +observer must combine with measurements, angular and linear, and with +geodetic operations to be conducted in the shaken country. + +The methods of application in detail are described fully, as well as +their actual application and results, in my work published in 1862 (2 +vols.), entitled "The First Principles of Observational Seismology, as +developed in the Report to the Royal Society of London of the Expedition +made by Command of the Society into the Interior of the Kingdom of +Naples, to investigate the Circumstances of the Great Earthquake of +December, 1857," to the many illustrations of which the pecuniary grant, +in aid, of L300 was most liberally made to the publishers (Messrs. +Chapman and Hall) by the Society. + +It is not my intention here, nor would space allow, of my going into the +details of observation, nor of the deductions and conclusions I have +recorded in those volumes. I have referred to their contents as marking +the advent of a new method. I have ventured to call it a new _organon_ +in the investigation of Earthquakes, and, through them, of the deep +interior of our earth; and will only add that the method, on this its +very first trial, proved fertile and successful. The depth of focus for +this shock of December, 1857, was about seven to eight geographical +miles below sea level, roughly stated. It gives me great pleasure to add +that my friend, Dr. Oldham, Director-General of the Geological Survey of +India, has since applied these same methods to the phenomena of the +great Cachar Earthquake of the 10th January, 1869, and with success. The +pressure of official duties has, he informs me, as yet prevented his +fully working out his results, but they appear so far to indicate, as we +should expect, a depth of focus or origin considerably greater than in +the European case of 1857. Some account of Dr. Oldham's results were +this year communicated to the Geological Society of London through +myself, they are of great interest and importance. + +Such, briefly and imperfectly sketched, is the existing state of +Seismology. As a branch of exact science it is, as it were, an affair of +yesterday. It is with reluctance that I have been compelled, in this +review, to refer to my own work so prominently. The harvest has been and +still is plenteous, but in this field of intellectual work the labourers +are few. This must continue to be so as long as Geology shall continue +to be viewed in public estimation (in England at least) as a fashionable +toy, that everyone who has been to school is supposed capable of +handling; and until all who profess to be geologists shall have learnt +that, to make sound progress, they must first become mathematicians, +physicists and chemists. + +It is to the general imperfect knowledge of these sciences amongst +geologists that speculative errors show such vitality, and that Geology +makes such poor progress towards becoming the interpretation of the +world as a machine (_Erdkunde_). + +It is for the same reason that Seismology and Vulcanology make little +progress; the first cannot be pursued beyond its present boundaries, nor +can even its present position be understood or explained by anyone +unfamiliar with the laws of wave motion, of all classes of waves; and it +would be easy to show, by quoting from various British or foreign +text-books on Geology, how extremely imperfect is the grasp of some of +the authors upon the subject of earthquake-wave motion, even such as +they admit and endeavour to explain and apply: in fact, many geologists +appear never to have framed to themselves any clear idea of what _is_ a +wave of any sort, liquid or elastic. The general silence as to seismic +theory of French geological writers is remarkable, to whatever cause +attributable. It has been said that French philosophers show themselves +little disposed to acknowledge or to follow the lead of their foreign +compeers in any branch of science. If this be true, or in so far as it +may be so, it is unworthy of French science, which has such boundless +claims upon our homage. I am disposed to attribute the fact in this case +to other circumstances; and, amongst these, to the small extent to which +our language is known amongst French scientific men. + +Germany has shown more desire to cultivate this branch of science. +Although, as yet, the distinct enunciation of its fundamental principles +has but sparsely found its way into her text-books, several able +monographs, such as those of Schmidt and of Hoettinger, prove how +completely some of her philosophers have mastered and how well applied +them. The men of science of Northern Italy, amongst whom so many +glorious names are to be found on the roll of discovery, have shown +themselves quite alive to the importance of Seismology; and I know of no +more clear, exact and popular exposition of its principles and +application, and of its cosmical relations, than is to be found in a +small volume by Professor Gerolamo Boccardo, published at Genoa in 1869, +entitled _Sismopirologia Terremoti, Vulcani e lente oscillazione del +suolo, saggio di una teoria di Geographia Fisica_. + +My object, so far, has been to mark the progress of ascertained +theoretic notions as to Seismology. I have, therefore, passed without +notice many speculative monographs, and the treatment upon Earthquakes, +whether speculative or historical, and however able, that constitutes a +prominent feature of nearly all systematic works on Geology. + +That which may be at present viewed as achieved and certainly +ascertained in theoretic Seismology is the clear conception of the +nature of earthquake motion; the relations to it of great sea or other +water wave commotions; the relations to it of sound waves--as to which, +however, more remains to be known; and the relations of all these to +secondary effects, tending in various ways to modify more or less the +topographic and other conditions of the land or sea bottom. And in +descriptive Seismology the present distribution of the earthquake bands +or regions of greatest seismic prevalence and activity are tolerably +ascertained, and their connection with volcanic lines and those of +elevation rendered more evident. Viewed alone, nothing can yet be said +to be absolutely ascertained as to the immediately antecedent cause or +causes of the impulse. The function of Earthquake, as part of the +cosmical machine, has become more clear, as the distinctive boundaries +between Earthquake and permanent elevation of the earth have been made +evident; and it has been seen that Earthquake, however contemporaneous +occasionally with permanent elevation, is not the cause, though it may +be one of the consequences of the same forces which produce elevation; +and thus, that an infinite number of Earthquakes, however violent, and +acting through however prolonged a time, can never act as an agent of +permanent elevation, unless, indeed, on that minute scale in which +surface elevation may arise from secondary effects, like that of the +Ullah Bund. + +Much remains to be done, and much may be expected even from the +continuation, if done in a systematic and organised manner, of the +statistic record of Earthquakes in connection with those other branches +of cosmical statistics, Climatology, Meteorology, Terrestrial Magnetism, +etc., the observation of which is already, to a certain extent, +organised over a large portion of the globe. + +And now let us look back for a moment to ask, How, by what mental path +of discovery, have we arrived at what we have passed in review? + +The facts of Earthquakes have been before men for unknown ages "open +secrets," as Nature's facts have been well called; "but eyes had they +and saw not." Facts viewed through the haze of superstition, or of +foregone notions of what Nature _ought_ to do, cease to be facts. When, +after the great Calabrian Earthquake of 1783, the Royal Academy of +Naples sent forth its commission of its learned members to examine into +the effects, they had spread around them in sad profusion all that was +necessary to have enabled them to arrive at a true notion of the nature +of the shock, and thence a sound explanation of the varied and great +secondary effects they witnessed, and of which they have left us the +records in their Report, and the engravings illustrative of it. But we +look in vain for any light; the things seen, often with distortion or +exaggeration, are heaped together as in the phantasmagoria of a wild +and terrible dream, from which neither order nor conclusion follow. + +Why was this? Why were these eminent _savants_ no more successful in +explaining what they saw than the ignorant peasants they found in the +Calabrian mountains? + +Because physical science itself was not sufficiently advanced, no doubt; +but also because they had no notion of applying such science as they +had, to the very central point itself of the main problem before them, +freed from all possible adventitious conditions, and so, as it were, +attacking it in the rear. How different might have been the result of +their labours, had they begun by asking themselves, What is an +earthquake? Can we not try to find out what it _is_ by observing and +_measuring_ what it has done? We see the converse mode of dealing with +Nature in Torricelli. "Nature abhors a vacuum," was told him, as the +wisdom of his day. Possibly: but her abhorrence is limited, for I find +it is _measured_ by the pressure of a column of water of thirty-four +feet in height. We need not pursue the story with Pascal, up to the top +of the Puy de Dome. + +This lesson is instructive generally to all investigators, and +particularly here; for Vulcanology, to which we are about now to turn, +has occupied until almost to-day much the same position that Seismology +did in those of the Neapolitan Commissioners. + +Whole libraries have been written with respect to it dealing with +_quality_, but _measure_ and _quantity_ remain to be applied to it. + +To a very preponderant class in the civilised world no knowledge is of +much interest or value that does not point to what is called a +"practical result," one measurable into utility or coin. I do not stop +to remark as to the bad or as to certain good results of this tendency +of mind; but I may venture to point out to all, that the exact knowledge +of the nature of earthquake motion, even during the short time that it +has become known, has not been barren in results absolutely practical +and utilitarian. The minute investigation of the destruction of +buildings, etc., and the deductions that have been made as to the +relations between the form, height, materials, methods of building, +combination of timber and of masonry, and many other architectural or +constructive conditions, have made it certain now that earthquake-proof +houses and other edifices can be constructed with facility, and at no +great increase, if any at all, of cost. I can affirm that there is no +physical necessity why in frequently and violently shaken countries, +such as Southern Italy or the Oriental end generally of the +Mediterranean, victims should hereafter continue by thousands to be +sacrificed by the fall of their ill-designed and badly built houses. + +Were a "Building Act" properly framed, put in force by the Italian +Government in the Basilicatas and Capitanata, etc., so that new houses +or existing ones, when rebuilt, should be so in accordance with certain +simple rules, a not very distant time can be foreseen when Earthquakes, +passing through these rich and fertile but now frequently sorely +afflicted regions, should come and go, having left but little trace of +ruin or death behind. Some disasters there must always be, for we +cannot make the flanks of mountains, nor the beds of torrents, etc., +always secure; but the main mortality of all Earthquakes is in the +houses or other inhabited buildings. Make these proof, and the wholesale +slaughter is at an end. + +The principles we have established have been thus practically applied in +another direction. The Japanese Government, with the keen and rapid +perception of the powers inherent in European science which +characterises now that wonderful people, has commenced to illuminate its +coasts by lighthouses constructed after the best European models. But +Japan is greatly convulsed by earthquakes, and lighthouses, as being +lofty buildings, are peculiarly liable to be destroyed by them. + +The engineer of the Japanese Government for these lights, Mr. Thomas +Stevenson, C.E. (one of the engineers to the Commissioners of Northern +Lights), was instructed to have regard, in the design of those +lighthouses, to their exposure to shock. I was consulted by Mr. +Stevenson as to the general principles to be observed; and those +edifices have been constructed so that they are presumedly proof against +the most violent shocks likely to visit Japan; not, perhaps, upon the +best possible plan, but upon such as is truly based upon the principles +I have developed. Mr. Stevenson has published some account of their +construction. + +The earthquake regions of South America might with incalculable benefit +apply those ideas; and, indeed, they have been, to some extent, already +applied by my friend, Mr. William Lloyd, Member of the Institution of +Civil Engineers, to the New Custom Houses constructed from his designs +at Valparaiso. + +As one of these utilitarian views, and an important one, it will occur +to many to ask--Can the moment of the occurrence or the degree of +intensity of earthquake shock be predicted, or is it probable that at a +future day we may be able to predict them? At present, any prediction, +either of the one or the other, is impossible; and those few who have +professed themselves in possession of sufficient grounds for such +prediction are deceivers or deceived. Nor is it likely that, for very +many years to come, if ever, science shall have advanced so as to render +any such prediction possible; but it is neither impossible nor +improbable that the time shall arrive when, within certain, perhaps +wide, limits as to space, previous time, and instant of occurrence, such +forewarnings may be obtainable. + +Earthquakes, like storms and tempests, and nearly all changes of +weather, are not periodic phenomena, nor yet absolutely uncertain or, so +to say, accidental as to recurrence. + +They are quasi-periodic, that is to say, some of their conditions as to +causation rest upon a really periodic basis, as, for example, the +recurrence of storms upon the periodic march of the earth, and sun and +moon, etc., and the recurrence of Earthquakes upon the secular cooling +of our earth; but the conditions in both are so numerous and complicated +with particulars, that we cannot fully analyse them--hence, cannot +reduce the phenomena to law, and so cannot predict recurrence. Yet +storms and tempests--which were, along with pestilences and Earthquakes, +amongst the natural phenomena which Bishop Butler deemed in his own day +impossible of human prediction--have already, through the persistent and +systematised efforts of meteorological observers, become to a certain +extent foreseeable; and medical science assures us that it has rendered +that, though to a much less degree of probability, true of pestilences. + +We may, therefore, give the utilitarian some hope, that if he will help +us along--who value our accessions of knowledge primarily upon a +different standard to his--in our talk of discovery, our posterity, in a +century or two hence, may not improbably possess the advantage of being +able, in some degree, to predict their Earthquakes. I fear the +inducement will go but a small way with the utilitarian generation, +whose bent tends much towards asking, "What has posterity ever done for +them?" + +But though we cannot as yet predict the time when an Earthquake may take +place in any locality, we can, on mixed statistic and dynamic grounds, +in many cases state the limits of probable violence of the next that may +recur. For example, the three shafts of marble columns of the Temple of +Serapis, at Pozzuoli, each of about 41-1/2 feet in height, and 4 feet 10 +inches in diameter at the base, remain standing alone, since they were +uncovered, in the year 1750. + +Now, as we can calculate exactly what velocity of earthquake-wave motion +would be required to overset these, we are certain that, during the last +one hundred and twenty-two years, the site of the Temple, and we may +say Naples and the Phlegraean fields generally, have never experienced a +shock as great as the very moderate one that would overset these +columns. A shock whose wave particle had a horizontal velocity of only +about 3-1/2 feet (British) per second would overturn these columns; +which is only about one-fourth the velocity (within the meizoseismic +area) of the great shock of 1857, that produced wide-spread destruction +in the Basilicatas, and not enough to throw down any reasonably +well-built house of moderate height. + +Naples, so far as Earthquake is concerned, whether coming from the +throes of Vesuvius or elsewhere, has a pretty good chance of safety. She +may possibly (though not probably) be some day smothered in ashes; but +is in little danger of being shaken to the earth. During this time there +have been taking place, larger eruptions of Vesuvius and earthquake +shocks from other centres, together probably about the same number of +times as the numbers of those years, when those columns have been more +or less shaken. + +We may therefore affirm that the probability (on the basis of this +experience _only_) is, say 120 to 1, that the next shock, whether +derived from Vesuvius, or elsewhere, that may shake Pozzuoli, will be +one less in power than would be needed to overturn the shafts of the +Temple of Serapis there. + + * * * * * + +Let us now turn to the second branch of our subject--viz., +Vulcanology--upon which, as yet, we have secured less firm standing +ground than we have seen we possess in Seismology, for which reason we +took that first into consideration. + +It is the part of Vulcanology to co-ordinate and explain all the +phenomena of past or present times visible on our globe which are +evidences of the existence and action, whether local or general, of +temperatures within our globe greatly in excess of those of the surface, +and which reach the fusing points of various mineral compounds as found +arriving, heated or fused, at the surface. + +The stratigraphic geologist sees that such heated or fused masses have +come up from beneath, throughout every epoch that he can trace; but he +cannot fail to discern more or less a change in the order or character +of those outcomings, as he traces them from the lowest and oldest +formations to those of the present day. He sees immense outpourings of +granitoid or porphyrytic rocks that have welled up and overflowed the +oldest strata--huge dykes filling miles of fissures that had been +previously opened for the reception of the molten matter that has filled +them, and often passing through those masses of previously outpoured +rock; later he sees huge tables of basaltic rock poured forth over all. +One grand characteristic common to all these--commonly called plutonic +products--being that, whether they were poured forth over the surface or +injected into cavities in other rocks, the movements of the fused +material were, on the whole, hydrostatic and _not explosive_. + +At the present day, whatever other evidences we have of high temperature +below our globe's surface, that which primarily fixes the eye of the +geologist is the Volcano, whose characteristic, as we see it in +activity, _is explosive_. But though there is this great characteristic +difference between the plutonic and the volcanic actions and their +products, the two, when looked at largely, are seen so to inosculate, +that it is impossible not to refer them to an agency common to both, +however changed the modes of its action have been between the earliest +epochs of which traces are presented to us and the present day. + +To us little men, who, as Herschell has well said, in referring to the +methods of measuring the size of our globe, "can never see it all at +once, but must creep like mites about its surface," the Volcano, in the +stupendous grandeur of its effects, tends to fix itself in our minds in +exaggerated proportions to its true place in the cosmic machine; and, in +fact, nearly all who have sought to expound its nature and mode of +origination have occupied themselves far too exclusively with describing +and theorising upon the strange and varied phenomena which the volcanic +cone itself and its eruptions present, and too often, in the splendour +and variety of these, have very much lost sight of what ought to be the +centre-point of all such studies, namely, to arrive at some sound +knowledge of what is the _primum mobile_ of all these wonderful efforts. +Nor has the distinction been very clearly seen between the main +phenomena presented at and about volcanic active mouths, which can be +employed to elucidate the nature of the causation at work far below, and +those most varied and curious, and in other respects most pregnant and +instructive phenomena, mechanical and chemical, which are called into +action in and by the ejected matter of the volcanic cone after its +ejection. It can help us but little or very indirectly, in getting at a +true conception of the nature and source of the heat itself of the +Volcano, to examine, for example, all the curious circumstances that are +seen in the movements and changes in the lava that has already flowed +from its mouth; but it would be of great importance if we can ascertain, +by any form of observation around the cone, from what depth it has come, +or at what depth the igneous origin lies. + +The physician, endeavouring to ascertain the real nature of small-pox or +measles, will scarcely make much progress who, however curiously or +minutely, confines his attention to the pustules that he sees upon the +skin. + +Yet the Volcano, or rather all volcanic activity as now operative upon +our globe, is, as it were, an experiment of Nature's own perpetually +going on before us, the results of which, if well chosen--that is, as +Bacon says, by keeping to the main and neglecting the accidents--can, +when colligated and correctly reasoned upon, in relation to our planet +as a whole, give us the key to the enigma of terrestrial Vulcanicity in +its most general sense, and at every epoch of our world's geognostic +history, and show us its true place and use in the cosmical machine. Let +us glance at the history of past speculation on this subject, from which +so little real knowledge is to be derived, and then at the salient facts +of Vulcanology as now seen upon our earth, and finally see if we can +connect these with other great cosmical conditions, so as to arrive at +a consistent explanation in harmony with all. + +We gain nothing absolutely from the knowledge of the so-called +"ancients" as to Volcanoes in Europe at least, where alone historic +records likely to refer to them exist. The Volcanoes of Europe are few +and widely scattered. The Greeks saw but little of them, and the Romans +were all and at all times most singularly unobservant of natural +phenomena. + +Caesar never mentions the existence in France of the Volcanoes of +Auvergne, so much like those he must have seen in Italy and Sicily; and +Roman writers pass in silence that great volcanic region, though +inhabited by them, and their language impressed upon the places, as +Volvic (_volcano-vicus_) seems with others to indicate; and though there +is some reason to believe that one or other of the Puys was in activity +within the first five hundred years of our epoch, the notices which +Humboldt and others have collected as from Plato, Pausanius, Pliny, +Ovid, etc., teach nothing. + +Whatever of mere speculation there may have been, volcanic theory, or +what has passed for such, there was none before 1700, when Lemery +brought forward a trivial experiment, the acceptance of which, even for +a moment, as a sufficient cause for volcanic heat (and it retarded other +or truer views for years), we can now only wonder at. Breislak's origin, +in the burning of subterranean petroleum or like combustibles, was +scarcely less absurd than Lemery's sulphur and iron filings. + +Davy, in the plenitude of his fame, and full of the intense chemical +activities of the metals of the alkalies which he had just isolated, +threw a new but transient verisimilitude upon the so-called chemical +theory of Volcanoes, by ascribing the source of heat to the oxidation of +those metals assumed to exist in vast, unproved and unindicated masses +in the interior of the earth. But Davy had too clear an intellect not to +see the baseless nature of his own hypothesis, which in his last work, +the "Consolations in Travel," he formally recanted; and it only survived +him in the long-continued though unconvincing advocacy of Dr. Daubeny. +So far, the origin of the heat had been sought always, in the crude +notion of some sort of _fuel consumed_, whether that were petroleum or +potassium and sodium; but as no fuel was to be found, nor any indicated +by the products, so far as known, of the volcanic heat, so what has been +called the mechanical theory, in a variety of shapes, took its place. + +This, in whatever form, takes its lava and other heated products of the +volcano ready made from a universal ocean of liquid material, which it +supposes constitutes the interior or nucleus of our globe, and which is +only skinned over by a thin, solid crust of cooled and consolidated +rock, which was variably estimated at from fourteen to perhaps fifty +miles in thickness. Here was a boundless supply of more than heat, of +hot lava ready made, the existence of which at these moderate depths the +then state of knowledge of hypogeal temperature, which was supposed to +go on increasing with depth at the rate of about 1 deg. Fahrenheit, for +every thirty or forty feet, seemed quite to sustain. + +The difficulty remained, how was this fiery ocean brought to the +surface or far above it? To account for this two main notions prevailed, +and, indeed, have not ceased to prevail. Some unknown elastic gases or +vapour forced it up through fissures or rents pre-existent, or produced +by the tension of the elastic and liquid pressure below. + +The form in which this view took most consistency, and approaching most +nearly to truth, finds the elastic vapour in steam generated from water +passed down through fissures from the sea or from the land surface. But +to this the difficulty was started, that fissures that could let down +water would pass up steam. The objection, when all the conditions are +adequately considered, has really no weight; and it has been completely +disposed of, since within a few years it has been proved that capillary +infiltration goes on in all porous rocks to enormous depths, and that +the capillary passages in such media, though giving free vent to +water--and the more as the water is warmer--are, when once filled with +liquid, proof against the return through them of gases or vapours. So +that the deeply seated walls of the ducts leading to the crater, if of +such material, may be red hot and yet continue to pass water from every +pore (like the walls of a well in chalk), which is flushed off into +steam that cannot return by the way the water came down, and must reach +the surface again, if at all, by the duct and crater, overcoming in its +way whatever obstructions they may be filled with. + +And this remarkable property of capillarity sufficiently shows how the +lava--fused below or even at or above the level of infiltration--may +become interpenetrated throughout its mass by steam bubbles, as it +usually but not invariably is found to be. + +Nor is it difficult to see such a mechanism between volcanic ducts and +fissures conveying down water, as large and open pipes, for a large part +of their depth, as shall bring down water to foci of volcanic heat, +without the power of the water flowing back except as steam and through +the crater. + +Indeed, the facts known as to geysers, and those of half-drowned-out +Volcanoes such as Stromboli--whose action is intermittent just as much +as that of a geyser--show that this is not merely probable. There is, +therefore, no need for the hypothesis of those who have supposed all the +huge volumes of steam blown off from Volcanoes in eruption to come from +vesicular water pre-existent in the minute cavities of crystalline or +other rocks before their fusion into lava: a fact not proved for many +classes of rock, and for none in sufficient quantity to account for the +vast volume of steam required and for the irregularity of its issue. + +It is rather to anticipate, but I may state at once that, so far as the +admission of superficial waters to the interior, and to any depth to +which fissures or dislocation can extend, I believe no valid physical or +mechanical difficulties exist, taking into account _all_ the conditions +that may come into play together. + +Another set of views has been suggested and supported by various +writers, which proposes to account for the rise of lava on purely +hydrostatic principles. The solid crust, fractured into isolated +fragments by tensions due to its own contraction, is supposed to sink +into the sea of lava on which it floats; and much ingenuity has been +expended in imagining the mechanism by which, in places, the liquid +matter is supposed to rise _above_ the surface of the crust. + +I have no space for discussing these views further than to assert that, +in the existing state of our globe, and even admitting a solid crust of +only 60,000 metres thick, dislocation of the crust by _tension_ is not +possible. The solid crust of our globe, as I hope we shall see further +on, is not in a state of tension, and has not been so since it was +extremely thin, a mere pellicle as compared with the liquid nucleus, but +is, on the contrary, in a state of _tangential compression_. + +However tenable, in other respects, may be the volcanic theory which +rests upon the assumption of a very _thin_ crust and a universal ocean +of fused rock beneath, it fails wholly to explain many of the most +important circumstances observable as to the distribution and movements +of existing Volcanoes on our globe. + +It affords no adequate explanation of the configuration of the lines of +Volcanoes, nor of their occurrence in the ocean bed, nor of their +existence in high latitudes, near the Poles, where, no matter how or at +what rate our globe cooled from liquidity, the crust must be thickest; +nor of the independence of eruptive action of closely adjacent volcanic +vents; nor of the non-periodicity, the sudden awakening-up to activity, +the as sudden exhaustion, the long repose, the gradual decay of action +at particular vents, and of much more that might be stated and +sustained as difficulties left by that theory unexplained, or that are +of a nature even opposed to it. + +The researches of the last few years have, however, as it appears to me, +rendered any theory that demands as its postulates a _very thin crust_, +and a universal liquid nucleus beneath it, absolutely untenable. + +Without attaching any importance to the arguments of Mr. Hopkins, based +upon precession and nutation, it appears to me, on various other +grounds, some of which have been urged by Sir William Thompson, that the +earth's solid crust is not a thin one, at least not thin enough to +render it conceivable that water can ever gain admission to a fluid +nucleus, if any such still exist, situated at so great a depth; and +without such access we can have no Volcano. It is not necessary to go to +the extent of a crust of 800 or 1,000 miles thick: with one of half the +minor thickness, I believe it may be proved, on various grounds, +hydraulic amongst others, that neither water could reach the nucleus, +nor the liquid matter of the nucleus reach the surface. Mr. Hopkins +having proved to his own satisfaction an enormous thickness for the +crust, and seeing clearly the difficulties that this involved to the +generally accepted volcanic theory, and having no other to substitute +for it, fell back upon that most vague and weak notion of the existence +of isolated lakes of liquid rock, existing at comparatively small depths +beneath the earth's surface within the solid and relatively cold crust, +each supplying its own Volcano, or more than one, with ready-made lava. +What is to produce these lakes of fused matter in the midst of similar +solidified matter? what is perpetually to maintain their fluidity in the +midst of solid matter continually cooling? what has given them their +local position? why near or less near the surface? what should have +arranged them in directions stretching in some cases nearly from Pole to +Pole? + +Surely this creation of imaginary lakes, merely because it happens to +fit the vacant chink that seems needed to wedge up a falling theory, is +an instance of that abuse of hypothesis against which Newton so +vehemently declaims--"_Hypotheses non fingo._" + +Hypothesis, to be a philosophic scaffolding to knowledge, must, as +Whewell has said, "be close to the facts, and not merely connected with +them by arbitrary and untried facts." Yet this appears accepted by Lyell +(10th edition, Vol. II., p. 227, and elsewhere); by Phillips +("Vesuvius," pp. 331, 332); by Scrope, if, as I hope, I mistake him not +("Volcanoes," pp. 265, 307-8); though none of these excellent +authorities seem either quite clear or quite satisfied with the notion; +and in the very passage referred to, Lyell _may_ have possibly a much +more philosophic notion in view, where he says: "It is only necessary, +in order to explain the action of Volcanoes, to _discover some cause +which is capable of bringing about such a concentration of heat as may +melt one after the other certain portions of the solid crust_, so as to +form seas, lakes or oceans of subterraneous lava." (Vol. II, pp. 226, +227). If by this is meant, that all that is needed to complete a true +theory of volcanic action is to discover _an adequate cosmical cause for +the heat_--that is to say, a prime mover to which all its phenomena may +be traced back, which shall be at once reconcilable with the conditions +of our planet as a cooling mass in space and with facts of Vulcanology +as they are now seen upon it--then I entirely agree with it. + +It has been my own object to endeavour to discover and develope that +adequate cause in a Paper "On Volcanic Energy, an Attempt to develope +its True Nature and Cosmical Relations," read (in abstract) before the +Royal Society of London ("Proceedings, Royal Society," Vol. XX., May, +1872), and now (October, 1872) under consideration of Council with a +view to publication. + +I propose concluding this review of the progress of Vulcanology (in +which I have had to limit myself to reviewing merely the chief stages of +advance towards knowledge of the nature and origin of volcanic heat +itself, and have had to pass without notice the vast and important mass +of facts and reasonings collected by so many labourers as to its visible +phenomena and products, and the still greater mass of speculation, good +and bad, on every branch of the subject), by giving a necessarily very +brief and imperfect sketch of my own views as in that Paper in part +developed. It will first be necessary to retrace our steps a little, in +order to gain such a point as shall afford us a fuller view of the whole +problem before us. + +It is not necessary to dilate, even did space allow, upon the many +points which bind together Earthquakes and Volcanoes as belonging to the +play of like forces. These are generally admitted; and in various ways, +more or less obscure, geologists generally have supposed some relations +between these and the forces of elevation, which have raised up mountain +chains, etc. + +No one, however, that I am aware of, prior to myself, in the Paper just +alluded to, has attempted to show, still less to prove upon an +experimental basis, that all the phenomena of elevation, of volcanic +action, and of Earthquakes, are explicable as parts of one simple +machinery--namely, the play of forces resulting from the secular cooling +of our globe. We have seen that, on the whole, both Earthquakes and +Volcanoes follow along the great lines of elevation of our surface. Any +true solution of the play of forces which has produced any one of those +three classes of phenomena must connect itself with them all, and be +adequate to account for all. And this would have earlier been seen, had +geologists generally framed for themselves any correct notions of the +mechanism of elevation itself, and seen its real relation with the +secular cooling of our planet. But the play of forces resulting from +this secular cooling has never, until very recently, been adequately or +truly stated. The arbitrary assumption and neglect of several essential +conditions by La Place, in his celebrated Paper "On the Cooling of the +Earth," in the fifth volume of the "Mecanique Celeste," and the +arbitrary and unsustainable hypothesis of Poisson upon the same subject, +have tended to retard the progress of physical Geology as to the nature +of elevation: the first, by leaving the geologist in doubt as to whether +our globe were cooling at all; the second, by suggesting distorted +notions as to the mode of its cooling and consolidation. On the other +hand, neither geologists nor mathematicians generally have framed for +themselves any clear notions of the mechanism of elevation. Had a true +conception been formed of the forces and interior movements brought +necessarily into operation by the secular cooling of the globe, +geologists could scarcely have failed to see that their notion as to the +way and direction in which the forces producing elevation have actually +acted could not, if arising from refrigeration, be those which they have +almost universally supposed, namely--some force acting vertically +upwards, _i.e._, radially from the centre of the sphere. Had geologists +only looked at Nature with open eye, they must have seen that mountain +ranges, and elevations generally (exclusive of volcanic cones), +presented circumstances absolutely incompatible with their having been +thrust up by any force _primarily_ acting in the direction of a radius +to the spheroid. + +Yet this is the erroneous notion of the mechanism of elevation which to +the present hour prevails amongst geologists, so far as they in general +have framed to themselves any distinct idea of such mechanism at all. + +Thus, only to cite two examples from recent authors of justly high +reputation. Lyell says of the probable subterranean sources, whether of +upward or downward movement, when permanently uplifting a country, and +in reference to the crumpling of strata on mountain flanks by lateral +pressure, it would be rash to assume these able to resist a power of +such stupendous energy, "_if its direction, instead of being vertical_, +happened to be oblique or horizontal." This is somewhat vague--and I +trust I do not mistake or misrepresent the illustrious author--yet it +is the most explicit expression I can find in the "Principles of +Geology" as to his notion of the primary direction of elevatory force +(Edit. 10, Vol. I., p. 133). That Mr. Scrope's idea is that only of +primary radial or vertical direction of such forces, is apparent on +inspecting his Diagram No. 64 ("Volcanoes," p. 285), and in the use of +the words, "an axial wedge of granite," which, on the next page, we find +is "liquefied granite;" and if we read on to page 294, and refer also to +pages 50 and 51, I believe there can be no doubt that _vertical_ or +_direct up-thrust_ is the author's notion of the primary direction of +all forces of elevation. The true nature of these forces was, however, +clearly seen and most justly stated by Constant Prevost ("Compt. Rend.," +Tome XXXI., 1850, and "Bulletin de la Societe Geolog. de France," Tome +II., 1840) as consisting, not in forces of some unknown origin acting +primarily in the vertical, but in _tangential pressures acting +horizontally, and resolved by mutual pressures at certain points into +vertical resultants_. These Prevost rightly attributed to the +contraction of the earth's solid crust. The same idea has been adopted +by Elie de Beaumont as the true mechanism of the elevation of mountain +ranges; and although De Beaumont's views as to the thinness he assigns +to the solid and contracting crust, and his strange deduction as to the +parallelism of contemporaneous mountain chains uplifted by its spasmodic +action along certain lines, may be untenable, his notion generally as to +the play of forces producing mountain elevation is much more nearly +correct. + +Mr. Hopkins's notion is simply that of the geologists. Anyone who reads +his well-known papers on elevation and the formation of fissures, etc., +must see that he views all elevatory forces as of liquids or +quasi-liquids forced up and acting primarily _vertically_ upon the +strata above them, and that these strata are not under tangential +compression, but under tension. Hence the mathematical deductions +contained in those papers as to the directions in which elevatory forces +act, and in which fissures are formed by them, are not in any way a +setting forth of such facts as occur in Nature, and, much attention as +they have attracted, can only now be viewed as exercises of mathematical +skill misapplied, because based upon data not to be found in Nature. In +fact, those papers do but misrepresent Nature, and, like many other +mathematical investigations based on untrue or insufficient data, have +tended to retard knowledge. + +The views which I have put forward in the Paper I have referred to, read +to the Royal Society, recapitulated in skeleton, so to say, are as +follows. Omitting those portions which treat of our globe from the +period of the first liquefaction out of a nebulous condition, and of the +earliest stages of the cooling by radiation into space, when the crust +was extremely thin, and of the deformation of the spheroid as one of the +first effects of its contraction, and through that the general shaping +out of continents and ocean beds; I have endeavoured to show that the +rate of contraction of the crust, while very thin, exceeded that of the +large fluid nucleus supporting it, and so gave rise to _tangential +tensions_ in the crust, and fracturing it into segments; next, that as +the crust thickened, these _tensions_ were gradually converted into +_tangential pressures_, the contraction of the nucleus now beginning to +exceed (for equal losses of heat) that of the crust through which it +cooled. At this stage these tangential pressures gave rise to the +_chief_ elevations of mountain chains--not by liquid matter by any +process being injected from beneath vertically, but by such pressures, +mutually reacting along certain lines, being resolved into the vertical, +and forcing upwards more or less of the crust itself. The great outlines +of the mountain ranges and the greater elevation of the land were +designated and formed during the long periods that elapsed in which the +continually increasing thickness of crust remained such that it was +still, as a whole, flexible enough, or opposed sufficiently little +resistance to crushing, to admit of this uprise of mountain chains by +resolved tangential pressures. I have shown that the simple mechanism of +such tangential pressures is competent to account for all the complex +phenomena both of the elevations and of the _depressions_ that we now +see on the earth's surface (other than continents and ocean beds), +including the production of gaping fissures (in directions generally +orthogonal to those of tangential pressure). And as our earth is still a +cooling body, and the crust, however now thicker and more rigid, is +still incapable of sustaining the tangential pressures to which it is +now exposed, so I by no means infer that slow and small (relatively) +movements of elevation and depression may not be still and now going on +upon the earth's surface; in fact all the phenomena of elevation and +depression, rending, etc., which at a much remoter epoch acted upon a +much grander and more effective scale. So that, for aught my views say +to the contrary, all the mountain chains in the world may be possibly +increasing in stature year by year, or at times; but in any case at a +rate almost infinitesimally small in its totality over the whole earth +to that with which their ridges were originally upreared. + +But the thickness of the earth's crust--thus constantly added to, by +accretion of solidifying matter from the still liquid or pasty nucleus, +as the whole mass has cooled--has now assumed such a thickness as to be +able to offer a too considerable resistance to the tangential pressures, +to admit of its giving way to any large extent by resolution upwards; +yet the cooling of the whole mass is going on, and contraction, though +unequal, both of thick crust and of hotter nucleus beneath also, whether +the latter be _now_ liquid or not. Were the contraction, lineal or +cubical, for equal decrements or losses of heat, or in equal +times--equal both in the material of the solidified crust and in that of +the hotter nucleus--there could be no such tangential pressures as are +here referred to, at any epoch of the earth's cooling. But in accordance +with the facts of experimental physics, we know that the co-efficient of +contraction for all bodies is greater as their actual temperature is +higher, and this both in their solid and liquid states. + +Hence for equal decrements of heat, or by the cooling in equal times, +the hotter nucleus contracts more than does its envelope of solid +matter. + +The result is now, as at all periods since the signs changed of the +tangential forces thus brought into play--_i.e._, since they became +tangential _pressures_--that the nucleus tends to shrink away as it +were from beneath the crust, and to leave the latter, unsupported or but +partially supported, as a spheroidal dome above it. + +Now what happens? If the hollow spheroidal shell were strong enough to +sustain, as a spheric dome, the tangential thrust of its own weight and +the attraction of the nucleus, the shell would be left behind altogether +by the nucleus, and the latter might be conceived as an independent +globe revolving, centrally or excentrically, within a shell outside of +it. This, however, is not what happens. + +The question then arises, Can the solid shell support the tangential +thrust to which it would be thus exposed? By the application to this +problem of an elegant theorem of Lagrange, I have proved that it cannot +possibly do so, no matter what may be its thickness nor what its +material, even were we to assume the latter not merely of the hardest +and most resistant rocks we know anything of, but even were it of +tempered cast-steel, the most resistant substance (unless possibly +iridio-osmium exceed it) that we know anything about. Lagrange has shown +that if P be the normal pressure upon any flexible plate curved in both +directions, the radii of these principal curvatures being r' and r'', +and T the tangential thrust at the point of application and due to the +force P, then: + + P = T (1/r' + 1/r'') + +When the surface is spherical, or may be viewed as such, r' = r'' and + + P = 2T/r or, T = P x r/2 + +In the present case P is for a unit square (taken relatively small and +so assumed as plane) of the shell, suppose a square mile, equal to the +effect of gravity upon that unit, r being the earth's radius, and if we +assume the unit square be also a unit in thickness, P is then the weight +of a cubic mile of its material; and if we take (roughly) the earth's +radius as 4,000 miles, the tangential pressure, T, is, on _each face_ of +the cubic mile, equal to + + (4000/2) P, + +or equal to the pressure of a column of the same material of 2,000 times +its weight. + +If the cubic mile that we have thus supposed cut out of the earth's +crust at the surface were of the hardest known granite or porphyry, it +would be exposed to a crushing tangential pressure equal to between 400 +and 500 times what it could withstand, and so must crush, even though +only left unsupported by the nucleus beneath, to the extent of 1/400 or +1/500 of its entire weight. And what is true here of a mile taken at the +surface, is true (neglecting some minute corrections for difference in +the co-efficient of gravity, etc.) if taken at any other depth within +the thick crust.[F] + +The crust of our earth, then, as it now is, must crush, to follow down +after the shrinking nucleus--if so be that the globe be still cooling, +and constituted as it is; even to the limited extent to which we know +anything of its nature--it must crush unequally, both regarded +superficially and as to depth; generally the crushing lines being +confined to the planes or places of greatest weakness; and the crushing +will not be absolutely constant and uniform anywhere, or at any time, or +at any of those places of weakness to which it will be principally +confined, but will be more or less irregular, quasi-periodic, or +paroxysmal: as is, indeed, the way in which all known material +substances (more or less rigid) give way to a slow and constantly +increasing, steady pressure. + +We have now to ask, _How much_ of this crushing is going on at present +year by year? And the answer to this depends upon what amount of heat +our world is losing into space year by year. + +Geologists who have taken on trust the statement, that La Place has +proved that the world has lost no sensible amount of heat for the last +10,000 years seem generally to suppose that to be a fact; but in reality +La Place has _proved_ nothing of the sort, as those geological teachers +who have echoed the conclusion should have known, had they deciphered +the mathematical argument upon which it has been supposed to rest. + +By application of Fourier's theorem (or definition) to the observed rate +of increment of heat in descending from the geothermal _couche_ of +invariable temperature, and the co-efficients of conductivity of the +rocks of our earth's crust, as given by the long-continued observations +made beneath the Observatories of Paris and of Edinburgh, it results +that the annual loss of heat into space of our globe at present is equal +to that which would liquefy into water, at 32 deg. Fahr., about 777 cubic +miles of ice; and this is the measuring unit for the amount of +contraction of our globe now going on. The figures are not probably +exact, for the data are not on a basis sufficiently full or exactly +established as yet; but they are not very widely wrong, and their +precise exactness is not material here. Now, how is this annual loss of +heat (great or small, as we may please to view it) from the interior of +our globe disposed of? + +What does it _do_ in the interior? We have already seen that it is +primarily disposed of by conversion into work; into the work of +diminishing the earth's volume as a whole, and in so doing crushing +portions of the solid surrounding shell. + +But does the transformation of lost heat into the work of vertical +descent, and of the crush as it follows down after the shrinking +nucleus, end the cycle? No. A very large portion of the mechanical work +thus produced, and resolved, as we have seen, into tangential crushing +pressure, is retransformed into heat again in the very act of crushing +the solid material of the shell. If we see a cartload of granite +paving-stones shot out in the dark, we see fire and light produced by +their collision; if we rub two pieces of quartz together, and crush thus +their surfaces against each other, we find we heat the pieces and evolve +light. + +The machinery used for crushing by steam-power, hard rocks into road +metal, gets so hot that the surfaces cannot be touched. + +These are familiar instances of one result of what is now taking place +by the crushing of the rocky masses of our cooling and descending +earth's crust, every hour beneath our feet, only upon a vastly greater +scale. It is in this local transformation of work into heat that I find +the true origin of volcanic heat within our globe. But if we are to test +this, so as in the only way possible to decide is it a true solution of +this great problem, we must again ask the question, _How much?_ and to +answer this, we must determine _experimentally_ how much heat can be +developed by the crushing of a given volume, say a cubic mile, of such +rocky materials as we know must constitute the crust of our globe down +to the bottom of the known sedimentary strata, and extending to such +crystalloid rocks as we may presume underlie these. We must also obtain +at least approximately what are the co-efficients of _total contraction_ +between fusion and atmospheric temperature of such melted rocks, basic +and acid silicates, as may be deemed representative of that co-efficient +for the range of volcanic fused products, basalts, trachytes, etc., +which probably sufficiently nearly coincide with that of the whole +non-metallic mass of our globe. + +The first I have determined experimentally by two different methods, but +principally by the direct one of the _work_ expended in crushing prisms +of sixteen representative classes of rock; the specific gravities and +specific heats of which I have also determined. + +If H be the height of a prism of rock crushed to powder by a pressure, +P, applied to two opposite faces, which, when the prism has been +reduced to its volume in powder, has acted through a range of H - t, +then + + P x (H - t) / 772 + +is the heat corresponding to the work expended in the crushing, +expressed in British units of heat. The following were the rocks +experimented upon: Caen stone, Portland (both oolites), magnesian +limestone, sandstones of various sorts, carboniferous limestones +(marbles), the older slates (Cambrian and Silurian), basalts, various +granites and porphyries, thus ranging from the newest and least +resistant to the oldest and most resistant rocks. The results have been +tabulated, and are given in detail in my Paper, now in possession of the +Royal Society. The minimum obtained is 331 and the maximum 7,867 British +units of heat developed, by transformation of the work of crushing one +cubic foot of rock. If we apply the results to a thickness of solid +crust of 100 miles (British), of which the upper twenty-one miles +consist of neozoic, newer palaeozoic, older palaeozoic and azoic rocks in +nearly equal proportion as to thickness, and the remaining eighty miles +of crystalloid rocks (acid and basic magmas of Durocher) of physical +properties which we may assume not very different from those of our +known granites and porphyries--and which, in so far as they may differ, +would give a still _higher_ co-efficient of work transformed into heat +than I have attributed to them by ranging them as only equal to the +granites, etc.--then we obtain a mean co-efficient for the entire +thickness of crust of 100 miles of 6,472 British units of heat, +developable from each cubic foot of its material, if crushed to powder. +It results from this that each cubic mile of the mean material of such +a crust, when crushed to powder, developes sufficient heat to melt 0.876 +cubic miles of ice into water at 32 deg., or to raise 7.600 cubic miles of +water from 32 deg. to 212 deg. Fahr., or to boil off 1.124 cubic miles of +water at 32 deg. into steam of one atmosphere, or, taking the average +melting point of rocky mixtures at 2,000 deg. Fahr., to melt nearly three +and a-half cubic miles of such rock, if of the same specific heat. + +Of the heat annually lost by our globe and dissipated into space, +represented by 777 cubic miles of ice melted, as before stated, the +chief part is derived from the actual hypogeal source of a hotter though +not necessarily fused nucleus, and nearly, if not wholly, is quite +independent of the heat of Vulcanicity, which is developed as a +consequence of its loss or dissipation. But were we to take the extreme +case, and suppose it possible that all the heat the globe loses annually +resulted from the transformation of the work of internal crushing of its +shell, we shall find that the total volume of rock needed to be crushed +in order to produce the required amount of lost heat is perfectly +insignificant as compared with the volume of the globe itself, or that +of its shell. For, as 1.270 cubic miles of crushed rock developes heat +equivalent to that required to melt one cubic mile of ice to water at +32 deg., and if we assume the volume of our globe's _solid_ crust to equal +one-fourth of the total volume of the entire globe, 987 cubic miles of +rock crushed annually would supply the whole of the heat dissipated in +that time. But that is less than the _one sixty-five millionth_ of the +volume of the crust only. + +But a very small portion of the total heat annually lost by our globe +is sufficient to account for the whole of the volcanic energy of every +sort, including thermal waters, manifested annually upon our earth. In +the absence of complete data, we can only approximately calculate what +is the annual amount of present volcanic energy of our planet. This +energy shows itself to us in three ways: 1. The heating or fusing of the +ejected solid matters at volcanic vents. 2. The evolution of steam and +other heated elastic fluids by which these are carried. 3. The work of +raising through a certain height all the materials ejected. To which we +must add a large allowance for waste, or thermal mechanical and chemical +energy ineffectually dissipated in and above the vents. All these are +measurable into units of heat. + +I have applied this method of calculation to test the adequacy of the +source I have assigned for volcanic heat, in two ways, viz.: 1. To the +phenomena presented during the last two thousand years by Vesuvius, the +best known Volcano in the world; and 2. To the whole of the four hundred +and odd volcanic cones observed so far upon our globe, of which not more +than one-half have ever been known in activity. + +It is impossible here to refer to the details of the method or steps of +these calculations. The result however is, that making large allowances +for presumably defective data, _less than one-fourth_ of the total +telluric heat annually dissipated (as already stated in amount) is +sufficient to account for the annual volcanic energy at present expended +by our globe. + +It is thus represented by the transformation into heat of the work of +crushing about 247 cubic miles of (mean) rock, a quantity so perfectly +insignificant, as compared with the volume of the globe itself, as to be +absolutely inappreciable in any way but by calculation; and as its +mechanical result is only the vertical transposition transitorily of +material within or upon our globe, the proportion of the mass of which +to the whole is equally insignificant, so not likely in any way to +produce changes recognisable by the astronomer. + +Space here forbids my entering at all upon that branch of my +investigation which is based upon the experimental results, above +mentioned, of the total contraction of fused rocks: for these, the +original Paper can, I hope, be hereafter referred to. I am enabled, +however, to prove thus how enormously more than needful has been the +store of energy dissipated since our globe was wholly a melted mass, for +the production, through the contraction of its volume, of all the +phenomena of elevation and of Vulcanicity which its surface presents. +And how very small is the amount of that energy in a unit of time as now +operative, when compared with the same at very remote epochs in our +planet's history. + +I have said that if we can find a true cause in Nature for the +origination of volcanic _heat_, all the other known phenomena, at and +about volcanic vents, become simple. Lavas and all other solid ejecta of +Volcanoes, from all parts of the earth's surface, as well as basalts, +present in chemical and physical constitution close resemblance, and may +be all referred to the melting of more or less fusible mixtures of +siliceous crystalloid rocks with aluminous (slates, etc.) and calcareous +rocks. Their general chemical composition, and the higher or lower +temperatures of fusion resulting therefrom, together with the higher or +lower temperatures to which they have been submitted at the different +volcanic foci, determine their difference of flow (under like surface +conditions) and of mineral character after ejection and cooling. + +St. Clair de Ville and Fouque have shown that the gaseous ejections, of +which steam forms probably 99 per cent., are such as arise from water +admitted to a _pre-existent focus of high temperature_. + +Whether sea or fresh water is not material, when we bear in mind that +the chemical constituents found in sea water and in natural fresh waters +that have penetrated the soil are, on the whole, alike in kind and only +differ in proportions. But I must pass almost without notice all the +varied and instructive phenomena which are presented by volcanic vents, +for to treat of these at all would be to more than double the size of +this sketch. + +In the source that has been pointed out as that from which volcanic heat +itself is derived, viz., the secular cooling of our globe, and the +effects of that upon its solid shell, we are enabled to point to that +which is the surest test of the truth of any theory--that it not only +enables us to account for all the phenomena, near or remote, but to +predict them. We see here linked together as parts of one grand play of +forces, those of contraction by cooling, producing by _direct_ +mechanical action the elevation of mountain chains, and by their +_indirect_ action, by transformation of mechanical work into heat, the +production of Volcanoes; and both by direct and by indirect action, of +Earthquakes, never previously shown to have thus the physical connection +of one common cause, but merely supposed, more or less, to be connected +by their distribution upon our earth's surface. + +We now discern thus the physical cause _why_ Volcanoes are distributed, +viewed largely, linearly, and follow the lines of elevation; we see +equally why their action is uncertain, non-periodic, fluctuating in +intensity, with longer or shorter periods of repose, shifting in +position, becoming extinct here, appearing in new activity or for the +first time there. We have an adequate solution of the before +inexplicable fact of their propinquity, and yet want of connection. We +have an adequate cause for the fusion of rock at local points without +resorting to the baseless hypothesis of perennial lakes of lava, etc. + +For the first time, too, we discern a true physical cause for earthquake +movement, where volcanic energy does not show itself. The crushing of +the world's solid shell, whether thick or thin, goes on _per saltum_ and +at ever-shifting places, however steadily the tangential pressures +producing it may act. Hence crushing _alone_ may be shown to develope +amply sufficient impulse to produce the most violent Earthquakes, +whether they be or be not at a given place or time connected with +volcanic outburst or possible injection, or with tangential pressures, +enough still, in some cases, to produce partial permanent elevation. + +When subterraneous crushing takes place, and the circumstances of the +site do not permit the access of water, there may be Earthquake, but can +be no Volcano; where water is admitted, there may be both. + +And thus we discern why there are comparatively few submarine +Volcanoes, the floor of the ocean being, on the whole, +water-tight--"puddled," as an engineer would say, by the huge deposit of +incoherent mud, etc., that covers most of it, and probably having a +thicker crust beneath it than beneath the land. + +We see, moreover, that the geological doctrine of absolute uniformity +cannot be true as to Vulcanicity, any more than it can for any other +energy in play in our world. Its development was greatest at its +earliest stages, when the great masses of the mountain chains were +elevated. It is even now--though as compared to men's experience, and +even to all historic time, apparently uniform and always the same--a +decaying energy. + +The regimen of our planet as part of the Cosmos, which seems to some +absolute (and presented to Playfair no trace of a beginning nor +indication of an end), is not absolute, and only seems to us to be so +because we see so little of it, and of its long perspective in time. +This the now established doctrine of the conservation of energy renders +certain. + +With this source for volcanic heat, too, in our possession, we can look +from our own world to others, and predict within certain limits, which +must widen as our knowledge of the facts of their substance and surface +becomes greater, what have been and what are the developments of +Vulcanicity which have taken place or are occurring in or upon them. +Looking to our own satellite, we see for the first time a sufficient +physical cause for the enormous display of volcanic energy there which +the telescope divulges to us; one which is not to be explained alone by +the commonly made statement of the small density of the moon, but by +the fact that as the rate of her cooling from a given temperature, as +compared with that of our earth (apart from questions of the chemical +nature of the two bodies, or of their specific heats, etc.), has been +inversely as their respective masses, and directly as their surfaces, so +has the rate of cooling of the moon been vastly greater than that of the +earth, and the energy due to contraction by cooling more intense and +rapidly developed in our satellite than upon our globe. + +We have thus traced, in meagre and broken outline only--because space +admitted no more--the progress of Science to its existing state as +respects Vulcanicity, in its two branches of Vulcanology and of +Seismology, and pointed out their more intimate relations and points of +connection, and been at length able to refer them, on the sure basis of +physical laws, to one common cause, and that one derived from no +hypothesis, but simply from the postulate of our world as a terr-aqueous +globe cooling in space. + +What I have here advanced with reference to volcanic energy, which +appertains to my own researches, I do not conceal from myself, nor from +the reader, has yet to await the reception generally and the award of +the true men of science of the world. + +That, like every new line of thought which has attempted or succeeded in +supplanting the old, it will meet with opposition, I make no doubt. + +My belief, however, is that in the end it will be found to have added a +fragment to the edifice of true knowledge. + +The interpretation which I have given of the nature and origin of +volcanic activity points at once to the function in the Cosmos which it +is its destiny to fulfil. It is the instrument provided for the purpose +of continually preserving the earth's solid shell in a state to follow +down after the descending nucleus. It does this by an apparatus or play +of mechanism whereby the material of the solid shell, locally or along +certain lines, is not only crushed, but the crushed material is blown +out as dust, or expelled as liquid rock from between the walls of the +shell, which are thus enabled to approach each other; and thus, by +relief of the tangential thrusts, to permit the shell to descend, which +it is obvious that crushing alone, unless it extended to the whole mass +of the shell, could not accomplish. + +It is a wonderful example of Nature's mechanism thus to see how simple +are the means by which this end is accomplished. The same inevitable +crush that dislocates the solid shell along certain lines, produces the +heat necessary to expel to the surface the material crushed. + +When attempted to be made the basis for philosophic discovery, "final +causes" are no doubt barren, as Bacon has said; but when we have +independently and by strict methods arrived at a result, we may justly +appeal, as a test of its truth, to its showing itself as plainly +fulfilling a needful end, and, by a distinctly discernible mechanism, +preserving that harmony and conservation which are the obvious law of +the universe. + +As has been said, if I mistake not by Daubeny, John Phillips, by +Herschell, and by myself, the function of the Earthquake and the +Volcano is not destructive but, preservative. But we now see that: that +the preservative scope of this function, as respects our earth, is far +wider than what has been previously attributed to it. The Volcano does +not merely throw up new fertile soil, and tend, in some small degree, to +restore to the dry land the waste for ever going on by rain and sea; it +fulfils a far weightier and more imperative task; it--by a mechanism the +power of which is exactly balanced to the variable calls demanded of it, +and which working almost imperceptibly, although in a manner however +terrible its surface-action may at times appear to us little +men[G]--prevents at longer intervals such sudden and unlooked-for +paroxysms in the mass of our subsiding earth's shell as would be +attended with wide-spread destruction to all that it inhabit. + +To the popular mind, Volcanoes and Earthquakes are only isolated items +of curiosity amongst "the wonders of the world:" few geologists even +appear to realise how great and important are the relations of +Vulcanicity to their science, viewed as a whole. Yet of Vulcanicity it +is not too much to say, that in proportion as its nature and doctrines +come to be known and understood as parts of the Cosmos, the nearer will +it be seen to lie at the basis of all Physical Geology. + + +[A] For a fuller account of the literature and history of advancement of +human knowledge as to Earthquakes, here merely glanced at, I must refer +to my First Report on the Facts of Earthquakes, "Reports, British +Association, 1850," and to the works of Daubeny, Lyell, Phillips and +others, its _complete_ history remaining yet to be written. + +[B] Yet how indistinctly formed were Young's ideas, and indistinct in +the same direction as those of Humboldt, becomes evident by a single +sentence: "When the agitation produced by an Earthquake extends further +than there is any reason to suspect a subterraneous communication, it is +probably propagated through the earth nearly in the same manner as a +noise is conveyed through the air."--_Lectures, Nat. Phil._, Vol. I. + +[C] The Right Rev. Charles Graves, F.R.S., etc., then Fellow of Trinity +College, Pres. R. I. Acad., and now Bishop of Limerick, on presentation +of the Academy's Cunningham Medal. + +[D] In this Report, though I have never before referred to it, and do so +now with reluctance, I have always felt that the Author did me some +injustice. The only reference made to my labours, published the +preceding year only, is in the following words: "Many persons have +regarded these phenomena (viz., Earthquakes) as due in a great measure +to vibrations ... and the subject has lately been brought under our +notice, in a Memoir by Mr. Mallet, 'On the Dynamics of Earthquakes,' in +which he has treated it in a more determinate manner, and in more +detail, than any preceding writer" (p. 74). If that Paper of mine be +collated with this Report, it will be, I believe, found that, as +respects the earthquake part, the latter tint parades, in a mathematical +dress, some portions of the general theory of earthquake movements, +previously published by me as above stated. So, also, in the chapter (p. +90) referring to Seismometry, and the important uses to Geology that +might be (and since have been, to some extent) made of it, no mention is +made of those instruments previously proposed by me, nor of my +anticipation of their important uses. This is but too mortifyingly +suggestive of the-- + + "Pereant qui mea ante mihi dixerunt." + +Having left this unnoticed for so many years, and during which the +Author has preceded me to that bourne where our errors to each other +must be forgotten, I should certainly not have now trespassed on the +good rule, _De mortuis nil nisi bonum_, had I not observed very recently +one amongst other results probably attributable to it. In Professor +Phillips's "Vesuvius," if any one will refer to the passage beginning +"The mechanism of earthquake movement has been investigated by competent +hands. The late eminent mathematician, Mr. Hopkins, explained these +tremors in the solid earth by the general theory of vibratory motion," +etc. (pages 257-259)--I think he must, in the absence of collateral +information, conclude that, not I, but Mr. Hopkins, was the discoverer +of the Theory of Earthquakes as explained by the general theory of +vibratory motion. + +Probably my friend, Professor Phillips, had not recently referred to +those Memoirs and Reports of twenty-four years back, and I am thoroughly +convinced that, if he has here perpetuated an injustice, he has done so +unintentionally and unwittingly. + +Still, the facts show how true it is that + + "The ill men do lives after them, + The good they do is oft interred with their bones." + +And I may venture to ask my friend, should his admirable book reach, as +I doubt not it will, another edition, to modify the passage. + +[E] Assuming the point of ejection of this block (the crater) to be +8,000 feet above where it landed, and allowing it as high a density as +admissible, and the angle of projection the best for large horizontal +range, it may be proved that this mass, to reach nine miles +horizontally, would require an initial velocity of projection of from +1,500 to 1,600 feet per second, one as great as that of a smooth-bore +cannon-shot at the muzzle, and perfectly inconceivable to be produced by +a volcano. + +[F] The Rev. O. Fisher, M.A., F.G.S., in a most interesting and valuable +Paper, "On the Elevation of Mountain Chains by Lateral Pressure, its +Cause, and the Amount of it, with a Speculation on the Origin of +Volcanic Action," read, April, 1868, and published in the Transactions +of the Cambridge Philosophical Society, Vol. XI., Part III., in 1869, +has deduced the necessary crushing of the earth's crust by a different +but closely analogous method. I had not seen this Paper until after my +own was in the hands of the Royal Society. The author's volcanic views +are wholly different from my own, and do not appear to me equally valid +with his notions as to elevation.--R. M. + +[G] "Magna ista quia parvi sumus"--SENECA, "Quaes. Nat." + + +END. + + + + +TRANSLATION +OF + +PROFESSOR PALMIERI'S + +_ACCOUNT OF_ +THE ERUPTION OF VESUVIUS +OF +_1871-1872_ + + + + +I. + +ACCOUNT OF THE ERUPTION. + + +The great and disastrous conflagration of Vesuvius, which took place on +the 26th of April, 1872, was, in my opinion, the last phase of an +eruption which commenced at the end of January, 1871, an account of +which I was unwilling to write, because I was convinced that it would +not really terminate without a more or less violent explosion, such as I +had often predicted. I shall now state the reasons upon which my +prediction was founded. + +When the central crater begins to heave, with slight eruptions, one may +always predict a series of slight convulsions of greater or less +duration, which are preparatory to the grand explosion, after which the +Volcano remains for the most part in repose. Thus, when I observed the +cone fissuring in November, 1868, and copious lava streams issuing from +it, and flowing over the beautiful and fertile plains of the Novelle, +through the Fossa della Vetrana, instead of announcing the beginning of +an eruption, I announced the termination of one which had been manifest +for upwards of a year by the constant flow of lava from the summit of +the cone. + +From the month of November, 1868, until the end of December, 1870, the +mountain remained quiet, except that the fumaroles at the head of the +fissure showed a degree of activity by which chlorides and sulphides of +copper, sulphide of potash and other products, were engendered. + +But in the beginning of 1871 the seismograph was disturbed,[1] and the +crater discharged, with a slight detonation, a few incandescent +projectiles. Then I announced that _a new eruption had commenced, which +might be of long duration, but with phases that could not possibly be +foreseen_; and on the 13th January, on the northern edge of the upper +plain of the Vesuvian cone, an aperture appeared, from which at first a +little lava issued, and then a small cone arose and threw out +incandescent projectiles, with much smoke of a reddish colour, whilst +the central crater continued to detonate more loudly and frequently. The +lava-flow continued to increase until the beginning of March, without +extending much beyond the base of the cone, although it had great +mobility. In March, this little cone appeared not only to subside, but +even partly to give way, as almost happens with eccentric cones when +their activity is at an end. Upon visiting it, I observed that four +prismatic or pillar-like masses remained standing, three of which were +formed of scoriae which had fallen back again in a pasty condition, and +had become soldered together, the fourth consisting of a pyramidal block +of compact and lithoidal lava, which appeared to have been forced up by +impetus from the ground beneath. A little smoke issued from the small +crater, and a loud hissing from the interior was audible. By lying +along the edge, I could see a cavity of cylindrical form about ten +metres in depth, tapestried with stalactitic scoriae covered with +sublimations of various colours. The bottom of this crater was level, +but in the centre a small cone of about two metres had formed, pointed +in such a manner that it possessed but a very narrow opening at the +apex, from which smoke issued with a hissing sound, and from which were +spurted a few very small incandescent scoriae. This little cone increased +in size as well as activity until it filled the crater, and rose four or +five metres above the brim.[A] New and more abundant lavas appeared near +the base of this cone, and, pouring continually into the Atria del +Cavallo, rushed into the Fossa della Vetrana in the direction of the +Observatory and towards the Crocella, where they accumulated to such an +extent as to cover the hill-side for a distance of about 300 metres; +then turning below the Canteroni, they formed a hillock there without +spreading much farther. These very leucitic lavas are capable of great +extension, the pieces which are ejected forming for the most part very +fine filiform masses, which may be collected on the mountain in great +quantities, and specimens of which I presented to the Academy under the +name of _filiform lapilli_. These threads were often of a clear +yellowish colour, and, when observed under the microscope, were found to +consist of very minute crystals of leucite embedded in a homogeneous +paste. The crystals were still smaller as the diameter of the threads +was less, and never formed knots or swellings even in the most hair-like +threads. These observations led me to reject the opinion of those who +hold that crystals of leucite are pre-existent in the lava. The viscous +nature of these lavas prevented their being covered with fragmentary +scoriae, but caused the formation at first of a skin, which, thickening, +became at last a more or less pliable shell, that, when more solidified, +allowed the still fluid part to run as in a tube formed of this solid +shell. For many months the lava descended thus from the cone and +traversed the Atria del Cavallo, always covered, appearing below the +Canteroni of a lively fluidity, until it could no longer be enveloped in +its skin, which was stretched by the addition of new lava, and finally +rent asunder to give room to the current until, owing to diminished +liquidity, it was constrained to stop. When the lava, having traversed +the covered channel it had made for itself from the top of the mountain +to below the Canteroni, made its appearance still running, it frequently +formed large bubbles on the surface, which mostly burst to give vent to +smoke, and then disappeared. + +In October, 1871, near the edge of the central crater, another small +crater was formed by falling in, which, after a few days, gave vent to +smoke and several jets of lava. The principal cone frequently opened in +some point of the slope to give egress to small currents of lava, which +quickly ceased. But towards the end of October the detonations +increased, the smoke from the central crater issued more densely and +mixed with ashes, and the seismograph and accompanying apparatus were +disturbed: for all these reasons, I said in one of my bulletins, _we +have either reached a new phase or the end of the eruption_, not knowing +whether the new phase would be the last. On the 3rd and 4th November +copious and splendid lava streams coursed down the principal cone on its +western side, but were soon exhausted. The cone of 1871 appeared again +at rest, and partly even fell in, but did not cease to emit smoke and to +show fire in the interior. + +In the beginning of January, 1872, the little cone again became active, +the crater of the preceding October resumed strength, with frequent +bellowings and projectiles, and soon after lavas of the same kind as +before reappeared. The cone of 1871, formed again by the lava ejected, +became so full that the lava poured from its summit in the most singular +and enchanting manner. So far only an eccentric or ephemeral cone had +risen close to the central crater, which, after exhaustion, regained +vigour and discharged lava from the apex instead of the base, as usually +happens. + +In the month of February matters were somewhat moderated; but in March, +with the full moon, the cone opened on the north-west side--the cleavage +being manifest by a line of fumaroles--and a lava stream issued from the +lowest part without any noise and with very little smoke, and poured +down into the Atria del Cavallo as far as the precipices of Monte di +Somma. This lava ceased flowing after a week, but the fumaroles pointed +out the cleft of the cone; and between the small re-made cone, which had +risen to the height of 35 metres, and the central crater, a new crater +of small dimensions and interrupted activity opened. + +On the 23rd April (another full moon) the Observatory instruments became +agitated, the activity of the craters increased, and on the evening of +the 24th splendid lavas descended the cone in various directions, +attracting on the same night the visits of a great many strangers. All +these lava streams were nearly exhausted on the morning of the 25th; +only one remained, which issued from the base of the cone, not far from +the spot whence that of the preceding month had issued. Numbers of +visitors, attracted by the splendour of the lava streams of the +preceding night, which they supposed still continued, soon arrived, but, +finding them exhausted, were for the most part conducted by their guides +to see the one still flowing. It was almost inaccessible, and to reach +it one had to walk over the rough inequalities of the scoriae. It took me +two hours to get there from the Observatory, when I visited it that +morning, and therefore I endeavoured to dissuade those who wished to +visit it at night from the attempt, but set out myself from the +Observatory at 7 p.m., leaving my only assistant there. The instruments +were agitated. After midnight the Observatory was closed, and my +assistant retired to rest. Late and unlucky visitors passed unobserved +with an escort of inexperienced guides; at half-past 3 o'clock in the +morning of the 26th they were in the Atria del Cavallo, when the +Vesuvian cone became rent in a north-westerly direction, the fissure +commencing at the little cone which disappeared, and extending to the +Atria del Cavallo, whence a copious torrent of lava issued. Two large +craters formed at the summit of the mountain, discharging numerous +incandescent projectiles with white ashes, and glittering with particles +of mica, which frequently recurred. + +A cloud of smoke enveloped these unfortunates, who were under a hail of +burning projectiles and close to the lava torrent. Some were buried +beneath it[B] and disappeared for ever; two dead bodies were picked up, +and eleven grievously injured, one of whom died close to the +Observatory. He alone revealed his name, Antonio Giannone. I learned +afterwards that he was a fine young fellow, and Assistant-Professor in +one of the Universities. + +Assistant-Professors Signor Franco, who is a priest, and Signor +Francesco Cozzolino, a priest also, entrusted with the festive mass for +the Observatory, hastened to assist the dying. On my own return thither, +the sad spectacle of the dead and dying awaited me; the former were +conveyed, through the assistance of the municipal officer of Resina, to +the Cemetery, and the latter to the Hospital. But we must leave this +scene of grief and sorrow, and return to the eruption. + +The fissure of the cone on the north-west side was large and deep, and +extended into the Atria del Cavallo, about 300 metres. No mouth opened +along the cleft of the cone itself; all the lava issued from that part +which extended into the Atria. From previous experience I should have +expected to have seen the formation of adventitious cones along the +widest part of the fissure, which is never that most elevated, and these +discharging from their summits aeriform matter frequently mixed with +projectiles, and from their base lava; but on this occasion no cone +appeared at the widest part of the fissure, but a long hillock was +formed like a little chain of mountains, one point of which was elevated +about fifty metres above the plain beneath, and bearing no resemblance +to a cone. + +Another fissure opened in the cone on the south side, which did not +extend to the base, and lava issued from this and flowed in the +direction of the Camaldoli. Streams of less importance furrowed the cone +in other directions, but the largest quantity of lava proceeded from the +fissure in the Atria del Cavallo, below the hillock or miniature chain +of collines just described. This lava stream was for some time +restrained within the Atria del Cavallo, among the holes and +inequalities of the lavas of 1871, but these being filled up and +overcome, it divided into two branches--the smaller one flowing through +a hollow which separated the lavas of 1867 from those of 1871, and made +its way over the lavas of 1858, threatening Resina, but stopped as soon +as it reached the first cultivated ground; the larger branch +precipitated itself into the Fossa della Vetrana, occupying the whole +width, about 800 metres; and traversing the entire length of 1,300 +metres in three hours. It dashed into the Fossa di Faraone; here it +again divided into two streams, one overlying the lava of 1868, on the +Plain of the Novelle, partially covering the cultivated ground and +country-houses; the other flowing on through the Fossa di Faraglione, +over the lava of 1855, reached the villages of Massa and St. Sebastiano, +covering a portion of the houses, and thence continued its course +through the bed of a foss or trench which, contrary to my advice, had +been excavated after the eruption of 1855, in the expectation of +diverting the course of that lava. I did not fail to observe that the +rains which previously descended through these steep channels, would in +future be kept back to filtrate through the scoriae, without ever +reaching the new channel. + +The lava of this eruption, meeting with this said excavation, flowed +into it, instead of pursuing its road over the lava of 1855, and thus +invaded highly cultivated ground and towns of considerable value, +extending to the very walls of a country-house belonging to the +celebrated painter, Luca Giordano. This lava stream, having surmounted +the obstacles which the heaps of scoriae in the Atria del Cavallo +presented to it, ran with great velocity (notwithstanding its being +greatly widened out in the Fossa del Vetrano), so that between 10 a.m. +and 11 p.m. it traversed about five kilometres of road, occupying a +surface of five to six square kilometres. If it had not greatly +slackened after midnight, from the failure of supply at its source, in +twenty-four hours more, by occupying Ponticelli, it would have reached +Naples, and flowed into the sea. + +Although I had often visited the two villages of Massa and St. +Sebastiano, previously greatly injured by the lava of 1855, yet I could +not well estimate, upon now seeing them again, the number of houses +which had disappeared. Massa seemed to me diminished by about one-third, +and St. Sebastiano by somewhat less than a fourth. But the way of escape +was open to the inhabitants of Massa; whilst a great river of lava +occupying the road leading to St. Giorgio a Cremano would have hindered +the flight of the inhabitants of St. Sebastiano, if they had been +dilatory. The lava stream now separating the two villages is little less +than a kilometre in width, and is about six metres in height. + +On the night of the 26th April, the Observatory lay between two torrents +of fire, which emitted an insufferable heat. The glass in the +window-frames, especially on the Vetrana side, was hot and cracking, and +a smell of scorching was perceptible in the rooms. The cone, besides +being furrowed by the lava streams just described, was traversed by +several others, which appeared and disappeared. It seemed completely +perforated, and the lava oozed as it were through its whole surface. I +cannot better express this phenomenon, than by saying that _Vesuvius +sweated fire_. In the day-time, the cone appeared momentarily covered +with white steam jets (fumaroles), which looked like flakes of cotton +against the dark mountain-side, appearing and disappearing at brief +intervals. + +Simultaneously with the grand fissure of the cone, two large craters +opened at the summit, discharging with a dreadful noise, audible at a +great distance, an immense cloud of smoke and ashes with bombs and +flakes, rising to the height of 1300 metres[C] above the brim of lava +(_sull' orlo de essi_). The white ashes, before described, although they +did not fall beyond the Crocella, were carried by the wind as far as +Cosenza, from whence they were sent to me by Dr. Conti. These ejections +were followed by dark sand, with lapilli and small fragments of scoriae +of the same colour. The smoke, driven up with violence, assumed the +usual aspect of a pine tree, of so sad a colour that it reminded us of +the shadowy elm of Virgil's dreams ("_ulmus opaca ingens_"). From the +trunk and branches of the pine-tree cloud fell a rain of incandescent +material, which frequently covered all the cone. The lapilli and the +ashes were carried to greater distances. + +The victims of the morning of the 26th, the torrents of fire which +threatened Resina, Bosco and Torre Annunziata, and which devastated the +fertile country of the Novelle, of Massa, St. Sebastiano and Cercola, +the two partially buried villages, the continual and threatening +growlings of the craters, caused such terror that numbers fled from +their dwellings near the mountain into Naples, and several in Naples +went to Rome or to other places. Very many delayed from the knowledge +that I was in the Observatory, and held themselves in readiness for +flight whenever I should abandon it. + +The rapidity with which the vast torrent of fire assailed the houses +(_i.e._, in these villages), and the great heat which spread to a +distance, scarcely allowed the fugitives to carry away any of their +belongings; many were completely destitute. The authorities vied with +each other in zealous efforts to relieve the distress, and the +municipality of Naples sheltered and fed the wretched beings for many +days. + +The igneous period of the eruption was short, for on the morning of the +27th the lava stream, bearing down upon Resina, having covered a few +cultivated fields, stopped; the lava descending from the summit of the +mountain towards the Camaldoli also stopped; and the great lava torrent, +which passed the shoulders of the Observatory through the Fossa della +Vetrana, lowered the level of its surface below those of its two sides, +which appeared like two parallel ramparts above it. + +If these streams had continued on the 27th, flowing in the same manner +as they did on the night of the 26th, they would have reached the sea, +bringing destruction to the very walls of Naples. + +But before leaving the subject of these lavas I must narrate an +important fact to which I was witness, and which was thrice repeated, +near the banks of the great river of fire that ran close to the +Observatory. At three several points, and at different times, I observed +great balls of black smoke issue from the lava, driven up with continued +violence, as if from a crater; through the smoke I frequently observed +numerous projectiles thrown up into the air, but I could not say whether +with noise or in silence, for the noise of the central crater was +deafening. Each of these little eruptions, which I may call _external +eruptions_, lasted from fifteen to twenty minutes. The first took place +at the most elevated point of the Fossa della Vetrana, on the right bank +of the torrent; the second, under the hill of Apicella, where the lava +divided into the two branches, before described; and the third near to +the Observatory on the left bank of the lava stream. These singular +explosions terminated without leaving little cones or craters, the lava +in its impetuosity carrying every trace away. These eruptions were seen +from Naples, and the Observatory was justly believed to be in danger. +One has been clearly photographed, the one which was the best seen from +Naples, being the nearest and the least darkened by the smoke of the +lava. (Plate 4.) Is this the first time that the phenomenon has been +remarked? I believe that it is at least the first time it has been +authenticated. The authority of Julius Schmidt, quoted by Scrope, has no +weight with me, for I was also a witness of what happened at Vesuvius in +1855; and, although these cones were in the midst of the lava in the +Atria del Cavallo, they originated, according to the opinion of +everyone, from the fissure from which the other and much larger cones +proceeded. The same phenomenon was observed in the Atria del Cavallo in +1858, when I caused two of the little cones to be brought to the +Observatory; but these also might belong to the fissure along which the +other cones were arranged. The same may be said of the little craters +observed, after they had been exhausted, by Professor Scacchi in 1850. +But the discharging mouths now observed in the Fossa della Vetrana, +which existed for twenty minutes and then disappeared, and which were +not at all in a continuous line, and could not be supposed to correspond +with any fissure beneath, constitute a circumstance which, if not new, +is evident for the first time, and cause the recognition of a power in +the lava itself to form eruptive fumaroles.[2] + +The igneous period of the eruption having terminated on the evening of +the 27th, the ashes, lapilli, and projectiles became a little more +abundant, whilst the roaring noises of the craters apparently became +greater. The pine-tree cloud was of a darker colour, and was furrowed by +continual lightning, visible by daylight from the Observatory. Many +writers on the subject of Vesuvius affirm that the flashes which appear +through the smoke cloud were lightning unaccompanied with thunder, but +they studied the phenomena from Naples, or some place more or less +distant from the crater, where the report of the thunder was inaudible, +or could not be distinguished from the bellowing and detonation of the +mountain. The fact is that these flashes were constantly followed by +thunder, after an interval of about seven seconds.[D] When the flash was +very short, a simple noise like the report of a gun was heard, but if it +were long, a protracted sound like that from torn paper ensued. + +On the 28th the ashes and lapilli, continuing to fall abundantly, +darkened the air, yet without diminishing the terrible noise; at Resina, +Portici, St. Giorgio a Cremano, Naples, etc., terror was universal. + +On the 29th, with a strong wind blowing from the east, scoriae of such a +size fell at the Observatory, that the glass of the windows unprotected +by external blinds was broken. The noise from the crater continued, but +the projectiles rose to a less height, indicating a diminution in the +dynamic power of the eruption. Towards midnight the noise of the craters +was no longer continuous, and recurred with less force and for shorter +intervals. Almost at the same hour a tempest burst over the Campania +with loud thunder and a little rain. The grass, the seeds, the vine +tendrils, the leaves and tops of the trees dried up immediately, and the +country was changed from spring to winter. The storm, although repeated +on the following days, passed away by degrees, and thus the floods, +which I strongly feared, did not occur. Almost always after great +eruptions of Vesuvius, storms of heavy rain have followed, and the +ground being covered with ashes, the water could not filtrate through +into the soil, but descended in muddy torrents over the adjacent +country, occasioning as much damage as the fire itself. + +On the 30th, the detonations were very few, and the smoke issued only at +intervals, and by the 1st May the eruption was completely over. + +When the smoke had cleared off the figure of the cone was seen to be +changed. (_Vide_ Plate 5a.) + +The ground was perpetually disturbed whilst the Volcano raged, so that +the Observatory oscillated continually. Some shocks were felt not only +in the adjacent territory, but at a greater distance, at Montovi and +elsewhere. The oscillations at the Observatory were chiefly undulatory, +from N.E. to S.W. They were observed for some days after the termination +of the eruption, but not continuously, although they maintained some +intensity. + +If we refer to January, 1871, we shall find that that eruption was +preceded by several earthquakes, among which were those of the months of +October, November and December, in the previous year, that wrought such +destruction in Calabria, and especially in the province of Cosenza; if +we consider that as only the last phase, we shall find that it was +preceded by great shocks of earthquake that devastated some regions of +Greece.[3] + +The great quantity of lapilli which fell buried the scoriae with which +the Vesuvius cone was covered, so that it became somewhat more difficult +to ascend to the summit, and much less difficult to descend. Having +reached the top of the mountain, I found a large crater divided into two +parts by what seemed a cyclopean wall. The two abysses had vertical +sides, and revealed the internal structure of the cone. Their vertical +depth was 250 metres; and beyond that I observed a sort of tunnel +perforated in the rock, with a covering arch raised above the bottom of +the eastern abyss about 12 metres, judging by the eye. The interior +walls of the crater showed neither the usual stalactitic scoriae nor +sublimations, nor fumaroles, but alternate beds of scoriae and of compact +lava. The fumaroles and sublimations abounded, only about the brims of +the craters. Hydrochloric and sulphuric acid and sometimes sulphuretted +hydrogen affected respiration, and the temperature rose sometimes to 150 +degrees. Various fissures about the brim of the double crater indicated +prolongations downwards, which allowed me to descend with a rope, in +order to examine the interior of the tunnel to which I have just +alluded. The highest brim of the crater was fissured for a distance of +80 metres, and the greatest depth of fissure was at that place. + +By measurement with the barometer, we ascertained approximately (for +only one barometer was used) that the height of the Vesuvian cone was +somewhat diminished. + +Not only the Vesuvian cone, but the whole adjacent country appeared +white for many days, as if covered with snow, when exposed to sunlight. +This was due to the sea-salt contained in the ashes with which the +surface was strewn. + +A great quantity of coleoptera assembled on the flat roof of the +Observatory, where the ashes and lapilli were heaped up two decimetres +in height. I found the same species on the cone, where many insects were +observed on other occasions, such as the _Cuccinella septempunctata_; +the crysomela populi, etc., were wanting. This phenomenon of the +extraordinary concourse of insects on the top of Vesuvius, in order to +die in some of the fumaroles, especially noted previous to and after +great eruptions, is a circumstance for which I cannot account.[4] The +whole of the lava emitted in this eruption occupies a surface of about +five square kilometres; allowing an average thickness of four metres, we +obtain a mass of twenty millions of cubic metres. About three-fifths of +this lava did no injury, being deposited upon other pre-existing lava. +However, the lava in the Novelle, which was deposited upon the lava of +1858, covered quarries of the best stone which had been worked at the +time, covered many paths that had been cleared, and buried the new +Church of St. Michele, with some houses that surrounded it, which had +been rebuilt on the site of the former church, which was covered by the +lava of 1868. The destruction of land in occupation, of buildings and of +crops, exceeded three million francs in value. Many proposals for +relieving the sufferers have been received. Wishing to aid in this +benevolent work, I gave a public lecture, admission for each person +being one franc; and this lecture, from notes badly taken, was printed +by private speculation, and I was compelled to repudiate the report of +it through the public papers. + +The evolutions of carbonic acid (_mofette_), which usually appear at the +end of great Vesuvian eruptions at low-situated spots or hollows, with +very rare exceptions, were observed on this occasion a few days after +the eruption had completely ceased. They appeared in the direction of +Resina. I found the most elevated at Tironi, and the most numerous +between La Favorita and the Bosco Reale di Portici. + +The water in wells was on this occasion neither deficient nor scarce +previous to the eruption, but was very acid after the appearance of the +carbonic acid evolutions in those neighbourhoods in which they +abounded. Having stated that the disastrous conflagration of the 26th +April ought, in my opinion, to be regarded as the last phase of a long +period of eruption, which commenced at the beginning of 1871, I consider +it right to discuss the question at somewhat greater length. + +Not only from twenty years' personal observations, but from the +attentive study of accounts of previous eruptions, I have found that +when the central crater awakens with small eruptions after a certain +time of previous repose, these almost always have a long duration, and, +after various phases of increase and decrease, terminate in a great +eccentric eruption, that is to say, with the production of an aperture +from which a copious lava stream issues. The eruptions of 1858, 1861, +1868 and 1872, furnish the most recent examples of what I affirm. I +might cite many others of earlier date, but I shall content myself with +recording the greatest conflagration of this century, that of October, +1822. + +Before the erection of the Vesuvian Observatory, it was impossible to +obtain a consecutive account of all the phases which the Volcano +presented; but we generally obtained the description of the more +splendid phases of the eruption which arrested the attention of +everyone. Hence, notices of the small phenomena which preceded a great +eruption are frequently wanting. We cannot always ascertain whether the +fumaroles of the craters became active and at what periods, what was +their temperature and what the diverse nature of their emanations, etc.: +whether and when any change in the crater with slight eruptive +manifestations occurred; discharges which sometimes commenced in the +bottom of a crater becoming active, and so are invisible at Naples. + +But it may be asked whether the inverse proposition be equally true, +that is, whether all the great eruptions of our Volcano were preceded by +small fiery manifestations of long duration? There have undoubtedly been +great eruptions not preceded by small central eruptions, but these also +had their period of preparation or precursory signs. After the great +eruption of 1850, Vesuvius remained in apparent repose until the end of +May, 1855, when there was an eccentric eruption and a great flow of lava +lasting twenty-seven days. But for a year before the fumaroles on the +top of the mountain had acquired great activity, their temperature +increased, and hydrochloric and sulphuric acid became more abundant, and +generated the usual coloured products on the adjacent scoriae. Finally, +in the month of January, a crater was formed by falling in of the +ground, and although it did not discharge fire, yet it poured forth +dense smoke. This was the beginning of the fissure manifested four +months afterwards. + +Ignazio Sorrentino, who spent a long life in the study of Vesuvius, and +frequently ascended it, considered the increase of those yellow +products--which are chiefly chlorides of iron, but were, at that time, +mistaken for sulphur--as the sign of an approaching eruption. + +The only grave objection that can be alleged is that of the memorable +eruption of 1631, which surprised the neighbouring population so +suddenly that many perished miserably, surrounded or covered with lava. +But that terrible conflagration occurred after centuries of repose, so +that trees had grown in the interior of the crater. No one suspected the +possibility of danger. It took place, too, at the end of autumn, when +the cone is usually covered with clouds, and, therefore, no one had an +opportunity of observing any precursory phenomena. + +When the Observatory was established, I was able--in the first instance, +at my own expense, and afterwards with some slight assistance from +Government--to undertake studies more assiduous than any previously +made. I had two instruments adjusted to indicate the internal efforts of +the Volcano, viz., M. Lamond's apparatus of variations, which, by means +of finely-balanced needles and methods of amplification proposed by +Gauss, indicates the slightest trepidation of the ground, and my own +electro-magnetic seismograph, a self-registering instrument of exquisite +delicacy. These instruments, when attentively observed, give the most +valuable information with respect to the activity of the adjacent +Volcano. + +If the very slightest eruption occurs, these instruments manifest slight +perturbation, increasing with the activity of the mountain. When the +Volcano attains a certain degree of activity, and the instruments are +proportionately disturbed, it is impossible to foresee a new phase of +increase without constantly watching the changes in the intensity of the +perturbations; and to effect this it is requisite to have upon the spot +a staff of assistants sufficiently numerous, scientific and intelligent. +If, therefore, on the night preceding the 26th of April the instruments +had been properly watched, they would have undoubtedly indicated the +great increase in the activity of the Volcano. The perturbations on the +23rd were steadily increasing, and on the evening of the 25th they were +much stronger than on the 24th, but on the morning of the 26th they had +become extraordinarily strong; they must, therefore, have increased +considerably during the night. + + + + +II. + +NATURE OF THE LAVAS. + + +When the observer is near the source of the lava, he sees matter in a +state of fusion, which, like a torrent of liquid fire, runs along, with +more or less impetuosity, between two banks formed by itself. But as +soon as the surface of the torrent cools to the point of congelation, it +loses the splendour of its first incandescence. The part which begins to +harden breaks readily in some lavas into fragments which float on the +viscous fluid beneath; these, increasing in number with distance from +the source, conceal the molten matter beneath and retard its progress, +and at last nothing is seen but the more or less red-hot scoriae moving +along. These lavas I shall call "_Lavas with fragmentary scoriae_." + +On other occasions, a skin forms on the surface of the lava, which, +gradually thickening, keeps flexible for some time, and then wrinkles or +swells or extends and breaks to give egress to the hot fluid within, +which, in its turn, skins over and repeats the same phenomena. This I +shall call "_Lavas with a united surface_." + +These, in their course, discharge less smoke than the first, draw out +more easily into threads, and, when cold, have a dark colour, something +like bitumen or pitch. _The lava with fragmentary scoriae_, when +stretched, breaks easily, discharges smoke copiously, and, when +hardened, has a more bluish tint, like clods of upturned earth (_formato +di zolle_). It is noisy in its course, because the incoherent scoriae +that it carries along strike and crunch against each other; the other +lava flows silently, except for a sort of crackling arising from the +actual fracturing up of the solid skin by distension from the liquid +matter within. If required to give the mineralogical characteristics of +this lava, I would say that it was rich in leucite and contained little +or no pyroxene; the fragmentary lava, on the contrary, is poor in +leucite and rich in pyroxene. The lavas of 1871 were of the "united +surface" character; those of 1872 were "fragmentary," with some +characteristics which I shall describe: + + 1. They were of the clearest tint I have ever seen, when + regarded superficially, but, when broken, the fracture was + darker than any other lava. + + 2. They had very little leucite and abounded in pyroxene and + olivine, and sometimes contained a few crystals of amphibole. + + 3. Their specific gravity varied with their porosity; the most + compact attained 2.75. + + 4. These lavas carried along in their course a quantity of + scoriae which had long been subjected to the action of the acids + of the fumaroles close to the craters, and also a great many + bombs (_bombe_)--that is, round masses similar to those ejected + from craters. These varied in size, some having a diameter of + four to five meters. They frequently contained a large nucleus + of very leucitic lava, like that of 1871, with a larger or + smaller quantity of feroligiste (peroxide of iron). Others + contained lavas changed by the action of the acid vapours near + the craters. These bombs must have flowed out with the lava, + for they are found through its whole course, and they were + certainly not ejected from the crater; for not only are they + found on the lava exclusively, but masses so enormous were not + thrown up from the craters during the eruption; those lying on + the cone near the craters seldom exceed a decimetre in + diameter. + +As to the qualitative chemical analysis of the lavas, it always presents +the same elements, with the exception of small quantities of some +metals, lead for example, which have escaped the researches of good +chemists, but which I have constantly found in the sublimations of the +fumaroles of the lava. With respect to the quantitative analysis, two +specimens of the same lava appear indeed to have their constituents in +different proportions. To arrive at any conclusion a long and patient +investigation, requiring means and assistance which the Observatory does +not possess, would be necessary. + +Professor Fuchs, of Heidelberg, has devoted himself to this work for +years past, and if he continue it with well-selected and sufficiently +large specimens we may hope some day to obtain satisfactory results. + + 5. Every specimen of lava which I examined with a very + sensitive magnetoscope improved by myself, was invariably + magneto-polar, not excepting the pieces of the bombs, whether + rejected from the crater or carried along with the lava. + + + + +III. + +FUMAROLES OF THE LAVAS. + + +Smoke generally issues from all lava when it cools down to a certain +degree, hence it is more abundant at the edges of the fiery torrent, or +is liberated from the scoriae that form on its surface. But when the lava +stops, the smoke issues only from certain vent-holes, through which we +can still see the fire, and at the edge of which different amorphous or +crystallized matters collect by sublimation. These centres of heat, of +more or less duration, are the fumaroles of the lavas. I believe I have +on other occasions shown that a fumarole is nothing but a communication +between the more or less cooled and hardened surface of the lava and the +interior, which is still incandescent. Some fumaroles last but a day, +others preserve their activity for weeks, months or years, according to +the depth of lava through which they penetrate; and when they cease to +be active, that is, when the sublimations are formed, or smoke or other +aeriform matters issue from them, they still retain a rather elevated +temperature. In the lavas of 1858, in a place where they had a +transverse width of 150 metres, a vent-hole may still be found where the +thermometer registers 60 deg. and the scoriae are warm. Sometimes, while +the lava is in process of cooling, new fumaroles appear, in which the fire +is visible. This phenomenon, which appeared marvellous and inexplicable +when I first observed it in 1855, is now very easily understood; the +cooled and hardened crust of the lava fractures with noise and suddenly, +and so a new communication is opened with the incandescent lava below, +thus creating a new fumarole. + +As the smoke of the fluid lava is perfectly neutral, that is, neither +acid nor alkaline, so the fumaroles at the first period of their +existence with sublimations of sea-salt, mixed frequently with oxide of +copper either in black powder or in shining laminae, ought also to be +neutral. But if the fumarole continues active, hydrochloric acid issues +with the smoke, and often some time after sulphuric acid. Then the +sublimations turn first yellow, then green, and more rarely azure. The +chemical reactions show that these sublimations are chlorides or +sulpho-chlorides, and sometimes sulphides, and they afford reactions, +indicative of soda, magnesia, copper, lead, and traces of other +substances, not excluding ammonia, which I must speak of separately. +This, I have observed, is the general law with the fumaroles of the +tranquil lavas, which occur with long and moderate eruptions--for +instance, the lavas of 1871, and even those of 1872, preceding the 26th +April. + +But in the great lavas of the great conflagrations of Vesuvius, chloride +of iron more or less in combination with all the other substances above +mentioned changes the appearance of the sublimations. The fumaroles in +the lava of the 26th April frequently indicated chloride of iron. +Sulphuretted hydrogen, by reaction of sulphurous acid, is decomposed, +and sulphur sublimed, having a particular aspect, collects on the +scoriae. This is never found but in fumaroles of the smaller lavas; it +was therefore absent in those of 1871, but frequently occurred in those +of 1872. + +Although the sublimations are generally mixtures, yet sometimes distinct +and crystallized chemical or mineral species are found, such as sulphur, +sal ammoniac, _tenorite_, _cotunuite_, etc. Micaceous peroxide of iron +(feroligiste), so common near eruptive cones, is very scarce on lava; +any found in it has been carried down from the craters, and proofs of +this transport are very abundant and striking in the lavas of this last +eruption. Even the iron found in the bombs is evidently transported; +there is a fumarole on the ridge of the lava in the Fossa di Faraone +which contains micaceous peroxide of iron, and this, at first sight, +appears to oppose what I have affirmed; nevertheless, it gives +additional force to my statement. This fumarole is only a bomb or +rounded mass of enormous size, four or five metres in diameter. Smoke +and hydrochloric acid issued from the aperture in its envelope, and +being partly broken it was seen to contain lapilli and pieces of +antecedent lava, covered with micaceous peroxide of iron. The internal +temperature of this mass was very high; the hydrochloric acid which it +discharged had, in some places, covered the micaceous iron with a yellow +coating of chloride of iron. From small apertures, on the lower side of +the mass, white and green stalactites of chloride of calcium were +visible. In one spot only of lava I found a fumarole, with a small +quantity of micaceous peroxide of iron, evidently in a state of +formation; but this was the very spot where the lava became eruptive, +and whence issued the column of smoke which was so well +photographed--the place under the hill of Apicella. (See Plate 4a.) + +I have enumerated the products which are constantly collected in +fumaroles, although they are not all found at the same time or place, in +order to show that the sublimations follow a certain law in their +appearance. _Tenorite_, for instance, was formerly considered an +accidental product of certain eruptions, and I have always found it; but +if you visit the fumarole when the acids have had time to transform it, +you will no longer see it. I found the crystallized chloride of lead, or +"cotunuite," as it is called, for the first time in the lavas of 1855, +and thought it a singular circumstance; but from that time I recognised +it in all the lavas, though not always so beautiful and abundant; and +even when not found as a distinct substance, I observed it in +combination with chloride of copper. In the lavas of the 26th April +_cotunuite_ and _tenorite_[E] were not very abundant, because the +chloride of iron disturbed the greater number of the sublimations. I +found sal ammoniac very abundantly on the fumaroles of the lavas that +invaded the cultivated ground. Although chloride of ammonia, contrary to +opinion, was not wanting in the sublimations of the fumaroles of the +lavas deposited on other lavas, yet it was neither abundant nor +crystallized, but combined in small quantities with other substances. It +appeared in great abundance in all the fumaroles of lavas which covered +cultivated or woody ground. At first it was scarce enough, and mixed +with chloride of sodium; but when the rains came the sea-salt was washed +away, and sal ammoniac formed beautiful crystals, nearly free from +adventitious matters, as was the case with the fumaroles of the last +lava. Afterwards, when chloride of iron was produced, ferro-chloride of +ammonia was found. Crystals of sal ammoniac were sometimes found of a +beautiful amber yellow. This colour was, in the opinion of my colleague, +Professor Scacchi, produced by such small traces of chloride of iron +that neither Professor Guiscardi nor I, nor indeed any other chemists to +whom I submitted specimens for examination, could detect any. What I can +affirm with certainty is, that these limpid crystals of a yellow colour +were almost always attached to an amorphous substance, soluble in water, +composed of various chlorides, in which iron was often detected. + +From these remarks, it is evident that in the tranquil lavas the +sublimations appear with a certain order of succession, and in the +violent lavas, and those which flow most copiously, they are more +complicated, and render both chemical analysis and spectroscopic +researches more difficult. Notwithstanding, I observed traces of lithium +and thallium, which I had previously perceived in some sublimations of +1871. I purpose submitting many sublimations which I have collected to +more complete spectroscopic investigation, although I am persuaded that +the discovery of traces of certain bodies in the sublimations or in the +lavas is a matter of small importance to the science of volcanoes. I +must say, however, that calcium was discovered on this occasion in great +abundance, not only by the spectroscope, but also by chemical analysis. +Sulphate of lime has often been found in larger or smaller proportions, +but this was the first time I had observed chloride of calcium both +close to the craters, and also in the sublimations of the fumaroles upon +the lavas. The white stalactites which I collected beneath the great +mass or bomb above described were almost exclusively composed of +chloride of calcium, and only a few green drops manifested, with the +usual re-agents, the presence of iron. + +I did not fail to look often at the spectrum of the flowing lavas +covered with the smoke which issued from them, but I always had a +continuous spectrum. The spectroscope employed was Hoffmann's +construction, with direct vision; but I think it would be better on +other occasions to use a spectroscope combined with a telescope, like +those used by astronomers. + +But avoiding minute particulars of these sublimates, let us see what is +the general direction and the order of their appearance. Sublimations +are generally oxides, chlorides and sulphates, sometimes sulphides. +Among the oxides, we must enumerate in the first place "tenorite" and +_feroligiste_ or micaceous peroxide of iron. The first is almost always +found at the commencement of activity in the fumaroles, simultaneously +with the sublimation of chloride of sodium; the second--which is, +perhaps, never wanting in eruptive cones that are often found lined with +it inside--is seldom generated in the fumaroles of the lava, and +therefore it is not easy to define the moment of its appearance. +Sometimes one collects micaceous peroxide of iron on the lava, but it is +often transported there from the mouths of eruption, as happened on this +occasion. + +Trustworthy writers are of opinion that all the oxides are derived from +the decomposition of the chlorides, but I think I have clearly +demonstrated that, with regard to copper and lead, the opposite +statement may be affirmed; for the oxides are changed into chlorides, +and hydrochloric acid liberated. Oxide of copper forms sublimates at the +beginning, at the same time as the sea-salt; and if the fumarole be +anhydrous or, as Deville would say, _dry_, this oxide does not change +into either a chloride or a sulphate; but if the fumarole gives watery +vapour, after a little hydrochloric acid is formed, which changes the +oxide into a chloride, and if whilst this is going on oxide of lead be +developed, it is changed into the chloride of lead, so frequently found +in combination with chloride of copper. Then the sublimations change +from white to red or yellow, and specimens when carried away gradually +turn light blue, but when heated on platinum over a spirit lamp they +resume their yellow tint. Sometimes the yellow colour remains longer, +and in time changes to green; this also happens on the fumarole itself, +the green commencing at the zones furthest removed from the centre, +where the temperature is highest. When these sublimations are greenish, +they become far less soluble than at first. The yellow, so common at a +certain period on the fumaroles of the tranquil lavas, never attracted +attention before I first examined it, doubtless, because it was +considered chloride of iron, and yet in small eruptions this is only +found close to the discharging mouths, and never in the sublimations of +the fumaroles of the lava; but, on the other hand, it is the most +copious and common product on the lavas of the great eruptions. This +probably also accounts for the fact that lead, which is so obvious in +the fumaroles of the lavas, had never previously been observed. In 1855, +I noticed the crystallized chloride of lead in a fumarole in the Fossa +della Vetrana, and this induced me always to look for it on the +fumaroles of the later lavas; and I ascertained that, if it did not +always appear as a distinct mineral, it was easily discovered in +combination with other chlorides. The specimens which I have collected +are not the most beautiful, but the presence of lead in the sublimations +is not less common. + +Micaceous peroxide of iron, when found on the lava, has been mostly +conveyed from the eruptive mouths, as I have already stated, and perhaps +never so abundantly and evidently as on this occasion. The lava of the +26th of April carried along a large quantity of round masses or bombs, +varying in size, among which were found antecedent lava more or less +covered with micaceous iron, either collected in the cavities of the +lava, or incorporated with its mass. Sometimes the micaceous iron +appears like little veins in the paste of new lava enveloping the +exterior of these rounded masses, an exterior compact and lithoidal, and +not resembling scoriae. Among these spherical masses I found one of +enormous size, four to five metres in diameter, which, having broken up +where the exterior envelope was thinnest, I found filled with a great +mass of lapilli and fragments of other lavas covered with micaceous +iron. This bomb still preserves (June 5th) an elevated temperature +within, and emits smoke and hydrochloric acid, which, meeting the +micaceous iron discovered by breaking the envelope with blows of a +hammer, transforms it superficially into chloride of iron, showing most +clearly how, on some occasions at least, chloride of iron is formed from +the oxide which precedes it. That those lapilli and the pieces of lava +were solid when enveloped in the paste of the new lava, we infer from +seeing the impressions on the inside of the said envelope. The chloride +of calcium, which I found in this spherical mass almost pure, caused me +to suspect that the sulphate of lime which is so often found on Vesuvius +is a transformation of the chloride produced by the contact of +sulphurous acid, which easily becomes transformed into sulphuric acid. +The hydrochloric acid which escapes from a fumarole coming into contact +with the scoriae near its mouth, produces chloride of iron, which is, +therefore, not always obtained by sublimation, although, when the +temperature is very high, chloride of iron is conveyed from the interior +of the lava, and sublimes on the exterior and colder parts; for +instance, the chloride of iron which issues from the eruptive cones is +sometimes found sublimed on the rocks of Monte di Somma. When chloride +of iron has been produced by sublimation, we may collect it inside a +glass bell placed over the fumarole, or upon a piece of brick; but when +it is produced by the action of hydrochloric acid on the scoriae, it will +only be found on the scoriae themselves. + +If, therefore, the origin of micaceous peroxide of iron were due to the +decomposition of the sesqui-chloride of iron requiring a more elevated +temperature for its decomposition, it would follow that its genesis +would be easier near the discharging mouths, and more difficult on the +lavas, but there the fact was verified: for example, in the great bomb +on the fumarole, where we observed micaceous iron transformed into +chloride of iron. We may therefore consider it _proved_ that some +chlorides--for instance, chloride of sodium--issue from the lava itself, +either being there pre-existent, or being formed there; and that others +are derived from the oxides which precede them, as undoubtedly is the +case with chloride of copper; hence, the theory that derives the oxides +always from the chlorides cannot be considered true. Granting that this +theory might be applicable to the origin of micaceous iron, we should +still want to know how it is found with the paste of the new lava +itself, which forms the exterior coating of the bombs above described. + +Many of these rounded masses, which have been rolled along by the lava, +contain scoriae partly decomposed by the long action of the acids found +on the fumaroles of the craters. They disintegrate easily, and have a +more or less yellowish tint. In the greater number of cases the interior +of these masses is formed of leucitic lava, with cavities lined with +micaceous iron. In short, their contents appeared to me quite similar to +the material of the cone of 1871 and 1872, which in all probability was +engulfed in the large crevasse or fissure that opened below it; and the +fragments having thus fallen down into the lava, were enveloped by it +and carried out by it after having been more or less rounded. The +external envelope of these spheres is not at all scoriaceous, but +compact and lithoidal, and sometimes composed of concentric folds or +plaits. + +As to the gaseous emanations of fumaroles, watery vapour with few +exceptions comes first; this conveys the material which first appears in +the sublimations, viz., sea-salt, and for the most part oxide of copper. +If the fumarole continue active, it passes from the neutral period to +the acid period, and first hydrochloric acid is produced, which, in +small lava streams, never conveys chloride of iron, and rarely attacks +the scoriae to form that salt, but expends its force in changing the +sublimations already there. For this reason chloride of iron, though +completely absent in the lavas of 1871, was abundantly found in those of +the 26th April, 1872. Sulphurous acid follows hydrochloric at a later +period, and sulphuretted hydrogen occasionally succeeds. + +Having examined the gases of fumaroles by means of a graduated tube, and +the pyrogallate of potash, I always found that it contained less oxygen +than the surrounding atmosphere. + +For several years I wished to see whether the fumaroles of the lavas had +a period of evolution of carbonic acid, as sometimes happens with +fumaroles near the craters, but I have always obtained negative +results. I often found that the atmosphere on the lavas contained an +excess of carbonic acid, but as these lavas had burnt many trees, and it +was probable that carbonic acid springs had formed under the lava, I +never considered it safe to form any conclusion on the subject. + + + + +IV. + +BOMBS, LAPILLI AND ASHES. + + +The bombs ejected from the craters are like those carried down by the +lavas, but of smaller size, and they seldomer contain a nucleus similar +to those found in the latter. With the bombs properly so called, many +pieces of incandescent lava were thrown up, and in their fall went +beyond the base of the cone. A quantity of small scoriae varying in size +accompanied these projectiles, and those fragments, which we call +_lapilli_, fell at a greater distance. With the lapilli, and sometimes +without them, the smoke carried a very minute dust or sand, which is +generally called ashes. These ashes, when washed with water, lose +soluble constituents which they have collected in the smoke--such as +chloride of sodium and other chlorides and often free acids. The +insoluble part originates in the detritus of lava, and with the +microscope we can detect abundant fragments of those crystals which most +frequently occur in the lava of the same eruption. + +The lavas of 1871, which were eminently leucitic, and almost entirely +deprived of pyroxene, resembled the ashes, which appeared to be +fragments of crystals of leucite, more or less enveloped in the paste of +the lava, so that having triturated the scoriae of the lava, and looked +at the powder through the microscope, it was apparently quite the same +as the ashes. + +But at the beginning of the eruption of the 26th April, a white sand +fell in the Atria del Cavallo, close to the Crocella[5], which on the +dark scoriae of 1871 looked like snow. Its fall had a limit so well +defined that one passed without any gradation from white to black. +Having collected some of this sand that very morning, I put it up in +white paper, for at that moment it was impossible for me to examine it. +Taking it out some days after, I found it had become reddish, and having +put it under the microscope, I observed that it was exclusively formed +of little pebbles more or less round, of a transparent vitreous matter, +partly covered with a red substance. Fragments of green crystals +occurred in this sand, upon which no red was perceptible. I consulted +our eminent crystallographer, Arcangelo Scacchi, whether these little +pebbles were leucite, as I suspected, and whether the green particles +were pyroxene: he confirmed my suspicion, and remarked that the red +colour was superficial only. We then washed a little of the sand in hot +water, and saw the pebbles become whitish; but having heated some on +platinum, we observed that they first turned black and then became +perfectly white, proving that the red was a deposit of organic matter. +To see these leucites, rounded like small pebbles transported by a +torrent, deprived of the soluble chlorides which generally accompany +Vesuvian ashes, is a matter worthy of attention. Whilst heating this +sand upon platinum, decrepitation was audible, which indicated the +cracking of some of the little pebbles. It is evident, therefore, that +crystals of leucite raised to a certain temperature may break, and thus +we can understand how almost all Vesuvian ashes contain fragments of +the said crystals enveloped in the paste of the lava. It is evident that +the soluble part of the ashes is obtained from the smoke through which +it passes. On this occasion the smoke from the craters did not +apparently contain much acids, for no bad smell was perceptible, and the +water in which I washed the ashes scarcely reddened litmus paper. Even +chloride of iron, which was so abundant in the lavas, was scarcely +perceptible in the smoke, which almost exclusively deposited sea-salt on +the surrounding rocks; I say sea-salt advisedly, and not chloride of +sodium, to show that I include all that sea-salt contains. The slight +disturbance it manifested with chloride of barium, and the small +precipitate with oxalate of ammonia, reveal sulphate of lime, without +excluding the possibility of the chloride. + +But how can these ashes do so much injury to the vegetation of the +ground they cover, especially at the first fall of rain? I think that +the damage is due partly to the sea-salt, and partly to the acids +contained either in the ashes or in the rain-water itself. Upon watering +the tender tops of some plants with a saturated solution of the salt +from Vesuvius itself, I noticed that they withered away after a few +hours. But very often the rain alone which traverses the smoke of +Vesuvius, or is produced by condensation from it, gives manifest acid +reactions, and destroys the grass and the tops of the trees. The +peasants believe that the rain is warm or of boiling water, from +observing that the tender parts of the plants are, by its deposit, all +burnt up. Vegetation is now recovering, but without flowers, and +consequently without fruit. + + + + +V. + +THE CRATERS AND THEIR FUMAROLES. + + +The greater part of the lava issued from the base of the great fissure +in the cone which I have described; and although two other lava streams +descended from the top of the mountain, neither proceeded from the +crater, but from apertures near it. The great crater, divided in two as +already described, opened wide on the morning of the 26th April, +destroying the brim of the antecedent crater, and remaking it in another +shape with ejected matter, except on the south-west side, where the brim +was split. (See Plate 5.) + +From this double crater, copious smoke, bombs and incandescent scoriae, +with ashes and lapilli, issued with violence, and from the depths below +came dreadful detonations and bellowings, producing great terror. And +yet the lava poured out into the Atria del Cavallo without any noise, +and not even a column of smoke marked its origin of issue--namely, from +the fissure. + +When the eruption was over, the sight of the vertical walls of these +deep craters, of almost horizontal strata of scoriae and lithoidal +masses, with a fracture fresh, and as if they had never undergone the +action of fire or of acid vapours, without recent scoriae and without +fumaroles, was to me a marvellous spectacle. The fumaroles were almost +all on the brims of the craters, with emanations of hydrochloric and +sulphurous acid. In a few that were more removed from the brim, +sulphuretted hydrogen was perceptible. In the sublimations, chloride of +iron was most abundant, in combination with other chlorides, for +example, of sodium, magnesium and calcium. This last chloride was +frequent even among the sublimations of the fumaroles of the lavas, and +it was the first time it was ever remarked, but I do not think it was +the first time that it was ever produced: being in combination with +chloride of iron, and very deliquescent, it did not attract attention +from anyone. In a hollow fragment of scoriae I observed a yellowish +substance, which looked like sulphur in a viscid state, and which boiled +at a temperature of 120 deg., and evolved hydrochloric acid. Having +collected this substance and poured it into a glass phial, it quickly +coagulated into an amorphous mass of the same colour; but before I +reached the Observatory, I found that it had become liquid by +deliquescence. It consisted of a mixture of the aforesaid chlorides, +according to an analysis made by Professor Silvestro Zinno and myself. +In some fumaroles, where I perceived the smell of sulphuretted hydrogen, +I found sublimed sulphur under the scoriae. + +At the source of the lava stream that flowed towards the Camaldoli, on +the seaward flank of Vesuvius, I observed large fumaroles of steam only, +pure aqueous vapour. + +There was no trace of carbonic acid in these fumaroles, but that fact +does not imply that there was none at a later period, for, since the +first investigations of Deville, it is known that carbonic acid is found +under certain conditions on the very summit of Vesuvius. + + + + +VI. + +THE ELECTRICITY OF THE SMOKE AND ASHES. + + +Our ancestors could judge that a great amount of electricity was +occasionally evolved in the smoke, from their observation of the +lightning flashes that darted through the Vesuvian pine tree; but they +had no proper instruments for ascertaining whether this evolution of +electricity was constant or accidental, or what laws regulated its +manifestations. My _apparatus, with movable conductor_, by which +comparative observations of electric meteorology can be made, and the +errors arising from dispersion corrected, supplied me with an easy +method of studying the electricity evolved during eruptions. + +I must begin by describing the bifilar electrometer, in order to explain +the apparatus which I have named as above, "_Apparechio a conduttore +mobile_." + +_A A_ (Plate VIa, Fig. 1) is a glass cylinder, the lower edge of which +is ground, well varnished with gum lac, and let into a wooden base, B, +furnished with three levelling screws. Through a sufficiently wide glass +tube, _a a_, runs a copper rod covered with insulating mastic, having a +little plate or cylindrical cavity of gilded brass at the top (Figs. 2 +and 3), with two arms _d d_, _d' d_. In the plate a disc of aluminium, +_m_, is suspended by means of two silk fibres, and to the disc a very +fine aluminium wire is attached, _f f'_, bent a little at the ends, as +are the arms, _d d_, _d' d_. The disc has about three millimetres less +diameter than the plate. The diameter of the plate may vary within +certain limits, but I have found it convenient to make it eighteen +millimetres. The glass tube, _a a_ (Fig. 1), should descend below the +base as much as it rises above it, that is three to four centimetres. +The length of the index is about one decimetre. + +The upper ends of the two silk fibres, by which the disc and index are +suspended, are attached to the top of the glass tube, _C_, by a +contrivance which permits a change in the distance between the two +points of suspension, and a screw, _p_, is provided to raise and lower +the disc with the index. At _n_, at the lower part of the tube, _C_, +there is a kind of torsion micrometer, arranged so as to bring the index +to the zero of the scale engraved on the graduated ring, _B_, which is +formed of a strip of good paper pasted on the rim of a glass disc. The +index must be placed at the zero of the scale, and must be some distance +from the ends of the arms of the plate with which it is parallel. The +plate is about three millimetres deep. + +Having levelled the instrument, so as to render the disc concentric with +the plate, and placed the index at zero, it is obvious that if an +electric charge through the wire, _h_, reach the plate with the arms, it +will electrify the disc and index: the disc will have the opposite +electricity, and the extremities of the index will take the same +electricity as the arms, and consequently the index will describe an arc +more or less great. The motion of the index is sufficiently slow to +allow the eye conveniently to follow it. Having traversed the first arc, +which I call the _impulsive_ one, the index returns, and, after only two +oscillations, comes to rest at what I shall call the _definite_ arc. + +When the electric charges are of very brief duration, the impulsive arcs +are within certain limits proportional to the tensions, and the ratio +between the impulsive and definite arcs is expressed by the following +equation: + + A (B - A) / B = tang. (1/2) A + +In which B is the impulsive arc and A the definite arc, showing that A +comes out nearly equal to 1/2 B. In dry weather all goes perfectly +within the limits of proportion, and I can tell whether, during the time +in which the index traversed the impulsive arc, there were any +_dispersions_ and of what nature; for if the definite arc is not close +to the limit of the impulsive arc, it is a sign of _dispersions_ having +taken place during the motions of the index. Every degree less in the +definite arc denotes two degrees of loss for the impulsive arc; but as +the index employs double the time traversing the definite as it does the +impulsive arc, we may consider the loss of one equal to the loss of the +other. + +In excessively damp weather the index gives no definite arc, and it is +necessary to resort to artificial heat in order to dry the insulators. +The most simple means I know of is to hold the instrument over some +hollow vessel, which, for the time, is converted into a stove by the +introduction of a spirit lamp. + +From Gauss's formula for the bifilar system of instruments of this +class, we learn that the maximum sensitiveness of such instruments is +given when the length of the suspending fibres is greatest, and the +distance between them is smallest, with the weight of the movable or +rotating member a minimum; and these elements being the same, the +sensitiveness of the instruments is invariable. + +To some electrometers, in order to avoid errors of parallax, a small +telescope, with a micrometer wire, has been added; but, with a little +practice, we can read accurately without this refinement. In order to +obtain comparative measurements, it is necessary to select some given +unit of tension. I have observed that by making a galvanic pile of +copper, zinc and distilled water, and insulating it well, each pole has +a tension which remains the same for many days, if the conditions of +temperature and the moisture of the surrounding atmosphere are not very +different. With thirty pairs of this pile, each element having +twenty-five square centimetres of surface, I have on the electrometer a +definite arc of 15 deg., with the temperature of the atmosphere at 20 +deg. C., and with the difference of 4 deg. to 5 deg. C. between the +thermometers of the psychrometer of August's construction. The first +observation was made twenty-four hours after mounting the pile. For unit +of tension I took that which corresponded to a single pair, that is, the +thirtieth part of the total tension. Other electrometers may be compared +with one already properly adjusted, without always having recourse to +the pile. + +This done, let us see the arrangement of all the apparatus: + +_H H_ (Plate VIIa, Fig. 1) is the ceiling of a well-situated lofty +room, with an opening, _o o_, at the upper part. + +_M M_, a bracket or table fastened against the wall, about a metre +distant from the ceiling, _H H_. + +_N N_, a wooden platform for the observer. + +_A_, the bifilar electrometer. + +_B_, Bohnenberger's electroscope. + +_a a_, a movable conductor formed of a brass rod 15 to 18 millimetres in +diameter, insulated below by means of a glass rod, well varnished with +gum lac, having a suspending pulley, _c_, and a wooden guide-rod +underneath it, _l_, within the guiding tube, _k_. At the upper part of +this conductor, _a a_, there is a sliding roof, _b_, which can be +adjusted so as to prevent rain entering at the opening, _o o_. The +conductor terminates in a disc made of a sheet of thin brass, _d_, 24 +centimetres in diameter. Upon this disc, or even in place of it, we may +use metallic points. + +As a support to the conductor at the upper part, I have made use of a +triangular ring, _x_, drawn at its full size in Fig. 2. The conductor +passes between three springs, and the triangular ring is held in place +by three silk cords, _m m m_. Their material should not be mixed with +any cotton, and it may be advisable to saturate them with an alcoholic +solution of gum lac. + +_f f f_ is a hempen cord, which is used to raise and lower the +conductor. + +_i_ is a copper wire covered with silk, by means of which the triangular +ring, _x_, and through that and its springs the conductor communicates +with either the electrometer or the electroscope. + +Quickly raising the conductor by pulling the cord, _f_, the index of the +electrometer will describe a more or less large impulsive arc, and, +after two oscillations, will stop at the definite arc. Having thus +measured the electric tension of the air, and having lowered the +conductor, I next place the wire, _i_, in communication with the +electroscope, _B_, and by again raising the conductor, I ascertain +whether the electricity be positive or negative. It is scarcely +necessary to say that the conductor, when raised, gives electricity of +the same nature as that prevailing at the moment in the atmosphere; and +when lowered, manifests the opposite. In some conjunctures we must keep +the conductor raised and in communication with the electroscope, in +order to observe certain phenomena which I shall presently describe: +this method I call observation with a _fixed conductor_. + +I have also constructed a similar but portable apparatus for use on +eruptive cones, when required. + +Having given this description of the apparatus, it remains for me to +relate the results obtained, especially on the occasion of the last +eruption of Vesuvius. + +The Observatory is distant, in a direct line from the central crater of +Vesuvius, 2,380 metres, so that, when the smoke is copious, it is +properly situated for the study of electricity, particularly when the +wind inclines the pine-tree cloud in the direction of the Observatory, +as frequently happened on the last occasion. + +With smoke alone, without ashes, we obtained strong tensions of positive +electricity; with ashes only, which sometimes fell while the smoke +turned in the other direction, we had strong negative electricity; when +the smoke inclined towards the Observatory, accompanied with ashes and +lapilli, we had sometimes one kind of electricity, and sometimes the +other, just as the smoke or the ashes predominated; and often with a +"fixed conductor" we obtained negative electricity, and with a "movable +conductor" positive electricity. In Naples, too, at the Meteorological +Observatory attached to the University, my colleague, Professor Eugenio +Semmola, observed negative electricity of strong tension whilst ashes +were falling there in abundance. The tensions on this occasion were so +strong as to equal those obtained at changes of weather or during storms +(_temporali_), and, being beyond measure with a delicate electrometer, +we marked them with the symbol for infinity: the same phenomena were +observed when lightnings flashed. + +When there is but little smoke, it is necessary to approach the eruptive +mouths with a portable apparatus, in order to observe those phenomena +which, in great eruptions, may be studied from the Observatory itself. + +The conditions under which (_folgori_) lightning flashes are seen from +the cloud of smoke are, that it is conveying great abundance of ashes. +In 1861, there were small flashes even from the line of eccentric mouths +above Torre del Greco, although the smoke was not very great; and when +these ceased to discharge, and the central crater became somewhat +active, with a moderate amount of smoke but a great deal of ashes, small +and frequent lightning flashes were observed in the twilight darting +through the smoke, which was dark in colour. In 1850 the eruption was +more vigorous, the smoke more abundant, and the ashes scarce, but the +flashes were very rare. In 1855, 1858, and 1868, with a scanty supply of +ashes and at intervals, no flashes were observed, and the electricity +remained constantly positive. But having regard to the facts of +antecedent eruptions, one sees that the flashes are always derived, from +the midst of smoke accompanied with ashes and lapilli, which separate +like rain from the rolling volumes of smoke, in the midst of which they +were ejected. + +But how can we account for the positive electricity of the smoke, and +the negative electricity of the falling ashes? Without denying the +probability that a part of the positive electricity depends upon the +elevation of the smoke, as in the case of every other conductor we raise +aloft, or with a jet of water sent from a vessel by compressed air, I +think that the greater part of the electricity proceeds from the rapid +condensation of vapours, which are changed from the gaseous condition +into dense clouds; for even when the smoke issues tranquilly and does +not rise, because carried away horizontally by the wind, it gives signs +of positive electricity. From all my studies of atmospheric electricity, +and from some experiments made specially, it follows that the +condensation of vapours is the origin of this development of positive +electricity. + +The negative electricity of the falling ashes certainly arises from the +fact itself of their fall; for if we place a metallic vessel full of +ashes upon an elevated and well-situated terrace, while the atmospheric +electricity is positive, and cause the ashes from the vessel to fall +gradually into an insulated metallic cup, communicating with +Bohnenberger's electroscope placed at three or four metres distance from +the vessel, the electroscope will manifest negative electricity. If the +upper vessel be insulated, and the ashes permitted to fall upon the +ground, we shall obtain, from the vessel, positive electricity. The +intensity of these electric manifestations depends (other things being +equal) upon that predominant at the moment in the air; so that if the +experiment be made while negative electricity prevails, the falling +ashes will manifest positive electricity, the upper vessel then showing +negative electricity. Now, as the ashes separate from the positively +electrified smoke in order to approach the ground, which is negatively +electrified, it follows that they must manifest negative electricity +upon touching the ground, leaving the positive electricity in the smoke +above. For this reason, the electric tension of the smoke is increased +by the descent of the ashes and lapilli, so that discharges between the +upper and lower part of the pine-tree cloud, or the surface of the +crater, are rendered possible. Hence it follows that the flashes of +lightning of Vesuvius play through the smoke, and with difficulty strike +bodies upon the earth; and from this circumstance our ancestors believed +the thunderbolts of Vesuvius to be harmless. However, if the smoke were +very great, and driven by the force of the wind to some distance from +the crater, with an abundant fall of ashes, it would be possible to have +lightning flashes proceed from the smoke to the earth. I possess some +documents which relate that, in 1631, thunderbolts fell upon the Church +of Santa Maria del Arco, and other places on the coast of Sorrento. + +After upwards of twenty years' study and observation of meteoric +electricity, I am enabled to prove that atmospheric electricity is never +manifested without rain, hail or snow, and that manifestations of light +are always accompanied by thunder--manifestations of light (_lampi_), +thunder and rain being most closely connected. We may have rain without +manifestations of light, but never the latter without rain or hail. I +cannot here repeat what I have demonstrated in other memoirs; I can only +say that the lightnings of Vesuvius, erroneously believed to be not +accompanied by thunder, are really not accompanied by rain, but are +induced by the descent of ashes and lapilli.[6] + + + + +GENERAL CONCLUSIONS. + + +We may conclude from what I have stated: + +1. That by the assiduous study of the central crater, and the +indications afforded by the "Apparatus of Variations" and the +"Electro-Magnetic Seismograph," we can obtain precursory signals of +eruptions; and that the other premonitory signs pointed out by our +ancestors, such as the drying up of wells, either only happen +occasionally or are mere coincidences, such as those of the coincidence +of a dry or a rainy season, the prevalence of certain winds, etc.[F] + +2. That the fumaroles of the lavas are communications between the +external surface of the lava, hardened and more or less cooled, and the +interior lava still pasty, or at least incandescent. + +3. That from the lava, while flowing, there is no escape of acid +vapours, neither from the fumaroles at the first period of their +existence, but these, if they last long enough, arrive at an acid +period. + +4. That hydrochloric is the first acid that appears, combined afterwards +with sulphurous acid, and, still later, with sulphuretted hydrogen. + +5. That vigorous lava streams may have eruptive fumaroles. (See +Translator's Note 2 to p. 94.) + +6. That the sublimations follow a certain order in their appearance. In +the neutral period we get sea-salt mixed with some metallic oxides, the +first of which is oxide of copper. But in the great lavas, chloride of +iron appears simultaneously with the acid period. Hydrochloric acid +transforms the oxides into chlorides, which, in their turn, change into +sulphurets or sulphates on the appearance of sulphurous acid. + +7. That the acids, by attacking the scoriae, create new chlorides and +sulphates, which are thus not products merely of sublimation. + +8. That micaceous peroxide of iron--so common and abundant near the +eruptive mouths--is very scarce and rare on the lavas, unless conveyed +there from the craters. + +9. That chloride of iron--so manifest on the fumaroles of the great +lavas--is only found in small eruptions close to the discharging mouths. + +10. That the frequency of chloride of iron in the lavas of great +eruptions masks the order of transformation of the other products. + +11. The fumaroles at the summit of Vesuvius present even greater +gradations, for they often emit carbonic acid or pure watery vapour. + +12. Lead, which I first discovered in the fumaroles of the lavas of +1855, is a constant product of fumaroles which have a certain duration. +It is often obtained as a distinct and crystallized chloride, and often +is found in combination with other products. + +13. Oxide of copper is also a constant and primary (_primitivo_) product +of fumaroles. The chloride and sulphate of copper are formed from the +oxide, directly contrary to general belief. + +14. I do not think that the chloride of calcium, which I found on this +occasion in almost all the deliquescent sublimations, is a product +peculiar to this eruption only, in which alone, however, I found it. I +was, therefore, induced to look for it in other sublimates, in which I +might possibly have overlooked it, as, without doubt, my predecessors +have done, owing to the deliquescence of the chloride of iron with which +it was constantly combined. I think that this chloride, in accordance +with the general law, is transformed into a sulphate--a transformation +which readily occurs on Vesuvius. + +15. Copious and well-crystallized sal ammoniac is only found on the +fumaroles of those lavas which have covered cultivated or wooded ground. + +16. The scarcity of oxygen in the gases of fumaroles may possibly arise +from the formation of the oxides which precede the chlorides. + +17. Lavas give a continuous spectrum, although covered with smoke, when +looked at with Hoffmann's spectroscope with direct vision.[G] + +18. The smoke gives positive electricity, and the falling ashes negative +electricity. + + + + +REFERENCE TO THE PLATES. + + +PLATE + +Ia. The Cone of Vesuvius, in 1870, from a Photograph taken + near the Observatory. + + _a._ The Atria del Cavallo. + _b b._ Fossa della Vetrana. + _c._ Punta del Crocella. + _d._ Lava of 1858 and 1867. + _e._ Police Barrack near the Observatory. + _f._ Part of Monte Somma. + +IIa. Profile of Vesuvius, taken from a Photograph of the + Observatory in the month of September, 1871. + + 1. The Cone, on the 13th January, 1871. + 2, 2. Lava of 1871. + +IIIa. Profile of Vesuvius on the 16th April, 1872, about ten + days before the last Conflagration. + +IVa. Vesuvius, on the 26th April, 1872, from a Photograph taken + in the neighbourhood of Naples. + + 1. The Observatory. + 2. Fossa della Vetrana. + 3. Eruption of Smoke and Ashes, with Stones, from the + surface of the Lava. + 4. The Novelle, St. Sebastiano, and Massa. + 5. Lava which took the direction of Resina. + 6. Lava which, from the Crater, took the direction of the + Camaldoli. + 7. The Grain Stores, near Naples. + 8. Resina. + 9. Torre del Greco. + 10. The Camaldoli. + +Va. Profile of Vesuvius after the Eruption of the 26th April, + 1872, from a Photograph taken near the Observatory. + + 1, 1. The Fissures of the 26th of April. + 2, 3. Small Hill thrown up on the morning of the 26th of + April, from below which issued the great current of + Lava. +4, 4, 4. The Mouths out of which the Lava issued. + 5, 5. The larger Lava Stream, which passed near the Observatory + by the Fossa della Vetrana. + 6, 6. The other Lava Stream, which, after dividing from + the last, took the direction of Resina. + 7, 7. The Lava which ran down towards the Camaldoli. + 8 & 9. The two Craters on the summit of the Cone. + +VIa. The Bifilar Electrometer of Signor Palmieri. + (_Details._) + +VIIa. The assemblage of the Electroscopic Apparatus of Signor + Palmieri, as arranged at the Vesuvian Observatory. + +VIII. Professor Palmieri's Seismographic Apparatus. + + +[A] This small cone, as it appeared on the 1st April, is described and +drawn in a Memoir of Professor von Rath, of the University of Bonn, on +"Vesuvius on the 1st and 17th of April, 1871." + +[B] Eight young medical students perished beneath the lava, with others +unknown by name. They were all youths of good promise; their names will +be recorded on the marble monument to be erected near the Observatory. +They are: Girolamo Pausini, Antonio and Maurizio Fraggiacomo, Francesco +Binetti da Molfettu, Giuseppe Carbone da Bari, Francesco Spezzaferri da +Trani, and Giovanni Busco da Casamassima and Vitangelo Poli. + +[C] If this enormous height of projection really means, that above the +brim of the crater, it involves an initial velocity of projection of +above 600 feet (British) per second. + +Observations of the height of ascent of volcanic blocks are always +difficult and deceptive, and never free from error.--_Translator._ + +[D] Assuming these flashes to have emanated from somewhere within the +cloudy volume of steam and dust called "the head of the pine-tree," this +interval would indicate that the mean height of this cloudy volume +itself was not more than about four thousand feet above the top of the +cone; and, if so, that is not very far from the limit in height of +projection of the dust and lapilli.--_Translator._ + +[E] COTUNUITE, chloride of lead, in white, lustrous, acicular crystals, +of the trimetric system, easily scratched, Sp. gr., 5.238. + +TENORITE, peroxide of copper, in thin, hexagonal plates or scales, +translucent when very thin, dark steel gray, of the cubic system; hard +and lustrous. Sp. gr. about 5.950.--_Translator._ + +[F] Earthquakes, though in distant regions, usually precede eruptions. +The Earthquake of Melfi preceded the great Eruption of Etna in 1852; the +Earthquake of Basilicata of December, 1857, terminated with the Eruption +of 1858, which filled the Fossa Grande with lava; the Earthquakes of +Calabria of 1867 and 1870 were the precursors of the Vesuvian +conflagrations of 1868, 1871, 1872. A Volcano, also, in the Island of +Java had a great eruption in the month of April, some days before the +last conflagration of Vesuvius, as I learnt from a letter addressed to +Signor Herzel, Swiss Consul at Palermo, communicated to me[7] by the +astronomer, Signor Cacciatore.--_Palmieri._ + +[G] I have made a large collection of sublimates, which I purpose +examining with the spectroscope, and I shall be able to place some at +the disposal of experimentalists who may desire to pursue investigations +of this kind. + + + + +NOTES + +BY THE TRANSLATOR. + + +[1] (P. 82, text). Professor Palmieri has not given any description +in this Memoir of his seismograph--the instruments described being those +only which have relation to atmospheric electricity. The following brief +account of his seismograph will, therefore, form a not unsuitable +complement to his Memoir. The instrument, in general terms, is of that +class in which the wave movements are indicated by the displacement, +relative or absolute, of columns of mercury in glass tubes. It is a +self-recording instrument, composed of two distinct portions--one for +record of horizontal, or rather of what are called undulatory shocks; +the other for vertical shocks. In point of general principle, therefore, +it is very similar to that proposed by me ("Transactions, Royal Irish +Academy," in 1846), and in certain respects appears to me less +advantageous than the latter. Some account of the Palmieri instrument, +together with some critical remarks as to its action, may be found in my +"Fourth Report on Earthquakes" ("Reports, British Association, 1858," +pp. 75-81). The following description of the instrument is derived from +"The Engineer," of 7th June, 1872, and the publishers have to thank the +proprietors of that journal for permission to use the illustration, +Plate 8. + +In Fig. 1, _E_ is a helix of brass wire (gauge about one millimetre); +the helix consists of fourteen or fifteen turns, and has a diameter of +from twenty to twenty-five millimetres; it hangs from a fine metal +spring, and can be raised or lowered by a thumb screw. From the lower +end of the helix hangs a copper cone with a platinum point; the latter +is kept close to the surface of mercury in the iron basin, _f_, which +rests on an insulating column of wood or marble, _G_. The distance of +the point from the surface of the mercury remains constant, as the metal +pillar, _T_, is of such a length that its expansion or contraction by +change of temperature compensates that of the helix; the latter is in +connection (by _T_) with one pole of a Daniell's battery of two cells, +and the basin, _f_, is connected with the other pole. Any vertical +movement, however slight, makes the platinum point dip into the mercury, +and thus completes the circuit. In this circuit are included two +electro-magnets, _C_ and _D_; these, during the circulation of a +current, attract their armatures, which are connected with levers. The +action of _C's_ lever is to stop the clock, _A_, which thus records, to +a half-second, the time of the occurrence of the shock, at the same +instant that the clock strikes an alarm bell, which attracts the +attention of an observer. The lever, attached to the armature of _D_, at +the first instant of the current frees the pendulum of the clock, _B_, +which was before kept from swinging, in a position out of the vertical; +the clock then acts as a time-piece, and its motion unrolls a band of +paper, _k k k_, at a rate of three metres an hour. At the same time the +armature of _D_, while attracted, presses a pencil point against the +band of paper which passes over the roller, _m_, marking on it, while +the earthquake lasts, a series of points or strokes which occupy a +length of paper corresponding to its duration, and which record the work +of the shock. After it is over the paper continues to unroll from the +drum, _i_, and passing round the clock, rolls on to the drum, _l_. If a +fresh shock occur the pencil indicates it, as before, on the paper, and +the length of blank paper between the two sets of marks is a measure of +the interval of time between the shocks. By way of additional check, +several helices, _h h h_, are hung from a stand, with small permanent +magnets suspended from their ends; below and close to these latter are +small basins, holding iron filings; into these the points of the magnets +dip, when their helices oscillate vertically, and some filings remain +sticking to the magnets as a record of the shock. One of the magnets has +a shoulder on it which moves an index hand along a graduated arc, as +shown in Fig. 2, thus again registering the amount of the vertical +movement. Such are the arrangements intended for the record of the +undulatory or horizontal elements of the wave of shock. + +The following are the arrangements proposed for recording the horizontal +motions: On the stand, to the right of the clock, _A_, are set four +U-shaped glass tubes, open at their ends. One of each pair of vertical +branches must have a diameter at least double that of the other. These +pairs, with their supporting columns, are shown in plan, where one pair +lies N. and S., another E. and W., a third N.E. and S.W., and the other +N.W. and S.E. It will be observed that metallic bars pass from the +pillar, _P_, over the ends of all the long branches, and similar bars +pass from _R_, over the ends of the short branches; the pillars +themselves, as in the case of the other instruments, are each connected +with one pole of a Daniell's battery, the connections including the +electro-magnets, _C_ and _D_. The description of one U tube, _n_, will +apply to all the others; _n_ is partly filled with mercury, and an iron +or platinum wire, _o_, suspended from the bar above the short branch, +dips into the mercury therein, while another platinum wire hung from the +bar over the mouth of the longer branch, has its end very close to the +surface of the mercury in that branch. Any shock which is not +perpendicular in direction to the plane of the branches of the U will +cause the mercury to oscillate in the tubes, and more sensibly in that +with the smaller diameter; when it rises up in the latter, so as to +touch the platinum point, the connection between _P_ and _R_ is made and +the circuit completed, starting the action of the electro-magnets _C_ +and _D_, which record the shock, as already described. By having the +planes of the tubes set in the different azimuths, already mentioned, +one or more of the pairs is sure to be acted upon, and by observing in +which the oscillation takes place the direction of the shock is supposed +to be ascertained. Besides this, each long branch of the U, viz., that +of smaller diameter, has a small ivory pulley, _q_, fixed above it, over +which passes a single fibre of silk, with an iron float at one end, +resting on the surface of the mercury; at the other end of the fibre +hangs a counterpoise; fixed to the pulley is a fine index hand, capable +of moving along a graduated arc. When the shock takes place the mercury, +rising in the long branch, raises the float on its surface, the silk +fibre at the same time makes the pulley revolve with its index hand, +which afterwards remains stationary, as the counterpoise prevents the +float from sinking again with the mercury. The reading on the graduated +arc is thus a measure of the movements produced in the instrument by the +horizontal element of the shock, and is supposed to measure that shock. +It is assumed that in all these instruments shocks, however small, can +be recorded with certainty by adjusting the distance between the +platinum points and the mercury. + +The arrangement of Daniell's battery used for the seismograph is shown +in Fig. 4, where, for convenience of cleaning, the copper element is +made of wire (about No. 8 Birmingham wire gauge) coiled flat without the +spirals touching. Crystals of sulphate of copper are placed at the +bottom of the outer cell, into which water is poured; and the inner +cell, into which the zinc plate goes, is filled with siliceous sand. + +In addition to the above some instruments of a rougher description are +employed as checks. Thus, at the foot of the pillar, _G_, there is a +wooden trough with eight holes, facing as many equidistant points of the +compass (two of them shown in section) round its inner circumference; +mercury is poured into the basin until its level is nearly up to the +lips of the holes. The effect of a shock is to throw some of the mercury +into one or more of these holes, and the greater the oscillation the +more mercury is thrown into the cells through the holes. The screws +shown outside are for drawing off the mercury from the cells, when its +quantity can be measured. The direction of the shock is shown by seeing +which cells are filled with mercury. This is the old Cacciatore +seismometer which has been long employed in Italy. (See 4 "Report of +British Association, 1858," p. 73), and Daubeny's "Volcanoes," Appendix. +The following is another contrivance. From the arm of the pillar, _G_, a +fine metal wire hangs, with a metal ball at its end, which, by its +oscillation, thrusts out one or more light glass tubes, set horizontally +in a stand, as shown in Fig. 3. The two rings are of wood, and the glass +tubes pass through holes in them; small leather washers are placed +outside the outer rings; the displacement of one or more tubes is +assumed to measure the horizontal element of the shock. By means of this +apparatus the time of the first shock is recorded, as well as the +interval between the shocks, and the duration of each; their direction, +whether vertical or horizontal, is given, as also the maximum of +intensity. Professor Palmieri has the instruments examined three times a +day, and an assistant-observer is always at hand to attend to the bell, +and put back the apparatus to its normal position for fresh observation. + +It has been stated that this instrument is sensible to most of the +shocks which occur in the Mediterranean basin. + +It is not my intention here to offer any criticism as to the +construction or performances of this instrument, the rather as I must +confess I do not quite share the high opinion of its inventor as to the +certainty or exactitude of its indications. + +There can be no question as to the extreme importance to science of the +establishment and continued use of a seismographic instrument of +unexceptionable construction at the Observatory upon Vesuvius; and it +would be a valuable gift to science, were the Italian Government to +enable Signor Palmieri to establish such an one. Its great value and the +very first problem to set the instrument to solve should be, by _a rigid +determination of the direction of propagation of the wave of shock_, of +those slight or stronger pulsations which precede or accompany the +Vesuvian like all other eruptions, on arriving at the Observatory, _to +fix the depth, and the position vertically beneath the cone, whence +these pulses are derived_. This would be, in fact, to fix the depth and +position beneath the mountain at which the volcanic focus is situated +for the time, or, at least, where the volcanic activity is at the time +greatest. And the assured knowledge, even within moderate limits of +accuracy, of this depth, and even for this single mountain, would be an +immense accession to our positive knowledge, and a really new stage +gained for future advances. At present, we know but little as to the +actual depth below our globe's surface at which volcanic activity +occurs, or to which it is limited, either upwards or downwards. I have, +myself, established some data upon the flanks of Etna, not yet +published, which may enable me to afford some information on the subject +hereafter. Meanwhile, Professor Palmieri possesses unrivalled +opportunities for such observations; and I trust health, life and means +may be afforded him, to become the first who shall have made this great +addition to our positive knowledge of Vulcanology. + +So far, popularly at least, the alleged chief uses and value of these +seismographic instruments, at the Observatory of Vesuvius, have been +made to depend upon their being presumed to afford means for foretelling +eruptions, or affording precursory warnings of their probable progress +and destructive course. + +I feel compelled to express my own total disbelief in the possibility of +any such predictions in the present state of science, by the help of any +instruments whatsoever, of such a nature as to be of any _practical +value_, or any certainty beyond that which a certain amount of _mere +experience_ as to the _role commonly played_ by Vesuvius or other +Volcanoes in pretty habitual activity affords to the observer for a +lengthened period. And even this affords scarcely any guide as to what +may happen next. Monte Nuovo was thrown up in a night; Vesuvius _might_ +double its volume in a night, or might sink into a hollow like that of +the Val del Bove in a not much longer time. A small _fusillade_ may go +on for months, and yet, without an hour's notice, by any premonitory +sign, may waken up to a roar and darken the air with ashes and lapilli +such as those which overwhelmed Pompeii. One eruption may blow forth +little but dust and ashes (so called), another may pour out rivers of +lava and little else. + +The _main_ mischief of all eruptions is effected in two ways: by the +deposit of dust and ashes, lapilli, etc., to the injury or destruction +of fertile land, and by the streams of lava which overwhelm it, as well +as buildings, etc. But what information of any value can seismographic +observation afford as to the course that either of these may take in any +eruption? The volume of pulverulent material that may be ejected cannot +be foreseen; its distribution depends mainly upon its nature and upon +the direction and force of the wind at the time; or again, how shall +these warn us as to the course that the lava, if it appear, shall take, +when we cannot possibly foretell when, how, or by what mouth it may +issue. Even in this late eruption of 1872, with Palmieri stoutly at his +post upon the mountain, and the Observatory instruments in full +activity, they gave no forewarning of the sudden and unexpected belch +forth from the base of the cone, of that tremendous gush of liquid lava +which in a few minutes cut off from life the unhappy visitors whose +deaths he has recorded. + +[2] (P. 94). It can scarcely be supposed that these small +eruptive-looking belchings forth from the lava stream, _en route_, are +truly of an eruptive nature at all, _i.e._, in any way connected with +forces seated deeply beneath the bed of the lava stream, or in any way +connected with the volcanic ducts of the cone or beneath it. They are +most probably merely the bursting upwards of large bubbles; that is, of +cavities formed in the mass of the more or less liquid lava by intestine +movements, as its mass winds and rolls along, and by the aggregation of +smaller cavities--all being filled with steam and gases--together with +dust and volatile products which are ejected when the cavity opens up, +and its contents escape at the upper surface of the lava stream in +virtue of the continuation of the twistings and convolutions due to the +stream motion itself, and to the unbalanced hydrostatic pressures acting +upon the parietes of the bubble. Very large single bubbles of like +character rise in the fluid lava within craters in vigorous action, and +often so regularly that their recurrence causes a sort of rhythmical +rush and roar in the column of steam, etc., issuing above the mouth. +This was evident in the discharges issuing in 1857 from the highly +instructive minor _bocca_, then existing, examined by me, and referred +to ("Report, Naples, Earthquakes," etc. Vol. II., pp. 313, 314), as +presenting at the time great facilities for determining pyrometrically +the temperature of the lava within, and of the dry superheated steam +issuing with a rhythmic roar from it. M. Le Coq ("Epoques Geologiques +d'Auvergne," Tome IV.) has recorded some examples of the formation and +opening-out of large bubble-like cavities in lava already ejected. +Perhaps that able and laborious vulcanologist, whose death a few months +ago science still deplores, attributes too much importance as well as +magnitude to them, when attributing the formation of what he has +denominated "craters of explosion," to the mechanism of the rise and +bursting of such bubbles upon a gigantic scale. Such blowings forth, +sudden or prolonged, from particular spots of lava streams, _en route_, +undoubtedly may also have their origin in damp places, or water or +air-filled cavities in or beneath the bed over which the lava rolls, +which, getting gradually heated, generate steam, or air or gases under +tension by expansion, etc., which thus at length blow through the liquid +or pasty lava flowing above, and which in bursting through delivers much +dust also, and so simulates a little eruptive crater. Examples of this, +upon a great and convincing scale, can be pointed to in the Val di +Calanna and elsewhere on Etna. + +[3] (P. 96). There are strong grounds for the gravest doubts that there +exists any real connection of a physical character between Volcanic +Eruptions, and Earthquakes more or less _approximately_ coincident only, +in time of occurrence; the respective sites being widely apart, and the +less the probability as the intervening distance is greater. The +discussions of the large number of records that are to be found of such +coincidences--mostly but partial, and in but _very_ few instances +complete coincidences--by Perrey, von Hoff, and others, as well as by +myself, do not tend to sustain the view that such imperfect +contemporaneity is based upon any causative connection. The seismic +region of Greece appears to have no _direct_ connection with that of +Southern Italy: the band of connection, if any, seems to lie between +Northern Italy, across the Northern Adriatic, by Ragusa, and thence +spreading into Asia Minor. + +[4] (P. 97). The abundance of coleoptera and of various other forms of +insect life about lava beds, both recent and old, is a very singular +fact, and one worthy of the careful observation of entomologists. In the +autumn of 1864, at mid-day, when sitting sketching upon the lava about +the middle of the Val del Bove (Etna), I found it almost impossible to +work, or even to remain for an instant still, in consequence of the +continual cloud of insects, large and small, that struck against me in +flight, endangered the eyes, and swarmed upon my clothes. It is quite +possible that this local superabundance of insect life may arise merely +from the general dryness and warmth of such places, and the plentiful +_nidus_ that the innumerable cavities in lava afford for the eggs and +earlier stages of insect life; still, this apparition of one form of +life may also be connected with other circumstances not unimportant to +discover. + +[5] (P. 120). The _Crocella_ is a small wooden cross, erected several +years ago, and which one passes to the right hand at the upper end of +the path along the ridge of tufa and volcanic conglomerate upon which +the Observatory stands, in ascending thence to the Atria del Cavallo. + +[6] (P. 134). That the causes assigned by Professor Palmieri for the +potent developments of electricity (positive or negative) which +characterise the ascent of the issuing columns of (chiefly if not +always) _dry_ steam, with a relatively small volume of various gases, +and throwing up, in their blast, volumes of small solid particles in +ashes and lapilli, etc., and the subsequent fall as a mineral or stony +hail-shower of the latter, through the partially condensing vapours and +the circumambient air, are the main causes of electrical development +evidencing itself in lightning flashes, is no doubt true. We must not, +however, lose sight of the many other and very effective agencies at +work here to produce electric excitement. The actual _bocca_ of the +volcanic vent whence the steam roars off constitute the cone a veritable +hydro-electric machine. Mechanical energy in various forms is +transformed into electric energy. Chemical action is going on both in +the solid and in the vapourous and gaseous emanations as they rush into +and remain in the air or descend from it, and chemical action is +transformed in part into electric energy. Percussion between ascending +and descending particles and fragments, fractures and breaking up of +more or less of these, thus and by sudden changes of temperature in +cooling, are likewise operative. In addition, great and violent +movements in the atmosphere itself result from the large local +accessions of temperature by the heated volume driven up into it, and +which in turn give rise to electric disturbance of the same character as +those produced in wind storms and whirlwinds, brought about by the +natural causes which every day effect disturbances in our atmosphere all +over the globe. + +[7] (P. 135). The views stated in note 3 (to page 96) may here again be +referred to as in point. How is it possible, in the present state of +science at least, to establish any physical connection between an +eruption in Java and one of Vesuvius, "with half the world between," +when not even having the solitary connecting link of complete +contemporaneity, and which, if it existed, yet might be nothing but +accidental? A list of shocks upon record, which have occurred more or +less nearly simultaneously at distant parts of the world, may be found +in my fourth Report, ("Facts of Earthquakes," "British Association +Reports, 1858") and the reasons are there given for rejecting the notion +of any direct physical connection between the origins of the respective +shocks. + +Shocks, emanating from the close neighbourhood of volcanic vents, or +simultaneity of eruption, in vents not far distant from each other, +stand upon a different footing. + + + + +Transcriber's Notes. + +Preserved the unusual, but consistent, spelling of "develope." + +Preserved the unusual, and inconsistent, references to the Plates. +Sometimes Arabic numerals are used, but usually Roman numerals. Most +have "A" attached to the name (which was changed to "a" to avoid +confusion in the Roman numerals), but not VIII, and sometimes not in the +references to them. + +Equations were converted to linear text, adding spacing and parentheses +as necessary. Greek characters were also replaced by Latin letters in +the Latin-1 version. + +Replaced the oe ligature with the two characters in "Goethe" in the +front material. + +Changed "fumarolles" to "fumaroles" on page 3: "fumaroles and +salfatares." + +Changed "Lyall" to "Lyell" in footnote originally on page 9: "Daubeny, +Lyell, Phillips and others." + +Changed "throught" to "through" on page 35: "passing through it." + +Removed duplicated word "the" on page 40: "the great Calabrian +Earthquake." + +Page 89 refers to the "Fossa del Vetrano;" elsewhere there are +references to "Fossa della Vetrana," which may be what was intended. +However, I did not change this. + +Changed "hydrochloride" to "hydrochloric" on page 109: "the hydrochloric +acid which it discharged." + +Changed "disk" to "disc" on page 126: "the disc and index." + +Replaced the infinity symbol on page 131 with "for infinity," in the +Latin-1 text version. + +Changed "azismuths" to "azimuths" on page 143: "the different azimuths." + +Changed "silicious" to "siliceous" on page 143: "filled with siliceous +sand." + + + + + +End of Project Gutenberg's The Eruption of Vesuvius in 1872, by Luigi Palmieri + +*** END OF THIS PROJECT GUTENBERG EBOOK THE ERUPTION OF VESUVIUS IN 1872 *** + +***** This file should be named 33483.txt or 33483.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/3/4/8/33483/ + +Produced by Steven Gibbs, Stephen H. Sentoff and the Online +Distributed Proofreading Team at https://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need are critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/33483.zip b/33483.zip Binary files differnew file mode 100644 index 0000000..52c6b71 --- /dev/null +++ b/33483.zip diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..faff7af --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #33483 (https://www.gutenberg.org/ebooks/33483) |
