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+The Project Gutenberg EBook of Meteorology, by J. G. M'Pherson
+
+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: Meteorology
+       or Weather Explained
+
+Author: J. G. M'Pherson
+
+Release Date: February 19, 2012 [EBook #38928]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK METEOROLOGY ***
+
+
+
+
+Produced by The Online Distributed Proofreading Team at
+https://www.pgdp.net (This file was produced from images
+generously made available by The Internet Archive.)
+
+
+
+
+
+
+
+
+
+SHILLING SCIENTIFIC SERIES
+
+
+
+
+[Illustration: DR. AITKEN'S DUST-COUNTER.
+
+R is the test-receiver; P the air-pump; M the measuring apparatus; L the
+illuminating arrangements; G the Gasometer; A the pipe through which the
+tested air is drawn.]
+
+
+
+
+  METEOROLOGY;
+  OR,
+  WEATHER EXPLAINED.
+
+
+  BY
+  J. G. M'PHERSON, Ph.D., F.R.S.E.,
+
+  GRADUATE WITH FIRST-CLASS HONOURS, AND FOR NINE YEARS
+  EXTENSION LECTURER ON METEOROLOGY AND MATHEMATICAL
+  EXAMINER IN THE UNIVERSITY OF ST. ANDREWS;
+  AUTHOR OF "TALES OF SCIENCE," ETC.
+
+
+  LONDON: T. C. & E. C. JACK,
+  34 HENRIETTA STREET, W.C.
+  AND EDINBURGH.
+  1905.
+
+
+
+
+THE SHILLING SCIENTIFIC SERIES
+
+
+_The following Vols. are now ready or in the Press_:--
+
+BALLOONS, AIRSHIPS, AND FLYING MACHINES. By GERTRUDE BACON.
+
+MOTORS AND MOTORING. By Professor HARRY SPOONER.
+
+RADIUM. By Dr. HAMPSON.
+
+TELEGRAPHY WITH AND WITHOUT WIRES. By W. J. WHITE.
+
+ELECTRIC LIGHTING. By S. F. WALKER, R.N., M.I.E.E.
+
+LOCAL GOVERNMENT. By PERCY ASHLEY, M.A.
+
+_Others in Preparation_
+
+  Printed by BALLANTYNE, HANSON & CO.
+  At the Ballantyne Press
+
+
+
+
+CONTENTS
+
+
+  CHAP.                                             PAGE
+
+       I. INTRODUCTION                                 9
+
+      II. THE FORMATION OF DEW                        13
+
+     III. TRUE AND FALSE DEW                          17
+
+      IV. HOAR-FROST                                  20
+
+       V. FOG                                         23
+
+      VI. THE NUMBERING OF THE DUST                   26
+
+     VII. DUST AND ATMOSPHERIC PHENOMENA              29
+
+    VIII. A FOG-COUNTER                               31
+
+      IX. FORMATION OF CLOUDS                         34
+
+       X. DECAY OF CLOUDS                             37
+
+      XI. IT ALWAYS RAINS                             40
+
+     XII. HAZE                                        43
+
+    XIII. HAZING EFFECTS OF ATMOSPHERIC DUST          47
+
+     XIV. THUNDER CLEARS THE AIR                      49
+
+      XV. DISEASE GERMS IN THE AIR                    53
+
+     XVI. A CHANGE OF AIR                             55
+
+    XVII. THE OLD MOON IN THE NEW MOON'S ARMS         58
+
+   XVIII. AN AUTUMN AFTERGLOW                         62
+
+     XIX. A WINTER FOREGLOW                           65
+
+      XX. THE RAINBOW                                 68
+
+     XXI. THE AURORA BOREALIS                         71
+
+    XXII. THE BLUE SKY                                74
+
+   XXIII. A SANITARY DETECTIVE                        78
+
+    XXIV. FOG AND SMOKE                               80
+
+     XXV. ELECTRICAL DEPOSITION OF SMOKE              83
+
+    XXVI. RADIATION FROM SNOW                         86
+
+   XXVII. MOUNTAIN GIANTS                             88
+
+  XXVIII. THE WIND                                    92
+
+    XXIX. CYCLONES AND ANTI-CYCLONES                  95
+
+     XXX. RAIN PHENOMENA                              98
+
+    XXXI. THE METEOROLOGY OF BEN NEVIS               102
+
+   XXXII. THE WEATHER AND INFLUENZA                  107
+
+  XXXIII. CLIMATE                                    110
+
+   XXXIV. THE "CHALLENGER" WEATHER REPORTS           114
+
+    XXXV. WEATHER-FORECASTING                        116
+
+          INDEX                                      124
+
+
+
+
+PREFATORY NOTE
+
+
+I am very much indebted to Dr. John Aitken, F.R.S., for his great kindness
+in carefully revising the proof sheets, and giving me most valuable
+suggestions. This is a sufficient guarantee that accuracy has not been
+sacrificed to popular explanation.
+
+J. G. M'P.
+
+  RUTHVEN MANSE,
+  _June 10, 1905_.
+
+
+
+
+METEOROLOGY
+
+
+
+
+CHAPTER I
+
+INTRODUCTION
+
+
+Though by familiarity made commonplace, the "weather" is one of the most
+important topics of conversation, and has constant bearings upon the work
+and prospects of business-men and men of pleasure. The state of the
+weather is the password when people meet on the country road: we could not
+do without the humble talisman. "A fine day" comes spontaneously to the
+lips, whatever be the state of the atmosphere, unless it is peculiarly and
+strikingly repulsive; then "A bitter day" would take the place of the
+expression. Yet I have heard "_Terrible_ guid wither" as often as
+"_Terrible_ bad day" among country people.
+
+Scarcely a friendly letter is penned without a reference to the weather,
+as to what has been, is, or may be. It is a new stimulus to a lagging
+conversation at any dinner-table. All are so dependent on the weather,
+especially those getting up in years or of delicate health.
+
+I remember, when at Strathpeffer, the great health-resort in the North of
+Scotland, in 1885, an anxious invalid at "The Pump" asking a
+weather-beaten, rheumatic old gamekeeper what sort of a day it was to be,
+considering that it had been wet for some time. The keeper crippled to the
+barometer outside the doorway, and returned with the matter-of-fact
+answer: "She's faurer doon ta tay nur she wass up yestreen." The barometer
+had evidently fallen during the night. "And what are we to expect?" sadly
+inquired the invalid. "It'll pe aither ferry wat, or mohr rain"--a poor
+consolation!
+
+Most men who are bent on business or pleasure, and all dwellers in the
+country who have the instruments, make a first call at the barometer in
+the lobby, or the aneroid in the breakfast-parlour, to "see what she
+says." A good rise of the black needle (that is, to the right) above the
+yellow needle is a source of rejoicing, as it will likely be clear, dry,
+and hard weather. A slight fall (that is, to the left) causes anxiety as
+to coming rain, and a big depression forebodes much rain or a violent
+storm of wind. In either case of "fall," the shutters come over the eyes
+of the observer. Next, even before breakfast, a move is made to the
+self-registering thermometer (set the night before) on a stone, a couple
+of feet above the grass. A good reading, above the freezing-point in
+winter and much above it in summer, indicates the absence of killing
+rimes, that are generally followed by rain. A very low register accounts
+for the feeling of cold during the night, though the fires were not out;
+and predicts precarious weather. Ordinarily careful observers--as I, who
+have been in one place for more than thirty years--can, with the morning
+indications of these two instruments, come pretty sure of their
+prognostics of the day's weather. Of course, the morning newspaper is
+carefully scanned as to the weather-forecasts from the London
+Meteorological Office--direction of wind; warm, mild, or cold; rain or
+fair, and so on--and in general these indications are wonderfully accurate
+for twenty-four hours; though the "three days'" prognostics seem to
+stretch a point. We are hardly up to that yet.
+
+The lower animals are very sensitive as to the state of approaching
+extremes of weather. "Thae sea beass," referring to sea-gulls over the
+inland leas during ploughing, are ordinary indicators of stormy weather.
+Wind is sure to follow violent wheelings of crows. "Beware of rain" when
+the sheep are restive, rubbing themselves on tree stumps. But all are
+familiar with Jenner's prognostics of rain.
+
+Science has come to the aid of ordinary weather-lore during the last
+twenty years, by leaps and bounds. Time-honoured notions and revered
+fictions, around which the hallowed associations of our early training
+fondly and firmly cling, must now yield to the exact handling of modern
+science; and with reluctance we have to part with them. Yet there is in
+all a fascination to account for certain ordinary phenomena. "The man in
+the street," as well as the strong reading man, wishes to know the "why"
+and the "how" of weather-forecasting. They are anxious to have
+weather-phenomena explained in a plain, interesting, but accurate way.
+
+The freshness of the marvellous results has an irresistible charm for the
+open mind, keen for useful information. The discoveries often seem so
+simple that one wonders why they were not made before.
+
+Until about twenty years ago, Meteorology was comparatively far back as a
+science; and in one important branch of it, no one has done more to put
+weather-lore on a scientific basis than Dr. John Aitken, F.R.S., who has
+very kindly given me his full permission to popularise what I like of his
+numerous and very valuable scientific papers in the _Transactions of the
+Royal Society of Edinburgh_. This I have done my best to carry out in the
+following pages. "The way of putting it" is my only claim.
+
+Many scientific men are decoyed on in the search for truth with a spell
+unknown to others: the anticipation of the results sometimes amounts to a
+passion. Many wrong tracks do they take, yet they start afresh, just as
+the detective has to take several courses before he hits upon the correct
+scent. When they succeed, they experience a pleasure which is
+indescribable; to them fame is more than a mere "fancied life in others'
+breath."
+
+Dr. Aitken's continued experiments, often of rare ingenuity and
+brilliancy, show that no truth is altogether barren; and even that which
+looks at first sight the very simplest and most trivial may turn out
+fruitful in precious results. Small things must not be overlooked, for
+great discoveries are sometimes at a man's very door. Dr. Aitken has shown
+us this in many of his discoveries which have revolutionised a branch of
+meteorology. Prudence, patience, observing power, and perseverance in
+scientific research will do much to bring about unexpected results, and
+not more so in any science than in accounting for weather-lore on a
+rational basis, which it is in the power of all my readers to further.
+
+"The old order changeth, giving place to new." With kaleidoscopic variety
+Nature's face changes to the touch of the anxious and reverent observer.
+And some of these curious weather-views will be disclosed in these pages,
+so as, in a brief but readable way, to explain the weather, and lay a safe
+basis for probable forecastings, which will be of great benefit to the man
+of business as well as the man of pleasure.
+
+  "Felix, qui potuit rerum cognoscere causas."
+                                          --VIRGIL.
+
+
+
+
+CHAPTER II
+
+THE FORMATION OF DEW
+
+
+The writer of the Book of Job gravely asked the important question, "Who
+hath begotten the drops of dew?" We repeat the question in another form,
+"Whence comes the real dew? Does it fall from the heavens above, or does
+it rise from the earth beneath?"
+
+Until about the beginning of the seventeenth century, scientific men held
+the opinion of ordinary observers that dew fell from the atmosphere. But
+there was then a reaction from this theory, for Nardius defined it as an
+exhalation from the earth. Of course, it was well known that dew was
+formed by the precipitation of the vapour of the air upon a colder body.
+You can see that any day for yourself by bringing a glass of very cold
+water into a warm room; the outer surface of the glass is dimmed at once
+by the moisture from the air. M. Picket was puzzled when he saw that a
+thermometer, suspended five feet above the ground, marked a lower
+temperature on clear nights than one suspended at the height of
+seventy-five feet; because it was always supposed that the cold of evening
+descended from above. Again he was puzzled when he observed that a buried
+thermometer read higher than one on the surface of the ground. Until
+recently the greatest authority on dew was Dr. Wells, who carefully
+converged all the rays of scientific light upon the subject. He came to
+the conclusion that dew was condensed out of the air.
+
+But the discovery of the true theory was left to Dr. John Aitken, F.R.S.,
+a distinguished observer and a practical physicist, of whom Scotland has
+reason to be proud. About twenty years ago he made the discovery, and it
+is now accepted by all scientific men on the Continent as well as in Great
+Britain. What first caused him to doubt Dr. Wells' theory, so universally
+accepted, that dew is formed of vapour existing at the time in the air,
+and to suppose that dew is mostly formed of vapour rising from the ground,
+was the result of some observations made in summer on the temperature of
+the soil at a small depth under the surface, and of the air over it, after
+sunset and at night. He was struck with the unvarying fact that the
+ground, a little below the surface, was warmer than the air over it. By
+placing a thermometer among stems below the surface, he found that it
+registered 18° Fahr. higher than one on the surface. So long, then, as
+the surface of the ground is above the dew-point (_i.e._ the temperature
+when dew begins to be formed), vapour must rise from the ground; this
+moist air will mingle with the air which it enters, and its moisture will
+be condensed and form dew, whenever it comes in contact with a surface
+cooled below the dew-point.
+
+You can verify this by simple experiments. Take a thin, shallow, metal
+tray, painted black, and place it over the ground after sunset. On dewy
+nights the _inside_ of the tray is dewed, and the grass inside is wetter
+than that outside. On some nights there is no dew outside the tray, and on
+all nights the deposit on the inner is heavier than that on the outside.
+If wool is used in the experiments, we are reminded of one of the forms of
+the dewing of Gideon's fleece--the fleece was bedewed when all outside was
+dry.
+
+You therefore naturally and rightly come to the conclusion that far more
+vapour rises out of the ground during the night than condenses as dew on
+the grass, and that this vapour from the ground is trapped by the tray.
+Much of the rising vapour is generally carried away by the passing wind,
+however gentle; hence we have it condensed as dew on the roofs of houses,
+and other places, where you would think that it had fallen from above. The
+vapour rising under the tray is not diluted by the mixture with the drier
+air which is occasioned by the passing wind; therefore, though only cooled
+to the same extent as the air outside, it yields a heavier deposit of
+dew.
+
+If you place the tray on bare ground, you will find on a dewy night that
+the inside of the tray is quite wet. On a dewy night you will observe that
+the under part of the gravel of the road is dripping wet when the top is
+dry. You will find, too, that around pieces of iron and old implements in
+the field, there is a very marked increase of grass, owing to the deposit
+of moisture on these articles--moisture which has been condensed by the
+cold metal from the vapour-charged air, which has risen from the ground on
+dewy nights.
+
+But all doubt upon this important matter is removed by a most successful
+experiment with a fine balance, which weighs to a quarter of a grain. If
+vapour rises from the ground for any length of time during dewy nights,
+the soil which gives off the vapour must lose weight. To test this, cut
+from the lawn a piece of turf six inches square and a quarter of an inch
+thick. Place this in a shallow pan, and carefully note the weight of both
+turf and pan with the sensitive balance. To prevent loss by evaporation,
+the weighing should be done in an open shed. Then place the pan and turf
+at sunset in the open cut. Five hours afterwards remove and weigh them,
+and it will be found that the turf has lost a part of its weight. The
+vapour which rose from the ground during the formation of the dew accounts
+for the difference of weight. This weighing-test will also succeed on bare
+ground.
+
+When dealing with hoar-frost, which is just frozen dew, we shall find
+visible evidence of the rising of dew from the ground.
+
+You know the beautiful song, "Annie Laurie," which begins with--
+
+  "Maxwelton's braes are bonnie,
+  Where early fa's the dew"--
+
+well, you can no longer say that the dew "falls," for it rises from the
+ground. The song, however, will be sung as sweetly as ever; for the spirit
+of true poetry defies the cold letter of science.
+
+
+
+
+CHAPTER III
+
+TRUE AND FALSE DEW
+
+
+Ever since men could observe and think, they have admired the diamond
+globules sparkling in the rising sun. These "dew-drops" were considered to
+be shed from the bosom of the morn into the blooming flowers and rich
+grass-leaves. Ballantine's beautiful song of Providential care tells us
+that "Ilka blade o' grass keps it's ain drap o' dew."
+
+But, alas! we have to bid "good-bye" to the appellation "dew-drop." What
+was popularly and poetically called dew _is not dew at all_. Then what is
+it?
+
+On what we have been accustomed to call a "dewy" night, after the
+brilliant summer sun has set, and the stars begin to peep out of the
+almost cloudless sky, let us take a look at the produce of our vegetable
+garden. On the broccoli are found glistening drops; but on the peas,
+growing next them, we find nothing.
+
+A closer examination shows us that the moisture on the plants is not
+arranged as would be expected from the ordinary laws of radiation and
+condensation. There is no generally filmy appearance over the leaves; the
+moisture is collected in little drops placed at short distances apart,
+along the edges of the leaves all round.
+
+Now place a lighted lantern below one of the blades of the broccoli, and a
+revelation will be made. The brilliant diamond-drops that fringe the edge
+of the blade are all placed at the points where the nearly colourless
+veins of the blade come to the outer edge. The drops are not dew at all,
+but the exudation of the healthy plant, which has been conveyed up these
+veins by strong root-pressure.
+
+The fact is that the root acts as a kind of force-pump, and keeps up a
+constant pressure inside the tissues of the plant. One of the simplest
+experiments suggested by Dr. Aitken is to lift a single grass-plant, with
+a clod of moist earth attached to it, and place it on a plate with an
+inverted tumbler over it. In about an hour, drops will begin to exude, and
+the tip of nearly every blade will be found to be studded with a
+diamond-like drop.
+
+Next substitute water-pressure. Remove a blade of broccoli and connect it
+by means of an india-rubber tube with a head of water of about forty
+inches. Place a glass receiver over it, so as to check evaporation, and
+leave it for an hour. The plant will be found to have excreted water
+freely, some parts of the leaves being quite wet, while drops are
+collected at the places where they appeared at night.
+
+If the water pressed into the leaf is coloured with aniline blue, the
+drops when they first appear are colourless; but before they grow to any
+size, the blue appears, showing that little water was held in the veins.
+The whole leaf soon gets coloured of a fine deep blue-green, like that
+seen when vegetation is rank; this shows that the injected liquid has
+penetrated through the whole leaf.
+
+Again, the surfaces of the leaves of these drop-exuding plants never seem
+to be wetted by the water. It is because of the rejection of water by the
+leaf-surface that the exuded moisture from the veins remains as a drop.
+
+These observations and experiments establish the fact that the drops which
+first make their appearance on grass on dewy nights are not dew-drops at
+all, but the exuded watery juices of the plants.
+
+If now we look at dead leaves we shall find a difference of formation of
+the moisture on a dewy night: the moisture is spread equally over, where
+equally exposed. The moisture exuded by the healthy grass is always found
+at a _point_ situated near the tip of the blade, forming a drop of some
+size; but the true dew collects later on _evenly_ all over the blade. The
+false dew forms a large glistening diamond-drop, whereas the true dew
+coats the blade with a fine pearly lustre. Brilliant globules are produced
+by the vital action of the plant, especially beautiful when the deep-red
+setting sun makes them glisten, all a-tremble, with gold light; while an
+infinite number of minute but shining opal-like particles of moisture
+bedecks the blade-surfaces, in the form of the gentle dew--
+
+  "Like that which kept the heart of Eden green
+  Before the useful trouble of the rain."
+
+
+
+
+CHAPTER IV
+
+HOAR-FROST
+
+
+All in this country are familiar with the beauty of hoar-frost. The
+children are delighted with the funny figures on the glass of the bedroom
+window on a cold winter morning. Frost is a wonderful artist; during the
+night he has been dipping his brush into something like diluted schist,
+and laying it gracefully on the smooth panes.
+
+And, as you walk over the meadows, you observe the thin white films of ice
+on the green pasture; and the clear, slender blades seem like crystal
+spears, or the "lashes of light that trim the stars."
+
+You all know what hoar-frost is, though most in the country give it the
+expressive name of "rime." But you are not all aware of how it is formed.
+Hoar-frost is just frozen dew. In a learned paper, written in 1784,
+Professor Wilson of Glasgow made this significant remark: "This is a
+subject which, besides its entire novelty, seems, upon other accounts, to
+have a claim to some attention." He observed, in that exceptionally cold
+winter, that, when sheets of paper and plates of metal were laid out, all
+began to attract hoar-frost as soon as they had time to cool down to the
+temperature of the air. He was struck with the fact that, while the
+thermometer indicated 36 degrees of frost a few feet above the ground and
+44 degrees of frost at the surface of the snow, there were only 8 degrees
+of frost at a point 3 inches below the surface of the snow. If he had
+only thought of placing the thermometer on the grass, under the snow, he
+would have found it to register the freezing-point only. And had he
+inserted the instrument below the ground, he would have found it
+registering a still higher temperature. That fact would have suggested to
+him the formation of hoar-frost; that the water-vapour from the warm soil
+was trapped by a cold stratum of air and frozen when in the form of dew.
+
+One of the most interesting experiments, without apparatus, which you can
+make is in connection with the formation of hoar-frost, when there is no
+snow on the ground, in very cold weather. If it has been a bright, clear,
+sunny day in January, the effect can be better observed. Look over the
+garden, grass, and walks on the morning after the intense cold of the
+night; big plane-tree leaves may be found scattered over the place. You
+see little or no hoar-frost on the _upper_ surface of the leaves. But turn
+up the surface next the earth, or the road, or the grass, and what do you
+see? You have only to handle the leaf in this way to be brightly
+astonished. A thick white coating of hoar-frost, as thick as a layer of
+snow, is on the _under_ surface. If a number of leaves have been
+overlapping each other, there will be no coating of hoar-frost under the
+top leaves; but when you reach the lowest layer, next the bare ground, you
+will find the hoar-frost on the under surface of the leaves. Now that is
+positive proof that the hoar-frost has not fallen from the air, but has
+risen from the earth.
+
+The sun's heat on the previous day warmed the earth. This heat the earth
+retained till evening. As the air chilled, the water-vapour from the
+warmer earth rose from its surface, and was arrested by the cold surface
+of the leaves. So cold was that surface that it froze the water-vapour
+when rising from the earth, and formed hoar-frost in very large
+quantities. When this happens later on in the season, one may be almost
+sure of having rain in the forenoon.
+
+As hoar-frost is just frozen dew, I can even more surely convince you of
+the formation of hoar-frost as rising from the ground by observations made
+by me at my manse in Strathmore, in June 1892. I mention this particularly
+because then was the most favourable testing-time that has _ever_ occurred
+during meteorological observations. June 9th was the warmest June day
+(with one exception) for twenty years. The thermometer reached 83° Fahr.
+in the shade. Next day was the coldest June day (with one exception) for
+twenty years, when the thermometer was as low as 51° in the shade. But
+during the night my thermometer on the grass registered 32°--the freezing
+point. On the evening of the sultry day I examined the soil at 10 o'clock.
+It was damp, and the grass round it was filmy moist. The leaves of the
+trees were crackling dry, and all above was void of moisture. The air
+became gradually chilly; and as gradually the moisture rose in height on
+the shrubs and lower branches of small trees. The moon shone bright, and
+the stars showed their clear, chilly eyes. The soil soon became quite wet,
+the low grass was dripping with moisture, and the longer grass was
+becoming dewed. This gave the best natural evidence of the rising of the
+dew that I ever witnessed. But everything was favourable for the
+observation--the cold air incumbent on the rising, warm, moist vapour from
+the soil fixing the dew-point, when the projecting blades seized the
+moisture greedily and formed dew. Had the temperature been a little below
+the freezing-point, hoar-frost would have been beautifully formed.
+
+
+
+
+CHAPTER V
+
+FOG
+
+
+To many nothing is more troublesome than a dense fog in a large town. It
+paralyses traffic, it is dangerous to pedestrians, it encourages theft, it
+chokes the asthmatic, and chills the weak-lunged.
+
+In the country it is disagreeable enough; but never so intensely raw and
+dense as in the city. On the sea, too, the fog is disagreeable and fraught
+with danger. The fog-horn is heard, in its deep, sombre note, from the
+lighthouse tower, when the strong artificial light is almost useless.
+
+But a peculiar sense of stagnation possesses the dweller of the large
+town, when enveloped in a dense fog. Sometimes during the day, through a
+thinner portion, the sun will be dimly seen in copper hue, like the moon
+under an eclipse. The smoke-impregnated mass assumes a peculiar "pea-soup"
+colour.
+
+Now, what is this fog? How is it formed? It has been ascertained that fogs
+are dependent upon _dust_ for their formation. Without dust there could
+be no fogs, there would be only dew on the grass and road. Instead of the
+dust-impregnated air that irritates the housekeeper, there would be the
+constant dripping of moisture on the walls, which would annoy her more.
+
+Ocular demonstration can testify to this. If two closed glass receivers be
+placed beside each other, the one containing ordinary air, and the other
+filtered air (_i.e._ air deprived of its dust by being driven through
+cotton wool), and if jets of steam be successively introduced into these,
+a strange effect is noticed. In the vessel containing common air the steam
+will be seen rising in a dense cloud; then a beautiful white foggy cloud
+will be formed, so dense that it cannot be seen through. But in the vessel
+containing the filtered air, the steam is not seen at all; there is not
+the slightest appearance of cloudiness. In the one case, where there was
+the ordinary atmospheric dust, fog at once appeared; in the other case,
+where there was no dust in suspension, the air remained clear and
+destitute of fog. Invisible dust, then, is necessary in the air for the
+formation of fogs.
+
+The reason of this is that a free-surface must exist for the condensation
+of the vapour-particles. The fine particles of dust in the air act as
+free-surfaces, on which the fog is formed. Where there is abundance of
+dust in the air and little water-vapour present, there is an
+over-proportion of dust-particles; and the fog-particles are, in
+consequence, closely packed, but light in form and small in size, and take
+the lighter appearance of fog. Accordingly, if the dust is increased in
+the air, there is a proportionate increase of fog. Every fog-particle,
+then, has embosomed in it an invisible dust-particle.
+
+But whence comes the dust? From many sources. It is organic and inorganic.
+So very fine is the inorganic dust in the atmosphere that, if the
+two-thousandth part of a grain of fine iron be heated, and the dust be
+driven off and carried into a glass receiver of filtered air, the
+introduction of a jet of steam into that receiver would at once occasion
+an appreciable cloudiness.
+
+This is why fogs are so prevalent in large towns. Next the minute
+brine-particles, driven into the air as fog forms above the ocean surface,
+are the burnt sulphur-particles emanating from the chimneys in towns. The
+brilliant flame, as well as the smoky flame, is a fog-producer. If gas is
+burnt in filtered air, intense fog is produced when water-vapour is
+introduced. Products of combustion from a clear fire and from a smoky one
+produce equal fogging. The fogs that densely fill our large towns are
+generally less bearable than those that veil the hills and overhang the
+rivers.
+
+It is the sulphur, however, from the consumed coals, which is the active
+producer of the fogs of a large town. The burnt sulphur condenses in the
+air to very fine particles, and the quantity of burnt sulphur is enormous.
+No less than seven and a half millions of tons of coals are consumed in
+London. Now, the average amount of sulphur in English coal is one and a
+quarter per cent. That would give no less than 93,750 tons of sulphur
+burned every year in London fires. Now, if we reckon that on an average
+twice the quantity of coals is consumed there on a winter day that is
+consumed on a summer day, no less than 347 tons of the products of
+combustion (in extremely fine particles) are driven into the
+superincumbent air of London every winter day. This is an enormous
+quantity, quite sufficient to account for the density of the fogs in that
+city.
+
+
+
+
+CHAPTER VI
+
+THE NUMBERING OF THE DUST
+
+
+If the shutters be all but closed in a room, when the sun is shining in,
+myriads of floating particles can be seen glistening in the stream of
+light. Their number seems inexhaustible. According to Milton, the follies
+of life are--
+
+                    "Thick and numberless,
+  As the gay motes that people the sunbeams."
+
+Can these, then, be counted? Yes, Dr. Aitken has numbered the dust of the
+air. I shall never forget my rapt astonishment the day I first numbered
+the dust in the lecture-room of the Royal Society of Edinburgh, with his
+instrument and under his direction.
+
+This wonderfully ingenious instrument was devised on this principle, that
+every fog-particle has entombed in it an invisible dust-particle. A
+definite small quantity of common air is diluted with a fixed large
+quantity of dustless air (_i.e._ air that has been filtered through
+cotton-wool). The mixture is allowed to be saturated with water-vapour.
+Then the few particles of dust seize the moisture, become visible in fine
+drops, fall on a divided plate, and are there counted by means of a
+magnifying glass. That is the secret!
+
+I shall now give you a general idea of the apparatus. Into a common glass
+flask of carafe shape, and flat-bottomed, of 30 cubic inches capacity, are
+passed two small tubes, at the end of one of which is attached a small
+square silver table, 1 inch in length. A little water having been
+inserted, the flask is inverted, and the table is placed exactly 1 inch
+from the inverted bottom, so that the contents of air right above the
+table are 1 cubic inch. This observing table is divided into 100 equal
+squares, and is highly polished, with the burnishing all in one direction,
+so that during the observations it appears dark, when the fine
+mist-particles glisten opal-like with the reflected light in order that
+they may be more easily counted. The tube to which the silver table is
+attached is connected with two stop-cocks, one of which can admit a small
+measured portion of the air to be examined. The other tube in the flask is
+connected with an air-pump of 10 cubic inches capacity. Over the flask is
+placed a covering, coloured black in the inside. In the top of this cover
+is inserted a powerful magnifying glass, through which the particles on
+the silver table can be easily counted. A little to the side of this
+magnifier is an opening in the cover, through which light is concentrated
+on the table.
+
+To perform the experiment, the air in the flask is exhausted by the
+air-pump. The flask is then filled with filtered air. One-tenth of a cubic
+inch of the air to be examined is then introduced into the flask, and
+mixed with the 30 cubic inches of dustless air. After one stroke of the
+air-pump, this mixed air is made to occupy an additional space of 10 cubic
+inches; and this rarefying of the air so chills it that condensation of
+the water-vapour takes place on the dust-particles. The observer, looking
+through the magnifying-glass upon the silver table, sees the
+mist-particles fall like an opal shower on the table. He counts the number
+on a single square in two or three places, striking an average in his
+mind. Suppose the average number upon a single square were five, then on
+the whole table there would be 500; and these 500 particles of dust are
+those which floated invisibly in the cubic inch of mixed air right above
+the table. But, as there are 40 cubic inches of mixed air in the flask and
+barrel, the number of dust-particles in the whole is 20,000. That is,
+there are 20,000 dust-particles in the same quantity of common air
+(one-tenth of a cubic inch) which was introduced for examination. In other
+words, a cubic inch of the air contained 200,000 dust-particles--nearly a
+quarter of a million.
+
+The day I used the instrument we counted 4,000,000 of dust-particles in a
+cubic inch of the air outside of the room, due to the quantity of smoke
+from the passing trains. Dr. Aitken has counted in 1 cubic inch of air
+immediately above a Bunsen flame the fabulous number of 489,000,000 of
+dust-particles.
+
+A small instrument has been constructed which can bring about results
+sufficiently accurate for ordinary purposes. It is so constructed that,
+when the different parts are unscrewed, they fit into a case 4-1/2 inches
+by 2-1/2 by 1-1/4 deep--about the size of an ordinary cigar-case.
+
+After knowing this, we are apt to wonder why our lungs do not get clogged
+up with the enormous number of dust-particles. In ordinary breathing, 30
+cubic inches of air pass in and out at every breath, and adults breathe
+about fifteen times every minute. But the warm lung-surface repels the
+colder dust-particles, and the continuous evaporation of moisture from the
+surface of the air-tubes prevents the dust from alighting or clinging to
+the surface at all.
+
+
+
+
+CHAPTER VII
+
+DUST AND ATMOSPHERIC PHENOMENA
+
+
+Dr. Aitken has devoted a vast amount of attention to the enumeration of
+dust-particles in the air, on the Continent as well as in Scotland, to
+determine the effects of their variation in number.
+
+On his first visit to Hyères, in 1890, he counted with the instrument
+12,000 dust-particles in a cubic inch of the air: whereas in the following
+year he counted 250,000. He observed, however, that where there was least
+dust, the air was very clear; whereas with the maximum of dust, there was
+a very thick haze.
+
+At Mentone, the corresponding number was 13,000, when the wind was blowing
+from the mountains; but increased to 430,000, when the wind was blowing
+from the populous town.
+
+On his first visit to the Rigi Kulm, in Switzerland, the air was
+remarkably clear and brilliant, and the corresponding number never
+exceeded 33,000; but, on his second visit, he counted no less than
+166,000. This was accounted for by a thick haze, which rendered the lower
+Alps scarcely visible. The upper limit of the haze was well defined; and
+though the sky was cloudless, the sun looked like a harvest moon, and
+required no eagle's eye to keep fixed on it.
+
+Next day there was a violent thunder-storm. At 6 P.M. the storm commenced,
+and 60,000 dust-particles to the cubic inch of air were registered; but in
+the middle of the storm he counted only 13,000. There was a heavy fall of
+hail at this time, and he accounts for the diminution of dust-particles by
+the down-rush of purer upper air, which displaced the contaminated lower
+air.
+
+At the Lake of Lucerne there was an exceptional diminution of the number
+in the course of an hour, viz. from 171,000 to 28,000 in a cubic inch. On
+looking about, he found that the direction of the wind had changed,
+bringing down the purer upper air to the place of observation. The bending
+downwards of the trees by the strong wind showed that it was coming from
+the upper air.
+
+Returning to Scotland, he continued his observations at Ben Nevis and at
+Kingairloch, opposite Appin, Mr. Rankin using the instrument at the top of
+the mountain. These observations showed in general that on the mountain
+southerly, south-easterly, and easterly winds were more impregnated with
+dust-particles, sometimes containing 133,000 per cubic inch. Northerly
+winds brought pure air. The observations at sea-level showed a certain
+parallelism to those on the summit of the mountain. With a north-westerly
+wind the dust-particles reached the low number of 300 per cubic inch, the
+lowest recorded at any low-level station.
+
+The general deductions which he made from his numerous observations during
+these two years are that (1) air coming from inhabited districts is always
+impure; (2) dust is carried by the wind to enormous distances; (3) dust
+rises to the tops of mountains during the day; (4) with much dust there is
+much haze; (5) high humidity causes great thickness of the atmosphere, if
+accompanied by a great amount of dust, whereas there is no evidence that
+humidity alone has any effect in producing thickness; (6) and there is
+generally a high amount of dust with high temperature, and a low amount of
+dust with low temperature.
+
+
+
+
+CHAPTER VIII
+
+A FOG-COUNTER
+
+
+Next to the enumeration of the dust-particles in the atmosphere is the
+marvellous accuracy of counting the number of particles in a fog. The same
+ingenious inventor has constructed a fog-counter for the purpose; and the
+number of fog-particles in a cubic inch can be ascertained. This
+instrument consists of a glass micrometer divided into squares of a known
+size, and a strong microscope for observing the drops on the stage. The
+space between the micrometer and the microscope is open, so that the air
+passes freely over the stage; and the drops that fall on its surface are
+easily seen. These drops are very small; many of them when spread on the
+glass are no more than the five-hundredth of an inch in diameter.
+
+In observing these drops, the attention requires to be confined to a
+limited area of the stage, as many of the drops rapidly evaporate, some
+almost as soon as they touch the glass, whilst the large ones remain a few
+seconds.
+
+In one set of Dr. Aitken's observations, in February 1891, the fog was so
+thick that objects beyond a hundred yards were quite invisible. The number
+of drops falling per second varied greatly from time to time. The greatest
+number was 323 drops per square inch in one second. The high number never
+lasted for long, and in the intervals the number fell as low as 32, or to
+one-tenth.
+
+If we knew the size of these drops, we might be able to calculate the
+velocity of their fall, and from that obtain the number in a cubic inch.
+
+An ingenious addition is put to the instrument in order to ascertain this
+directly. It is constructed so as to ascertain the number of particles
+that fall from a known height. Under a low-power microscope, and
+concentric with it, is mounted a tube 2 inches long and 1-1/2 inch in
+diameter, with a bottom and a cover, which are fixed to an axis parallel
+with the axis of the tube, so that, by turning a handle, these can be slid
+sideways, closing or opening the tube at both ends when required. In the
+top is a small opening, corresponding to the lens of the microscope, and
+in the centre of the bottom is placed the observing-stage illumined by a
+spot-mirror. The handle is turned, and the ends are open to admit the
+foggy air. The handle is quickly reversed, and the ends are closed,
+enabling the observer to count on the stage all the fog-particles in the
+two inches of air over it.
+
+The number of dust-particles in the air which become centres of
+condensation depends on the rate at which the condensation is taking
+place. The most recent observations show that quick condensation causes a
+large number of particles to become active, whereas slow condensation
+causes a small number. After the condensation has ceased, a process of
+differentiation takes place, the larger particles robbing the smaller ones
+of their moisture, owing to the vapour-pressure at the surface of the
+drops of large curvature being less than at the surface of drops of
+smaller curvature.
+
+By this process the particles in a cloud are reduced in number; the
+remaining ones, becoming larger, fall quicker. The cloud thus becomes
+thinner for a time. A strong wind, suddenly arising, will cause the
+cloud-particles to be rapidly formed: these will be very numerous, but
+very small--so small that they are just visible with great care under a
+strong magnifying lens used in the instrument. But in slowly formed clouds
+the particles are larger, and therefore more easily visible to the naked
+eye.
+
+Though the particles in a fog are slightly finer, the number is about the
+same as in a cloud--that is, generally. As clouds vary in density, the
+number of particles varies. Sometimes in a cloud one cannot see farther
+than 30 yards; whereas in a few minutes it clears up a little, so that we
+can see 100 yards. Of course, the denser the cloud the greater the number
+of water-particles falling on the calculating-stage of the instrument.
+
+Very heavy falls of cloud-particles seldom last more than a few seconds,
+the average being about 325 on the square inch per second, the maximum
+reaching to 1290. This is about four times the number counted in a fog.
+Yet the particles are so very small that they evaporate instantly when
+they reach a slight increase of temperature.
+
+
+
+
+CHAPTER IX
+
+FORMATION OF CLOUDS
+
+
+In our ordinary atmosphere there can be no clouds without dust. A
+dust-particle is the nucleus that at a certain humidity becomes the centre
+of condensation of the water-vapour so as to form a cloud-particle; and a
+collection of these forms a cloud.
+
+This condensation of vapour round a number of dust-particles in visible
+form gives rise to a vast variety of cloud-shapes. There are two distinct
+ways in which the formation of clouds generally takes place. Either a
+layer of air is cooled in a body below the dew-point; or a mass of warm
+and moist air rises into a mass which is cold and dry. The first forms a
+cloud, called, from being a layer, _stratus_; the second forms a cloud,
+called, from its heap appearance, _cumulus_. The first is widely extended
+and horizontal, averaging 1800 feet in height; the second is convex or
+conical, like the head of a sheaf, increasing upward from a level base,
+averaging from 4500 feet to 6000 feet in height.
+
+There are endless combinations of these two; but at the height of 27,000
+feet, where the cloud-particles are frozen, the structure of the cloud is
+finer, like "mares' tails," receiving the name _cirrus_. When the cirrus
+and cumulus are combined, in well-defined roundish masses, what is
+familiarly described as a "mackerel sky" is beautifully presented. The
+dark mass of cloud, called _nimbus_, is the threatening rain-cloud, about
+4500 feet in height.
+
+At the International Meteorological Conference at Munich, in 1892, twelve
+varieties of clouds were classified, but those named above are the
+principal. In a beautiful sunset one can sometimes notice two or three
+distances of clouds, the sun shedding its gold light on the full front of
+one set, and only fringing with vivid light the nearer range.
+
+Although no man has wrought so hard as Dr. Aitken to establish the
+principle that clouds are mainly due to the existence of dust-particles
+which attract moisture on certain conditions, yet even twenty years ago he
+said that it was probable that sunshine might cause the formation of
+nuclei and allow cloudy condensation to take place where there was no
+dust.
+
+Under certain conditions the sun gives rise to a great increase in the
+number of nuclei. Accordingly, he has carefully tested a few of the
+ordinary constituents and impurities in our atmosphere to see if sunshine
+acted on them in such a way as to make them probable formers of
+cloud-particles.
+
+He tested various gases, with more or less success. He found that ordinary
+air, after being deprived of its dust-particles and exposed to sunshine,
+does not show any cloudy condensation on expansion; but, when certain
+gases are in the dustless air, a very different result is obtained.
+
+He first used ammonia, putting one drop into six cubic inches of water in
+a flask, and sunning this for one minute; the result was a considerable
+quantity of condensation, even with such a weak solution. When the flask
+was exposed for five minutes, the condensation by the action of the
+sunshine was made more dense.
+
+Hydrogen peroxide was tested in the same way, and it was found to be a
+powerful generator of nuclei. Curious is it that sulphurous acid is
+puzzling to the experimentalist for cloud formation. It gives rise to
+condensation in the dark; but sunshine very conclusively increases the
+condensation.
+
+Chlorine causes condensation to take place without supersaturation;
+sulphuretted hydrogen (which one always associates with the smell of
+rotten eggs) gives dense condensation after being exposed to sunshine.
+
+Though the most of these nuclei, due to the action of sunshine in the
+gases, remain active for cloudy condensation for a comparatively short
+space of time--fifteen minutes to half-an-hour--yet the experiments show
+that it is possible for the cloudy condensation to take place in certain
+circumstances in the absence of dust. This seems paradoxical in the light
+of the former beautiful experiments; but, in ordinary circumstances, dust
+is needed for the formation of clouds. However, supposing there is any
+part of the upper air free from dust, it is now found possible, when any
+of these gases experimented on be present, for the sun to convert them
+into nuclei of condensation, and permit of clouds being formed in dustless
+air, miles above the surface of the earth.
+
+In the lower atmosphere there are always plenty of dust-particles to form
+cloudy condensation, whether the sun shines or not. These are produced by
+the waste from the millions of meteors that daily fall into the air.
+
+But in the higher atmosphere, clouds can be formed by the action of the
+sun's rays on certain gases. This is a great boon to us on the earth; for
+it assures us of clouds being ever existing to defend us from the sun's
+extra-powerful rays, even when our atmosphere is fairly clear. This is
+surely of some meteorological importance.
+
+
+
+
+CHAPTER X
+
+DECAY OF CLOUDS
+
+
+From the earliest ages clouds have attracted the attention of observers.
+Varied are their forms and colours, yet in our atmosphere there is one law
+in their formation. Cloud-particles are formed by the condensation of
+water-vapour on the dust-particles invisibly floating in the atmosphere,
+up to thousands--and even millions--in the cubic inch of air.
+
+But observers have not directed their attention so much to the decay of
+clouds--in fact, the subject is quite new. And yet how suggestive is the
+subject!
+
+The process of decay in clouds takes place in various ways. A careful
+observer may witness the gradual wasting away and dilution into thin air
+of even great stretches of cloud, when circumstances are favourable. In
+May 1896 my attention was particularly drawn to this at my manse in
+Strathmore. In the middle of that exceptionally sultry month, I was
+arrested by a remarkable transformation scene. It was the hottest May for
+seventy-two years, and the driest for twenty-five years. The whole parched
+earth was thirsting for rain. All the morning my eyes were turned to the
+clouds in the hope that the much-desired shower should fall. Till ten
+o'clock the sun was not seen, and there was no blue in the sky. Nor was
+there any haze or fog.
+
+But suddenly the sun shone through a thinner portion of the enveloping
+clouds, and, to the north, the sky began to open. As if by some magic
+spell there was, in a quarter of an hour, more blue to be seen than
+clouds. At the same time, near the horizon, a haze was forming, gradually
+becoming denser as time wore on. In an hour the whole clouds were gone,
+and the glorious orb of day dispelled the moisture to its thin-air form.
+
+This was a pointed and rapid illustration of the decay from cloud-form to
+haze, and then to the pure vapoury sky. It was an instance of the
+_reverse_ process. As the sun cleared through, the temperature in the
+cloud-land rose and evaporation took place on the surface of the
+cloud-particles, until by an untraceable, but still a gradual process
+through fog, the haze was formed. Even then the heat was too great for a
+definite haze, and the water-vapour returned to the air, leaving the
+dust-particles in invisible suspension.
+
+But clouds decay in another way. This I will illustrate in the next
+chapter on "It always rains."
+
+What strikes a close observer is the difference of structure in clouds
+which are in the process of formation and those which are in the process
+of decay. In the former the water-particles are much smaller and far more
+numerous than in the latter. While the particles in clouds in decay are
+large enough to be seen with the unaided eye, when they fall on a properly
+lighted measuring table, they are so small in clouds in rapid formation
+that the particles cannot be seen without the aid of a strong magnifying
+glass.
+
+Observers have assumed that the whole explanation of the fantastic shapes
+taken by clouds is founded on the process of formation; but Dr. Aitken has
+pointed out that ripple-marked clouds, for instance, have been clouds of
+decay. When what is called a cirro-stratus cloud--mackerel-like against
+the blue sky--is carefully observed in fine weather, it will be found that
+it frequently changes the ripple-marked cirrus in the process of decay to
+vanishing. Where the cloud is thin enough to be broken through by the
+clear air that is drawn in between the eddies, the ripple markings get
+nearer and nearer the centre, as the cloud decays. And, at last, when
+nearly dissolved, these markings are extended quite across the cloud.
+
+Whether, then, we consider the cases of clouds gradually melting away back
+into their original state of blue water-vapour, or the constant fine
+raining from clouds and re-formation by evaporation, or the transformation
+of such clouds as the cirro-stratus into the ripple-marked cirrus, we are
+forced to the conclusion that in clouds there is not always development,
+but sometimes degeneration; not always formation, but sometimes decay.
+
+
+
+
+CHAPTER XI
+
+IT ALWAYS RAINS
+
+
+All are familiar with the answer given by the native of Skye to the irate
+tourist on that island, who, for the sixth day drenched, asked the
+question: "Does it always rain here?" "Na!" answered the workman, without
+at all understanding the joke; "feiles it snaas" (sometimes it snows).
+Yet, strange to say, the tourist's question has been answered in the
+affirmative in every place where a cloud is overhead, visible or
+invisible.
+
+Whenever a cloud is formed, it begins to rain; and the drops shower down
+in immense numbers, though most minute in size--"the playful fancies of
+the mighty sky."
+
+No doubt it is only in certain circumstances that these drops are
+attracted together so as to form large drops, which fall to the earth in
+genial showers to refresh the thirsty soil, or in a terrible deluge to
+cause great destruction. But when the temperature and pressure are not
+suitable for the formation of what we commonly know as the rain, the fine
+drops fall into the air under the cloud, where they immediately evaporate
+from their dust free-surfaces, if the air is dry and warm. This is, in
+other words, the decay of clouds.
+
+It is a curious fact that objects in a fog may not be wetted, when the
+number of water-particles is great. It seems that these water-particles
+all evaporate so quickly that even one's hand or face is not sensible of
+being wetted. The particles are minutely small; and they may evaporate
+even before reaching the warm skin, by reason of the heated air over the
+skin.
+
+There is a peculiarly warm sensation in the centre of a cumulus cloud,
+especially when it is not dense. A glow of heat seems to radiate from all
+points. Yet the face and hands are quite dry, and exposed objects are not
+wetted; but it is really _always raining_. That is a curious discovery.
+
+It is radiant heat that is the cause of the remarkable result. The rays of
+the sun, which strike the upper part of the cloud, not only heat that
+surface but also penetrate the cloud and fall on the surface of bodies
+within, generating heat there. These heated surfaces again radiate heat
+into the air attached to them. This warm air receives the fine raindrops
+in the cloud, and dissolves the moisture from the dust-particles before
+the moisture can reach the surfaces exposed. That a vast amount of radiant
+heat rushes through a cloud is clearly shown by exposing a thermometer
+with black bulb _in vacuo_. On some occasions, a thermometer would
+indicate from 40° to 50° above the temperature of the air, thus proving
+the surface to be quite dry.
+
+These observations have been corroborated on Mount Pilatus, near
+Lucerne--1000 feet higher and more isolated than the Rigi. The summit was
+quite enveloped in cloud, and, though one might naturally conclude that
+the air was dense with moisture, yet the wooden seats, walls, and all
+exposed surfaces were quite dry. Strange to say, however, the thermometers
+hung up got wet rapidly, and the pins driven into the wooden post to
+support them rapidly became moist. A thermometer lying on a wooden seat
+stood at 60°, while one hung up read only 48°. This difference was caused
+by radiant heat.
+
+It is well known that, when bodies are exposed to radiant heat, they are
+heated in proportion to their size; the smaller, then, may be moist, when
+the larger are dry by radiation. The effect of the sun's penetrating heat
+through the cloud is to heat exposed objects above the temperature of the
+air; and if the objects are of any size they are considerably heated, and
+retain their heat more, while at the same time around them is a layer of
+warm air which is quite sufficient to force the water-vapour to leave the
+dust-particles in the fine rain.
+
+Hence seats, walls, posts, &c., are quite dry, though they are in the
+middle of a cloud. They are large enough to throw off the moisture by the
+retained heat, or by the large amount of surrounding heat; whereas, small
+bodies, which are not heated to the same degree and cannot therefore
+retain their heat so easily, have not heat-power sufficient to withstand
+the moisture, and they become wetted. Hence, by the radiant heat, the
+large exposed objects are dry in the cloud; whereas small objects are
+damp, and, in some cases, dripping with wet.
+
+The fact is, then, that whenever a cloud overhangs, _rain is falling_,
+though it may not reach the earth on account of the dryness of the stratum
+of air below the cloud, and the heat of the air over the earth. So that on
+a summer day, with the gold-fringed, fleecy clouds sailing overhead, it is
+really raining; but the drops, being very small, evaporate long before
+reaching the earth. As Ariel sings at the end of "The Tempest" of
+Shakespeare, "The rain, it raineth every day." It rains, but much of the
+melting of the clouds is reproduced by a wonderful circularity--the
+moisture evaporating, seizing other dust-particles, forming
+cloud-particles, falling again, and so on _ad infinitum_, during the
+existing circumstances.
+
+
+
+
+CHAPTER XII
+
+HAZE
+
+
+What is haze? The dictionary says, "a fog." Well, haze is _not_ a fog. In
+a fog, the dust-particles in the air have been fully clothed with
+water-vapour; in a haze, the process of condensation has been arrested.
+
+Cloudy condensation is changed to haze by the reduction of its humidity.
+Dr. Aitken invented a simple apparatus for testing the condensing power of
+dust, and observing if water-vapour condensed on the deposited dust in
+unsaturated air.
+
+The dust from the air has first to be collected. This is done by placing a
+glass plate vertically, and in close contact with one of the panes of
+glass in the window, by means of a little india-rubber solution. The plate
+being thus rendered colder than the air in the room, the dust is deposited
+on it.
+
+Construct a rectangular box, with a square bottom, 1-1/2 inches a side and
+3/4 inch deep, and open at the top. Cover the top edge of the box with a
+thickness of india-rubber. Place the dusty plate--a square glass mirror, 4
+inches a side--on the top of the india-rubber, and hold it down by spring
+catches, so as to make the box water-tight. The box has been provided with
+two pipes, one for taking in water and the other for taking away the
+overflow, with the bulb of a thermometer in the centre. Clean the dust
+carefully off one half of the mirror, so that one half of the glass
+covering the box is clean and the other half dusty. Pour cold water
+through the pipe into the box, so as to lower the temperature of the
+mirror, and carefully observe when condensation begins on the clean part
+and on the dusty part, taking a note of the difference of temperature. The
+condensation of the water-vapour will appear on the dust-particles before
+coming down to the natural dew-point temperature of the clean glass. And
+the difference between the two temperatures indicates the temperature
+above the dew-point at which the dust has condensed the water-vapour.
+
+Magnesia dust has small affinity for water-vapour; accordingly, it
+condenses at almost exactly the same temperature as the glass. But
+gunpowder has great condensing power. All have noticed that the smoke
+from exploded gunpowder is far more dense in damp than in dry weather. In
+the experiment it will be found that the dust from gunpowder smoke begins
+to show signs of condensing the vapour at a temperature of 9° Fahr. above
+the dew-point. In the case of sodium dust, the vapour is condensed from
+the air at a temperature of 30° above the dew-point.
+
+Dust collected in a smoking-room shows a decidedly greater condensing
+power than that from the outer air.
+
+We can now understand why the glass in picture frames and other places
+sometimes appears damp when the air is not saturated. When in winter the
+windows are not often cleaned, a damp deposit may be frequently seen on
+the glass. Any one can try the experiment. Clean one half of a dusty pane
+of glass in cold weather, and the clean part will remain undewed and
+clear, while the dusty part is damp to the eye and greasy to the touch.
+
+These observations indicate that moisture is deposited on the
+dust-particles from air, which is not saturated, and that the condensation
+takes place while the air is comparatively dry, _before_ the temperature
+is lowered to the dew-point. There is, then, no definite demarcation
+between what seems to us clear air and thick haze. The clearest air has
+some haze, and, as the humidity increases, the thickness of the air
+increases.
+
+In all haze the temperature is above the dew-point. The dust-particles
+have only condensed a very small amount of the moisture so as to form
+haze, before the fuller condensation takes place at the dew-point.
+
+At the Italian lakes, on many occasions when the air is damp and still,
+every stage of condensation may be observed in close proximity, not
+separated by a hard and fast line, but when no one could determine where
+the clear air ended and the cloud began. Sometimes in the sky overhead a
+gradual change can be observed from perfect clearness to thick air, and
+then the cloud.
+
+A thick haze may be occasioned by an increased number of dust-particles
+with little moisture, or of a diminished number of dust-particles with
+much moisture, above the point of saturation. The haze is cleared by this
+temperature rising, so as to allow the moisture to evaporate from the
+dust-particles.
+
+Whenever the air is dry and hazy, much dust is found in it; as the dust
+decreases the haze also decreases. For example, Dr. Aitken, at
+Kingairloch, in one of the clearest districts of Argyleshire, on a clear
+July afternoon, counted 4000 dust-particles in a cubic inch of the air;
+whereas, two days before, in thick haze, he counted no fewer than 64,000
+in the cubic inch. At Dumfries the number counted on a very hazy day in
+October increased twenty-fold over the number counted the day before, when
+it was clear.
+
+All know that thick haze is usual in very sultry weather. The wavy,
+will-o'-the-wisp ripples near the horizon indicate its presence very
+plainly. During the intense heat there is generally much dust in the
+atmosphere; this dust, by the high temperature, attracts moisture from the
+apparently dry air, though above the saturation point. In all
+circumstances, then, the haze can be accounted for by the condensing power
+of the dust-particles in the atmosphere, at a higher temperature than that
+required for the formation of fogs, or mists, or rain.
+
+
+
+
+CHAPTER XIII
+
+HAZING EFFECTS OF ATMOSPHERIC DUST
+
+
+The transparency of the atmosphere is very much destroyed by the
+impurities communicated to it while passing over the inhabited areas of
+the country. Dr. Aitken devoted eighteen months to compare the amount of
+dusty impurities in different masses of air, or of different airs brought
+in by winds from different directions.
+
+He took Falkirk for his centre of observations. This town lies a little to
+the north of a line drawn between Edinburgh and Glasgow, and is nearly
+midway between them. If we draw a line due west from it, and another due
+north, we find that, in the north-west quadrant so enclosed, the
+population of that part of Scotland is extremely thin, the country over
+that area being chiefly mountainous. In all other directions, the
+conditions are quite different. In the north-east quadrant are the fairly
+well-populated areas of Aberdeenshire, Forfarshire, and the thickly
+populated county of Fife. In the south-east quadrant are situated
+Edinburgh and the well-populated districts of the south-east of Scotland.
+And in the south-west quadrant are Glasgow and the large manufacturing
+towns which surround it. The winds from three of these quadrants bring air
+polluted in its passage over populated areas, whereas the winds from the
+north-west come comparatively pure.
+
+The general plan of estimating the amount of haze is to note the most
+distant hill that can be seen through the haze. The distance in miles of
+the farthest away hill visible is then called "the limit of visibility" of
+the air at the time. For the observations made at Falkirk, only three
+hills are available, one about four miles distant, the Ochils about
+fifteen miles distant, and Ben Ledi about twenty-five miles distant--all
+in the north-west quadrant. When the air is thick, only the near hill can
+be seen; then the Ochils become visible as the air clears; and at last Ben
+Ledi is seen, when the haze becomes still less. After Ben Ledi is visible,
+it then becomes necessary to estimate the amount of haze on it, in order
+to get the limit of visibility of the air at the time. Thus, if Ben Ledi
+be half-hazed, then the limit of visibility will be fifty miles. In this
+way all the estimates of haze have been reduced to one scale for
+comparison.
+
+As the result of all the observations it was found that, as the dryness of
+the air increases, the limit of visibility also increases. A very marked
+difference in the transparency of the air was found with winds from the
+different directions. In the north-west quadrant the winds made the air
+very clear, whereas winds from all other directions made the air very much
+hazed. The winds in the other three areas are nearly ten times more hazed
+than those from the north-west quadrant. That is very striking.
+
+The conclusion come to is that the air from densely inhabited districts is
+so polluted that it is fully nine times more hazed than the air that comes
+from the thinly inhabited districts; in other words, the atmosphere at
+Falkirk is about ten times thicker when the wind is east or south than it
+would be if there were no fires and no inhabitants.
+
+It is interesting to notice that the limit varies considerably for the
+same wind at the same humidity. This is what might have been expected,
+because from the observations made by the dust-counter the number of
+particles varied greatly in winds from the same directions, but at
+different times. This depends upon the rise and fall of the wind, changes
+in the state of trade, season of the year, and other causes. During a
+strike, the dearth of coal will make a considerable diminution in the
+number of dust-particles in the air of large towns. With a north wind, the
+extreme limits of visibility are 120 to 200 miles; and with a north-west
+wind, from 70 to 250 miles. An east wind has as limits 4 to 50 miles, and
+a south-east wind 2 to 60 miles.
+
+One interesting fact to be noticed, after wading through these tables, is
+this--that, as a general result, the transparency of the air increases
+about 3·7 times for any increase in dryness from 2° to 8° of wet-bulb
+depression. That is, the clearness of the air is inversely proportional to
+the relative humidity; or, put another way, if the air is four times drier
+it is about four times clearer.
+
+
+
+
+CHAPTER XIV
+
+THUNDER CLEARS THE AIR
+
+
+The phrase "thunder clears the air" is familiar to all. It contains a very
+vital truth, yet even scientific men did not know its full meaning until
+just the other day. It came by experience to people who had been for ages
+observing the weather; and it is one of the most pointed of the
+"weather-lore" expressions. Folks got to know, by a sort of rule-of-thumb,
+truths which scientifically they were unable to learn. And this is one.
+
+Perhaps, therefore, we should respect a little more what is called
+"folk-lore," or ordinary people's sayings. Experience has taught men many
+wonderful things. In olden times they were keener natural observers. They
+had few books, but they had plenty of time. They studied the habits of
+animals and moods of nature, and they came wonderfully near to reaching
+the full truth, though they could not give a reason for it. The
+awe-inspiring in nature has especially riveted the attention of man.
+
+And no appearance in nature joins more powerfully the elements of grandeur
+and awe than a heavy thunder-storm. When, suddenly, from the breast of a
+dark thunder-cloud a brilliant flash of light darts zigzag to the earth,
+followed by a loud crackling noise which softens in the distance into
+weaker volumes of sound, terror seizes the birds of the air and the cattle
+in the field. The man who is born to rule the storm rejoices in the
+powerful display; but kings have trembled at the sight.
+
+Byron thus pictures a storm in the Alps:--
+
+                              "Far along
+    From peak to peak, the rattling crags among
+  Leaps the live thunder! Not from one lone cloud,
+    But every mountain now hath found a tongue,
+  And Jura answers, through her misty shroud,
+  Back to the joyous Alps, who call to her aloud!"
+
+Franklin found that lightning is just a kind of electricity. No one can
+tell how it is produced; yet a flash has been photographed. When the flash
+is from one cloud to another there is sheet-lightning, which is beautiful
+but not dangerous; but, when the electricity passes from a cloud to the
+earth in a forked form, it is very dangerous indeed. The flash is
+instantaneous, but the sound of the thunder takes some time to travel.
+Roughly speaking, the sound takes five seconds or six beats of the pulse
+to the mile.
+
+All are now taught at school that it is the oxygen in the air which is
+necessary to keep us in life. If mice are put into a glass jar of pure
+oxygen gas, they will at once dance with exhilarating joy. It occurred to
+Sir Benjamin Richardson, some time ago, that it would be interesting to
+continue some experiments with animals and oxygen. He put a number of mice
+into a jar of pure oxygen for a time; they breathed in the gas, and
+breathed out water-vapour and carbonic acid. After the mice had continued
+this for some time, he removed them by an arrangement. By chemical means
+he removed the water-vapour and carbonic acid from the mixed air in the
+vessel. When a blown-out taper was inserted, it at once burst into flame,
+showing that the remaining gas was oxygen.
+
+Again, the mice were put into this vessel to breathe away. But, strange to
+say, the animals soon became drowsy; the smartness of the oxygen was gone.
+At last they died; there was nothing in the gas to keep them in life; yet,
+by the ordinary chemical tests, it was still oxygen. It had repeatedly
+passed through the lungs of the mice, and during this passage there had
+been an action in the air-cells which absorbed the life-giving element of
+the gas. It is oxygen, so far as chemistry is concerned, but it has no
+life-giving power. It has been _devitalised_.
+
+But the startling discovery still remains. Sir Benjamin had previously
+fitted up the vessel with two short wires, opposite each other in the
+sides--part outside and part inside. Two wires are fastened to the outside
+knobs. These wires are attached to an electric machine, and a flash of
+electricity is made to pass between the inner points of the vessel. The
+wires are again removed; nothing strange is seen in the vessel. But, when
+living mice are put into the vessel, they dance as joyfully as if pure
+oxygen were in it. The oxygen in which the first mice died has now been
+quite refreshed by the electricity. The bad air has been cleared and made
+life-supporting by the electric discharge. It has been again vitalised.
+
+Now, to apply this: before a thunder-storm, everything has been so still
+for days that the oxygen in the air has been to some extent robbed of its
+life-sustaining power. The air feels "close," a feeling of drowsiness
+comes over all. But, after the air has been pierced by several flashes of
+lightning, the life-force in the air is restored. Your spirits revive; you
+feel restored; your breathing is far freer; your drowsiness is gone. Then
+there is a burst of heavenly music from the exhilarated birds. Thus a
+thunder-storm "clears the air."
+
+After the passage of lightning through the air ozone is produced--the gas
+that is produced after a flash of electricity. It is a kind of oxygen,
+with fine exciting effects on the body. If, then, the life-sustaining
+power of oxygen depends on a trace of ozone, and this is being made by
+lightning's work, how pleased should we be at the occasional
+thunder-storm!
+
+
+
+
+CHAPTER XV
+
+DISEASE-GERMS IN THE AIR
+
+
+The gay motes that dance in the sunbeams are not all harmless. All are
+annoying to the tidy housekeeper; but some are dangerous. There are living
+particles that float in the air as the messengers of disease and death.
+Some, falling on fresh wounds, find there a suitable feeding-place; and,
+if not destroyed, generate the deadly influence. Others are drawn in with
+the breath; and, unless the lungs can withstand them, they seize hold and
+spread some sickness or disease. From stagnant pools, common sewers, and
+filthy rooms, disease-germs are constantly contaminating the air. Yet
+these can be counted.
+
+The simplest method is that of Professor Frankland. It depends on this
+principle: a certain quantity of air is drawn through some cotton-wool;
+this wool seizes the organisms as the air passes through; these organisms
+are afterwards allowed to feed upon a suitable nutritive medium until they
+reach maturity; they are then counted easily.
+
+About an inch from each end of a glass tube (5 inches long and 1 inch
+bore), the glass is pressed in during the process of blowing. Some
+cotton-wool is squeezed in to form a plug at the farther constricted part
+of the glass. The important plug is now inserted at the same open end, but
+is not allowed to go beyond the constricted part at its end. A piece of
+long lead tubing is attached to the former end by an india-rubber tube.
+The other end of the lead tubing is connected with an exhausting syringe.
+Sixty strokes of the 18 cubic inches syringe will draw 1080 cubic inches
+of the air to be examined through the plugs, the first retaining the
+organisms.
+
+The impregnated plug is then put into a flask containing in solution some
+gelatine-peptone. The flask is made to revolve horizontally until an
+almost perfectly even film of gelatine and the organisms from the
+broken-up plug cover its inner surface.
+
+The flask is allowed to remain for an hour in a cool place, and is then
+placed under a bell-jar, at a temperature of 70° Fahr. There it remains,
+to allow the germs to incubate, for four or five days. The surface of the
+flask having been previously divided into equal parts by ink lines, the
+counting is now commenced. If the average be taken for each segment, the
+number of the whole is easily ascertained. A simple arithmetical
+calculation then determines the number of organisms in a cubic foot, since
+the number is known for the 1080 cubic inches. That is the process for
+determining the number of living organisms in a fixed quantity of air.
+
+No less than thirty colonies of organisms were counted in a cubic foot of
+air taken from the Golden Gallery of St. Paul's Cathedral, London, and 140
+from the air of the churchyard. An ordinary man would breathe there
+thirty-six micro-organisms every minute.
+
+Electricity has a powerful effect in destroying these organisms. Ozone is
+generated in the air by lightning, and it is detrimental to them. In fine
+ozoned Highland air scarcely a disease-germ can be detected. Open sea air
+contains about one germ in two cubic feet. It has been found that in Paris
+the average in summer is about 140 per cubic foot of air, but in bedrooms
+the number is double. During the twenty-four hours of the day the number
+of germs is highest about 6 A.M., and lowest about mid-day.
+
+Raindrops carry the germs to the ground. Hence the advantage of a thunder
+plout in a sanitary way. A cubic foot of rain has been found to contain
+5500 organic dust-germs, besides 7,000,000,000 of inorganic
+dust-particles. In a dirty town the rain will bring down in a year, upon a
+square foot of surface, no less than 3,000,000 of bacteria, many of them
+being disease-bearing and death-bearing. No wonder, then, that scientific
+men are using every endeavour to protect the human frame, as well as the
+frame of the lower animals, from the baneful inroads of these floating
+nuclei of disease and death.
+
+
+
+
+CHAPTER XVI
+
+A CHANGE OF AIR
+
+
+For weakness of body and fatigue of mind a very common and essentially
+serviceable recommendation is "a change of air." Of course, the change of
+scene from coast to country, or from town to hillside, may help much the
+depressed in body or mind; and this is very commendable. But, strange to
+say, there is a healing virtue in breathing different air.
+
+At first one is apt to think that air is the same all over, as he thinks
+water is--especially outside smoky towns; but both have varied qualities
+in different parts. You have only to be assured that in a cubic inch of
+bedroom air in the denser parts of a large town there are about 20,000,000
+of dust-particles, and in the open air of a heathery mountain-side there
+are only some hundreds, to see that there is something after all on the
+face of it in the "old wives' saw."
+
+Not that the dust-particles are all injurious; for most of them are
+inorganic, and many of the organic particles are quite wholesome; yet
+there is a change wrought, often very marked, in going from one place to
+another for different air.
+
+Even in the country, especially in summer-time, one distinctly notices the
+great difference in the air of lowland and highland localities. The ten
+miles change from Strathmore to Glenisla shows a marked difference in the
+air. Below, it is close, weakening, enervating; above, it is exhilarating,
+invigorating, and strong.
+
+So people must have a change--at least those who can afford it--for health
+must be seen to first of all, if one has means to do so. Oh! the blessing
+of good health! How many who enjoy it never think of the misery of its
+loss! In fact, health is the soul that animates all enjoyments of life;
+for without it those would soon be tasteless. A man starves at the
+best-spread table, and is poor in the midst of the greatest treasures
+without health.
+
+In these days half of our diseases come from the neglect of the body in
+the overwork of the brain. The wear and tear of labour and intellect go on
+without pause or self-pity. Men may live as long as their forefathers, but
+they suffer more from a thousand artificial anxieties and cares. The men
+of old fatigued only the muscles, we exhaust the finer strength of the
+nerves. Even more so now, then, do we require a change of air to soothe
+our overwrought nervous system.
+
+And when that magic power, concealed from mortal view, works such wonders
+on the health, surely it is one's duty to save up and have it, when it is
+within one's means. For is not health the greatest of all possessions?
+What a rich colour clothes the countenance of the young after a month's
+outing in the hill country! How fine and pure has the blood become! All
+stagnant humours, accumulated in winter town life, have been dispelled by
+the ozone-brightening charm. The weary looking office or shop man is now
+transfigured into a sprightly youth once more, ready with strongly
+recuperated power for another winter's labours. The pale wife, who has
+been stifled for months in close-aired rooms, has now a healthy flush on
+her becoming countenance that speaks of gladly restored health. And all
+this has been brought about by a "change of air"!
+
+For a thorough change to a town man, he should make for the Highlands.
+There he is never tired of walking, for the air which he breathes is full
+of ozone. This revivifying element in the air is produced by the
+lightning-bursts from hill to hill. There is in the Highlands a continual
+rush of electricity, whether seen or not. Hence the air is very pure, free
+from organic germs, intensely exhilarating and buoyant.
+
+Sportsmen are livingly aware of the recuperative power of the Highland
+air. Perhaps these city men do not benefit so much by the easy walking
+exercise on the grouse moors as in breathing the splendidly
+delight-inspiring air. What a change one feels there in a very few hours!
+
+"A change of air" is an old wives' adage. But much of the weather-lore of
+our forefathers was based on real scientific principles only now coming to
+light. Nature is ever true, but it requires patience to unravel her
+secrets. We therefore advocate an occasional "change of air" to improve
+the health--
+
+                        "The chiefest good,
+  Bestow'd by Heaven, but seldom understood."
+
+
+
+
+CHAPTER XVII
+
+THE OLD MOON IN THE NEW MOON'S ARMS
+
+
+After the sun's broad beams have tired the sight, the moon with more sober
+light charms us to descry her beauty, as she shines sublimely in her
+virgin modesty. There is always a most fascinating freshness in the first
+sight of the new moon. The superstition of centuries adds to this charm.
+Why boys and girls like to turn over a coin in their pocket at this sight
+one cannot tell: yet it is done. No young lady likes to look at the new
+moon through a pane of glass. And farmers are always confident of a change
+of weather with a new moon: at least in bad weather they earnestly hope
+for it.
+
+But, banishing all superstition, we welcome the pale silver sickle in the
+heavens, once more appearing from the bosom of the azure. And no language
+can equal these beautiful words of the youthful Shelley:--
+
+                    "Like the young moon,
+  When on the sunlit limits of the night
+    Her white shell trembles amid crimson air,
+  And while the sleeping tempest gathers might,
+    Doth, as the herald of his coming, bear
+  The ghost of its dead mother, whose dim form
+    Bends in dark ether from her infant's chair."
+
+That is a more charming way of putting the ordinary expression, "the old
+moon in the new moon's arms." We are regularly accustomed to the
+moonshine, but only occasionally is the _earthshine_ on the moon so
+regulated that the shadowed part is visible. This is not seen at the
+appearance of every new moon. It depends upon the positions of the sun and
+moon, the state of the atmosphere, and the absence of heavy clouds. I
+never in my life saw the phenomenon so marvellously beautiful as on May
+7th, 1894, at my manse in Strathmore. I took particular note of it, as
+some exceedingly curious things were connected with it.
+
+At nine o'clock in the evening, the new moon issued from some clouds in
+the western heavens, the sun having set, about an hour before. The
+crescent was thin and silvery, and the outline of the shadowed part was
+just visible. The sky near the horizon was clear and greenish-hued. As
+the night advanced the moon descended, and at ten o'clock she was
+approaching a purple stratum of clouds that stretched over the hills,
+while the position of the sun was only known a little to the east, by the
+back-thrown light upon the dim sky. Through the moisture-laden air the
+sun's rays, reflected by the moon, threw a golden stream from the crescent
+moon, for the silvery shell became more golden-hued.
+
+The horns of the moon now seemed to project, and the shadowed part became
+more distinct, though the circle appeared smaller. By means of a
+field-glass I noticed that this was extra lighted, with points here and
+there quite golden-tinged. The darker spots showed the deep caverns; the
+brighter points brought into relief the mountain peaks.
+
+Why was the surface brighter than usual? I cannot go into detail about the
+phases of the moon; but, in a word, I may say that, while the sun can
+illuminate the side of the moon turned towards it, it is unable to throw
+any light on the shadow, seeing that there is no atmosphere around the
+moon to refract the light.
+
+If we, in imagination, looked from the moon upon the earth, we should see
+the same phases as are now noticed in the moon; and when it is just before
+new moon on the earth, the earth will appear fully illuminated from the
+moon. We would also observe (from the moon) that the brightness of the
+illuminated part of the earth would vary from time to time, according to
+the changes in the earth's atmosphere. More light would be reflected to
+the moon from the clouds in our atmosphere than from the bare earth or
+cloudless sea, since clouds reflect more light than either land or sea.
+Accordingly, we arrive at this curious fact--that the extra brightness of
+the _dark_ body of the moon is mainly determined by the amount of _cloud
+in our atmosphere_.
+
+Accordingly, I concluded that there must be clouds to the west, though I
+could not see them, which reflected rays of light and faintly illuminated
+the shadowed part of the moon. It had become much colder, and I concluded
+that during the night the cloud-particles, if driven near by the wind,
+would condense into rain. And, assuredly, next morning I was gratified to
+find that rain had fallen in large quantities, substantiating the theory.
+
+There is much pleasure in verifying such an interesting problem. The dark
+body of the moon being more than usually visible is one of our well-known
+and oldest indications of coming bad weather. And at once came to my
+memory the lines of Sir Patrick Spens, as he foreboded rain for his
+crossing the North Sea:--
+
+  "I saw the new moon late yestreen
+  Wi' the auld moon in her arm;
+  And if we gang to sea, master,
+  I fear we'll come to harm."
+
+This lunar indication, then, has a sound physical basis, showing that near
+the observer there are vast areas of clouds, which are reflecting light
+upon the moon at the time, before they condense into rain by the chilling
+of the air. According to the old Greek poet, Aratus: "If the new moon is
+ruddy, and you can trace the shadow of the complete circle, a storm is
+approaching."
+
+
+
+
+CHAPTER XVIII
+
+AN AUTUMN AFTERGLOW
+
+
+A brilliant afterglow is welcomed for its surpassing beauty and a
+precursor of fine fixed weather.
+
+A glorious sunset has always had a charm for the lover of nature's
+beauties. The zenith spreads its canopy of sapphire, and not a breath
+creeps through the rosy air. A magnificent array of clouds of numberless
+shapes come smartly into view. Some, far off, are voyaging their
+sun-bright paths in silvery folds; others float in golden groups. Some
+masses are embroidered with burning crimson; others are like "islands all
+lovely in an emerald sea." Over the glowing sky are splendid colourings.
+The flood of rosy light looks as if a great conflagration were below the
+horizon.
+
+I remember witnessing an especially brilliant sunset last autumn on the
+high-road between Kirriemuir and Blairgowrie. The setting sun shone upon
+the back of certain long trailing clouds which were much nearer me than a
+range behind. The fringes of the front range were brilliantly golden,
+while the face of those behind was sparklingly bright. Then the sun
+disappeared over the western hills, and his place was full of spokes of
+living light.
+
+Looking eastward, I observed on the horizon the base of the northern line
+of a beautiful rainbow--"the shepherd's delight" for fine weather.
+
+Soon in the west the light faded; but there came out of the east a lovely
+flush, and the general sky was presently flamboyant with afterglow. The
+front set of clouds was darker except on the edges, the red being on the
+clouds behind; and the horizon in the east was particularly rich with dark
+red hues.
+
+Gradually the eastern glow rose and reddened all the clouds, but the front
+clouds were still grey. The effect was very fine in contrast. The fleecy
+clouds overhead became transparently light red, as they stretched over to
+reach the silver-streaked west. The new moon was just appearing upright
+against a slightly less bright opening in the sky, betokening the firm
+hardness of autumn.
+
+Soon the colouring melted away, and the peaceful reign of the later
+twilight possessed the land.
+
+Now why that brilliancy of the east, when the west was colourless? Most of
+all you note the immense variety and wealth of reds. These are due to dust
+in the atmosphere. We are the more convinced of this by the very
+remarkable and beautiful sunsets which occurred after the tremendous
+eruption at Krakatoa, in the Straits of Sunda, thirty years ago. There was
+then ejected an enormous quantity of fine dust, which spread over the
+whole world's atmosphere. So long as that vast amount of dust remained in
+the air did the sunsets and afterglows display an exceptional wealth of
+colouring. All observers were struck with the vividly brilliant red
+colours in all shades and tints.
+
+The minute particles of dust in the atmosphere arrest the sun's rays and
+scatter them in all directions; they are so small, however, that they
+cannot reflect and scatter all; their power is limited to the scattering
+of the rays at the blue end of the spectrum, while the red rays pass on
+unarrested. The display of the colours of the blue end are found in
+numberless shades, from the full deep blue in the zenith to the
+greenish-blue near the horizon.
+
+If there were no fine dust-particles in the upper strata, the sunset
+effect would be whiter; if there were no large dust-particles, there would
+be no colouring at all. If there were no dust-particles in the air at all,
+the light would simply pass through into space without revealing itself,
+and the moment the sun disappeared there would be total darkness. The very
+existence of our twilight depends on the dust in the air; and its length
+depends on the amount and extension upwards of the dust-particles.
+
+But how have the particles been increased in size in the east? Because, as
+the sun was sinking, but before its rays failed to illumine the heavens,
+the temperature of the air began to fall. This cooling made the
+dust-particles seize the water-vapour to form haze-particles of a larger
+size. The particles in the east first lose the sun's heat, and first
+become cool; and the rays of light are then best sifted, producing a more
+distinct and darker red. As the sun dipped lower, the particles overhead
+became a turn larger, and thereby better reflected the red rays.
+Accordingly, the roseate bands in the east spread over to the zenith, and
+passed over to the west, producing in a few minutes a universal
+transformation glow.
+
+To produce the full effect often witnessed, there must be, besides the
+ordinary dust-particles, small crystals floating in the air, which
+increase the reflection from their surfaces and enhance the glow effects.
+In autumn, after sunset, the water-covered dust-particles become frozen
+and the red light streams with rare brilliancy, causing all reddish and
+coloured objects to glow with a rare brightness. Then the air glows with a
+strange light as of the northern dawn. From all this it is clear that,
+though the colouring of sunset is produced by the direct rays of the sun,
+the afterglow is produced by reflection, or, rather, radiation from the
+illuminated particles near the horizon.
+
+The effect in autumn is a stream of red light, of varied tones, and rare
+brilliancy in all quarters, unseen during the warmer summer. We have to
+witness the sunsets at Ballachulish to be assured that Waller Paton really
+imitated nature in the characteristic bronze tints of his richly painted
+landscapes.
+
+
+
+
+CHAPTER XIX
+
+A WINTER FOREGLOW
+
+
+Little attention has been paid to foreglows compared with afterglows,
+either with regard to their natural beauty or their weather forecasting.
+But either the ordinary red-cloud surroundings at sunrise, or the western
+foreglow at rarer intervals, betokens to the weather-prophet wet and
+gloomy weather. The farmer and the sailor do not like the sight, they
+depend so much on favourable weather conditions.
+
+Of course, sunrise to the æsthetic observer has always its charms. The
+powerful king of day rejoices "as a bridegroom coming out of his chamber"
+as he steps upon the earth over the dewy mountain tops, bathing all in
+light, and spreading gladness and deep joy before him. The lessening
+cloud, the kindling azure, and the mountain's brow illumined with golden
+streaks, mark his approach; he is encompassed with bright beams, as he
+throws his unutterable love upon the clouds, "the beauteous robes of
+heaven." Aslant the dew-bright earth and coloured air he looks in
+boundless majesty abroad, touching the green leaves all a-tremble with
+gold light.
+
+But glorious, and educating, and inspiring as is the sunrise in itself in
+many cases, there is occasionally something very remarkable that is
+connected with it. Rare is it, but how charming when witnessed, though
+till very recently it was all but unexplained. This is the _foreglow_.
+
+It is in no respect so splendid as the afterglow succeeding sunset; but,
+because of its comparative rarity, its beauty is enhanced. I remember a
+foreglow most vividly which was seen at my manse, in Strathmore, in
+January 1893. My bedroom window looked due west; I slept with the blind
+up. On that morning I was struck, just after the darkness was fading away,
+with a slight colouring all along the western horizon. The skeleton
+branches of the trees stood out strongly against it. The colouring
+gradually increased, and the roseate hue stretched higher. The old
+well-known faces that I used to conjure up out of the thin blended boughs
+became more life-like, as the cheeks flushed. There was rare warmth on a
+winter morning to cheer a half-despairing soul, tired out with the long
+hours of oil reading, and pierced to the heart by the never-ceasing
+rimes; yet I could not understand it.
+
+I went to the room opposite to watch the sunrise, for I had observed in
+the diary that the appearance of the sun would not be for a few minutes.
+There were streaks of light in the east above the horizon, but no colour
+was visible. That hectic flush--slight, yet well marked--which was
+deepening in the western heavens, had no counterpart in the east, except
+the colourless light which marked the wintry sun's near approach. As soon
+as the sun's rays shot up into the eastern clouds, and his orb appeared
+above the horizon, the western sky paled, the colour left it, as if
+ashamed of its assumed glory. A foreglow like that I have very rarely
+seen, and its existence was a puzzle to me till I studied Dr. Aitken's
+explanation of the afterglows after sunset. I had never come across any
+description of a foreglow; and, of course, across no explanation of the
+curious phenomenon. The western heavens were coloured with fairly bright
+roseate hues, while the eastern horizon was only silvery bright before the
+sun rose; whereas, after the sun appeared and coloured the eastern hills
+and clouds, the western sky resumed its leaden grey and colourless
+appearance. Why was that? What is the explanation?
+
+I have not space enough to repeat the explanation given already in the
+last chapter of the glorious phenomenon of the afterglow. But the
+explanation is similar. Before sunrise, the rays of the sun are reflected
+by dust-particles in the zenith to the western clouds. The colouring is
+intensified by the frozen water-vapour on these particles in the west.
+
+One thing I carefully noted. Ere mid-day, snow began to fall, and for some
+days a severe snow-storm kept us indoors. Then, at any rate, the foreglow
+betokened a coming storm. It was, like a rainbow in a summer morning, a
+decided warning of the approaching wet weather.
+
+
+
+
+CHAPTER XX
+
+THE RAINBOW
+
+
+The poet Wordsworth rapturously exclaimed--
+
+  "My heart leaps up when I behold
+  A rainbow in the sky."
+
+And old and young have always been enchanted with the beautiful
+phenomenon. How glorious is the parti-coloured girdle which, on an April
+morning or September evening, is cast o'er mountain, tower, and town, or
+even mirrored in the ocean's depths! No colours are so vividly bright as
+when this triumphal arch bespans a dark nimbus: then it unfolds them in
+due prismatic proportion, "running from the red to where the violet fades
+into the sky."
+
+A plain description of the formation of the rainbow is not very easily
+given, but a short sketch may be useful. Beautiful as is the ethereal bow,
+"born of the shower and colour'd by the sun," yet the marvellous effect is
+more exquisitely intensified in its gorgeous display when the hand of
+science points out the path in which the sun's rays, from above the
+western horizon, fall on the watery cloud, indicating fine weather--"the
+shepherd's delight."
+
+One law of reflection is that, when a ray of light falls on a plane or
+spherical surface, it goes off at the same angle to the surface as it
+fell. One law of refraction is that, when a ray of light passes through
+one medium and enters a denser medium (as from air to water), it is bent
+back a little. By refraction you see the sun's rays long after the sun has
+set; when the sun is just below the horizon, an observer, on the surface
+of the earth, will see it raised by an amount which is generally equal to
+its apparent diameter.
+
+The rays of different colours are bent back (when passing through the
+water) at different rates, some slightly, others more, from the red to the
+violet end. The rainbow, then, is produced by refraction and reflection of
+the several coloured rays of sunlight in the drops of water which make up
+falling rain.
+
+The sun is behind the observer, and its rays fall in a parallel direction
+upon the drops of rain before him. In each drop the light is dispersively
+refracted, and then reflected from the farther face of the drop; it
+travels back through the drop, and comes out with dispersing colours.
+
+According to the height of the sun, or the slope of its rays, a higher or
+lower rainbow will be formed. And, strange, no two people can see the very
+same bow; in fact the rainbow, as seen by the one eye, is not formed by
+the same water-drops as the rainbow seen by the other eye.
+
+When the primary bow is seen in most vivid colours on a dark cloud, a
+second arch, larger and fainter, is often seen. But the order of the
+colours is quite reversed. At a greater elevation, the sun's ray enters
+the lower side of a drop of rain-water, is refracted, reflected _twice_,
+and then refracted again before being sent out to the observer's eye. That
+is why the colours are reversed.
+
+_A one-coloured rainbow_ is a curious and rare phenomenon. It is a strange
+paradox, for the very idea of a rainbow brings up the seven colours--red,
+orange, yellow, green, blue, indigo, and violet. Yet Dr. Aitken tells us
+of a rainbow with one colour which he observed on Christmas Day, in 1888.
+
+He was taking his walk on the high ground south of Falkirk. In the east he
+observed a strange pillar-like cloud, lit up with the light of the setting
+sun. Then the red pillar extended, curved over, and formed a perfect arch
+across the north-eastern sky. When fully developed, this rainbow was the
+most extraordinary one which he had ever seen. There was no colour in it
+but red. It consisted simply of a red arch, and even the red had a
+sameness about it.
+
+Outside the rainbow there was part of a secondary bow. The Ochil Hills
+were north of his point of observation. These hills were covered with
+snow, and the setting sun was glowing with rosy light. Never had he seen
+such a depth of colour as was on them on this occasion. It was a deep,
+furnacy red. The sun's light was shorn of all the rays of short-wave
+length on its passage through the atmosphere, and only the red rays
+reached the earth. The reason why the Ochils glowed with so deep a red
+was owing to their being overhung by a dense curtain of clouds, which
+screened off the light of the sky. The illumination was thus principally
+that of the direct softer light of the sun.
+
+
+
+
+CHAPTER XXI
+
+THE AURORA BOREALIS
+
+
+He must be a very careless observer who has not been struck with the
+appearance of the streamers which occasionally light up the northern
+heavens, and which farmers consider to be indicators of strong wind or
+broken weather.
+
+The time was when the phenomenon was considered to be supernatural and
+portentous, as the chroniclers of spectral battles, when "fierce, fiery
+warriors fought upon the clouds, in ranks and squadrons, and right form of
+war." And even in the rural districts of Britain, the blood-coloured
+aurora, of October 24th, 1870, was considered to be the reflection of an
+enormous Prussian bonfire, fed by the beleaguered French capital.
+
+In joyful spirit, the Shetlanders call the beautiful natural phenomenon,
+"Merry Dancers." Burns associated their evanescence with the
+transitoriness of sensuous gratification:--"they flit ere you can point
+their place." And Tennyson spoke of his cousin's face lit up with the
+colour and light of love, "as I have seen the rosy red flushing in the
+northern night."
+
+Yet this phenomenon is to a great extent under the control of cosmical
+laws. One of the most difficult problems of our day has been to
+disentangle the irregular webwork of auroræ, and bring them under a law of
+periodicity, which depends upon the fluctuations of the sun's photosphere
+and the variations on the earth's magnetism, and which have such an
+important influence upon the fluctuations of the weather.
+
+The name "Aurora Borealis" was given to it by Gassendi in 1621.
+Afterwards, the old almanacs described it as the "Great Amazing Light in
+the North." In the Lowlands of Scotland, the name it long went by, of
+"Lord Derwentwater's Lights," was given because it suddenly appeared on
+the night before the execution of the rebel lord. In Ceylon auroræ were
+called "Buddha Lights."
+
+The first symptom of an aurora borealis is commonly a low arch of pale,
+greenish-yellow light, placed at right angles to the magnetic meridian.
+Sometimes rays cover the whole sky, frequently showing tremulous motion
+from end to end; and sometimes they appear to hang from the sky like the
+fringes of a mantle. They are among the most capricious of natural
+phenomena, so full of individualities and vagaries. To the glitter of
+rapid movement they add the charm of vivid colouring. It is strongly
+asserted that auroræ are preceded by the same general phenomena as
+thunder-storms. This was borne out by Piazzi Smith (late Astronomer-Royal
+for Scotland), who observed that their monthly frequency varies inversely
+with that of thunder-storms--both being safety-valves for the discharge of
+surplus electricity.
+
+Careful observers have, moreover, noticed a remarkable coincidence
+between the display of auroræ and the maxima of the sun's spots and of the
+earth's magnetic disturbances. Some have supposed that the light of the
+aurora is caused by clouds of meteoric dust, composed of iron, which is
+ignited by friction with the atmosphere. But there is this difficulty in
+the way, shooting stars are more frequent in the morning, while the
+reverse is the case with the aurora. The highest authorities have
+concluded, pretty uniformly, that auroræ are electric discharges through
+highly rarefied air, taking place in a magnetic field, and under the sway
+of the earth's magnetic induction. They are not inappropriately called
+"Polar lightnings," for when electricity misses the one channel it must
+traverse the other.
+
+The natives of the Arctic regions of North America pretend to foretell
+wind by the rapidity of the motions of the streamers. When they spread
+over the whole sky, in a uniform sheet of light, fine weather ensues.
+Fitzroy believed that auroræ in northern latitudes indicated and
+accompanied stormy weather at a distance. The same idea is still current
+among many farmers and fishermen in Scotland.
+
+Is there any audible accompaniment to the brilliant spectacle? The natives
+of some parts, with subtle hearing-power, speak of the "whizzing" sound
+which is often heard during auroral displays. Burns tells of their
+"hissing, eerie din," as echoes of the far-off songs of the Valkyries.
+Perhaps the most striking incident which corroborates this opinion
+occurred during the Franco-Prussian War. Rolier, a practised aëronaut,
+left Paris in a balloon, on his mission of city defence, and fourteen
+hours afterwards landed in Norway. He had reached the height of two and a
+half miles. When descending, he passed through a peculiar cloud of
+sulphurous odour, which emitted flashed light and a slight scratching or
+rustling noise. On landing, he witnessed a splendid aurora borealis. He
+must, therefore, have passed through a cloud in which an electrical
+discharge of an auroral nature was proceeding, accompanied with an audible
+sound. There is, moreover, no improbability of such sounds being
+occasionally heard, since a somewhat similar phenomenon accompanies the
+brush discharge of the electric machinery, to which the aurora bears
+considerable resemblance.
+
+Though no fixed conclusions are yet established about the causes of the
+brilliant auroral display, yet, as the results of laborious observations,
+we are assured that the stabler centre of our solar system holds in its
+powerful sway the several planets at their respective distances, supplying
+them all with their seasonable light and heat, vibrating sympathetic
+chords in all, and even controlling under certain--though to us still
+unknown--laws the electric streamers that flit, apparently lawlessly, in
+the distant earth's atmosphere.
+
+
+
+
+CHAPTER XXII
+
+THE BLUE SKY
+
+
+If we look at the sky overhead, when cloudless in the sunshine, we wonder
+what gives the air such a deep-blue colour. We are not looking, as
+children seem to do, into vacancy, away into the far unknown. And even, if
+that were the case, would not the space be quite colourless? What, then,
+produces the blueness?
+
+Some of the very fine dust-particles, even when clothed with an
+exceedingly thin coating of water-vapour, are carried very high; and,
+looking through a vast accumulation of these, we find the effect of a
+deep-blue colour.
+
+Why so? Because these particles are so small that they can only reflect
+the rays of the blue end of the spectrum; and the higher we ascend, the
+smaller are the particles and the deeper is the blue. But it is also
+because water, even in its very finest and purest form, is blue in colour.
+For long this was disputed. Even Sir Robert Christison concluded, after
+years of experimenting on Highland streams, that water was colourless.
+
+Of course, he admitted that the water in the Indian and Pacific Oceans has
+frequent patches of red, brown, or white colour, from the myriads of
+animalcules suspended in the water. Ehrenberg found that it was vegetable
+matter which gave to the Red Sea its characteristic name. But these, and
+similar waters, are not pure.
+
+It is to Dr. Aitken that the final discovery of the real colour of water
+is due. When on a visit to several towns on the shores of the
+Mediterranean, he set about making some very interesting experiments,
+which the reader will follow with pleasure.
+
+It is a well-known fact that colour transmitted through different bodies
+differs considerably from colour reflected by them. In his first
+experiment he took a long empty metal tube, open at one end, and closed
+at the other end by a clear-glass plate. This was let down vertically into
+the water, near to a fixed object, which appeared of most beautiful deep
+and delicate blue at a depth of 20 feet. Scientific men know that, if the
+colour of water is due to the light reflected by extremely small particles
+of matter suspended in the water, then the object looked at through it
+would have been illuminated with yellow (the complementary colour of
+blue). A blackened tube was then filled with water (which had a
+clear-glass plate fixed to the bottom), and white, red, yellow, and purple
+objects were sunk in the water, and these colours were found to change in
+the same way as if they were looked at through a piece of pale-blue glass.
+The white object appeared blue, the red darkened very rapidly as it sank,
+and soon lost its colour; at the depth of seven feet a very brilliant red
+was so darkened as to appear dark brick-red. The yellow object changed to
+green, and the purple to dark blue.
+
+But, still further to satisfy himself that water is really blue in itself,
+even without any particles suspended in it, he tested the colour of
+_distilled_ water. He filled a darkened tube with this water (clear-glass
+plates being at the ends of the tube), and looked through it at a white
+surface. The effect was the same as before, the colour was blue, almost
+exactly of the same hue as a solution of Prussian blue.
+
+This is corroborated by the fact that, the purer the water is in nature,
+the bluer is the tint when a large quantity is looked through. Some
+Highland lochs have crystal waters of the most extraordinary blue. Of
+course, some cling to the old idea that this is accounted for by the
+reflected blue of the clear heavens above. No doubt, if the sky be deep
+blue, then this blue light, when reflected by the surface of the water,
+will enrich and deepen the hue. But the water itself is _really_ blue.
+
+At the same time, the dust-particles suspended in the water have a great
+effect in making the water appear more beautiful, brilliant, and varied in
+its colouring; because little or no light is reflected by the interior of
+a mass of water itself. If a dark metal vessel be filled with a weak
+solution of Prussian blue, the liquid will appear quite dark and void of
+colour. But throw in some fine white powder, and the liquid will at once
+become of a brilliant blue colour. This accounts for the change of depth
+and brilliancy of colour in the several shores of the Mediterranean.
+
+When, then, you look at the face of a deep-blue lake on a summer
+evening--the heavens all aglow with the unrivalled display of colour from
+the zenith, stretching in lighter hues of glory to the horizon--though to
+you the calm water appears like a lake of molten metal glowing with
+sky-reflected light, so powerful and brilliant as entirely to overpower
+the light which is internally reflected, yet blue is the normal colour of
+the water: _blueness is its inherent hue_.
+
+Looking upwards, we observe three distinct kinds of blue in the sky from
+the horizon to the zenith. All painters in water-colours know that. Newton
+thought that the colour of the sky was produced in the same way as the
+colours in thin plates, the order of succession of the colours gradually
+increasing in intensity.
+
+
+
+
+CHAPTER XXIII
+
+A SANITARY DETECTIVE
+
+
+The impure state of the air in the rooms of a house can now be determined
+by means of colour alone. Dr. Aitken has invented a very simple instrument
+for that purpose; and this ought to be of great service to sanitary
+officers. It is called the koniscope--or dust-detective.
+
+The instrument consists of an air-pump and a metal tube with glass ends.
+Near one end of the test-tube is a passage by which it communicates with
+the air-pump, and near the other end is attached a stop-cock for admitting
+the air to be tested. It is not nearly so accurate as the dust-counter;
+but it is cheaper, more easily wrought, and more handy for quick work. All
+the grades of blue, from what is scarcely visible to deep, dark blue, may
+be attached alongside the tube on pieces of coloured glass; and opposite
+these colours are the numbers of dust-particles in the cubic inch of the
+similar air, as determined by the dust-counter.
+
+While the number of particles was counted by means of the dust-counter,
+the depth of blue given by the koniscope was noted; and the piece of glass
+of that exact depth of blue attached. A metal tube was fitted up
+vertically in the room, in such a way that it could be raised to any
+desired height into the impure air near the ceiling, so that supplies of
+air of different degrees of impurity might be obtained. To produce the
+impurity, the gas was lit and kept burning during the experiments. The air
+was drawn down through the pipe by means of the air-pump of the koniscope,
+and it passed through the measuring apparatus of the dust-counter on its
+way to the koniscope. It may be remarked that, by a stroke of the
+air-pump, the air within the test-tube is rarefied and the dust-particles
+seize the moisture in the super-saturated air to form fog-particles;
+through this fog the colour is observed, and the shade of colour
+determines the number of dust-particles in the air. These colours are
+named "just visible," "very pale blue," "pale blue," "fine blue," "deep
+blue," and "very deep blue."
+
+When making a sanitary inspection, the pure air should be examined first,
+and the colour corresponding to that should be considered as the normal
+health colour. Any increase from the depth would indicate that the air was
+being gradually contaminated; and the amount of increase in the depth of
+colour would indicate the amount of increase of pollution.
+
+As an illustration of what this instrument can detect, a room of 24 by 17
+by 13 feet was selected. The air was examined before the gas was lighted,
+and the colour in the test-tube was very faint, indicating a clear
+atmosphere. In all parts of the room this was found the same. A small tube
+was attached to the test-tube, open at the other end, for taking air from
+different parts of the room. Three jets of gas were then lit in the centre
+of the room, and observations at once begun with the koniscope.
+
+Within thirty-five seconds of striking the match to light the gas, the
+products of combustion had extended near the ceiling to the end of the
+room; this was indicated by the colour in the koniscope suddenly becoming
+a deep blue. In four minutes the deep-blue-producing air was got at a
+distance of two feet from the ceiling. In ten minutes there was strong
+evidence of the pollution all through the room. In half-an-hour the
+impurity at nine feet from the floor was very great, the colour being an
+intensely deep blue.
+
+The wide range of the indications of the instrument, from pure clearness
+to nearly black blue, makes the estimate of the impurity very easily taken
+with it; and, as there are few parts to get out of order, it is hoped it
+may come into general use for sanitary work.
+
+
+
+
+CHAPTER XXIV
+
+FOG AND SMOKE
+
+
+Just two hundred and forty years ago, Mr. John Evelyn, F.R.S., a
+well-known writer on meteorology, sent a curious tract to King Charles
+II., which was ordered to be printed by his Majesty. It was entitled
+"Fumifugium," and dealt with the great smoke nuisance in London. I find
+from the thesis that he had a very hazy idea of the connection between fog
+and smoke; and no wonder, for it is only lately that the connection has
+been fully explained.
+
+We know that without dust-particles there can be no fog, and that smoke
+supplies a vast amount of such particles. Therefore, in certain states of
+the atmosphere, the more smoke the more fog. In Mr. Evelyn's day the fog,
+which he called "presumptuous smoake," was at times so dense that men
+could hardly discern each other for the "clowd." His Majesty's only sister
+had complained of the damage done to her lungs by the contamination, and
+Mr. Evelyn was disgusted at the apathy of the people to do anything to
+remedy the nuisance. He deplored that that glorious and ancient city of
+London should wrap her stately head in "clowds of smoake, so full of stink
+and darknesse." He was of opinion that a method of charring coal so as to
+divest it of its smoke, while leaving it serviceable for many purposes,
+should be made the object of a very strict inquiry. And he was right. For
+it is now known that fog in a town is intensified by much smoke.
+
+In a city like London or Glasgow, where a great river, fed by warm streams
+of water from gigantic works, passes through its centre, fogs can never be
+entirely obliterated, for the dust-particles in the air (often four
+millions and upwards in the cubic inch) will seize with terrible avidity
+the warm vapour rising from the river. That is the main reason why fogs
+cannot there be put down. Smoke is being consumed to a great extent; yet
+we find particles of sulphur remaining, which seize the warm vapour and
+form fogs dense enough to check all traffic. The worst form of city fogs
+seems to be produced when the air, after first flowing slowly in one
+direction, then turns on its tracks and flows back over the city,
+bringing with it a black pall, the accumulated products of previous days,
+to which gets added the smoke and other impurities produced at the time.
+
+What irritated Mr. Evelyn was that, outside of London, the air was clear
+when passengers could not walk in safety within the city. So vexed was he
+about the contamination, that he made it the occasion of all the "cathars,
+phthisicks, coughs, and consumption in the city." He appealed to common
+sense to testify that those who repair to London soon take some serious
+illness. "I know a man," he said, "who came up to London and took a great
+cold, which he could never afterwards claw off again."
+
+Mr. Evelyn proposed that, by an Act of Parliament, the nuisance be
+removed; enjoining that all breweries, dye-works, soap and salt boilers,
+lime-burners, and the like, be removed five or six miles distant from
+London below the river Thames. That would have materially helped his
+cause.
+
+But there is more difficulty in the purification than he anticipated. Yet
+there was pluck in the old man pointing out the killing contamination and
+suggesting a possible remedy. He had the fond idea that thereby a certain
+charm, "or innocent magick," would make a transformation scene like
+Arabia, which is therefore "styl'd the Happy, attracting all with its gums
+and precious spices." In purer air fogs would be less dense, breathing
+would be easier, business would be livelier, life would be happier.
+
+Few, I suppose, have laid their hands on this curious Latin thesis, or its
+quaint translation, directing the King's attention to the fogs that were
+ruining London. Since that time the city has increased, from little more
+than a village, to be the dwelling-place of six millions of human beings,
+yet too little improvement has been made in the removal of this fog
+nuisance. King Edward's drive through London would be even more dangerous
+on a muggy, frosty day than was Charles II.'s, when science was little
+known.
+
+
+
+
+CHAPTER XXV
+
+ELECTRICAL DEPOSITION OF SMOKE
+
+
+A good deal of scientific work is being done in the way of clearing away
+fog and smoke; and this, through time, may have some practical results in
+removing a great source of annoyance, illness, and danger in large towns.
+Sir Oliver Lodge and Dr. Aitken have been throwing light upon the
+deposition of smoke in the air by means of electricity.
+
+If an electric discharge be passed through a jar containing the smoke from
+burnt magnesium wire, tobacco, brown paper, and other substances, the dust
+will be deposited so as to make the air clear. Brush discharge, or
+anything that electrifies the air itself, is the most expeditious.
+
+If water be forced upwards through a vertical tube (with a nozzle
+one-twentieth of an inch in diameter), it will fall to the ground in a
+fine rain; but, if a piece of rubbed (electrified) sealing-wax be held a
+yard distant from the place where the jet breaks into drops, they at once
+fall in large spots as in a thunder-shower. If paper be put on the ground
+during the experiment, the sound of pattering will be observed to be
+quite different. If a kite be flown into a cloud, and made to give off
+electricity for some time, that cloud will begin to condense into rain.
+
+Experiments with Lord Kelvin's recorder show that variations in the
+electrical state of the atmosphere precede a change of weather. Then, with
+a very large voltaic battery, a tremendous quantity of electricity could
+be poured into the atmosphere, and its electrical condition could be
+certainly disturbed. If this could be made practically available, how
+useful it would be to farmers when the crops were suffering from excessive
+drought! It might be more powerfully available than the imagined
+condensation of a cloud into rain by the reverberation caused by the
+firing of a range of cannon.
+
+But what is the practical benefit of this information? If electricity
+deposits smoke, it might be made available in many ways. The fumes from
+chemical works might be condensed; and the air in large cities, otherwise
+polluted, might be purified and rendered innocuous. The smoke of chimneys
+in manufacturing works might be prevented from entering the atmosphere at
+all. In flour-mills and coal-mines the fine dust is dangerously explosive.
+In lead, copper, and arsenic works, it is both poisonous and valuable.
+
+Lead smelters labour under this difficulty of condensing the fume which
+escapes along with the smoke from red-lead smelting furnaces; and it was
+considered that an electrical process of condensation might be made
+serviceable for the purpose. At Bagillt, the method used for collecting or
+condensing the lead fume is a large flue two miles long; much is retained
+in this flue, but still a visible cloud of white-lead fume continually
+escapes from the top of the chimney. There is a difficulty in the way of
+depositing fumes in the flue by means of a sufficient discharge of
+electricity, viz. the violent draught which is liable to exist there, and
+which would mechanically blow away any deposited dust.
+
+But Dr. Aitken suggests that regenerators might be used along with the
+electricity. The warm fumes might be taken to a cold depositor, where (by
+the ordinary law of cold surfaces attracting warm dust-particles) the
+impurities would be removed, and, when purified, the air would again be
+taken through a hot regenerator before being sent up the chimney. By a
+succession of these chambers, with the assistance of electric currents,
+the air, impregnated with the most deleterious particles, or valuable
+dust, could be rendered innocuous.
+
+The sewage of our towns must be cleaned of its deleterious parts before
+being run into the streams which give drink to the lower animals, because
+an Act of Parliament enforces the process. Why, then, ought we not to have
+similar compulsion for making the smoke from chemical and other noxious
+works quite harmless before being thrown into the air which contains the
+oxygen necessary for the life of human beings?
+
+There seems to be a good field before electricians to catch the smoke on
+the wing and deposit its dust on a large scale. This seems to be a matter
+beyond our reach at present, except in the scientist's laboratory; but
+certainly it is a "consummation devoutly to be wished."
+
+
+
+
+CHAPTER XXVI
+
+RADIATION FROM SNOW
+
+
+One night a most interesting paper by Dr. Aitken, on "Radiation from
+Snow," was read by Professor Tait to the Fellows of the Royal Society of
+Edinburgh. I remember that Dr. Alex. Buchan--the greatest meteorologist
+living--spoke afterwards in the very highest terms of the subject-matter
+of the paper. This was corroborated by Lord Kelvin, Lord MacLaren, and
+Professor Chrystal.
+
+Dr. Aitken had been testing the radiating powers of different substances.
+Snow in the shade on a bright day at noon is 7° Fahr. colder than the air
+that floats upon it, whereas a black surface at the same is only 4°
+colder. This difference diminishes as the sun gets lower; and at night
+both radiate almost equally well.
+
+I select, among the careful and numerous observations, the notes on
+January 19, 1886; for I took note of the cold of that day in my diary. It
+was the coldest day of the whole of that winter. The barometer was 28·8
+inches, and the thermometer 4°--that is, 28° of frost. According to Dr.
+Buchan, that January had only two equal in average cold for fifty years.
+
+On January 19, at 10 A.M., when the air was at 20° and the sky clear, a
+black surface registered 16° and the upper layer of snow 12°, showing a
+difference of 4° when both surfaces were colder than the superincumbent
+air. It is curious to note that, on February 5 of the same year, at the
+same hour, when the sky was overcast, the air was at 23°, the black
+surface registered 29°, and the snow 25°, showing again the difference of
+4°; but, in this case, both surfaces were warmer than the air. In both
+cases the radiation at night was equal.
+
+This small absorbing power of snow for heat reflected and radiated from
+the sky during the day must have a most important effect on the
+temperature of the air. The temperature of lands when covered with snow
+must be much lower than when free from it. And, when once a country has
+become covered with snow, there will be a tendency towards glacial
+conditions.
+
+But, besides being a bad absorber of heat from the sky, snow is also a
+very poor conductor of heat. On that very cold night (January 18), when
+there was a depth of 5-1/2 inches of snow on the ground, and the night
+clear, with strong radiation, the temperature of the surface of the snow
+was 3° Fahr., and a minimum thermometer on the snow showed that it had
+been down to zero some time before. A thermometer, plunged into the snow
+down to the grass, gave the most remarkable register of 32°. Through the
+depth of 5-1/2 inches of snow there was a difference of temperature of
+29°. This was confirmed by removing the snow, and finding that the grass
+was unfrozen. As the ground was frozen when the snow fell, it would appear
+that the earth's heat slowly thawed it under the protection of the snow.
+
+The protection afforded by the bad-conducting power of snow is of great
+importance in the economy of nature. How vegetation would suffer, were it
+exposed to a low temperature, unprotected by the snow-mantle! So that,
+though the continued snow cools the air for animals that can look after
+their own heating, it keeps warm the soil; and vegetation prospers under
+the genial covering. The fine rich look of the young wheat-blades, after a
+continued snow has melted, must strike the most careless observer. Instead
+of the half-blackened tips and semi-sickly blades, which we see in a field
+of young wheat after a considerable course of dry frost without snow, we
+have a rich, healthy green which shows the vital energy at work in the
+plants. Or even in the town gardens, after a continued snow has been
+melted away by a soft, western breeze, we are struck with the white,
+peeping buds of the snowdrop and the finely springing grass in the sward.
+
+Yet the snow-covering gives durability to cold weather. This has been
+demonstrated by Dr. Woeikof, the distinguished Russian meteorologist. On
+this account the spring months of Russia and Siberia are intensely cold.
+The plants, then, which in winter are unable by locomotion to keep
+themselves in health, are protected by the snow-mantle which chills the
+air for animals that can keep themselves in heat by exercise. What a grand
+compensating power is here!
+
+
+
+
+CHAPTER XXVII
+
+MOUNTAIN GIANTS
+
+
+Some mysterious physical phenomena can be clearly explained by the aid of
+science. The mountain giants that at times haunt the lonely valleys, and
+strike with fear the superstitious dwellers there, are only the enlarged
+shadows of living human beings cast upon a dense mist.
+
+The two most startling of these "eerie" phenomena are the spectres of
+Adam's Peak and the Brocken.
+
+The phenomena sometimes to be observed at Adam's Peak, in Ceylon, are very
+remarkable. Many travellers have given vivid accounts of these. On one
+occasion the Hon. Ralph Abercromby, in his praiseworthy enthusiasm for
+meteorological research, went there with two scientific friends to witness
+the strange appearance. The conical peak, a mile and a half high,
+overlooks a gorge west of it. When, then, the north-east monsoon blows the
+morning mist up the valley, light wreaths of condensed vapour pass to the
+right of the Peak, and catch the shadows at sunrise.
+
+This party reached the summit early one morning in February. The foreglow
+began to brighten the under-surface of the stratus-cloud with orange, and
+patches of white mist filled the hollows. Soon the sun peeped through a
+chink in the clouds, and they saw the pointed shadow of the Peak lying on
+the misty land. Then a prismatic circle, with the red inside, formed round
+the shadow. The meteorologist waved his arms about, and immediately he
+found giant shadowy arms moving in the centre of the rainbow.
+
+Soon they saw a brighter and sharper shadow of the Peak, encircled by a
+double bow, and their own spectral arms more clearly visible. The shadow,
+the double bow, and the giant forms, combined to make this phenomenon the
+most marked in the whole world.
+
+The question has been frequently asked: Why are such aërial effects not
+more widely observed? There are not many mountains of this height and of a
+conical shape; and still fewer can there be where a steady wind, for
+months together, blows up a valley so as to project the rising morning
+mist at a suitable height and distance on the western side, to catch the
+shadow of the peak at sunrise.
+
+The most famous place in Europe for witnessing the awe-inspiring
+phenomenon is the Brocken, in Germany--3740 feet in height. The only great
+disappointment there is that the conditions rarely combine at sunrise or
+sunset to have "the spectre" successful.
+
+In July 1892, my daughter and I were spending some weeks at Harzburg, and,
+of course, we had to visit the Brocken and take stock of the world-known
+phenomenon. At mid-day, the air at the flat summit was cold, clear, and
+hard. The boulders are of enormous size; and near the "Noah's Ark" Hotel
+and Observatory many are piled up in a mass, on which the observers stand
+at the appointed time for having their shadows projected on the misty air
+in the valleys.
+
+At five o'clock in the afternoon the sky was brilliantly clear on the
+summit of the Brocken; but the wind was rising from the sun's direction,
+and the mist was filling up the wide-spread eastern valley. We stood on
+the "spectre" boulders, and our shadows were thrown on the grass, just as
+at home. However, they fell upon large patches of white heather, which
+there is very plentiful.
+
+At six o'clock the sun was still shining beautifully, and we anxiously
+waited for the time when it would be low enough to raise our shadows to
+the misty wall. An hour afterwards, a hundred visitors were out, and many
+of us were on the "spectre" stones. There was great excitement in
+anticipation of the weird appearances, which had attracted us from such a
+distance.
+
+But, almost at the moment of success, the sun descended behind a belt of
+purple cloud, and all we saw was part of a rainbow on the misty hollow.
+For the sun never appeared again. This was intensely saddening, seeing
+that, but for that stratum of cloud above the horizon, the phenomenon
+would have been graphically displayed.
+
+The cold became suddenly intense, and we had to sleep with a freezing mist
+enveloping the hotel. In vain did we wait for the wakening call, to tell
+us of sunrise; for the sun could not pierce the mist, and we had to return
+home disappointed.
+
+Sometimes the rainbow colours assume the shapes of crosses instead of
+circles. Occasionally a bright halo will be seen above the shadow-head of
+the observer, concentric rainbows enclosing all. In some recorded cases
+the grand effect must have been simply glorious.
+
+Scientific observation has done much to dispel the superstition which has
+clung so tenaciously to the Highland mind. The lonely grandeur of the
+weird mountain giants has been clearly explained as perfectly natural, yet
+the awe-striking feeling cannot be entirely driven off.
+
+
+
+
+CHAPTER XXVIII
+
+THE WIND
+
+
+Once was the remark pointedly made: "The wind bloweth where it listeth."
+And that is nearly true still. The leading winds are under the calculation
+of the meteorologist, but the others will not be bound by laws.
+
+Yet there are instruments for measuring the velocity and force of the
+wind, after it is on; but "whence it comes" is a different matter. A
+gentle air moves at the rate of 7 miles an hour; a hurricane from 80 to
+150 miles, pressing with 50 lbs. on the square foot exposed to its fury.
+Some of the gusts of the Tay Bridge storm, in 1879, had a velocity of 150
+miles an hour, with a pressure of 80 to 90 lbs. to the square foot.
+
+Before steamers supplanted so many sailing vessels, seamen required to be
+always on the alert as to the direction and strength of the wind, and the
+likelihood of any sudden change; and they chronicled twelve different
+strengths from "faint air" to a "storm."
+
+In general, the wind may be considered to be the result of a change of
+pressure and temperature in the atmosphere at the same level. The air of a
+warmer region, being lighter, ascends, and gives place to a current of
+wind from a colder region. These two currents--the higher and the
+lower--will continue to blow until there is equilibrium.
+
+The trade winds are regular and constant. These were much followed in the
+days of old. A vast amount of air in the tropics gets heated and ascends,
+being lighter, and travels to the colder north. A strong current rushes in
+from the north to take its place. But the earth rotates round its axis
+from west to east, and the combined motions make two slant wind
+directions, which are called the "trade winds," because they were so
+important in trade navigation.
+
+Among the periodical winds are the "land and sea breezes." During the day,
+the land on the sea coast is warmer than the sea; accordingly, the air
+over the land becomes heated and ascends, the fine cool breeze from the
+sea taking its place. Towards evening there is the equilibrium of
+temperature which produces a temporary calm. Soon the earth chills, and
+the sea is counterbalancingly warm--as sea-water is steadier as to
+temperature than is land--the air over the sea becomes warmer, and
+ascends, the current from the land rushing in to take its place. Hence
+during the night the wind is reversed, until in the morning again the
+equilibrium is restored and there is a calm, so far as these are
+concerned. These are therefore called the "land and sea breezes." Of
+course, it is within the tropics that these breezes are most marked. By
+the assistance of other winds, a hurricane will there occasionally destroy
+towns and bring about much damage and loss of life; but better that
+hundreds should perish by a hurricane than thousands by the pestilence
+which, but for the storm, would have done its dire work.
+
+In countries where the differences of pressure are more marked than the
+differences of temperature, in the surrounding regions the strength of
+the wind thereby occasioned is far stronger than the land and sea breezes.
+
+The variable winds are more conflicting. These depend on purely local
+causes for a time, such as "the nature of the ground, covered with
+vegetation or bare; the physical configuration of the surface, level or
+mountainous; the vicinity of the sea or lakes, and the passage of storms."
+Among these winds are the simoom and sirocco.
+
+The _east_ winds, which one does not care about in the British Islands
+during the spring time, are occasioned by the powerful northern current
+which rushes south from the northern regions in Europe. Dr. Buchan points
+out a very common mistake among even intelligent observers who shudder at
+the hard east winds. It is generally held that these winds are damp. They
+are unhealthy, but they are dry. It is quite true that many easterly winds
+are peculiarly moist; all that precede storms are so far damp and rainy;
+and it is owing to this circumstance that, on the east coast of Scotland,
+the east winds are searching and carry most of the annual rainfall there.
+But all of these moist easterly winds, however, soon turn to some westerly
+point. The real east wind, so much feared by invalids, does not turn to
+the west; it is exceeding dry. Curious is it that brain diseases, as well
+as consumption, reach their height in Britain while east winds prevail.
+Once in Edinburgh, during the early spring, I had rheumatic fever, and
+during my convalescence my medical adviser, Dr. Menzies, would not let me
+have a short drive until the wind changed to the west. The first thing I
+anxiously watched in the morning was the flag on the Castle; and for
+nearly two months it always waved from the east. How heart-depressing!
+
+Creatures are we in the hands of nature's messengers. We so much depend
+upon the weather for our happiness. Joyful are we when the honey-laden
+zephyr waves the long grass in June, or when
+
+  "The gentle wind, a sweet and passionate wooer,
+  Kisses the blushing leaf."
+
+Compared with this, how terrible is Shakespeare's allusion to the
+appalling aspects of the storm:--
+
+  "I have seen tempests, when the scolding winds
+  Have rived the knotty oaks; and I have seen
+  The ambitious ocean swell, and rage and foam,
+  To be exalted with the threat'ning clouds;
+  But never till to-night, never till now,
+  Did I go through a tempest dropping fire."
+
+
+
+
+CHAPTER XXIX
+
+CYCLONES AND ANTI-CYCLONES
+
+
+The criticism of the weather in the meteorological column of our daily
+newspapers invariably speaks of "cyclones." It is, therefore, advisable to
+give as plain an explanation of these as possible. Cyclones are
+"storm-winds." Their nature has to be carefully studied by meteorologists,
+who are industriously at work to ascertain some scientific basis for the
+atmospheric movements.
+
+What is the cause of the spiral movement in storm-winds? In their centre
+the depression of the barometer is lowest, because the atmosphere there is
+lightest. As the walls of the spiral are approached, the barometer rises.
+
+Dr. Aitken has ingeniously hit upon an experiment to illustrate a spiral
+in air. All that is necessary is a good fire, a free-going chimney, and a
+wet cloth. The cloth is hung up in front of the fire, and pretty near it,
+so that steam rises readily from its surface; and, when there are no
+air-currents in the room, the steam will rise vertically, keeping close to
+the cloth. But if the room has a window in the wall, at right angles to
+the fireplace, so as to cause the air coming from it to make a
+cross-current past the fire, then a cyclone will be formed, and the vapour
+from the cloth will be seen circling round. When the cyclone is well
+formed, all the vapour is collected into the centre of the cyclone, and
+forms a white pillar extending from the cloth to the chimney. This
+experiment shows that no cyclone can form without some tangential motion
+in the air entering the area of low-pressure.
+
+Now to illustrate the spiral approach. Fill with water a cylindrical glass
+vessel, say 15 inches in diameter and 6 inches deep. Have an orifice with
+a plug a little from the centre of the bottom. Remove the plug, the water
+runs out, passing round the vessel in a vortex form. But, as the passage
+between the orifice (or centre of the cyclone) and the temporary division
+is narrower than in any other place, the water has to pass this part much
+more quickly than at any other place. And this curious result is observed:
+the top of the cyclone no longer remains over the orifice, but _travels_
+in the direction of the water which is moving most speedily. Similar to
+this is the cyclone in the atmosphere; its centre also moves in the
+direction of the quickest flowing wind that enters it.
+
+Dr. Aitken is of opinion that, in forecasting storms, too little attention
+has been paid to the _anti-cyclones_. They do more than simply follow and
+fill up the depression made by the cyclones. They initiate and keep up
+their own circulation, and collect the materials with which the cyclones
+produce their effect. Neither could work efficiently without the other.
+
+Suppose a large area on the earth over which the air is still in bright
+sunshine. After a time, when the air gets heated and charged with vapour,
+columns of air would begin to ascend in a disorderly fashion. But suppose
+an anti-cyclone is blowing at one side of this area. When the upper air
+descends to the earth, it spreads outwards in all directions; but the
+earth's rotation interferes and changes the radial into a spiral motion.
+The anti-cyclonic winds will prevent the formation of local cyclones, and
+drive all the moist, hot air to its circumference, just above the earth.
+The anti-cyclone forces its air tangentially into the cyclone, and gives
+it its direction and velocity of rotation, also the direction and rate of
+travel of the centre of depression. The earth's rotation is the original
+source of the rotatory movements, but both intensify the initial motion.
+
+Accordingly, the cyclone must travel in the direction of the strongest
+winds blowing into it, just as the vortex in the vessel with the eccentric
+orifice travelled in the direction of the quickest moving water. This is
+verified by a study of the synoptic charts of the Meteorological Office.
+
+The sun's heat has always been looked upon as the main source of the
+energy of our winds, but some account must also be taken of the effects of
+cold. It is well known that the mean pressure over Continental areas is
+high during winter and low during summer. As the sun's rays during summer
+give rise to the cyclonic conditions, so the cooling of the earth during
+winter gives rise to anti-cyclonic conditions. It is found during the
+winter months in several parts of the Continent that as the temperature
+falls the pressure rises, producing anti-cyclones over the cold area;
+whereas, when the temperature begins to rise, the pressure falls, and
+cyclones are attracted to the warming area.
+
+Small natural cyclones are often seen on dusty roads, the whirling column
+having a core of dusty air, and the centre of the vortex travelling along
+the road, tossing up the dust in a very disagreeable way to pedestrians.
+Sometimes such a cyclone will toss up dry leaves to a height of four or
+five feet. They are very common; but it is only when dust, leaves, or
+other light material is present that they are visible to the eye.
+
+
+
+
+CHAPTER XXX
+
+RAIN PHENOMENA
+
+
+The soft rain on a genial evening, or the heavy thunder-showers on a
+broiling day, are too well known to be written about. Sometimes rain is
+earnestly wished for, at other times it is dreaded, according to the
+season, seed-time or harvest. Some years, like 1826, are very deficient in
+rainfall, when the corn is stunted and everything is being burnt up; other
+years, like 1903, there is an over-supply, causing great damage to
+agriculture. The year 1903 will long be remembered for its continuous
+rainfall; it is the record year; no year comes near it for the total
+rainfall all over the kingdom.
+
+Rain is caused by anything that lowers the temperature of the air below
+the dew-point, but especially by winds. When a wind has blown over a
+considerable area of ocean on to the land, there is a likelihood of rain.
+When this wind is carried on to higher latitudes, or colder parts, there
+is a certainty of rain. Of course, in the latter case the rain will fall
+heavier on the wind side than on the lee side.
+
+For short periods, the heaviest falls or "plouts" of rain are during
+thunder-storms. When the raindrops fall through a broad, cold stratum of
+air, they are frozen into hail, the particles of which sometimes reach a
+large size, like stones. Of course, water-spouts now and again are of
+terrible violence.
+
+One of the heaviest rainfalls yet recorded in Great Britain was about
+2-1/4 inches in forty minutes at Lednathie, Forfarshire, in 1887. Now 1
+inch deep of rain means 100 tons on an imperial acre; so the amount of
+water falling on a field during that short time is simply startling. The
+heaviest fall for one day was at Ben Nevis Observatory, being fully 7-1/4
+inches in 1890. In other parts of the world this is far exceeded. In one
+day at Brownsville, Texas, nearly 13 inches fell in 1886. On the Khasi
+hills, India, 30 inches on each of five successive days were registered.
+At Gibraltar, 33 inches were recorded in twenty-six hours.
+
+The heaviest rainfalls of the globe are occasioned by the winds that have
+swept over the most extensive ocean-areas in the tropics. On the summer
+winds the rainfall of India mainly depends; when this fails, there is most
+distressing drought. Reservoirs are being erected to meet emergencies.
+
+From Dr. Buchan's statistics it is found that the annual rainfall at
+Mahabaleshwar is 263 inches; at Sandoway 214; and at Cherra-pungi 472
+inches, the largest known rainfall anywhere on the globe. Over a large
+part of the Highlands of Scotland more than 80 inches fall annually, while
+in some of the best agricultural districts there it does not exceed 30
+inches.
+
+Of all meteorological phenomena, rainfall is the most variable and
+uncertain. Symons gives as tentative results from twenty years'
+observations in London--(1) In winter, the nights are wetter than the
+days; (2) in spring and autumn, there is not much difference; (3) in
+summer, nearly half as much again by day as by night.
+
+The wearisomeness of statistics may be here relieved by a short
+consideration of the _splash_ of a drop of rain. Watching the
+drop-splashes on a rainy day in the outskirts of the city, when unable to
+get out, I brought to my recollection the marvellous series of experiments
+made by Professor A. M. Worthington in connection with these phenomena. Of
+course, I could not see to proper advantage the formation of the
+splashes, as the heavy raindrops fell into these tiny lakes on the quiet
+road. There is not the effect of the huge thunder-drops in a stream or
+pool. The building up of the bubbles is not here perfect, for the domes
+fail to close, nor are the emergent columns visible to the naked eye. It
+is a pity; for R. L. Stevenson once wrote of them in his delightful
+"Inland Voyage," when he canoed in the Belgian canals, as thrown up by the
+rain into "an infinity of little crystal fountains."
+
+Beautiful is this effect if one is under shelter, every dome seeming quite
+different in contour and individuality from all the rest. But terrible is
+it when out fishing on Loch Earn, even with the good-humoured old Admiral,
+when the heavy thunder-drops splash up the crystal water, and one gets
+soaked to the skin, sportsman-like despising an umbrella.
+
+There is, however, a scientific interest about the splash of a drop. The
+phenomenon can be best seen indoors by letting a drop of ink fall upon the
+surface of pure water in a tumbler, which stands on white paper. It is an
+exquisitely regulated phenomenon, which very ideally illustrates some of
+the fundamental properties of fluids.
+
+When a drop of milk is let fall upon water coloured with aniline dye, the
+centre column of the splash is nearly cylindrical, and breaks up into
+drops before or during its subsequent descent into the liquid. As it
+disappears below the surface, the outward and downward flow causes a
+hollow to be again formed, up the sides of which a ring of milk is
+carried; while the remainder descends to be torn a second time into a
+beautiful vortex ring. This shell or dome is a characteristic of all
+splashes made by large drops falling from a considerable height, and is
+extremely pretty. Sometimes the dome closes permanently over the
+imprisoned air, and forms a large bubble floating upon the water. The most
+successful experiments, however, have been carried through by means of
+instantaneous photography, with the aid of a Leyden-jar spark, whose
+duration was less than the ten-millionth of a second. But the simple
+experiments, without the use of the apparatus, will while away a few hours
+on a rainy afternoon, when condemned to the penance of keeping within
+doors.
+
+
+
+
+CHAPTER XXXI
+
+THE METEOROLOGY OF BEN NEVIS
+
+
+Several large and very important volumes of the Royal Society of Edinburgh
+are devoted to statistics connected with the meteorology of Ben Nevis.
+Most of the abstracts have been arranged by Dr. Buchan; while Messrs.
+Buchanan, Omond, and Rankine have taken a fair share of the work.
+
+This Observatory, as Mr. Buchanan remarks, is unique, for it is
+established in the clouds; and the observations made in it furnish a
+record of the meteorology of the clouds. It is 4406 feet above the level
+of the sea; and as there is a corresponding Observatory at Fort William,
+at the base of the mountain, it is peculiarly well fitted for important
+observations and weather forecasting. The mountain, too, is on the west
+sea-coast of Scotland, exposed immediately to the winds from the Atlantic,
+catching them at first hand. It is lamentable to think that, when the
+importance of the observations made at the two Observatories was becoming
+world known, funds could not be got to carry them on. Ben Nevis is the
+highest mountain in the British Islands, best fitted for meteorological
+observations; yet these have been stopped for want of money.
+
+Dr. Buchan's valuable papers were published before any one dreamed of the
+stoppage of the work, which had such an important bearing on men engaged
+in business or taken up with open-air sport. From these I shall sift out a
+few facts that even "mute, inglorious" meteorologists may be interested in
+knowing.
+
+For a considerable time the importance of the study of the changes of the
+weather has come gradually to be recognised, and an additional impetus was
+given to the prosecution of this branch of meteorology when it was seen
+that the subject had intimate relations to the practical question of
+weather forecasts, including storm warnings. Weather maps, showing the
+state of the weather over an extensive part of the surface of the globe,
+began to be constructed; but these were only indicators from places at the
+level of the sea.
+
+The singular advantages of a high-level observatory occurred to Mr. Milne
+Home in 1877; and Ben Nevis was considered to be in every respect the most
+suitable in this country. The Meteorological Council of the Royal Society
+of London offered in 1880, unsolicited, £100 annually to the Scottish
+Meteorological Society, to aid in the support of an Observatory, the only
+stipulation being that the Council be supplied with copies of the
+observations.
+
+From June to October, in 1881, Mr. Wragge made daily observations at the
+top of the Ben; and simultaneous observations were made, by Mrs. Wragge,
+at Fort William. A second series, on a much more extended scale, was made
+in the following summer.
+
+Funds were secured to build an Observatory; and, in November 1883, the
+regular work commenced, consisting of hourly observations by night as well
+as by day. Until a short time ago, these were carried on uninterruptedly.
+Telegraphic communications of each day's observations were sent to the
+morning newspapers; and now we are disappointed at not seeing them for
+comparison.
+
+The whole of the observations of temperature and humidity were of
+necessity eye-observations. For self-registering thermometers were
+comparatively useless when the wind was sometimes blowing at the rate of
+100 miles an hour. Saturation was so complete in the atmosphere that
+everything exposed to it was dripping wet. Every object exposed to the
+outside frosts of winter soon became thickly incrusted with ice.
+Snowdrifts blocked up exposed instruments. Accordingly, the observers had
+to use their own eyes, often at great risks.
+
+The instruments in the Ben Nevis Observatory, and in the Observing Station
+at Fort William, were of the best description. Both stations were in
+positions where the effects of solar and terrestrial radiation were
+minimised. No other pair of meteorological stations anywhere in the world
+are so favourably situated as these two stations, for supplying the
+necessary observations for investigating the vertical changes of the
+atmosphere. It is to be earnestly hoped, therefore, that funds will be
+secured to resume the valuable work.
+
+The rate of the decrease of temperature with height there is 1° Fahr. for
+every 275 feet of ascent, on the mean of the year. The rate is most rapid
+in April and May, when it is 1° for each 247 feet; and least rapid in
+November and December, when it is 1° for 307 feet. This rate agrees
+closely with the results of the most carefully conducted balloon ascents.
+The departures from the normal differences of temperature, but more
+especially the inversions of temperature, and the extraordinarily rapid
+rates of diminution with height, are intimately connected with the
+cyclones and anti-cyclones of North-Western Europe; and form data, as
+valuable as they are unique, in forecasting storms.
+
+The most striking feature of the climate of Ben Nevis is the repeated
+occurrence of excessive droughts. For instance, in the summer and early
+autumn of 1885, low humidities and dew-points frequently occurred.
+Corresponding notes were observed at sea-level. During nights when
+temperature falls through the effects of terrestrial radiation, those
+parts of the country suffer most from frosts over which very dry states of
+the air pass or rest; whereas, those districts, over which a more humid
+atmosphere hangs, will escape. On the night of August 31 of that year, the
+potato crop on Speyside was totally destroyed by the frost; whereas at
+Dalnaspidal, in the district immediately adjoining, potatoes were
+scarcely--if at all--blackened.
+
+The mean annual pressure at Ben Nevis was 25·3 inches, and at Fort William
+29·8, the difference being 4-1/2 inches for the 4400 feet.
+
+For the whole year, the difference between the mean coldest hour, 5 A.M.,
+and the warmest hour, 2 P.M., is 2°. For the five months, from October to
+February, the mean daily range of temperature varied only from O·6 to 1·5.
+This is the time of the year when storms are most frequent; and this small
+range in the diurnal march of the temperature is an important feature in
+the climatology of Ben Nevis; for it presents, in nearly their simple
+form, the great changes of temperature accompanying storms and other
+weather changes, which it is so essential to know in forecasting weather.
+
+The daily maximum velocity of the wind occurs during the night, the daily
+differences being greatest in summer and least in winter. A blazing sun in
+the summer daily pours its rays on the atmosphere, and a thick envelope of
+cloud has apparently but little influence on the effect of the sun's rays.
+Thunder-storms are essentially autumn and winter phenomena, being rare in
+summer.
+
+According to Mr. Buchanan, the weather on Ben Nevis is characterised by
+great prevalence of fog or mist. In continuously clear weather it
+practically never rains on the mountain at all. In continuously foggy
+weather, on the other hand, the average daily rainfall is 1 inch. There is
+a large and continuous excess of pressure in clear weather over that of
+foggy weather. The mean temperature of the year is 3-1/2 degrees higher
+in clear than in foggy weather. In June the excess is 10 degrees. The
+nocturnal heating in the winter is very clearly observed. This has been
+noticed before in balloons as well as on mountains. The fog and mist in
+winter are much denser than in summer. Whether wet or dry, the fog which
+characterises the climate of the mountain is nothing but _cloud_ under
+another name.
+
+
+
+
+CHAPTER XXXII
+
+THE WEATHER AND INFLUENZA
+
+
+Some remarkable facts have been deduced by the late Dr. L. Gillespie,
+Medical Registrar, from the records of the Royal Infirmary of Edinburgh.
+He considered that it might lead to interesting results if the admissions
+into the medical wards were contrasted with the varying states of the
+atmosphere. The repeated attacks of influenza made him pay particular
+attention to the influence of the weather on that disease.
+
+The meteorological facts taken comprise the weekly type of weather, _i.e._
+cyclonic or anti-cyclonic, the extremes of temperature for the district
+for each week, and the mean weekly rainfall for the same district. More
+use is made of the extremes than of the mean, for rapid changes of
+temperature have a greater influence on disease than the actual mean.
+
+The period which he took up comprises the seven years 1888-1895. There was
+a yearly average of admissions of 3938; so that he had a good field for
+observation. Six distinct epidemics of influenza, varying in intensity,
+occurred during that period; yet there had been only twenty-three attacks
+between 1510 and 1890. Accordingly, these six epidemics must have had a
+great influence on the incidence of disease in the same period, knowing
+the vigorous action of the poison on the respiratory, the circulatory, and
+the nervous systems. The epidemics of influenza recorded in this country
+have usually occurred during the winter months.
+
+The first epidemic, which began on the 15th of December 1889 and continued
+for nine weeks, was preceded by six weeks of cyclonic weather, which was
+not, however, accompanied by a heavy rainfall. Throughout the course of
+the disease, the type continued to be almost exclusively cyclonic, with a
+heavy rainfall, a high temperature, and a great deficiency of sunshine.
+The four weeks immediately following were also chiefly cyclonic, but with
+a smaller rainfall.
+
+The summer epidemic of 1891 followed a fine winter and spring, during
+which anti-cyclonic conditions were largely prevalent. But the epidemic
+was immediately preceded by wet weather and a low barometer. It took place
+in dry weather, and was followed by wet, cyclonic weather in turn.
+
+The great winter epidemic of 1891 followed an extremely wet and broken
+autumn. Simultaneously with the establishment of an anti-cyclone, with
+east wind, practically no rain, and a lowering temperature, the influenza
+commenced. Great extremes in the temperature followed, the advent of
+warmer weather and more equable days witnessing the disappearance of the
+disease.
+
+The fourth epidemic was preceded by a wet period, ushered in by dry
+weather, accompanied by great heat; and its close occurred in slightly
+wetter weather, but under anti-cyclonic conditions. The fifth outbreak
+began after a short anti-cyclone had become established over our islands,
+continued during a long spell of cyclonic weather with a considerable
+rainfall, but was drowned out by heavy rains. The last appearance of the
+modern plague, of which Dr. Gillespie's paper treats, commenced after cold
+and wet weather, continued in very cold but drier weather, and subsided in
+warmth with a moderate rainfall.
+
+The conditions of these six epidemics were very variable in some respects,
+and regular in others. The most constant condition was the decreased
+rainfall at the time, when the disease was becoming epidemic.
+Anti-cyclonic weather prevailed at the time.
+
+According to Dr. Gillespie, the tables seem to suggest that a type of
+weather, which is liable to cause catarrhs and other affections of the
+respiratory tract, precedes the attacks of influenza; but that the
+occurrence of influenza in _epidemic form_ does not appear to take place
+until another and drier type has been established. As the weather changes,
+the affected patients increase with a rush.
+
+He is of opinion that the supposed rapid spread of influenza on the
+establishment of anti-cyclonic conditions may be explained in this way.
+The air in the cyclonic vortex, drawn chiefly from the atmosphere over the
+ocean, is moist, and contains none of the contagion; the air of the
+anti-cyclone, derived from the higher strata, and thus from distant
+cyclones, descending, blows gently over the land to the nearest cyclone,
+and, being drier, is more able to carry suspended particles with it. He
+considers that temperature has nothing to do with the problem, except in
+so far as the different types of weather may modify it. The Infirmary
+records point to the occurrence of similar phenomena, recorded on previous
+occasions. Accordingly, if such meteorological conditions are not
+indispensable to the spread of influenza in epidemic form, they at least
+afford favourable facilities for it.
+
+
+
+
+CHAPTER XXXIII
+
+CLIMATE
+
+
+One is not far up in years, in Scotland at any rate, without practically
+realising what climate means. He may not be able to put it in words, but
+easterly haars, chilling rimes, drizzling mists, dagging fogs, and
+soddening rains speak eloquently to him of the meaning of climate.
+
+Climate is an expression for the conditions of a district with regard to
+temperature, and its influence on the health of animals and plants. The
+sun is the great source of heat, and when its rays are nearly
+perpendicular--as at the Tropics--the heat is greater on the earth than
+when the slanted rays are gradually cooled in their passage. As one passes
+to a higher level, he feels the air colder, until he reaches the
+fluctuating snow-line that marks perpetual snow.
+
+The temperature of the atmosphere also depends upon the radiation from the
+earth. Heat is quite differently radiated from a long stretch of sand, a
+dense forest, and a wide breadth of water. Strange is it that a newly
+ploughed field absorbs and radiates more heat than an open lea. The
+equable temperature of the sea-water has an influence on coast towns. The
+Gulf Stream, from the Gulf of Mexico, heats the ocean on to the west coast
+of Britain, and mellows the climate there.
+
+The rainfall of a district has a telling effect on the climate. Boggy land
+produces a deleterious climate, if not malaria. Over the world, generally,
+the prevailing winds are grand regulators of the climate in the
+distinctive districts. A wooded valley--like the greatest in Britain,
+Strathmore--has a health-invigorating power: what a calamity it is, then,
+that so many extensive woods, destroyed by the awful hurricane twelve
+years ago, are not replanted!
+
+Some people can stand with impunity any climate; their "leather lungs"
+cannot be touched by extremes of temperature; but ordinary mortals are
+mere puppets in the hands of the goddess climate. Hence health-resorts are
+munificently got up, and splendidly patronised by people of means. The
+poor, fortunately, have been successful in the struggle for existence, by
+innate hardiness, otherwise they would have had a bad chance without ready
+cash for purchasing health.
+
+It may look ludicrous at first sight, but it seems none the less true,
+that the variation of the spots on the sun have something to do with
+climate, even to the produce of the fields. On close examination, with a
+proper instrument, the disc of the sun is found to be here and there
+studded with dark spots. These vary in size and position day after day.
+They always make their first appearance on the same side of the sun, they
+travel across it in about fourteen days, and then they disappear on the
+other side. There is a great difference in the number of spots visible
+from time to time; indeed, there is what is called the minimum period,
+when none are seen for weeks together, and a maximum period, when more are
+seen than at any other time. The interval between two maximum periods of
+sun-spots is about eleven years. This is a very important fact, which has
+wonderful coincidences in the varied economy of nature.
+
+Kirchhoff has shown, by means of the spectroscope, that the temperature of
+a sun-spot must be lower than that of the remainder of the solar surface.
+As we must get less heat from the sun when it is covered with spots than
+when there are none, it may be considered a variable star, with a period
+of eleven years. Balfour Stewart and Lockyer have shown that this period
+is in some way connected with the action of the planets on the
+photosphere. As we have already mentioned, the variations of the magnetic
+needle have a period of the same length, its greatest variations occurring
+when there are most sun-spots. Auroræ, and the currents of electricity
+which traverse the earth's surface, follow the same law. This remarkable
+coincidence set men a-thinking. Can the varying condition of the sun exert
+any influences upon terrestrial affairs? Is it connected with the
+variation of rainfall, the temperature and pressure of the atmosphere,
+and the frequency of storms? Has the regular periodicity of eleven years
+in the sun-spots no effect upon climate and agricultural produce?
+
+Mr. F. Chambers, of Bombay, has taken great trouble to strike, as far as
+possible, a connection between the recurring eleven years of sun-spots and
+the variation of grain prices. He arranged the years from 1783 to 1882 in
+nine groups of eleven years; and, from an examination of his tables, we
+find that there is a decided tendency for high prices to recur at more or
+less regular intervals of about eleven years, and a similar tendency for
+low prices. An occasional slight difference can be accounted for by some
+abnormal cause, as war or famine.
+
+Amid all the apparently irregular fluctuations of the yearly prices, there
+is in every one of the ten provinces of India a periodical rise and fall
+of prices once every eleven years, corresponding to the regular variation
+which takes place in the number of sun-spots during the same period. If it
+were possible to obtain statistics to show the actual out-turn of the
+crops each year, the eleven yearly variations calculated therefrom might
+reasonably correspond with the sun-spot variations even more closely than
+do the price variations.
+
+This is a remarkable coincidence, if nothing more. What if it were yet
+possible to predict the variations of prices in the coming sun-spot cycle?
+Such a power would be of immense service. By its aid it could be predicted
+that, as the present period of low prices has followed the last maximum of
+sun-spots, which was in the year 1904, it will not last much longer, but
+that prices must gradually keep rising for the next five years. Could
+science really predict this, it would be studied by many and blessed by
+more. Yet the strange coincidence of a century's observations renders the
+conclusions not only possible, but to some extent probable.
+
+
+
+
+CHAPTER XXXIV
+
+THE "CHALLENGER" WEATHER REPORTS
+
+
+The _Challenger_ Expedition, commenced by Sir Wyville Thomson, and after
+his death continued by Sir John Murray, with an able staff of assistants
+for the several departments, was one of the splendid exceptions to the
+ordinary British Government stinginess in the furtherance of science. The
+results of the Expedition were printed in a great number of very handsome
+volumes at the expense of the Government.
+
+And the valuable deductions from the _Challenger's_ Weather Reports by Dr.
+Alex. Buchan, in his "Atmospheric Circulation," have thrown considerable
+light upon oceanic weather phenomena. For some of his matured opinions on
+these, I am here much indebted to him.
+
+Humboldt, in 1817, published a treatise on "Isothermal Lines," which
+initiated a fresh line for the study of atmospheric phenomena. An isotherm
+is an imaginary line on the earth's surface, passing through places having
+a corresponding temperature either throughout the year or at any
+particular period. An isobar is an imaginary line on the earth's surface,
+connecting places at which the mean height of the barometer at sea-level
+is the same. To isobars, as well as to isotherms, Dr. Buchan has devoted
+considerable attention. In 1868, he published an important series of
+charts containing these, with arrows for prevailing winds over the earth
+for the months of the year. In this way what are called synoptic charts
+were established.
+
+In the _Challenger_ Report are shown the various movements of the
+atmosphere, with their corresponding causes. It is thus observed that the
+prevailing winds are produced by the inequality of the mass of air at
+different places. The air flows from a region of higher to a region of
+lower pressure, _i.e._ from where there is an excessive mass of air to
+fill up some deficiency. And this is the great principle on which the
+science of meteorology rests, not only as to winds, but as to weather
+changes.
+
+Of the sun's rays which reach the earth, those that fall on the land are
+absorbed by the surface layer of about 4 feet in thickness. But those that
+fall on the surface of the ocean penetrate, as shown by the observations
+of the _Challenger_ Expedition, to a depth of about 500 feet. Hence, in
+deep waters the temperature of the surface is only partially heated by the
+direct rays of the sun. In mid-ocean the temperature of the surface
+scarcely differs 1° Fahr. during the whole day, while the daily variation
+of the surface layer of land is sometimes 50°. The temperature of the air
+over the ocean is about three times greater than that of the surface of
+the open sea over which it lies; but, near land, this increases to five
+times.
+
+The elastic force of vapour is seen in its simplest form on the open sea,
+as disclosed by these Reports. It is lowest at 4 A.M. and highest at 2
+P.M. The relative humidity is just the reverse. When the temperature is
+highest, the saturation of the air is lowest, and _vice versâ_. So on land
+when the air, by radiation of heat from the earth, is cooled below the
+dew-point, dew is produced, and, at the freezing-point, hoar-frost.
+
+The _Challenger_ Reports, too, show that the force of the winds on the
+open sea is subject to no distinct and uniform daily variation, but that
+on nearing land the force of the wind gives a curve as distinctly marked
+as the ordinary curve of temperature. That force is lowest from 2 to 4
+A.M., and highest from 2 to 4 P.M. Each of the five great oceans gives the
+same result. At Ben Nevis, on the other hand, these forces are just
+reversed in strength.
+
+It is also shown by the _Challenger_ observations that on the open sea the
+greatest number of thunder-storms occur from 10 P.M. to 8 A.M. And, from
+this, Dr. Buchan concludes that over the ocean terrestrial radiation is
+more powerful than solar radiation in causing those vertical disturbances
+in the equilibrium of the atmosphere which give rise to the thunder-storm.
+
+
+
+
+CHAPTER XXXV
+
+WEATHER-FORECASTING
+
+
+To foretell with any degree of certainty the state of the weather for
+twenty-four hours is of immense advantage to business men, tourists,
+fishermen, and many others. The weather is everybody's business. And the
+probabilities of accurate forecasts are so improving that all are more or
+less giving attention to the morning meteorological reports.
+
+Weather-forecasting depends on the principle from vast experience that, if
+one event happens, a second is likely to follow. According to the extent
+and accuracy of the data, will be the strength of the probability of
+correct forecasts. And the great end of popular meteorology is to
+demonstrate this.
+
+We have given some explanations of the weather in some respects unique;
+and a careful consideration of these explanations will the more convince
+the reader of the importance of the subject. No doubt the changes of the
+weather are extremely complex, at times baffling; and the wonder is that
+forecasts come so near the truth.
+
+For instance, the year 1903 almost defied the ordinary rules of weather,
+for it broke the record for rainfall. And, last year, so repulsive and
+unseasonable was the spring, that there seemed to be a virtual
+"withdrawal" of the season. I wrote on it as "The Recession of Spring."
+Speak about Borrowing Days! We had the equinoctial gales of March about
+the middle of April. On very few days had we "clear shining to cheer us
+after rain," for the bitter cold dried up any genial moisture. An old
+farmer remarked that "We're gaun ower faur North." No one could account
+for the backwardness of the season. Unless for the cheering songs of the
+grove-charmers, one would have forgotten the time of the year.
+
+In March of this year, at Strathmore, the barometer fell from 30·5 inches
+(the highest for years) to 28·65 in five days without unfavourable weather
+following. It again rose to 30·05, then fell to 28·45, followed by a rise
+to 28·7 without any peculiar change. But in two days it fell to 28·4 (the
+lowest for years), followed by a deluge of rain and a perfect hurricane
+for several hours, while the temperature was fortunately mild. It was only
+evident at the end that this universal storm had been "brewing" some days
+before.
+
+All are familiar with the ordinary prognostics of good and bad weather. A
+"broch" round the moon, in her troubled heaven, indicates a storm of rain
+or wind. When the dark crimson sun in the evening throws a brilliant
+bronzed light on the gables and dead leaves, we are sure that there is an
+intense radiation from the earth to form dew, or even hoar-frost.
+
+According to the meteorological folk-lore, the weather of the summer
+season is indicated by the foliation of the oak and ash trees. If the oak
+comes first into leaf, the summer will be hot and dry, if the ash has the
+precedence it will be wet and cold. Looking over the observations of the
+budding of these two trees for half a century, I find that the
+weather-lore adage has been pretty correct. The ash was out before the oak
+a full month in the years 1816, '17, '21, '23, '28, '29, '30, '38, '40,
+'45, '50, and '59; and the summer and autumn in these years were
+unfavourable. Again, the oak was out before the ash several weeks in the
+years 1818, '19, '20, '22, '24, '25, '26, '27, '33, '34, '35, '36, '37,
+'42, '46, '54, '68, and '69; the summers during these years were dry and
+warm, and the harvests were abundant. One can never think of this weather
+prognostic from nature without recalling the Swallow Song of Tennyson's
+"Princess":--
+
+  "Why lingereth she to clothe her heart with love,
+  Delaying, as the tender ash delays
+  To clothe herself, when all the woods are green?"
+
+On a muggy morning a sudden clearness in the south "drowns the ploughman."
+And yet enough blue in the sky "tae mak' a pair o' breeks" cheers one with
+the assurance of coming dry and sunny weather. The low flying of the
+swallows betokens rain, as well as any unseasonable dancing of midges in
+the evening. Sore corns on the feet, and rheumatism in the joints, are
+direful precursors. The leaves are all a-tremble before the approach of
+thunder. But throughout this volume I have given many illustrations.
+
+But one of the largest and most important practical problems of
+meteorology is to ascertain the course which storms follow, and the causes
+by which that course is determined, so that a forecast may thereby be
+made, not only of the certain approach of a storm, but the particular
+direction and force of the storm. The method of conducting this large
+inquiry most effectively was devised by the French astronomer, Le
+Verrier--the great aspirant, with our own Couch Adams, for the discovery
+of the planet Neptune. He began to carry this out in 1858 by the daily
+publication of weather data, followed by a synchronous weather map, which
+showed graphically for the morning of the day of publication the
+atmospheric pressure and the direction and force of the wind, together
+with tables of temperature, rainfall, cloud, and sea disturbances from a
+large number of places in all parts of Europe. It is from similar maps
+that forecasts of storms are still framed, and suitable warnings issued;
+and a mass of information is being collected by telegraph from sixty
+stations in the British Islands, &c., of the state of the weather at eight
+o'clock every morning, and analysed and arranged at the Meteorological
+Office in London for the evening's forecasts over the different districts
+of the country. A juster knowledge is being now acquired of those great
+atmospheric movements, and other changes, which form the groundwork of
+weather-forecasting.
+
+The Meteorological Office, Westminster (entirely distinct from the Royal
+Meteorological Society), is administered by a Council (Chairman, Sir R.
+Strachey; Scottish member, Dr. Buchan), selected by the Royal Society. It
+employs a staff of over forty. The chief departments relate to: (1) Ocean
+Meteorology, including the collection, tabulation, and discussion of
+meteorological data from British ships, the preparation of ocean weather
+charts, and the issue of meteorological instruments to the Royal Navy and
+Mercantile Marine; (2) Weather Telegraphy, including the reception of
+telegrams thrice a day from selected stations for the preparation of the
+daily reports and weather forecasts. Representatives of newspapers, &c.,
+receive copies of the 11 A.M. forecast based on the 8 A.M. observations;
+and also of the 8.30 P.M. forecasts based on the observations received
+earlier in the day. In summer and autumn harvest forecasts are issued by
+telegraph to individuals who will defray the cost. The Office also
+collects climatological data from a number of voluntary and some
+subsidised stations. The "first order" stations include Valentia,
+Falmouth, Kew, and Aberdeen. These have self-recording instruments of high
+precision, giving a continuous record of the meteorological elements.
+
+A Government Commission which sat last year, under the Rt. Hon. Sir
+Herbert Maxwell, Bart., have issued a Report, recommending a number of
+changes in the management and constitution of the Meteorological Office;
+and considerable modifications are not unlikely to take place in the near
+future. In his evidence before that Commission, the Chairman of the
+Council acknowledged that the great function of meteorologists is the
+collection of facts; but the interpretation of those collected facts, in a
+scientific manner, is still in a very immature condition. Dr. Buchan, in
+his evidence, confessed that forecasting by the Council is purely "by rule
+of thumb." It is not possible to lay down hard and fast rules for
+forecasting.
+
+With regard to the storm-warning telegrams, as a rule, the earliest
+trustworthy indication of the approach of a dangerous storm to the coasts
+of the British Isles precedes the storm by only a few hours. Delays are
+therefore very serious.
+
+It is admitted by the best British meteorologists that the observations of
+the United States are better conducted, although the best instruments in
+the world are set and registered at Kew, in England. The work of weather
+forecasts and storm warnings is carried on with the highest degree of
+promptitude and efficiency at the Washington Central Office. This is
+because the work of predictions has been hitherto the chief work of the
+Office: the entire time of the observers, on whose telegraphic reports the
+forecasts are based, is controlled by the United States Weather Bureau;
+and the right of precedence in the use of wires is maintained.
+
+Professor Brückner, of Berne, has devoted a lifetime to the comparatively
+new treatment of climatic oscillations, based upon observations made at
+321 points on the earth's surface, distributed as follows: Europe, 198;
+Asia, 39; N. America, 50; Cen. and S. America, 16; Australia, 12; Africa,
+6. One of his conclusions is that an average time of about thirty-five
+years is found to intervene between one period of excess or deficiency of
+warmth and the next, accompanied by the opposite relative condition of
+moisture.
+
+All are familiar with the hoisting of cone-warning as indication of a
+coming storm. This work is exceedingly important, especially for those
+connected with the sea by business or pleasure. On the known approach of a
+cyclone of dangerous intensity, special messages are sent from the London
+Meteorological Office, warning the coasts likely to be affected. When the
+cone is hoisted with its apex downwards, it means that strong south or
+south-west winds are to be looked for. When the cone is hoisted with its
+apex upwards, it indicates that strong winds from the north or north-east
+are expected. Of course they are merely useful precautions; but they are
+universally attended to by people on the sea-coast.
+
+Though one may have reasonable doubts about the use that can be made of
+weather forecasts for three days, such as are now regularly issued, on
+account of the finical, coy, spasmodic interludes on short notice, yet
+there is a wonderful certainty in the daily prognostics of the direction
+and strength of the wind, the temperature of the air, and the likelihood
+of rainy or fair weather, dependent on the broad uniformity of nature.
+This is very serviceable for people who have now to live at high pressure
+in business, in the enthralling days of keen competition. And it is a
+great boon to those who are in search of health by travelling, or who, in
+innocent pleasure, desire to live as much as possible in the open air.
+Very little credit is given to the "gas" of the isolated "weather
+prophet"; but those who have confidence in the usual weather forecasts
+from the Meteorological Office are satisfied in their belief; and those
+who, in self-confidence, ignore all weather prognostics, are still weak
+enough to read them and act up to them.
+
+       *       *       *       *       *
+
+In practical meteorology, in the scientific explanation of popular
+weather-lore, and in the study of atmospheric phenomena, which so
+powerfully influence us, for gladness or discomfort, we may, as with other
+branches of science, even all our days, cheerfully go on in "the noiseless
+tenor of our way,"
+
+                        "Nourishing a youth sublime,
+  With the fairy tales of science and the long results of time."
+
+
+
+
+INDEX
+
+
+  Abercromby, spectre on Adam's Peak, 89
+
+  Adam's Peak, spectre, 89
+
+  Afterglow described, 62;
+    dust-particles to form, 64
+
+  Air, change of, 55;
+    clearness and dryness, 49;
+    devitalised, 52;
+    disease-germs in, 53;
+    thunder-clouds, 49
+
+  Aitken, Dr., afterglows, 67;
+    anti-cyclones, 97;
+    colour of water, 75;
+    condensing power of dust, 2;
+    decay of clouds, 39;
+    dew-formation, 14;
+    dust and atmospheric phenomena, 29;
+    electrical deposition of smoke, 83;
+    false dew, 18;
+    fog-counter, 82;
+    foreglows, 67;
+    formation of clouds, 35;
+    haze, 44;
+    hazing effects of atmospheric dust, 47;
+    Kingairloch experiments, 30;
+    one-coloured rainbow, 70;
+    radiation from snow, 86;
+    regenerators, 85;
+    sanitary detective, 78
+
+  Ammonia and cloud formation, 36
+
+  Annie Laurie, 17
+
+  Anti-cyclones, forecasting by, 97;
+    formation, 97;
+    cause of influenza, 109
+
+  Aratus, forecasting by moon, 61
+
+  Ariel's song, 42
+
+  Aurora Borealis, 71;
+    forebodings, 71-73;
+    name by Gassendi, 72;
+    other names, 72;
+    safety valve of electricity, 72;
+    sun's spots, 72;
+    sun control, 74;
+    symptoms, 72
+
+
+  Bagillt, condensing lead fumes, 84
+
+  Ballachulish, sunsets, 64
+
+  Ballantine's song, 17
+
+  Barometer, indications, 10
+
+  Ben Nevis, dust-particles, 30;
+    instruments, 104;
+    meteorology, 102;
+    observations, 105;
+    rainfall, 103;
+    regret at stoppage of Observatory, 103
+
+  Blairgowrie, personal description of afterglow, 62
+
+  Blue sky, 74;
+    cause of, 75, 77
+
+  Borrowing days, 117
+
+  Brocken, spectre, 89;
+    personal description, 90;
+    Noah's Ark, 90
+
+  Brückner, climatic oscillations, 122
+
+  Buchan, Dr., Aitken's radiation from snow, 86;
+    Ben Nevis, papers on, 103;
+    _Challenger_ Reports, 114;
+    cold of 1886, 86;
+    east winds, 94;
+    isobars, 115;
+    rainfall statistics, 100;
+    on forecasting, 121
+
+  Buchanan, Ben Nevis Observatory, 102;
+    great prevalence of fog, 106
+
+  Buddha's Lights, of Ceylon, 72
+
+  Burns, allusions to aurora, 71, 73
+
+  Byron, storm in Alps, 50
+
+
+  _Challenger_ Expedition, 114;
+    temperature, 115;
+    thunder-storms, 116;
+    winds, 116
+
+  Chambers on sun-spots and grain prices, 113
+
+  Change of air, 55;
+    Strathmore to Glenisla, 56
+
+  Charles II., fog and smoke, 80
+
+  Chlorine and cloud formation, 36
+
+  Christison and colour of water, 75
+
+  Chrystal on Aitken's radiation from snow, 86
+
+  Cirro-stratus cloud, mackerel-like, 39
+
+  Climate, _Challenger_ notes, 115;
+    cone-warnings, 120;
+    Gulf Stream, 111;
+    oscillations, 120;
+    rainfall, 111;
+    sun-spots on, 112;
+    wooded country on, 111
+
+  Clouds, decay of, 37;
+    distances of, 35;
+    dry, 42;
+    even without dust, 36;
+    formation of, 34;
+    height of, 34;
+    numbering of cloud-particles, 34;
+    sunshine on cloud formation, 35;
+    varieties of, 35
+
+  Cone-warnings, 121
+
+  Continental winds, 98
+
+  Cyclones, 95;
+    formation of, 96, 98;
+    small natural, 98
+
+
+  Decay of clouds, 37;
+    in thin rain, 41;
+    process, 38;
+    ripple markings, 39
+
+  Dew, evidence of rising, 22;
+    experiments, 15, 16;
+    false dew, 17;
+    formation of, 13
+
+  Disease-germs in air, 53;
+    causes, 53;
+    deposited by rain, 55
+
+  Diseases, and east wind, 94;
+    personal notes, 95
+
+  Dumfries, dust in air at, 46
+
+  Dust, condensing power, 43;
+    from meteors, 37;
+    generally necessary for cloud formation, 26;
+    hazing effects, 47;
+    numbering, 26;
+    instruments for numbering, 27;
+    produces afterglows, 64;
+    produces foreglows, 67;
+    quantity in Bunsen flame, 28;
+    at Ben Nevis, 30;
+    Hyères, Mentone, Rigi Kulm, 29;
+    Lucerne, Kingairloch, 30;
+    when not necessary, 36
+
+  Dust enumeration, deductions on, 31
+
+
+  Earn, Loch, splash of drop at, 101
+
+  Earthshine, 59
+
+  Ehrenberg, on colour of water, 75
+
+  Evelyn, fumifugium, 80;
+    remedy for smoke, 82
+
+
+  Falkirk, Dr. Aitken's experiments on haze, 47
+
+  False dew, 19
+
+  Fitzroy on aurora as a foreboder, 73
+
+  Fog, counter, 31;
+    dry, 41;
+    formation, 24;
+    more in towns, 25;
+    and smoke, 80
+
+  Folk-lore, 50
+
+  Foreglow, described, 66;
+    how produced, 67
+
+  Fort William Observatory, 102
+
+  Frankland, disease-germs, 53
+
+  Franklin, lightning, 51
+
+
+  Gassendi, named aurora, 72
+
+  Gillespie, Dr., on weather and influenza, 107
+
+  Glasgow, fog, 81
+
+  Glass, appearing damp, 44
+
+  Glenisla, ozoned air, 56
+
+  Grain crops and sun-spots, 112;
+    Chambers' tables, 113
+
+  Great amazing light in the north, 72
+
+  Gulf Stream, effects on climate, 111
+
+  Gunpowder, great condensing power, 44
+
+
+  Haze, what is, 43;
+    how produced, 44;
+    in clearest air, 45;
+    stages of condensation, 46;
+    in sultry weather, 46;
+    dryness of air and visibility, 48
+
+  Health improved by change of air, 56
+
+  Highland air, few disease-germs, 55
+
+  Hoar-frost, frozen dew, 20;
+    on under surfaces, 21
+
+  Humboldt, isotherms, 114
+
+  Hydrogen peroxide and cloud formation, 36
+
+  Hyères, dust-particles, 29
+
+
+  Indian Ocean, colour, 75
+
+  Influenza, weather and, 107;
+    six distinct epidemics, 108;
+    spread of anti-cyclonic conditions, 109
+
+  Isobars by Buchan, 115
+
+  Isotherms by Humboldt, 114
+
+  Italian lakes, stages of condensation, 45
+
+
+  Job, on dew formation, 13
+
+
+  Kelvin recorder, 84;
+    Aitken's radiation from snow, 86
+
+  Kew, instruments set, 121
+
+  Kingairloch, dust-particles, 30, 46
+
+  Kirchhoff, lower temperature of sun-spot, 112
+
+  Krakatoa, eruption of, dust-particles, 63
+
+
+  Le Verrier and weathercharts, 119
+
+  Lockyer, and sun-spots, 112
+
+  Lightning, electricity, 51;
+    photographed, 51;
+    sheet and forked, 51;
+    ozone, 52
+
+  Lodge, electrical deposition of smoke, 83
+
+  London, coals consumed, 25;
+    sulphur and fog, 25;
+    fog in reign of Charles II., 81;
+    Meteorological Office, 11, 120
+
+  Lord Derwentwater's Lights, 72
+
+  Lower animals, sensitiveness, 11
+
+  Lucerne, dust-particles, 30
+
+
+  MacLaren, Aitken's radiation from snow, 86
+
+  Magnesia, small affinity for water-vapour, 44
+
+  Man in the street, 11
+
+  Mediterranean, brilliant colour, 77
+
+  Mentone, dust-particles, 29
+
+  Merry Dancers of Shetland, 71
+
+  Meteors, producing dust, 37
+
+  Meteorological Council, London, 103;
+    Office, 120;
+    cone-warnings, 121;
+    regular forecasts, 123
+
+  Milne Home on Ben Nevis, 103
+
+  Milton, dust numberless, 26
+
+  Moon, old, in new moon's arms, 58;
+    weather indications, 59, 61
+
+  Mountain giants, 88;
+    Adam's Peak, 89;
+    Brocken, 89
+
+  Munich, International Meteorological Conference, 35
+
+  Murray, _Challenger_ Expedition, 114
+
+
+  Nardius, dew exhalation, 13
+
+  Newton, colour of sky, 77
+
+  Nimbus, cloud, 35
+
+
+  Oak and ash, on climate, 118
+
+  Ochils, one-coloured rainbow, 70
+
+
+  Pacific, colour, 75
+
+  Paris, aurora, 71;
+    disease-germs, 55
+
+  Paton, Waller, bronze tints in sunsets, 64
+
+  Piazzi Smith, aurora, 72
+
+  Picket, dew-formation, 14
+
+  Pilatus, fine rain, 42
+
+  Polar lightnings, 72
+
+
+  Radiant heat, producing fine rain, 41
+
+  Radiation from snow, 86
+
+  Rain, 98;
+    heavy rainfalls, 99
+
+  Rainbow, 68;
+    forecasts, 62, 69;
+    formation, 69;
+    one-coloured, 70
+
+  Rains, it always, 40;
+    radiant heat in process, 41;
+    Ariel's song, 43
+
+  Rankin, dust-particles, Ben Nevis, 30
+
+  Richardson, devitalised air, 51
+
+  Rigi Kulm, dust-particles, 29
+
+  Rolier, aurora, 73
+
+
+  St. Paul's, London, disease-germs in air, 54
+
+  Sanitary detective, 78
+
+  Shakespeare, tempest, 95
+
+  Shelley, old moon in new moon's arms, 59
+
+  Simoom and sirocco, 94
+
+  Skye, rainy, 40
+
+  Smoke, electrical deposition of, 83;
+    regenerators, 85
+
+  Smoking-room, condensing power, 44
+
+  Snow, bad conducting, 87;
+    radiation from, 86
+
+  Sodium dust, condensing power, 45
+
+  Spens, forebodings of moon, 61
+
+  Splash of a drop, experiments, 101
+
+  Stevenson, R. L., splash of drop, 101
+
+  Stewart, sun-spots, 112
+
+  Strachey on forecasts, 121
+
+  Strathmore, observations on hoar-frost, 22;
+    on decay of clouds, 38;
+    to Glenisla, change of air, 56;
+    observations on old moon in new moon's arms, 59;
+    afterglow described, 62;
+    foreglow, 66;
+    cold of 1886, 86;
+    healthy by woods, 111;
+    observations on barometer, 118
+
+  Strathpeffer, 9
+
+  Sulphur as a fog-former, 25
+
+  Sulphuretted hydrogen and cloud-formation, 36
+
+  Sunshine on cloud-formation, 35
+
+  Sun's spots, and aurora, 72, 112;
+    and grain crops, 112
+
+  Symons, rainfall, 100
+
+  Synoptic charts, 98
+
+
+  Tait, on Aitken's radiation from snow, 86
+
+  Tay Bridge, fall of, 92
+
+  Tennyson, aurora, 71;
+    dew, 19;
+    oak and ash, 119
+
+  Thermometer, indications, 10
+
+  Thomson, Wyville, _Challenger_ Expedition, 114
+
+  Thunder-storm described, 50
+
+
+  Valkyries, aurora, 73
+
+  Visibility, limit of, 48
+
+
+  Washington, Meteorological Office, 121
+
+  Water, pressure to show plant exudation, 18;
+    colour of, 75;
+    experiments on distilled, 76;
+    dust-particles vary colour, 77
+
+  Weather and influenza, 107
+
+  Weather-forecasting, 116;
+    advantages, 117;
+    principle, 117;
+    examples, 118;
+    old moon in new moon's arms, 59;
+    by moon, 61;
+    oak and ash, 118;
+    cone-warnings, 122;
+    three days', 123
+
+  Weather-lore, 50, 118
+
+  Weather talisman, 9;
+    call on barometer and thermometer, 10;
+    exceptional years, 117
+
+  Wells, Dr., on dew, 14
+
+  Wilson, Prof., on hoar-frost, 20
+
+  Wind, 92;
+    rates, 92;
+    trade, 93;
+    land and sea, 93
+
+  Woeikof, durability of cold, 88
+
+  Wordsworth, rainbow, 68
+
+  Worthington, splash of drop, 100
+
+  Wragge, observations at Ben Nevis, 104
+
+
+  Printed by BALLANTYNE, HANSON & CO.
+  Edinburgh & London
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Meteorology, by J. G. M'Pherson
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diff --git a/38928-8.zip b/38928-8.zip
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+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
+    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" />
+    <title>
+      Meteorology; or Weather Explained, by J. G. M&#8217;Pherson&mdash;A Project Gutenberg eBook
+    </title>
+
+    <style type="text/css">
+
+    p {margin-top: .75em; text-align: justify; margin-bottom: .75em;}
+
+    body {margin-left: 12%; margin-right: 12%;}
+
+    .pagenum {position: absolute; left: 92%; font-size: smaller; text-align: right; font-style: normal;}
+
+    h1,h2,h3,h4,h5,h6 {text-align: center; clear: both;}
+
+    hr {width: 33%; margin-top: 2em; margin-bottom: 2em; margin-left: auto; margin-right: auto; clear: both;}
+
+    table {margin-left: auto; margin-right: auto;}
+
+    .giant {font-size: 200%}
+    .huge {font-size: 150%}
+    .large {font-size: 125%}
+
+    .poem {margin-left: 15%;}
+    .note {margin-left: 20%; margin-right: 20%;}
+    .hang {margin-left: 2em; text-indent: -2em;}
+    .index {margin-left: 20%;}
+    .title {text-align: center; font-size: 150%;}
+
+    .right {text-align: right;}
+    .center {text-align: center;}
+
+    .smcap {font-variant: small-caps;}
+    .smcaplc {text-transform: lowercase; font-variant: small-caps;}
+
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+
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+    a:visited {color:#6633cc; text-decoration:none}
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+    .border {border: solid 2px; padding-left: 1em; padding-right: 1em; margin: auto; width: 25em;}
+
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+  </head>
+<body>
+
+
+<pre>
+
+The Project Gutenberg EBook of Meteorology, by J. G. M'Pherson
+
+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: Meteorology
+       or Weather Explained
+
+Author: J. G. M'Pherson
+
+Release Date: February 19, 2012 [EBook #38928]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK METEOROLOGY ***
+
+
+
+
+Produced by The Online Distributed Proofreading Team at
+https://www.pgdp.net (This file was produced from images
+generously made available by The Internet Archive.)
+
+
+
+
+
+
+</pre>
+
+
+
+
+<div class="figcenter"><img src="images/cover.jpg" alt="" /></div>
+<p>&nbsp;</p><p>&nbsp;</p>
+
+
+<p class="center"><span class="large">SHILLING SCIENTIFIC SERIES</span></p>
+
+<p>&nbsp;</p><p>&nbsp;</p>
+
+<div class="figcenter"><img src="images/frontis.jpg" alt="" /></div>
+<p class="center"><span class="smcap">Dr. Aitken&#8217;s Dust-Counter.</span></p>
+
+<p class="center">R is the test-receiver; P the air-pump; M the measuring apparatus; L the
+illuminating<br />arrangements; G the Gasometer; A the pipe through which the tested air is drawn.</p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<h1><small>METEOROLOGY;<br />
+OR,<br />
+WEATHER EXPLAINED.</small></h1>
+<p>&nbsp;</p>
+<p class="center"><small>BY</small><br />
+<span class="large">J. G. M&#8217;PHERSON</span>, Ph.D., F.R.S.E.,<br />
+<small>GRADUATE WITH FIRST-CLASS HONOURS, AND FOR NINE YEARS<br />
+EXTENSION LECTURER ON METEOROLOGY AND MATHEMATICAL<br />
+EXAMINER IN THE UNIVERSITY OF ST. ANDREWS;<br />
+AUTHOR OF &#8220;TALES OF SCIENCE,&#8221; ETC.</small></p>
+<p>&nbsp;</p>
+<p class="center">LONDON: T. C. &amp; E. C. JACK,<br />
+34 HENRIETTA STREET, W.C.<br />
+AND EDINBURGH.<br />
+1905.</p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<div class="border">
+<p class="center"><span class="huge"><span class="smcap">The<br />Shilling Scientific Series</span></span></p>
+
+<p class="center"><i>The following Vols. are now ready or in the Press</i>:&mdash;</p>
+
+<p class="hang">BALLOONS, AIRSHIPS, AND FLYING MACHINES. By <span class="smcap">Gertrude Bacon</span>.</p>
+<p class="hang">MOTORS AND MOTORING. By Professor <span class="smcap">Harry Spooner</span>.</p>
+<p class="hang">RADIUM. By Dr. <span class="smcap">Hampson</span>.</p>
+<p class="hang">TELEGRAPHY WITH AND WITHOUT WIRES. By <span class="smcap">W. J. White</span>.</p>
+<p class="hang">ELECTRIC LIGHTING. By <span class="smcap">S. F. Walker</span>, R.N., M.I.E.E.</p>
+<p class="hang">LOCAL GOVERNMENT. By <span class="smcap">Percy Ashley</span>, M.A.</p>
+
+<p class="center"><i>Others in Preparation</i></p>
+
+<p class="center">Printed by <span class="smcap">Ballantyne, Hanson &amp; Co.</span><br />
+At the Ballantyne Press</p></div>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p>
+<p class="title">CONTENTS</p>
+
+
+<table border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td><small>CHAP.</small></td><td>&nbsp;</td><td align="right"><small>PAGE</small></td></tr>
+<tr><td align="right"><a href="#CHAPTER_I">I.</a></td>
+    <td><span class="smcap">Introduction</span></td>
+    <td align="right"><a href="#Page_9">9</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_II">II.</a></td>
+    <td><span class="smcap">The Formation of Dew</span></td>
+    <td align="right"><a href="#Page_13">13</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_III">III.</a></td>
+    <td><span class="smcap">True and False Dew</span></td>
+    <td align="right"><a href="#Page_17">17</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_IV">IV.</a></td>
+    <td><span class="smcap">Hoar-Frost</span></td>
+    <td align="right"><a href="#Page_20">20</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_V">V.</a></td>
+    <td><span class="smcap">Fog</span></td>
+    <td align="right"><a href="#Page_23">23</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_VI">VI.</a></td>
+    <td><span class="smcap">The Numbering of the Dust</span></td>
+    <td align="right"><a href="#Page_26">26</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_VII">VII.</a></td>
+    <td><span class="smcap">Dust and Atmospheric Phenomena</span></td>
+    <td align="right"><a href="#Page_29">29</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_VIII">VIII.</a></td>
+    <td><span class="smcap">A Fog-Counter</span></td>
+    <td align="right"><a href="#Page_31">31</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_IX">IX.</a></td>
+    <td><span class="smcap">Formation of Clouds</span></td>
+    <td align="right"><a href="#Page_34">34</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_X">X.</a></td>
+    <td><span class="smcap">Decay of Clouds</span></td>
+    <td align="right"><a href="#Page_37">37</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XI">XI.</a></td>
+    <td><span class="smcap">It always Rains</span></td>
+    <td align="right"><a href="#Page_40">40</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XII">XII.</a></td>
+    <td><span class="smcap">Haze</span></td>
+    <td align="right"><a href="#Page_43">43</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XIII">XIII.</a></td>
+    <td><span class="smcap">Hazing Effects of Atmospheric Dust</span></td>
+    <td align="right"><a href="#Page_47">47</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XIV">XIV.</a></td>
+    <td><span class="smcap">Thunder Clears the Air</span></td>
+    <td align="right"><a href="#Page_49">49</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XV">XV.</a></td>
+    <td><span class="smcap">Disease Germs in the Air</span></td>
+    <td align="right"><a href="#Page_53">53</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XVI">XVI.</a></td>
+    <td><span class="smcap">A Change of Air</span></td>
+    <td align="right"><a href="#Page_55">55</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XVII">XVII.</a></td>
+    <td><span class="smcap">The Old Moon in the New Moon&#8217;s Arms</span></td>
+    <td align="right"><a href="#Page_58">58</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XVIII">XVIII.</a></td>
+    <td><span class="smcap">An Autumn Afterglow</span></td>
+    <td align="right"><a href="#Page_62">62</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XIX">XIX.</a></td>
+    <td><span class="smcap">A Winter Foreglow</span></td>
+    <td align="right"><a href="#Page_65">65</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XX">XX.</a></td>
+    <td><span class="smcap">The Rainbow</span></td>
+    <td align="right"><a href="#Page_68">68</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXI">XXI.</a></td>
+    <td><span class="smcap">The Aurora Borealis</span></td>
+    <td align="right"><a href="#Page_71">71</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXII">XXII.</a></td>
+    <td><span class="smcap">The Blue Sky</span></td>
+    <td align="right"><a href="#Page_74">74</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXIII">XXIII.</a></td>
+    <td><span class="smcap">A Sanitary Detective</span></td>
+    <td align="right"><a href="#Page_78">78</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXIV">XXIV.</a></td>
+    <td><span class="smcap">Fog and Smoke</span></td>
+    <td align="right"><a href="#Page_80">80</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXV">XXV.</a></td>
+    <td><span class="smcap">Electrical Deposition of Smoke</span></td>
+    <td align="right"><a href="#Page_83">83</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXVI">XXVI.</a></td>
+    <td><span class="smcap">Radiation from Snow</span></td>
+    <td align="right"><a href="#Page_86">86</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXVII">XXVII.</a></td>
+    <td><span class="smcap">Mountain Giants</span></td>
+    <td align="right"><a href="#Page_88">88</a></td></tr>
+<tr><td align="right"><span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span><a href="#CHAPTER_XXVIII">XXVIII.</a></td>
+    <td><span class="smcap">The Wind</span></td>
+    <td align="right"><a href="#Page_92">92</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXIX">XXIX.</a></td>
+    <td><span class="smcap">Cyclones and Anti-Cyclones</span></td>
+    <td align="right"><a href="#Page_95">95</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXX">XXX.</a></td>
+    <td><span class="smcap">Rain Phenomena</span></td>
+    <td align="right"><a href="#Page_98">98</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXXI">XXXI.</a></td>
+    <td><span class="smcap">The Meteorology of Ben Nevis</span></td>
+    <td align="right"><a href="#Page_102">102</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXXII">XXXII.</a></td>
+    <td><span class="smcap">The Weather and Influenza</span></td>
+    <td align="right"><a href="#Page_107">107</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXXIII">XXXIII.</a></td>
+    <td><span class="smcap">Climate</span></td>
+    <td align="right"><a href="#Page_110">110</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXXIV">XXXIV.</a></td>
+    <td><span class="smcap">The &#8220;Challenger&#8221; Weather Reports</span></td>
+    <td align="right"><a href="#Page_114">114</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXXV">XXXV.</a></td>
+    <td><span class="smcap">Weather-Forecasting</span></td>
+    <td align="right"><a href="#Page_116">116</a></td></tr>
+<tr><td>&nbsp;</td>
+    <td>INDEX</td>
+    <td align="right"><a href="#Page_124">124</a></td></tr></table>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p class="title">PREFATORY NOTE</p>
+
+<div class="note">
+<p>I am very much indebted to Dr. John Aitken, F.R.S., for his great kindness
+in carefully revising the proof sheets, and giving me most valuable
+suggestions. This is a sufficient guarantee that accuracy has not been
+sacrificed to popular explanation.</p>
+
+<p class="right">J. G. M&#8217;P.</p>
+
+<p><span class="smcap">Ruthven Manse</span>,<br />
+<span style="margin-left: 2em;"><i>June 10, 1905</i>.</span></p></div>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span></p>
+<p class="center"><span class="giant">METEOROLOGY</span></p>
+<p>&nbsp;</p>
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I</h2>
+<p class="title">INTRODUCTION</p>
+
+
+<p>Though by familiarity made commonplace, the &#8220;weather&#8221; is one of the most
+important topics of conversation, and has constant bearings upon the work
+and prospects of business-men and men of pleasure. The state of the
+weather is the password when people meet on the country road: we could not
+do without the humble talisman. &#8220;A fine day&#8221; comes spontaneously to the
+lips, whatever be the state of the atmosphere, unless it is peculiarly and
+strikingly repulsive; then &#8220;A bitter day&#8221; would take the place of the
+expression. Yet I have heard &#8220;<i>Terrible</i> guid wither&#8221; as often as
+&#8220;<i>Terrible</i> bad day&#8221; among country people.</p>
+
+<p>Scarcely a friendly letter is penned without a reference to the weather,
+as to what has been, is, or may be. It is a new stimulus to a lagging
+conversation at any dinner-table. All are so dependent on the weather,
+especially those getting up in years or of delicate health.</p>
+
+<p>I remember, when at Strathpeffer, the great health-resort in the North of
+Scotland, in 1885, an<span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span> anxious invalid at &#8220;The Pump&#8221; asking a
+weather-beaten, rheumatic old gamekeeper what sort of a day it was to be,
+considering that it had been wet for some time. The keeper crippled to the
+barometer outside the doorway, and returned with the matter-of-fact
+answer: &#8220;She&#8217;s faurer doon ta tay nur she wass up yestreen.&#8221; The barometer
+had evidently fallen during the night. &#8220;And what are we to expect?&#8221; sadly
+inquired the invalid. &#8220;It&#8217;ll pe aither ferry wat, or mohr rain&#8221;&mdash;a poor
+consolation!</p>
+
+<p>Most men who are bent on business or pleasure, and all dwellers in the
+country who have the instruments, make a first call at the barometer in
+the lobby, or the aneroid in the breakfast-parlour, to &#8220;see what she
+says.&#8221; A good rise of the black needle (that is, to the right) above the
+yellow needle is a source of rejoicing, as it will likely be clear, dry,
+and hard weather. A slight fall (that is, to the left) causes anxiety as
+to coming rain, and a big depression forebodes much rain or a violent
+storm of wind. In either case of &#8220;fall,&#8221; the shutters come over the eyes
+of the observer. Next, even before breakfast, a move is made to the
+self-registering thermometer (set the night before) on a stone, a couple
+of feet above the grass. A good reading, above the freezing-point in
+winter and much above it in summer, indicates the absence of killing
+rimes, that are generally followed by rain. A very low register accounts
+for the feeling of cold during the night, though the fires were not out;
+and predicts precarious weather. Ordinarily careful observers&mdash;as I, who
+have been in one place for more than thirty<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> years&mdash;can, with the morning
+indications of these two instruments, come pretty sure of their
+prognostics of the day&#8217;s weather. Of course, the morning newspaper is
+carefully scanned as to the weather-forecasts from the London
+Meteorological Office&mdash;direction of wind; warm, mild, or cold; rain or
+fair, and so on&mdash;and in general these indications are wonderfully accurate
+for twenty-four hours; though the &#8220;three days&#8217;&#8221; prognostics seem to
+stretch a point. We are hardly up to that yet.</p>
+
+<p>The lower animals are very sensitive as to the state of approaching
+extremes of weather. &#8220;Thae sea beass,&#8221; referring to sea-gulls over the
+inland leas during ploughing, are ordinary indicators of stormy weather.
+Wind is sure to follow violent wheelings of crows. &#8220;Beware of rain&#8221; when
+the sheep are restive, rubbing themselves on tree stumps. But all are
+familiar with Jenner&#8217;s prognostics of rain.</p>
+
+<p>Science has come to the aid of ordinary weather-lore during the last
+twenty years, by leaps and bounds. Time-honoured notions and revered
+fictions, around which the hallowed associations of our early training
+fondly and firmly cling, must now yield to the exact handling of modern
+science; and with reluctance we have to part with them. Yet there is in
+all a fascination to account for certain ordinary phenomena. &#8220;The man in
+the street,&#8221; as well as the strong reading man, wishes to know the &#8220;why&#8221;
+and the &#8220;how&#8221; of weather-forecasting. They are anxious to have
+weather-phenomena explained in a plain, interesting, but accurate way.</p>
+
+<p>The freshness of the marvellous results has an irresistible charm for the
+open mind, keen for useful<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> information. The discoveries often seem so
+simple that one wonders why they were not made before.</p>
+
+<p>Until about twenty years ago, Meteorology was comparatively far back as a
+science; and in one important branch of it, no one has done more to put
+weather-lore on a scientific basis than Dr. John Aitken, F.R.S., who has
+very kindly given me his full permission to popularise what I like of his
+numerous and very valuable scientific papers in the <i>Transactions of the
+Royal Society of Edinburgh</i>. This I have done my best to carry out in the
+following pages. &#8220;The way of putting it&#8221; is my only claim.</p>
+
+<p>Many scientific men are decoyed on in the search for truth with a spell
+unknown to others: the anticipation of the results sometimes amounts to a
+passion. Many wrong tracks do they take, yet they start afresh, just as
+the detective has to take several courses before he hits upon the correct
+scent. When they succeed, they experience a pleasure which is
+indescribable; to them fame is more than a mere &#8220;fancied life in others&#8217;
+breath.&#8221;</p>
+
+<p>Dr. Aitken&#8217;s continued experiments, often of rare ingenuity and
+brilliancy, show that no truth is altogether barren; and even that which
+looks at first sight the very simplest and most trivial may turn out
+fruitful in precious results. Small things must not be overlooked, for
+great discoveries are sometimes at a man&#8217;s very door. Dr. Aitken has shown
+us this in many of his discoveries which have revolutionised a branch of
+meteorology. Prudence, patience, observing power, and perseverance in
+scientific research will do much to bring about unexpected results, and
+not more so in any science<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> than in accounting for weather-lore on a
+rational basis, which it is in the power of all my readers to further.</p>
+
+<p>&#8220;The old order changeth, giving place to new.&#8221; With kaleidoscopic variety
+Nature&#8217;s face changes to the touch of the anxious and reverent observer.
+And some of these curious weather-views will be disclosed in these pages,
+so as, in a brief but readable way, to explain the weather, and lay a safe
+basis for probable forecastings, which will be of great benefit to the man
+of business as well as the man of pleasure.</p>
+
+<p class="poem">&#8220;Felix, qui potuit rerum cognoscere causas.&#8221;<br />
+<span style="margin-left: 16em;">&mdash;<span class="smcap">Virgil.</span></span></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II</h2>
+<p class="title">THE FORMATION OF DEW</p>
+
+
+<p>The writer of the Book of Job gravely asked the important question, &#8220;Who
+hath begotten the drops of dew?&#8221; We repeat the question in another form,
+&#8220;Whence comes the real dew? Does it fall from the heavens above, or does
+it rise from the earth beneath?&#8221;</p>
+
+<p>Until about the beginning of the seventeenth century, scientific men held
+the opinion of ordinary observers that dew fell from the atmosphere. But
+there was then a reaction from this theory, for Nardius defined it as an
+exhalation from the earth. Of course, it was well known that dew was
+formed by the precipitation of the vapour of the air upon a colder body.
+You can see that any day for yourself<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span> by bringing a glass of very cold
+water into a warm room; the outer surface of the glass is dimmed at once
+by the moisture from the air. M. Picket was puzzled when he saw that a
+thermometer, suspended five feet above the ground, marked a lower
+temperature on clear nights than one suspended at the height of
+seventy-five feet; because it was always supposed that the cold of evening
+descended from above. Again he was puzzled when he observed that a buried
+thermometer read higher than one on the surface of the ground. Until
+recently the greatest authority on dew was Dr. Wells, who carefully
+converged all the rays of scientific light upon the subject. He came to
+the conclusion that dew was condensed out of the air.</p>
+
+<p>But the discovery of the true theory was left to Dr. John Aitken, F.R.S.,
+a distinguished observer and a practical physicist, of whom Scotland has
+reason to be proud. About twenty years ago he made the discovery, and it
+is now accepted by all scientific men on the Continent as well as in Great
+Britain. What first caused him to doubt Dr. Wells&#8217; theory, so universally
+accepted, that dew is formed of vapour existing at the time in the air,
+and to suppose that dew is mostly formed of vapour rising from the ground,
+was the result of some observations made in summer on the temperature of
+the soil at a small depth under the surface, and of the air over it, after
+sunset and at night. He was struck with the unvarying fact that the
+ground, a little below the surface, was warmer than the air over it. By
+placing a thermometer among stems below the surface, he found that it
+registered 18&deg; Fahr. higher<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> than one on the surface. So long, then, as
+the surface of the ground is above the dew-point (<i>i.e.</i> the temperature
+when dew begins to be formed), vapour must rise from the ground; this
+moist air will mingle with the air which it enters, and its moisture will
+be condensed and form dew, whenever it comes in contact with a surface
+cooled below the dew-point.</p>
+
+<p>You can verify this by simple experiments. Take a thin, shallow, metal
+tray, painted black, and place it over the ground after sunset. On dewy
+nights the <i>inside</i> of the tray is dewed, and the grass inside is wetter
+than that outside. On some nights there is no dew outside the tray, and on
+all nights the deposit on the inner is heavier than that on the outside.
+If wool is used in the experiments, we are reminded of one of the forms of
+the dewing of Gideon&#8217;s fleece&mdash;the fleece was bedewed when all outside was
+dry.</p>
+
+<p>You therefore naturally and rightly come to the conclusion that far more
+vapour rises out of the ground during the night than condenses as dew on
+the grass, and that this vapour from the ground is trapped by the tray.
+Much of the rising vapour is generally carried away by the passing wind,
+however gentle; hence we have it condensed as dew on the roofs of houses,
+and other places, where you would think that it had fallen from above. The
+vapour rising under the tray is not diluted by the mixture with the drier
+air which is occasioned by the passing wind; therefore, though only cooled
+to the same extent as the air outside, it yields a heavier deposit of dew.</p>
+
+<p><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span>If you place the tray on bare ground, you will find on a dewy night that
+the inside of the tray is quite wet. On a dewy night you will observe that
+the under part of the gravel of the road is dripping wet when the top is
+dry. You will find, too, that around pieces of iron and old implements in
+the field, there is a very marked increase of grass, owing to the deposit
+of moisture on these articles&mdash;moisture which has been condensed by the
+cold metal from the vapour-charged air, which has risen from the ground on
+dewy nights.</p>
+
+<p>But all doubt upon this important matter is removed by a most successful
+experiment with a fine balance, which weighs to a quarter of a grain. If
+vapour rises from the ground for any length of time during dewy nights,
+the soil which gives off the vapour must lose weight. To test this, cut
+from the lawn a piece of turf six inches square and a quarter of an inch
+thick. Place this in a shallow pan, and carefully note the weight of both
+turf and pan with the sensitive balance. To prevent loss by evaporation,
+the weighing should be done in an open shed. Then place the pan and turf
+at sunset in the open cut. Five hours afterwards remove and weigh them,
+and it will be found that the turf has lost a part of its weight. The
+vapour which rose from the ground during the formation of the dew accounts
+for the difference of weight. This weighing-test will also succeed on bare
+ground.</p>
+
+<p>When dealing with hoar-frost, which is just frozen dew, we shall find
+visible evidence of the rising of dew from the ground.</p>
+
+<p><span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span>You know the beautiful song, &#8220;Annie Laurie,&#8221; which begins with&mdash;</p>
+
+<p class="poem">&#8220;Maxwelton&#8217;s braes are bonnie,<br />
+Where early fa&#8217;s the dew&#8221;&mdash;</p>
+
+<p>well, you can no longer say that the dew &#8220;falls,&#8221; for it rises from the
+ground. The song, however, will be sung as sweetly as ever; for the spirit
+of true poetry defies the cold letter of science.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III</h2>
+<p class="title">TRUE AND FALSE DEW</p>
+
+
+<p>Ever since men could observe and think, they have admired the diamond
+globules sparkling in the rising sun. These &#8220;dew-drops&#8221; were considered to
+be shed from the bosom of the morn into the blooming flowers and rich
+grass-leaves. Ballantine&#8217;s beautiful song of Providential care tells us
+that &#8220;Ilka blade o&#8217; grass keps it&#8217;s ain drap o&#8217; dew.&#8221;</p>
+
+<p>But, alas! we have to bid &#8220;good-bye&#8221; to the appellation &#8220;dew-drop.&#8221; What
+was popularly and poetically called dew <i>is not dew at all</i>. Then what is
+it?</p>
+
+<p>On what we have been accustomed to call a &#8220;dewy&#8221; night, after the
+brilliant summer sun has set, and the stars begin to peep out of the
+almost cloudless sky, let us take a look at the produce of our vegetable
+garden. On the broccoli are found glistening drops; but on the peas,
+growing next them, we find nothing.</p>
+
+<p>A closer examination shows us that the moisture<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> on the plants is not
+arranged as would be expected from the ordinary laws of radiation and
+condensation. There is no generally filmy appearance over the leaves; the
+moisture is collected in little drops placed at short distances apart,
+along the edges of the leaves all round.</p>
+
+<p>Now place a lighted lantern below one of the blades of the broccoli, and a
+revelation will be made. The brilliant diamond-drops that fringe the edge
+of the blade are all placed at the points where the nearly colourless
+veins of the blade come to the outer edge. The drops are not dew at all,
+but the exudation of the healthy plant, which has been conveyed up these
+veins by strong root-pressure.</p>
+
+<p>The fact is that the root acts as a kind of force-pump, and keeps up a
+constant pressure inside the tissues of the plant. One of the simplest
+experiments suggested by Dr. Aitken is to lift a single grass-plant, with
+a clod of moist earth attached to it, and place it on a plate with an
+inverted tumbler over it. In about an hour, drops will begin to exude, and
+the tip of nearly every blade will be found to be studded with a
+diamond-like drop.</p>
+
+<p>Next substitute water-pressure. Remove a blade of broccoli and connect it
+by means of an india-rubber tube with a head of water of about forty
+inches. Place a glass receiver over it, so as to check evaporation, and
+leave it for an hour. The plant will be found to have excreted water
+freely, some parts of the leaves being quite wet, while drops are
+collected at the places where they appeared at night.</p>
+
+<p>If the water pressed into the leaf is coloured with aniline blue, the
+drops when they first appear are<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> colourless; but before they grow to any
+size, the blue appears, showing that little water was held in the veins.
+The whole leaf soon gets coloured of a fine deep blue-green, like that
+seen when vegetation is rank; this shows that the injected liquid has
+penetrated through the whole leaf.</p>
+
+<p>Again, the surfaces of the leaves of these drop-exuding plants never seem
+to be wetted by the water. It is because of the rejection of water by the
+leaf-surface that the exuded moisture from the veins remains as a drop.</p>
+
+<p>These observations and experiments establish the fact that the drops which
+first make their appearance on grass on dewy nights are not dew-drops at
+all, but the exuded watery juices of the plants.</p>
+
+<p>If now we look at dead leaves we shall find a difference of formation of
+the moisture on a dewy night: the moisture is spread equally over, where
+equally exposed. The moisture exuded by the healthy grass is always found
+at a <i>point</i> situated near the tip of the blade, forming a drop of some
+size; but the true dew collects later on <i>evenly</i> all over the blade. The
+false dew forms a large glistening diamond-drop, whereas the true dew
+coats the blade with a fine pearly lustre. Brilliant globules are produced
+by the vital action of the plant, especially beautiful when the deep-red
+setting sun makes them glisten, all a-tremble, with gold light; while an
+infinite number of minute but shining opal-like particles of moisture
+bedecks the blade-surfaces, in the form of the gentle dew&mdash;</p>
+
+<p class="poem">&#8220;Like that which kept the heart of Eden green<br />
+Before the useful trouble of the rain.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span></p>
+<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV</h2>
+<p class="title">HOAR-FROST</p>
+
+
+<p>All in this country are familiar with the beauty of hoar-frost. The
+children are delighted with the funny figures on the glass of the bedroom
+window on a cold winter morning. Frost is a wonderful artist; during the
+night he has been dipping his brush into something like diluted schist,
+and laying it gracefully on the smooth panes.</p>
+
+<p>And, as you walk over the meadows, you observe the thin white films of ice
+on the green pasture; and the clear, slender blades seem like crystal
+spears, or the &#8220;lashes of light that trim the stars.&#8221;</p>
+
+<p>You all know what hoar-frost is, though most in the country give it the
+expressive name of &#8220;rime.&#8221; But you are not all aware of how it is formed.
+Hoar-frost is just frozen dew. In a learned paper, written in 1784,
+Professor Wilson of Glasgow made this significant remark: &#8220;This is a
+subject which, besides its entire novelty, seems, upon other accounts, to
+have a claim to some attention.&#8221; He observed, in that exceptionally cold
+winter, that, when sheets of paper and plates of metal were laid out, all
+began to attract hoar-frost as soon as they had time to cool down to the
+temperature of the air. He was struck with the fact that, while the
+thermometer indicated 36 degrees of frost a few feet above the ground and
+44 degrees of frost at the surface of the snow, there were only 8 degrees
+of frost at a point 3 inches<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> below the surface of the snow. If he had
+only thought of placing the thermometer on the grass, under the snow, he
+would have found it to register the freezing-point only. And had he
+inserted the instrument below the ground, he would have found it
+registering a still higher temperature. That fact would have suggested to
+him the formation of hoar-frost; that the water-vapour from the warm soil
+was trapped by a cold stratum of air and frozen when in the form of dew.</p>
+
+<p>One of the most interesting experiments, without apparatus, which you can
+make is in connection with the formation of hoar-frost, when there is no
+snow on the ground, in very cold weather. If it has been a bright, clear,
+sunny day in January, the effect can be better observed. Look over the
+garden, grass, and walks on the morning after the intense cold of the
+night; big plane-tree leaves may be found scattered over the place. You
+see little or no hoar-frost on the <i>upper</i> surface of the leaves. But turn
+up the surface next the earth, or the road, or the grass, and what do you
+see? You have only to handle the leaf in this way to be brightly
+astonished. A thick white coating of hoar-frost, as thick as a layer of
+snow, is on the <i>under</i> surface. If a number of leaves have been
+overlapping each other, there will be no coating of hoar-frost under the
+top leaves; but when you reach the lowest layer, next the bare ground, you
+will find the hoar-frost on the under surface of the leaves. Now that is
+positive proof that the hoar-frost has not fallen from the air, but has
+risen from the earth.</p>
+
+<p>The sun&#8217;s heat on the previous day warmed the<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> earth. This heat the earth
+retained till evening. As the air chilled, the water-vapour from the
+warmer earth rose from its surface, and was arrested by the cold surface
+of the leaves. So cold was that surface that it froze the water-vapour
+when rising from the earth, and formed hoar-frost in very large
+quantities. When this happens later on in the season, one may be almost
+sure of having rain in the forenoon.</p>
+
+<p>As hoar-frost is just frozen dew, I can even more surely convince you of
+the formation of hoar-frost as rising from the ground by observations made
+by me at my manse in Strathmore, in June 1892. I mention this particularly
+because then was the most favourable testing-time that has <i>ever</i> occurred
+during meteorological observations. June 9th was the warmest June day
+(with one exception) for twenty years. The thermometer reached 83&deg; Fahr.
+in the shade. Next day was the coldest June day (with one exception) for
+twenty years, when the thermometer was as low as 51&deg; in the shade. But
+during the night my thermometer on the grass registered 32&deg;&mdash;the freezing
+point. On the evening of the sultry day I examined the soil at 10 o&#8217;clock.
+It was damp, and the grass round it was filmy moist. The leaves of the
+trees were crackling dry, and all above was void of moisture. The air
+became gradually chilly; and as gradually the moisture rose in height on
+the shrubs and lower branches of small trees. The moon shone bright, and
+the stars showed their clear, chilly eyes. The soil soon became quite wet,
+the low grass was dripping with moisture, and the longer grass was
+becoming dewed. This gave the best natural evidence of the rising of the
+dew that I ever<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span> witnessed. But everything was favourable for the
+observation&mdash;the cold air incumbent on the rising, warm, moist vapour from
+the soil fixing the dew-point, when the projecting blades seized the
+moisture greedily and formed dew. Had the temperature been a little below
+the freezing-point, hoar-frost would have been beautifully formed.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V</h2>
+<p class="title">FOG</p>
+
+
+<p>To many nothing is more troublesome than a dense fog in a large town. It
+paralyses traffic, it is dangerous to pedestrians, it encourages theft, it
+chokes the asthmatic, and chills the weak-lunged.</p>
+
+<p>In the country it is disagreeable enough; but never so intensely raw and
+dense as in the city. On the sea, too, the fog is disagreeable and fraught
+with danger. The fog-horn is heard, in its deep, sombre note, from the
+lighthouse tower, when the strong artificial light is almost useless.</p>
+
+<p>But a peculiar sense of stagnation possesses the dweller of the large
+town, when enveloped in a dense fog. Sometimes during the day, through a
+thinner portion, the sun will be dimly seen in copper hue, like the moon
+under an eclipse. The smoke-impregnated mass assumes a peculiar &#8220;pea-soup&#8221;
+colour.</p>
+
+<p>Now, what is this fog? How is it formed? It has been ascertained that fogs
+are dependent upon <i>dust</i> for their formation. Without dust there could<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span>
+be no fogs, there would be only dew on the grass and road. Instead of the
+dust-impregnated air that irritates the housekeeper, there would be the
+constant dripping of moisture on the walls, which would annoy her more.</p>
+
+<p>Ocular demonstration can testify to this. If two closed glass receivers be
+placed beside each other, the one containing ordinary air, and the other
+filtered air (<i>i.e.</i> air deprived of its dust by being driven through
+cotton wool), and if jets of steam be successively introduced into these,
+a strange effect is noticed. In the vessel containing common air the steam
+will be seen rising in a dense cloud; then a beautiful white foggy cloud
+will be formed, so dense that it cannot be seen through. But in the vessel
+containing the filtered air, the steam is not seen at all; there is not
+the slightest appearance of cloudiness. In the one case, where there was
+the ordinary atmospheric dust, fog at once appeared; in the other case,
+where there was no dust in suspension, the air remained clear and
+destitute of fog. Invisible dust, then, is necessary in the air for the
+formation of fogs.</p>
+
+<p>The reason of this is that a free-surface must exist for the condensation
+of the vapour-particles. The fine particles of dust in the air act as
+free-surfaces, on which the fog is formed. Where there is abundance of
+dust in the air and little water-vapour present, there is an
+over-proportion of dust-particles; and the fog-particles are, in
+consequence, closely packed, but light in form and small in size, and take
+the lighter appearance of fog. Accordingly, if the dust is increased in
+the air, there is a proportionate increase<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span> of fog. Every fog-particle,
+then, has embosomed in it an invisible dust-particle.</p>
+
+<p>But whence comes the dust? From many sources. It is organic and inorganic.
+So very fine is the inorganic dust in the atmosphere that, if the
+two-thousandth part of a grain of fine iron be heated, and the dust be
+driven off and carried into a glass receiver of filtered air, the
+introduction of a jet of steam into that receiver would at once occasion
+an appreciable cloudiness.</p>
+
+<p>This is why fogs are so prevalent in large towns. Next the minute
+brine-particles, driven into the air as fog forms above the ocean surface,
+are the burnt sulphur-particles emanating from the chimneys in towns. The
+brilliant flame, as well as the smoky flame, is a fog-producer. If gas is
+burnt in filtered air, intense fog is produced when water-vapour is
+introduced. Products of combustion from a clear fire and from a smoky one
+produce equal fogging. The fogs that densely fill our large towns are
+generally less bearable than those that veil the hills and overhang the
+rivers.</p>
+
+<p>It is the sulphur, however, from the consumed coals, which is the active
+producer of the fogs of a large town. The burnt sulphur condenses in the
+air to very fine particles, and the quantity of burnt sulphur is enormous.
+No less than seven and a half millions of tons of coals are consumed in
+London. Now, the average amount of sulphur in English coal is one and a
+quarter per cent. That would give no less than 93,750 tons of sulphur
+burned every year in London fires. Now, if we reckon that on an average
+twice the quantity of coals is consumed there on a<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> winter day that is
+consumed on a summer day, no less than 347 tons of the products of
+combustion (in extremely fine particles) are driven into the
+superincumbent air of London every winter day. This is an enormous
+quantity, quite sufficient to account for the density of the fogs in that
+city.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI</h2>
+<p class="title">THE NUMBERING OF THE DUST</p>
+
+
+<p>If the shutters be all but closed in a room, when the sun is shining in,
+myriads of floating particles can be seen glistening in the stream of
+light. Their number seems inexhaustible. According to Milton, the follies
+of life are&mdash;</p>
+
+<p class="poem"><span style="margin-left: 7em;">&#8220;Thick and numberless,</span><br />
+As the gay motes that people the sunbeams.&#8221;</p>
+
+<p>Can these, then, be counted? Yes, Dr. Aitken has numbered the dust of the
+air. I shall never forget my rapt astonishment the day I first numbered
+the dust in the lecture-room of the Royal Society of Edinburgh, with his
+instrument and under his direction.</p>
+
+<p>This wonderfully ingenious instrument was devised on this principle, that
+every fog-particle has entombed in it an invisible dust-particle. A
+definite small quantity of common air is diluted with a fixed large
+quantity of dustless air (<i>i.e.</i> air that has been filtered through
+cotton-wool). The mixture is allowed to be saturated with water-vapour.
+Then the few <span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span>particles of dust seize the moisture, become visible in fine
+drops, fall on a divided plate, and are there counted by means of a
+magnifying glass. That is the secret!</p>
+
+<p>I shall now give you a general idea of the apparatus. Into a common glass
+flask of carafe shape, and flat-bottomed, of 30 cubic inches capacity, are
+passed two small tubes, at the end of one of which is attached a small
+square silver table, 1 inch in length. A little water having been
+inserted, the flask is inverted, and the table is placed exactly 1 inch
+from the inverted bottom, so that the contents of air right above the
+table are 1 cubic inch. This observing table is divided into 100 equal
+squares, and is highly polished, with the burnishing all in one direction,
+so that during the observations it appears dark, when the fine
+mist-particles glisten opal-like with the reflected light in order that
+they may be more easily counted. The tube to which the silver table is
+attached is connected with two stop-cocks, one of which can admit a small
+measured portion of the air to be examined. The other tube in the flask is
+connected with an air-pump of 10 cubic inches capacity. Over the flask is
+placed a covering, coloured black in the inside. In the top of this cover
+is inserted a powerful magnifying glass, through which the particles on
+the silver table can be easily counted. A little to the side of this
+magnifier is an opening in the cover, through which light is concentrated
+on the table.</p>
+
+<p>To perform the experiment, the air in the flask is exhausted by the
+air-pump. The flask is then filled with filtered air. One-tenth of a cubic
+inch of the air to be examined is then introduced into the flask, and
+mixed with the 30 cubic inches of dustless air.<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> After one stroke of the
+air-pump, this mixed air is made to occupy an additional space of 10 cubic
+inches; and this rarefying of the air so chills it that condensation of
+the water-vapour takes place on the dust-particles. The observer, looking
+through the magnifying-glass upon the silver table, sees the
+mist-particles fall like an opal shower on the table. He counts the number
+on a single square in two or three places, striking an average in his
+mind. Suppose the average number upon a single square were five, then on
+the whole table there would be 500; and these 500 particles of dust are
+those which floated invisibly in the cubic inch of mixed air right above
+the table. But, as there are 40 cubic inches of mixed air in the flask and
+barrel, the number of dust-particles in the whole is 20,000. That is,
+there are 20,000 dust-particles in the same quantity of common air
+(one-tenth of a cubic inch) which was introduced for examination. In other
+words, a cubic inch of the air contained 200,000 dust-particles&mdash;nearly a
+quarter of a million.</p>
+
+<p>The day I used the instrument we counted 4,000,000 of dust-particles in a
+cubic inch of the air outside of the room, due to the quantity of smoke
+from the passing trains. Dr. Aitken has counted in 1 cubic inch of air
+immediately above a Bunsen flame the fabulous number of 489,000,000 of
+dust-particles.</p>
+
+<p>A small instrument has been constructed which can bring about results
+sufficiently accurate for ordinary purposes. It is so constructed that,
+when the different parts are unscrewed, they fit into a case 4&#189; inches
+by 2&#189; by 1&#188; deep&mdash;about the size of an ordinary cigar-case.</p>
+
+<p><span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span>After knowing this, we are apt to wonder why our lungs do not get clogged
+up with the enormous number of dust-particles. In ordinary breathing, 30
+cubic inches of air pass in and out at every breath, and adults breathe
+about fifteen times every minute. But the warm lung-surface repels the
+colder dust-particles, and the continuous evaporation of moisture from the
+surface of the air-tubes prevents the dust from alighting or clinging to
+the surface at all.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII</h2>
+<p class="title">DUST AND ATMOSPHERIC PHENOMENA</p>
+
+
+<p>Dr. Aitken has devoted a vast amount of attention to the enumeration of
+dust-particles in the air, on the Continent as well as in Scotland, to
+determine the effects of their variation in number.</p>
+
+<p>On his first visit to Hy&egrave;res, in 1890, he counted with the instrument
+12,000 dust-particles in a cubic inch of the air: whereas in the following
+year he counted 250,000. He observed, however, that where there was least
+dust, the air was very clear; whereas with the maximum of dust, there was
+a very thick haze.</p>
+
+<p>At Mentone, the corresponding number was 13,000, when the wind was blowing
+from the mountains; but increased to 430,000, when the wind was blowing
+from the populous town.</p>
+
+<p>On his first visit to the Rigi Kulm, in Switzerland, the air was
+remarkably clear and brilliant, and the<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> corresponding number never
+exceeded 33,000; but, on his second visit, he counted no less than
+166,000. This was accounted for by a thick haze, which rendered the lower
+Alps scarcely visible. The upper limit of the haze was well defined; and
+though the sky was cloudless, the sun looked like a harvest moon, and
+required no eagle&#8217;s eye to keep fixed on it.</p>
+
+<p>Next day there was a violent thunder-storm. At 6 <span class="smcaplc">P.M.</span> the storm commenced,
+and 60,000 dust-particles to the cubic inch of air were registered; but in
+the middle of the storm he counted only 13,000. There was a heavy fall of
+hail at this time, and he accounts for the diminution of dust-particles by
+the down-rush of purer upper air, which displaced the contaminated lower
+air.</p>
+
+<p>At the Lake of Lucerne there was an exceptional diminution of the number
+in the course of an hour, viz. from 171,000 to 28,000 in a cubic inch. On
+looking about, he found that the direction of the wind had changed,
+bringing down the purer upper air to the place of observation. The bending
+downwards of the trees by the strong wind showed that it was coming from
+the upper air.</p>
+
+<p>Returning to Scotland, he continued his observations at Ben Nevis and at
+Kingairloch, opposite Appin, Mr. Rankin using the instrument at the top of
+the mountain. These observations showed in general that on the mountain
+southerly, south-easterly, and easterly winds were more impregnated with
+dust-particles, sometimes containing 133,000 per cubic inch. Northerly
+winds brought pure air. The observations at sea-level showed a certain<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span>
+parallelism to those on the summit of the mountain. With a north-westerly
+wind the dust-particles reached the low number of 300 per cubic inch, the
+lowest recorded at any low-level station.</p>
+
+<p>The general deductions which he made from his numerous observations during
+these two years are that (1) air coming from inhabited districts is always
+impure; (2) dust is carried by the wind to enormous distances; (3) dust
+rises to the tops of mountains during the day; (4) with much dust there is
+much haze; (5) high humidity causes great thickness of the atmosphere, if
+accompanied by a great amount of dust, whereas there is no evidence that
+humidity alone has any effect in producing thickness; (6) and there is
+generally a high amount of dust with high temperature, and a low amount of
+dust with low temperature.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII</h2>
+<p class="title">A FOG-COUNTER</p>
+
+
+<p>Next to the enumeration of the dust-particles in the atmosphere is the
+marvellous accuracy of counting the number of particles in a fog. The same
+ingenious inventor has constructed a fog-counter for the purpose; and the
+number of fog-particles in a cubic inch can be ascertained. This
+instrument consists of a glass micrometer divided into squares of a known
+size, and a strong microscope for observing the drops on the stage. The
+space between the<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span> micrometer and the microscope is open, so that the air
+passes freely over the stage; and the drops that fall on its surface are
+easily seen. These drops are very small; many of them when spread on the
+glass are no more than the five-hundredth of an inch in diameter.</p>
+
+<p>In observing these drops, the attention requires to be confined to a
+limited area of the stage, as many of the drops rapidly evaporate, some
+almost as soon as they touch the glass, whilst the large ones remain a few
+seconds.</p>
+
+<p>In one set of Dr. Aitken&#8217;s observations, in February 1891, the fog was so
+thick that objects beyond a hundred yards were quite invisible. The number
+of drops falling per second varied greatly from time to time. The greatest
+number was 323 drops per square inch in one second. The high number never
+lasted for long, and in the intervals the number fell as low as 32, or to
+one-tenth.</p>
+
+<p>If we knew the size of these drops, we might be able to calculate the
+velocity of their fall, and from that obtain the number in a cubic inch.</p>
+
+<p>An ingenious addition is put to the instrument in order to ascertain this
+directly. It is constructed so as to ascertain the number of particles
+that fall from a known height. Under a low-power microscope, and
+concentric with it, is mounted a tube 2 inches long and 1&#189; inch in
+diameter, with a bottom and a cover, which are fixed to an axis parallel
+with the axis of the tube, so that, by turning a handle, these can be slid
+sideways, closing or opening the tube at both ends when required. In the
+top is a small opening, corresponding to the lens of the microscope,<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> and
+in the centre of the bottom is placed the observing-stage illumined by a
+spot-mirror. The handle is turned, and the ends are open to admit the
+foggy air. The handle is quickly reversed, and the ends are closed,
+enabling the observer to count on the stage all the fog-particles in the
+two inches of air over it.</p>
+
+<p>The number of dust-particles in the air which become centres of
+condensation depends on the rate at which the condensation is taking
+place. The most recent observations show that quick condensation causes a
+large number of particles to become active, whereas slow condensation
+causes a small number. After the condensation has ceased, a process of
+differentiation takes place, the larger particles robbing the smaller ones
+of their moisture, owing to the vapour-pressure at the surface of the
+drops of large curvature being less than at the surface of drops of
+smaller curvature.</p>
+
+<p>By this process the particles in a cloud are reduced in number; the
+remaining ones, becoming larger, fall quicker. The cloud thus becomes
+thinner for a time. A strong wind, suddenly arising, will cause the
+cloud-particles to be rapidly formed: these will be very numerous, but
+very small&mdash;so small that they are just visible with great care under a
+strong magnifying lens used in the instrument. But in slowly formed clouds
+the particles are larger, and therefore more easily visible to the naked
+eye.</p>
+
+<p>Though the particles in a fog are slightly finer, the number is about the
+same as in a cloud&mdash;that is, generally. As clouds vary in density, the
+number of particles varies. Sometimes in a cloud one cannot see farther
+than 30 yards; whereas in a few minutes<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> it clears up a little, so that we
+can see 100 yards. Of course, the denser the cloud the greater the number
+of water-particles falling on the calculating-stage of the instrument.</p>
+
+<p>Very heavy falls of cloud-particles seldom last more than a few seconds,
+the average being about 325 on the square inch per second, the maximum
+reaching to 1290. This is about four times the number counted in a fog.
+Yet the particles are so very small that they evaporate instantly when
+they reach a slight increase of temperature.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX</h2>
+<p class="title">FORMATION OF CLOUDS</p>
+
+
+<p>In our ordinary atmosphere there can be no clouds without dust. A
+dust-particle is the nucleus that at a certain humidity becomes the centre
+of condensation of the water-vapour so as to form a cloud-particle; and a
+collection of these forms a cloud.</p>
+
+<p>This condensation of vapour round a number of dust-particles in visible
+form gives rise to a vast variety of cloud-shapes. There are two distinct
+ways in which the formation of clouds generally takes place. Either a
+layer of air is cooled in a body below the dew-point; or a mass of warm
+and moist air rises into a mass which is cold and dry. The first forms a
+cloud, called, from being a layer, <i>stratus</i>; the second forms a cloud,
+called, from its heap appearance, <i>cumulus</i>. The first is widely extended
+and horizontal, averaging 1800 feet in<span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span> height; the second is convex or
+conical, like the head of a sheaf, increasing upward from a level base,
+averaging from 4500 feet to 6000 feet in height.</p>
+
+<p>There are endless combinations of these two; but at the height of 27,000
+feet, where the cloud-particles are frozen, the structure of the cloud is
+finer, like &#8220;mares&#8217; tails,&#8221; receiving the name <i>cirrus</i>. When the cirrus
+and cumulus are combined, in well-defined roundish masses, what is
+familiarly described as a &#8220;mackerel sky&#8221; is beautifully presented. The
+dark mass of cloud, called <i>nimbus</i>, is the threatening rain-cloud, about
+4500 feet in height.</p>
+
+<p>At the International Meteorological Conference at Munich, in 1892, twelve
+varieties of clouds were classified, but those named above are the
+principal. In a beautiful sunset one can sometimes notice two or three
+distances of clouds, the sun shedding its gold light on the full front of
+one set, and only fringing with vivid light the nearer range.</p>
+
+<p>Although no man has wrought so hard as Dr. Aitken to establish the
+principle that clouds are mainly due to the existence of dust-particles
+which attract moisture on certain conditions, yet even twenty years ago he
+said that it was probable that sunshine might cause the formation of
+nuclei and allow cloudy condensation to take place where there was no
+dust.</p>
+
+<p>Under certain conditions the sun gives rise to a great increase in the
+number of nuclei. Accordingly, he has carefully tested a few of the
+ordinary constituents and impurities in our atmosphere to see if sunshine
+acted on them in such a way as to make them probable formers of
+cloud-particles.</p>
+
+<p><span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span>He tested various gases, with more or less success. He found that ordinary
+air, after being deprived of its dust-particles and exposed to sunshine,
+does not show any cloudy condensation on expansion; but, when certain
+gases are in the dustless air, a very different result is obtained.</p>
+
+<p>He first used ammonia, putting one drop into six cubic inches of water in
+a flask, and sunning this for one minute; the result was a considerable
+quantity of condensation, even with such a weak solution. When the flask
+was exposed for five minutes, the condensation by the action of the
+sunshine was made more dense.</p>
+
+<p>Hydrogen peroxide was tested in the same way, and it was found to be a
+powerful generator of nuclei. Curious is it that sulphurous acid is
+puzzling to the experimentalist for cloud formation. It gives rise to
+condensation in the dark; but sunshine very conclusively increases the
+condensation.</p>
+
+<p>Chlorine causes condensation to take place without supersaturation;
+sulphuretted hydrogen (which one always associates with the smell of
+rotten eggs) gives dense condensation after being exposed to sunshine.</p>
+
+<p>Though the most of these nuclei, due to the action of sunshine in the
+gases, remain active for cloudy condensation for a comparatively short
+space of time&mdash;fifteen minutes to half-an-hour&mdash;yet the experiments show
+that it is possible for the cloudy condensation to take place in certain
+circumstances in the absence of dust. This seems paradoxical in the light
+of the former beautiful experiments; but, in ordinary circumstances, dust
+is needed for the<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span> formation of clouds. However, supposing there is any
+part of the upper air free from dust, it is now found possible, when any
+of these gases experimented on be present, for the sun to convert them
+into nuclei of condensation, and permit of clouds being formed in dustless
+air, miles above the surface of the earth.</p>
+
+<p>In the lower atmosphere there are always plenty of dust-particles to form
+cloudy condensation, whether the sun shines or not. These are produced by
+the waste from the millions of meteors that daily fall into the air.</p>
+
+<p>But in the higher atmosphere, clouds can be formed by the action of the
+sun&#8217;s rays on certain gases. This is a great boon to us on the earth; for
+it assures us of clouds being ever existing to defend us from the sun&#8217;s
+extra-powerful rays, even when our atmosphere is fairly clear. This is
+surely of some meteorological importance.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X</h2>
+<p class="title">DECAY OF CLOUDS</p>
+
+
+<p>From the earliest ages clouds have attracted the attention of observers.
+Varied are their forms and colours, yet in our atmosphere there is one law
+in their formation. Cloud-particles are formed by the condensation of
+water-vapour on the dust-particles invisibly floating in the atmosphere,
+up to thousands&mdash;and even millions&mdash;in the cubic inch of air.</p>
+
+<p>But observers have not directed their attention so<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> much to the decay of
+clouds&mdash;in fact, the subject is quite new. And yet how suggestive is the
+subject!</p>
+
+<p>The process of decay in clouds takes place in various ways. A careful
+observer may witness the gradual wasting away and dilution into thin air
+of even great stretches of cloud, when circumstances are favourable. In
+May 1896 my attention was particularly drawn to this at my manse in
+Strathmore. In the middle of that exceptionally sultry month, I was
+arrested by a remarkable transformation scene. It was the hottest May for
+seventy-two years, and the driest for twenty-five years. The whole parched
+earth was thirsting for rain. All the morning my eyes were turned to the
+clouds in the hope that the much-desired shower should fall. Till ten
+o&#8217;clock the sun was not seen, and there was no blue in the sky. Nor was
+there any haze or fog.</p>
+
+<p>But suddenly the sun shone through a thinner portion of the enveloping
+clouds, and, to the north, the sky began to open. As if by some magic
+spell there was, in a quarter of an hour, more blue to be seen than
+clouds. At the same time, near the horizon, a haze was forming, gradually
+becoming denser as time wore on. In an hour the whole clouds were gone,
+and the glorious orb of day dispelled the moisture to its thin-air form.</p>
+
+<p>This was a pointed and rapid illustration of the decay from cloud-form to
+haze, and then to the pure vapoury sky. It was an instance of the
+<i>reverse</i> process. As the sun cleared through, the temperature in the
+cloud-land rose and evaporation took place on the surface of the
+cloud-particles, until by an <span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span>untraceable, but still a gradual process
+through fog, the haze was formed. Even then the heat was too great for a
+definite haze, and the water-vapour returned to the air, leaving the
+dust-particles in invisible suspension.</p>
+
+<p>But clouds decay in another way. This I will illustrate in the next
+chapter on &#8220;It always rains.&#8221;</p>
+
+<p>What strikes a close observer is the difference of structure in clouds
+which are in the process of formation and those which are in the process
+of decay. In the former the water-particles are much smaller and far more
+numerous than in the latter. While the particles in clouds in decay are
+large enough to be seen with the unaided eye, when they fall on a properly
+lighted measuring table, they are so small in clouds in rapid formation
+that the particles cannot be seen without the aid of a strong magnifying
+glass.</p>
+
+<p>Observers have assumed that the whole explanation of the fantastic shapes
+taken by clouds is founded on the process of formation; but Dr. Aitken has
+pointed out that ripple-marked clouds, for instance, have been clouds of
+decay. When what is called a cirro-stratus cloud&mdash;mackerel-like against
+the blue sky&mdash;is carefully observed in fine weather, it will be found that
+it frequently changes the ripple-marked cirrus in the process of decay to
+vanishing. Where the cloud is thin enough to be broken through by the
+clear air that is drawn in between the eddies, the ripple markings get
+nearer and nearer the centre, as the cloud decays. And, at last, when
+nearly dissolved, these markings are extended quite across the cloud.</p>
+
+<p><span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span>Whether, then, we consider the cases of clouds gradually melting away back
+into their original state of blue water-vapour, or the constant fine
+raining from clouds and re-formation by evaporation, or the transformation
+of such clouds as the cirro-stratus into the ripple-marked cirrus, we are
+forced to the conclusion that in clouds there is not always development,
+but sometimes degeneration; not always formation, but sometimes decay.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI</h2>
+<p class="title">IT ALWAYS RAINS</p>
+
+
+<p>All are familiar with the answer given by the native of Skye to the irate
+tourist on that island, who, for the sixth day drenched, asked the
+question: &#8220;Does it always rain here?&#8221; &#8220;Na!&#8221; answered the workman, without
+at all understanding the joke; &#8220;feiles it snaas&#8221; (sometimes it snows).
+Yet, strange to say, the tourist&#8217;s question has been answered in the
+affirmative in every place where a cloud is overhead, visible or
+invisible.</p>
+
+<p>Whenever a cloud is formed, it begins to rain; and the drops shower down
+in immense numbers, though most minute in size&mdash;&#8220;the playful fancies of
+the mighty sky.&#8221;</p>
+
+<p>No doubt it is only in certain circumstances that these drops are
+attracted together so as to form large drops, which fall to the earth in
+genial showers to refresh the thirsty soil, or in a terrible deluge to
+cause great destruction. But when the temperature<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span> and pressure are not
+suitable for the formation of what we commonly know as the rain, the fine
+drops fall into the air under the cloud, where they immediately evaporate
+from their dust free-surfaces, if the air is dry and warm. This is, in
+other words, the decay of clouds.</p>
+
+<p>It is a curious fact that objects in a fog may not be wetted, when the
+number of water-particles is great. It seems that these water-particles
+all evaporate so quickly that even one&#8217;s hand or face is not sensible of
+being wetted. The particles are minutely small; and they may evaporate
+even before reaching the warm skin, by reason of the heated air over the
+skin.</p>
+
+<p>There is a peculiarly warm sensation in the centre of a cumulus cloud,
+especially when it is not dense. A glow of heat seems to radiate from all
+points. Yet the face and hands are quite dry, and exposed objects are not
+wetted; but it is really <i>always raining</i>. That is a curious discovery.</p>
+
+<p>It is radiant heat that is the cause of the remarkable result. The rays of
+the sun, which strike the upper part of the cloud, not only heat that
+surface but also penetrate the cloud and fall on the surface of bodies
+within, generating heat there. These heated surfaces again radiate heat
+into the air attached to them. This warm air receives the fine raindrops
+in the cloud, and dissolves the moisture from the dust-particles before
+the moisture can reach the surfaces exposed. That a vast amount of radiant
+heat rushes through a cloud is clearly shown by exposing a thermometer
+with black bulb <i>in vacuo</i>. On some occasions, a thermometer would
+indicate<span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span> from 40&deg; to 50&deg; above the temperature of the air, thus proving
+the surface to be quite dry.</p>
+
+<p>These observations have been corroborated on Mount Pilatus, near
+Lucerne&mdash;1000 feet higher and more isolated than the Rigi. The summit was
+quite enveloped in cloud, and, though one might naturally conclude that
+the air was dense with moisture, yet the wooden seats, walls, and all
+exposed surfaces were quite dry. Strange to say, however, the thermometers
+hung up got wet rapidly, and the pins driven into the wooden post to
+support them rapidly became moist. A thermometer lying on a wooden seat
+stood at 60&deg;, while one hung up read only 48&deg;. This difference was caused
+by radiant heat.</p>
+
+<p>It is well known that, when bodies are exposed to radiant heat, they are
+heated in proportion to their size; the smaller, then, may be moist, when
+the larger are dry by radiation. The effect of the sun&#8217;s penetrating heat
+through the cloud is to heat exposed objects above the temperature of the
+air; and if the objects are of any size they are considerably heated, and
+retain their heat more, while at the same time around them is a layer of
+warm air which is quite sufficient to force the water-vapour to leave the
+dust-particles in the fine rain.</p>
+
+<p>Hence seats, walls, posts, &amp;c., are quite dry, though they are in the
+middle of a cloud. They are large enough to throw off the moisture by the
+retained heat, or by the large amount of surrounding heat; whereas, small
+bodies, which are not heated to the same degree and cannot therefore
+retain their heat so easily, have not heat-power sufficient to withstand
+the moisture, and they become wetted. Hence, by<span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span> the radiant heat, the
+large exposed objects are dry in the cloud; whereas small objects are
+damp, and, in some cases, dripping with wet.</p>
+
+<p>The fact is, then, that whenever a cloud overhangs, <i>rain is falling</i>,
+though it may not reach the earth on account of the dryness of the stratum
+of air below the cloud, and the heat of the air over the earth. So that on
+a summer day, with the gold-fringed, fleecy clouds sailing overhead, it is
+really raining; but the drops, being very small, evaporate long before
+reaching the earth. As Ariel sings at the end of &#8220;The Tempest&#8221; of
+Shakespeare, &#8220;The rain, it raineth every day.&#8221; It rains, but much of the
+melting of the clouds is reproduced by a wonderful circularity&mdash;the
+moisture evaporating, seizing other dust-particles, forming
+cloud-particles, falling again, and so on <i>ad infinitum</i>, during the
+existing circumstances.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII</h2>
+<p class="title">HAZE</p>
+
+
+<p>What is haze? The dictionary says, &#8220;a fog.&#8221; Well, haze is <i>not</i> a fog. In
+a fog, the dust-particles in the air have been fully clothed with
+water-vapour; in a haze, the process of condensation has been arrested.</p>
+
+<p>Cloudy condensation is changed to haze by the reduction of its humidity.
+Dr. Aitken invented a simple apparatus for testing the condensing power of
+dust, and observing if water-vapour condensed on the deposited dust in
+unsaturated air.</p>
+
+<p><span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span>The dust from the air has first to be collected. This is done by placing a
+glass plate vertically, and in close contact with one of the panes of
+glass in the window, by means of a little india-rubber solution. The plate
+being thus rendered colder than the air in the room, the dust is deposited
+on it.</p>
+
+<p>Construct a rectangular box, with a square bottom, 1&#189; inches a side and
+&#190; inch deep, and open at the top. Cover the top edge of the box with a
+thickness of india-rubber. Place the dusty plate&mdash;a square glass mirror, 4
+inches a side&mdash;on the top of the india-rubber, and hold it down by spring
+catches, so as to make the box water-tight. The box has been provided with
+two pipes, one for taking in water and the other for taking away the
+overflow, with the bulb of a thermometer in the centre. Clean the dust
+carefully off one half of the mirror, so that one half of the glass
+covering the box is clean and the other half dusty. Pour cold water
+through the pipe into the box, so as to lower the temperature of the
+mirror, and carefully observe when condensation begins on the clean part
+and on the dusty part, taking a note of the difference of temperature. The
+condensation of the water-vapour will appear on the dust-particles before
+coming down to the natural dew-point temperature of the clean glass. And
+the difference between the two temperatures indicates the temperature
+above the dew-point at which the dust has condensed the water-vapour.</p>
+
+<p>Magnesia dust has small affinity for water-vapour; accordingly, it
+condenses at almost exactly the same temperature as the glass. But
+gunpowder has great condensing power. All have noticed that the smoke<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span>
+from exploded gunpowder is far more dense in damp than in dry weather. In
+the experiment it will be found that the dust from gunpowder smoke begins
+to show signs of condensing the vapour at a temperature of 9&deg; Fahr. above
+the dew-point. In the case of sodium dust, the vapour is condensed from
+the air at a temperature of 30&deg; above the dew-point.</p>
+
+<p>Dust collected in a smoking-room shows a decidedly greater condensing
+power than that from the outer air.</p>
+
+<p>We can now understand why the glass in picture frames and other places
+sometimes appears damp when the air is not saturated. When in winter the
+windows are not often cleaned, a damp deposit may be frequently seen on
+the glass. Any one can try the experiment. Clean one half of a dusty pane
+of glass in cold weather, and the clean part will remain undewed and
+clear, while the dusty part is damp to the eye and greasy to the touch.</p>
+
+<p>These observations indicate that moisture is deposited on the
+dust-particles from air, which is not saturated, and that the condensation
+takes place while the air is comparatively dry, <i>before</i> the temperature
+is lowered to the dew-point. There is, then, no definite demarcation
+between what seems to us clear air and thick haze. The clearest air has
+some haze, and, as the humidity increases, the thickness of the air
+increases.</p>
+
+<p>In all haze the temperature is above the dew-point. The dust-particles
+have only condensed a very small amount of the moisture so as to form
+haze, before the fuller condensation takes place at the dew-point.</p>
+
+<p>At the Italian lakes, on many occasions when the air is damp and still,
+every stage of condensation<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span> may be observed in close proximity, not
+separated by a hard and fast line, but when no one could determine where
+the clear air ended and the cloud began. Sometimes in the sky overhead a
+gradual change can be observed from perfect clearness to thick air, and
+then the cloud.</p>
+
+<p>A thick haze may be occasioned by an increased number of dust-particles
+with little moisture, or of a diminished number of dust-particles with
+much moisture, above the point of saturation. The haze is cleared by this
+temperature rising, so as to allow the moisture to evaporate from the
+dust-particles.</p>
+
+<p>Whenever the air is dry and hazy, much dust is found in it; as the dust
+decreases the haze also decreases. For example, Dr. Aitken, at
+Kingairloch, in one of the clearest districts of Argyleshire, on a clear
+July afternoon, counted 4000 dust-particles in a cubic inch of the air;
+whereas, two days before, in thick haze, he counted no fewer than 64,000
+in the cubic inch. At Dumfries the number counted on a very hazy day in
+October increased twenty-fold over the number counted the day before, when
+it was clear.</p>
+
+<p>All know that thick haze is usual in very sultry weather. The wavy,
+will-o&#8217;-the-wisp ripples near the horizon indicate its presence very
+plainly. During the intense heat there is generally much dust in the
+atmosphere; this dust, by the high temperature, attracts moisture from the
+apparently dry air, though above the saturation point. In all
+circumstances, then, the haze can be accounted for by the condensing power
+of the dust-particles in the atmosphere, at a higher temperature than that
+required for the formation of fogs, or mists, or rain.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span></p>
+<h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII</h2>
+<p class="title">HAZING EFFECTS OF ATMOSPHERIC DUST</p>
+
+
+<p>The transparency of the atmosphere is very much destroyed by the
+impurities communicated to it while passing over the inhabited areas of
+the country. Dr. Aitken devoted eighteen months to compare the amount of
+dusty impurities in different masses of air, or of different airs brought
+in by winds from different directions.</p>
+
+<p>He took Falkirk for his centre of observations. This town lies a little to
+the north of a line drawn between Edinburgh and Glasgow, and is nearly
+midway between them. If we draw a line due west from it, and another due
+north, we find that, in the north-west quadrant so enclosed, the
+population of that part of Scotland is extremely thin, the country over
+that area being chiefly mountainous. In all other directions, the
+conditions are quite different. In the north-east quadrant are the fairly
+well-populated areas of Aberdeenshire, Forfarshire, and the thickly
+populated county of Fife. In the south-east quadrant are situated
+Edinburgh and the well-populated districts of the south-east of Scotland.
+And in the south-west quadrant are Glasgow and the large manufacturing
+towns which surround it. The winds from three of these quadrants bring air
+polluted in its passage over populated areas, whereas the winds from the
+north-west come comparatively pure.</p>
+
+<p>The general plan of estimating the amount of<span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span> haze is to note the most
+distant hill that can be seen through the haze. The distance in miles of
+the farthest away hill visible is then called &#8220;the limit of visibility&#8221; of
+the air at the time. For the observations made at Falkirk, only three
+hills are available, one about four miles distant, the Ochils about
+fifteen miles distant, and Ben Ledi about twenty-five miles distant&mdash;all
+in the north-west quadrant. When the air is thick, only the near hill can
+be seen; then the Ochils become visible as the air clears; and at last Ben
+Ledi is seen, when the haze becomes still less. After Ben Ledi is visible,
+it then becomes necessary to estimate the amount of haze on it, in order
+to get the limit of visibility of the air at the time. Thus, if Ben Ledi
+be half-hazed, then the limit of visibility will be fifty miles. In this
+way all the estimates of haze have been reduced to one scale for
+comparison.</p>
+
+<p>As the result of all the observations it was found that, as the dryness of
+the air increases, the limit of visibility also increases. A very marked
+difference in the transparency of the air was found with winds from the
+different directions. In the north-west quadrant the winds made the air
+very clear, whereas winds from all other directions made the air very much
+hazed. The winds in the other three areas are nearly ten times more hazed
+than those from the north-west quadrant. That is very striking.</p>
+
+<p>The conclusion come to is that the air from densely inhabited districts is
+so polluted that it is fully nine times more hazed than the air that comes
+from the thinly inhabited districts; in other words, the atmosphere at
+Falkirk is about ten times thicker<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span> when the wind is east or south than it
+would be if there were no fires and no inhabitants.</p>
+
+<p>It is interesting to notice that the limit varies considerably for the
+same wind at the same humidity. This is what might have been expected,
+because from the observations made by the dust-counter the number of
+particles varied greatly in winds from the same directions, but at
+different times. This depends upon the rise and fall of the wind, changes
+in the state of trade, season of the year, and other causes. During a
+strike, the dearth of coal will make a considerable diminution in the
+number of dust-particles in the air of large towns. With a north wind, the
+extreme limits of visibility are 120 to 200 miles; and with a north-west
+wind, from 70 to 250 miles. An east wind has as limits 4 to 50 miles, and
+a south-east wind 2 to 60 miles.</p>
+
+<p>One interesting fact to be noticed, after wading through these tables, is
+this&mdash;that, as a general result, the transparency of the air increases
+about 3&middot;7 times for any increase in dryness from 2&deg; to 8&deg; of wet-bulb
+depression. That is, the clearness of the air is inversely proportional to
+the relative humidity; or, put another way, if the air is four times drier
+it is about four times clearer.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV</h2>
+<p class="title">THUNDER CLEARS THE AIR</p>
+
+
+<p>The phrase &#8220;thunder clears the air&#8221; is familiar to all. It contains a very
+vital truth, yet even scientific<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> men did not know its full meaning until
+just the other day. It came by experience to people who had been for ages
+observing the weather; and it is one of the most pointed of the
+&#8220;weather-lore&#8221; expressions. Folks got to know, by a sort of rule-of-thumb,
+truths which scientifically they were unable to learn. And this is one.</p>
+
+<p>Perhaps, therefore, we should respect a little more what is called
+&#8220;folk-lore,&#8221; or ordinary people&#8217;s sayings. Experience has taught men many
+wonderful things. In olden times they were keener natural observers. They
+had few books, but they had plenty of time. They studied the habits of
+animals and moods of nature, and they came wonderfully near to reaching
+the full truth, though they could not give a reason for it. The
+awe-inspiring in nature has especially riveted the attention of man.</p>
+
+<p>And no appearance in nature joins more powerfully the elements of grandeur
+and awe than a heavy thunder-storm. When, suddenly, from the breast of a
+dark thunder-cloud a brilliant flash of light darts zigzag to the earth,
+followed by a loud crackling noise which softens in the distance into
+weaker volumes of sound, terror seizes the birds of the air and the cattle
+in the field. The man who is born to rule the storm rejoices in the
+powerful display; but kings have trembled at the sight.</p>
+
+<p>Byron thus pictures a storm in the Alps:&mdash;</p>
+
+<p class="poem"><span style="margin-left: 11em;">&#8220;Far along</span><br />
+<span style="margin-left: 1em;">From peak to peak, the rattling crags among</span><br />
+Leaps the live thunder! Not from one lone cloud,<br />
+<span style="margin-left: 1em;">But every mountain now hath found a tongue,</span><br />
+And Jura answers, through her misty shroud,<br />
+Back to the joyous Alps, who call to her aloud!&#8221;</p>
+
+<p><span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span>Franklin found that lightning is just a kind of electricity. No one can
+tell how it is produced; yet a flash has been photographed. When the flash
+is from one cloud to another there is sheet-lightning, which is beautiful
+but not dangerous; but, when the electricity passes from a cloud to the
+earth in a forked form, it is very dangerous indeed. The flash is
+instantaneous, but the sound of the thunder takes some time to travel.
+Roughly speaking, the sound takes five seconds or six beats of the pulse
+to the mile.</p>
+
+<p>All are now taught at school that it is the oxygen in the air which is
+necessary to keep us in life. If mice are put into a glass jar of pure
+oxygen gas, they will at once dance with exhilarating joy. It occurred to
+Sir Benjamin Richardson, some time ago, that it would be interesting to
+continue some experiments with animals and oxygen. He put a number of mice
+into a jar of pure oxygen for a time; they breathed in the gas, and
+breathed out water-vapour and carbonic acid. After the mice had continued
+this for some time, he removed them by an arrangement. By chemical means
+he removed the water-vapour and carbonic acid from the mixed air in the
+vessel. When a blown-out taper was inserted, it at once burst into flame,
+showing that the remaining gas was oxygen.</p>
+
+<p>Again, the mice were put into this vessel to breathe away. But, strange to
+say, the animals soon became drowsy; the smartness of the oxygen was gone.
+At last they died; there was nothing in the gas to keep them in life; yet,
+by the ordinary chemical tests, it was still oxygen. It had repeatedly<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span>
+passed through the lungs of the mice, and during this passage there had
+been an action in the air-cells which absorbed the life-giving element of
+the gas. It is oxygen, so far as chemistry is concerned, but it has no
+life-giving power. It has been <i>devitalised</i>.</p>
+
+<p>But the startling discovery still remains. Sir Benjamin had previously
+fitted up the vessel with two short wires, opposite each other in the
+sides&mdash;part outside and part inside. Two wires are fastened to the outside
+knobs. These wires are attached to an electric machine, and a flash of
+electricity is made to pass between the inner points of the vessel. The
+wires are again removed; nothing strange is seen in the vessel. But, when
+living mice are put into the vessel, they dance as joyfully as if pure
+oxygen were in it. The oxygen in which the first mice died has now been
+quite refreshed by the electricity. The bad air has been cleared and made
+life-supporting by the electric discharge. It has been again vitalised.</p>
+
+<p>Now, to apply this: before a thunder-storm, everything has been so still
+for days that the oxygen in the air has been to some extent robbed of its
+life-sustaining power. The air feels &#8220;close,&#8221; a feeling of drowsiness
+comes over all. But, after the air has been pierced by several flashes of
+lightning, the life-force in the air is restored. Your spirits revive; you
+feel restored; your breathing is far freer; your drowsiness is gone. Then
+there is a burst of heavenly music from the exhilarated birds. Thus a
+thunder-storm &#8220;clears the air.&#8221;</p>
+
+<p>After the passage of lightning through the air ozone is produced&mdash;the gas
+that is produced after a flash of electricity. It is a kind of oxygen,
+with<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> fine exciting effects on the body. If, then, the life-sustaining
+power of oxygen depends on a trace of ozone, and this is being made by
+lightning&#8217;s work, how pleased should we be at the occasional
+thunder-storm!</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV</h2>
+<p class="title">DISEASE-GERMS IN THE AIR</p>
+
+
+<p>The gay motes that dance in the sunbeams are not all harmless. All are
+annoying to the tidy housekeeper; but some are dangerous. There are living
+particles that float in the air as the messengers of disease and death.
+Some, falling on fresh wounds, find there a suitable feeding-place; and,
+if not destroyed, generate the deadly influence. Others are drawn in with
+the breath; and, unless the lungs can withstand them, they seize hold and
+spread some sickness or disease. From stagnant pools, common sewers, and
+filthy rooms, disease-germs are constantly contaminating the air. Yet
+these can be counted.</p>
+
+<p>The simplest method is that of Professor Frankland. It depends on this
+principle: a certain quantity of air is drawn through some cotton-wool;
+this wool seizes the organisms as the air passes through; these organisms
+are afterwards allowed to feed upon a suitable nutritive medium until they
+reach maturity; they are then counted easily.</p>
+
+<p>About an inch from each end of a glass tube (5 inches long and 1 inch
+bore), the glass is pressed<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> in during the process of blowing. Some
+cotton-wool is squeezed in to form a plug at the farther constricted part
+of the glass. The important plug is now inserted at the same open end, but
+is not allowed to go beyond the constricted part at its end. A piece of
+long lead tubing is attached to the former end by an india-rubber tube.
+The other end of the lead tubing is connected with an exhausting syringe.
+Sixty strokes of the 18 cubic inches syringe will draw 1080 cubic inches
+of the air to be examined through the plugs, the first retaining the
+organisms.</p>
+
+<p>The impregnated plug is then put into a flask containing in solution some
+gelatine-peptone. The flask is made to revolve horizontally until an
+almost perfectly even film of gelatine and the organisms from the
+broken-up plug cover its inner surface.</p>
+
+<p>The flask is allowed to remain for an hour in a cool place, and is then
+placed under a bell-jar, at a temperature of 70&deg; Fahr. There it remains,
+to allow the germs to incubate, for four or five days. The surface of the
+flask having been previously divided into equal parts by ink lines, the
+counting is now commenced. If the average be taken for each segment, the
+number of the whole is easily ascertained. A simple arithmetical
+calculation then determines the number of organisms in a cubic foot, since
+the number is known for the 1080 cubic inches. That is the process for
+determining the number of living organisms in a fixed quantity of air.</p>
+
+<p>No less than thirty colonies of organisms were counted in a cubic foot of
+air taken from the Golden Gallery of St. Paul&#8217;s Cathedral, London, and 140
+from the air of the churchyard. An ordinary man<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> would breathe there
+thirty-six micro-organisms every minute.</p>
+
+<p>Electricity has a powerful effect in destroying these organisms. Ozone is
+generated in the air by lightning, and it is detrimental to them. In fine
+ozoned Highland air scarcely a disease-germ can be detected. Open sea air
+contains about one germ in two cubic feet. It has been found that in Paris
+the average in summer is about 140 per cubic foot of air, but in bedrooms
+the number is double. During the twenty-four hours of the day the number
+of germs is highest about 6 <span class="smcaplc">A.M.</span>, and lowest about mid-day.</p>
+
+<p>Raindrops carry the germs to the ground. Hence the advantage of a thunder
+plout in a sanitary way. A cubic foot of rain has been found to contain
+5500 organic dust-germs, besides 7,000,000,000 of inorganic
+dust-particles. In a dirty town the rain will bring down in a year, upon a
+square foot of surface, no less than 3,000,000 of bacteria, many of them
+being disease-bearing and death-bearing. No wonder, then, that scientific
+men are using every endeavour to protect the human frame, as well as the
+frame of the lower animals, from the baneful inroads of these floating
+nuclei of disease and death.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI</h2>
+<p class="title">A CHANGE OF AIR</p>
+
+
+<p>For weakness of body and fatigue of mind a very common and essentially
+serviceable recommendation is &#8220;a change of air.&#8221; Of course, the change of
+scene<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span> from coast to country, or from town to hillside, may help much the
+depressed in body or mind; and this is very commendable. But, strange to
+say, there is a healing virtue in breathing different air.</p>
+
+<p>At first one is apt to think that air is the same all over, as he thinks
+water is&mdash;especially outside smoky towns; but both have varied qualities
+in different parts. You have only to be assured that in a cubic inch of
+bedroom air in the denser parts of a large town there are about 20,000,000
+of dust-particles, and in the open air of a heathery mountain-side there
+are only some hundreds, to see that there is something after all on the
+face of it in the &#8220;old wives&#8217; saw.&#8221;</p>
+
+<p>Not that the dust-particles are all injurious; for most of them are
+inorganic, and many of the organic particles are quite wholesome; yet
+there is a change wrought, often very marked, in going from one place to
+another for different air.</p>
+
+<p>Even in the country, especially in summer-time, one distinctly notices the
+great difference in the air of lowland and highland localities. The ten
+miles change from Strathmore to Glenisla shows a marked difference in the
+air. Below, it is close, weakening, enervating; above, it is exhilarating,
+invigorating, and strong.</p>
+
+<p>So people must have a change&mdash;at least those who can afford it&mdash;for health
+must be seen to first of all, if one has means to do so. Oh! the blessing
+of good health! How many who enjoy it never think of the misery of its
+loss! In fact, health is the soul that animates all enjoyments of life;
+for without it those would soon be tasteless. A man starves at the
+<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span>best-spread table, and is poor in the midst of the greatest treasures
+without health.</p>
+
+<p>In these days half of our diseases come from the neglect of the body in
+the overwork of the brain. The wear and tear of labour and intellect go on
+without pause or self-pity. Men may live as long as their forefathers, but
+they suffer more from a thousand artificial anxieties and cares. The men
+of old fatigued only the muscles, we exhaust the finer strength of the
+nerves. Even more so now, then, do we require a change of air to soothe
+our overwrought nervous system.</p>
+
+<p>And when that magic power, concealed from mortal view, works such wonders
+on the health, surely it is one&#8217;s duty to save up and have it, when it is
+within one&#8217;s means. For is not health the greatest of all possessions?
+What a rich colour clothes the countenance of the young after a month&#8217;s
+outing in the hill country! How fine and pure has the blood become! All
+stagnant humours, accumulated in winter town life, have been dispelled by
+the ozone-brightening charm. The weary looking office or shop man is now
+transfigured into a sprightly youth once more, ready with strongly
+recuperated power for another winter&#8217;s labours. The pale wife, who has
+been stifled for months in close-aired rooms, has now a healthy flush on
+her becoming countenance that speaks of gladly restored health. And all
+this has been brought about by a &#8220;change of air&#8221;!</p>
+
+<p>For a thorough change to a town man, he should make for the Highlands.
+There he is never tired of walking, for the air which he breathes is full
+of ozone. This revivifying element in the air is produced by<span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span> the
+lightning-bursts from hill to hill. There is in the Highlands a continual
+rush of electricity, whether seen or not. Hence the air is very pure, free
+from organic germs, intensely exhilarating and buoyant.</p>
+
+<p>Sportsmen are livingly aware of the recuperative power of the Highland
+air. Perhaps these city men do not benefit so much by the easy walking
+exercise on the grouse moors as in breathing the splendidly
+delight-inspiring air. What a change one feels there in a very few hours!</p>
+
+<p>&#8220;A change of air&#8221; is an old wives&#8217; adage. But much of the weather-lore of
+our forefathers was based on real scientific principles only now coming to
+light. Nature is ever true, but it requires patience to unravel her
+secrets. We therefore advocate an occasional &#8220;change of air&#8221; to improve
+the health&mdash;</p>
+
+<p class="poem"><span style="margin-left: 9em;">&#8220;The chiefest good,</span><br />
+Bestow&#8217;d by Heaven, but seldom understood.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XVII" id="CHAPTER_XVII"></a>CHAPTER XVII</h2>
+<p class="title">THE OLD MOON IN THE NEW MOON&#8217;S ARMS</p>
+
+
+<p>After the sun&#8217;s broad beams have tired the sight, the moon with more sober
+light charms us to descry her beauty, as she shines sublimely in her
+virgin modesty. There is always a most fascinating freshness in the first
+sight of the new moon. The superstition of centuries adds to this charm.
+Why boys and girls like to turn over a coin in their pocket at this sight
+one cannot tell: yet it is done. No<span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span> young lady likes to look at the new
+moon through a pane of glass. And farmers are always confident of a change
+of weather with a new moon: at least in bad weather they earnestly hope
+for it.</p>
+
+<p>But, banishing all superstition, we welcome the pale silver sickle in the
+heavens, once more appearing from the bosom of the azure. And no language
+can equal these beautiful words of the youthful Shelley:&mdash;</p>
+
+<p class="poem"><span style="margin-left: 6em;">&#8220;Like the young moon,</span><br />
+When on the sunlit limits of the night<br />
+<span style="margin-left: 1em;">Her white shell trembles amid crimson air,</span><br />
+And while the sleeping tempest gathers might,<br />
+<span style="margin-left: 1em;">Doth, as the herald of his coming, bear</span><br />
+The ghost of its dead mother, whose dim form<br />
+<span style="margin-left: 1em;">Bends in dark ether from her infant&#8217;s chair.&#8221;</span></p>
+
+<p>That is a more charming way of putting the ordinary expression, &#8220;the old
+moon in the new moon&#8217;s arms.&#8221; We are regularly accustomed to the
+moonshine, but only occasionally is the <i>earthshine</i> on the moon so
+regulated that the shadowed part is visible. This is not seen at the
+appearance of every new moon. It depends upon the positions of the sun and
+moon, the state of the atmosphere, and the absence of heavy clouds. I
+never in my life saw the phenomenon so marvellously beautiful as on May
+7th, 1894, at my manse in Strathmore. I took particular note of it, as
+some exceedingly curious things were connected with it.</p>
+
+<p>At nine o&#8217;clock in the evening, the new moon issued from some clouds in
+the western heavens, the sun having set, about an hour before. The
+crescent was thin and silvery, and the outline of the shadowed part was
+just visible. The sky near the horizon was<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> clear and greenish-hued. As
+the night advanced the moon descended, and at ten o&#8217;clock she was
+approaching a purple stratum of clouds that stretched over the hills,
+while the position of the sun was only known a little to the east, by the
+back-thrown light upon the dim sky. Through the moisture-laden air the
+sun&#8217;s rays, reflected by the moon, threw a golden stream from the crescent
+moon, for the silvery shell became more golden-hued.</p>
+
+<p>The horns of the moon now seemed to project, and the shadowed part became
+more distinct, though the circle appeared smaller. By means of a
+field-glass I noticed that this was extra lighted, with points here and
+there quite golden-tinged. The darker spots showed the deep caverns; the
+brighter points brought into relief the mountain peaks.</p>
+
+<p>Why was the surface brighter than usual? I cannot go into detail about the
+phases of the moon; but, in a word, I may say that, while the sun can
+illuminate the side of the moon turned towards it, it is unable to throw
+any light on the shadow, seeing that there is no atmosphere around the
+moon to refract the light.</p>
+
+<p>If we, in imagination, looked from the moon upon the earth, we should see
+the same phases as are now noticed in the moon; and when it is just before
+new moon on the earth, the earth will appear fully illuminated from the
+moon. We would also observe (from the moon) that the brightness of the
+illuminated part of the earth would vary from time to time, according to
+the changes in the earth&#8217;s atmosphere. More light would be reflected to
+the moon from the clouds in our atmosphere than from the bare earth or<span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span>
+cloudless sea, since clouds reflect more light than either land or sea.
+Accordingly, we arrive at this curious fact&mdash;that the extra brightness of
+the <i>dark</i> body of the moon is mainly determined by the amount of <i>cloud
+in our atmosphere</i>.</p>
+
+<p>Accordingly, I concluded that there must be clouds to the west, though I
+could not see them, which reflected rays of light and faintly illuminated
+the shadowed part of the moon. It had become much colder, and I concluded
+that during the night the cloud-particles, if driven near by the wind,
+would condense into rain. And, assuredly, next morning I was gratified to
+find that rain had fallen in large quantities, substantiating the theory.</p>
+
+<p>There is much pleasure in verifying such an interesting problem. The dark
+body of the moon being more than usually visible is one of our well-known
+and oldest indications of coming bad weather. And at once came to my
+memory the lines of Sir Patrick Spens, as he foreboded rain for his
+crossing the North Sea:&mdash;</p>
+
+<p class="poem">&#8220;I saw the new moon late yestreen<br />
+Wi&#8217; the auld moon in her arm;<br />
+And if we gang to sea, master,<br />
+I fear we&#8217;ll come to harm.&#8221;</p>
+
+<p>This lunar indication, then, has a sound physical basis, showing that near
+the observer there are vast areas of clouds, which are reflecting light
+upon the moon at the time, before they condense into rain by the chilling
+of the air. According to the old Greek poet, Aratus: &#8220;If the new moon is
+ruddy, and you can trace the shadow of the complete circle, a storm is
+approaching.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span></p>
+<h2><a name="CHAPTER_XVIII" id="CHAPTER_XVIII"></a>CHAPTER XVIII</h2>
+<p class="title">AN AUTUMN AFTERGLOW</p>
+
+
+<p>A brilliant afterglow is welcomed for its surpassing beauty and a
+precursor of fine fixed weather.</p>
+
+<p>A glorious sunset has always had a charm for the lover of nature&#8217;s
+beauties. The zenith spreads its canopy of sapphire, and not a breath
+creeps through the rosy air. A magnificent array of clouds of numberless
+shapes come smartly into view. Some, far off, are voyaging their
+sun-bright paths in silvery folds; others float in golden groups. Some
+masses are embroidered with burning crimson; others are like &#8220;islands all
+lovely in an emerald sea.&#8221; Over the glowing sky are splendid colourings.
+The flood of rosy light looks as if a great conflagration were below the
+horizon.</p>
+
+<p>I remember witnessing an especially brilliant sunset last autumn on the
+high-road between Kirriemuir and Blairgowrie. The setting sun shone upon
+the back of certain long trailing clouds which were much nearer me than a
+range behind. The fringes of the front range were brilliantly golden,
+while the face of those behind was sparklingly bright. Then the sun
+disappeared over the western hills, and his place was full of spokes of
+living light.</p>
+
+<p>Looking eastward, I observed on the horizon the base of the northern line
+of a beautiful rainbow&mdash;&#8220;the shepherd&#8217;s delight&#8221; for fine weather.</p>
+
+<p>Soon in the west the light faded; but there came<span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span> out of the east a lovely
+flush, and the general sky was presently flamboyant with afterglow. The
+front set of clouds was darker except on the edges, the red being on the
+clouds behind; and the horizon in the east was particularly rich with dark
+red hues.</p>
+
+<p>Gradually the eastern glow rose and reddened all the clouds, but the front
+clouds were still grey. The effect was very fine in contrast. The fleecy
+clouds overhead became transparently light red, as they stretched over to
+reach the silver-streaked west. The new moon was just appearing upright
+against a slightly less bright opening in the sky, betokening the firm
+hardness of autumn.</p>
+
+<p>Soon the colouring melted away, and the peaceful reign of the later
+twilight possessed the land.</p>
+
+<p>Now why that brilliancy of the east, when the west was colourless? Most of
+all you note the immense variety and wealth of reds. These are due to dust
+in the atmosphere. We are the more convinced of this by the very
+remarkable and beautiful sunsets which occurred after the tremendous
+eruption at Krakatoa, in the Straits of Sunda, thirty years ago. There was
+then ejected an enormous quantity of fine dust, which spread over the
+whole world&#8217;s atmosphere. So long as that vast amount of dust remained in
+the air did the sunsets and afterglows display an exceptional wealth of
+colouring. All observers were struck with the vividly brilliant red
+colours in all shades and tints.</p>
+
+<p>The minute particles of dust in the atmosphere arrest the sun&#8217;s rays and
+scatter them in all directions; they are so small, however, that they
+cannot reflect and scatter all; their power is limited to<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span> the scattering
+of the rays at the blue end of the spectrum, while the red rays pass on
+unarrested. The display of the colours of the blue end are found in
+numberless shades, from the full deep blue in the zenith to the
+greenish-blue near the horizon.</p>
+
+<p>If there were no fine dust-particles in the upper strata, the sunset
+effect would be whiter; if there were no large dust-particles, there would
+be no colouring at all. If there were no dust-particles in the air at all,
+the light would simply pass through into space without revealing itself,
+and the moment the sun disappeared there would be total darkness. The very
+existence of our twilight depends on the dust in the air; and its length
+depends on the amount and extension upwards of the dust-particles.</p>
+
+<p>But how have the particles been increased in size in the east? Because, as
+the sun was sinking, but before its rays failed to illumine the heavens,
+the temperature of the air began to fall. This cooling made the
+dust-particles seize the water-vapour to form haze-particles of a larger
+size. The particles in the east first lose the sun&#8217;s heat, and first
+become cool; and the rays of light are then best sifted, producing a more
+distinct and darker red. As the sun dipped lower, the particles overhead
+became a turn larger, and thereby better reflected the red rays.
+Accordingly, the roseate bands in the east spread over to the zenith, and
+passed over to the west, producing in a few minutes a universal
+transformation glow.</p>
+
+<p>To produce the full effect often witnessed, there must be, besides the
+ordinary dust-particles, small crystals floating in the air, which
+increase the reflection from their surfaces and enhance the glow effects.<span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span>
+In autumn, after sunset, the water-covered dust-particles become frozen
+and the red light streams with rare brilliancy, causing all reddish and
+coloured objects to glow with a rare brightness. Then the air glows with a
+strange light as of the northern dawn. From all this it is clear that,
+though the colouring of sunset is produced by the direct rays of the sun,
+the afterglow is produced by reflection, or, rather, radiation from the
+illuminated particles near the horizon.</p>
+
+<p>The effect in autumn is a stream of red light, of varied tones, and rare
+brilliancy in all quarters, unseen during the warmer summer. We have to
+witness the sunsets at Ballachulish to be assured that Waller Paton really
+imitated nature in the characteristic bronze tints of his richly painted
+landscapes.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XIX" id="CHAPTER_XIX"></a>CHAPTER XIX</h2>
+<p class="title">A WINTER FOREGLOW</p>
+
+
+<p>Little attention has been paid to foreglows compared with afterglows,
+either with regard to their natural beauty or their weather forecasting.
+But either the ordinary red-cloud surroundings at sunrise, or the western
+foreglow at rarer intervals, betokens to the weather-prophet wet and
+gloomy weather. The farmer and the sailor do not like the sight, they
+depend so much on favourable weather conditions.</p>
+
+<p>Of course, sunrise to the &aelig;sthetic observer has always its charms. The
+powerful king of day rejoices &#8220;as a bridegroom coming out of his<span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span> chamber&#8221;
+as he steps upon the earth over the dewy mountain tops, bathing all in
+light, and spreading gladness and deep joy before him. The lessening
+cloud, the kindling azure, and the mountain&#8217;s brow illumined with golden
+streaks, mark his approach; he is encompassed with bright beams, as he
+throws his unutterable love upon the clouds, &#8220;the beauteous robes of
+heaven.&#8221; Aslant the dew-bright earth and coloured air he looks in
+boundless majesty abroad, touching the green leaves all a-tremble with
+gold light.</p>
+
+<p>But glorious, and educating, and inspiring as is the sunrise in itself in
+many cases, there is occasionally something very remarkable that is
+connected with it. Rare is it, but how charming when witnessed, though
+till very recently it was all but unexplained. This is the <i>foreglow</i>.</p>
+
+<p>It is in no respect so splendid as the afterglow succeeding sunset; but,
+because of its comparative rarity, its beauty is enhanced. I remember a
+foreglow most vividly which was seen at my manse, in Strathmore, in
+January 1893. My bedroom window looked due west; I slept with the blind
+up. On that morning I was struck, just after the darkness was fading away,
+with a slight colouring all along the western horizon. The skeleton
+branches of the trees stood out strongly against it. The colouring
+gradually increased, and the roseate hue stretched higher. The old
+well-known faces that I used to conjure up out of the thin blended boughs
+became more life-like, as the cheeks flushed. There was rare warmth on a
+winter morning to cheer a half-despairing soul, tired out with the long
+hours of oil<span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span> reading, and pierced to the heart by the never-ceasing
+rimes; yet I could not understand it.</p>
+
+<p>I went to the room opposite to watch the sunrise, for I had observed in
+the diary that the appearance of the sun would not be for a few minutes.
+There were streaks of light in the east above the horizon, but no colour
+was visible. That hectic flush&mdash;slight, yet well marked&mdash;which was
+deepening in the western heavens, had no counterpart in the east, except
+the colourless light which marked the wintry sun&#8217;s near approach. As soon
+as the sun&#8217;s rays shot up into the eastern clouds, and his orb appeared
+above the horizon, the western sky paled, the colour left it, as if
+ashamed of its assumed glory. A foreglow like that I have very rarely
+seen, and its existence was a puzzle to me till I studied Dr. Aitken&#8217;s
+explanation of the afterglows after sunset. I had never come across any
+description of a foreglow; and, of course, across no explanation of the
+curious phenomenon. The western heavens were coloured with fairly bright
+roseate hues, while the eastern horizon was only silvery bright before the
+sun rose; whereas, after the sun appeared and coloured the eastern hills
+and clouds, the western sky resumed its leaden grey and colourless
+appearance. Why was that? What is the explanation?</p>
+
+<p>I have not space enough to repeat the explanation given already in the
+last chapter of the glorious phenomenon of the afterglow. But the
+explanation is similar. Before sunrise, the rays of the sun are reflected
+by dust-particles in the zenith to the western clouds. The colouring is
+intensified by the frozen water-vapour on these particles in the west.</p>
+
+<p><span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span>One thing I carefully noted. Ere mid-day, snow began to fall, and for some
+days a severe snow-storm kept us indoors. Then, at any rate, the foreglow
+betokened a coming storm. It was, like a rainbow in a summer morning, a
+decided warning of the approaching wet weather.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XX" id="CHAPTER_XX"></a>CHAPTER XX</h2>
+<p class="title">THE RAINBOW</p>
+
+
+<p>The poet Wordsworth rapturously exclaimed&mdash;</p>
+
+<p class="poem">&#8220;My heart leaps up when I behold<br />
+A rainbow in the sky.&#8221;</p>
+
+<p>And old and young have always been enchanted with the beautiful
+phenomenon. How glorious is the parti-coloured girdle which, on an April
+morning or September evening, is cast o&#8217;er mountain, tower, and town, or
+even mirrored in the ocean&#8217;s depths! No colours are so vividly bright as
+when this triumphal arch bespans a dark nimbus: then it unfolds them in
+due prismatic proportion, &#8220;running from the red to where the violet fades
+into the sky.&#8221;</p>
+
+<p>A plain description of the formation of the rainbow is not very easily
+given, but a short sketch may be useful. Beautiful as is the ethereal bow,
+&#8220;born of the shower and colour&#8217;d by the sun,&#8221; yet the marvellous effect is
+more exquisitely intensified in its gorgeous display when the hand of
+science points<span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span> out the path in which the sun&#8217;s rays, from above the
+western horizon, fall on the watery cloud, indicating fine weather&mdash;&#8220;the
+shepherd&#8217;s delight.&#8221;</p>
+
+<p>One law of reflection is that, when a ray of light falls on a plane or
+spherical surface, it goes off at the same angle to the surface as it
+fell. One law of refraction is that, when a ray of light passes through
+one medium and enters a denser medium (as from air to water), it is bent
+back a little. By refraction you see the sun&#8217;s rays long after the sun has
+set; when the sun is just below the horizon, an observer, on the surface
+of the earth, will see it raised by an amount which is generally equal to
+its apparent diameter.</p>
+
+<p>The rays of different colours are bent back (when passing through the
+water) at different rates, some slightly, others more, from the red to the
+violet end. The rainbow, then, is produced by refraction and reflection of
+the several coloured rays of sunlight in the drops of water which make up
+falling rain.</p>
+
+<p>The sun is behind the observer, and its rays fall in a parallel direction
+upon the drops of rain before him. In each drop the light is dispersively
+refracted, and then reflected from the farther face of the drop; it
+travels back through the drop, and comes out with dispersing colours.</p>
+
+<p>According to the height of the sun, or the slope of its rays, a higher or
+lower rainbow will be formed. And, strange, no two people can see the very
+same bow; in fact the rainbow, as seen by the one eye, is not formed by
+the same water-drops as the rainbow seen by the other eye.</p>
+
+<p>When the primary bow is seen in most vivid<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span> colours on a dark cloud, a
+second arch, larger and fainter, is often seen. But the order of the
+colours is quite reversed. At a greater elevation, the sun&#8217;s ray enters
+the lower side of a drop of rain-water, is refracted, reflected <i>twice</i>,
+and then refracted again before being sent out to the observer&#8217;s eye. That
+is why the colours are reversed.</p>
+
+<p><i>A one-coloured rainbow</i> is a curious and rare phenomenon. It is a strange
+paradox, for the very idea of a rainbow brings up the seven colours&mdash;red,
+orange, yellow, green, blue, indigo, and violet. Yet Dr. Aitken tells us
+of a rainbow with one colour which he observed on Christmas Day, in 1888.</p>
+
+<p>He was taking his walk on the high ground south of Falkirk. In the east he
+observed a strange pillar-like cloud, lit up with the light of the setting
+sun. Then the red pillar extended, curved over, and formed a perfect arch
+across the north-eastern sky. When fully developed, this rainbow was the
+most extraordinary one which he had ever seen. There was no colour in it
+but red. It consisted simply of a red arch, and even the red had a
+sameness about it.</p>
+
+<p>Outside the rainbow there was part of a secondary bow. The Ochil Hills
+were north of his point of observation. These hills were covered with
+snow, and the setting sun was glowing with rosy light. Never had he seen
+such a depth of colour as was on them on this occasion. It was a deep,
+furnacy red. The sun&#8217;s light was shorn of all the rays of short-wave
+length on its passage through the atmosphere, and only the red rays
+reached the earth. The reason why the Ochils glowed with so deep a<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span> red
+was owing to their being overhung by a dense curtain of clouds, which
+screened off the light of the sky. The illumination was thus principally
+that of the direct softer light of the sun.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXI" id="CHAPTER_XXI"></a>CHAPTER XXI</h2>
+<p class="title">THE AURORA BOREALIS</p>
+
+
+<p>He must be a very careless observer who has not been struck with the
+appearance of the streamers which occasionally light up the northern
+heavens, and which farmers consider to be indicators of strong wind or
+broken weather.</p>
+
+<p>The time was when the phenomenon was considered to be supernatural and
+portentous, as the chroniclers of spectral battles, when &#8220;fierce, fiery
+warriors fought upon the clouds, in ranks and squadrons, and right form of
+war.&#8221; And even in the rural districts of Britain, the blood-coloured
+aurora, of October 24th, 1870, was considered to be the reflection of an
+enormous Prussian bonfire, fed by the beleaguered French capital.</p>
+
+<p>In joyful spirit, the Shetlanders call the beautiful natural phenomenon,
+&#8220;Merry Dancers.&#8221; Burns associated their evanescence with the
+transitoriness of sensuous gratification:&mdash;&#8220;they flit ere you can point
+their place.&#8221; And Tennyson spoke of his cousin&#8217;s face lit up with the
+colour and light of love, &#8220;as I have seen the rosy red flushing in the
+northern night.&#8221;</p>
+
+<p>Yet this phenomenon is to a great extent under the control of cosmical
+laws. One of the most difficult<span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span> problems of our day has been to
+disentangle the irregular webwork of auror&aelig;, and bring them under a law of
+periodicity, which depends upon the fluctuations of the sun&#8217;s photosphere
+and the variations on the earth&#8217;s magnetism, and which have such an
+important influence upon the fluctuations of the weather.</p>
+
+<p>The name &#8220;Aurora Borealis&#8221; was given to it by Gassendi in 1621.
+Afterwards, the old almanacs described it as the &#8220;Great Amazing Light in
+the North.&#8221; In the Lowlands of Scotland, the name it long went by, of
+&#8220;Lord Derwentwater&#8217;s Lights,&#8221; was given because it suddenly appeared on
+the night before the execution of the rebel lord. In Ceylon auror&aelig; were
+called &#8220;Buddha Lights.&#8221;</p>
+
+<p>The first symptom of an aurora borealis is commonly a low arch of pale,
+greenish-yellow light, placed at right angles to the magnetic meridian.
+Sometimes rays cover the whole sky, frequently showing tremulous motion
+from end to end; and sometimes they appear to hang from the sky like the
+fringes of a mantle. They are among the most capricious of natural
+phenomena, so full of individualities and vagaries. To the glitter of
+rapid movement they add the charm of vivid colouring. It is strongly
+asserted that auror&aelig; are preceded by the same general phenomena as
+thunder-storms. This was borne out by Piazzi Smith (late Astronomer-Royal
+for Scotland), who observed that their monthly frequency varies inversely
+with that of thunder-storms&mdash;both being safety-valves for the discharge of
+surplus electricity.</p>
+
+<p>Careful observers have, moreover, noticed a <span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span>remarkable coincidence
+between the display of auror&aelig; and the maxima of the sun&#8217;s spots and of the
+earth&#8217;s magnetic disturbances. Some have supposed that the light of the
+aurora is caused by clouds of meteoric dust, composed of iron, which is
+ignited by friction with the atmosphere. But there is this difficulty in
+the way, shooting stars are more frequent in the morning, while the
+reverse is the case with the aurora. The highest authorities have
+concluded, pretty uniformly, that auror&aelig; are electric discharges through
+highly rarefied air, taking place in a magnetic field, and under the sway
+of the earth&#8217;s magnetic induction. They are not inappropriately called
+&#8220;Polar lightnings,&#8221; for when electricity misses the one channel it must
+traverse the other.</p>
+
+<p>The natives of the Arctic regions of North America pretend to foretell
+wind by the rapidity of the motions of the streamers. When they spread
+over the whole sky, in a uniform sheet of light, fine weather ensues.
+Fitzroy believed that auror&aelig; in northern latitudes indicated and
+accompanied stormy weather at a distance. The same idea is still current
+among many farmers and fishermen in Scotland.</p>
+
+<p>Is there any audible accompaniment to the brilliant spectacle? The natives
+of some parts, with subtle hearing-power, speak of the &#8220;whizzing&#8221; sound
+which is often heard during auroral displays. Burns tells of their
+&#8220;hissing, eerie din,&#8221; as echoes of the far-off songs of the Valkyries.
+Perhaps the most striking incident which corroborates this opinion
+occurred during the Franco-Prussian War. Rolier, a practised a&euml;ronaut,
+left Paris in a balloon, on his mission of city defence, and fourteen
+hours afterwards landed<span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span> in Norway. He had reached the height of two and a
+half miles. When descending, he passed through a peculiar cloud of
+sulphurous odour, which emitted flashed light and a slight scratching or
+rustling noise. On landing, he witnessed a splendid aurora borealis. He
+must, therefore, have passed through a cloud in which an electrical
+discharge of an auroral nature was proceeding, accompanied with an audible
+sound. There is, moreover, no improbability of such sounds being
+occasionally heard, since a somewhat similar phenomenon accompanies the
+brush discharge of the electric machinery, to which the aurora bears
+considerable resemblance.</p>
+
+<p>Though no fixed conclusions are yet established about the causes of the
+brilliant auroral display, yet, as the results of laborious observations,
+we are assured that the stabler centre of our solar system holds in its
+powerful sway the several planets at their respective distances, supplying
+them all with their seasonable light and heat, vibrating sympathetic
+chords in all, and even controlling under certain&mdash;though to us still
+unknown&mdash;laws the electric streamers that flit, apparently lawlessly, in
+the distant earth&#8217;s atmosphere.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXII" id="CHAPTER_XXII"></a>CHAPTER XXII</h2>
+<p class="title">THE BLUE SKY</p>
+
+
+<p>If we look at the sky overhead, when cloudless in the sunshine, we wonder
+what gives the air such a deep-blue colour. We are not looking, as<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span>
+children seem to do, into vacancy, away into the far unknown. And even, if
+that were the case, would not the space be quite colourless? What, then,
+produces the blueness?</p>
+
+<p>Some of the very fine dust-particles, even when clothed with an
+exceedingly thin coating of water-vapour, are carried very high; and,
+looking through a vast accumulation of these, we find the effect of a
+deep-blue colour.</p>
+
+<p>Why so? Because these particles are so small that they can only reflect
+the rays of the blue end of the spectrum; and the higher we ascend, the
+smaller are the particles and the deeper is the blue. But it is also
+because water, even in its very finest and purest form, is blue in colour.
+For long this was disputed. Even Sir Robert Christison concluded, after
+years of experimenting on Highland streams, that water was colourless.</p>
+
+<p>Of course, he admitted that the water in the Indian and Pacific Oceans has
+frequent patches of red, brown, or white colour, from the myriads of
+animalcules suspended in the water. Ehrenberg found that it was vegetable
+matter which gave to the Red Sea its characteristic name. But these, and
+similar waters, are not pure.</p>
+
+<p>It is to Dr. Aitken that the final discovery of the real colour of water
+is due. When on a visit to several towns on the shores of the
+Mediterranean, he set about making some very interesting experiments,
+which the reader will follow with pleasure.</p>
+
+<p>It is a well-known fact that colour transmitted through different bodies
+differs considerably from colour reflected by them. In his first
+experiment he<span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span> took a long empty metal tube, open at one end, and closed
+at the other end by a clear-glass plate. This was let down vertically into
+the water, near to a fixed object, which appeared of most beautiful deep
+and delicate blue at a depth of 20 feet. Scientific men know that, if the
+colour of water is due to the light reflected by extremely small particles
+of matter suspended in the water, then the object looked at through it
+would have been illuminated with yellow (the complementary colour of
+blue). A blackened tube was then filled with water (which had a
+clear-glass plate fixed to the bottom), and white, red, yellow, and purple
+objects were sunk in the water, and these colours were found to change in
+the same way as if they were looked at through a piece of pale-blue glass.
+The white object appeared blue, the red darkened very rapidly as it sank,
+and soon lost its colour; at the depth of seven feet a very brilliant red
+was so darkened as to appear dark brick-red. The yellow object changed to
+green, and the purple to dark blue.</p>
+
+<p>But, still further to satisfy himself that water is really blue in itself,
+even without any particles suspended in it, he tested the colour of
+<i>distilled</i> water. He filled a darkened tube with this water (clear-glass
+plates being at the ends of the tube), and looked through it at a white
+surface. The effect was the same as before, the colour was blue, almost
+exactly of the same hue as a solution of Prussian blue.</p>
+
+<p>This is corroborated by the fact that, the purer the water is in nature,
+the bluer is the tint when a large quantity is looked through. Some
+Highland lochs have crystal waters of the most extraordinary blue. Of
+course, some cling to the old idea that this<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span> is accounted for by the
+reflected blue of the clear heavens above. No doubt, if the sky be deep
+blue, then this blue light, when reflected by the surface of the water,
+will enrich and deepen the hue. But the water itself is <i>really</i> blue.</p>
+
+<p>At the same time, the dust-particles suspended in the water have a great
+effect in making the water appear more beautiful, brilliant, and varied in
+its colouring; because little or no light is reflected by the interior of
+a mass of water itself. If a dark metal vessel be filled with a weak
+solution of Prussian blue, the liquid will appear quite dark and void of
+colour. But throw in some fine white powder, and the liquid will at once
+become of a brilliant blue colour. This accounts for the change of depth
+and brilliancy of colour in the several shores of the Mediterranean.</p>
+
+<p>When, then, you look at the face of a deep-blue lake on a summer
+evening&mdash;the heavens all aglow with the unrivalled display of colour from
+the zenith, stretching in lighter hues of glory to the horizon&mdash;though to
+you the calm water appears like a lake of molten metal glowing with
+sky-reflected light, so powerful and brilliant as entirely to overpower
+the light which is internally reflected, yet blue is the normal colour of
+the water: <i>blueness is its inherent hue</i>.</p>
+
+<p>Looking upwards, we observe three distinct kinds of blue in the sky from
+the horizon to the zenith. All painters in water-colours know that. Newton
+thought that the colour of the sky was produced in the same way as the
+colours in thin plates, the order of succession of the colours gradually
+increasing in intensity.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span></p>
+<h2><a name="CHAPTER_XXIII" id="CHAPTER_XXIII"></a>CHAPTER XXIII</h2>
+<p class="title">A SANITARY DETECTIVE</p>
+
+
+<p>The impure state of the air in the rooms of a house can now be determined
+by means of colour alone. Dr. Aitken has invented a very simple instrument
+for that purpose; and this ought to be of great service to sanitary
+officers. It is called the koniscope&mdash;or dust-detective.</p>
+
+<p>The instrument consists of an air-pump and a metal tube with glass ends.
+Near one end of the test-tube is a passage by which it communicates with
+the air-pump, and near the other end is attached a stop-cock for admitting
+the air to be tested. It is not nearly so accurate as the dust-counter;
+but it is cheaper, more easily wrought, and more handy for quick work. All
+the grades of blue, from what is scarcely visible to deep, dark blue, may
+be attached alongside the tube on pieces of coloured glass; and opposite
+these colours are the numbers of dust-particles in the cubic inch of the
+similar air, as determined by the dust-counter.</p>
+
+<p>While the number of particles was counted by means of the dust-counter,
+the depth of blue given by the koniscope was noted; and the piece of glass
+of that exact depth of blue attached. A metal tube was fitted up
+vertically in the room, in such a way that it could be raised to any
+desired height into the impure air near the ceiling, so that supplies of
+air of different degrees of impurity might be obtained. To<span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span> produce the
+impurity, the gas was lit and kept burning during the experiments. The air
+was drawn down through the pipe by means of the air-pump of the koniscope,
+and it passed through the measuring apparatus of the dust-counter on its
+way to the koniscope. It may be remarked that, by a stroke of the
+air-pump, the air within the test-tube is rarefied and the dust-particles
+seize the moisture in the super-saturated air to form fog-particles;
+through this fog the colour is observed, and the shade of colour
+determines the number of dust-particles in the air. These colours are
+named &#8220;just visible,&#8221; &#8220;very pale blue,&#8221; &#8220;pale blue,&#8221; &#8220;fine blue,&#8221; &#8220;deep
+blue,&#8221; and &#8220;very deep blue.&#8221;</p>
+
+<p>When making a sanitary inspection, the pure air should be examined first,
+and the colour corresponding to that should be considered as the normal
+health colour. Any increase from the depth would indicate that the air was
+being gradually contaminated; and the amount of increase in the depth of
+colour would indicate the amount of increase of pollution.</p>
+
+<p>As an illustration of what this instrument can detect, a room of 24 by 17
+by 13 feet was selected. The air was examined before the gas was lighted,
+and the colour in the test-tube was very faint, indicating a clear
+atmosphere. In all parts of the room this was found the same. A small tube
+was attached to the test-tube, open at the other end, for taking air from
+different parts of the room. Three jets of gas were then lit in the centre
+of the room, and observations at once begun with the koniscope.</p>
+
+<p>Within thirty-five seconds of striking the match to<span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span> light the gas, the
+products of combustion had extended near the ceiling to the end of the
+room; this was indicated by the colour in the koniscope suddenly becoming
+a deep blue. In four minutes the deep-blue-producing air was got at a
+distance of two feet from the ceiling. In ten minutes there was strong
+evidence of the pollution all through the room. In half-an-hour the
+impurity at nine feet from the floor was very great, the colour being an
+intensely deep blue.</p>
+
+<p>The wide range of the indications of the instrument, from pure clearness
+to nearly black blue, makes the estimate of the impurity very easily taken
+with it; and, as there are few parts to get out of order, it is hoped it
+may come into general use for sanitary work.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXIV" id="CHAPTER_XXIV"></a>CHAPTER XXIV</h2>
+<p class="title">FOG AND SMOKE</p>
+
+
+<p>Just two hundred and forty years ago, Mr. John Evelyn, F.R.S., a
+well-known writer on meteorology, sent a curious tract to King Charles
+II., which was ordered to be printed by his Majesty. It was entitled
+&#8220;Fumifugium,&#8221; and dealt with the great smoke nuisance in London. I find
+from the thesis that he had a very hazy idea of the connection between fog
+and smoke; and no wonder, for it is only lately that the connection has
+been fully explained.</p>
+
+<p>We know that without dust-particles there can<span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span> be no fog, and that smoke
+supplies a vast amount of such particles. Therefore, in certain states of
+the atmosphere, the more smoke the more fog. In Mr. Evelyn&#8217;s day the fog,
+which he called &#8220;presumptuous smoake,&#8221; was at times so dense that men
+could hardly discern each other for the &#8220;clowd.&#8221; His Majesty&#8217;s only sister
+had complained of the damage done to her lungs by the contamination, and
+Mr. Evelyn was disgusted at the apathy of the people to do anything to
+remedy the nuisance. He deplored that that glorious and ancient city of
+London should wrap her stately head in &#8220;clowds of smoake, so full of stink
+and darknesse.&#8221; He was of opinion that a method of charring coal so as to
+divest it of its smoke, while leaving it serviceable for many purposes,
+should be made the object of a very strict inquiry. And he was right. For
+it is now known that fog in a town is intensified by much smoke.</p>
+
+<p>In a city like London or Glasgow, where a great river, fed by warm streams
+of water from gigantic works, passes through its centre, fogs can never be
+entirely obliterated, for the dust-particles in the air (often four
+millions and upwards in the cubic inch) will seize with terrible avidity
+the warm vapour rising from the river. That is the main reason why fogs
+cannot there be put down. Smoke is being consumed to a great extent; yet
+we find particles of sulphur remaining, which seize the warm vapour and
+form fogs dense enough to check all traffic. The worst form of city fogs
+seems to be produced when the air, after first flowing slowly in one
+direction, then turns on its tracks and flows<span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span> back over the city,
+bringing with it a black pall, the accumulated products of previous days,
+to which gets added the smoke and other impurities produced at the time.</p>
+
+<p>What irritated Mr. Evelyn was that, outside of London, the air was clear
+when passengers could not walk in safety within the city. So vexed was he
+about the contamination, that he made it the occasion of all the &#8220;cathars,
+phthisicks, coughs, and consumption in the city.&#8221; He appealed to common
+sense to testify that those who repair to London soon take some serious
+illness. &#8220;I know a man,&#8221; he said, &#8220;who came up to London and took a great
+cold, which he could never afterwards claw off again.&#8221;</p>
+
+<p>Mr. Evelyn proposed that, by an Act of Parliament, the nuisance be
+removed; enjoining that all breweries, dye-works, soap and salt boilers,
+lime-burners, and the like, be removed five or six miles distant from
+London below the river Thames. That would have materially helped his
+cause.</p>
+
+<p>But there is more difficulty in the purification than he anticipated. Yet
+there was pluck in the old man pointing out the killing contamination and
+suggesting a possible remedy. He had the fond idea that thereby a certain
+charm, &#8220;or innocent magick,&#8221; would make a transformation scene like
+Arabia, which is therefore &#8220;styl&#8217;d the Happy, attracting all with its gums
+and precious spices.&#8221; In purer air fogs would be less dense, breathing
+would be easier, business would be livelier, life would be happier.</p>
+
+<p>Few, I suppose, have laid their hands on this curious Latin thesis, or its
+quaint translation, directing the King&#8217;s attention to the fogs that were
+ruining<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span> London. Since that time the city has increased, from little more
+than a village, to be the dwelling-place of six millions of human beings,
+yet too little improvement has been made in the removal of this fog
+nuisance. King Edward&#8217;s drive through London would be even more dangerous
+on a muggy, frosty day than was Charles II.&#8217;s, when science was little
+known.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXV" id="CHAPTER_XXV"></a>CHAPTER XXV</h2>
+<p class="title">ELECTRICAL DEPOSITION OF SMOKE</p>
+
+
+<p>A good deal of scientific work is being done in the way of clearing away
+fog and smoke; and this, through time, may have some practical results in
+removing a great source of annoyance, illness, and danger in large towns.
+Sir Oliver Lodge and Dr. Aitken have been throwing light upon the
+deposition of smoke in the air by means of electricity.</p>
+
+<p>If an electric discharge be passed through a jar containing the smoke from
+burnt magnesium wire, tobacco, brown paper, and other substances, the dust
+will be deposited so as to make the air clear. Brush discharge, or
+anything that electrifies the air itself, is the most expeditious.</p>
+
+<p>If water be forced upwards through a vertical tube (with a nozzle
+one-twentieth of an inch in diameter), it will fall to the ground in a
+fine rain; but, if a piece of rubbed (electrified) sealing-wax be held a
+yard distant from the place where the jet breaks into drops, they at once
+fall in large spots as in a thunder-shower. If paper be put on the ground
+during the<span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span> experiment, the sound of pattering will be observed to be
+quite different. If a kite be flown into a cloud, and made to give off
+electricity for some time, that cloud will begin to condense into rain.</p>
+
+<p>Experiments with Lord Kelvin&#8217;s recorder show that variations in the
+electrical state of the atmosphere precede a change of weather. Then, with
+a very large voltaic battery, a tremendous quantity of electricity could
+be poured into the atmosphere, and its electrical condition could be
+certainly disturbed. If this could be made practically available, how
+useful it would be to farmers when the crops were suffering from excessive
+drought! It might be more powerfully available than the imagined
+condensation of a cloud into rain by the reverberation caused by the
+firing of a range of cannon.</p>
+
+<p>But what is the practical benefit of this information? If electricity
+deposits smoke, it might be made available in many ways. The fumes from
+chemical works might be condensed; and the air in large cities, otherwise
+polluted, might be purified and rendered innocuous. The smoke of chimneys
+in manufacturing works might be prevented from entering the atmosphere at
+all. In flour-mills and coal-mines the fine dust is dangerously explosive.
+In lead, copper, and arsenic works, it is both poisonous and valuable.</p>
+
+<p>Lead smelters labour under this difficulty of condensing the fume which
+escapes along with the smoke from red-lead smelting furnaces; and it was
+considered that an electrical process of condensation might be made
+serviceable for the purpose. At Bagillt, the method used for collecting or
+condensing<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span> the lead fume is a large flue two miles long; much is retained
+in this flue, but still a visible cloud of white-lead fume continually
+escapes from the top of the chimney. There is a difficulty in the way of
+depositing fumes in the flue by means of a sufficient discharge of
+electricity, viz. the violent draught which is liable to exist there, and
+which would mechanically blow away any deposited dust.</p>
+
+<p>But Dr. Aitken suggests that regenerators might be used along with the
+electricity. The warm fumes might be taken to a cold depositor, where (by
+the ordinary law of cold surfaces attracting warm dust-particles) the
+impurities would be removed, and, when purified, the air would again be
+taken through a hot regenerator before being sent up the chimney. By a
+succession of these chambers, with the assistance of electric currents,
+the air, impregnated with the most deleterious particles, or valuable
+dust, could be rendered innocuous.</p>
+
+<p>The sewage of our towns must be cleaned of its deleterious parts before
+being run into the streams which give drink to the lower animals, because
+an Act of Parliament enforces the process. Why, then, ought we not to have
+similar compulsion for making the smoke from chemical and other noxious
+works quite harmless before being thrown into the air which contains the
+oxygen necessary for the life of human beings?</p>
+
+<p>There seems to be a good field before electricians to catch the smoke on
+the wing and deposit its dust on a large scale. This seems to be a matter
+beyond our reach at present, except in the scientist&#8217;s laboratory; but
+certainly it is a &#8220;consummation devoutly to be wished.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span></p>
+<h2><a name="CHAPTER_XXVI" id="CHAPTER_XXVI"></a>CHAPTER XXVI</h2>
+<p class="title">RADIATION FROM SNOW</p>
+
+
+<p>One night a most interesting paper by Dr. Aitken, on &#8220;Radiation from
+Snow,&#8221; was read by Professor Tait to the Fellows of the Royal Society of
+Edinburgh. I remember that Dr. Alex. Buchan&mdash;the greatest meteorologist
+living&mdash;spoke afterwards in the very highest terms of the subject-matter
+of the paper. This was corroborated by Lord Kelvin, Lord MacLaren, and
+Professor Chrystal.</p>
+
+<p>Dr. Aitken had been testing the radiating powers of different substances.
+Snow in the shade on a bright day at noon is 7&deg; Fahr. colder than the air
+that floats upon it, whereas a black surface at the same is only 4&deg;
+colder. This difference diminishes as the sun gets lower; and at night
+both radiate almost equally well.</p>
+
+<p>I select, among the careful and numerous observations, the notes on
+January 19, 1886; for I took note of the cold of that day in my diary. It
+was the coldest day of the whole of that winter. The barometer was 28&middot;8
+inches, and the thermometer 4&deg;&mdash;that is, 28&deg; of frost. According to Dr.
+Buchan, that January had only two equal in average cold for fifty years.</p>
+
+<p>On January 19, at 10 <span class="smcaplc">A.M.</span>, when the air was at 20&deg; and the sky clear, a
+black surface registered 16&deg; and the upper layer of snow 12&deg;, showing a
+difference of 4&deg; when both surfaces were colder than the superincumbent
+air. It is curious to note that, on February 5<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span> of the same year, at the
+same hour, when the sky was overcast, the air was at 23&deg;, the black
+surface registered 29&deg;, and the snow 25&deg;, showing again the difference of
+4&deg;; but, in this case, both surfaces were warmer than the air. In both
+cases the radiation at night was equal.</p>
+
+<p>This small absorbing power of snow for heat reflected and radiated from
+the sky during the day must have a most important effect on the
+temperature of the air. The temperature of lands when covered with snow
+must be much lower than when free from it. And, when once a country has
+become covered with snow, there will be a tendency towards glacial
+conditions.</p>
+
+<p>But, besides being a bad absorber of heat from the sky, snow is also a
+very poor conductor of heat. On that very cold night (January 18), when
+there was a depth of 5&#189; inches of snow on the ground, and the night
+clear, with strong radiation, the temperature of the surface of the snow
+was 3&deg; Fahr., and a minimum thermometer on the snow showed that it had
+been down to zero some time before. A thermometer, plunged into the snow
+down to the grass, gave the most remarkable register of 32&deg;. Through the
+depth of 5&#189; inches of snow there was a difference of temperature of
+29&deg;. This was confirmed by removing the snow, and finding that the grass
+was unfrozen. As the ground was frozen when the snow fell, it would appear
+that the earth&#8217;s heat slowly thawed it under the protection of the snow.</p>
+
+<p>The protection afforded by the bad-conducting power of snow is of great
+importance in the economy of nature. How vegetation would suffer, were it
+<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span>exposed to a low temperature, unprotected by the snow-mantle! So that,
+though the continued snow cools the air for animals that can look after
+their own heating, it keeps warm the soil; and vegetation prospers under
+the genial covering. The fine rich look of the young wheat-blades, after a
+continued snow has melted, must strike the most careless observer. Instead
+of the half-blackened tips and semi-sickly blades, which we see in a field
+of young wheat after a considerable course of dry frost without snow, we
+have a rich, healthy green which shows the vital energy at work in the
+plants. Or even in the town gardens, after a continued snow has been
+melted away by a soft, western breeze, we are struck with the white,
+peeping buds of the snowdrop and the finely springing grass in the sward.</p>
+
+<p>Yet the snow-covering gives durability to cold weather. This has been
+demonstrated by Dr. W&oelig;ikof, the distinguished Russian meteorologist. On
+this account the spring months of Russia and Siberia are intensely cold.
+The plants, then, which in winter are unable by locomotion to keep
+themselves in health, are protected by the snow-mantle which chills the
+air for animals that can keep themselves in heat by exercise. What a grand
+compensating power is here!</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXVII" id="CHAPTER_XXVII"></a>CHAPTER XXVII</h2>
+<p class="title">MOUNTAIN GIANTS</p>
+
+
+<p>Some mysterious physical phenomena can be clearly explained by the aid of
+science. The mountain<span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span> giants that at times haunt the lonely valleys, and
+strike with fear the superstitious dwellers there, are only the enlarged
+shadows of living human beings cast upon a dense mist.</p>
+
+<p>The two most startling of these &#8220;eerie&#8221; phenomena are the spectres of
+Adam&#8217;s Peak and the Brocken.</p>
+
+<p>The phenomena sometimes to be observed at Adam&#8217;s Peak, in Ceylon, are very
+remarkable. Many travellers have given vivid accounts of these. On one
+occasion the Hon. Ralph Abercromby, in his praiseworthy enthusiasm for
+meteorological research, went there with two scientific friends to witness
+the strange appearance. The conical peak, a mile and a half high,
+overlooks a gorge west of it. When, then, the north-east monsoon blows the
+morning mist up the valley, light wreaths of condensed vapour pass to the
+right of the Peak, and catch the shadows at sunrise.</p>
+
+<p>This party reached the summit early one morning in February. The foreglow
+began to brighten the under-surface of the stratus-cloud with orange, and
+patches of white mist filled the hollows. Soon the sun peeped through a
+chink in the clouds, and they saw the pointed shadow of the Peak lying on
+the misty land. Then a prismatic circle, with the red inside, formed round
+the shadow. The meteorologist waved his arms about, and immediately he
+found giant shadowy arms moving in the centre of the rainbow.</p>
+
+<p>Soon they saw a brighter and sharper shadow of the Peak, encircled by a
+double bow, and their own spectral arms more clearly visible. The shadow,<span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span>
+the double bow, and the giant forms, combined to make this phenomenon the
+most marked in the whole world.</p>
+
+<p>The question has been frequently asked: Why are such a&euml;rial effects not
+more widely observed? There are not many mountains of this height and of a
+conical shape; and still fewer can there be where a steady wind, for
+months together, blows up a valley so as to project the rising morning
+mist at a suitable height and distance on the western side, to catch the
+shadow of the peak at sunrise.</p>
+
+<p>The most famous place in Europe for witnessing the awe-inspiring
+phenomenon is the Brocken, in Germany&mdash;3740 feet in height. The only great
+disappointment there is that the conditions rarely combine at sunrise or
+sunset to have &#8220;the spectre&#8221; successful.</p>
+
+<p>In July 1892, my daughter and I were spending some weeks at Harzburg, and,
+of course, we had to visit the Brocken and take stock of the world-known
+phenomenon. At mid-day, the air at the flat summit was cold, clear, and
+hard. The boulders are of enormous size; and near the &#8220;Noah&#8217;s Ark&#8221; Hotel
+and Observatory many are piled up in a mass, on which the observers stand
+at the appointed time for having their shadows projected on the misty air
+in the valleys.</p>
+
+<p>At five o&#8217;clock in the afternoon the sky was brilliantly clear on the
+summit of the Brocken; but the wind was rising from the sun&#8217;s direction,
+and the mist was filling up the wide-spread eastern valley. We stood on
+the &#8220;spectre&#8221; boulders, and our shadows were thrown on the grass, just as
+at home. <span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span>However, they fell upon large patches of white heather, which
+there is very plentiful.</p>
+
+<p>At six o&#8217;clock the sun was still shining beautifully, and we anxiously
+waited for the time when it would be low enough to raise our shadows to
+the misty wall. An hour afterwards, a hundred visitors were out, and many
+of us were on the &#8220;spectre&#8221; stones. There was great excitement in
+anticipation of the weird appearances, which had attracted us from such a
+distance.</p>
+
+<p>But, almost at the moment of success, the sun descended behind a belt of
+purple cloud, and all we saw was part of a rainbow on the misty hollow.
+For the sun never appeared again. This was intensely saddening, seeing
+that, but for that stratum of cloud above the horizon, the phenomenon
+would have been graphically displayed.</p>
+
+<p>The cold became suddenly intense, and we had to sleep with a freezing mist
+enveloping the hotel. In vain did we wait for the wakening call, to tell
+us of sunrise; for the sun could not pierce the mist, and we had to return
+home disappointed.</p>
+
+<p>Sometimes the rainbow colours assume the shapes of crosses instead of
+circles. Occasionally a bright halo will be seen above the shadow-head of
+the observer, concentric rainbows enclosing all. In some recorded cases
+the grand effect must have been simply glorious.</p>
+
+<p>Scientific observation has done much to dispel the superstition which has
+clung so tenaciously to the Highland mind. The lonely grandeur of the
+weird mountain giants has been clearly explained as perfectly natural, yet
+the awe-striking feeling cannot be entirely driven off.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span></p>
+<h2><a name="CHAPTER_XXVIII" id="CHAPTER_XXVIII"></a>CHAPTER XXVIII</h2>
+<p class="title">THE WIND</p>
+
+
+<p>Once was the remark pointedly made: &#8220;The wind bloweth where it listeth.&#8221;
+And that is nearly true still. The leading winds are under the calculation
+of the meteorologist, but the others will not be bound by laws.</p>
+
+<p>Yet there are instruments for measuring the velocity and force of the
+wind, after it is on; but &#8220;whence it comes&#8221; is a different matter. A
+gentle air moves at the rate of 7 miles an hour; a hurricane from 80 to
+150 miles, pressing with 50 lbs. on the square foot exposed to its fury.
+Some of the gusts of the Tay Bridge storm, in 1879, had a velocity of 150
+miles an hour, with a pressure of 80 to 90 lbs. to the square foot.</p>
+
+<p>Before steamers supplanted so many sailing vessels, seamen required to be
+always on the alert as to the direction and strength of the wind, and the
+likelihood of any sudden change; and they chronicled twelve different
+strengths from &#8220;faint air&#8221; to a &#8220;storm.&#8221;</p>
+
+<p>In general, the wind may be considered to be the result of a change of
+pressure and temperature in the atmosphere at the same level. The air of a
+warmer region, being lighter, ascends, and gives place to a current of
+wind from a colder region. These two currents&mdash;the higher and the
+lower&mdash;will continue to blow until there is equilibrium.</p>
+
+<p>The trade winds are regular and constant. These<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span> were much followed in the
+days of old. A vast amount of air in the tropics gets heated and ascends,
+being lighter, and travels to the colder north. A strong current rushes in
+from the north to take its place. But the earth rotates round its axis
+from west to east, and the combined motions make two slant wind
+directions, which are called the &#8220;trade winds,&#8221; because they were so
+important in trade navigation.</p>
+
+<p>Among the periodical winds are the &#8220;land and sea breezes.&#8221; During the day,
+the land on the sea coast is warmer than the sea; accordingly, the air
+over the land becomes heated and ascends, the fine cool breeze from the
+sea taking its place. Towards evening there is the equilibrium of
+temperature which produces a temporary calm. Soon the earth chills, and
+the sea is counterbalancingly warm&mdash;as sea-water is steadier as to
+temperature than is land&mdash;the air over the sea becomes warmer, and
+ascends, the current from the land rushing in to take its place. Hence
+during the night the wind is reversed, until in the morning again the
+equilibrium is restored and there is a calm, so far as these are
+concerned. These are therefore called the &#8220;land and sea breezes.&#8221; Of
+course, it is within the tropics that these breezes are most marked. By
+the assistance of other winds, a hurricane will there occasionally destroy
+towns and bring about much damage and loss of life; but better that
+hundreds should perish by a hurricane than thousands by the pestilence
+which, but for the storm, would have done its dire work.</p>
+
+<p>In countries where the differences of pressure are more marked than the
+differences of temperature,<span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span> in the surrounding regions the strength of
+the wind thereby occasioned is far stronger than the land and sea breezes.</p>
+
+<p>The variable winds are more conflicting. These depend on purely local
+causes for a time, such as &#8220;the nature of the ground, covered with
+vegetation or bare; the physical configuration of the surface, level or
+mountainous; the vicinity of the sea or lakes, and the passage of storms.&#8221;
+Among these winds are the simoom and sirocco.</p>
+
+<p>The <i>east</i> winds, which one does not care about in the British Islands
+during the spring time, are occasioned by the powerful northern current
+which rushes south from the northern regions in Europe. Dr. Buchan points
+out a very common mistake among even intelligent observers who shudder at
+the hard east winds. It is generally held that these winds are damp. They
+are unhealthy, but they are dry. It is quite true that many easterly winds
+are peculiarly moist; all that precede storms are so far damp and rainy;
+and it is owing to this circumstance that, on the east coast of Scotland,
+the east winds are searching and carry most of the annual rainfall there.
+But all of these moist easterly winds, however, soon turn to some westerly
+point. The real east wind, so much feared by invalids, does not turn to
+the west; it is exceeding dry. Curious is it that brain diseases, as well
+as consumption, reach their height in Britain while east winds prevail.
+Once in Edinburgh, during the early spring, I had rheumatic fever, and
+during my convalescence my medical adviser, Dr. Menzies, would not let me
+have a short drive until the wind changed to the west. The first thing I<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span>
+anxiously watched in the morning was the flag on the Castle; and for
+nearly two months it always waved from the east. How heart-depressing!</p>
+
+<p>Creatures are we in the hands of nature&#8217;s messengers. We so much depend
+upon the weather for our happiness. Joyful are we when the honey-laden
+zephyr waves the long grass in June, or when</p>
+
+<p class="poem">&#8220;The gentle wind, a sweet and passionate wooer,<br />
+Kisses the blushing leaf.&#8221;</p>
+
+<p>Compared with this, how terrible is Shakespeare&#8217;s allusion to the
+appalling aspects of the storm:&mdash;</p>
+
+<p class="poem">&#8220;I have seen tempests, when the scolding winds<br />
+Have rived the knotty oaks; and I have seen<br />
+The ambitious ocean swell, and rage and foam,<br />
+To be exalted with the threat&#8217;ning clouds;<br />
+But never till to-night, never till now,<br />
+Did I go through a tempest dropping fire.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXIX" id="CHAPTER_XXIX"></a>CHAPTER XXIX</h2>
+<p class="title">CYCLONES AND ANTI-CYCLONES</p>
+
+
+<p>The criticism of the weather in the meteorological column of our daily
+newspapers invariably speaks of &#8220;cyclones.&#8221; It is, therefore, advisable to
+give as plain an explanation of these as possible. Cyclones are
+&#8220;storm-winds.&#8221; Their nature has to be carefully studied by meteorologists,
+who are industriously at work to ascertain some scientific basis for the
+atmospheric movements.</p>
+
+<p>What is the cause of the spiral movement in<span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span> storm-winds? In their centre
+the depression of the barometer is lowest, because the atmosphere there is
+lightest. As the walls of the spiral are approached, the barometer rises.</p>
+
+<p>Dr. Aitken has ingeniously hit upon an experiment to illustrate a spiral
+in air. All that is necessary is a good fire, a free-going chimney, and a
+wet cloth. The cloth is hung up in front of the fire, and pretty near it,
+so that steam rises readily from its surface; and, when there are no
+air-currents in the room, the steam will rise vertically, keeping close to
+the cloth. But if the room has a window in the wall, at right angles to
+the fireplace, so as to cause the air coming from it to make a
+cross-current past the fire, then a cyclone will be formed, and the vapour
+from the cloth will be seen circling round. When the cyclone is well
+formed, all the vapour is collected into the centre of the cyclone, and
+forms a white pillar extending from the cloth to the chimney. This
+experiment shows that no cyclone can form without some tangential motion
+in the air entering the area of low-pressure.</p>
+
+<p>Now to illustrate the spiral approach. Fill with water a cylindrical glass
+vessel, say 15 inches in diameter and 6 inches deep. Have an orifice with
+a plug a little from the centre of the bottom. Remove the plug, the water
+runs out, passing round the vessel in a vortex form. But, as the passage
+between the orifice (or centre of the cyclone) and the temporary division
+is narrower than in any other place, the water has to pass this part much
+more quickly than at any other place. And this curious result is observed:
+the top of the cyclone no longer remains<span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span> over the orifice, but <i>travels</i>
+in the direction of the water which is moving most speedily. Similar to
+this is the cyclone in the atmosphere; its centre also moves in the
+direction of the quickest flowing wind that enters it.</p>
+
+<p>Dr. Aitken is of opinion that, in forecasting storms, too little attention
+has been paid to the <i>anti-cyclones</i>. They do more than simply follow and
+fill up the depression made by the cyclones. They initiate and keep up
+their own circulation, and collect the materials with which the cyclones
+produce their effect. Neither could work efficiently without the other.</p>
+
+<p>Suppose a large area on the earth over which the air is still in bright
+sunshine. After a time, when the air gets heated and charged with vapour,
+columns of air would begin to ascend in a disorderly fashion. But suppose
+an anti-cyclone is blowing at one side of this area. When the upper air
+descends to the earth, it spreads outwards in all directions; but the
+earth&#8217;s rotation interferes and changes the radial into a spiral motion.
+The anti-cyclonic winds will prevent the formation of local cyclones, and
+drive all the moist, hot air to its circumference, just above the earth.
+The anti-cyclone forces its air tangentially into the cyclone, and gives
+it its direction and velocity of rotation, also the direction and rate of
+travel of the centre of depression. The earth&#8217;s rotation is the original
+source of the rotatory movements, but both intensify the initial motion.</p>
+
+<p>Accordingly, the cyclone must travel in the direction of the strongest
+winds blowing into it, just as the vortex in the vessel with the eccentric
+orifice<span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span> travelled in the direction of the quickest moving water. This is
+verified by a study of the synoptic charts of the Meteorological Office.</p>
+
+<p>The sun&#8217;s heat has always been looked upon as the main source of the
+energy of our winds, but some account must also be taken of the effects of
+cold. It is well known that the mean pressure over Continental areas is
+high during winter and low during summer. As the sun&#8217;s rays during summer
+give rise to the cyclonic conditions, so the cooling of the earth during
+winter gives rise to anti-cyclonic conditions. It is found during the
+winter months in several parts of the Continent that as the temperature
+falls the pressure rises, producing anti-cyclones over the cold area;
+whereas, when the temperature begins to rise, the pressure falls, and
+cyclones are attracted to the warming area.</p>
+
+<p>Small natural cyclones are often seen on dusty roads, the whirling column
+having a core of dusty air, and the centre of the vortex travelling along
+the road, tossing up the dust in a very disagreeable way to pedestrians.
+Sometimes such a cyclone will toss up dry leaves to a height of four or
+five feet. They are very common; but it is only when dust, leaves, or
+other light material is present that they are visible to the eye.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXX" id="CHAPTER_XXX"></a>CHAPTER XXX</h2>
+<p class="title">RAIN PHENOMENA</p>
+
+
+<p>The soft rain on a genial evening, or the heavy thunder-showers on a
+broiling day, are too well known<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span> to be written about. Sometimes rain is
+earnestly wished for, at other times it is dreaded, according to the
+season, seed-time or harvest. Some years, like 1826, are very deficient in
+rainfall, when the corn is stunted and everything is being burnt up; other
+years, like 1903, there is an over-supply, causing great damage to
+agriculture. The year 1903 will long be remembered for its continuous
+rainfall; it is the record year; no year comes near it for the total
+rainfall all over the kingdom.</p>
+
+<p>Rain is caused by anything that lowers the temperature of the air below
+the dew-point, but especially by winds. When a wind has blown over a
+considerable area of ocean on to the land, there is a likelihood of rain.
+When this wind is carried on to higher latitudes, or colder parts, there
+is a certainty of rain. Of course, in the latter case the rain will fall
+heavier on the wind side than on the lee side.</p>
+
+<p>For short periods, the heaviest falls or &#8220;plouts&#8221; of rain are during
+thunder-storms. When the raindrops fall through a broad, cold stratum of
+air, they are frozen into hail, the particles of which sometimes reach a
+large size, like stones. Of course, water-spouts now and again are of
+terrible violence.</p>
+
+<p>One of the heaviest rainfalls yet recorded in Great Britain was about
+2&#188; inches in forty minutes at Lednathie, Forfarshire, in 1887. Now 1
+inch deep of rain means 100 tons on an imperial acre; so the amount of
+water falling on a field during that short time is simply startling. The
+heaviest fall for one day was at Ben Nevis Observatory, being fully 7&#188;
+inches in 1890. In other parts of the world this is far exceeded. In one
+day at Brownsville, Texas,<span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span> nearly 13 inches fell in 1886. On the Khasi
+hills, India, 30 inches on each of five successive days were registered.
+At Gibraltar, 33 inches were recorded in twenty-six hours.</p>
+
+<p>The heaviest rainfalls of the globe are occasioned by the winds that have
+swept over the most extensive ocean-areas in the tropics. On the summer
+winds the rainfall of India mainly depends; when this fails, there is most
+distressing drought. Reservoirs are being erected to meet emergencies.</p>
+
+<p>From Dr. Buchan&#8217;s statistics it is found that the annual rainfall at
+Mahabaleshwar is 263 inches; at Sandoway 214; and at Cherra-pungi 472
+inches, the largest known rainfall anywhere on the globe. Over a large
+part of the Highlands of Scotland more than 80 inches fall annually, while
+in some of the best agricultural districts there it does not exceed 30
+inches.</p>
+
+<p>Of all meteorological phenomena, rainfall is the most variable and
+uncertain. Symons gives as tentative results from twenty years&#8217;
+observations in London&mdash;(1) In winter, the nights are wetter than the
+days; (2) in spring and autumn, there is not much difference; (3) in
+summer, nearly half as much again by day as by night.</p>
+
+<p>The wearisomeness of statistics may be here relieved by a short
+consideration of the <i>splash</i> of a drop of rain. Watching the
+drop-splashes on a rainy day in the outskirts of the city, when unable to
+get out, I brought to my recollection the marvellous series of experiments
+made by Professor A. M. Worthington in connection with these phenomena. Of
+course, I could not see to proper advantage the formation of<span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span> the
+splashes, as the heavy raindrops fell into these tiny lakes on the quiet
+road. There is not the effect of the huge thunder-drops in a stream or
+pool. The building up of the bubbles is not here perfect, for the domes
+fail to close, nor are the emergent columns visible to the naked eye. It
+is a pity; for R. L. Stevenson once wrote of them in his delightful
+&#8220;Inland Voyage,&#8221; when he canoed in the Belgian canals, as thrown up by the
+rain into &#8220;an infinity of little crystal fountains.&#8221;</p>
+
+<p>Beautiful is this effect if one is under shelter, every dome seeming quite
+different in contour and individuality from all the rest. But terrible is
+it when out fishing on Loch Earn, even with the good-humoured old Admiral,
+when the heavy thunder-drops splash up the crystal water, and one gets
+soaked to the skin, sportsman-like despising an umbrella.</p>
+
+<p>There is, however, a scientific interest about the splash of a drop. The
+phenomenon can be best seen indoors by letting a drop of ink fall upon the
+surface of pure water in a tumbler, which stands on white paper. It is an
+exquisitely regulated phenomenon, which very ideally illustrates some of
+the fundamental properties of fluids.</p>
+
+<p>When a drop of milk is let fall upon water coloured with aniline dye, the
+centre column of the splash is nearly cylindrical, and breaks up into
+drops before or during its subsequent descent into the liquid. As it
+disappears below the surface, the outward and downward flow causes a
+hollow to be again formed, up the sides of which a ring of milk is
+carried; while the remainder descends to be torn a second time into a
+beautiful vortex ring. This<span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span> shell or dome is a characteristic of all
+splashes made by large drops falling from a considerable height, and is
+extremely pretty. Sometimes the dome closes permanently over the
+imprisoned air, and forms a large bubble floating upon the water. The most
+successful experiments, however, have been carried through by means of
+instantaneous photography, with the aid of a Leyden-jar spark, whose
+duration was less than the ten-millionth of a second. But the simple
+experiments, without the use of the apparatus, will while away a few hours
+on a rainy afternoon, when condemned to the penance of keeping within
+doors.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXXI" id="CHAPTER_XXXI"></a>CHAPTER XXXI</h2>
+<p class="title">THE METEOROLOGY OF BEN NEVIS</p>
+
+
+<p>Several large and very important volumes of the Royal Society of Edinburgh
+are devoted to statistics connected with the meteorology of Ben Nevis.
+Most of the abstracts have been arranged by Dr. Buchan; while Messrs.
+Buchanan, Omond, and Rankine have taken a fair share of the work.</p>
+
+<p>This Observatory, as Mr. Buchanan remarks, is unique, for it is
+established in the clouds; and the observations made in it furnish a
+record of the meteorology of the clouds. It is 4406 feet above the level
+of the sea; and as there is a corresponding Observatory at Fort William,
+at the base of the mountain, it is peculiarly well fitted for important
+observations and weather forecasting. The <span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span>mountain, too, is on the west
+sea-coast of Scotland, exposed immediately to the winds from the Atlantic,
+catching them at first hand. It is lamentable to think that, when the
+importance of the observations made at the two Observatories was becoming
+world known, funds could not be got to carry them on. Ben Nevis is the
+highest mountain in the British Islands, best fitted for meteorological
+observations; yet these have been stopped for want of money.</p>
+
+<p>Dr. Buchan&#8217;s valuable papers were published before any one dreamed of the
+stoppage of the work, which had such an important bearing on men engaged
+in business or taken up with open-air sport. From these I shall sift out a
+few facts that even &#8220;mute, inglorious&#8221; meteorologists may be interested in
+knowing.</p>
+
+<p>For a considerable time the importance of the study of the changes of the
+weather has come gradually to be recognised, and an additional impetus was
+given to the prosecution of this branch of meteorology when it was seen
+that the subject had intimate relations to the practical question of
+weather forecasts, including storm warnings. Weather maps, showing the
+state of the weather over an extensive part of the surface of the globe,
+began to be constructed; but these were only indicators from places at the
+level of the sea.</p>
+
+<p>The singular advantages of a high-level observatory occurred to Mr. Milne
+Home in 1877; and Ben Nevis was considered to be in every respect the most
+suitable in this country. The Meteorological Council of the Royal Society
+of London offered in 1880, unsolicited, &pound;100 annually to the Scottish<span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span>
+Meteorological Society, to aid in the support of an Observatory, the only
+stipulation being that the Council be supplied with copies of the
+observations.</p>
+
+<p>From June to October, in 1881, Mr. Wragge made daily observations at the
+top of the Ben; and simultaneous observations were made, by Mrs. Wragge,
+at Fort William. A second series, on a much more extended scale, was made
+in the following summer.</p>
+
+<p>Funds were secured to build an Observatory; and, in November 1883, the
+regular work commenced, consisting of hourly observations by night as well
+as by day. Until a short time ago, these were carried on uninterruptedly.
+Telegraphic communications of each day&#8217;s observations were sent to the
+morning newspapers; and now we are disappointed at not seeing them for
+comparison.</p>
+
+<p>The whole of the observations of temperature and humidity were of
+necessity eye-observations. For self-registering thermometers were
+comparatively useless when the wind was sometimes blowing at the rate of
+100 miles an hour. Saturation was so complete in the atmosphere that
+everything exposed to it was dripping wet. Every object exposed to the
+outside frosts of winter soon became thickly incrusted with ice.
+Snowdrifts blocked up exposed instruments. Accordingly, the observers had
+to use their own eyes, often at great risks.</p>
+
+<p>The instruments in the Ben Nevis Observatory, and in the Observing Station
+at Fort William, were of the best description. Both stations were in
+positions where the effects of solar and terrestrial radiation were
+minimised. No other pair of meteorological stations anywhere in the world
+are so favourably<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span> situated as these two stations, for supplying the
+necessary observations for investigating the vertical changes of the
+atmosphere. It is to be earnestly hoped, therefore, that funds will be
+secured to resume the valuable work.</p>
+
+<p>The rate of the decrease of temperature with height there is 1&deg; Fahr. for
+every 275 feet of ascent, on the mean of the year. The rate is most rapid
+in April and May, when it is 1&deg; for each 247 feet; and least rapid in
+November and December, when it is 1&deg; for 307 feet. This rate agrees
+closely with the results of the most carefully conducted balloon ascents.
+The departures from the normal differences of temperature, but more
+especially the inversions of temperature, and the extraordinarily rapid
+rates of diminution with height, are intimately connected with the
+cyclones and anti-cyclones of North-Western Europe; and form data, as
+valuable as they are unique, in forecasting storms.</p>
+
+<p>The most striking feature of the climate of Ben Nevis is the repeated
+occurrence of excessive droughts. For instance, in the summer and early
+autumn of 1885, low humidities and dew-points frequently occurred.
+Corresponding notes were observed at sea-level. During nights when
+temperature falls through the effects of terrestrial radiation, those
+parts of the country suffer most from frosts over which very dry states of
+the air pass or rest; whereas, those districts, over which a more humid
+atmosphere hangs, will escape. On the night of August 31 of that year, the
+potato crop on Speyside was totally destroyed by the frost; whereas at
+Dalnaspidal, in the<span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span> district immediately adjoining, potatoes were
+scarcely&mdash;if at all&mdash;blackened.</p>
+
+<p>The mean annual pressure at Ben Nevis was 25&middot;3 inches, and at Fort William
+29&middot;8, the difference being 4&#189; inches for the 4400 feet.</p>
+
+<p>For the whole year, the difference between the mean coldest hour, 5 <span class="smcaplc">A.M.</span>,
+and the warmest hour, 2 <span class="smcaplc">P.M.</span>, is 2&deg;. For the five months, from October to
+February, the mean daily range of temperature varied only from O&middot;6 to 1&middot;5.
+This is the time of the year when storms are most frequent; and this small
+range in the diurnal march of the temperature is an important feature in
+the climatology of Ben Nevis; for it presents, in nearly their simple
+form, the great changes of temperature accompanying storms and other
+weather changes, which it is so essential to know in forecasting weather.</p>
+
+<p>The daily maximum velocity of the wind occurs during the night, the daily
+differences being greatest in summer and least in winter. A blazing sun in
+the summer daily pours its rays on the atmosphere, and a thick envelope of
+cloud has apparently but little influence on the effect of the sun&#8217;s rays.
+Thunder-storms are essentially autumn and winter phenomena, being rare in
+summer.</p>
+
+<p>According to Mr. Buchanan, the weather on Ben Nevis is characterised by
+great prevalence of fog or mist. In continuously clear weather it
+practically never rains on the mountain at all. In continuously foggy
+weather, on the other hand, the average daily rainfall is 1 inch. There is
+a large and continuous excess of pressure in clear weather over that of
+foggy weather. The mean temperature of the year is<span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span> 3&#189; degrees higher
+in clear than in foggy weather. In June the excess is 10 degrees. The
+nocturnal heating in the winter is very clearly observed. This has been
+noticed before in balloons as well as on mountains. The fog and mist in
+winter are much denser than in summer. Whether wet or dry, the fog which
+characterises the climate of the mountain is nothing but <i>cloud</i> under
+another name.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXXII" id="CHAPTER_XXXII"></a>CHAPTER XXXII</h2>
+<p class="title">THE WEATHER AND INFLUENZA</p>
+
+
+<p>Some remarkable facts have been deduced by the late Dr. L. Gillespie,
+Medical Registrar, from the records of the Royal Infirmary of Edinburgh.
+He considered that it might lead to interesting results if the admissions
+into the medical wards were contrasted with the varying states of the
+atmosphere. The repeated attacks of influenza made him pay particular
+attention to the influence of the weather on that disease.</p>
+
+<p>The meteorological facts taken comprise the weekly type of weather, <i>i.e.</i>
+cyclonic or anti-cyclonic, the extremes of temperature for the district
+for each week, and the mean weekly rainfall for the same district. More
+use is made of the extremes than of the mean, for rapid changes of
+temperature have a greater influence on disease than the actual mean.</p>
+
+<p>The period which he took up comprises the seven years 1888-1895. There was
+a yearly average of admissions of 3938; so that he had a good field for<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span>
+observation. Six distinct epidemics of influenza, varying in intensity,
+occurred during that period; yet there had been only twenty-three attacks
+between 1510 and 1890. Accordingly, these six epidemics must have had a
+great influence on the incidence of disease in the same period, knowing
+the vigorous action of the poison on the respiratory, the circulatory, and
+the nervous systems. The epidemics of influenza recorded in this country
+have usually occurred during the winter months.</p>
+
+<p>The first epidemic, which began on the 15th of December 1889 and continued
+for nine weeks, was preceded by six weeks of cyclonic weather, which was
+not, however, accompanied by a heavy rainfall. Throughout the course of
+the disease, the type continued to be almost exclusively cyclonic, with a
+heavy rainfall, a high temperature, and a great deficiency of sunshine.
+The four weeks immediately following were also chiefly cyclonic, but with
+a smaller rainfall.</p>
+
+<p>The summer epidemic of 1891 followed a fine winter and spring, during
+which anti-cyclonic conditions were largely prevalent. But the epidemic
+was immediately preceded by wet weather and a low barometer. It took place
+in dry weather, and was followed by wet, cyclonic weather in turn.</p>
+
+<p>The great winter epidemic of 1891 followed an extremely wet and broken
+autumn. Simultaneously with the establishment of an anti-cyclone, with
+east wind, practically no rain, and a lowering temperature, the influenza
+commenced. Great extremes in the temperature followed, the advent of
+warmer weather<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span> and more equable days witnessing the disappearance of the
+disease.</p>
+
+<p>The fourth epidemic was preceded by a wet period, ushered in by dry
+weather, accompanied by great heat; and its close occurred in slightly
+wetter weather, but under anti-cyclonic conditions. The fifth outbreak
+began after a short anti-cyclone had become established over our islands,
+continued during a long spell of cyclonic weather with a considerable
+rainfall, but was drowned out by heavy rains. The last appearance of the
+modern plague, of which Dr. Gillespie&#8217;s paper treats, commenced after cold
+and wet weather, continued in very cold but drier weather, and subsided in
+warmth with a moderate rainfall.</p>
+
+<p>The conditions of these six epidemics were very variable in some respects,
+and regular in others. The most constant condition was the decreased
+rainfall at the time, when the disease was becoming epidemic.
+Anti-cyclonic weather prevailed at the time.</p>
+
+<p>According to Dr. Gillespie, the tables seem to suggest that a type of
+weather, which is liable to cause catarrhs and other affections of the
+respiratory tract, precedes the attacks of influenza; but that the
+occurrence of influenza in <i>epidemic form</i> does not appear to take place
+until another and drier type has been established. As the weather changes,
+the affected patients increase with a rush.</p>
+
+<p>He is of opinion that the supposed rapid spread of influenza on the
+establishment of anti-cyclonic conditions may be explained in this way.
+The air in the cyclonic vortex, drawn chiefly from the atmosphere over the
+ocean, is moist, and contains none of<span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span> the contagion; the air of the
+anti-cyclone, derived from the higher strata, and thus from distant
+cyclones, descending, blows gently over the land to the nearest cyclone,
+and, being drier, is more able to carry suspended particles with it. He
+considers that temperature has nothing to do with the problem, except in
+so far as the different types of weather may modify it. The Infirmary
+records point to the occurrence of similar phenomena, recorded on previous
+occasions. Accordingly, if such meteorological conditions are not
+indispensable to the spread of influenza in epidemic form, they at least
+afford favourable facilities for it.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXXIII" id="CHAPTER_XXXIII"></a>CHAPTER XXXIII</h2>
+<p class="title">CLIMATE</p>
+
+
+<p>One is not far up in years, in Scotland at any rate, without practically
+realising what climate means. He may not be able to put it in words, but
+easterly haars, chilling rimes, drizzling mists, dagging fogs, and
+soddening rains speak eloquently to him of the meaning of climate.</p>
+
+<p>Climate is an expression for the conditions of a district with regard to
+temperature, and its influence on the health of animals and plants. The
+sun is the great source of heat, and when its rays are nearly
+perpendicular&mdash;as at the Tropics&mdash;the heat is greater on the earth than
+when the slanted rays are gradually cooled in their passage. As one passes
+to a higher level, he feels the air colder, until he<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span> reaches the
+fluctuating snow-line that marks perpetual snow.</p>
+
+<p>The temperature of the atmosphere also depends upon the radiation from the
+earth. Heat is quite differently radiated from a long stretch of sand, a
+dense forest, and a wide breadth of water. Strange is it that a newly
+ploughed field absorbs and radiates more heat than an open lea. The
+equable temperature of the sea-water has an influence on coast towns. The
+Gulf Stream, from the Gulf of Mexico, heats the ocean on to the west coast
+of Britain, and mellows the climate there.</p>
+
+<p>The rainfall of a district has a telling effect on the climate. Boggy land
+produces a deleterious climate, if not malaria. Over the world, generally,
+the prevailing winds are grand regulators of the climate in the
+distinctive districts. A wooded valley&mdash;like the greatest in Britain,
+Strathmore&mdash;has a health-invigorating power: what a calamity it is, then,
+that so many extensive woods, destroyed by the awful hurricane twelve
+years ago, are not replanted!</p>
+
+<p>Some people can stand with impunity any climate; their &#8220;leather lungs&#8221;
+cannot be touched by extremes of temperature; but ordinary mortals are
+mere puppets in the hands of the goddess climate. Hence health-resorts are
+munificently got up, and splendidly patronised by people of means. The
+poor, fortunately, have been successful in the struggle for existence, by
+innate hardiness, otherwise they would have had a bad chance without ready
+cash for purchasing health.</p>
+
+<p>It may look ludicrous at first sight, but it seems none the less true,
+that the variation of the spots on the sun have something to do with
+climate, even to<span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span> the produce of the fields. On close examination, with a
+proper instrument, the disc of the sun is found to be here and there
+studded with dark spots. These vary in size and position day after day.
+They always make their first appearance on the same side of the sun, they
+travel across it in about fourteen days, and then they disappear on the
+other side. There is a great difference in the number of spots visible
+from time to time; indeed, there is what is called the minimum period,
+when none are seen for weeks together, and a maximum period, when more are
+seen than at any other time. The interval between two maximum periods of
+sun-spots is about eleven years. This is a very important fact, which has
+wonderful coincidences in the varied economy of nature.</p>
+
+<p>Kirchhoff has shown, by means of the spectroscope, that the temperature of
+a sun-spot must be lower than that of the remainder of the solar surface.
+As we must get less heat from the sun when it is covered with spots than
+when there are none, it may be considered a variable star, with a period
+of eleven years. Balfour Stewart and Lockyer have shown that this period
+is in some way connected with the action of the planets on the
+photosphere. As we have already mentioned, the variations of the magnetic
+needle have a period of the same length, its greatest variations occurring
+when there are most sun-spots. Auror&aelig;, and the currents of electricity
+which traverse the earth&#8217;s surface, follow the same law. This remarkable
+coincidence set men a-thinking. Can the varying condition of the sun exert
+any influences upon terrestrial affairs? Is it connected with the
+variation of rainfall, the temperature and<span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span> pressure of the atmosphere,
+and the frequency of storms? Has the regular periodicity of eleven years
+in the sun-spots no effect upon climate and agricultural produce?</p>
+
+<p>Mr. F. Chambers, of Bombay, has taken great trouble to strike, as far as
+possible, a connection between the recurring eleven years of sun-spots and
+the variation of grain prices. He arranged the years from 1783 to 1882 in
+nine groups of eleven years; and, from an examination of his tables, we
+find that there is a decided tendency for high prices to recur at more or
+less regular intervals of about eleven years, and a similar tendency for
+low prices. An occasional slight difference can be accounted for by some
+abnormal cause, as war or famine.</p>
+
+<p>Amid all the apparently irregular fluctuations of the yearly prices, there
+is in every one of the ten provinces of India a periodical rise and fall
+of prices once every eleven years, corresponding to the regular variation
+which takes place in the number of sun-spots during the same period. If it
+were possible to obtain statistics to show the actual out-turn of the
+crops each year, the eleven yearly variations calculated therefrom might
+reasonably correspond with the sun-spot variations even more closely than
+do the price variations.</p>
+
+<p>This is a remarkable coincidence, if nothing more. What if it were yet
+possible to predict the variations of prices in the coming sun-spot cycle?
+Such a power would be of immense service. By its aid it could be predicted
+that, as the present period of low prices has followed the last maximum of
+sun-spots, which was in the year 1904, it will not last much<span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span> longer, but
+that prices must gradually keep rising for the next five years. Could
+science really predict this, it would be studied by many and blessed by
+more. Yet the strange coincidence of a century&#8217;s observations renders the
+conclusions not only possible, but to some extent probable.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXXIV" id="CHAPTER_XXXIV"></a>CHAPTER XXXIV</h2>
+<p class="title">THE &#8220;CHALLENGER&#8221; WEATHER REPORTS</p>
+
+
+<p>The <i>Challenger</i> Expedition, commenced by Sir Wyville Thomson, and after
+his death continued by Sir John Murray, with an able staff of assistants
+for the several departments, was one of the splendid exceptions to the
+ordinary British Government stinginess in the furtherance of science. The
+results of the Expedition were printed in a great number of very handsome
+volumes at the expense of the Government.</p>
+
+<p>And the valuable deductions from the <i>Challenger&#8217;s</i> Weather Reports by Dr.
+Alex. Buchan, in his &#8220;Atmospheric Circulation,&#8221; have thrown considerable
+light upon oceanic weather phenomena. For some of his matured opinions on
+these, I am here much indebted to him.</p>
+
+<p>Humboldt, in 1817, published a treatise on &#8220;Isothermal Lines,&#8221; which
+initiated a fresh line for the study of atmospheric phenomena. An isotherm
+is an imaginary line on the earth&#8217;s surface, passing through places having
+a corresponding temperature either throughout the year or at any
+particular period. An isobar is an imaginary line on the earth&#8217;s surface,<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span>
+connecting places at which the mean height of the barometer at sea-level
+is the same. To isobars, as well as to isotherms, Dr. Buchan has devoted
+considerable attention. In 1868, he published an important series of
+charts containing these, with arrows for prevailing winds over the earth
+for the months of the year. In this way what are called synoptic charts
+were established.</p>
+
+<p>In the <i>Challenger</i> Report are shown the various movements of the
+atmosphere, with their corresponding causes. It is thus observed that the
+prevailing winds are produced by the inequality of the mass of air at
+different places. The air flows from a region of higher to a region of
+lower pressure, <i>i.e.</i> from where there is an excessive mass of air to
+fill up some deficiency. And this is the great principle on which the
+science of meteorology rests, not only as to winds, but as to weather
+changes.</p>
+
+<p>Of the sun&#8217;s rays which reach the earth, those that fall on the land are
+absorbed by the surface layer of about 4 feet in thickness. But those that
+fall on the surface of the ocean penetrate, as shown by the observations
+of the <i>Challenger</i> Expedition, to a depth of about 500 feet. Hence, in
+deep waters the temperature of the surface is only partially heated by the
+direct rays of the sun. In mid-ocean the temperature of the surface
+scarcely differs 1&deg; Fahr. during the whole day, while the daily variation
+of the surface layer of land is sometimes 50&deg;. The temperature of the air
+over the ocean is about three times greater than that of the surface of
+the open sea over which it lies; but, near land, this increases to five times.</p>
+
+<p><span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>The elastic force of vapour is seen in its simplest form on the open sea,
+as disclosed by these Reports. It is lowest at 4 <span class="smcaplc">A.M.</span> and highest at 2
+<span class="smcaplc">P.M.</span> The relative humidity is just the reverse. When the temperature is
+highest, the saturation of the air is lowest, and <i>vice vers&acirc;</i>. So on land
+when the air, by radiation of heat from the earth, is cooled below the
+dew-point, dew is produced, and, at the freezing-point, hoar-frost.</p>
+
+<p>The <i>Challenger</i> Reports, too, show that the force of the winds on the
+open sea is subject to no distinct and uniform daily variation, but that
+on nearing land the force of the wind gives a curve as distinctly marked
+as the ordinary curve of temperature. That force is lowest from 2 to 4
+<span class="smcaplc">A.M.</span>, and highest from 2 to 4 <span class="smcaplc">P.M.</span> Each of the five great oceans gives the
+same result. At Ben Nevis, on the other hand, these forces are just
+reversed in strength.</p>
+
+<p>It is also shown by the <i>Challenger</i> observations that on the open sea the
+greatest number of thunder-storms occur from 10 <span class="smcaplc">P.M.</span> to 8 <span class="smcaplc">A.M.</span> And, from
+this, Dr. Buchan concludes that over the ocean terrestrial radiation is
+more powerful than solar radiation in causing those vertical disturbances
+in the equilibrium of the atmosphere which give rise to the thunder-storm.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2><a name="CHAPTER_XXXV" id="CHAPTER_XXXV"></a>CHAPTER XXXV</h2>
+<p class="title">WEATHER-FORECASTING</p>
+
+
+<p>To foretell with any degree of certainty the state of the weather for
+twenty-four hours is of immense<span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span> advantage to business men, tourists,
+fishermen, and many others. The weather is everybody&#8217;s business. And the
+probabilities of accurate forecasts are so improving that all are more or
+less giving attention to the morning meteorological reports.</p>
+
+<p>Weather-forecasting depends on the principle from vast experience that, if
+one event happens, a second is likely to follow. According to the extent
+and accuracy of the data, will be the strength of the probability of
+correct forecasts. And the great end of popular meteorology is to
+demonstrate this.</p>
+
+<p>We have given some explanations of the weather in some respects unique;
+and a careful consideration of these explanations will the more convince
+the reader of the importance of the subject. No doubt the changes of the
+weather are extremely complex, at times baffling; and the wonder is that
+forecasts come so near the truth.</p>
+
+<p>For instance, the year 1903 almost defied the ordinary rules of weather,
+for it broke the record for rainfall. And, last year, so repulsive and
+unseasonable was the spring, that there seemed to be a virtual
+&#8220;withdrawal&#8221; of the season. I wrote on it as &#8220;The Recession of Spring.&#8221;
+Speak about Borrowing Days! We had the equinoctial gales of March about
+the middle of April. On very few days had we &#8220;clear shining to cheer us
+after rain,&#8221; for the bitter cold dried up any genial moisture. An old
+farmer remarked that &#8220;We&#8217;re gaun ower faur North.&#8221; No one could account
+for the backwardness of the season. Unless for the cheering songs of the
+grove-charmers, one would have forgotten the time of the year.</p>
+
+<p><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span>In March of this year, at Strathmore, the barometer fell from 30&middot;5 inches
+(the highest for years) to 28&middot;65 in five days without unfavourable weather
+following. It again rose to 30&middot;05, then fell to 28&middot;45, followed by a rise
+to 28&middot;7 without any peculiar change. But in two days it fell to 28&middot;4 (the
+lowest for years), followed by a deluge of rain and a perfect hurricane
+for several hours, while the temperature was fortunately mild. It was only
+evident at the end that this universal storm had been &#8220;brewing&#8221; some days
+before.</p>
+
+<p>All are familiar with the ordinary prognostics of good and bad weather. A
+&#8220;broch&#8221; round the moon, in her troubled heaven, indicates a storm of rain
+or wind. When the dark crimson sun in the evening throws a brilliant
+bronzed light on the gables and dead leaves, we are sure that there is an
+intense radiation from the earth to form dew, or even hoar-frost.</p>
+
+<p>According to the meteorological folk-lore, the weather of the summer
+season is indicated by the foliation of the oak and ash trees. If the oak
+comes first into leaf, the summer will be hot and dry, if the ash has the
+precedence it will be wet and cold. Looking over the observations of the
+budding of these two trees for half a century, I find that the
+weather-lore adage has been pretty correct. The ash was out before the oak
+a full month in the years 1816, &#8217;17, &#8217;21, &#8217;23, &#8217;28, &#8217;29, &#8217;30, &#8217;38, &#8217;40,
+&#8217;45, &#8217;50, and &#8217;59; and the summer and autumn in these years were
+unfavourable. Again, the oak was out before the ash several weeks in the
+years 1818, &#8217;19, &#8217;20, &#8217;22, &#8217;24, &#8217;25, &#8217;26, &#8217;27, &#8217;33, &#8217;34, &#8217;35, &#8217;36, &#8217;37,
+&#8217;42, &#8217;46, &#8217;54, &#8217;68, and &#8217;69; the summers during these years were dry and
+warm, and the harvests were<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span> abundant. One can never think of this weather
+prognostic from nature without recalling the Swallow Song of Tennyson&#8217;s
+&#8220;Princess&#8221;:&mdash;</p>
+
+<p class="poem">&#8220;Why lingereth she to clothe her heart with love,<br />
+Delaying, as the tender ash delays<br />
+To clothe herself, when all the woods are green?&#8221;</p>
+
+<p>On a muggy morning a sudden clearness in the south &#8220;drowns the ploughman.&#8221;
+And yet enough blue in the sky &#8220;tae mak&#8217; a pair o&#8217; breeks&#8221; cheers one with
+the assurance of coming dry and sunny weather. The low flying of the
+swallows betokens rain, as well as any unseasonable dancing of midges in
+the evening. Sore corns on the feet, and rheumatism in the joints, are
+direful precursors. The leaves are all a-tremble before the approach of
+thunder. But throughout this volume I have given many illustrations.</p>
+
+<p>But one of the largest and most important practical problems of
+meteorology is to ascertain the course which storms follow, and the causes
+by which that course is determined, so that a forecast may thereby be
+made, not only of the certain approach of a storm, but the particular
+direction and force of the storm. The method of conducting this large
+inquiry most effectively was devised by the French astronomer, Le
+Verrier&mdash;the great aspirant, with our own Couch Adams, for the discovery
+of the planet Neptune. He began to carry this out in 1858 by the daily
+publication of weather data, followed by a synchronous weather map, which
+showed graphically for the morning of the day of publication the
+atmospheric pressure and the direction and force of<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span> the wind, together
+with tables of temperature, rainfall, cloud, and sea disturbances from a
+large number of places in all parts of Europe. It is from similar maps
+that forecasts of storms are still framed, and suitable warnings issued;
+and a mass of information is being collected by telegraph from sixty
+stations in the British Islands, &amp;c., of the state of the weather at eight
+o&#8217;clock every morning, and analysed and arranged at the Meteorological
+Office in London for the evening&#8217;s forecasts over the different districts
+of the country. A juster knowledge is being now acquired of those great
+atmospheric movements, and other changes, which form the groundwork of
+weather-forecasting.</p>
+
+<p>The Meteorological Office, Westminster (entirely distinct from the Royal
+Meteorological Society), is administered by a Council (Chairman, Sir R.
+Strachey; Scottish member, Dr. Buchan), selected by the Royal Society. It
+employs a staff of over forty. The chief departments relate to: (1) Ocean
+Meteorology, including the collection, tabulation, and discussion of
+meteorological data from British ships, the preparation of ocean weather
+charts, and the issue of meteorological instruments to the Royal Navy and
+Mercantile Marine; (2) Weather Telegraphy, including the reception of
+telegrams thrice a day from selected stations for the preparation of the
+daily reports and weather forecasts. Representatives of newspapers, &amp;c.,
+receive copies of the 11 <span class="smcaplc">A.M.</span> forecast based on the 8 <span class="smcaplc">A.M.</span> observations;
+and also of the 8.30 <span class="smcaplc">P.M.</span> forecasts based on the observations received
+earlier in the day. In summer and autumn harvest forecasts are issued by
+telegraph to individuals who will defray the cost.<span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span> The Office also
+collects climatological data from a number of voluntary and some
+subsidised stations. The &#8220;first order&#8221; stations include Valentia,
+Falmouth, Kew, and Aberdeen. These have self-recording instruments of high
+precision, giving a continuous record of the meteorological elements.</p>
+
+<p>A Government Commission which sat last year, under the Rt. Hon. Sir
+Herbert Maxwell, Bart., have issued a Report, recommending a number of
+changes in the management and constitution of the Meteorological Office;
+and considerable modifications are not unlikely to take place in the near
+future. In his evidence before that Commission, the Chairman of the
+Council acknowledged that the great function of meteorologists is the
+collection of facts; but the interpretation of those collected facts, in a
+scientific manner, is still in a very immature condition. Dr. Buchan, in
+his evidence, confessed that forecasting by the Council is purely &#8220;by rule
+of thumb.&#8221; It is not possible to lay down hard and fast rules for
+forecasting.</p>
+
+<p>With regard to the storm-warning telegrams, as a rule, the earliest
+trustworthy indication of the approach of a dangerous storm to the coasts
+of the British Isles precedes the storm by only a few hours. Delays are
+therefore very serious.</p>
+
+<p>It is admitted by the best British meteorologists that the observations of
+the United States are better conducted, although the best instruments in
+the world are set and registered at Kew, in England. The work of weather
+forecasts and storm warnings is carried on with the highest degree of
+promptitude and efficiency at the Washington Central Office.<span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span> This is
+because the work of predictions has been hitherto the chief work of the
+Office: the entire time of the observers, on whose telegraphic reports the
+forecasts are based, is controlled by the United States Weather Bureau;
+and the right of precedence in the use of wires is maintained.</p>
+
+<p>Professor Br&uuml;ckner, of Berne, has devoted a lifetime to the comparatively
+new treatment of climatic oscillations, based upon observations made at
+321 points on the earth&#8217;s surface, distributed as follows: Europe, 198;
+Asia, 39; N. America, 50; Cen. and S. America, 16; Australia, 12; Africa,
+6. One of his conclusions is that an average time of about thirty-five
+years is found to intervene between one period of excess or deficiency of
+warmth and the next, accompanied by the opposite relative condition of
+moisture.</p>
+
+<p>All are familiar with the hoisting of cone-warning as indication of a
+coming storm. This work is exceedingly important, especially for those
+connected with the sea by business or pleasure. On the known approach of a
+cyclone of dangerous intensity, special messages are sent from the London
+Meteorological Office, warning the coasts likely to be affected. When the
+cone is hoisted with its apex downwards, it means that strong south or
+south-west winds are to be looked for. When the cone is hoisted with its
+apex upwards, it indicates that strong winds from the north or north-east
+are expected. Of course they are merely useful precautions; but they are
+universally attended to by people on the sea-coast.</p>
+
+<p>Though one may have reasonable doubts about the use that can be made of
+weather forecasts for<span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span> three days, such as are now regularly issued, on
+account of the finical, coy, spasmodic interludes on short notice, yet
+there is a wonderful certainty in the daily prognostics of the direction
+and strength of the wind, the temperature of the air, and the likelihood
+of rainy or fair weather, dependent on the broad uniformity of nature.
+This is very serviceable for people who have now to live at high pressure
+in business, in the enthralling days of keen competition. And it is a
+great boon to those who are in search of health by travelling, or who, in
+innocent pleasure, desire to live as much as possible in the open air.
+Very little credit is given to the &#8220;gas&#8221; of the isolated &#8220;weather
+prophet&#8221;; but those who have confidence in the usual weather forecasts
+from the Meteorological Office are satisfied in their belief; and those
+who, in self-confidence, ignore all weather prognostics, are still weak
+enough to read them and act up to them.</p>
+
+<hr style="width: 25%;" />
+
+<p>In practical meteorology, in the scientific explanation of popular
+weather-lore, and in the study of atmospheric phenomena, which so
+powerfully influence us, for gladness or discomfort, we may, as with other
+branches of science, even all our days, cheerfully go on in &#8220;the noiseless
+tenor of our way,&#8221;</p>
+
+<p class="poem"><span style="margin-left: 8em;">&#8220;Nourishing a youth sublime,</span><br />
+With the fairy tales of science and the long results of time.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span></p>
+<p class="title">INDEX</p>
+
+
+<p class="index">
+Abercromby, spectre on Adam&#8217;s Peak, <a href="#Page_89">89</a><br />
+<br />
+Adam&#8217;s Peak, spectre, <a href="#Page_89">89</a><br />
+<br />
+Afterglow described, <a href="#Page_62">62</a>;<br />
+<span style="margin-left: 1em;">dust-particles to form, <a href="#Page_64">64</a></span><br />
+<br />
+Air, change of, <a href="#Page_55">55</a>;<br />
+<span style="margin-left: 1em;">clearness and dryness, <a href="#Page_49">49</a>;</span><br />
+<span style="margin-left: 1em;">devitalised, <a href="#Page_52">52</a>;</span><br />
+<span style="margin-left: 1em;">disease-germs in, <a href="#Page_53">53</a>;</span><br />
+<span style="margin-left: 1em;">thunder-clouds, <a href="#Page_49">49</a></span><br />
+<br />
+Aitken, Dr., afterglows, <a href="#Page_67">67</a>;<br />
+<span style="margin-left: 1em;">anti-cyclones, <a href="#Page_97">97</a>;</span><br />
+<span style="margin-left: 1em;">colour of water, <a href="#Page_75">75</a>;</span><br />
+<span style="margin-left: 1em;">condensing power of dust, <a href="#Page_43">43</a>;</span><br />
+<span style="margin-left: 1em;">decay of clouds, <a href="#Page_39">39</a>;</span><br />
+<span style="margin-left: 1em;">dew-formation, <a href="#Page_14">14</a>;</span><br />
+<span style="margin-left: 1em;">dust and atmospheric phenomena, <a href="#Page_29">29</a>;</span><br />
+<span style="margin-left: 1em;">electrical deposition of smoke, <a href="#Page_83">83</a>;</span><br />
+<span style="margin-left: 1em;">false dew, <a href="#Page_18">18</a>;</span><br />
+<span style="margin-left: 1em;">fog-counter, <a href="#Page_82">82</a>;</span><br />
+<span style="margin-left: 1em;">foreglows, <a href="#Page_67">67</a>;</span><br />
+<span style="margin-left: 1em;">formation of clouds, <a href="#Page_35">35</a>;</span><br />
+<span style="margin-left: 1em;">haze, <a href="#Page_44">44</a>;</span><br />
+<span style="margin-left: 1em;">hazing effects of atmospheric dust, <a href="#Page_47">47</a>;</span><br />
+<span style="margin-left: 1em;">Kingairloch experiments, <a href="#Page_30">30</a>;</span><br />
+<span style="margin-left: 1em;">one-coloured rainbow, <a href="#Page_70">70</a>;</span><br />
+<span style="margin-left: 1em;">radiation from snow, <a href="#Page_86">86</a>;</span><br />
+<span style="margin-left: 1em;">regenerators, <a href="#Page_85">85</a>;</span><br />
+<span style="margin-left: 1em;">sanitary detective, <a href="#Page_78">78</a></span><br />
+<br />
+Ammonia and cloud formation, <a href="#Page_36">36</a><br />
+<br />
+Annie Laurie, <a href="#Page_17">17</a><br />
+<br />
+Anti-cyclones, forecasting by, <a href="#Page_97">97</a>;<br />
+<span style="margin-left: 1em;">formation, <a href="#Page_97">97</a>;</span><br />
+<span style="margin-left: 1em;">cause of influenza, <a href="#Page_109">109</a></span><br />
+<br />
+Aratus, forecasting by moon, <a href="#Page_61">61</a><br />
+<br />
+Ariel&#8217;s song, <a href="#Page_42">42</a><br />
+<br />
+Aurora Borealis, <a href="#Page_71">71</a>;<br />
+<span style="margin-left: 1em;">forebodings, <a href="#Page_71">71-73</a>;</span><br />
+<span style="margin-left: 1em;">name by Gassendi, <a href="#Page_72">72</a>;</span><br />
+<span style="margin-left: 1em;">other names, <a href="#Page_72">72</a>;</span><br />
+<span style="margin-left: 1em;">safety valve of electricity, <a href="#Page_72">72</a>;</span><br />
+<span style="margin-left: 1em;">sun&#8217;s spots, <a href="#Page_72">72</a>;</span><br />
+<span style="margin-left: 1em;">sun control, <a href="#Page_74">74</a>;</span><br />
+<span style="margin-left: 1em;">symptoms, <a href="#Page_72">72</a></span><br />
+<br />
+<br />
+Bagillt, condensing lead fumes, <a href="#Page_84">84</a><br />
+<br />
+Ballachulish, sunsets, <a href="#Page_64">64</a><br />
+<br />
+Ballantine&#8217;s song, <a href="#Page_17">17</a><br />
+<br />
+Barometer, indications, <a href="#Page_10">10</a><br />
+<br />
+Ben Nevis, dust-particles, <a href="#Page_30">30</a>;<br />
+<span style="margin-left: 1em;">instruments, <a href="#Page_104">104</a>;</span><br />
+<span style="margin-left: 1em;">meteorology, <a href="#Page_102">102</a>;</span><br />
+<span style="margin-left: 1em;">observations, <a href="#Page_105">105</a>;</span><br />
+<span style="margin-left: 1em;">rainfall, <a href="#Page_103">103</a>;</span><br />
+<span style="margin-left: 1em;">regret at stoppage of Observatory, <a href="#Page_103">103</a></span><br />
+<br />
+Blairgowrie, personal description of afterglow, <a href="#Page_62">62</a><br />
+<br />
+Blue sky, <a href="#Page_74">74</a>;<br />
+<span style="margin-left: 1em;">cause of, <a href="#Page_75">75</a>, <a href="#Page_77">77</a></span><br />
+<br />
+Borrowing days, <a href="#Page_117">117</a><br />
+<br />
+Brocken, spectre, <a href="#Page_89">89</a>;<br />
+<span style="margin-left: 1em;">personal description, <a href="#Page_90">90</a>;</span><br />
+<span style="margin-left: 1em;">Noah&#8217;s Ark, <a href="#Page_90">90</a></span><br />
+<br />
+Br&uuml;ckner, climatic oscillations, <a href="#Page_122">122</a><br />
+<br />
+Buchan, Dr., Aitken&#8217;s radiation from snow, <a href="#Page_86">86</a>;<br />
+<span style="margin-left: 1em;">Ben Nevis, papers on, <a href="#Page_103">103</a>;</span><br />
+<span style="margin-left: 1em;"><i>Challenger</i> Reports, <a href="#Page_114">114</a>;</span><br />
+<span style="margin-left: 1em;">cold of 1886, <a href="#Page_86">86</a>;</span><br />
+<span style="margin-left: 1em;">east winds, <a href="#Page_94">94</a>;</span><br />
+<span style="margin-left: 1em;">isobars, <a href="#Page_115">115</a>;</span><br />
+<span style="margin-left: 1em;">rainfall statistics, <a href="#Page_100">100</a>;</span><br />
+<span style="margin-left: 1em;">on forecasting, <a href="#Page_121">121</a></span><br />
+<br />
+Buchanan, Ben Nevis Observatory, <a href="#Page_102">102</a>;<br />
+<span style="margin-left: 1em;">great prevalence of fog, <a href="#Page_106">106</a></span><br />
+<br />
+Buddha&#8217;s Lights, of Ceylon, <a href="#Page_72">72</a><br />
+<br />
+Burns, allusions to aurora, <a href="#Page_71">71</a>, <a href="#Page_73">73</a><br />
+<br />
+Byron, storm in Alps, <a href="#Page_50">50</a><br />
+<br />
+<br />
+<i>Challenger</i> Expedition, <a href="#Page_114">114</a>;<br />
+<span style="margin-left: 1em;">temperature, <a href="#Page_115">115</a>;</span><br />
+<span style="margin-left: 1em;">thunder-storms, <a href="#Page_116">116</a>;</span><br />
+<span style="margin-left: 1em;">winds, <a href="#Page_116">116</a></span><br />
+<br />
+Chambers on sun-spots and grain prices, <a href="#Page_113">113</a><br />
+<br />
+Change of air, <a href="#Page_55">55</a>;<br />
+<span style="margin-left: 1em;">Strathmore to Glenisla, <a href="#Page_56">56</a></span><br />
+<br />
+Charles II., fog and smoke, <a href="#Page_80">80</a><br />
+<br />
+Chlorine and cloud formation, <a href="#Page_36">36</a><br />
+<br />
+Christison and colour of water, <a href="#Page_75">75</a><br />
+<br />
+Chrystal on Aitken&#8217;s radiation from snow, <a href="#Page_86">86</a><br />
+<br />
+Cirro-stratus cloud, mackerel-like, <a href="#Page_39">39</a><br />
+<br />
+Climate, <i>Challenger</i> notes, <a href="#Page_115">115</a>;<br />
+<span style="margin-left: 1em;">cone-warnings, <a href="#Page_120">120</a>;</span><br />
+<span style="margin-left: 1em;">Gulf Stream, <a href="#Page_111">111</a>;</span><br />
+<span style="margin-left: 1em;">oscillations, <a href="#Page_120">120</a>;</span><br />
+<span style="margin-left: 1em;">rainfall, <a href="#Page_111">111</a>;</span><br />
+<span style="margin-left: 1em;">sun-spots on, <a href="#Page_112">112</a>;</span><br />
+<span style="margin-left: 1em;">wooded country on, <a href="#Page_111">111</a></span><br />
+<br />
+Clouds, decay of, <a href="#Page_37">37</a>;<br />
+<span style="margin-left: 1em;">distances of, <a href="#Page_35">35</a>;</span><br />
+<span style="margin-left: 1em;">dry, <a href="#Page_42">42</a>;</span><br />
+<span style="margin-left: 1em;">even without dust, <a href="#Page_36">36</a>;</span><br />
+<span style="margin-left: 1em;">formation of, <a href="#Page_34">34</a>;</span><br />
+<span style="margin-left: 1em;">height of, <a href="#Page_34">34</a>;</span><br />
+<span style="margin-left: 1em;">numbering of cloud-particles, <a href="#Page_34">34</a>;</span><br />
+<span style="margin-left: 1em;">sunshine on cloud formation, <a href="#Page_35">35</a>;</span><br />
+<span style="margin-left: 1em;">varieties of, <a href="#Page_35">35</a></span><br />
+<br />
+Cone-warnings, <a href="#Page_121">121</a><br />
+<br />
+Continental winds, <a href="#Page_98">98</a><br />
+<br />
+Cyclones, <a href="#Page_95">95</a>;<br />
+<span style="margin-left: 1em;">formation of, <a href="#Page_96">96</a>, <a href="#Page_98">98</a>;</span><br />
+<span style="margin-left: 1em;">small natural, <a href="#Page_98">98</a></span><br />
+<br />
+<br />
+Decay of clouds, <a href="#Page_37">37</a>;<br />
+<span style="margin-left: 1em;">in thin rain, <a href="#Page_41">41</a>;</span><br />
+<span style="margin-left: 1em;">process, <a href="#Page_38">38</a>;</span><br />
+<span style="margin-left: 1em;">ripple markings, <a href="#Page_39">39</a></span><br />
+<br />
+Dew, evidence of rising, <a href="#Page_22">22</a>;<br />
+<span style="margin-left: 1em;">experiments, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>;</span><br />
+<span style="margin-left: 1em;">false dew, <a href="#Page_17">17</a>;</span><br />
+<span style="margin-left: 1em;">formation of, <a href="#Page_13">13</a></span><br />
+<br />
+Disease-germs in air, <a href="#Page_53">53</a>;<br />
+<span style="margin-left: 1em;">causes, <a href="#Page_53">53</a>;</span><br />
+<span style="margin-left: 1em;">deposited by rain, <a href="#Page_55">55</a></span><br />
+<br />
+Diseases, and east wind, <a href="#Page_94">94</a>;<br />
+<span style="margin-left: 1em;">personal notes, <a href="#Page_95">95</a></span><br />
+<br />
+Dumfries, dust in air at, <a href="#Page_46">46</a><br />
+<span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span><br />
+Dust, condensing power, <a href="#Page_43">43</a>;<br />
+<span style="margin-left: 1em;">from meteors, <a href="#Page_37">37</a>;</span><br />
+<span style="margin-left: 1em;">generally necessary for cloud formation, <a href="#Page_26">26</a>;</span><br />
+<span style="margin-left: 1em;">hazing effects, <a href="#Page_47">47</a>;</span><br />
+<span style="margin-left: 1em;">numbering, <a href="#Page_26">26</a>;</span><br />
+<span style="margin-left: 1em;">instruments for numbering, <a href="#Page_27">27</a>;</span><br />
+<span style="margin-left: 1em;">produces afterglows, <a href="#Page_64">64</a>;</span><br />
+<span style="margin-left: 1em;">produces foreglows, <a href="#Page_67">67</a>;</span><br />
+<span style="margin-left: 1em;">quantity in Bunsen flame, <a href="#Page_28">28</a>;</span><br />
+<span style="margin-left: 1em;">at Ben Nevis, <a href="#Page_30">30</a>;</span><br />
+<span style="margin-left: 1em;">Hy&egrave;res, Mentone, Rigi Kulm, <a href="#Page_29">29</a>;</span><br />
+<span style="margin-left: 1em;">Lucerne, Kingairloch, <a href="#Page_30">30</a>;</span><br />
+<span style="margin-left: 1em;">when not necessary, <a href="#Page_36">36</a></span><br />
+<br />
+Dust enumeration, deductions on, <a href="#Page_31">31</a><br />
+<br />
+<br />
+Earn, Loch, splash of drop at, <a href="#Page_101">101</a><br />
+<br />
+Earthshine, <a href="#Page_59">59</a><br />
+<br />
+Ehrenberg, on colour of water, <a href="#Page_75">75</a><br />
+<br />
+Evelyn, fumifugium, <a href="#Page_80">80</a>;<br />
+<span style="margin-left: 1em;">remedy for smoke, <a href="#Page_82">82</a></span><br />
+<br />
+<br />
+Falkirk, Dr. Aitken&#8217;s experiments on haze, <a href="#Page_47">47</a><br />
+<br />
+False dew, <a href="#Page_19">19</a><br />
+<br />
+Fitzroy on aurora as a foreboder, <a href="#Page_73">73</a><br />
+<br />
+Fog, counter, <a href="#Page_31">31</a>;<br />
+<span style="margin-left: 1em;">dry, <a href="#Page_41">41</a>;</span><br />
+<span style="margin-left: 1em;">formation, <a href="#Page_24">24</a>;</span><br />
+<span style="margin-left: 1em;">more in towns, <a href="#Page_25">25</a>;</span><br />
+<span style="margin-left: 1em;">and smoke, <a href="#Page_80">80</a></span><br />
+<br />
+Folk-lore, <a href="#Page_50">50</a><br />
+<br />
+Foreglow, described, <a href="#Page_66">66</a>;<br />
+<span style="margin-left: 1em;">how produced, <a href="#Page_67">67</a></span><br />
+<br />
+Fort William Observatory, <a href="#Page_102">102</a><br />
+<br />
+Frankland, disease-germs, <a href="#Page_53">53</a><br />
+<br />
+Franklin, lightning, <a href="#Page_51">51</a><br />
+<br />
+<br />
+Gassendi, named aurora, <a href="#Page_72">72</a><br />
+<br />
+Gillespie, Dr., on weather and influenza, <a href="#Page_107">107</a><br />
+<br />
+Glasgow, fog, <a href="#Page_81">81</a><br />
+<br />
+Glass, appearing damp, <a href="#Page_44">44</a><br />
+<br />
+Glenisla, ozoned air, <a href="#Page_56">56</a><br />
+<br />
+Grain crops and sun-spots, <a href="#Page_112">112</a>;<br />
+<span style="margin-left: 1em;">Chambers&#8217; tables, <a href="#Page_113">113</a></span><br />
+<br />
+Great amazing light in the north, <a href="#Page_72">72</a><br />
+<br />
+Gulf Stream, effects on climate, <a href="#Page_111">111</a><br />
+<br />
+Gunpowder, great condensing power, <a href="#Page_44">44</a><br />
+<br />
+<br />
+Haze, what is, <a href="#Page_43">43</a>;<br />
+<span style="margin-left: 1em;">how produced, <a href="#Page_44">44</a>;</span><br />
+<span style="margin-left: 1em;">in clearest air, <a href="#Page_45">45</a>;</span><br />
+<span style="margin-left: 1em;">stages of condensation, <a href="#Page_46">46</a>;</span><br />
+<span style="margin-left: 1em;">in sultry weather, <a href="#Page_46">46</a>;</span><br />
+<span style="margin-left: 1em;">dryness of air and visibility, <a href="#Page_48">48</a></span><br />
+<br />
+Health improved by change of air, <a href="#Page_56">56</a><br />
+<br />
+Highland air, few disease-germs, <a href="#Page_55">55</a><br />
+<br />
+Hoar-frost, frozen dew, <a href="#Page_20">20</a>;<br />
+<span style="margin-left: 1em;">on under surfaces, <a href="#Page_21">21</a></span><br />
+<br />
+Humboldt, isotherms, <a href="#Page_114">114</a><br />
+<br />
+Hydrogen peroxide and cloud formation, <a href="#Page_36">36</a><br />
+<br />
+Hy&egrave;res, dust-particles, <a href="#Page_29">29</a><br />
+<br />
+<br />
+Indian Ocean, colour, <a href="#Page_75">75</a><br />
+<br />
+Influenza, weather and, <a href="#Page_107">107</a>;<br />
+<span style="margin-left: 1em;">six distinct epidemics, <a href="#Page_108">108</a>;</span><br />
+<span style="margin-left: 1em;">spread of anti-cyclonic conditions, <a href="#Page_109">109</a></span><br />
+<br />
+Isobars by Buchan, <a href="#Page_115">115</a><br />
+<br />
+Isotherms by Humboldt, <a href="#Page_114">114</a><br />
+<br />
+Italian lakes, stages of condensation, <a href="#Page_45">45</a><br />
+<br />
+<br />
+Job, on dew formation, <a href="#Page_13">13</a><br />
+<br />
+<br />
+Kelvin recorder, <a href="#Page_84">84</a>;<br />
+<span style="margin-left: 1em;">Aitken&#8217;s radiation from snow, <a href="#Page_86">86</a></span><br />
+<br />
+Kew, instruments set, <a href="#Page_121">121</a><br />
+<br />
+Kingairloch, dust-particles, <a href="#Page_30">30</a>, <a href="#Page_46">46</a><br />
+<br />
+Kirchhoff, lower temperature of sun-spot, <a href="#Page_112">112</a><br />
+<br />
+Krakatoa, eruption of, dust-particles, <a href="#Page_63">63</a><br />
+<br />
+<br />
+Le Verrier and weathercharts, <a href="#Page_119">119</a><br />
+<br />
+Lockyer, and sun-spots, <a href="#Page_112">112</a><br />
+<br />
+Lightning, electricity, <a href="#Page_51">51</a>;<br />
+<span style="margin-left: 1em;">photographed, <a href="#Page_51">51</a>;</span><br />
+<span style="margin-left: 1em;">sheet and forked, <a href="#Page_51">51</a>;</span><br />
+<span style="margin-left: 1em;">ozone, <a href="#Page_52">52</a></span><br />
+<br />
+Lodge, electrical deposition of smoke, <a href="#Page_83">83</a><br />
+<br />
+London, coals consumed, <a href="#Page_25">25</a>;<br />
+<span style="margin-left: 1em;">sulphur and fog, <a href="#Page_25">25</a>;</span><br />
+<span style="margin-left: 1em;">fog in reign of Charles II., <a href="#Page_81">81</a>;</span><br />
+<span style="margin-left: 1em;">Meteorological Office, <a href="#Page_11">11</a>, <a href="#Page_120">120</a></span><br />
+<br />
+Lord Derwentwater&#8217;s Lights, <a href="#Page_72">72</a><br />
+<br />
+Lower animals, sensitiveness, <a href="#Page_11">11</a><br />
+<br />
+Lucerne, dust-particles, <a href="#Page_30">30</a><br />
+<br />
+<br />
+MacLaren, Aitken&#8217;s radiation from snow, <a href="#Page_86">86</a><br />
+<br />
+Magnesia, small affinity for water-vapour, <a href="#Page_44">44</a><br />
+<br />
+Man in the street, <a href="#Page_11">11</a><br />
+<br />
+Mediterranean, brilliant colour, <a href="#Page_77">77</a><br />
+<br />
+Mentone, dust-particles, <a href="#Page_29">29</a><br />
+<br />
+Merry Dancers of Shetland, <a href="#Page_71">71</a><br />
+<br />
+Meteors, producing dust, <a href="#Page_37">37</a><br />
+<br />
+Meteorological Council, London, <a href="#Page_103">103</a>;<br />
+<span style="margin-left: 1em;">Office, <a href="#Page_120">120</a>;</span><br />
+<span style="margin-left: 1em;">cone-warnings, <a href="#Page_121">121</a>;</span><br />
+<span style="margin-left: 1em;">regular forecasts, <a href="#Page_123">123</a></span><br />
+<br />
+Milne Home on Ben Nevis, <a href="#Page_103">103</a><br />
+<br />
+Milton, dust numberless, <a href="#Page_26">26</a><br />
+<br />
+Moon, old, in new moon&#8217;s arms, <a href="#Page_58">58</a>;<br />
+<span style="margin-left: 1em;">weather indications, <a href="#Page_59">59</a>, <a href="#Page_61">61</a></span><br />
+<br />
+Mountain giants, <a href="#Page_88">88</a>;<br />
+<span style="margin-left: 1em;">Adam&#8217;s Peak, <a href="#Page_89">89</a>;</span><br />
+<span style="margin-left: 1em;">Brocken, <a href="#Page_89">89</a></span><br />
+<br />
+Munich, International Meteorological Conference, <a href="#Page_35">35</a><br />
+<br />
+Murray, <i>Challenger</i> Expedition, <a href="#Page_114">114</a><br />
+<span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span><br />
+<br />
+Nardius, dew exhalation, <a href="#Page_13">13</a><br />
+<br />
+Newton, colour of sky, <a href="#Page_77">77</a><br />
+<br />
+Nimbus, cloud, <a href="#Page_35">35</a><br />
+<br />
+<br />
+Oak and ash, on climate, <a href="#Page_118">118</a><br />
+<br />
+Ochils, one-coloured rainbow, <a href="#Page_70">70</a><br />
+<br />
+<br />
+Pacific, colour, <a href="#Page_75">75</a><br />
+<br />
+Paris, aurora, <a href="#Page_71">71</a>;<br />
+<span style="margin-left: 1em;">disease-germs, <a href="#Page_55">55</a></span><br />
+<br />
+Paton, Waller, bronze tints in sunsets, <a href="#Page_64">64</a><br />
+<br />
+Piazzi Smith, aurora, <a href="#Page_72">72</a><br />
+<br />
+Picket, dew-formation, <a href="#Page_14">14</a><br />
+<br />
+Pilatus, fine rain, <a href="#Page_42">42</a><br />
+<br />
+Polar lightnings, <a href="#Page_72">72</a><br />
+<br />
+<br />
+Radiant heat, producing fine rain, <a href="#Page_41">41</a><br />
+<br />
+Radiation from snow, <a href="#Page_86">86</a><br />
+<br />
+Rain, <a href="#Page_98">98</a>;<br />
+<span style="margin-left: 1em;">heavy rainfalls, <a href="#Page_99">99</a></span><br />
+<br />
+Rainbow, <a href="#Page_68">68</a>;<br />
+<span style="margin-left: 1em;">forecasts, <a href="#Page_62">62</a>, <a href="#Page_69">69</a>;</span><br />
+<span style="margin-left: 1em;">formation, <a href="#Page_69">69</a>;</span><br />
+<span style="margin-left: 1em;">one-coloured, <a href="#Page_70">70</a></span><br />
+<br />
+Rains, it always, <a href="#Page_40">40</a>;<br />
+<span style="margin-left: 1em;">radiant heat in process, <a href="#Page_41">41</a>;</span><br />
+<span style="margin-left: 1em;">Ariel&#8217;s song, <a href="#Page_43">43</a></span><br />
+<br />
+Rankin, dust-particles, Ben Nevis, <a href="#Page_30">30</a><br />
+<br />
+Richardson, devitalised air, <a href="#Page_51">51</a><br />
+<br />
+Rigi Kulm, dust-particles, <a href="#Page_29">29</a><br />
+<br />
+Rolier, aurora, <a href="#Page_73">73</a><br />
+<br />
+<br />
+St. Paul&#8217;s, London, disease-germs in air, <a href="#Page_54">54</a><br />
+<br />
+Sanitary detective, <a href="#Page_78">78</a><br />
+<br />
+Shakespeare, tempest, <a href="#Page_95">95</a><br />
+<br />
+Shelley, old moon in new moon&#8217;s arms, <a href="#Page_59">59</a><br />
+<br />
+Simoom and sirocco, <a href="#Page_94">94</a><br />
+<br />
+Skye, rainy, <a href="#Page_40">40</a><br />
+<br />
+Smoke, electrical deposition of, <a href="#Page_83">83</a>;<br />
+<span style="margin-left: 1em;">regenerators, <a href="#Page_85">85</a></span><br />
+<br />
+Smoking-room, condensing power, <a href="#Page_44">44</a><br />
+<br />
+Snow, bad conducting, <a href="#Page_87">87</a>;<br />
+<span style="margin-left: 1em;">radiation from, <a href="#Page_86">86</a></span><br />
+<br />
+Sodium dust, condensing power, <a href="#Page_45">45</a><br />
+<br />
+Spens, forebodings of moon, <a href="#Page_61">61</a><br />
+<br />
+Splash of a drop, experiments, <a href="#Page_101">101</a><br />
+<br />
+Stevenson, R. L., splash of drop, <a href="#Page_101">101</a><br />
+<br />
+Stewart, sun-spots, <a href="#Page_112">112</a><br />
+<br />
+Strachey on forecasts, <a href="#Page_121">121</a><br />
+<br />
+Strathmore, observations on hoar-frost, <a href="#Page_22">22</a>;<br />
+<span style="margin-left: 1em;">on decay of clouds, <a href="#Page_38">38</a>;</span><br />
+<span style="margin-left: 1em;">to Glenisla, change of air, <a href="#Page_56">56</a>;</span><br />
+<span style="margin-left: 1em;">observations on old moon in new moon&#8217;s arms, <a href="#Page_59">59</a>;</span><br />
+<span style="margin-left: 1em;">afterglow described, <a href="#Page_62">62</a>;</span><br />
+<span style="margin-left: 1em;">foreglow, <a href="#Page_66">66</a>;</span><br />
+<span style="margin-left: 1em;">cold of 1886, <a href="#Page_86">86</a>;</span><br />
+<span style="margin-left: 1em;">healthy by woods, <a href="#Page_111">111</a>;</span><br />
+<span style="margin-left: 1em;">observations on barometer, <a href="#Page_118">118</a></span><br />
+<br />
+Strathpeffer, <a href="#Page_9">9</a><br />
+<br />
+Sulphur as a fog-former, <a href="#Page_25">25</a><br />
+<br />
+Sulphuretted hydrogen and cloud-formation, <a href="#Page_36">36</a><br />
+<br />
+Sunshine on cloud-formation, <a href="#Page_35">35</a><br />
+<br />
+Sun&#8217;s spots, and aurora, <a href="#Page_72">72</a>, <a href="#Page_112">112</a>;<br />
+<span style="margin-left: 1em;">and grain crops, <a href="#Page_112">112</a></span><br />
+<br />
+Symons, rainfall, <a href="#Page_100">100</a><br />
+<br />
+Synoptic charts, <a href="#Page_98">98</a><br />
+<br />
+<br />
+Tait, on Aitken&#8217;s radiation from snow, <a href="#Page_86">86</a><br />
+<br />
+Tay Bridge, fall of, <a href="#Page_92">92</a><br />
+<br />
+Tennyson, aurora, <a href="#Page_71">71</a>;<br />
+<span style="margin-left: 1em;">dew, <a href="#Page_19">19</a>;</span><br />
+<span style="margin-left: 1em;">oak and ash, <a href="#Page_119">119</a></span><br />
+<br />
+Thermometer, indications, <a href="#Page_10">10</a><br />
+<br />
+Thomson, Wyville, <i>Challenger</i> Expedition, <a href="#Page_114">114</a><br />
+<br />
+Thunder-storm described, <a href="#Page_50">50</a><br />
+<br />
+<br />
+Valkyries, aurora, <a href="#Page_73">73</a><br />
+<br />
+Visibility, limit of, <a href="#Page_48">48</a><br />
+<br />
+<br />
+Washington, Meteorological Office, <a href="#Page_121">121</a><br />
+<br />
+Water, pressure to show plant exudation, <a href="#Page_18">18</a>;<br />
+<span style="margin-left: 1em;">colour of, <a href="#Page_75">75</a>;</span><br />
+<span style="margin-left: 1em;">experiments on distilled, <a href="#Page_76">76</a>;</span><br />
+<span style="margin-left: 1em;">dust-particles vary colour, <a href="#Page_77">77</a></span><br />
+<br />
+Weather and influenza, <a href="#Page_107">107</a><br />
+<br />
+Weather-forecasting, <a href="#Page_116">116</a>;<br />
+<span style="margin-left: 1em;">advantages, <a href="#Page_117">117</a>;</span><br />
+<span style="margin-left: 1em;">principle, <a href="#Page_117">117</a>;</span><br />
+<span style="margin-left: 1em;">examples, <a href="#Page_118">118</a>;</span><br />
+<span style="margin-left: 1em;">old moon in new moon&#8217;s arms, <a href="#Page_59">59</a>;</span><br />
+<span style="margin-left: 1em;">by moon, <a href="#Page_61">61</a>;</span><br />
+<span style="margin-left: 1em;">oak and ash, <a href="#Page_118">118</a>;</span><br />
+<span style="margin-left: 1em;">cone-warnings, <a href="#Page_122">122</a>;</span><br />
+<span style="margin-left: 1em;">three days&#8217;, <a href="#Page_123">123</a></span><br />
+<br />
+Weather-lore, <a href="#Page_50">50</a>, <a href="#Page_118">118</a><br />
+<br />
+Weather talisman, <a href="#Page_9">9</a>;<br />
+<span style="margin-left: 1em;">call on barometer and thermometer, <a href="#Page_10">10</a>;</span><br />
+<span style="margin-left: 1em;">exceptional years, <a href="#Page_117">117</a></span><br />
+<br />
+Wells, Dr., on dew, <a href="#Page_14">14</a><br />
+<br />
+Wilson, Prof., on hoar-frost, <a href="#Page_20">20</a><br />
+<br />
+Wind, <a href="#Page_92">92</a>;<br />
+<span style="margin-left: 1em;">rates, <a href="#Page_92">92</a>;</span><br />
+<span style="margin-left: 1em;">trade, <a href="#Page_93">93</a>;</span><br />
+<span style="margin-left: 1em;">land and sea, <a href="#Page_93">93</a></span><br />
+<br />
+W&oelig;ikof, durability of cold, <a href="#Page_88">88</a><br />
+<br />
+Wordsworth, rainbow, <a href="#Page_68">68</a><br />
+<br />
+Worthington, splash of drop, <a href="#Page_100">100</a><br />
+<br />
+Wragge, observations at Ben Nevis, <a href="#Page_104">104</a><br />
+</p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<p class="center">Printed by <span class="smcap">Ballantyne, Hanson &amp; Co.</span><br />
+Edinburgh &amp; London</p>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Meteorology, by J. G. M'Pherson
+
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+</pre>
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+</body>
+</html>
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+The Project Gutenberg EBook of Meteorology, by J. G. M'Pherson
+
+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: Meteorology
+       or Weather Explained
+
+Author: J. G. M'Pherson
+
+Release Date: February 19, 2012 [EBook #38928]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK METEOROLOGY ***
+
+
+
+
+Produced by The Online Distributed Proofreading Team at
+https://www.pgdp.net (This file was produced from images
+generously made available by The Internet Archive.)
+
+
+
+
+
+
+
+
+
+SHILLING SCIENTIFIC SERIES
+
+
+
+
+[Illustration: DR. AITKEN'S DUST-COUNTER.
+
+R is the test-receiver; P the air-pump; M the measuring apparatus; L the
+illuminating arrangements; G the Gasometer; A the pipe through which the
+tested air is drawn.]
+
+
+
+
+  METEOROLOGY;
+  OR,
+  WEATHER EXPLAINED.
+
+
+  BY
+  J. G. M'PHERSON, Ph.D., F.R.S.E.,
+
+  GRADUATE WITH FIRST-CLASS HONOURS, AND FOR NINE YEARS
+  EXTENSION LECTURER ON METEOROLOGY AND MATHEMATICAL
+  EXAMINER IN THE UNIVERSITY OF ST. ANDREWS;
+  AUTHOR OF "TALES OF SCIENCE," ETC.
+
+
+  LONDON: T. C. & E. C. JACK,
+  34 HENRIETTA STREET, W.C.
+  AND EDINBURGH.
+  1905.
+
+
+
+
+THE SHILLING SCIENTIFIC SERIES
+
+
+_The following Vols. are now ready or in the Press_:--
+
+BALLOONS, AIRSHIPS, AND FLYING MACHINES. By GERTRUDE BACON.
+
+MOTORS AND MOTORING. By Professor HARRY SPOONER.
+
+RADIUM. By Dr. HAMPSON.
+
+TELEGRAPHY WITH AND WITHOUT WIRES. By W. J. WHITE.
+
+ELECTRIC LIGHTING. By S. F. WALKER, R.N., M.I.E.E.
+
+LOCAL GOVERNMENT. By PERCY ASHLEY, M.A.
+
+_Others in Preparation_
+
+  Printed by BALLANTYNE, HANSON & CO.
+  At the Ballantyne Press
+
+
+
+
+CONTENTS
+
+
+  CHAP.                                             PAGE
+
+       I. INTRODUCTION                                 9
+
+      II. THE FORMATION OF DEW                        13
+
+     III. TRUE AND FALSE DEW                          17
+
+      IV. HOAR-FROST                                  20
+
+       V. FOG                                         23
+
+      VI. THE NUMBERING OF THE DUST                   26
+
+     VII. DUST AND ATMOSPHERIC PHENOMENA              29
+
+    VIII. A FOG-COUNTER                               31
+
+      IX. FORMATION OF CLOUDS                         34
+
+       X. DECAY OF CLOUDS                             37
+
+      XI. IT ALWAYS RAINS                             40
+
+     XII. HAZE                                        43
+
+    XIII. HAZING EFFECTS OF ATMOSPHERIC DUST          47
+
+     XIV. THUNDER CLEARS THE AIR                      49
+
+      XV. DISEASE GERMS IN THE AIR                    53
+
+     XVI. A CHANGE OF AIR                             55
+
+    XVII. THE OLD MOON IN THE NEW MOON'S ARMS         58
+
+   XVIII. AN AUTUMN AFTERGLOW                         62
+
+     XIX. A WINTER FOREGLOW                           65
+
+      XX. THE RAINBOW                                 68
+
+     XXI. THE AURORA BOREALIS                         71
+
+    XXII. THE BLUE SKY                                74
+
+   XXIII. A SANITARY DETECTIVE                        78
+
+    XXIV. FOG AND SMOKE                               80
+
+     XXV. ELECTRICAL DEPOSITION OF SMOKE              83
+
+    XXVI. RADIATION FROM SNOW                         86
+
+   XXVII. MOUNTAIN GIANTS                             88
+
+  XXVIII. THE WIND                                    92
+
+    XXIX. CYCLONES AND ANTI-CYCLONES                  95
+
+     XXX. RAIN PHENOMENA                              98
+
+    XXXI. THE METEOROLOGY OF BEN NEVIS               102
+
+   XXXII. THE WEATHER AND INFLUENZA                  107
+
+  XXXIII. CLIMATE                                    110
+
+   XXXIV. THE "CHALLENGER" WEATHER REPORTS           114
+
+    XXXV. WEATHER-FORECASTING                        116
+
+          INDEX                                      124
+
+
+
+
+PREFATORY NOTE
+
+
+I am very much indebted to Dr. John Aitken, F.R.S., for his great kindness
+in carefully revising the proof sheets, and giving me most valuable
+suggestions. This is a sufficient guarantee that accuracy has not been
+sacrificed to popular explanation.
+
+J. G. M'P.
+
+  RUTHVEN MANSE,
+  _June 10, 1905_.
+
+
+
+
+METEOROLOGY
+
+
+
+
+CHAPTER I
+
+INTRODUCTION
+
+
+Though by familiarity made commonplace, the "weather" is one of the most
+important topics of conversation, and has constant bearings upon the work
+and prospects of business-men and men of pleasure. The state of the
+weather is the password when people meet on the country road: we could not
+do without the humble talisman. "A fine day" comes spontaneously to the
+lips, whatever be the state of the atmosphere, unless it is peculiarly and
+strikingly repulsive; then "A bitter day" would take the place of the
+expression. Yet I have heard "_Terrible_ guid wither" as often as
+"_Terrible_ bad day" among country people.
+
+Scarcely a friendly letter is penned without a reference to the weather,
+as to what has been, is, or may be. It is a new stimulus to a lagging
+conversation at any dinner-table. All are so dependent on the weather,
+especially those getting up in years or of delicate health.
+
+I remember, when at Strathpeffer, the great health-resort in the North of
+Scotland, in 1885, an anxious invalid at "The Pump" asking a
+weather-beaten, rheumatic old gamekeeper what sort of a day it was to be,
+considering that it had been wet for some time. The keeper crippled to the
+barometer outside the doorway, and returned with the matter-of-fact
+answer: "She's faurer doon ta tay nur she wass up yestreen." The barometer
+had evidently fallen during the night. "And what are we to expect?" sadly
+inquired the invalid. "It'll pe aither ferry wat, or mohr rain"--a poor
+consolation!
+
+Most men who are bent on business or pleasure, and all dwellers in the
+country who have the instruments, make a first call at the barometer in
+the lobby, or the aneroid in the breakfast-parlour, to "see what she
+says." A good rise of the black needle (that is, to the right) above the
+yellow needle is a source of rejoicing, as it will likely be clear, dry,
+and hard weather. A slight fall (that is, to the left) causes anxiety as
+to coming rain, and a big depression forebodes much rain or a violent
+storm of wind. In either case of "fall," the shutters come over the eyes
+of the observer. Next, even before breakfast, a move is made to the
+self-registering thermometer (set the night before) on a stone, a couple
+of feet above the grass. A good reading, above the freezing-point in
+winter and much above it in summer, indicates the absence of killing
+rimes, that are generally followed by rain. A very low register accounts
+for the feeling of cold during the night, though the fires were not out;
+and predicts precarious weather. Ordinarily careful observers--as I, who
+have been in one place for more than thirty years--can, with the morning
+indications of these two instruments, come pretty sure of their
+prognostics of the day's weather. Of course, the morning newspaper is
+carefully scanned as to the weather-forecasts from the London
+Meteorological Office--direction of wind; warm, mild, or cold; rain or
+fair, and so on--and in general these indications are wonderfully accurate
+for twenty-four hours; though the "three days'" prognostics seem to
+stretch a point. We are hardly up to that yet.
+
+The lower animals are very sensitive as to the state of approaching
+extremes of weather. "Thae sea beass," referring to sea-gulls over the
+inland leas during ploughing, are ordinary indicators of stormy weather.
+Wind is sure to follow violent wheelings of crows. "Beware of rain" when
+the sheep are restive, rubbing themselves on tree stumps. But all are
+familiar with Jenner's prognostics of rain.
+
+Science has come to the aid of ordinary weather-lore during the last
+twenty years, by leaps and bounds. Time-honoured notions and revered
+fictions, around which the hallowed associations of our early training
+fondly and firmly cling, must now yield to the exact handling of modern
+science; and with reluctance we have to part with them. Yet there is in
+all a fascination to account for certain ordinary phenomena. "The man in
+the street," as well as the strong reading man, wishes to know the "why"
+and the "how" of weather-forecasting. They are anxious to have
+weather-phenomena explained in a plain, interesting, but accurate way.
+
+The freshness of the marvellous results has an irresistible charm for the
+open mind, keen for useful information. The discoveries often seem so
+simple that one wonders why they were not made before.
+
+Until about twenty years ago, Meteorology was comparatively far back as a
+science; and in one important branch of it, no one has done more to put
+weather-lore on a scientific basis than Dr. John Aitken, F.R.S., who has
+very kindly given me his full permission to popularise what I like of his
+numerous and very valuable scientific papers in the _Transactions of the
+Royal Society of Edinburgh_. This I have done my best to carry out in the
+following pages. "The way of putting it" is my only claim.
+
+Many scientific men are decoyed on in the search for truth with a spell
+unknown to others: the anticipation of the results sometimes amounts to a
+passion. Many wrong tracks do they take, yet they start afresh, just as
+the detective has to take several courses before he hits upon the correct
+scent. When they succeed, they experience a pleasure which is
+indescribable; to them fame is more than a mere "fancied life in others'
+breath."
+
+Dr. Aitken's continued experiments, often of rare ingenuity and
+brilliancy, show that no truth is altogether barren; and even that which
+looks at first sight the very simplest and most trivial may turn out
+fruitful in precious results. Small things must not be overlooked, for
+great discoveries are sometimes at a man's very door. Dr. Aitken has shown
+us this in many of his discoveries which have revolutionised a branch of
+meteorology. Prudence, patience, observing power, and perseverance in
+scientific research will do much to bring about unexpected results, and
+not more so in any science than in accounting for weather-lore on a
+rational basis, which it is in the power of all my readers to further.
+
+"The old order changeth, giving place to new." With kaleidoscopic variety
+Nature's face changes to the touch of the anxious and reverent observer.
+And some of these curious weather-views will be disclosed in these pages,
+so as, in a brief but readable way, to explain the weather, and lay a safe
+basis for probable forecastings, which will be of great benefit to the man
+of business as well as the man of pleasure.
+
+  "Felix, qui potuit rerum cognoscere causas."
+                                          --VIRGIL.
+
+
+
+
+CHAPTER II
+
+THE FORMATION OF DEW
+
+
+The writer of the Book of Job gravely asked the important question, "Who
+hath begotten the drops of dew?" We repeat the question in another form,
+"Whence comes the real dew? Does it fall from the heavens above, or does
+it rise from the earth beneath?"
+
+Until about the beginning of the seventeenth century, scientific men held
+the opinion of ordinary observers that dew fell from the atmosphere. But
+there was then a reaction from this theory, for Nardius defined it as an
+exhalation from the earth. Of course, it was well known that dew was
+formed by the precipitation of the vapour of the air upon a colder body.
+You can see that any day for yourself by bringing a glass of very cold
+water into a warm room; the outer surface of the glass is dimmed at once
+by the moisture from the air. M. Picket was puzzled when he saw that a
+thermometer, suspended five feet above the ground, marked a lower
+temperature on clear nights than one suspended at the height of
+seventy-five feet; because it was always supposed that the cold of evening
+descended from above. Again he was puzzled when he observed that a buried
+thermometer read higher than one on the surface of the ground. Until
+recently the greatest authority on dew was Dr. Wells, who carefully
+converged all the rays of scientific light upon the subject. He came to
+the conclusion that dew was condensed out of the air.
+
+But the discovery of the true theory was left to Dr. John Aitken, F.R.S.,
+a distinguished observer and a practical physicist, of whom Scotland has
+reason to be proud. About twenty years ago he made the discovery, and it
+is now accepted by all scientific men on the Continent as well as in Great
+Britain. What first caused him to doubt Dr. Wells' theory, so universally
+accepted, that dew is formed of vapour existing at the time in the air,
+and to suppose that dew is mostly formed of vapour rising from the ground,
+was the result of some observations made in summer on the temperature of
+the soil at a small depth under the surface, and of the air over it, after
+sunset and at night. He was struck with the unvarying fact that the
+ground, a little below the surface, was warmer than the air over it. By
+placing a thermometer among stems below the surface, he found that it
+registered 18 deg. Fahr. higher than one on the surface. So long, then, as
+the surface of the ground is above the dew-point (_i.e._ the temperature
+when dew begins to be formed), vapour must rise from the ground; this
+moist air will mingle with the air which it enters, and its moisture will
+be condensed and form dew, whenever it comes in contact with a surface
+cooled below the dew-point.
+
+You can verify this by simple experiments. Take a thin, shallow, metal
+tray, painted black, and place it over the ground after sunset. On dewy
+nights the _inside_ of the tray is dewed, and the grass inside is wetter
+than that outside. On some nights there is no dew outside the tray, and on
+all nights the deposit on the inner is heavier than that on the outside.
+If wool is used in the experiments, we are reminded of one of the forms of
+the dewing of Gideon's fleece--the fleece was bedewed when all outside was
+dry.
+
+You therefore naturally and rightly come to the conclusion that far more
+vapour rises out of the ground during the night than condenses as dew on
+the grass, and that this vapour from the ground is trapped by the tray.
+Much of the rising vapour is generally carried away by the passing wind,
+however gentle; hence we have it condensed as dew on the roofs of houses,
+and other places, where you would think that it had fallen from above. The
+vapour rising under the tray is not diluted by the mixture with the drier
+air which is occasioned by the passing wind; therefore, though only cooled
+to the same extent as the air outside, it yields a heavier deposit of
+dew.
+
+If you place the tray on bare ground, you will find on a dewy night that
+the inside of the tray is quite wet. On a dewy night you will observe that
+the under part of the gravel of the road is dripping wet when the top is
+dry. You will find, too, that around pieces of iron and old implements in
+the field, there is a very marked increase of grass, owing to the deposit
+of moisture on these articles--moisture which has been condensed by the
+cold metal from the vapour-charged air, which has risen from the ground on
+dewy nights.
+
+But all doubt upon this important matter is removed by a most successful
+experiment with a fine balance, which weighs to a quarter of a grain. If
+vapour rises from the ground for any length of time during dewy nights,
+the soil which gives off the vapour must lose weight. To test this, cut
+from the lawn a piece of turf six inches square and a quarter of an inch
+thick. Place this in a shallow pan, and carefully note the weight of both
+turf and pan with the sensitive balance. To prevent loss by evaporation,
+the weighing should be done in an open shed. Then place the pan and turf
+at sunset in the open cut. Five hours afterwards remove and weigh them,
+and it will be found that the turf has lost a part of its weight. The
+vapour which rose from the ground during the formation of the dew accounts
+for the difference of weight. This weighing-test will also succeed on bare
+ground.
+
+When dealing with hoar-frost, which is just frozen dew, we shall find
+visible evidence of the rising of dew from the ground.
+
+You know the beautiful song, "Annie Laurie," which begins with--
+
+  "Maxwelton's braes are bonnie,
+  Where early fa's the dew"--
+
+well, you can no longer say that the dew "falls," for it rises from the
+ground. The song, however, will be sung as sweetly as ever; for the spirit
+of true poetry defies the cold letter of science.
+
+
+
+
+CHAPTER III
+
+TRUE AND FALSE DEW
+
+
+Ever since men could observe and think, they have admired the diamond
+globules sparkling in the rising sun. These "dew-drops" were considered to
+be shed from the bosom of the morn into the blooming flowers and rich
+grass-leaves. Ballantine's beautiful song of Providential care tells us
+that "Ilka blade o' grass keps it's ain drap o' dew."
+
+But, alas! we have to bid "good-bye" to the appellation "dew-drop." What
+was popularly and poetically called dew _is not dew at all_. Then what is
+it?
+
+On what we have been accustomed to call a "dewy" night, after the
+brilliant summer sun has set, and the stars begin to peep out of the
+almost cloudless sky, let us take a look at the produce of our vegetable
+garden. On the broccoli are found glistening drops; but on the peas,
+growing next them, we find nothing.
+
+A closer examination shows us that the moisture on the plants is not
+arranged as would be expected from the ordinary laws of radiation and
+condensation. There is no generally filmy appearance over the leaves; the
+moisture is collected in little drops placed at short distances apart,
+along the edges of the leaves all round.
+
+Now place a lighted lantern below one of the blades of the broccoli, and a
+revelation will be made. The brilliant diamond-drops that fringe the edge
+of the blade are all placed at the points where the nearly colourless
+veins of the blade come to the outer edge. The drops are not dew at all,
+but the exudation of the healthy plant, which has been conveyed up these
+veins by strong root-pressure.
+
+The fact is that the root acts as a kind of force-pump, and keeps up a
+constant pressure inside the tissues of the plant. One of the simplest
+experiments suggested by Dr. Aitken is to lift a single grass-plant, with
+a clod of moist earth attached to it, and place it on a plate with an
+inverted tumbler over it. In about an hour, drops will begin to exude, and
+the tip of nearly every blade will be found to be studded with a
+diamond-like drop.
+
+Next substitute water-pressure. Remove a blade of broccoli and connect it
+by means of an india-rubber tube with a head of water of about forty
+inches. Place a glass receiver over it, so as to check evaporation, and
+leave it for an hour. The plant will be found to have excreted water
+freely, some parts of the leaves being quite wet, while drops are
+collected at the places where they appeared at night.
+
+If the water pressed into the leaf is coloured with aniline blue, the
+drops when they first appear are colourless; but before they grow to any
+size, the blue appears, showing that little water was held in the veins.
+The whole leaf soon gets coloured of a fine deep blue-green, like that
+seen when vegetation is rank; this shows that the injected liquid has
+penetrated through the whole leaf.
+
+Again, the surfaces of the leaves of these drop-exuding plants never seem
+to be wetted by the water. It is because of the rejection of water by the
+leaf-surface that the exuded moisture from the veins remains as a drop.
+
+These observations and experiments establish the fact that the drops which
+first make their appearance on grass on dewy nights are not dew-drops at
+all, but the exuded watery juices of the plants.
+
+If now we look at dead leaves we shall find a difference of formation of
+the moisture on a dewy night: the moisture is spread equally over, where
+equally exposed. The moisture exuded by the healthy grass is always found
+at a _point_ situated near the tip of the blade, forming a drop of some
+size; but the true dew collects later on _evenly_ all over the blade. The
+false dew forms a large glistening diamond-drop, whereas the true dew
+coats the blade with a fine pearly lustre. Brilliant globules are produced
+by the vital action of the plant, especially beautiful when the deep-red
+setting sun makes them glisten, all a-tremble, with gold light; while an
+infinite number of minute but shining opal-like particles of moisture
+bedecks the blade-surfaces, in the form of the gentle dew--
+
+  "Like that which kept the heart of Eden green
+  Before the useful trouble of the rain."
+
+
+
+
+CHAPTER IV
+
+HOAR-FROST
+
+
+All in this country are familiar with the beauty of hoar-frost. The
+children are delighted with the funny figures on the glass of the bedroom
+window on a cold winter morning. Frost is a wonderful artist; during the
+night he has been dipping his brush into something like diluted schist,
+and laying it gracefully on the smooth panes.
+
+And, as you walk over the meadows, you observe the thin white films of ice
+on the green pasture; and the clear, slender blades seem like crystal
+spears, or the "lashes of light that trim the stars."
+
+You all know what hoar-frost is, though most in the country give it the
+expressive name of "rime." But you are not all aware of how it is formed.
+Hoar-frost is just frozen dew. In a learned paper, written in 1784,
+Professor Wilson of Glasgow made this significant remark: "This is a
+subject which, besides its entire novelty, seems, upon other accounts, to
+have a claim to some attention." He observed, in that exceptionally cold
+winter, that, when sheets of paper and plates of metal were laid out, all
+began to attract hoar-frost as soon as they had time to cool down to the
+temperature of the air. He was struck with the fact that, while the
+thermometer indicated 36 degrees of frost a few feet above the ground and
+44 degrees of frost at the surface of the snow, there were only 8 degrees
+of frost at a point 3 inches below the surface of the snow. If he had
+only thought of placing the thermometer on the grass, under the snow, he
+would have found it to register the freezing-point only. And had he
+inserted the instrument below the ground, he would have found it
+registering a still higher temperature. That fact would have suggested to
+him the formation of hoar-frost; that the water-vapour from the warm soil
+was trapped by a cold stratum of air and frozen when in the form of dew.
+
+One of the most interesting experiments, without apparatus, which you can
+make is in connection with the formation of hoar-frost, when there is no
+snow on the ground, in very cold weather. If it has been a bright, clear,
+sunny day in January, the effect can be better observed. Look over the
+garden, grass, and walks on the morning after the intense cold of the
+night; big plane-tree leaves may be found scattered over the place. You
+see little or no hoar-frost on the _upper_ surface of the leaves. But turn
+up the surface next the earth, or the road, or the grass, and what do you
+see? You have only to handle the leaf in this way to be brightly
+astonished. A thick white coating of hoar-frost, as thick as a layer of
+snow, is on the _under_ surface. If a number of leaves have been
+overlapping each other, there will be no coating of hoar-frost under the
+top leaves; but when you reach the lowest layer, next the bare ground, you
+will find the hoar-frost on the under surface of the leaves. Now that is
+positive proof that the hoar-frost has not fallen from the air, but has
+risen from the earth.
+
+The sun's heat on the previous day warmed the earth. This heat the earth
+retained till evening. As the air chilled, the water-vapour from the
+warmer earth rose from its surface, and was arrested by the cold surface
+of the leaves. So cold was that surface that it froze the water-vapour
+when rising from the earth, and formed hoar-frost in very large
+quantities. When this happens later on in the season, one may be almost
+sure of having rain in the forenoon.
+
+As hoar-frost is just frozen dew, I can even more surely convince you of
+the formation of hoar-frost as rising from the ground by observations made
+by me at my manse in Strathmore, in June 1892. I mention this particularly
+because then was the most favourable testing-time that has _ever_ occurred
+during meteorological observations. June 9th was the warmest June day
+(with one exception) for twenty years. The thermometer reached 83 deg. Fahr.
+in the shade. Next day was the coldest June day (with one exception) for
+twenty years, when the thermometer was as low as 51 deg. in the shade. But
+during the night my thermometer on the grass registered 32 deg.--the freezing
+point. On the evening of the sultry day I examined the soil at 10 o'clock.
+It was damp, and the grass round it was filmy moist. The leaves of the
+trees were crackling dry, and all above was void of moisture. The air
+became gradually chilly; and as gradually the moisture rose in height on
+the shrubs and lower branches of small trees. The moon shone bright, and
+the stars showed their clear, chilly eyes. The soil soon became quite wet,
+the low grass was dripping with moisture, and the longer grass was
+becoming dewed. This gave the best natural evidence of the rising of the
+dew that I ever witnessed. But everything was favourable for the
+observation--the cold air incumbent on the rising, warm, moist vapour from
+the soil fixing the dew-point, when the projecting blades seized the
+moisture greedily and formed dew. Had the temperature been a little below
+the freezing-point, hoar-frost would have been beautifully formed.
+
+
+
+
+CHAPTER V
+
+FOG
+
+
+To many nothing is more troublesome than a dense fog in a large town. It
+paralyses traffic, it is dangerous to pedestrians, it encourages theft, it
+chokes the asthmatic, and chills the weak-lunged.
+
+In the country it is disagreeable enough; but never so intensely raw and
+dense as in the city. On the sea, too, the fog is disagreeable and fraught
+with danger. The fog-horn is heard, in its deep, sombre note, from the
+lighthouse tower, when the strong artificial light is almost useless.
+
+But a peculiar sense of stagnation possesses the dweller of the large
+town, when enveloped in a dense fog. Sometimes during the day, through a
+thinner portion, the sun will be dimly seen in copper hue, like the moon
+under an eclipse. The smoke-impregnated mass assumes a peculiar "pea-soup"
+colour.
+
+Now, what is this fog? How is it formed? It has been ascertained that fogs
+are dependent upon _dust_ for their formation. Without dust there could
+be no fogs, there would be only dew on the grass and road. Instead of the
+dust-impregnated air that irritates the housekeeper, there would be the
+constant dripping of moisture on the walls, which would annoy her more.
+
+Ocular demonstration can testify to this. If two closed glass receivers be
+placed beside each other, the one containing ordinary air, and the other
+filtered air (_i.e._ air deprived of its dust by being driven through
+cotton wool), and if jets of steam be successively introduced into these,
+a strange effect is noticed. In the vessel containing common air the steam
+will be seen rising in a dense cloud; then a beautiful white foggy cloud
+will be formed, so dense that it cannot be seen through. But in the vessel
+containing the filtered air, the steam is not seen at all; there is not
+the slightest appearance of cloudiness. In the one case, where there was
+the ordinary atmospheric dust, fog at once appeared; in the other case,
+where there was no dust in suspension, the air remained clear and
+destitute of fog. Invisible dust, then, is necessary in the air for the
+formation of fogs.
+
+The reason of this is that a free-surface must exist for the condensation
+of the vapour-particles. The fine particles of dust in the air act as
+free-surfaces, on which the fog is formed. Where there is abundance of
+dust in the air and little water-vapour present, there is an
+over-proportion of dust-particles; and the fog-particles are, in
+consequence, closely packed, but light in form and small in size, and take
+the lighter appearance of fog. Accordingly, if the dust is increased in
+the air, there is a proportionate increase of fog. Every fog-particle,
+then, has embosomed in it an invisible dust-particle.
+
+But whence comes the dust? From many sources. It is organic and inorganic.
+So very fine is the inorganic dust in the atmosphere that, if the
+two-thousandth part of a grain of fine iron be heated, and the dust be
+driven off and carried into a glass receiver of filtered air, the
+introduction of a jet of steam into that receiver would at once occasion
+an appreciable cloudiness.
+
+This is why fogs are so prevalent in large towns. Next the minute
+brine-particles, driven into the air as fog forms above the ocean surface,
+are the burnt sulphur-particles emanating from the chimneys in towns. The
+brilliant flame, as well as the smoky flame, is a fog-producer. If gas is
+burnt in filtered air, intense fog is produced when water-vapour is
+introduced. Products of combustion from a clear fire and from a smoky one
+produce equal fogging. The fogs that densely fill our large towns are
+generally less bearable than those that veil the hills and overhang the
+rivers.
+
+It is the sulphur, however, from the consumed coals, which is the active
+producer of the fogs of a large town. The burnt sulphur condenses in the
+air to very fine particles, and the quantity of burnt sulphur is enormous.
+No less than seven and a half millions of tons of coals are consumed in
+London. Now, the average amount of sulphur in English coal is one and a
+quarter per cent. That would give no less than 93,750 tons of sulphur
+burned every year in London fires. Now, if we reckon that on an average
+twice the quantity of coals is consumed there on a winter day that is
+consumed on a summer day, no less than 347 tons of the products of
+combustion (in extremely fine particles) are driven into the
+superincumbent air of London every winter day. This is an enormous
+quantity, quite sufficient to account for the density of the fogs in that
+city.
+
+
+
+
+CHAPTER VI
+
+THE NUMBERING OF THE DUST
+
+
+If the shutters be all but closed in a room, when the sun is shining in,
+myriads of floating particles can be seen glistening in the stream of
+light. Their number seems inexhaustible. According to Milton, the follies
+of life are--
+
+                    "Thick and numberless,
+  As the gay motes that people the sunbeams."
+
+Can these, then, be counted? Yes, Dr. Aitken has numbered the dust of the
+air. I shall never forget my rapt astonishment the day I first numbered
+the dust in the lecture-room of the Royal Society of Edinburgh, with his
+instrument and under his direction.
+
+This wonderfully ingenious instrument was devised on this principle, that
+every fog-particle has entombed in it an invisible dust-particle. A
+definite small quantity of common air is diluted with a fixed large
+quantity of dustless air (_i.e._ air that has been filtered through
+cotton-wool). The mixture is allowed to be saturated with water-vapour.
+Then the few particles of dust seize the moisture, become visible in fine
+drops, fall on a divided plate, and are there counted by means of a
+magnifying glass. That is the secret!
+
+I shall now give you a general idea of the apparatus. Into a common glass
+flask of carafe shape, and flat-bottomed, of 30 cubic inches capacity, are
+passed two small tubes, at the end of one of which is attached a small
+square silver table, 1 inch in length. A little water having been
+inserted, the flask is inverted, and the table is placed exactly 1 inch
+from the inverted bottom, so that the contents of air right above the
+table are 1 cubic inch. This observing table is divided into 100 equal
+squares, and is highly polished, with the burnishing all in one direction,
+so that during the observations it appears dark, when the fine
+mist-particles glisten opal-like with the reflected light in order that
+they may be more easily counted. The tube to which the silver table is
+attached is connected with two stop-cocks, one of which can admit a small
+measured portion of the air to be examined. The other tube in the flask is
+connected with an air-pump of 10 cubic inches capacity. Over the flask is
+placed a covering, coloured black in the inside. In the top of this cover
+is inserted a powerful magnifying glass, through which the particles on
+the silver table can be easily counted. A little to the side of this
+magnifier is an opening in the cover, through which light is concentrated
+on the table.
+
+To perform the experiment, the air in the flask is exhausted by the
+air-pump. The flask is then filled with filtered air. One-tenth of a cubic
+inch of the air to be examined is then introduced into the flask, and
+mixed with the 30 cubic inches of dustless air. After one stroke of the
+air-pump, this mixed air is made to occupy an additional space of 10 cubic
+inches; and this rarefying of the air so chills it that condensation of
+the water-vapour takes place on the dust-particles. The observer, looking
+through the magnifying-glass upon the silver table, sees the
+mist-particles fall like an opal shower on the table. He counts the number
+on a single square in two or three places, striking an average in his
+mind. Suppose the average number upon a single square were five, then on
+the whole table there would be 500; and these 500 particles of dust are
+those which floated invisibly in the cubic inch of mixed air right above
+the table. But, as there are 40 cubic inches of mixed air in the flask and
+barrel, the number of dust-particles in the whole is 20,000. That is,
+there are 20,000 dust-particles in the same quantity of common air
+(one-tenth of a cubic inch) which was introduced for examination. In other
+words, a cubic inch of the air contained 200,000 dust-particles--nearly a
+quarter of a million.
+
+The day I used the instrument we counted 4,000,000 of dust-particles in a
+cubic inch of the air outside of the room, due to the quantity of smoke
+from the passing trains. Dr. Aitken has counted in 1 cubic inch of air
+immediately above a Bunsen flame the fabulous number of 489,000,000 of
+dust-particles.
+
+A small instrument has been constructed which can bring about results
+sufficiently accurate for ordinary purposes. It is so constructed that,
+when the different parts are unscrewed, they fit into a case 4-1/2 inches
+by 2-1/2 by 1-1/4 deep--about the size of an ordinary cigar-case.
+
+After knowing this, we are apt to wonder why our lungs do not get clogged
+up with the enormous number of dust-particles. In ordinary breathing, 30
+cubic inches of air pass in and out at every breath, and adults breathe
+about fifteen times every minute. But the warm lung-surface repels the
+colder dust-particles, and the continuous evaporation of moisture from the
+surface of the air-tubes prevents the dust from alighting or clinging to
+the surface at all.
+
+
+
+
+CHAPTER VII
+
+DUST AND ATMOSPHERIC PHENOMENA
+
+
+Dr. Aitken has devoted a vast amount of attention to the enumeration of
+dust-particles in the air, on the Continent as well as in Scotland, to
+determine the effects of their variation in number.
+
+On his first visit to Hyeres, in 1890, he counted with the instrument
+12,000 dust-particles in a cubic inch of the air: whereas in the following
+year he counted 250,000. He observed, however, that where there was least
+dust, the air was very clear; whereas with the maximum of dust, there was
+a very thick haze.
+
+At Mentone, the corresponding number was 13,000, when the wind was blowing
+from the mountains; but increased to 430,000, when the wind was blowing
+from the populous town.
+
+On his first visit to the Rigi Kulm, in Switzerland, the air was
+remarkably clear and brilliant, and the corresponding number never
+exceeded 33,000; but, on his second visit, he counted no less than
+166,000. This was accounted for by a thick haze, which rendered the lower
+Alps scarcely visible. The upper limit of the haze was well defined; and
+though the sky was cloudless, the sun looked like a harvest moon, and
+required no eagle's eye to keep fixed on it.
+
+Next day there was a violent thunder-storm. At 6 P.M. the storm commenced,
+and 60,000 dust-particles to the cubic inch of air were registered; but in
+the middle of the storm he counted only 13,000. There was a heavy fall of
+hail at this time, and he accounts for the diminution of dust-particles by
+the down-rush of purer upper air, which displaced the contaminated lower
+air.
+
+At the Lake of Lucerne there was an exceptional diminution of the number
+in the course of an hour, viz. from 171,000 to 28,000 in a cubic inch. On
+looking about, he found that the direction of the wind had changed,
+bringing down the purer upper air to the place of observation. The bending
+downwards of the trees by the strong wind showed that it was coming from
+the upper air.
+
+Returning to Scotland, he continued his observations at Ben Nevis and at
+Kingairloch, opposite Appin, Mr. Rankin using the instrument at the top of
+the mountain. These observations showed in general that on the mountain
+southerly, south-easterly, and easterly winds were more impregnated with
+dust-particles, sometimes containing 133,000 per cubic inch. Northerly
+winds brought pure air. The observations at sea-level showed a certain
+parallelism to those on the summit of the mountain. With a north-westerly
+wind the dust-particles reached the low number of 300 per cubic inch, the
+lowest recorded at any low-level station.
+
+The general deductions which he made from his numerous observations during
+these two years are that (1) air coming from inhabited districts is always
+impure; (2) dust is carried by the wind to enormous distances; (3) dust
+rises to the tops of mountains during the day; (4) with much dust there is
+much haze; (5) high humidity causes great thickness of the atmosphere, if
+accompanied by a great amount of dust, whereas there is no evidence that
+humidity alone has any effect in producing thickness; (6) and there is
+generally a high amount of dust with high temperature, and a low amount of
+dust with low temperature.
+
+
+
+
+CHAPTER VIII
+
+A FOG-COUNTER
+
+
+Next to the enumeration of the dust-particles in the atmosphere is the
+marvellous accuracy of counting the number of particles in a fog. The same
+ingenious inventor has constructed a fog-counter for the purpose; and the
+number of fog-particles in a cubic inch can be ascertained. This
+instrument consists of a glass micrometer divided into squares of a known
+size, and a strong microscope for observing the drops on the stage. The
+space between the micrometer and the microscope is open, so that the air
+passes freely over the stage; and the drops that fall on its surface are
+easily seen. These drops are very small; many of them when spread on the
+glass are no more than the five-hundredth of an inch in diameter.
+
+In observing these drops, the attention requires to be confined to a
+limited area of the stage, as many of the drops rapidly evaporate, some
+almost as soon as they touch the glass, whilst the large ones remain a few
+seconds.
+
+In one set of Dr. Aitken's observations, in February 1891, the fog was so
+thick that objects beyond a hundred yards were quite invisible. The number
+of drops falling per second varied greatly from time to time. The greatest
+number was 323 drops per square inch in one second. The high number never
+lasted for long, and in the intervals the number fell as low as 32, or to
+one-tenth.
+
+If we knew the size of these drops, we might be able to calculate the
+velocity of their fall, and from that obtain the number in a cubic inch.
+
+An ingenious addition is put to the instrument in order to ascertain this
+directly. It is constructed so as to ascertain the number of particles
+that fall from a known height. Under a low-power microscope, and
+concentric with it, is mounted a tube 2 inches long and 1-1/2 inch in
+diameter, with a bottom and a cover, which are fixed to an axis parallel
+with the axis of the tube, so that, by turning a handle, these can be slid
+sideways, closing or opening the tube at both ends when required. In the
+top is a small opening, corresponding to the lens of the microscope, and
+in the centre of the bottom is placed the observing-stage illumined by a
+spot-mirror. The handle is turned, and the ends are open to admit the
+foggy air. The handle is quickly reversed, and the ends are closed,
+enabling the observer to count on the stage all the fog-particles in the
+two inches of air over it.
+
+The number of dust-particles in the air which become centres of
+condensation depends on the rate at which the condensation is taking
+place. The most recent observations show that quick condensation causes a
+large number of particles to become active, whereas slow condensation
+causes a small number. After the condensation has ceased, a process of
+differentiation takes place, the larger particles robbing the smaller ones
+of their moisture, owing to the vapour-pressure at the surface of the
+drops of large curvature being less than at the surface of drops of
+smaller curvature.
+
+By this process the particles in a cloud are reduced in number; the
+remaining ones, becoming larger, fall quicker. The cloud thus becomes
+thinner for a time. A strong wind, suddenly arising, will cause the
+cloud-particles to be rapidly formed: these will be very numerous, but
+very small--so small that they are just visible with great care under a
+strong magnifying lens used in the instrument. But in slowly formed clouds
+the particles are larger, and therefore more easily visible to the naked
+eye.
+
+Though the particles in a fog are slightly finer, the number is about the
+same as in a cloud--that is, generally. As clouds vary in density, the
+number of particles varies. Sometimes in a cloud one cannot see farther
+than 30 yards; whereas in a few minutes it clears up a little, so that we
+can see 100 yards. Of course, the denser the cloud the greater the number
+of water-particles falling on the calculating-stage of the instrument.
+
+Very heavy falls of cloud-particles seldom last more than a few seconds,
+the average being about 325 on the square inch per second, the maximum
+reaching to 1290. This is about four times the number counted in a fog.
+Yet the particles are so very small that they evaporate instantly when
+they reach a slight increase of temperature.
+
+
+
+
+CHAPTER IX
+
+FORMATION OF CLOUDS
+
+
+In our ordinary atmosphere there can be no clouds without dust. A
+dust-particle is the nucleus that at a certain humidity becomes the centre
+of condensation of the water-vapour so as to form a cloud-particle; and a
+collection of these forms a cloud.
+
+This condensation of vapour round a number of dust-particles in visible
+form gives rise to a vast variety of cloud-shapes. There are two distinct
+ways in which the formation of clouds generally takes place. Either a
+layer of air is cooled in a body below the dew-point; or a mass of warm
+and moist air rises into a mass which is cold and dry. The first forms a
+cloud, called, from being a layer, _stratus_; the second forms a cloud,
+called, from its heap appearance, _cumulus_. The first is widely extended
+and horizontal, averaging 1800 feet in height; the second is convex or
+conical, like the head of a sheaf, increasing upward from a level base,
+averaging from 4500 feet to 6000 feet in height.
+
+There are endless combinations of these two; but at the height of 27,000
+feet, where the cloud-particles are frozen, the structure of the cloud is
+finer, like "mares' tails," receiving the name _cirrus_. When the cirrus
+and cumulus are combined, in well-defined roundish masses, what is
+familiarly described as a "mackerel sky" is beautifully presented. The
+dark mass of cloud, called _nimbus_, is the threatening rain-cloud, about
+4500 feet in height.
+
+At the International Meteorological Conference at Munich, in 1892, twelve
+varieties of clouds were classified, but those named above are the
+principal. In a beautiful sunset one can sometimes notice two or three
+distances of clouds, the sun shedding its gold light on the full front of
+one set, and only fringing with vivid light the nearer range.
+
+Although no man has wrought so hard as Dr. Aitken to establish the
+principle that clouds are mainly due to the existence of dust-particles
+which attract moisture on certain conditions, yet even twenty years ago he
+said that it was probable that sunshine might cause the formation of
+nuclei and allow cloudy condensation to take place where there was no
+dust.
+
+Under certain conditions the sun gives rise to a great increase in the
+number of nuclei. Accordingly, he has carefully tested a few of the
+ordinary constituents and impurities in our atmosphere to see if sunshine
+acted on them in such a way as to make them probable formers of
+cloud-particles.
+
+He tested various gases, with more or less success. He found that ordinary
+air, after being deprived of its dust-particles and exposed to sunshine,
+does not show any cloudy condensation on expansion; but, when certain
+gases are in the dustless air, a very different result is obtained.
+
+He first used ammonia, putting one drop into six cubic inches of water in
+a flask, and sunning this for one minute; the result was a considerable
+quantity of condensation, even with such a weak solution. When the flask
+was exposed for five minutes, the condensation by the action of the
+sunshine was made more dense.
+
+Hydrogen peroxide was tested in the same way, and it was found to be a
+powerful generator of nuclei. Curious is it that sulphurous acid is
+puzzling to the experimentalist for cloud formation. It gives rise to
+condensation in the dark; but sunshine very conclusively increases the
+condensation.
+
+Chlorine causes condensation to take place without supersaturation;
+sulphuretted hydrogen (which one always associates with the smell of
+rotten eggs) gives dense condensation after being exposed to sunshine.
+
+Though the most of these nuclei, due to the action of sunshine in the
+gases, remain active for cloudy condensation for a comparatively short
+space of time--fifteen minutes to half-an-hour--yet the experiments show
+that it is possible for the cloudy condensation to take place in certain
+circumstances in the absence of dust. This seems paradoxical in the light
+of the former beautiful experiments; but, in ordinary circumstances, dust
+is needed for the formation of clouds. However, supposing there is any
+part of the upper air free from dust, it is now found possible, when any
+of these gases experimented on be present, for the sun to convert them
+into nuclei of condensation, and permit of clouds being formed in dustless
+air, miles above the surface of the earth.
+
+In the lower atmosphere there are always plenty of dust-particles to form
+cloudy condensation, whether the sun shines or not. These are produced by
+the waste from the millions of meteors that daily fall into the air.
+
+But in the higher atmosphere, clouds can be formed by the action of the
+sun's rays on certain gases. This is a great boon to us on the earth; for
+it assures us of clouds being ever existing to defend us from the sun's
+extra-powerful rays, even when our atmosphere is fairly clear. This is
+surely of some meteorological importance.
+
+
+
+
+CHAPTER X
+
+DECAY OF CLOUDS
+
+
+From the earliest ages clouds have attracted the attention of observers.
+Varied are their forms and colours, yet in our atmosphere there is one law
+in their formation. Cloud-particles are formed by the condensation of
+water-vapour on the dust-particles invisibly floating in the atmosphere,
+up to thousands--and even millions--in the cubic inch of air.
+
+But observers have not directed their attention so much to the decay of
+clouds--in fact, the subject is quite new. And yet how suggestive is the
+subject!
+
+The process of decay in clouds takes place in various ways. A careful
+observer may witness the gradual wasting away and dilution into thin air
+of even great stretches of cloud, when circumstances are favourable. In
+May 1896 my attention was particularly drawn to this at my manse in
+Strathmore. In the middle of that exceptionally sultry month, I was
+arrested by a remarkable transformation scene. It was the hottest May for
+seventy-two years, and the driest for twenty-five years. The whole parched
+earth was thirsting for rain. All the morning my eyes were turned to the
+clouds in the hope that the much-desired shower should fall. Till ten
+o'clock the sun was not seen, and there was no blue in the sky. Nor was
+there any haze or fog.
+
+But suddenly the sun shone through a thinner portion of the enveloping
+clouds, and, to the north, the sky began to open. As if by some magic
+spell there was, in a quarter of an hour, more blue to be seen than
+clouds. At the same time, near the horizon, a haze was forming, gradually
+becoming denser as time wore on. In an hour the whole clouds were gone,
+and the glorious orb of day dispelled the moisture to its thin-air form.
+
+This was a pointed and rapid illustration of the decay from cloud-form to
+haze, and then to the pure vapoury sky. It was an instance of the
+_reverse_ process. As the sun cleared through, the temperature in the
+cloud-land rose and evaporation took place on the surface of the
+cloud-particles, until by an untraceable, but still a gradual process
+through fog, the haze was formed. Even then the heat was too great for a
+definite haze, and the water-vapour returned to the air, leaving the
+dust-particles in invisible suspension.
+
+But clouds decay in another way. This I will illustrate in the next
+chapter on "It always rains."
+
+What strikes a close observer is the difference of structure in clouds
+which are in the process of formation and those which are in the process
+of decay. In the former the water-particles are much smaller and far more
+numerous than in the latter. While the particles in clouds in decay are
+large enough to be seen with the unaided eye, when they fall on a properly
+lighted measuring table, they are so small in clouds in rapid formation
+that the particles cannot be seen without the aid of a strong magnifying
+glass.
+
+Observers have assumed that the whole explanation of the fantastic shapes
+taken by clouds is founded on the process of formation; but Dr. Aitken has
+pointed out that ripple-marked clouds, for instance, have been clouds of
+decay. When what is called a cirro-stratus cloud--mackerel-like against
+the blue sky--is carefully observed in fine weather, it will be found that
+it frequently changes the ripple-marked cirrus in the process of decay to
+vanishing. Where the cloud is thin enough to be broken through by the
+clear air that is drawn in between the eddies, the ripple markings get
+nearer and nearer the centre, as the cloud decays. And, at last, when
+nearly dissolved, these markings are extended quite across the cloud.
+
+Whether, then, we consider the cases of clouds gradually melting away back
+into their original state of blue water-vapour, or the constant fine
+raining from clouds and re-formation by evaporation, or the transformation
+of such clouds as the cirro-stratus into the ripple-marked cirrus, we are
+forced to the conclusion that in clouds there is not always development,
+but sometimes degeneration; not always formation, but sometimes decay.
+
+
+
+
+CHAPTER XI
+
+IT ALWAYS RAINS
+
+
+All are familiar with the answer given by the native of Skye to the irate
+tourist on that island, who, for the sixth day drenched, asked the
+question: "Does it always rain here?" "Na!" answered the workman, without
+at all understanding the joke; "feiles it snaas" (sometimes it snows).
+Yet, strange to say, the tourist's question has been answered in the
+affirmative in every place where a cloud is overhead, visible or
+invisible.
+
+Whenever a cloud is formed, it begins to rain; and the drops shower down
+in immense numbers, though most minute in size--"the playful fancies of
+the mighty sky."
+
+No doubt it is only in certain circumstances that these drops are
+attracted together so as to form large drops, which fall to the earth in
+genial showers to refresh the thirsty soil, or in a terrible deluge to
+cause great destruction. But when the temperature and pressure are not
+suitable for the formation of what we commonly know as the rain, the fine
+drops fall into the air under the cloud, where they immediately evaporate
+from their dust free-surfaces, if the air is dry and warm. This is, in
+other words, the decay of clouds.
+
+It is a curious fact that objects in a fog may not be wetted, when the
+number of water-particles is great. It seems that these water-particles
+all evaporate so quickly that even one's hand or face is not sensible of
+being wetted. The particles are minutely small; and they may evaporate
+even before reaching the warm skin, by reason of the heated air over the
+skin.
+
+There is a peculiarly warm sensation in the centre of a cumulus cloud,
+especially when it is not dense. A glow of heat seems to radiate from all
+points. Yet the face and hands are quite dry, and exposed objects are not
+wetted; but it is really _always raining_. That is a curious discovery.
+
+It is radiant heat that is the cause of the remarkable result. The rays of
+the sun, which strike the upper part of the cloud, not only heat that
+surface but also penetrate the cloud and fall on the surface of bodies
+within, generating heat there. These heated surfaces again radiate heat
+into the air attached to them. This warm air receives the fine raindrops
+in the cloud, and dissolves the moisture from the dust-particles before
+the moisture can reach the surfaces exposed. That a vast amount of radiant
+heat rushes through a cloud is clearly shown by exposing a thermometer
+with black bulb _in vacuo_. On some occasions, a thermometer would
+indicate from 40 deg. to 50 deg. above the temperature of the air, thus proving
+the surface to be quite dry.
+
+These observations have been corroborated on Mount Pilatus, near
+Lucerne--1000 feet higher and more isolated than the Rigi. The summit was
+quite enveloped in cloud, and, though one might naturally conclude that
+the air was dense with moisture, yet the wooden seats, walls, and all
+exposed surfaces were quite dry. Strange to say, however, the thermometers
+hung up got wet rapidly, and the pins driven into the wooden post to
+support them rapidly became moist. A thermometer lying on a wooden seat
+stood at 60 deg., while one hung up read only 48 deg. This difference was caused
+by radiant heat.
+
+It is well known that, when bodies are exposed to radiant heat, they are
+heated in proportion to their size; the smaller, then, may be moist, when
+the larger are dry by radiation. The effect of the sun's penetrating heat
+through the cloud is to heat exposed objects above the temperature of the
+air; and if the objects are of any size they are considerably heated, and
+retain their heat more, while at the same time around them is a layer of
+warm air which is quite sufficient to force the water-vapour to leave the
+dust-particles in the fine rain.
+
+Hence seats, walls, posts, &c., are quite dry, though they are in the
+middle of a cloud. They are large enough to throw off the moisture by the
+retained heat, or by the large amount of surrounding heat; whereas, small
+bodies, which are not heated to the same degree and cannot therefore
+retain their heat so easily, have not heat-power sufficient to withstand
+the moisture, and they become wetted. Hence, by the radiant heat, the
+large exposed objects are dry in the cloud; whereas small objects are
+damp, and, in some cases, dripping with wet.
+
+The fact is, then, that whenever a cloud overhangs, _rain is falling_,
+though it may not reach the earth on account of the dryness of the stratum
+of air below the cloud, and the heat of the air over the earth. So that on
+a summer day, with the gold-fringed, fleecy clouds sailing overhead, it is
+really raining; but the drops, being very small, evaporate long before
+reaching the earth. As Ariel sings at the end of "The Tempest" of
+Shakespeare, "The rain, it raineth every day." It rains, but much of the
+melting of the clouds is reproduced by a wonderful circularity--the
+moisture evaporating, seizing other dust-particles, forming
+cloud-particles, falling again, and so on _ad infinitum_, during the
+existing circumstances.
+
+
+
+
+CHAPTER XII
+
+HAZE
+
+
+What is haze? The dictionary says, "a fog." Well, haze is _not_ a fog. In
+a fog, the dust-particles in the air have been fully clothed with
+water-vapour; in a haze, the process of condensation has been arrested.
+
+Cloudy condensation is changed to haze by the reduction of its humidity.
+Dr. Aitken invented a simple apparatus for testing the condensing power of
+dust, and observing if water-vapour condensed on the deposited dust in
+unsaturated air.
+
+The dust from the air has first to be collected. This is done by placing a
+glass plate vertically, and in close contact with one of the panes of
+glass in the window, by means of a little india-rubber solution. The plate
+being thus rendered colder than the air in the room, the dust is deposited
+on it.
+
+Construct a rectangular box, with a square bottom, 1-1/2 inches a side and
+3/4 inch deep, and open at the top. Cover the top edge of the box with a
+thickness of india-rubber. Place the dusty plate--a square glass mirror, 4
+inches a side--on the top of the india-rubber, and hold it down by spring
+catches, so as to make the box water-tight. The box has been provided with
+two pipes, one for taking in water and the other for taking away the
+overflow, with the bulb of a thermometer in the centre. Clean the dust
+carefully off one half of the mirror, so that one half of the glass
+covering the box is clean and the other half dusty. Pour cold water
+through the pipe into the box, so as to lower the temperature of the
+mirror, and carefully observe when condensation begins on the clean part
+and on the dusty part, taking a note of the difference of temperature. The
+condensation of the water-vapour will appear on the dust-particles before
+coming down to the natural dew-point temperature of the clean glass. And
+the difference between the two temperatures indicates the temperature
+above the dew-point at which the dust has condensed the water-vapour.
+
+Magnesia dust has small affinity for water-vapour; accordingly, it
+condenses at almost exactly the same temperature as the glass. But
+gunpowder has great condensing power. All have noticed that the smoke
+from exploded gunpowder is far more dense in damp than in dry weather. In
+the experiment it will be found that the dust from gunpowder smoke begins
+to show signs of condensing the vapour at a temperature of 9 deg. Fahr. above
+the dew-point. In the case of sodium dust, the vapour is condensed from
+the air at a temperature of 30 deg. above the dew-point.
+
+Dust collected in a smoking-room shows a decidedly greater condensing
+power than that from the outer air.
+
+We can now understand why the glass in picture frames and other places
+sometimes appears damp when the air is not saturated. When in winter the
+windows are not often cleaned, a damp deposit may be frequently seen on
+the glass. Any one can try the experiment. Clean one half of a dusty pane
+of glass in cold weather, and the clean part will remain undewed and
+clear, while the dusty part is damp to the eye and greasy to the touch.
+
+These observations indicate that moisture is deposited on the
+dust-particles from air, which is not saturated, and that the condensation
+takes place while the air is comparatively dry, _before_ the temperature
+is lowered to the dew-point. There is, then, no definite demarcation
+between what seems to us clear air and thick haze. The clearest air has
+some haze, and, as the humidity increases, the thickness of the air
+increases.
+
+In all haze the temperature is above the dew-point. The dust-particles
+have only condensed a very small amount of the moisture so as to form
+haze, before the fuller condensation takes place at the dew-point.
+
+At the Italian lakes, on many occasions when the air is damp and still,
+every stage of condensation may be observed in close proximity, not
+separated by a hard and fast line, but when no one could determine where
+the clear air ended and the cloud began. Sometimes in the sky overhead a
+gradual change can be observed from perfect clearness to thick air, and
+then the cloud.
+
+A thick haze may be occasioned by an increased number of dust-particles
+with little moisture, or of a diminished number of dust-particles with
+much moisture, above the point of saturation. The haze is cleared by this
+temperature rising, so as to allow the moisture to evaporate from the
+dust-particles.
+
+Whenever the air is dry and hazy, much dust is found in it; as the dust
+decreases the haze also decreases. For example, Dr. Aitken, at
+Kingairloch, in one of the clearest districts of Argyleshire, on a clear
+July afternoon, counted 4000 dust-particles in a cubic inch of the air;
+whereas, two days before, in thick haze, he counted no fewer than 64,000
+in the cubic inch. At Dumfries the number counted on a very hazy day in
+October increased twenty-fold over the number counted the day before, when
+it was clear.
+
+All know that thick haze is usual in very sultry weather. The wavy,
+will-o'-the-wisp ripples near the horizon indicate its presence very
+plainly. During the intense heat there is generally much dust in the
+atmosphere; this dust, by the high temperature, attracts moisture from the
+apparently dry air, though above the saturation point. In all
+circumstances, then, the haze can be accounted for by the condensing power
+of the dust-particles in the atmosphere, at a higher temperature than that
+required for the formation of fogs, or mists, or rain.
+
+
+
+
+CHAPTER XIII
+
+HAZING EFFECTS OF ATMOSPHERIC DUST
+
+
+The transparency of the atmosphere is very much destroyed by the
+impurities communicated to it while passing over the inhabited areas of
+the country. Dr. Aitken devoted eighteen months to compare the amount of
+dusty impurities in different masses of air, or of different airs brought
+in by winds from different directions.
+
+He took Falkirk for his centre of observations. This town lies a little to
+the north of a line drawn between Edinburgh and Glasgow, and is nearly
+midway between them. If we draw a line due west from it, and another due
+north, we find that, in the north-west quadrant so enclosed, the
+population of that part of Scotland is extremely thin, the country over
+that area being chiefly mountainous. In all other directions, the
+conditions are quite different. In the north-east quadrant are the fairly
+well-populated areas of Aberdeenshire, Forfarshire, and the thickly
+populated county of Fife. In the south-east quadrant are situated
+Edinburgh and the well-populated districts of the south-east of Scotland.
+And in the south-west quadrant are Glasgow and the large manufacturing
+towns which surround it. The winds from three of these quadrants bring air
+polluted in its passage over populated areas, whereas the winds from the
+north-west come comparatively pure.
+
+The general plan of estimating the amount of haze is to note the most
+distant hill that can be seen through the haze. The distance in miles of
+the farthest away hill visible is then called "the limit of visibility" of
+the air at the time. For the observations made at Falkirk, only three
+hills are available, one about four miles distant, the Ochils about
+fifteen miles distant, and Ben Ledi about twenty-five miles distant--all
+in the north-west quadrant. When the air is thick, only the near hill can
+be seen; then the Ochils become visible as the air clears; and at last Ben
+Ledi is seen, when the haze becomes still less. After Ben Ledi is visible,
+it then becomes necessary to estimate the amount of haze on it, in order
+to get the limit of visibility of the air at the time. Thus, if Ben Ledi
+be half-hazed, then the limit of visibility will be fifty miles. In this
+way all the estimates of haze have been reduced to one scale for
+comparison.
+
+As the result of all the observations it was found that, as the dryness of
+the air increases, the limit of visibility also increases. A very marked
+difference in the transparency of the air was found with winds from the
+different directions. In the north-west quadrant the winds made the air
+very clear, whereas winds from all other directions made the air very much
+hazed. The winds in the other three areas are nearly ten times more hazed
+than those from the north-west quadrant. That is very striking.
+
+The conclusion come to is that the air from densely inhabited districts is
+so polluted that it is fully nine times more hazed than the air that comes
+from the thinly inhabited districts; in other words, the atmosphere at
+Falkirk is about ten times thicker when the wind is east or south than it
+would be if there were no fires and no inhabitants.
+
+It is interesting to notice that the limit varies considerably for the
+same wind at the same humidity. This is what might have been expected,
+because from the observations made by the dust-counter the number of
+particles varied greatly in winds from the same directions, but at
+different times. This depends upon the rise and fall of the wind, changes
+in the state of trade, season of the year, and other causes. During a
+strike, the dearth of coal will make a considerable diminution in the
+number of dust-particles in the air of large towns. With a north wind, the
+extreme limits of visibility are 120 to 200 miles; and with a north-west
+wind, from 70 to 250 miles. An east wind has as limits 4 to 50 miles, and
+a south-east wind 2 to 60 miles.
+
+One interesting fact to be noticed, after wading through these tables, is
+this--that, as a general result, the transparency of the air increases
+about 3.7 times for any increase in dryness from 2 deg. to 8 deg. of wet-bulb
+depression. That is, the clearness of the air is inversely proportional to
+the relative humidity; or, put another way, if the air is four times drier
+it is about four times clearer.
+
+
+
+
+CHAPTER XIV
+
+THUNDER CLEARS THE AIR
+
+
+The phrase "thunder clears the air" is familiar to all. It contains a very
+vital truth, yet even scientific men did not know its full meaning until
+just the other day. It came by experience to people who had been for ages
+observing the weather; and it is one of the most pointed of the
+"weather-lore" expressions. Folks got to know, by a sort of rule-of-thumb,
+truths which scientifically they were unable to learn. And this is one.
+
+Perhaps, therefore, we should respect a little more what is called
+"folk-lore," or ordinary people's sayings. Experience has taught men many
+wonderful things. In olden times they were keener natural observers. They
+had few books, but they had plenty of time. They studied the habits of
+animals and moods of nature, and they came wonderfully near to reaching
+the full truth, though they could not give a reason for it. The
+awe-inspiring in nature has especially riveted the attention of man.
+
+And no appearance in nature joins more powerfully the elements of grandeur
+and awe than a heavy thunder-storm. When, suddenly, from the breast of a
+dark thunder-cloud a brilliant flash of light darts zigzag to the earth,
+followed by a loud crackling noise which softens in the distance into
+weaker volumes of sound, terror seizes the birds of the air and the cattle
+in the field. The man who is born to rule the storm rejoices in the
+powerful display; but kings have trembled at the sight.
+
+Byron thus pictures a storm in the Alps:--
+
+                              "Far along
+    From peak to peak, the rattling crags among
+  Leaps the live thunder! Not from one lone cloud,
+    But every mountain now hath found a tongue,
+  And Jura answers, through her misty shroud,
+  Back to the joyous Alps, who call to her aloud!"
+
+Franklin found that lightning is just a kind of electricity. No one can
+tell how it is produced; yet a flash has been photographed. When the flash
+is from one cloud to another there is sheet-lightning, which is beautiful
+but not dangerous; but, when the electricity passes from a cloud to the
+earth in a forked form, it is very dangerous indeed. The flash is
+instantaneous, but the sound of the thunder takes some time to travel.
+Roughly speaking, the sound takes five seconds or six beats of the pulse
+to the mile.
+
+All are now taught at school that it is the oxygen in the air which is
+necessary to keep us in life. If mice are put into a glass jar of pure
+oxygen gas, they will at once dance with exhilarating joy. It occurred to
+Sir Benjamin Richardson, some time ago, that it would be interesting to
+continue some experiments with animals and oxygen. He put a number of mice
+into a jar of pure oxygen for a time; they breathed in the gas, and
+breathed out water-vapour and carbonic acid. After the mice had continued
+this for some time, he removed them by an arrangement. By chemical means
+he removed the water-vapour and carbonic acid from the mixed air in the
+vessel. When a blown-out taper was inserted, it at once burst into flame,
+showing that the remaining gas was oxygen.
+
+Again, the mice were put into this vessel to breathe away. But, strange to
+say, the animals soon became drowsy; the smartness of the oxygen was gone.
+At last they died; there was nothing in the gas to keep them in life; yet,
+by the ordinary chemical tests, it was still oxygen. It had repeatedly
+passed through the lungs of the mice, and during this passage there had
+been an action in the air-cells which absorbed the life-giving element of
+the gas. It is oxygen, so far as chemistry is concerned, but it has no
+life-giving power. It has been _devitalised_.
+
+But the startling discovery still remains. Sir Benjamin had previously
+fitted up the vessel with two short wires, opposite each other in the
+sides--part outside and part inside. Two wires are fastened to the outside
+knobs. These wires are attached to an electric machine, and a flash of
+electricity is made to pass between the inner points of the vessel. The
+wires are again removed; nothing strange is seen in the vessel. But, when
+living mice are put into the vessel, they dance as joyfully as if pure
+oxygen were in it. The oxygen in which the first mice died has now been
+quite refreshed by the electricity. The bad air has been cleared and made
+life-supporting by the electric discharge. It has been again vitalised.
+
+Now, to apply this: before a thunder-storm, everything has been so still
+for days that the oxygen in the air has been to some extent robbed of its
+life-sustaining power. The air feels "close," a feeling of drowsiness
+comes over all. But, after the air has been pierced by several flashes of
+lightning, the life-force in the air is restored. Your spirits revive; you
+feel restored; your breathing is far freer; your drowsiness is gone. Then
+there is a burst of heavenly music from the exhilarated birds. Thus a
+thunder-storm "clears the air."
+
+After the passage of lightning through the air ozone is produced--the gas
+that is produced after a flash of electricity. It is a kind of oxygen,
+with fine exciting effects on the body. If, then, the life-sustaining
+power of oxygen depends on a trace of ozone, and this is being made by
+lightning's work, how pleased should we be at the occasional
+thunder-storm!
+
+
+
+
+CHAPTER XV
+
+DISEASE-GERMS IN THE AIR
+
+
+The gay motes that dance in the sunbeams are not all harmless. All are
+annoying to the tidy housekeeper; but some are dangerous. There are living
+particles that float in the air as the messengers of disease and death.
+Some, falling on fresh wounds, find there a suitable feeding-place; and,
+if not destroyed, generate the deadly influence. Others are drawn in with
+the breath; and, unless the lungs can withstand them, they seize hold and
+spread some sickness or disease. From stagnant pools, common sewers, and
+filthy rooms, disease-germs are constantly contaminating the air. Yet
+these can be counted.
+
+The simplest method is that of Professor Frankland. It depends on this
+principle: a certain quantity of air is drawn through some cotton-wool;
+this wool seizes the organisms as the air passes through; these organisms
+are afterwards allowed to feed upon a suitable nutritive medium until they
+reach maturity; they are then counted easily.
+
+About an inch from each end of a glass tube (5 inches long and 1 inch
+bore), the glass is pressed in during the process of blowing. Some
+cotton-wool is squeezed in to form a plug at the farther constricted part
+of the glass. The important plug is now inserted at the same open end, but
+is not allowed to go beyond the constricted part at its end. A piece of
+long lead tubing is attached to the former end by an india-rubber tube.
+The other end of the lead tubing is connected with an exhausting syringe.
+Sixty strokes of the 18 cubic inches syringe will draw 1080 cubic inches
+of the air to be examined through the plugs, the first retaining the
+organisms.
+
+The impregnated plug is then put into a flask containing in solution some
+gelatine-peptone. The flask is made to revolve horizontally until an
+almost perfectly even film of gelatine and the organisms from the
+broken-up plug cover its inner surface.
+
+The flask is allowed to remain for an hour in a cool place, and is then
+placed under a bell-jar, at a temperature of 70 deg. Fahr. There it remains,
+to allow the germs to incubate, for four or five days. The surface of the
+flask having been previously divided into equal parts by ink lines, the
+counting is now commenced. If the average be taken for each segment, the
+number of the whole is easily ascertained. A simple arithmetical
+calculation then determines the number of organisms in a cubic foot, since
+the number is known for the 1080 cubic inches. That is the process for
+determining the number of living organisms in a fixed quantity of air.
+
+No less than thirty colonies of organisms were counted in a cubic foot of
+air taken from the Golden Gallery of St. Paul's Cathedral, London, and 140
+from the air of the churchyard. An ordinary man would breathe there
+thirty-six micro-organisms every minute.
+
+Electricity has a powerful effect in destroying these organisms. Ozone is
+generated in the air by lightning, and it is detrimental to them. In fine
+ozoned Highland air scarcely a disease-germ can be detected. Open sea air
+contains about one germ in two cubic feet. It has been found that in Paris
+the average in summer is about 140 per cubic foot of air, but in bedrooms
+the number is double. During the twenty-four hours of the day the number
+of germs is highest about 6 A.M., and lowest about mid-day.
+
+Raindrops carry the germs to the ground. Hence the advantage of a thunder
+plout in a sanitary way. A cubic foot of rain has been found to contain
+5500 organic dust-germs, besides 7,000,000,000 of inorganic
+dust-particles. In a dirty town the rain will bring down in a year, upon a
+square foot of surface, no less than 3,000,000 of bacteria, many of them
+being disease-bearing and death-bearing. No wonder, then, that scientific
+men are using every endeavour to protect the human frame, as well as the
+frame of the lower animals, from the baneful inroads of these floating
+nuclei of disease and death.
+
+
+
+
+CHAPTER XVI
+
+A CHANGE OF AIR
+
+
+For weakness of body and fatigue of mind a very common and essentially
+serviceable recommendation is "a change of air." Of course, the change of
+scene from coast to country, or from town to hillside, may help much the
+depressed in body or mind; and this is very commendable. But, strange to
+say, there is a healing virtue in breathing different air.
+
+At first one is apt to think that air is the same all over, as he thinks
+water is--especially outside smoky towns; but both have varied qualities
+in different parts. You have only to be assured that in a cubic inch of
+bedroom air in the denser parts of a large town there are about 20,000,000
+of dust-particles, and in the open air of a heathery mountain-side there
+are only some hundreds, to see that there is something after all on the
+face of it in the "old wives' saw."
+
+Not that the dust-particles are all injurious; for most of them are
+inorganic, and many of the organic particles are quite wholesome; yet
+there is a change wrought, often very marked, in going from one place to
+another for different air.
+
+Even in the country, especially in summer-time, one distinctly notices the
+great difference in the air of lowland and highland localities. The ten
+miles change from Strathmore to Glenisla shows a marked difference in the
+air. Below, it is close, weakening, enervating; above, it is exhilarating,
+invigorating, and strong.
+
+So people must have a change--at least those who can afford it--for health
+must be seen to first of all, if one has means to do so. Oh! the blessing
+of good health! How many who enjoy it never think of the misery of its
+loss! In fact, health is the soul that animates all enjoyments of life;
+for without it those would soon be tasteless. A man starves at the
+best-spread table, and is poor in the midst of the greatest treasures
+without health.
+
+In these days half of our diseases come from the neglect of the body in
+the overwork of the brain. The wear and tear of labour and intellect go on
+without pause or self-pity. Men may live as long as their forefathers, but
+they suffer more from a thousand artificial anxieties and cares. The men
+of old fatigued only the muscles, we exhaust the finer strength of the
+nerves. Even more so now, then, do we require a change of air to soothe
+our overwrought nervous system.
+
+And when that magic power, concealed from mortal view, works such wonders
+on the health, surely it is one's duty to save up and have it, when it is
+within one's means. For is not health the greatest of all possessions?
+What a rich colour clothes the countenance of the young after a month's
+outing in the hill country! How fine and pure has the blood become! All
+stagnant humours, accumulated in winter town life, have been dispelled by
+the ozone-brightening charm. The weary looking office or shop man is now
+transfigured into a sprightly youth once more, ready with strongly
+recuperated power for another winter's labours. The pale wife, who has
+been stifled for months in close-aired rooms, has now a healthy flush on
+her becoming countenance that speaks of gladly restored health. And all
+this has been brought about by a "change of air"!
+
+For a thorough change to a town man, he should make for the Highlands.
+There he is never tired of walking, for the air which he breathes is full
+of ozone. This revivifying element in the air is produced by the
+lightning-bursts from hill to hill. There is in the Highlands a continual
+rush of electricity, whether seen or not. Hence the air is very pure, free
+from organic germs, intensely exhilarating and buoyant.
+
+Sportsmen are livingly aware of the recuperative power of the Highland
+air. Perhaps these city men do not benefit so much by the easy walking
+exercise on the grouse moors as in breathing the splendidly
+delight-inspiring air. What a change one feels there in a very few hours!
+
+"A change of air" is an old wives' adage. But much of the weather-lore of
+our forefathers was based on real scientific principles only now coming to
+light. Nature is ever true, but it requires patience to unravel her
+secrets. We therefore advocate an occasional "change of air" to improve
+the health--
+
+                        "The chiefest good,
+  Bestow'd by Heaven, but seldom understood."
+
+
+
+
+CHAPTER XVII
+
+THE OLD MOON IN THE NEW MOON'S ARMS
+
+
+After the sun's broad beams have tired the sight, the moon with more sober
+light charms us to descry her beauty, as she shines sublimely in her
+virgin modesty. There is always a most fascinating freshness in the first
+sight of the new moon. The superstition of centuries adds to this charm.
+Why boys and girls like to turn over a coin in their pocket at this sight
+one cannot tell: yet it is done. No young lady likes to look at the new
+moon through a pane of glass. And farmers are always confident of a change
+of weather with a new moon: at least in bad weather they earnestly hope
+for it.
+
+But, banishing all superstition, we welcome the pale silver sickle in the
+heavens, once more appearing from the bosom of the azure. And no language
+can equal these beautiful words of the youthful Shelley:--
+
+                    "Like the young moon,
+  When on the sunlit limits of the night
+    Her white shell trembles amid crimson air,
+  And while the sleeping tempest gathers might,
+    Doth, as the herald of his coming, bear
+  The ghost of its dead mother, whose dim form
+    Bends in dark ether from her infant's chair."
+
+That is a more charming way of putting the ordinary expression, "the old
+moon in the new moon's arms." We are regularly accustomed to the
+moonshine, but only occasionally is the _earthshine_ on the moon so
+regulated that the shadowed part is visible. This is not seen at the
+appearance of every new moon. It depends upon the positions of the sun and
+moon, the state of the atmosphere, and the absence of heavy clouds. I
+never in my life saw the phenomenon so marvellously beautiful as on May
+7th, 1894, at my manse in Strathmore. I took particular note of it, as
+some exceedingly curious things were connected with it.
+
+At nine o'clock in the evening, the new moon issued from some clouds in
+the western heavens, the sun having set, about an hour before. The
+crescent was thin and silvery, and the outline of the shadowed part was
+just visible. The sky near the horizon was clear and greenish-hued. As
+the night advanced the moon descended, and at ten o'clock she was
+approaching a purple stratum of clouds that stretched over the hills,
+while the position of the sun was only known a little to the east, by the
+back-thrown light upon the dim sky. Through the moisture-laden air the
+sun's rays, reflected by the moon, threw a golden stream from the crescent
+moon, for the silvery shell became more golden-hued.
+
+The horns of the moon now seemed to project, and the shadowed part became
+more distinct, though the circle appeared smaller. By means of a
+field-glass I noticed that this was extra lighted, with points here and
+there quite golden-tinged. The darker spots showed the deep caverns; the
+brighter points brought into relief the mountain peaks.
+
+Why was the surface brighter than usual? I cannot go into detail about the
+phases of the moon; but, in a word, I may say that, while the sun can
+illuminate the side of the moon turned towards it, it is unable to throw
+any light on the shadow, seeing that there is no atmosphere around the
+moon to refract the light.
+
+If we, in imagination, looked from the moon upon the earth, we should see
+the same phases as are now noticed in the moon; and when it is just before
+new moon on the earth, the earth will appear fully illuminated from the
+moon. We would also observe (from the moon) that the brightness of the
+illuminated part of the earth would vary from time to time, according to
+the changes in the earth's atmosphere. More light would be reflected to
+the moon from the clouds in our atmosphere than from the bare earth or
+cloudless sea, since clouds reflect more light than either land or sea.
+Accordingly, we arrive at this curious fact--that the extra brightness of
+the _dark_ body of the moon is mainly determined by the amount of _cloud
+in our atmosphere_.
+
+Accordingly, I concluded that there must be clouds to the west, though I
+could not see them, which reflected rays of light and faintly illuminated
+the shadowed part of the moon. It had become much colder, and I concluded
+that during the night the cloud-particles, if driven near by the wind,
+would condense into rain. And, assuredly, next morning I was gratified to
+find that rain had fallen in large quantities, substantiating the theory.
+
+There is much pleasure in verifying such an interesting problem. The dark
+body of the moon being more than usually visible is one of our well-known
+and oldest indications of coming bad weather. And at once came to my
+memory the lines of Sir Patrick Spens, as he foreboded rain for his
+crossing the North Sea:--
+
+  "I saw the new moon late yestreen
+  Wi' the auld moon in her arm;
+  And if we gang to sea, master,
+  I fear we'll come to harm."
+
+This lunar indication, then, has a sound physical basis, showing that near
+the observer there are vast areas of clouds, which are reflecting light
+upon the moon at the time, before they condense into rain by the chilling
+of the air. According to the old Greek poet, Aratus: "If the new moon is
+ruddy, and you can trace the shadow of the complete circle, a storm is
+approaching."
+
+
+
+
+CHAPTER XVIII
+
+AN AUTUMN AFTERGLOW
+
+
+A brilliant afterglow is welcomed for its surpassing beauty and a
+precursor of fine fixed weather.
+
+A glorious sunset has always had a charm for the lover of nature's
+beauties. The zenith spreads its canopy of sapphire, and not a breath
+creeps through the rosy air. A magnificent array of clouds of numberless
+shapes come smartly into view. Some, far off, are voyaging their
+sun-bright paths in silvery folds; others float in golden groups. Some
+masses are embroidered with burning crimson; others are like "islands all
+lovely in an emerald sea." Over the glowing sky are splendid colourings.
+The flood of rosy light looks as if a great conflagration were below the
+horizon.
+
+I remember witnessing an especially brilliant sunset last autumn on the
+high-road between Kirriemuir and Blairgowrie. The setting sun shone upon
+the back of certain long trailing clouds which were much nearer me than a
+range behind. The fringes of the front range were brilliantly golden,
+while the face of those behind was sparklingly bright. Then the sun
+disappeared over the western hills, and his place was full of spokes of
+living light.
+
+Looking eastward, I observed on the horizon the base of the northern line
+of a beautiful rainbow--"the shepherd's delight" for fine weather.
+
+Soon in the west the light faded; but there came out of the east a lovely
+flush, and the general sky was presently flamboyant with afterglow. The
+front set of clouds was darker except on the edges, the red being on the
+clouds behind; and the horizon in the east was particularly rich with dark
+red hues.
+
+Gradually the eastern glow rose and reddened all the clouds, but the front
+clouds were still grey. The effect was very fine in contrast. The fleecy
+clouds overhead became transparently light red, as they stretched over to
+reach the silver-streaked west. The new moon was just appearing upright
+against a slightly less bright opening in the sky, betokening the firm
+hardness of autumn.
+
+Soon the colouring melted away, and the peaceful reign of the later
+twilight possessed the land.
+
+Now why that brilliancy of the east, when the west was colourless? Most of
+all you note the immense variety and wealth of reds. These are due to dust
+in the atmosphere. We are the more convinced of this by the very
+remarkable and beautiful sunsets which occurred after the tremendous
+eruption at Krakatoa, in the Straits of Sunda, thirty years ago. There was
+then ejected an enormous quantity of fine dust, which spread over the
+whole world's atmosphere. So long as that vast amount of dust remained in
+the air did the sunsets and afterglows display an exceptional wealth of
+colouring. All observers were struck with the vividly brilliant red
+colours in all shades and tints.
+
+The minute particles of dust in the atmosphere arrest the sun's rays and
+scatter them in all directions; they are so small, however, that they
+cannot reflect and scatter all; their power is limited to the scattering
+of the rays at the blue end of the spectrum, while the red rays pass on
+unarrested. The display of the colours of the blue end are found in
+numberless shades, from the full deep blue in the zenith to the
+greenish-blue near the horizon.
+
+If there were no fine dust-particles in the upper strata, the sunset
+effect would be whiter; if there were no large dust-particles, there would
+be no colouring at all. If there were no dust-particles in the air at all,
+the light would simply pass through into space without revealing itself,
+and the moment the sun disappeared there would be total darkness. The very
+existence of our twilight depends on the dust in the air; and its length
+depends on the amount and extension upwards of the dust-particles.
+
+But how have the particles been increased in size in the east? Because, as
+the sun was sinking, but before its rays failed to illumine the heavens,
+the temperature of the air began to fall. This cooling made the
+dust-particles seize the water-vapour to form haze-particles of a larger
+size. The particles in the east first lose the sun's heat, and first
+become cool; and the rays of light are then best sifted, producing a more
+distinct and darker red. As the sun dipped lower, the particles overhead
+became a turn larger, and thereby better reflected the red rays.
+Accordingly, the roseate bands in the east spread over to the zenith, and
+passed over to the west, producing in a few minutes a universal
+transformation glow.
+
+To produce the full effect often witnessed, there must be, besides the
+ordinary dust-particles, small crystals floating in the air, which
+increase the reflection from their surfaces and enhance the glow effects.
+In autumn, after sunset, the water-covered dust-particles become frozen
+and the red light streams with rare brilliancy, causing all reddish and
+coloured objects to glow with a rare brightness. Then the air glows with a
+strange light as of the northern dawn. From all this it is clear that,
+though the colouring of sunset is produced by the direct rays of the sun,
+the afterglow is produced by reflection, or, rather, radiation from the
+illuminated particles near the horizon.
+
+The effect in autumn is a stream of red light, of varied tones, and rare
+brilliancy in all quarters, unseen during the warmer summer. We have to
+witness the sunsets at Ballachulish to be assured that Waller Paton really
+imitated nature in the characteristic bronze tints of his richly painted
+landscapes.
+
+
+
+
+CHAPTER XIX
+
+A WINTER FOREGLOW
+
+
+Little attention has been paid to foreglows compared with afterglows,
+either with regard to their natural beauty or their weather forecasting.
+But either the ordinary red-cloud surroundings at sunrise, or the western
+foreglow at rarer intervals, betokens to the weather-prophet wet and
+gloomy weather. The farmer and the sailor do not like the sight, they
+depend so much on favourable weather conditions.
+
+Of course, sunrise to the aesthetic observer has always its charms. The
+powerful king of day rejoices "as a bridegroom coming out of his chamber"
+as he steps upon the earth over the dewy mountain tops, bathing all in
+light, and spreading gladness and deep joy before him. The lessening
+cloud, the kindling azure, and the mountain's brow illumined with golden
+streaks, mark his approach; he is encompassed with bright beams, as he
+throws his unutterable love upon the clouds, "the beauteous robes of
+heaven." Aslant the dew-bright earth and coloured air he looks in
+boundless majesty abroad, touching the green leaves all a-tremble with
+gold light.
+
+But glorious, and educating, and inspiring as is the sunrise in itself in
+many cases, there is occasionally something very remarkable that is
+connected with it. Rare is it, but how charming when witnessed, though
+till very recently it was all but unexplained. This is the _foreglow_.
+
+It is in no respect so splendid as the afterglow succeeding sunset; but,
+because of its comparative rarity, its beauty is enhanced. I remember a
+foreglow most vividly which was seen at my manse, in Strathmore, in
+January 1893. My bedroom window looked due west; I slept with the blind
+up. On that morning I was struck, just after the darkness was fading away,
+with a slight colouring all along the western horizon. The skeleton
+branches of the trees stood out strongly against it. The colouring
+gradually increased, and the roseate hue stretched higher. The old
+well-known faces that I used to conjure up out of the thin blended boughs
+became more life-like, as the cheeks flushed. There was rare warmth on a
+winter morning to cheer a half-despairing soul, tired out with the long
+hours of oil reading, and pierced to the heart by the never-ceasing
+rimes; yet I could not understand it.
+
+I went to the room opposite to watch the sunrise, for I had observed in
+the diary that the appearance of the sun would not be for a few minutes.
+There were streaks of light in the east above the horizon, but no colour
+was visible. That hectic flush--slight, yet well marked--which was
+deepening in the western heavens, had no counterpart in the east, except
+the colourless light which marked the wintry sun's near approach. As soon
+as the sun's rays shot up into the eastern clouds, and his orb appeared
+above the horizon, the western sky paled, the colour left it, as if
+ashamed of its assumed glory. A foreglow like that I have very rarely
+seen, and its existence was a puzzle to me till I studied Dr. Aitken's
+explanation of the afterglows after sunset. I had never come across any
+description of a foreglow; and, of course, across no explanation of the
+curious phenomenon. The western heavens were coloured with fairly bright
+roseate hues, while the eastern horizon was only silvery bright before the
+sun rose; whereas, after the sun appeared and coloured the eastern hills
+and clouds, the western sky resumed its leaden grey and colourless
+appearance. Why was that? What is the explanation?
+
+I have not space enough to repeat the explanation given already in the
+last chapter of the glorious phenomenon of the afterglow. But the
+explanation is similar. Before sunrise, the rays of the sun are reflected
+by dust-particles in the zenith to the western clouds. The colouring is
+intensified by the frozen water-vapour on these particles in the west.
+
+One thing I carefully noted. Ere mid-day, snow began to fall, and for some
+days a severe snow-storm kept us indoors. Then, at any rate, the foreglow
+betokened a coming storm. It was, like a rainbow in a summer morning, a
+decided warning of the approaching wet weather.
+
+
+
+
+CHAPTER XX
+
+THE RAINBOW
+
+
+The poet Wordsworth rapturously exclaimed--
+
+  "My heart leaps up when I behold
+  A rainbow in the sky."
+
+And old and young have always been enchanted with the beautiful
+phenomenon. How glorious is the parti-coloured girdle which, on an April
+morning or September evening, is cast o'er mountain, tower, and town, or
+even mirrored in the ocean's depths! No colours are so vividly bright as
+when this triumphal arch bespans a dark nimbus: then it unfolds them in
+due prismatic proportion, "running from the red to where the violet fades
+into the sky."
+
+A plain description of the formation of the rainbow is not very easily
+given, but a short sketch may be useful. Beautiful as is the ethereal bow,
+"born of the shower and colour'd by the sun," yet the marvellous effect is
+more exquisitely intensified in its gorgeous display when the hand of
+science points out the path in which the sun's rays, from above the
+western horizon, fall on the watery cloud, indicating fine weather--"the
+shepherd's delight."
+
+One law of reflection is that, when a ray of light falls on a plane or
+spherical surface, it goes off at the same angle to the surface as it
+fell. One law of refraction is that, when a ray of light passes through
+one medium and enters a denser medium (as from air to water), it is bent
+back a little. By refraction you see the sun's rays long after the sun has
+set; when the sun is just below the horizon, an observer, on the surface
+of the earth, will see it raised by an amount which is generally equal to
+its apparent diameter.
+
+The rays of different colours are bent back (when passing through the
+water) at different rates, some slightly, others more, from the red to the
+violet end. The rainbow, then, is produced by refraction and reflection of
+the several coloured rays of sunlight in the drops of water which make up
+falling rain.
+
+The sun is behind the observer, and its rays fall in a parallel direction
+upon the drops of rain before him. In each drop the light is dispersively
+refracted, and then reflected from the farther face of the drop; it
+travels back through the drop, and comes out with dispersing colours.
+
+According to the height of the sun, or the slope of its rays, a higher or
+lower rainbow will be formed. And, strange, no two people can see the very
+same bow; in fact the rainbow, as seen by the one eye, is not formed by
+the same water-drops as the rainbow seen by the other eye.
+
+When the primary bow is seen in most vivid colours on a dark cloud, a
+second arch, larger and fainter, is often seen. But the order of the
+colours is quite reversed. At a greater elevation, the sun's ray enters
+the lower side of a drop of rain-water, is refracted, reflected _twice_,
+and then refracted again before being sent out to the observer's eye. That
+is why the colours are reversed.
+
+_A one-coloured rainbow_ is a curious and rare phenomenon. It is a strange
+paradox, for the very idea of a rainbow brings up the seven colours--red,
+orange, yellow, green, blue, indigo, and violet. Yet Dr. Aitken tells us
+of a rainbow with one colour which he observed on Christmas Day, in 1888.
+
+He was taking his walk on the high ground south of Falkirk. In the east he
+observed a strange pillar-like cloud, lit up with the light of the setting
+sun. Then the red pillar extended, curved over, and formed a perfect arch
+across the north-eastern sky. When fully developed, this rainbow was the
+most extraordinary one which he had ever seen. There was no colour in it
+but red. It consisted simply of a red arch, and even the red had a
+sameness about it.
+
+Outside the rainbow there was part of a secondary bow. The Ochil Hills
+were north of his point of observation. These hills were covered with
+snow, and the setting sun was glowing with rosy light. Never had he seen
+such a depth of colour as was on them on this occasion. It was a deep,
+furnacy red. The sun's light was shorn of all the rays of short-wave
+length on its passage through the atmosphere, and only the red rays
+reached the earth. The reason why the Ochils glowed with so deep a red
+was owing to their being overhung by a dense curtain of clouds, which
+screened off the light of the sky. The illumination was thus principally
+that of the direct softer light of the sun.
+
+
+
+
+CHAPTER XXI
+
+THE AURORA BOREALIS
+
+
+He must be a very careless observer who has not been struck with the
+appearance of the streamers which occasionally light up the northern
+heavens, and which farmers consider to be indicators of strong wind or
+broken weather.
+
+The time was when the phenomenon was considered to be supernatural and
+portentous, as the chroniclers of spectral battles, when "fierce, fiery
+warriors fought upon the clouds, in ranks and squadrons, and right form of
+war." And even in the rural districts of Britain, the blood-coloured
+aurora, of October 24th, 1870, was considered to be the reflection of an
+enormous Prussian bonfire, fed by the beleaguered French capital.
+
+In joyful spirit, the Shetlanders call the beautiful natural phenomenon,
+"Merry Dancers." Burns associated their evanescence with the
+transitoriness of sensuous gratification:--"they flit ere you can point
+their place." And Tennyson spoke of his cousin's face lit up with the
+colour and light of love, "as I have seen the rosy red flushing in the
+northern night."
+
+Yet this phenomenon is to a great extent under the control of cosmical
+laws. One of the most difficult problems of our day has been to
+disentangle the irregular webwork of aurorae, and bring them under a law of
+periodicity, which depends upon the fluctuations of the sun's photosphere
+and the variations on the earth's magnetism, and which have such an
+important influence upon the fluctuations of the weather.
+
+The name "Aurora Borealis" was given to it by Gassendi in 1621.
+Afterwards, the old almanacs described it as the "Great Amazing Light in
+the North." In the Lowlands of Scotland, the name it long went by, of
+"Lord Derwentwater's Lights," was given because it suddenly appeared on
+the night before the execution of the rebel lord. In Ceylon aurorae were
+called "Buddha Lights."
+
+The first symptom of an aurora borealis is commonly a low arch of pale,
+greenish-yellow light, placed at right angles to the magnetic meridian.
+Sometimes rays cover the whole sky, frequently showing tremulous motion
+from end to end; and sometimes they appear to hang from the sky like the
+fringes of a mantle. They are among the most capricious of natural
+phenomena, so full of individualities and vagaries. To the glitter of
+rapid movement they add the charm of vivid colouring. It is strongly
+asserted that aurorae are preceded by the same general phenomena as
+thunder-storms. This was borne out by Piazzi Smith (late Astronomer-Royal
+for Scotland), who observed that their monthly frequency varies inversely
+with that of thunder-storms--both being safety-valves for the discharge of
+surplus electricity.
+
+Careful observers have, moreover, noticed a remarkable coincidence
+between the display of aurorae and the maxima of the sun's spots and of the
+earth's magnetic disturbances. Some have supposed that the light of the
+aurora is caused by clouds of meteoric dust, composed of iron, which is
+ignited by friction with the atmosphere. But there is this difficulty in
+the way, shooting stars are more frequent in the morning, while the
+reverse is the case with the aurora. The highest authorities have
+concluded, pretty uniformly, that aurorae are electric discharges through
+highly rarefied air, taking place in a magnetic field, and under the sway
+of the earth's magnetic induction. They are not inappropriately called
+"Polar lightnings," for when electricity misses the one channel it must
+traverse the other.
+
+The natives of the Arctic regions of North America pretend to foretell
+wind by the rapidity of the motions of the streamers. When they spread
+over the whole sky, in a uniform sheet of light, fine weather ensues.
+Fitzroy believed that aurorae in northern latitudes indicated and
+accompanied stormy weather at a distance. The same idea is still current
+among many farmers and fishermen in Scotland.
+
+Is there any audible accompaniment to the brilliant spectacle? The natives
+of some parts, with subtle hearing-power, speak of the "whizzing" sound
+which is often heard during auroral displays. Burns tells of their
+"hissing, eerie din," as echoes of the far-off songs of the Valkyries.
+Perhaps the most striking incident which corroborates this opinion
+occurred during the Franco-Prussian War. Rolier, a practised aeronaut,
+left Paris in a balloon, on his mission of city defence, and fourteen
+hours afterwards landed in Norway. He had reached the height of two and a
+half miles. When descending, he passed through a peculiar cloud of
+sulphurous odour, which emitted flashed light and a slight scratching or
+rustling noise. On landing, he witnessed a splendid aurora borealis. He
+must, therefore, have passed through a cloud in which an electrical
+discharge of an auroral nature was proceeding, accompanied with an audible
+sound. There is, moreover, no improbability of such sounds being
+occasionally heard, since a somewhat similar phenomenon accompanies the
+brush discharge of the electric machinery, to which the aurora bears
+considerable resemblance.
+
+Though no fixed conclusions are yet established about the causes of the
+brilliant auroral display, yet, as the results of laborious observations,
+we are assured that the stabler centre of our solar system holds in its
+powerful sway the several planets at their respective distances, supplying
+them all with their seasonable light and heat, vibrating sympathetic
+chords in all, and even controlling under certain--though to us still
+unknown--laws the electric streamers that flit, apparently lawlessly, in
+the distant earth's atmosphere.
+
+
+
+
+CHAPTER XXII
+
+THE BLUE SKY
+
+
+If we look at the sky overhead, when cloudless in the sunshine, we wonder
+what gives the air such a deep-blue colour. We are not looking, as
+children seem to do, into vacancy, away into the far unknown. And even, if
+that were the case, would not the space be quite colourless? What, then,
+produces the blueness?
+
+Some of the very fine dust-particles, even when clothed with an
+exceedingly thin coating of water-vapour, are carried very high; and,
+looking through a vast accumulation of these, we find the effect of a
+deep-blue colour.
+
+Why so? Because these particles are so small that they can only reflect
+the rays of the blue end of the spectrum; and the higher we ascend, the
+smaller are the particles and the deeper is the blue. But it is also
+because water, even in its very finest and purest form, is blue in colour.
+For long this was disputed. Even Sir Robert Christison concluded, after
+years of experimenting on Highland streams, that water was colourless.
+
+Of course, he admitted that the water in the Indian and Pacific Oceans has
+frequent patches of red, brown, or white colour, from the myriads of
+animalcules suspended in the water. Ehrenberg found that it was vegetable
+matter which gave to the Red Sea its characteristic name. But these, and
+similar waters, are not pure.
+
+It is to Dr. Aitken that the final discovery of the real colour of water
+is due. When on a visit to several towns on the shores of the
+Mediterranean, he set about making some very interesting experiments,
+which the reader will follow with pleasure.
+
+It is a well-known fact that colour transmitted through different bodies
+differs considerably from colour reflected by them. In his first
+experiment he took a long empty metal tube, open at one end, and closed
+at the other end by a clear-glass plate. This was let down vertically into
+the water, near to a fixed object, which appeared of most beautiful deep
+and delicate blue at a depth of 20 feet. Scientific men know that, if the
+colour of water is due to the light reflected by extremely small particles
+of matter suspended in the water, then the object looked at through it
+would have been illuminated with yellow (the complementary colour of
+blue). A blackened tube was then filled with water (which had a
+clear-glass plate fixed to the bottom), and white, red, yellow, and purple
+objects were sunk in the water, and these colours were found to change in
+the same way as if they were looked at through a piece of pale-blue glass.
+The white object appeared blue, the red darkened very rapidly as it sank,
+and soon lost its colour; at the depth of seven feet a very brilliant red
+was so darkened as to appear dark brick-red. The yellow object changed to
+green, and the purple to dark blue.
+
+But, still further to satisfy himself that water is really blue in itself,
+even without any particles suspended in it, he tested the colour of
+_distilled_ water. He filled a darkened tube with this water (clear-glass
+plates being at the ends of the tube), and looked through it at a white
+surface. The effect was the same as before, the colour was blue, almost
+exactly of the same hue as a solution of Prussian blue.
+
+This is corroborated by the fact that, the purer the water is in nature,
+the bluer is the tint when a large quantity is looked through. Some
+Highland lochs have crystal waters of the most extraordinary blue. Of
+course, some cling to the old idea that this is accounted for by the
+reflected blue of the clear heavens above. No doubt, if the sky be deep
+blue, then this blue light, when reflected by the surface of the water,
+will enrich and deepen the hue. But the water itself is _really_ blue.
+
+At the same time, the dust-particles suspended in the water have a great
+effect in making the water appear more beautiful, brilliant, and varied in
+its colouring; because little or no light is reflected by the interior of
+a mass of water itself. If a dark metal vessel be filled with a weak
+solution of Prussian blue, the liquid will appear quite dark and void of
+colour. But throw in some fine white powder, and the liquid will at once
+become of a brilliant blue colour. This accounts for the change of depth
+and brilliancy of colour in the several shores of the Mediterranean.
+
+When, then, you look at the face of a deep-blue lake on a summer
+evening--the heavens all aglow with the unrivalled display of colour from
+the zenith, stretching in lighter hues of glory to the horizon--though to
+you the calm water appears like a lake of molten metal glowing with
+sky-reflected light, so powerful and brilliant as entirely to overpower
+the light which is internally reflected, yet blue is the normal colour of
+the water: _blueness is its inherent hue_.
+
+Looking upwards, we observe three distinct kinds of blue in the sky from
+the horizon to the zenith. All painters in water-colours know that. Newton
+thought that the colour of the sky was produced in the same way as the
+colours in thin plates, the order of succession of the colours gradually
+increasing in intensity.
+
+
+
+
+CHAPTER XXIII
+
+A SANITARY DETECTIVE
+
+
+The impure state of the air in the rooms of a house can now be determined
+by means of colour alone. Dr. Aitken has invented a very simple instrument
+for that purpose; and this ought to be of great service to sanitary
+officers. It is called the koniscope--or dust-detective.
+
+The instrument consists of an air-pump and a metal tube with glass ends.
+Near one end of the test-tube is a passage by which it communicates with
+the air-pump, and near the other end is attached a stop-cock for admitting
+the air to be tested. It is not nearly so accurate as the dust-counter;
+but it is cheaper, more easily wrought, and more handy for quick work. All
+the grades of blue, from what is scarcely visible to deep, dark blue, may
+be attached alongside the tube on pieces of coloured glass; and opposite
+these colours are the numbers of dust-particles in the cubic inch of the
+similar air, as determined by the dust-counter.
+
+While the number of particles was counted by means of the dust-counter,
+the depth of blue given by the koniscope was noted; and the piece of glass
+of that exact depth of blue attached. A metal tube was fitted up
+vertically in the room, in such a way that it could be raised to any
+desired height into the impure air near the ceiling, so that supplies of
+air of different degrees of impurity might be obtained. To produce the
+impurity, the gas was lit and kept burning during the experiments. The air
+was drawn down through the pipe by means of the air-pump of the koniscope,
+and it passed through the measuring apparatus of the dust-counter on its
+way to the koniscope. It may be remarked that, by a stroke of the
+air-pump, the air within the test-tube is rarefied and the dust-particles
+seize the moisture in the super-saturated air to form fog-particles;
+through this fog the colour is observed, and the shade of colour
+determines the number of dust-particles in the air. These colours are
+named "just visible," "very pale blue," "pale blue," "fine blue," "deep
+blue," and "very deep blue."
+
+When making a sanitary inspection, the pure air should be examined first,
+and the colour corresponding to that should be considered as the normal
+health colour. Any increase from the depth would indicate that the air was
+being gradually contaminated; and the amount of increase in the depth of
+colour would indicate the amount of increase of pollution.
+
+As an illustration of what this instrument can detect, a room of 24 by 17
+by 13 feet was selected. The air was examined before the gas was lighted,
+and the colour in the test-tube was very faint, indicating a clear
+atmosphere. In all parts of the room this was found the same. A small tube
+was attached to the test-tube, open at the other end, for taking air from
+different parts of the room. Three jets of gas were then lit in the centre
+of the room, and observations at once begun with the koniscope.
+
+Within thirty-five seconds of striking the match to light the gas, the
+products of combustion had extended near the ceiling to the end of the
+room; this was indicated by the colour in the koniscope suddenly becoming
+a deep blue. In four minutes the deep-blue-producing air was got at a
+distance of two feet from the ceiling. In ten minutes there was strong
+evidence of the pollution all through the room. In half-an-hour the
+impurity at nine feet from the floor was very great, the colour being an
+intensely deep blue.
+
+The wide range of the indications of the instrument, from pure clearness
+to nearly black blue, makes the estimate of the impurity very easily taken
+with it; and, as there are few parts to get out of order, it is hoped it
+may come into general use for sanitary work.
+
+
+
+
+CHAPTER XXIV
+
+FOG AND SMOKE
+
+
+Just two hundred and forty years ago, Mr. John Evelyn, F.R.S., a
+well-known writer on meteorology, sent a curious tract to King Charles
+II., which was ordered to be printed by his Majesty. It was entitled
+"Fumifugium," and dealt with the great smoke nuisance in London. I find
+from the thesis that he had a very hazy idea of the connection between fog
+and smoke; and no wonder, for it is only lately that the connection has
+been fully explained.
+
+We know that without dust-particles there can be no fog, and that smoke
+supplies a vast amount of such particles. Therefore, in certain states of
+the atmosphere, the more smoke the more fog. In Mr. Evelyn's day the fog,
+which he called "presumptuous smoake," was at times so dense that men
+could hardly discern each other for the "clowd." His Majesty's only sister
+had complained of the damage done to her lungs by the contamination, and
+Mr. Evelyn was disgusted at the apathy of the people to do anything to
+remedy the nuisance. He deplored that that glorious and ancient city of
+London should wrap her stately head in "clowds of smoake, so full of stink
+and darknesse." He was of opinion that a method of charring coal so as to
+divest it of its smoke, while leaving it serviceable for many purposes,
+should be made the object of a very strict inquiry. And he was right. For
+it is now known that fog in a town is intensified by much smoke.
+
+In a city like London or Glasgow, where a great river, fed by warm streams
+of water from gigantic works, passes through its centre, fogs can never be
+entirely obliterated, for the dust-particles in the air (often four
+millions and upwards in the cubic inch) will seize with terrible avidity
+the warm vapour rising from the river. That is the main reason why fogs
+cannot there be put down. Smoke is being consumed to a great extent; yet
+we find particles of sulphur remaining, which seize the warm vapour and
+form fogs dense enough to check all traffic. The worst form of city fogs
+seems to be produced when the air, after first flowing slowly in one
+direction, then turns on its tracks and flows back over the city,
+bringing with it a black pall, the accumulated products of previous days,
+to which gets added the smoke and other impurities produced at the time.
+
+What irritated Mr. Evelyn was that, outside of London, the air was clear
+when passengers could not walk in safety within the city. So vexed was he
+about the contamination, that he made it the occasion of all the "cathars,
+phthisicks, coughs, and consumption in the city." He appealed to common
+sense to testify that those who repair to London soon take some serious
+illness. "I know a man," he said, "who came up to London and took a great
+cold, which he could never afterwards claw off again."
+
+Mr. Evelyn proposed that, by an Act of Parliament, the nuisance be
+removed; enjoining that all breweries, dye-works, soap and salt boilers,
+lime-burners, and the like, be removed five or six miles distant from
+London below the river Thames. That would have materially helped his
+cause.
+
+But there is more difficulty in the purification than he anticipated. Yet
+there was pluck in the old man pointing out the killing contamination and
+suggesting a possible remedy. He had the fond idea that thereby a certain
+charm, "or innocent magick," would make a transformation scene like
+Arabia, which is therefore "styl'd the Happy, attracting all with its gums
+and precious spices." In purer air fogs would be less dense, breathing
+would be easier, business would be livelier, life would be happier.
+
+Few, I suppose, have laid their hands on this curious Latin thesis, or its
+quaint translation, directing the King's attention to the fogs that were
+ruining London. Since that time the city has increased, from little more
+than a village, to be the dwelling-place of six millions of human beings,
+yet too little improvement has been made in the removal of this fog
+nuisance. King Edward's drive through London would be even more dangerous
+on a muggy, frosty day than was Charles II.'s, when science was little
+known.
+
+
+
+
+CHAPTER XXV
+
+ELECTRICAL DEPOSITION OF SMOKE
+
+
+A good deal of scientific work is being done in the way of clearing away
+fog and smoke; and this, through time, may have some practical results in
+removing a great source of annoyance, illness, and danger in large towns.
+Sir Oliver Lodge and Dr. Aitken have been throwing light upon the
+deposition of smoke in the air by means of electricity.
+
+If an electric discharge be passed through a jar containing the smoke from
+burnt magnesium wire, tobacco, brown paper, and other substances, the dust
+will be deposited so as to make the air clear. Brush discharge, or
+anything that electrifies the air itself, is the most expeditious.
+
+If water be forced upwards through a vertical tube (with a nozzle
+one-twentieth of an inch in diameter), it will fall to the ground in a
+fine rain; but, if a piece of rubbed (electrified) sealing-wax be held a
+yard distant from the place where the jet breaks into drops, they at once
+fall in large spots as in a thunder-shower. If paper be put on the ground
+during the experiment, the sound of pattering will be observed to be
+quite different. If a kite be flown into a cloud, and made to give off
+electricity for some time, that cloud will begin to condense into rain.
+
+Experiments with Lord Kelvin's recorder show that variations in the
+electrical state of the atmosphere precede a change of weather. Then, with
+a very large voltaic battery, a tremendous quantity of electricity could
+be poured into the atmosphere, and its electrical condition could be
+certainly disturbed. If this could be made practically available, how
+useful it would be to farmers when the crops were suffering from excessive
+drought! It might be more powerfully available than the imagined
+condensation of a cloud into rain by the reverberation caused by the
+firing of a range of cannon.
+
+But what is the practical benefit of this information? If electricity
+deposits smoke, it might be made available in many ways. The fumes from
+chemical works might be condensed; and the air in large cities, otherwise
+polluted, might be purified and rendered innocuous. The smoke of chimneys
+in manufacturing works might be prevented from entering the atmosphere at
+all. In flour-mills and coal-mines the fine dust is dangerously explosive.
+In lead, copper, and arsenic works, it is both poisonous and valuable.
+
+Lead smelters labour under this difficulty of condensing the fume which
+escapes along with the smoke from red-lead smelting furnaces; and it was
+considered that an electrical process of condensation might be made
+serviceable for the purpose. At Bagillt, the method used for collecting or
+condensing the lead fume is a large flue two miles long; much is retained
+in this flue, but still a visible cloud of white-lead fume continually
+escapes from the top of the chimney. There is a difficulty in the way of
+depositing fumes in the flue by means of a sufficient discharge of
+electricity, viz. the violent draught which is liable to exist there, and
+which would mechanically blow away any deposited dust.
+
+But Dr. Aitken suggests that regenerators might be used along with the
+electricity. The warm fumes might be taken to a cold depositor, where (by
+the ordinary law of cold surfaces attracting warm dust-particles) the
+impurities would be removed, and, when purified, the air would again be
+taken through a hot regenerator before being sent up the chimney. By a
+succession of these chambers, with the assistance of electric currents,
+the air, impregnated with the most deleterious particles, or valuable
+dust, could be rendered innocuous.
+
+The sewage of our towns must be cleaned of its deleterious parts before
+being run into the streams which give drink to the lower animals, because
+an Act of Parliament enforces the process. Why, then, ought we not to have
+similar compulsion for making the smoke from chemical and other noxious
+works quite harmless before being thrown into the air which contains the
+oxygen necessary for the life of human beings?
+
+There seems to be a good field before electricians to catch the smoke on
+the wing and deposit its dust on a large scale. This seems to be a matter
+beyond our reach at present, except in the scientist's laboratory; but
+certainly it is a "consummation devoutly to be wished."
+
+
+
+
+CHAPTER XXVI
+
+RADIATION FROM SNOW
+
+
+One night a most interesting paper by Dr. Aitken, on "Radiation from
+Snow," was read by Professor Tait to the Fellows of the Royal Society of
+Edinburgh. I remember that Dr. Alex. Buchan--the greatest meteorologist
+living--spoke afterwards in the very highest terms of the subject-matter
+of the paper. This was corroborated by Lord Kelvin, Lord MacLaren, and
+Professor Chrystal.
+
+Dr. Aitken had been testing the radiating powers of different substances.
+Snow in the shade on a bright day at noon is 7 deg. Fahr. colder than the air
+that floats upon it, whereas a black surface at the same is only 4 deg.
+colder. This difference diminishes as the sun gets lower; and at night
+both radiate almost equally well.
+
+I select, among the careful and numerous observations, the notes on
+January 19, 1886; for I took note of the cold of that day in my diary. It
+was the coldest day of the whole of that winter. The barometer was 28.8
+inches, and the thermometer 4 deg.--that is, 28 deg. of frost. According to Dr.
+Buchan, that January had only two equal in average cold for fifty years.
+
+On January 19, at 10 A.M., when the air was at 20 deg. and the sky clear, a
+black surface registered 16 deg. and the upper layer of snow 12 deg., showing a
+difference of 4 deg. when both surfaces were colder than the superincumbent
+air. It is curious to note that, on February 5 of the same year, at the
+same hour, when the sky was overcast, the air was at 23 deg., the black
+surface registered 29 deg., and the snow 25 deg., showing again the difference of
+4 deg.; but, in this case, both surfaces were warmer than the air. In both
+cases the radiation at night was equal.
+
+This small absorbing power of snow for heat reflected and radiated from
+the sky during the day must have a most important effect on the
+temperature of the air. The temperature of lands when covered with snow
+must be much lower than when free from it. And, when once a country has
+become covered with snow, there will be a tendency towards glacial
+conditions.
+
+But, besides being a bad absorber of heat from the sky, snow is also a
+very poor conductor of heat. On that very cold night (January 18), when
+there was a depth of 5-1/2 inches of snow on the ground, and the night
+clear, with strong radiation, the temperature of the surface of the snow
+was 3 deg. Fahr., and a minimum thermometer on the snow showed that it had
+been down to zero some time before. A thermometer, plunged into the snow
+down to the grass, gave the most remarkable register of 32 deg. Through the
+depth of 5-1/2 inches of snow there was a difference of temperature of
+29 deg. This was confirmed by removing the snow, and finding that the grass
+was unfrozen. As the ground was frozen when the snow fell, it would appear
+that the earth's heat slowly thawed it under the protection of the snow.
+
+The protection afforded by the bad-conducting power of snow is of great
+importance in the economy of nature. How vegetation would suffer, were it
+exposed to a low temperature, unprotected by the snow-mantle! So that,
+though the continued snow cools the air for animals that can look after
+their own heating, it keeps warm the soil; and vegetation prospers under
+the genial covering. The fine rich look of the young wheat-blades, after a
+continued snow has melted, must strike the most careless observer. Instead
+of the half-blackened tips and semi-sickly blades, which we see in a field
+of young wheat after a considerable course of dry frost without snow, we
+have a rich, healthy green which shows the vital energy at work in the
+plants. Or even in the town gardens, after a continued snow has been
+melted away by a soft, western breeze, we are struck with the white,
+peeping buds of the snowdrop and the finely springing grass in the sward.
+
+Yet the snow-covering gives durability to cold weather. This has been
+demonstrated by Dr. Woeikof, the distinguished Russian meteorologist. On
+this account the spring months of Russia and Siberia are intensely cold.
+The plants, then, which in winter are unable by locomotion to keep
+themselves in health, are protected by the snow-mantle which chills the
+air for animals that can keep themselves in heat by exercise. What a grand
+compensating power is here!
+
+
+
+
+CHAPTER XXVII
+
+MOUNTAIN GIANTS
+
+
+Some mysterious physical phenomena can be clearly explained by the aid of
+science. The mountain giants that at times haunt the lonely valleys, and
+strike with fear the superstitious dwellers there, are only the enlarged
+shadows of living human beings cast upon a dense mist.
+
+The two most startling of these "eerie" phenomena are the spectres of
+Adam's Peak and the Brocken.
+
+The phenomena sometimes to be observed at Adam's Peak, in Ceylon, are very
+remarkable. Many travellers have given vivid accounts of these. On one
+occasion the Hon. Ralph Abercromby, in his praiseworthy enthusiasm for
+meteorological research, went there with two scientific friends to witness
+the strange appearance. The conical peak, a mile and a half high,
+overlooks a gorge west of it. When, then, the north-east monsoon blows the
+morning mist up the valley, light wreaths of condensed vapour pass to the
+right of the Peak, and catch the shadows at sunrise.
+
+This party reached the summit early one morning in February. The foreglow
+began to brighten the under-surface of the stratus-cloud with orange, and
+patches of white mist filled the hollows. Soon the sun peeped through a
+chink in the clouds, and they saw the pointed shadow of the Peak lying on
+the misty land. Then a prismatic circle, with the red inside, formed round
+the shadow. The meteorologist waved his arms about, and immediately he
+found giant shadowy arms moving in the centre of the rainbow.
+
+Soon they saw a brighter and sharper shadow of the Peak, encircled by a
+double bow, and their own spectral arms more clearly visible. The shadow,
+the double bow, and the giant forms, combined to make this phenomenon the
+most marked in the whole world.
+
+The question has been frequently asked: Why are such aerial effects not
+more widely observed? There are not many mountains of this height and of a
+conical shape; and still fewer can there be where a steady wind, for
+months together, blows up a valley so as to project the rising morning
+mist at a suitable height and distance on the western side, to catch the
+shadow of the peak at sunrise.
+
+The most famous place in Europe for witnessing the awe-inspiring
+phenomenon is the Brocken, in Germany--3740 feet in height. The only great
+disappointment there is that the conditions rarely combine at sunrise or
+sunset to have "the spectre" successful.
+
+In July 1892, my daughter and I were spending some weeks at Harzburg, and,
+of course, we had to visit the Brocken and take stock of the world-known
+phenomenon. At mid-day, the air at the flat summit was cold, clear, and
+hard. The boulders are of enormous size; and near the "Noah's Ark" Hotel
+and Observatory many are piled up in a mass, on which the observers stand
+at the appointed time for having their shadows projected on the misty air
+in the valleys.
+
+At five o'clock in the afternoon the sky was brilliantly clear on the
+summit of the Brocken; but the wind was rising from the sun's direction,
+and the mist was filling up the wide-spread eastern valley. We stood on
+the "spectre" boulders, and our shadows were thrown on the grass, just as
+at home. However, they fell upon large patches of white heather, which
+there is very plentiful.
+
+At six o'clock the sun was still shining beautifully, and we anxiously
+waited for the time when it would be low enough to raise our shadows to
+the misty wall. An hour afterwards, a hundred visitors were out, and many
+of us were on the "spectre" stones. There was great excitement in
+anticipation of the weird appearances, which had attracted us from such a
+distance.
+
+But, almost at the moment of success, the sun descended behind a belt of
+purple cloud, and all we saw was part of a rainbow on the misty hollow.
+For the sun never appeared again. This was intensely saddening, seeing
+that, but for that stratum of cloud above the horizon, the phenomenon
+would have been graphically displayed.
+
+The cold became suddenly intense, and we had to sleep with a freezing mist
+enveloping the hotel. In vain did we wait for the wakening call, to tell
+us of sunrise; for the sun could not pierce the mist, and we had to return
+home disappointed.
+
+Sometimes the rainbow colours assume the shapes of crosses instead of
+circles. Occasionally a bright halo will be seen above the shadow-head of
+the observer, concentric rainbows enclosing all. In some recorded cases
+the grand effect must have been simply glorious.
+
+Scientific observation has done much to dispel the superstition which has
+clung so tenaciously to the Highland mind. The lonely grandeur of the
+weird mountain giants has been clearly explained as perfectly natural, yet
+the awe-striking feeling cannot be entirely driven off.
+
+
+
+
+CHAPTER XXVIII
+
+THE WIND
+
+
+Once was the remark pointedly made: "The wind bloweth where it listeth."
+And that is nearly true still. The leading winds are under the calculation
+of the meteorologist, but the others will not be bound by laws.
+
+Yet there are instruments for measuring the velocity and force of the
+wind, after it is on; but "whence it comes" is a different matter. A
+gentle air moves at the rate of 7 miles an hour; a hurricane from 80 to
+150 miles, pressing with 50 lbs. on the square foot exposed to its fury.
+Some of the gusts of the Tay Bridge storm, in 1879, had a velocity of 150
+miles an hour, with a pressure of 80 to 90 lbs. to the square foot.
+
+Before steamers supplanted so many sailing vessels, seamen required to be
+always on the alert as to the direction and strength of the wind, and the
+likelihood of any sudden change; and they chronicled twelve different
+strengths from "faint air" to a "storm."
+
+In general, the wind may be considered to be the result of a change of
+pressure and temperature in the atmosphere at the same level. The air of a
+warmer region, being lighter, ascends, and gives place to a current of
+wind from a colder region. These two currents--the higher and the
+lower--will continue to blow until there is equilibrium.
+
+The trade winds are regular and constant. These were much followed in the
+days of old. A vast amount of air in the tropics gets heated and ascends,
+being lighter, and travels to the colder north. A strong current rushes in
+from the north to take its place. But the earth rotates round its axis
+from west to east, and the combined motions make two slant wind
+directions, which are called the "trade winds," because they were so
+important in trade navigation.
+
+Among the periodical winds are the "land and sea breezes." During the day,
+the land on the sea coast is warmer than the sea; accordingly, the air
+over the land becomes heated and ascends, the fine cool breeze from the
+sea taking its place. Towards evening there is the equilibrium of
+temperature which produces a temporary calm. Soon the earth chills, and
+the sea is counterbalancingly warm--as sea-water is steadier as to
+temperature than is land--the air over the sea becomes warmer, and
+ascends, the current from the land rushing in to take its place. Hence
+during the night the wind is reversed, until in the morning again the
+equilibrium is restored and there is a calm, so far as these are
+concerned. These are therefore called the "land and sea breezes." Of
+course, it is within the tropics that these breezes are most marked. By
+the assistance of other winds, a hurricane will there occasionally destroy
+towns and bring about much damage and loss of life; but better that
+hundreds should perish by a hurricane than thousands by the pestilence
+which, but for the storm, would have done its dire work.
+
+In countries where the differences of pressure are more marked than the
+differences of temperature, in the surrounding regions the strength of
+the wind thereby occasioned is far stronger than the land and sea breezes.
+
+The variable winds are more conflicting. These depend on purely local
+causes for a time, such as "the nature of the ground, covered with
+vegetation or bare; the physical configuration of the surface, level or
+mountainous; the vicinity of the sea or lakes, and the passage of storms."
+Among these winds are the simoom and sirocco.
+
+The _east_ winds, which one does not care about in the British Islands
+during the spring time, are occasioned by the powerful northern current
+which rushes south from the northern regions in Europe. Dr. Buchan points
+out a very common mistake among even intelligent observers who shudder at
+the hard east winds. It is generally held that these winds are damp. They
+are unhealthy, but they are dry. It is quite true that many easterly winds
+are peculiarly moist; all that precede storms are so far damp and rainy;
+and it is owing to this circumstance that, on the east coast of Scotland,
+the east winds are searching and carry most of the annual rainfall there.
+But all of these moist easterly winds, however, soon turn to some westerly
+point. The real east wind, so much feared by invalids, does not turn to
+the west; it is exceeding dry. Curious is it that brain diseases, as well
+as consumption, reach their height in Britain while east winds prevail.
+Once in Edinburgh, during the early spring, I had rheumatic fever, and
+during my convalescence my medical adviser, Dr. Menzies, would not let me
+have a short drive until the wind changed to the west. The first thing I
+anxiously watched in the morning was the flag on the Castle; and for
+nearly two months it always waved from the east. How heart-depressing!
+
+Creatures are we in the hands of nature's messengers. We so much depend
+upon the weather for our happiness. Joyful are we when the honey-laden
+zephyr waves the long grass in June, or when
+
+  "The gentle wind, a sweet and passionate wooer,
+  Kisses the blushing leaf."
+
+Compared with this, how terrible is Shakespeare's allusion to the
+appalling aspects of the storm:--
+
+  "I have seen tempests, when the scolding winds
+  Have rived the knotty oaks; and I have seen
+  The ambitious ocean swell, and rage and foam,
+  To be exalted with the threat'ning clouds;
+  But never till to-night, never till now,
+  Did I go through a tempest dropping fire."
+
+
+
+
+CHAPTER XXIX
+
+CYCLONES AND ANTI-CYCLONES
+
+
+The criticism of the weather in the meteorological column of our daily
+newspapers invariably speaks of "cyclones." It is, therefore, advisable to
+give as plain an explanation of these as possible. Cyclones are
+"storm-winds." Their nature has to be carefully studied by meteorologists,
+who are industriously at work to ascertain some scientific basis for the
+atmospheric movements.
+
+What is the cause of the spiral movement in storm-winds? In their centre
+the depression of the barometer is lowest, because the atmosphere there is
+lightest. As the walls of the spiral are approached, the barometer rises.
+
+Dr. Aitken has ingeniously hit upon an experiment to illustrate a spiral
+in air. All that is necessary is a good fire, a free-going chimney, and a
+wet cloth. The cloth is hung up in front of the fire, and pretty near it,
+so that steam rises readily from its surface; and, when there are no
+air-currents in the room, the steam will rise vertically, keeping close to
+the cloth. But if the room has a window in the wall, at right angles to
+the fireplace, so as to cause the air coming from it to make a
+cross-current past the fire, then a cyclone will be formed, and the vapour
+from the cloth will be seen circling round. When the cyclone is well
+formed, all the vapour is collected into the centre of the cyclone, and
+forms a white pillar extending from the cloth to the chimney. This
+experiment shows that no cyclone can form without some tangential motion
+in the air entering the area of low-pressure.
+
+Now to illustrate the spiral approach. Fill with water a cylindrical glass
+vessel, say 15 inches in diameter and 6 inches deep. Have an orifice with
+a plug a little from the centre of the bottom. Remove the plug, the water
+runs out, passing round the vessel in a vortex form. But, as the passage
+between the orifice (or centre of the cyclone) and the temporary division
+is narrower than in any other place, the water has to pass this part much
+more quickly than at any other place. And this curious result is observed:
+the top of the cyclone no longer remains over the orifice, but _travels_
+in the direction of the water which is moving most speedily. Similar to
+this is the cyclone in the atmosphere; its centre also moves in the
+direction of the quickest flowing wind that enters it.
+
+Dr. Aitken is of opinion that, in forecasting storms, too little attention
+has been paid to the _anti-cyclones_. They do more than simply follow and
+fill up the depression made by the cyclones. They initiate and keep up
+their own circulation, and collect the materials with which the cyclones
+produce their effect. Neither could work efficiently without the other.
+
+Suppose a large area on the earth over which the air is still in bright
+sunshine. After a time, when the air gets heated and charged with vapour,
+columns of air would begin to ascend in a disorderly fashion. But suppose
+an anti-cyclone is blowing at one side of this area. When the upper air
+descends to the earth, it spreads outwards in all directions; but the
+earth's rotation interferes and changes the radial into a spiral motion.
+The anti-cyclonic winds will prevent the formation of local cyclones, and
+drive all the moist, hot air to its circumference, just above the earth.
+The anti-cyclone forces its air tangentially into the cyclone, and gives
+it its direction and velocity of rotation, also the direction and rate of
+travel of the centre of depression. The earth's rotation is the original
+source of the rotatory movements, but both intensify the initial motion.
+
+Accordingly, the cyclone must travel in the direction of the strongest
+winds blowing into it, just as the vortex in the vessel with the eccentric
+orifice travelled in the direction of the quickest moving water. This is
+verified by a study of the synoptic charts of the Meteorological Office.
+
+The sun's heat has always been looked upon as the main source of the
+energy of our winds, but some account must also be taken of the effects of
+cold. It is well known that the mean pressure over Continental areas is
+high during winter and low during summer. As the sun's rays during summer
+give rise to the cyclonic conditions, so the cooling of the earth during
+winter gives rise to anti-cyclonic conditions. It is found during the
+winter months in several parts of the Continent that as the temperature
+falls the pressure rises, producing anti-cyclones over the cold area;
+whereas, when the temperature begins to rise, the pressure falls, and
+cyclones are attracted to the warming area.
+
+Small natural cyclones are often seen on dusty roads, the whirling column
+having a core of dusty air, and the centre of the vortex travelling along
+the road, tossing up the dust in a very disagreeable way to pedestrians.
+Sometimes such a cyclone will toss up dry leaves to a height of four or
+five feet. They are very common; but it is only when dust, leaves, or
+other light material is present that they are visible to the eye.
+
+
+
+
+CHAPTER XXX
+
+RAIN PHENOMENA
+
+
+The soft rain on a genial evening, or the heavy thunder-showers on a
+broiling day, are too well known to be written about. Sometimes rain is
+earnestly wished for, at other times it is dreaded, according to the
+season, seed-time or harvest. Some years, like 1826, are very deficient in
+rainfall, when the corn is stunted and everything is being burnt up; other
+years, like 1903, there is an over-supply, causing great damage to
+agriculture. The year 1903 will long be remembered for its continuous
+rainfall; it is the record year; no year comes near it for the total
+rainfall all over the kingdom.
+
+Rain is caused by anything that lowers the temperature of the air below
+the dew-point, but especially by winds. When a wind has blown over a
+considerable area of ocean on to the land, there is a likelihood of rain.
+When this wind is carried on to higher latitudes, or colder parts, there
+is a certainty of rain. Of course, in the latter case the rain will fall
+heavier on the wind side than on the lee side.
+
+For short periods, the heaviest falls or "plouts" of rain are during
+thunder-storms. When the raindrops fall through a broad, cold stratum of
+air, they are frozen into hail, the particles of which sometimes reach a
+large size, like stones. Of course, water-spouts now and again are of
+terrible violence.
+
+One of the heaviest rainfalls yet recorded in Great Britain was about
+2-1/4 inches in forty minutes at Lednathie, Forfarshire, in 1887. Now 1
+inch deep of rain means 100 tons on an imperial acre; so the amount of
+water falling on a field during that short time is simply startling. The
+heaviest fall for one day was at Ben Nevis Observatory, being fully 7-1/4
+inches in 1890. In other parts of the world this is far exceeded. In one
+day at Brownsville, Texas, nearly 13 inches fell in 1886. On the Khasi
+hills, India, 30 inches on each of five successive days were registered.
+At Gibraltar, 33 inches were recorded in twenty-six hours.
+
+The heaviest rainfalls of the globe are occasioned by the winds that have
+swept over the most extensive ocean-areas in the tropics. On the summer
+winds the rainfall of India mainly depends; when this fails, there is most
+distressing drought. Reservoirs are being erected to meet emergencies.
+
+From Dr. Buchan's statistics it is found that the annual rainfall at
+Mahabaleshwar is 263 inches; at Sandoway 214; and at Cherra-pungi 472
+inches, the largest known rainfall anywhere on the globe. Over a large
+part of the Highlands of Scotland more than 80 inches fall annually, while
+in some of the best agricultural districts there it does not exceed 30
+inches.
+
+Of all meteorological phenomena, rainfall is the most variable and
+uncertain. Symons gives as tentative results from twenty years'
+observations in London--(1) In winter, the nights are wetter than the
+days; (2) in spring and autumn, there is not much difference; (3) in
+summer, nearly half as much again by day as by night.
+
+The wearisomeness of statistics may be here relieved by a short
+consideration of the _splash_ of a drop of rain. Watching the
+drop-splashes on a rainy day in the outskirts of the city, when unable to
+get out, I brought to my recollection the marvellous series of experiments
+made by Professor A. M. Worthington in connection with these phenomena. Of
+course, I could not see to proper advantage the formation of the
+splashes, as the heavy raindrops fell into these tiny lakes on the quiet
+road. There is not the effect of the huge thunder-drops in a stream or
+pool. The building up of the bubbles is not here perfect, for the domes
+fail to close, nor are the emergent columns visible to the naked eye. It
+is a pity; for R. L. Stevenson once wrote of them in his delightful
+"Inland Voyage," when he canoed in the Belgian canals, as thrown up by the
+rain into "an infinity of little crystal fountains."
+
+Beautiful is this effect if one is under shelter, every dome seeming quite
+different in contour and individuality from all the rest. But terrible is
+it when out fishing on Loch Earn, even with the good-humoured old Admiral,
+when the heavy thunder-drops splash up the crystal water, and one gets
+soaked to the skin, sportsman-like despising an umbrella.
+
+There is, however, a scientific interest about the splash of a drop. The
+phenomenon can be best seen indoors by letting a drop of ink fall upon the
+surface of pure water in a tumbler, which stands on white paper. It is an
+exquisitely regulated phenomenon, which very ideally illustrates some of
+the fundamental properties of fluids.
+
+When a drop of milk is let fall upon water coloured with aniline dye, the
+centre column of the splash is nearly cylindrical, and breaks up into
+drops before or during its subsequent descent into the liquid. As it
+disappears below the surface, the outward and downward flow causes a
+hollow to be again formed, up the sides of which a ring of milk is
+carried; while the remainder descends to be torn a second time into a
+beautiful vortex ring. This shell or dome is a characteristic of all
+splashes made by large drops falling from a considerable height, and is
+extremely pretty. Sometimes the dome closes permanently over the
+imprisoned air, and forms a large bubble floating upon the water. The most
+successful experiments, however, have been carried through by means of
+instantaneous photography, with the aid of a Leyden-jar spark, whose
+duration was less than the ten-millionth of a second. But the simple
+experiments, without the use of the apparatus, will while away a few hours
+on a rainy afternoon, when condemned to the penance of keeping within
+doors.
+
+
+
+
+CHAPTER XXXI
+
+THE METEOROLOGY OF BEN NEVIS
+
+
+Several large and very important volumes of the Royal Society of Edinburgh
+are devoted to statistics connected with the meteorology of Ben Nevis.
+Most of the abstracts have been arranged by Dr. Buchan; while Messrs.
+Buchanan, Omond, and Rankine have taken a fair share of the work.
+
+This Observatory, as Mr. Buchanan remarks, is unique, for it is
+established in the clouds; and the observations made in it furnish a
+record of the meteorology of the clouds. It is 4406 feet above the level
+of the sea; and as there is a corresponding Observatory at Fort William,
+at the base of the mountain, it is peculiarly well fitted for important
+observations and weather forecasting. The mountain, too, is on the west
+sea-coast of Scotland, exposed immediately to the winds from the Atlantic,
+catching them at first hand. It is lamentable to think that, when the
+importance of the observations made at the two Observatories was becoming
+world known, funds could not be got to carry them on. Ben Nevis is the
+highest mountain in the British Islands, best fitted for meteorological
+observations; yet these have been stopped for want of money.
+
+Dr. Buchan's valuable papers were published before any one dreamed of the
+stoppage of the work, which had such an important bearing on men engaged
+in business or taken up with open-air sport. From these I shall sift out a
+few facts that even "mute, inglorious" meteorologists may be interested in
+knowing.
+
+For a considerable time the importance of the study of the changes of the
+weather has come gradually to be recognised, and an additional impetus was
+given to the prosecution of this branch of meteorology when it was seen
+that the subject had intimate relations to the practical question of
+weather forecasts, including storm warnings. Weather maps, showing the
+state of the weather over an extensive part of the surface of the globe,
+began to be constructed; but these were only indicators from places at the
+level of the sea.
+
+The singular advantages of a high-level observatory occurred to Mr. Milne
+Home in 1877; and Ben Nevis was considered to be in every respect the most
+suitable in this country. The Meteorological Council of the Royal Society
+of London offered in 1880, unsolicited, L100 annually to the Scottish
+Meteorological Society, to aid in the support of an Observatory, the only
+stipulation being that the Council be supplied with copies of the
+observations.
+
+From June to October, in 1881, Mr. Wragge made daily observations at the
+top of the Ben; and simultaneous observations were made, by Mrs. Wragge,
+at Fort William. A second series, on a much more extended scale, was made
+in the following summer.
+
+Funds were secured to build an Observatory; and, in November 1883, the
+regular work commenced, consisting of hourly observations by night as well
+as by day. Until a short time ago, these were carried on uninterruptedly.
+Telegraphic communications of each day's observations were sent to the
+morning newspapers; and now we are disappointed at not seeing them for
+comparison.
+
+The whole of the observations of temperature and humidity were of
+necessity eye-observations. For self-registering thermometers were
+comparatively useless when the wind was sometimes blowing at the rate of
+100 miles an hour. Saturation was so complete in the atmosphere that
+everything exposed to it was dripping wet. Every object exposed to the
+outside frosts of winter soon became thickly incrusted with ice.
+Snowdrifts blocked up exposed instruments. Accordingly, the observers had
+to use their own eyes, often at great risks.
+
+The instruments in the Ben Nevis Observatory, and in the Observing Station
+at Fort William, were of the best description. Both stations were in
+positions where the effects of solar and terrestrial radiation were
+minimised. No other pair of meteorological stations anywhere in the world
+are so favourably situated as these two stations, for supplying the
+necessary observations for investigating the vertical changes of the
+atmosphere. It is to be earnestly hoped, therefore, that funds will be
+secured to resume the valuable work.
+
+The rate of the decrease of temperature with height there is 1 deg. Fahr. for
+every 275 feet of ascent, on the mean of the year. The rate is most rapid
+in April and May, when it is 1 deg. for each 247 feet; and least rapid in
+November and December, when it is 1 deg. for 307 feet. This rate agrees
+closely with the results of the most carefully conducted balloon ascents.
+The departures from the normal differences of temperature, but more
+especially the inversions of temperature, and the extraordinarily rapid
+rates of diminution with height, are intimately connected with the
+cyclones and anti-cyclones of North-Western Europe; and form data, as
+valuable as they are unique, in forecasting storms.
+
+The most striking feature of the climate of Ben Nevis is the repeated
+occurrence of excessive droughts. For instance, in the summer and early
+autumn of 1885, low humidities and dew-points frequently occurred.
+Corresponding notes were observed at sea-level. During nights when
+temperature falls through the effects of terrestrial radiation, those
+parts of the country suffer most from frosts over which very dry states of
+the air pass or rest; whereas, those districts, over which a more humid
+atmosphere hangs, will escape. On the night of August 31 of that year, the
+potato crop on Speyside was totally destroyed by the frost; whereas at
+Dalnaspidal, in the district immediately adjoining, potatoes were
+scarcely--if at all--blackened.
+
+The mean annual pressure at Ben Nevis was 25.3 inches, and at Fort William
+29.8, the difference being 4-1/2 inches for the 4400 feet.
+
+For the whole year, the difference between the mean coldest hour, 5 A.M.,
+and the warmest hour, 2 P.M., is 2 deg. For the five months, from October to
+February, the mean daily range of temperature varied only from O.6 to 1.5.
+This is the time of the year when storms are most frequent; and this small
+range in the diurnal march of the temperature is an important feature in
+the climatology of Ben Nevis; for it presents, in nearly their simple
+form, the great changes of temperature accompanying storms and other
+weather changes, which it is so essential to know in forecasting weather.
+
+The daily maximum velocity of the wind occurs during the night, the daily
+differences being greatest in summer and least in winter. A blazing sun in
+the summer daily pours its rays on the atmosphere, and a thick envelope of
+cloud has apparently but little influence on the effect of the sun's rays.
+Thunder-storms are essentially autumn and winter phenomena, being rare in
+summer.
+
+According to Mr. Buchanan, the weather on Ben Nevis is characterised by
+great prevalence of fog or mist. In continuously clear weather it
+practically never rains on the mountain at all. In continuously foggy
+weather, on the other hand, the average daily rainfall is 1 inch. There is
+a large and continuous excess of pressure in clear weather over that of
+foggy weather. The mean temperature of the year is 3-1/2 degrees higher
+in clear than in foggy weather. In June the excess is 10 degrees. The
+nocturnal heating in the winter is very clearly observed. This has been
+noticed before in balloons as well as on mountains. The fog and mist in
+winter are much denser than in summer. Whether wet or dry, the fog which
+characterises the climate of the mountain is nothing but _cloud_ under
+another name.
+
+
+
+
+CHAPTER XXXII
+
+THE WEATHER AND INFLUENZA
+
+
+Some remarkable facts have been deduced by the late Dr. L. Gillespie,
+Medical Registrar, from the records of the Royal Infirmary of Edinburgh.
+He considered that it might lead to interesting results if the admissions
+into the medical wards were contrasted with the varying states of the
+atmosphere. The repeated attacks of influenza made him pay particular
+attention to the influence of the weather on that disease.
+
+The meteorological facts taken comprise the weekly type of weather, _i.e._
+cyclonic or anti-cyclonic, the extremes of temperature for the district
+for each week, and the mean weekly rainfall for the same district. More
+use is made of the extremes than of the mean, for rapid changes of
+temperature have a greater influence on disease than the actual mean.
+
+The period which he took up comprises the seven years 1888-1895. There was
+a yearly average of admissions of 3938; so that he had a good field for
+observation. Six distinct epidemics of influenza, varying in intensity,
+occurred during that period; yet there had been only twenty-three attacks
+between 1510 and 1890. Accordingly, these six epidemics must have had a
+great influence on the incidence of disease in the same period, knowing
+the vigorous action of the poison on the respiratory, the circulatory, and
+the nervous systems. The epidemics of influenza recorded in this country
+have usually occurred during the winter months.
+
+The first epidemic, which began on the 15th of December 1889 and continued
+for nine weeks, was preceded by six weeks of cyclonic weather, which was
+not, however, accompanied by a heavy rainfall. Throughout the course of
+the disease, the type continued to be almost exclusively cyclonic, with a
+heavy rainfall, a high temperature, and a great deficiency of sunshine.
+The four weeks immediately following were also chiefly cyclonic, but with
+a smaller rainfall.
+
+The summer epidemic of 1891 followed a fine winter and spring, during
+which anti-cyclonic conditions were largely prevalent. But the epidemic
+was immediately preceded by wet weather and a low barometer. It took place
+in dry weather, and was followed by wet, cyclonic weather in turn.
+
+The great winter epidemic of 1891 followed an extremely wet and broken
+autumn. Simultaneously with the establishment of an anti-cyclone, with
+east wind, practically no rain, and a lowering temperature, the influenza
+commenced. Great extremes in the temperature followed, the advent of
+warmer weather and more equable days witnessing the disappearance of the
+disease.
+
+The fourth epidemic was preceded by a wet period, ushered in by dry
+weather, accompanied by great heat; and its close occurred in slightly
+wetter weather, but under anti-cyclonic conditions. The fifth outbreak
+began after a short anti-cyclone had become established over our islands,
+continued during a long spell of cyclonic weather with a considerable
+rainfall, but was drowned out by heavy rains. The last appearance of the
+modern plague, of which Dr. Gillespie's paper treats, commenced after cold
+and wet weather, continued in very cold but drier weather, and subsided in
+warmth with a moderate rainfall.
+
+The conditions of these six epidemics were very variable in some respects,
+and regular in others. The most constant condition was the decreased
+rainfall at the time, when the disease was becoming epidemic.
+Anti-cyclonic weather prevailed at the time.
+
+According to Dr. Gillespie, the tables seem to suggest that a type of
+weather, which is liable to cause catarrhs and other affections of the
+respiratory tract, precedes the attacks of influenza; but that the
+occurrence of influenza in _epidemic form_ does not appear to take place
+until another and drier type has been established. As the weather changes,
+the affected patients increase with a rush.
+
+He is of opinion that the supposed rapid spread of influenza on the
+establishment of anti-cyclonic conditions may be explained in this way.
+The air in the cyclonic vortex, drawn chiefly from the atmosphere over the
+ocean, is moist, and contains none of the contagion; the air of the
+anti-cyclone, derived from the higher strata, and thus from distant
+cyclones, descending, blows gently over the land to the nearest cyclone,
+and, being drier, is more able to carry suspended particles with it. He
+considers that temperature has nothing to do with the problem, except in
+so far as the different types of weather may modify it. The Infirmary
+records point to the occurrence of similar phenomena, recorded on previous
+occasions. Accordingly, if such meteorological conditions are not
+indispensable to the spread of influenza in epidemic form, they at least
+afford favourable facilities for it.
+
+
+
+
+CHAPTER XXXIII
+
+CLIMATE
+
+
+One is not far up in years, in Scotland at any rate, without practically
+realising what climate means. He may not be able to put it in words, but
+easterly haars, chilling rimes, drizzling mists, dagging fogs, and
+soddening rains speak eloquently to him of the meaning of climate.
+
+Climate is an expression for the conditions of a district with regard to
+temperature, and its influence on the health of animals and plants. The
+sun is the great source of heat, and when its rays are nearly
+perpendicular--as at the Tropics--the heat is greater on the earth than
+when the slanted rays are gradually cooled in their passage. As one passes
+to a higher level, he feels the air colder, until he reaches the
+fluctuating snow-line that marks perpetual snow.
+
+The temperature of the atmosphere also depends upon the radiation from the
+earth. Heat is quite differently radiated from a long stretch of sand, a
+dense forest, and a wide breadth of water. Strange is it that a newly
+ploughed field absorbs and radiates more heat than an open lea. The
+equable temperature of the sea-water has an influence on coast towns. The
+Gulf Stream, from the Gulf of Mexico, heats the ocean on to the west coast
+of Britain, and mellows the climate there.
+
+The rainfall of a district has a telling effect on the climate. Boggy land
+produces a deleterious climate, if not malaria. Over the world, generally,
+the prevailing winds are grand regulators of the climate in the
+distinctive districts. A wooded valley--like the greatest in Britain,
+Strathmore--has a health-invigorating power: what a calamity it is, then,
+that so many extensive woods, destroyed by the awful hurricane twelve
+years ago, are not replanted!
+
+Some people can stand with impunity any climate; their "leather lungs"
+cannot be touched by extremes of temperature; but ordinary mortals are
+mere puppets in the hands of the goddess climate. Hence health-resorts are
+munificently got up, and splendidly patronised by people of means. The
+poor, fortunately, have been successful in the struggle for existence, by
+innate hardiness, otherwise they would have had a bad chance without ready
+cash for purchasing health.
+
+It may look ludicrous at first sight, but it seems none the less true,
+that the variation of the spots on the sun have something to do with
+climate, even to the produce of the fields. On close examination, with a
+proper instrument, the disc of the sun is found to be here and there
+studded with dark spots. These vary in size and position day after day.
+They always make their first appearance on the same side of the sun, they
+travel across it in about fourteen days, and then they disappear on the
+other side. There is a great difference in the number of spots visible
+from time to time; indeed, there is what is called the minimum period,
+when none are seen for weeks together, and a maximum period, when more are
+seen than at any other time. The interval between two maximum periods of
+sun-spots is about eleven years. This is a very important fact, which has
+wonderful coincidences in the varied economy of nature.
+
+Kirchhoff has shown, by means of the spectroscope, that the temperature of
+a sun-spot must be lower than that of the remainder of the solar surface.
+As we must get less heat from the sun when it is covered with spots than
+when there are none, it may be considered a variable star, with a period
+of eleven years. Balfour Stewart and Lockyer have shown that this period
+is in some way connected with the action of the planets on the
+photosphere. As we have already mentioned, the variations of the magnetic
+needle have a period of the same length, its greatest variations occurring
+when there are most sun-spots. Aurorae, and the currents of electricity
+which traverse the earth's surface, follow the same law. This remarkable
+coincidence set men a-thinking. Can the varying condition of the sun exert
+any influences upon terrestrial affairs? Is it connected with the
+variation of rainfall, the temperature and pressure of the atmosphere,
+and the frequency of storms? Has the regular periodicity of eleven years
+in the sun-spots no effect upon climate and agricultural produce?
+
+Mr. F. Chambers, of Bombay, has taken great trouble to strike, as far as
+possible, a connection between the recurring eleven years of sun-spots and
+the variation of grain prices. He arranged the years from 1783 to 1882 in
+nine groups of eleven years; and, from an examination of his tables, we
+find that there is a decided tendency for high prices to recur at more or
+less regular intervals of about eleven years, and a similar tendency for
+low prices. An occasional slight difference can be accounted for by some
+abnormal cause, as war or famine.
+
+Amid all the apparently irregular fluctuations of the yearly prices, there
+is in every one of the ten provinces of India a periodical rise and fall
+of prices once every eleven years, corresponding to the regular variation
+which takes place in the number of sun-spots during the same period. If it
+were possible to obtain statistics to show the actual out-turn of the
+crops each year, the eleven yearly variations calculated therefrom might
+reasonably correspond with the sun-spot variations even more closely than
+do the price variations.
+
+This is a remarkable coincidence, if nothing more. What if it were yet
+possible to predict the variations of prices in the coming sun-spot cycle?
+Such a power would be of immense service. By its aid it could be predicted
+that, as the present period of low prices has followed the last maximum of
+sun-spots, which was in the year 1904, it will not last much longer, but
+that prices must gradually keep rising for the next five years. Could
+science really predict this, it would be studied by many and blessed by
+more. Yet the strange coincidence of a century's observations renders the
+conclusions not only possible, but to some extent probable.
+
+
+
+
+CHAPTER XXXIV
+
+THE "CHALLENGER" WEATHER REPORTS
+
+
+The _Challenger_ Expedition, commenced by Sir Wyville Thomson, and after
+his death continued by Sir John Murray, with an able staff of assistants
+for the several departments, was one of the splendid exceptions to the
+ordinary British Government stinginess in the furtherance of science. The
+results of the Expedition were printed in a great number of very handsome
+volumes at the expense of the Government.
+
+And the valuable deductions from the _Challenger's_ Weather Reports by Dr.
+Alex. Buchan, in his "Atmospheric Circulation," have thrown considerable
+light upon oceanic weather phenomena. For some of his matured opinions on
+these, I am here much indebted to him.
+
+Humboldt, in 1817, published a treatise on "Isothermal Lines," which
+initiated a fresh line for the study of atmospheric phenomena. An isotherm
+is an imaginary line on the earth's surface, passing through places having
+a corresponding temperature either throughout the year or at any
+particular period. An isobar is an imaginary line on the earth's surface,
+connecting places at which the mean height of the barometer at sea-level
+is the same. To isobars, as well as to isotherms, Dr. Buchan has devoted
+considerable attention. In 1868, he published an important series of
+charts containing these, with arrows for prevailing winds over the earth
+for the months of the year. In this way what are called synoptic charts
+were established.
+
+In the _Challenger_ Report are shown the various movements of the
+atmosphere, with their corresponding causes. It is thus observed that the
+prevailing winds are produced by the inequality of the mass of air at
+different places. The air flows from a region of higher to a region of
+lower pressure, _i.e._ from where there is an excessive mass of air to
+fill up some deficiency. And this is the great principle on which the
+science of meteorology rests, not only as to winds, but as to weather
+changes.
+
+Of the sun's rays which reach the earth, those that fall on the land are
+absorbed by the surface layer of about 4 feet in thickness. But those that
+fall on the surface of the ocean penetrate, as shown by the observations
+of the _Challenger_ Expedition, to a depth of about 500 feet. Hence, in
+deep waters the temperature of the surface is only partially heated by the
+direct rays of the sun. In mid-ocean the temperature of the surface
+scarcely differs 1 deg. Fahr. during the whole day, while the daily variation
+of the surface layer of land is sometimes 50 deg. The temperature of the air
+over the ocean is about three times greater than that of the surface of
+the open sea over which it lies; but, near land, this increases to five
+times.
+
+The elastic force of vapour is seen in its simplest form on the open sea,
+as disclosed by these Reports. It is lowest at 4 A.M. and highest at 2
+P.M. The relative humidity is just the reverse. When the temperature is
+highest, the saturation of the air is lowest, and _vice versa_. So on land
+when the air, by radiation of heat from the earth, is cooled below the
+dew-point, dew is produced, and, at the freezing-point, hoar-frost.
+
+The _Challenger_ Reports, too, show that the force of the winds on the
+open sea is subject to no distinct and uniform daily variation, but that
+on nearing land the force of the wind gives a curve as distinctly marked
+as the ordinary curve of temperature. That force is lowest from 2 to 4
+A.M., and highest from 2 to 4 P.M. Each of the five great oceans gives the
+same result. At Ben Nevis, on the other hand, these forces are just
+reversed in strength.
+
+It is also shown by the _Challenger_ observations that on the open sea the
+greatest number of thunder-storms occur from 10 P.M. to 8 A.M. And, from
+this, Dr. Buchan concludes that over the ocean terrestrial radiation is
+more powerful than solar radiation in causing those vertical disturbances
+in the equilibrium of the atmosphere which give rise to the thunder-storm.
+
+
+
+
+CHAPTER XXXV
+
+WEATHER-FORECASTING
+
+
+To foretell with any degree of certainty the state of the weather for
+twenty-four hours is of immense advantage to business men, tourists,
+fishermen, and many others. The weather is everybody's business. And the
+probabilities of accurate forecasts are so improving that all are more or
+less giving attention to the morning meteorological reports.
+
+Weather-forecasting depends on the principle from vast experience that, if
+one event happens, a second is likely to follow. According to the extent
+and accuracy of the data, will be the strength of the probability of
+correct forecasts. And the great end of popular meteorology is to
+demonstrate this.
+
+We have given some explanations of the weather in some respects unique;
+and a careful consideration of these explanations will the more convince
+the reader of the importance of the subject. No doubt the changes of the
+weather are extremely complex, at times baffling; and the wonder is that
+forecasts come so near the truth.
+
+For instance, the year 1903 almost defied the ordinary rules of weather,
+for it broke the record for rainfall. And, last year, so repulsive and
+unseasonable was the spring, that there seemed to be a virtual
+"withdrawal" of the season. I wrote on it as "The Recession of Spring."
+Speak about Borrowing Days! We had the equinoctial gales of March about
+the middle of April. On very few days had we "clear shining to cheer us
+after rain," for the bitter cold dried up any genial moisture. An old
+farmer remarked that "We're gaun ower faur North." No one could account
+for the backwardness of the season. Unless for the cheering songs of the
+grove-charmers, one would have forgotten the time of the year.
+
+In March of this year, at Strathmore, the barometer fell from 30.5 inches
+(the highest for years) to 28.65 in five days without unfavourable weather
+following. It again rose to 30.05, then fell to 28.45, followed by a rise
+to 28.7 without any peculiar change. But in two days it fell to 28.4 (the
+lowest for years), followed by a deluge of rain and a perfect hurricane
+for several hours, while the temperature was fortunately mild. It was only
+evident at the end that this universal storm had been "brewing" some days
+before.
+
+All are familiar with the ordinary prognostics of good and bad weather. A
+"broch" round the moon, in her troubled heaven, indicates a storm of rain
+or wind. When the dark crimson sun in the evening throws a brilliant
+bronzed light on the gables and dead leaves, we are sure that there is an
+intense radiation from the earth to form dew, or even hoar-frost.
+
+According to the meteorological folk-lore, the weather of the summer
+season is indicated by the foliation of the oak and ash trees. If the oak
+comes first into leaf, the summer will be hot and dry, if the ash has the
+precedence it will be wet and cold. Looking over the observations of the
+budding of these two trees for half a century, I find that the
+weather-lore adage has been pretty correct. The ash was out before the oak
+a full month in the years 1816, '17, '21, '23, '28, '29, '30, '38, '40,
+'45, '50, and '59; and the summer and autumn in these years were
+unfavourable. Again, the oak was out before the ash several weeks in the
+years 1818, '19, '20, '22, '24, '25, '26, '27, '33, '34, '35, '36, '37,
+'42, '46, '54, '68, and '69; the summers during these years were dry and
+warm, and the harvests were abundant. One can never think of this weather
+prognostic from nature without recalling the Swallow Song of Tennyson's
+"Princess":--
+
+  "Why lingereth she to clothe her heart with love,
+  Delaying, as the tender ash delays
+  To clothe herself, when all the woods are green?"
+
+On a muggy morning a sudden clearness in the south "drowns the ploughman."
+And yet enough blue in the sky "tae mak' a pair o' breeks" cheers one with
+the assurance of coming dry and sunny weather. The low flying of the
+swallows betokens rain, as well as any unseasonable dancing of midges in
+the evening. Sore corns on the feet, and rheumatism in the joints, are
+direful precursors. The leaves are all a-tremble before the approach of
+thunder. But throughout this volume I have given many illustrations.
+
+But one of the largest and most important practical problems of
+meteorology is to ascertain the course which storms follow, and the causes
+by which that course is determined, so that a forecast may thereby be
+made, not only of the certain approach of a storm, but the particular
+direction and force of the storm. The method of conducting this large
+inquiry most effectively was devised by the French astronomer, Le
+Verrier--the great aspirant, with our own Couch Adams, for the discovery
+of the planet Neptune. He began to carry this out in 1858 by the daily
+publication of weather data, followed by a synchronous weather map, which
+showed graphically for the morning of the day of publication the
+atmospheric pressure and the direction and force of the wind, together
+with tables of temperature, rainfall, cloud, and sea disturbances from a
+large number of places in all parts of Europe. It is from similar maps
+that forecasts of storms are still framed, and suitable warnings issued;
+and a mass of information is being collected by telegraph from sixty
+stations in the British Islands, &c., of the state of the weather at eight
+o'clock every morning, and analysed and arranged at the Meteorological
+Office in London for the evening's forecasts over the different districts
+of the country. A juster knowledge is being now acquired of those great
+atmospheric movements, and other changes, which form the groundwork of
+weather-forecasting.
+
+The Meteorological Office, Westminster (entirely distinct from the Royal
+Meteorological Society), is administered by a Council (Chairman, Sir R.
+Strachey; Scottish member, Dr. Buchan), selected by the Royal Society. It
+employs a staff of over forty. The chief departments relate to: (1) Ocean
+Meteorology, including the collection, tabulation, and discussion of
+meteorological data from British ships, the preparation of ocean weather
+charts, and the issue of meteorological instruments to the Royal Navy and
+Mercantile Marine; (2) Weather Telegraphy, including the reception of
+telegrams thrice a day from selected stations for the preparation of the
+daily reports and weather forecasts. Representatives of newspapers, &c.,
+receive copies of the 11 A.M. forecast based on the 8 A.M. observations;
+and also of the 8.30 P.M. forecasts based on the observations received
+earlier in the day. In summer and autumn harvest forecasts are issued by
+telegraph to individuals who will defray the cost. The Office also
+collects climatological data from a number of voluntary and some
+subsidised stations. The "first order" stations include Valentia,
+Falmouth, Kew, and Aberdeen. These have self-recording instruments of high
+precision, giving a continuous record of the meteorological elements.
+
+A Government Commission which sat last year, under the Rt. Hon. Sir
+Herbert Maxwell, Bart., have issued a Report, recommending a number of
+changes in the management and constitution of the Meteorological Office;
+and considerable modifications are not unlikely to take place in the near
+future. In his evidence before that Commission, the Chairman of the
+Council acknowledged that the great function of meteorologists is the
+collection of facts; but the interpretation of those collected facts, in a
+scientific manner, is still in a very immature condition. Dr. Buchan, in
+his evidence, confessed that forecasting by the Council is purely "by rule
+of thumb." It is not possible to lay down hard and fast rules for
+forecasting.
+
+With regard to the storm-warning telegrams, as a rule, the earliest
+trustworthy indication of the approach of a dangerous storm to the coasts
+of the British Isles precedes the storm by only a few hours. Delays are
+therefore very serious.
+
+It is admitted by the best British meteorologists that the observations of
+the United States are better conducted, although the best instruments in
+the world are set and registered at Kew, in England. The work of weather
+forecasts and storm warnings is carried on with the highest degree of
+promptitude and efficiency at the Washington Central Office. This is
+because the work of predictions has been hitherto the chief work of the
+Office: the entire time of the observers, on whose telegraphic reports the
+forecasts are based, is controlled by the United States Weather Bureau;
+and the right of precedence in the use of wires is maintained.
+
+Professor Brueckner, of Berne, has devoted a lifetime to the comparatively
+new treatment of climatic oscillations, based upon observations made at
+321 points on the earth's surface, distributed as follows: Europe, 198;
+Asia, 39; N. America, 50; Cen. and S. America, 16; Australia, 12; Africa,
+6. One of his conclusions is that an average time of about thirty-five
+years is found to intervene between one period of excess or deficiency of
+warmth and the next, accompanied by the opposite relative condition of
+moisture.
+
+All are familiar with the hoisting of cone-warning as indication of a
+coming storm. This work is exceedingly important, especially for those
+connected with the sea by business or pleasure. On the known approach of a
+cyclone of dangerous intensity, special messages are sent from the London
+Meteorological Office, warning the coasts likely to be affected. When the
+cone is hoisted with its apex downwards, it means that strong south or
+south-west winds are to be looked for. When the cone is hoisted with its
+apex upwards, it indicates that strong winds from the north or north-east
+are expected. Of course they are merely useful precautions; but they are
+universally attended to by people on the sea-coast.
+
+Though one may have reasonable doubts about the use that can be made of
+weather forecasts for three days, such as are now regularly issued, on
+account of the finical, coy, spasmodic interludes on short notice, yet
+there is a wonderful certainty in the daily prognostics of the direction
+and strength of the wind, the temperature of the air, and the likelihood
+of rainy or fair weather, dependent on the broad uniformity of nature.
+This is very serviceable for people who have now to live at high pressure
+in business, in the enthralling days of keen competition. And it is a
+great boon to those who are in search of health by travelling, or who, in
+innocent pleasure, desire to live as much as possible in the open air.
+Very little credit is given to the "gas" of the isolated "weather
+prophet"; but those who have confidence in the usual weather forecasts
+from the Meteorological Office are satisfied in their belief; and those
+who, in self-confidence, ignore all weather prognostics, are still weak
+enough to read them and act up to them.
+
+       *       *       *       *       *
+
+In practical meteorology, in the scientific explanation of popular
+weather-lore, and in the study of atmospheric phenomena, which so
+powerfully influence us, for gladness or discomfort, we may, as with other
+branches of science, even all our days, cheerfully go on in "the noiseless
+tenor of our way,"
+
+                        "Nourishing a youth sublime,
+  With the fairy tales of science and the long results of time."
+
+
+
+
+INDEX
+
+
+  Abercromby, spectre on Adam's Peak, 89
+
+  Adam's Peak, spectre, 89
+
+  Afterglow described, 62;
+    dust-particles to form, 64
+
+  Air, change of, 55;
+    clearness and dryness, 49;
+    devitalised, 52;
+    disease-germs in, 53;
+    thunder-clouds, 49
+
+  Aitken, Dr., afterglows, 67;
+    anti-cyclones, 97;
+    colour of water, 75;
+    condensing power of dust, 2;
+    decay of clouds, 39;
+    dew-formation, 14;
+    dust and atmospheric phenomena, 29;
+    electrical deposition of smoke, 83;
+    false dew, 18;
+    fog-counter, 82;
+    foreglows, 67;
+    formation of clouds, 35;
+    haze, 44;
+    hazing effects of atmospheric dust, 47;
+    Kingairloch experiments, 30;
+    one-coloured rainbow, 70;
+    radiation from snow, 86;
+    regenerators, 85;
+    sanitary detective, 78
+
+  Ammonia and cloud formation, 36
+
+  Annie Laurie, 17
+
+  Anti-cyclones, forecasting by, 97;
+    formation, 97;
+    cause of influenza, 109
+
+  Aratus, forecasting by moon, 61
+
+  Ariel's song, 42
+
+  Aurora Borealis, 71;
+    forebodings, 71-73;
+    name by Gassendi, 72;
+    other names, 72;
+    safety valve of electricity, 72;
+    sun's spots, 72;
+    sun control, 74;
+    symptoms, 72
+
+
+  Bagillt, condensing lead fumes, 84
+
+  Ballachulish, sunsets, 64
+
+  Ballantine's song, 17
+
+  Barometer, indications, 10
+
+  Ben Nevis, dust-particles, 30;
+    instruments, 104;
+    meteorology, 102;
+    observations, 105;
+    rainfall, 103;
+    regret at stoppage of Observatory, 103
+
+  Blairgowrie, personal description of afterglow, 62
+
+  Blue sky, 74;
+    cause of, 75, 77
+
+  Borrowing days, 117
+
+  Brocken, spectre, 89;
+    personal description, 90;
+    Noah's Ark, 90
+
+  Brueckner, climatic oscillations, 122
+
+  Buchan, Dr., Aitken's radiation from snow, 86;
+    Ben Nevis, papers on, 103;
+    _Challenger_ Reports, 114;
+    cold of 1886, 86;
+    east winds, 94;
+    isobars, 115;
+    rainfall statistics, 100;
+    on forecasting, 121
+
+  Buchanan, Ben Nevis Observatory, 102;
+    great prevalence of fog, 106
+
+  Buddha's Lights, of Ceylon, 72
+
+  Burns, allusions to aurora, 71, 73
+
+  Byron, storm in Alps, 50
+
+
+  _Challenger_ Expedition, 114;
+    temperature, 115;
+    thunder-storms, 116;
+    winds, 116
+
+  Chambers on sun-spots and grain prices, 113
+
+  Change of air, 55;
+    Strathmore to Glenisla, 56
+
+  Charles II., fog and smoke, 80
+
+  Chlorine and cloud formation, 36
+
+  Christison and colour of water, 75
+
+  Chrystal on Aitken's radiation from snow, 86
+
+  Cirro-stratus cloud, mackerel-like, 39
+
+  Climate, _Challenger_ notes, 115;
+    cone-warnings, 120;
+    Gulf Stream, 111;
+    oscillations, 120;
+    rainfall, 111;
+    sun-spots on, 112;
+    wooded country on, 111
+
+  Clouds, decay of, 37;
+    distances of, 35;
+    dry, 42;
+    even without dust, 36;
+    formation of, 34;
+    height of, 34;
+    numbering of cloud-particles, 34;
+    sunshine on cloud formation, 35;
+    varieties of, 35
+
+  Cone-warnings, 121
+
+  Continental winds, 98
+
+  Cyclones, 95;
+    formation of, 96, 98;
+    small natural, 98
+
+
+  Decay of clouds, 37;
+    in thin rain, 41;
+    process, 38;
+    ripple markings, 39
+
+  Dew, evidence of rising, 22;
+    experiments, 15, 16;
+    false dew, 17;
+    formation of, 13
+
+  Disease-germs in air, 53;
+    causes, 53;
+    deposited by rain, 55
+
+  Diseases, and east wind, 94;
+    personal notes, 95
+
+  Dumfries, dust in air at, 46
+
+  Dust, condensing power, 43;
+    from meteors, 37;
+    generally necessary for cloud formation, 26;
+    hazing effects, 47;
+    numbering, 26;
+    instruments for numbering, 27;
+    produces afterglows, 64;
+    produces foreglows, 67;
+    quantity in Bunsen flame, 28;
+    at Ben Nevis, 30;
+    Hyeres, Mentone, Rigi Kulm, 29;
+    Lucerne, Kingairloch, 30;
+    when not necessary, 36
+
+  Dust enumeration, deductions on, 31
+
+
+  Earn, Loch, splash of drop at, 101
+
+  Earthshine, 59
+
+  Ehrenberg, on colour of water, 75
+
+  Evelyn, fumifugium, 80;
+    remedy for smoke, 82
+
+
+  Falkirk, Dr. Aitken's experiments on haze, 47
+
+  False dew, 19
+
+  Fitzroy on aurora as a foreboder, 73
+
+  Fog, counter, 31;
+    dry, 41;
+    formation, 24;
+    more in towns, 25;
+    and smoke, 80
+
+  Folk-lore, 50
+
+  Foreglow, described, 66;
+    how produced, 67
+
+  Fort William Observatory, 102
+
+  Frankland, disease-germs, 53
+
+  Franklin, lightning, 51
+
+
+  Gassendi, named aurora, 72
+
+  Gillespie, Dr., on weather and influenza, 107
+
+  Glasgow, fog, 81
+
+  Glass, appearing damp, 44
+
+  Glenisla, ozoned air, 56
+
+  Grain crops and sun-spots, 112;
+    Chambers' tables, 113
+
+  Great amazing light in the north, 72
+
+  Gulf Stream, effects on climate, 111
+
+  Gunpowder, great condensing power, 44
+
+
+  Haze, what is, 43;
+    how produced, 44;
+    in clearest air, 45;
+    stages of condensation, 46;
+    in sultry weather, 46;
+    dryness of air and visibility, 48
+
+  Health improved by change of air, 56
+
+  Highland air, few disease-germs, 55
+
+  Hoar-frost, frozen dew, 20;
+    on under surfaces, 21
+
+  Humboldt, isotherms, 114
+
+  Hydrogen peroxide and cloud formation, 36
+
+  Hyeres, dust-particles, 29
+
+
+  Indian Ocean, colour, 75
+
+  Influenza, weather and, 107;
+    six distinct epidemics, 108;
+    spread of anti-cyclonic conditions, 109
+
+  Isobars by Buchan, 115
+
+  Isotherms by Humboldt, 114
+
+  Italian lakes, stages of condensation, 45
+
+
+  Job, on dew formation, 13
+
+
+  Kelvin recorder, 84;
+    Aitken's radiation from snow, 86
+
+  Kew, instruments set, 121
+
+  Kingairloch, dust-particles, 30, 46
+
+  Kirchhoff, lower temperature of sun-spot, 112
+
+  Krakatoa, eruption of, dust-particles, 63
+
+
+  Le Verrier and weathercharts, 119
+
+  Lockyer, and sun-spots, 112
+
+  Lightning, electricity, 51;
+    photographed, 51;
+    sheet and forked, 51;
+    ozone, 52
+
+  Lodge, electrical deposition of smoke, 83
+
+  London, coals consumed, 25;
+    sulphur and fog, 25;
+    fog in reign of Charles II., 81;
+    Meteorological Office, 11, 120
+
+  Lord Derwentwater's Lights, 72
+
+  Lower animals, sensitiveness, 11
+
+  Lucerne, dust-particles, 30
+
+
+  MacLaren, Aitken's radiation from snow, 86
+
+  Magnesia, small affinity for water-vapour, 44
+
+  Man in the street, 11
+
+  Mediterranean, brilliant colour, 77
+
+  Mentone, dust-particles, 29
+
+  Merry Dancers of Shetland, 71
+
+  Meteors, producing dust, 37
+
+  Meteorological Council, London, 103;
+    Office, 120;
+    cone-warnings, 121;
+    regular forecasts, 123
+
+  Milne Home on Ben Nevis, 103
+
+  Milton, dust numberless, 26
+
+  Moon, old, in new moon's arms, 58;
+    weather indications, 59, 61
+
+  Mountain giants, 88;
+    Adam's Peak, 89;
+    Brocken, 89
+
+  Munich, International Meteorological Conference, 35
+
+  Murray, _Challenger_ Expedition, 114
+
+
+  Nardius, dew exhalation, 13
+
+  Newton, colour of sky, 77
+
+  Nimbus, cloud, 35
+
+
+  Oak and ash, on climate, 118
+
+  Ochils, one-coloured rainbow, 70
+
+
+  Pacific, colour, 75
+
+  Paris, aurora, 71;
+    disease-germs, 55
+
+  Paton, Waller, bronze tints in sunsets, 64
+
+  Piazzi Smith, aurora, 72
+
+  Picket, dew-formation, 14
+
+  Pilatus, fine rain, 42
+
+  Polar lightnings, 72
+
+
+  Radiant heat, producing fine rain, 41
+
+  Radiation from snow, 86
+
+  Rain, 98;
+    heavy rainfalls, 99
+
+  Rainbow, 68;
+    forecasts, 62, 69;
+    formation, 69;
+    one-coloured, 70
+
+  Rains, it always, 40;
+    radiant heat in process, 41;
+    Ariel's song, 43
+
+  Rankin, dust-particles, Ben Nevis, 30
+
+  Richardson, devitalised air, 51
+
+  Rigi Kulm, dust-particles, 29
+
+  Rolier, aurora, 73
+
+
+  St. Paul's, London, disease-germs in air, 54
+
+  Sanitary detective, 78
+
+  Shakespeare, tempest, 95
+
+  Shelley, old moon in new moon's arms, 59
+
+  Simoom and sirocco, 94
+
+  Skye, rainy, 40
+
+  Smoke, electrical deposition of, 83;
+    regenerators, 85
+
+  Smoking-room, condensing power, 44
+
+  Snow, bad conducting, 87;
+    radiation from, 86
+
+  Sodium dust, condensing power, 45
+
+  Spens, forebodings of moon, 61
+
+  Splash of a drop, experiments, 101
+
+  Stevenson, R. L., splash of drop, 101
+
+  Stewart, sun-spots, 112
+
+  Strachey on forecasts, 121
+
+  Strathmore, observations on hoar-frost, 22;
+    on decay of clouds, 38;
+    to Glenisla, change of air, 56;
+    observations on old moon in new moon's arms, 59;
+    afterglow described, 62;
+    foreglow, 66;
+    cold of 1886, 86;
+    healthy by woods, 111;
+    observations on barometer, 118
+
+  Strathpeffer, 9
+
+  Sulphur as a fog-former, 25
+
+  Sulphuretted hydrogen and cloud-formation, 36
+
+  Sunshine on cloud-formation, 35
+
+  Sun's spots, and aurora, 72, 112;
+    and grain crops, 112
+
+  Symons, rainfall, 100
+
+  Synoptic charts, 98
+
+
+  Tait, on Aitken's radiation from snow, 86
+
+  Tay Bridge, fall of, 92
+
+  Tennyson, aurora, 71;
+    dew, 19;
+    oak and ash, 119
+
+  Thermometer, indications, 10
+
+  Thomson, Wyville, _Challenger_ Expedition, 114
+
+  Thunder-storm described, 50
+
+
+  Valkyries, aurora, 73
+
+  Visibility, limit of, 48
+
+
+  Washington, Meteorological Office, 121
+
+  Water, pressure to show plant exudation, 18;
+    colour of, 75;
+    experiments on distilled, 76;
+    dust-particles vary colour, 77
+
+  Weather and influenza, 107
+
+  Weather-forecasting, 116;
+    advantages, 117;
+    principle, 117;
+    examples, 118;
+    old moon in new moon's arms, 59;
+    by moon, 61;
+    oak and ash, 118;
+    cone-warnings, 122;
+    three days', 123
+
+  Weather-lore, 50, 118
+
+  Weather talisman, 9;
+    call on barometer and thermometer, 10;
+    exceptional years, 117
+
+  Wells, Dr., on dew, 14
+
+  Wilson, Prof., on hoar-frost, 20
+
+  Wind, 92;
+    rates, 92;
+    trade, 93;
+    land and sea, 93
+
+  Woeikof, durability of cold, 88
+
+  Wordsworth, rainbow, 68
+
+  Worthington, splash of drop, 100
+
+  Wragge, observations at Ben Nevis, 104
+
+
+  Printed by BALLANTYNE, HANSON & CO.
+  Edinburgh & London
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Meteorology, by J. G. M'Pherson
+
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