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<div>*** START OF THE PROJECT GUTENBERG EBOOK 44167 ***</div>
<h1>The Project Gutenberg eBook, The Royal Observatory Greenwich, by E. Walter
(Edwared Walter) Maunder</h1>
<p> </p>
<p> </p>
<table border="0" style="background-color: #ccccff;margin: 0 auto;" cellpadding="10">
<tr>
<td valign="top">
Note:
</td>
<td>
Images of the original pages are available through
Internet Archive. See
<a href="https://archive.org/details/royalobservatory00maun">
https://archive.org/details/royalobservatory00maun</a>
</td>
</tr>
</table>
<p> </p>
<hr class="full" />
<p> </p>
<p><span class="pagenum"><a name="Page_1" id="Page_1"> </a></span></p>
<div class="figcenter" style="width: 549px;">
<img src="images/coverpage.jpg" width="549" height="784" alt="cover" />
</div>
<hr class="chap" />
<div class="figcenter bord" style="width: 380px;">
<img src="images/title_page.jpg" width="380" height="600" alt="titlepage" />
</div>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_2" id="Page_2"> </a></span></p>
<div class="figcenter bord" style="width: 445px;">
<img src="images/i_002.jpg" width="445" height="600" alt="Flamsteed" />
<div class="caption"><p class="center">FLAMSTEED, THE FIRST ASTRONOMER ROYAL.<br />
(<em>From the portrait in the 'Historia Cœlestis.'</em>)</p></div>
</div>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_3" id="Page_3"> </a></span></p>
<h1>
THE<br />
ROYAL OBSERVATORY<br />
GREENWICH<br />
<br />
<small>A GLANCE AT ITS HISTORY<br />
AND WORK</small></h1>
<p class="center b12 space-above">
BY</p>
<h2>E. WALTER MAUNDER, F.R.A.S.</h2>
<p class="center space-above">
<em>WITH MANY PORTRAITS AND ILLUSTRATIONS FROM<br />
OLD PRINTS AND ORIGINAL PHOTOGRAPHS</em></p>
<p> </p>
<p> </p>
<p class="center space-above">LONDON</p>
<p class="center b13">THE RELIGIOUS TRACT SOCIETY</p>
<p class="center"><span class="smcap">56 Paternoster Row, and 65 St. Paul's Churchyard</span><br />
1900
</p>
<p><span class="pagenum"><a name="Page_4" id="Page_4"> </a></span></p>
<hr class="chap" />
<p class="center s08">
LONDON:<br />
PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,<br />
STAMFORD STREET AND CHARING CROSS.
</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_5" id="Page_5">[5]</a></span></p>
<h2>PREFACE</h2>
<p>I was present on one occasion at a popular lecture
delivered in Greenwich, when the lecturer referred
to the way in which so many English people travel
to the ends of the earth in order to see interesting
or wonderful places, and yet entirely neglect places
of at least equal importance in their own land.
'Ten minutes' walk from this hall,' he said, 'is
Greenwich Observatory, the most famous observatory
in the world. Most of you see it every day of
your lives, and yet I dare say that not one in a
hundred of you has ever been inside.'</p>
<p>Whether the lecturer was justified in the general
scope of his stricture or not, the particular instance
he selected was certainly unfortunate. It was not
the fault of the majority of his audience that they
had not entered Greenwich Observatory, since the
regulations by which it is governed forbade them
doing so. These rules are none too stringent, for
the efficiency of the institution would certainly suffer
if it were made a 'show' place, like a picture<span class="pagenum"><a name="Page_6" id="Page_6">[6]</a></span>
gallery or museum. The work carried on therein
is too continuous and important to allow of interruption
by daily streams of sightseers.</p>
<p>To those who may at some time or other visit
the Observatory it may be of interest to have at
hand a short account of its history, principal instruments,
and work. To the far greater number who
will never be able to enter it, but who yet feel an
interest in it, I would trust that this little book
may prove some sort of a substitute for a personal
visit.</p>
<p>I would wish to take this opportunity of thanking
the Astronomer Royal for his kind permission to
reproduce some of the astronomical photographs
taken at the Observatory and to photograph the
domes and instruments. I would also express my
thanks to Miss Airy, for permission to reproduce the
photograph of Sir G. B. Airy; to Mr. J. Nevil
Maskelyne, F.R.A.S., for the portrait of Dr. Maskelyne;
to Mr. Bowyer, for procuring the portraits of
Bliss and Pond; to Messrs. Edney and Lacey, for
many photographs of the Royal Observatory; and
to the Editor of <cite>Engineering</cite>, for permission to copy
two engravings of the Astrographic telescope.</p>
<p class="sig">
E. W. M.</p>
<p class="noin"><span class="smcap">Royal Observatory, Greenwich</span>,<br />
<em>August, 1900</em>.
</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_7" id="Page_7">[7]</a></span></p>
<div class="figcenter bord" style="width: 450px;"><a name="building" id="building"></a>
<img src="images/i_007.jpg" width="450" height="384" alt="new building" />
<div class="caption"><p class="center">THE NEW BUILDING.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<hr class="chap" />
<h2>CONTENTS</h2>
<div class="center">
<table border="0" cellpadding="4" cellspacing="0" summary="contents">
<tr><td align="left" colspan="2">CHAPTER</td><td align="right"><small>PAGE</small></td></tr>
<tr><td align="right">I.</td><td align="left"><span class="smcap">Introduction</span></td><td align="right"><a href="#Page_13">13</a></td></tr>
<tr><td align="right">II.</td><td align="left"><span class="smcap">Flamsteed</span></td><td align="right"><a href="#Page_25">25</a></td></tr>
<tr><td align="right">III.</td><td align="left"><span class="smcap">Halley and his Successors</span></td><td align="right"><a href="#Page_60">60</a></td></tr>
<tr><td align="right">IV.</td><td align="left"><span class="smcap">Airy</span></td><td align="right"><a href="#Page_102">102</a></td></tr>
<tr><td align="right">V.</td><td align="left"><span class="smcap">The Observatory Buildings</span></td><td align="right"><a href="#Page_124">124</a></td></tr>
<tr><td align="right"><span class="pagenum"><a name="Page_8" id="Page_8">[8]</a></span>VI.</td><td align="left"><span class="smcap">The Time Department</span></td><td align="right"><a href="#Page_146">146</a></td></tr>
<tr><td align="right">VII.</td><td align="left"><span class="smcap">The Transit and Circle Departments</span></td><td align="right"><a href="#Page_181">181</a></td></tr>
<tr><td align="right">VIII.</td><td align="left"><span class="smcap">The Altazimuth Department</span></td><td align="right"><a href="#Page_205">205</a></td></tr>
<tr><td align="right">IX.</td><td align="left"><span class="smcap">The Magnetic and Meteorological Departments</span></td><td align="right"><a href="#Page_228">228</a></td></tr>
<tr><td align="right">X.</td><td align="left"><span class="smcap">The Heliographic Department</span></td><td align="right"><a href="#Page_251">251</a></td></tr>
<tr><td align="right">XI.</td><td align="left"><span class="smcap">The Spectroscopic Department</span></td><td align="right"><a href="#Page_266">266</a></td></tr>
<tr><td align="right">XII.</td><td align="left"><span class="smcap">The Astrographic Department</span></td><td align="right"><a href="#Page_284">284</a></td></tr>
<tr><td align="right">XIII.</td><td align="left"><span class="smcap">The Double-Star Department</span></td><td align="right"><a href="#Page_303">303</a></td></tr>
<tr><td align="right"> </td><td align="left"><span class="smcap">Index</span></td><td align="right"><a href="#Page_317">317</a></td></tr>
</table></div>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_9" id="Page_9">[9]</a></span></p>
<h2>LIST OF ILLUSTRATIONS</h2>
<div class="center">
<table border="0" cellpadding="4" cellspacing="0" summary="illustrations">
<tr><td align="left"> </td><td align="right"><small>PAGE</small></td></tr>
<tr><td align="left"><span class="smcap">Flamsteed, the First Astronomer Royal</span></td><td align="left"><a href="#Page_7"><em>Frontispiece</em></a></td></tr>
<tr><td align="left"><span class="smcap">The New Building</span></td><td align="right"><a href="#building">7</a></td></tr>
<tr><td align="left"><span class="smcap">General View of the Observatory Buildings from the New Dome</span></td><td align="right"><a href="#general">12</a></td></tr>
<tr><td align="left"><span class="smcap">Flamsteed's Sextant</span></td><td align="right"><a href="#sextant">36</a></td></tr>
<tr><td align="left"><span class="smcap">The Royal Observatory in Flamsteed's Time</span></td><td align="right"><a href="#engraving">44</a></td></tr>
<tr><td align="left"><span class="smcap">The 'Camera Stellata' in Flamsteed's Time</span></td><td align="right"><a href="#stellata">52</a></td></tr>
<tr><td align="left"><span class="smcap">Edmund Halley</span></td><td align="right"><a href="#halley">61</a></td></tr>
<tr><td align="left"><span class="smcap">Halley's Quadrant</span></td><td align="right"><a href="#quadrant">69</a></td></tr>
<tr><td align="left"><span class="smcap">James Bradley</span></td><td align="right"><a href="#bradley">72</a></td></tr>
<tr><td align="left"><span class="smcap">Graham's Zenith Sector</span></td><td align="right"><a href="#zenith">77</a></td></tr>
<tr><td align="left"><span class="smcap">Nathaniel Bliss</span></td><td align="right"><a href="#bliss">83</a></td></tr>
<tr><td align="left"><span class="smcap">Nevil Maskelyne</span></td><td align="right"><a href="#nevil">87</a></td></tr>
<tr><td align="left"><span class="smcap">Hadley's Quadrant</span></td><td align="right"><a href="#hadley">91</a></td></tr>
<tr><td align="left"><span class="smcap">John Pond</span></td><td align="right"><a href="#pond">96</a></td></tr>
<tr><td align="left"><span class="smcap">George Biddell Airy, Astronomer Royal</span></td><td align="right"><a href="#airy">103</a></td></tr>
<tr><td align="left"><span class="smcap">The Astronomer Royal's Room</span></td><td align="right"><a href="#royal">110</a></td></tr>
<tr><td align="left"><span class="smcap">The South-east Tower</span></td><td align="right"><a href="#tower">115</a></td></tr>
<tr><td align="left"><span class="smcap">W. H. M. Christie, Astronomer Royal</span></td><td align="right"><a href="#christie">121</a></td></tr>
<tr><td align="left"><span class="smcap">The Astronomer Royal's House</span></td><td align="right"><a href="#astro">127</a></td></tr>
<tr><td align="left"><span class="smcap">The Courtyard</span></td><td align="right"><a href="#court">130</a></td></tr>
<tr><td align="left"><span class="smcap">Plan of Observatory at Present Time</span></td><td align="right"><a href="#plan">134</a></td></tr>
<tr><td align="left"><span class="smcap">The Great Clock and Porter's Lodge</span></td><td align="right"><a href="#clock">147</a></td></tr>
<tr><td align="left"><span class="smcap">The Chronograph</span></td><td align="right"><a href="#graph">158</a></td></tr>
<tr><td align="left"><span class="smcap">The Time-desk</span></td><td align="right"><a href="#desk">164</a></td></tr>
<tr><td align="left"><span class="smcap">Harrison's Chronometer</span></td><td align="right"><a href="#harrison">165</a></td></tr>
<tr><td align="left"><span class="pagenum"><a name="Page_10" id="Page_10">[10]</a></span><span class="smcap">The Chronometer Room</span></td><td align="right"><a href="#room">167</a></td></tr>
<tr><td align="left"><span class="smcap">The Chronometer Oven</span></td><td align="right"><a href="#oven">171</a></td></tr>
<tr><td align="left"><span class="smcap">The Transit Pavilion</span></td><td align="right"><a href="#transit">174</a></td></tr>
<tr><td align="left"><span class="smcap">'Lost in the Birkenhead'</span></td><td align="right"><a href="#lost">179</a></td></tr>
<tr><td align="left"><span class="smcap">The Transit Circle</span></td><td align="right"><a href="#circle">189</a></td></tr>
<tr><td align="left"><span class="smcap">The Mural Circle</span></td><td align="right"><a href="#mural">195</a></td></tr>
<tr><td align="left"><span class="smcap">Airy's Altazimuth</span></td><td align="right"><a href="#alta">208</a></td></tr>
<tr><td align="left"><span class="smcap">New Altazimuth Building</span></td><td align="right"><a href="#zimuth">211</a></td></tr>
<tr><td align="left"><span class="smcap">The New Altazimuth</span></td><td align="right"><a href="#news">213</a></td></tr>
<tr><td align="left"><span class="smcap">The New Observatory as seen from Flamsteed's Observatory</span></td><td align="right"><a href="#observe">219</a></td></tr>
<tr><td align="left"><span class="smcap">The Self-registering Thermometers</span></td><td align="right"><a href="#self">235</a></td></tr>
<tr><td align="left"><span class="smcap">The Anemometer Room, North-west Turret</span></td><td align="right"><a href="#anemone">240</a></td></tr>
<tr><td align="left"><span class="smcap">The Anemometer Trace</span></td><td align="right"><a href="#trace">243</a></td></tr>
<tr><td align="left"><span class="smcap">Magnetic Pavilion—Exterior</span></td><td align="right"><a href="#ext">246</a></td></tr>
<tr><td align="left"><span class="smcap">Magnetic Pavilion—Interior</span></td><td align="right"><a href="#int">248</a></td></tr>
<tr><td align="left"><span class="smcap">The Dallmeyer Photo-heliograph</span></td><td align="right"><a href="#helio">254</a></td></tr>
<tr><td align="left"><span class="smcap">Photograph of a Group of Sun-spots</span></td><td align="right"><a href="#spots">259</a></td></tr>
<tr><td align="left"><span class="smcap">The Great Nebula in Orion</span></td><td align="right"><a href="#orion">269</a></td></tr>
<tr><td align="left"><span class="smcap">The Half-prism Spectroscope on the South-east Equatorial</span></td><td align="right"><a href="#prism">273</a></td></tr>
<tr><td align="left"><span class="smcap">The Workshop</span></td><td align="right"><a href="#workshop">276</a></td></tr>
<tr><td align="left"><span class="smcap">The 30-inch Reflector with the New Spectroscope attached</span></td><td align="right"><a href="#reflect">278</a></td></tr>
<tr><td align="left"><span class="smcap">'Chart Plate' of the Pleiades</span></td><td align="right"><a href="#plate">286</a></td></tr>
<tr><td align="left"><span class="smcap">The Control Pendulum and the Base of the Thompson Telescope</span></td><td align="right"><a href="#pendulum">289</a></td></tr>
<tr><td align="left"><span class="smcap">The Astrographic Telescope</span></td><td align="right"><a href="#telescope">291</a></td></tr>
<tr><td align="left"><span class="smcap">The Driving Clock of the Astrographic Telescope</span></td><td align="right"><a href="#driving">294</a></td></tr>
<tr><td align="left"><span class="smcap">The Thompson Telescope in the New Dome</span></td><td align="right"><a href="#thompson">297</a></td></tr>
<tr><td align="left"><span class="smcap">The Nebulæ of the Pleiades</span></td><td align="right"><a href="#neb">300</a></td></tr>
<tr><td align="left"><span class="smcap">Double-star Observation with the South-east Equatorial</span></td><td align="right"><a href="#star">308</a></td></tr>
<tr><td align="left"><span class="smcap">The South-east Dome with the Shutter Open</span></td><td align="right"><a href="#shutter">314</a></td></tr>
</table></div>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_11" id="Page_11"> </a><br /><a name="Page_12" id="Page_12"> </a></span></p>
<div class="figcenter bord" style="width: 600px;"><a name="general" id="general"></a>
<img src="images/i_012.jpg" width="600" height="360" alt="general" />
<div class="caption"><p class="center">GENERAL VIEW OF THE OBSERVATORY BUILDINGS FROM THE NEW DOME.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_13" id="Page_13">[13]</a></span></p>
<h2>THE ROYAL OBSERVATORY</h2>
<h3>GREENWICH</h3>
<hr class="chap" />
<h2>CHAPTER I</h2>
<h3>INTRODUCTION</h3>
<p>I had parted from a friend one day just as he met
an acquaintance of his to whom I was unknown.
'Who is that?' said the newcomer, referring to me.
My friend replied that I was an astronomer from
Greenwich Observatory.</p>
<p>'Indeed; and what does he do there?'</p>
<p>This question completely exhausted my friend's
information, for as his tastes did not lead him in
the direction of astronomy, he had at no time ever
concerned himself to inquire as to the nature of my
official duties. 'Oh—er—why—he <em>observes</em>, don't
you know?' and the answer, vague as it was,
completely slaked the inquirer's thirst for knowledge.</p>
<p>It is not every one who has such exceedingly
nebulous ideas of an astronomer's duties. More
frequently we find that the inquirer has already
formed a vivid and highly-coloured picture of the
astronomer at his 'soul-entrancing work.' Resting<span class="pagenum"><a name="Page_14" id="Page_14">[14]</a></span>
on a comfortable couch, fixed at a luxurious angle,
the eye-piece of some great and perfect instrument
brought most conveniently to his eye, there passes
before him, in grand procession, a sight such as the
winter nights, when clear and frosty, give to the
ordinary gazer, but increased ten thousand times in
beauty, brilliance, and wonder by the power of his
telescope. For him Jupiter reveals his wind-drifted
clouds and sunset colours; for him Saturn spreads
his rings; for him the snows of Mars fall and melt,
and a thousand lunar plains are ramparted with
titanic crags; his are the star-clusters, where suns
in their first warm youth swarm thicker than hiving
bees; his the faint veils of nebulous smoke, the first
hint of shape in worlds about to be, or, perchance,
the last relics of worlds for ever dead. And beside
the enjoyment of all this entrancing spectacle of
celestial beauty, the fortunate astronomer sits at his
telescope and <em>discovers</em>—always he <em>discovers</em>.</p>
<p>This, or something like it, is a very popular
conception of an astronomer's experiences and duty;
and consequently many, when they are told that
'discoveries' are not made at Greenwich, are inclined
to consider that the Observatory has failed in its
purpose. An astronomer without 'discoveries' to
his record is like an angler who casts all day and
comes home without fish—obviously an idle or incompetent
person.</p>
<p>Again, it is considered that astronomy is a most
transcendental science. It deals with infinite distances,
with numbers beyond all power of human intellect
to appreciate, and therefore it is supposed, on the<span class="pagenum"><a name="Page_15" id="Page_15">[15]</a></span>
one hand, that it is a most elevating study, keeping
the mind continually on the stretch of ecstasy, and,
on the other hand, that it is utterly removed from all
connection with practical, everyday, ordinary life.</p>
<p>These ideas as to the Royal Observatory, or ideas
like them, are very widely current, and they are, in
every respect, exactly and wholly wrong. First of
all, Greenwich Observatory was originally founded,
and has been maintained to the present day, for a
strictly practical purpose. Next, instead of leading
a life of dreamy ecstasy or transcendental speculation,
the astronomer has, perhaps, more than any man, to
give the keenest attention to minute practical details.
His life, on the one side, approximates to that of the
engineer; on the other, to that of the accountant.
Thirdly, the professional astronomer has hardly anything
to do with the show places of the sky. It is
quite possible that there are many people whose sole
opportunity of looking through a telescope is the
penny peep through the instrument of some itinerant
showman, who may have seen more of these than
an active astronomer in a lifetime; while as to 'discoveries,'
these lie no more within the scope of our
national observatory than do geographical discoveries
within that of the captain and officers of an ocean liner.</p>
<p>If it is not to afford the astronomer beautiful
spectacles, nor to enable him to make thrilling
discoveries, what is the purpose of Greenwich Observatory?</p>
<p>First and foremost, it is to assist navigation. The
ease and certainty with which to-day thousands of
miles of ocean are navigated have ceased to excite<span class="pagenum"><a name="Page_16" id="Page_16">[16]</a></span>
any wonder. We do not even think about it. We
go down to the docks and see, it may be, one steamer
bound for Halifax, another for New York, a third for
Charleston, a fourth for the West Indies, a fifth for
Rio de Janeiro; and we unhesitatingly go on board
the one bound for our chosen destination, without
the faintest misgiving as to its direction. We have
no more doubt about the matter than we have in
choosing our train at a railway station. Yet, whilst
the train is obliged to follow a narrow track already
laid for it, from which it cannot swerve an inch, the
steamer goes forth to traverse for many days an
ocean without a single fixed mark or indication of
direction; and it is exposed, moreover, to the full
force of winds and currents, which may turn it from
its desired path.</p>
<p>But for this facility of navigation, Great Britain
could never have obtained her present commercial
position and world-wide empire.</p>
<div class="poem"><div class="stanza">
<span class="i0">'For the Lord our God most High,<br /></span>
<span class="i0">He hath made the deep as dry;<br /></span>
<span class="i0">He has smote for us a pathway,<br /></span>
<span class="i0">To the ends of all the earth.'<br /></span>
</div></div>
<p>Part of this facility is, of course, due to the invention
of the steam engine, but much less than is
generally supposed. Even yet the clippers, with
their roods of white canvas, are not entirely superseded;
and if we could conceive of all steamships
being suddenly annihilated, ere long the sailing
vessels would again, as of yore, prove the</p>
<div class="poem"><div class="stanza">
<span class="i0">'Swift shuttles of an empire's loom,<br /></span>
<span class="i0">That weave us main to main.'<br /></span>
</div></div>
<p><span class="pagenum"><a name="Page_17" id="Page_17">[17]</a></span></p>
<p>But with the art of navigation thrust back into
its condition of a hundred and fifty years ago, it is
doubtful whether a sufficient tide of commerce could
be carried on to keep our home population supplied,
or to maintain a sufficiently close political connection
between these islands and our colonies.</p>
<p>Navigation was in a most primitive condition even
as late as the middle of last century. Then the
method of finding a ship's longitude at sea was the
insufficient one of dead reckoning. In other words,
the direction and speed of the ship were estimated
as closely as possible, and so the position was carried
on from day to day. The uncertainty of the method
was very great, and many terrible stories might be
told of the disastrous consequences which might, and
often did, follow in the train of this method by
guess-work. It will be sufficient, however, to cite
the instance of Commodore Anson. He wanted to
make the island of Juan Fernandez, where he hoped
to obtain fresh water and provisions, and to recruit
his crew, many of whom were suffering from that
scourge of old-time navigators—scurvy. He got
into its latitude easily enough, and ran eastward,
believing himself to be west of the island. He was,
however, really east of it, and therefore made the
mainland of America. He had therefore to turn
round and sail westwards, losing many days, during
which the scurvy increased upon his crew, many of
whom died from the terrible disease before he
reached the desired island.</p>
<p>The necessity for finding out a ship's place when
at sea had not been very keenly felt until the end<span class="pagenum"><a name="Page_18" id="Page_18">[18]</a></span>
of the fifteenth century. It was always possible for
the sailor to ascertain his latitude pretty closely,
either by observing the height of the pole-star at
night or the height of the sun at noonday; and so
long as voyages were chiefly confined to the Mediterranean
Sea, and the navigators were content for
the most part to coast from point to point, rarely
losing sight of land, the urgency of solving the
second problem—the longitude of the ship—was not
so keenly felt. But immediately the discoveries of
the great Portuguese and Spanish navigators brought
a wider, bolder navigation into vogue, it became a
matter of the first necessity.</p>
<p>To take, for example, the immortal voyage of
Christopher Columbus. His purpose in setting out
into the west was to discover a new way to India.
The Venetians and Genoese practically possessed
the overland route across the Isthmus of Suez and
down the Red Sea. Vasco da Gama had opened
out the route eastward round the Cape. Firmly
convinced that the world was a globe, Columbus saw
that a third route was possible, namely, one nearly
due west; and when, therefore, he reached the
Bahamas, after traversing some 66° of longitude, he
believed that he was in the islands of the China Sea,
some 230° from Spain. Those who followed him
still laboured under the same impression, and when
they reached the mainland of America, believed that
they were close to the shores of India, which was
still distant from them by half the circumference of
the globe.</p>
<p>Little by little the intrepid sailors of the sixteenth<span class="pagenum"><a name="Page_19" id="Page_19">[19]</a></span>
century forced their way to a true knowledge of the
size of the globe, and of the relative position of the
great continents. But this knowledge was only
attained after many disasters and terrible miseries;
and though a new kind of navigation was established—the
navigation of the open ocean, far away from any
possible landmark, a navigation as different as could
be conceived from the old method of coasting—yet it
remained terribly risky and uncertain throughout the
sixteenth century. Therefore many mathematicians
endeavoured to solve the problem of determining the
position of a ship when at sea. Their suggestions,
however, remained entirely fruitless at the time,
though in several instances they struck upon principles
which are being employed at the present day.</p>
<p>The first country to profit by the discovery of
America was Spain, and hence Spain was the first
to feel keenly the pinch of the problem. In 1598,
therefore, Philip III. offered a prize of 100,000
crowns to any one who would devise a method by
which a captain of a vessel could determine his
position when out of sight of land. Holland, which
had recently started on its national existence, and
which was challenging the colonial empire of Spain,
followed very shortly after with the offer of a reward
of 30,000 florins. Not very long after the offer of
these rewards, a master mind did work out a simple
method for determining the longitude, a method
theoretically complete, though practically it proved
inapplicable. This was Galileo, who, with his newly
invented telescope, had discovered that Jupiter was
attended by four satellites.</p>
<p><span class="pagenum"><a name="Page_20" id="Page_20">[20]</a></span></p>
<p>At first sight such a discovery, however interesting,
would seem to have not the slightest bearing
upon the sailor's craft, or upon the commercial
progress of one nation or another. But Galileo
quickly saw in it the promise of great practical
usefulness. The question of the determination of
the place of a ship when in the open ocean really
resolved itself into this: How could the navigator
ascertain at any time what was the true time, say at
the port from which he sailed? As already pointed
out, it was possible, by observing the height of the
sun at noon, or of the pole-star at night, to infer the
latitude of the ship. The longitude was the point
of difficulty. Now, the longitude may be expressed
as the difference between the local time of the place
of observation and the local time at the place chosen
as the standard meridian. The sailor could, indeed,
obtain his own local time by observations of the
height of the sun. The sun reached its greatest
height at local noon, and a number of observations
before and after noon would enable him to determine
this with sufficient nicety.</p>
<p>But how was he to determine when he, perhaps,
was half-way across the Atlantic, what was the local
time at Genoa, Cadiz, Lisbon, Bristol, or Amsterdam,
or whatever was the port from which he sailed?
Galileo thought out a way by which the satellites of
Jupiter could give him this information.</p>
<p>For as they circle round their primary, they
pass in turn into its shadow, and are eclipsed by it.
It needed, then, only that the satellites should be
so carefully watched, that their motions, and,<span class="pagenum"><a name="Page_21" id="Page_21">[21]</a></span>
consequently, the times of their eclipses could be
foretold. It would follow, then, that if the mariner
had in his almanac the local time of the standard city
at which a given satellite would enter into eclipse,
and he were able to note from the deck of his vessel
the disappearance of the tiny point, he would ascertain
the difference between the local times of the two
places, or, in other words, the difference of their
longitudes.</p>
<p>The plan was simplicity itself, but there were
difficulties in carrying it out, the greatest being the
impossibility of satisfactorily making telescopic
observations from the moving deck of a ship at sea.
Nor were the observations sufficiently sharp to be of
much help. The entry of a satellite into the shadow
of Jupiter is in most cases a somewhat slow process,
and the moment of complete disappearance would
vary according to the size of the telescope, the keenness
of the observer's sight, and the transparency of
the air.</p>
<p>As the power and commerce of Spain declined,
two other nations entered into the contest for the
sovereignty of the seas, and with that sovereignty
predominance in the New World of America—France
and England. The problem of the longitude at sea,
or, as already pointed out, what amounts to the same
thing, the problem how to determine when at sea
the local time at some standard place, became, in
consequence, of greater necessity to them.</p>
<p>The standard time would be easily known, if a
thoroughly good chronometer which did not change
its rate, and which was set to the standard time before<span class="pagenum"><a name="Page_22" id="Page_22">[22]</a></span>
starting, was carried on board the ship. This plan
had been proposed by Gemma Frisius as early as
1526, but at the time was a mere suggestion, as there
were no chronometers or watches sufficiently good
for the purpose. There was, however, another method
of ascertaining the standard time. The moon moves
pretty quickly amongst the stars, and at the present
time, when its motions are well known, it is possible
to draw up a table of its distances from a number
of given stars at definite times for long periods in
advance. This is actually done to-day in the <cite>Nautical
Almanac</cite>, the moon's distance from certain stars
being given for every three hours of Greenwich time.
It is possible, then, by measuring these distances,
and making, as in the case of the latitude, certain
corrections, to find out the time at Greenwich. In
short, the whole sky may be considered as a vast
clock set to Greenwich time, the stars being the
numbers on the dial face, and the moon the hand
(for this clock has only one hand) moving amongst
them.</p>
<p>The local apparent time—that is, the time at the
place at which the ship itself was—is a simpler matter.
It is noon at any place when the sun is due south—or,
as we may put it a little differently, when it
culminates—that is, when it reaches its highest point.</p>
<p>To find the longitude at sea, therefore, it was
necessary to be able to predict precisely the apparent
position of the moon in the sky for any time throughout
the entire year, and it was also necessary that the
places of the stars themselves should be very accurately
known. It was therefore to gather the materials for<span class="pagenum"><a name="Page_23" id="Page_23">[23]</a></span>
a better knowledge of the motions of the moon and
the position of the stars that Greenwich Observatory
was founded, whilst the <cite>Nautical Almanac</cite> was
instituted to convey this information to mariners in
a convenient form.</p>
<p>This proposal was actually made in the reign of
Charles II. by a Frenchman, Le Sieur de Saint-Pierre,
who, having secured an introduction to the
Duchess of Portsmouth, endeavoured to obtain a
reward for his scheme. It would appear that he had
simply borrowed the idea from a book which an
eminent French mathematician brought out forty
years before, without having himself any real knowledge
of the subject. But when the matter was
brought before the king's notice, he desired some
of the leading scientific men of the day to report
upon its practicability, and the Rev. John Flamsteed
was the man selected for the task. He reported that
the scheme in itself was a good one, but impracticable
in the then state of science. The king, who, in spite
of the evil reputation which he has earned for himself,
took a real interest in science, was startled when this
was reported to him, and commanded the man who
had drawn his attention to these deficiencies 'to
apply himself,' as the king's astronomer, 'with the
most exact care and diligence to the Rectifying the
Tables of the Motions of the Heavens and the Places
of the Fixed Stars, in order to find out the so much
desired Longitude at Sea, for the perfecting the Art
of Navigation.'</p>
<p>This man, the Rev. John Flamsteed, was accordingly
appointed first Astronomer Royal at the meagre<span class="pagenum"><a name="Page_24" id="Page_24">[24]</a></span>
salary of £100 a year, with full permission to provide
himself with the instruments he might require, at his
own expense. He followed out the task assigned
to him with extreme devotion, amidst many difficulties
and annoyances, until his death in 1719. He has
been succeeded by seven Astronomers Royal, each
of whom has made it his first object to carry out
the original scheme of the institution; and the chief
purpose of Greenwich Observatory to-day, as when
it was founded in 1675, is to observe the motions
of the sun, moon, and planets, and to issue accurate
star catalogues.</p>
<p>It will be seen, therefore, that the establishment
of Greenwich Observatory arose from the actual
necessity of the nation. It was an essential step in
its progress towards its present position as the first
commercial nation. No thoughts of abstract science
were in the minds of its founders; there was no
desire to watch the cloud-changes on Jupiter, or to
find out what Sirius was made of. The Observatory
was founded for the benefit of the Royal Navy and
of the general commerce of the realm; and, in essence,
that which was the sole object of its foundation at
the beginning has continued to be its first object
down to the present time.</p>
<p>It was impossible that the work of the Observatory
should be always confined within the above limits,
and it will be my purpose, in the pages which follow,
to describe when and how the chief expansions of its
programme have taken place. But assistance to
navigation is now, and has always been, the dominant
note in its management.</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_25" id="Page_25">[25]</a></span></p>
<h2>CHAPTER II</h2>
<h3>FLAMSTEED</h3>
<p>For the first century of its existence, the lives of its
Astronomers Royal formed practically the history
of the Royal Observatory. During this period, the
Observatory was itself so small that the Astronomer
Royal, with a single assistant, sufficed for the entire
work. Everything, therefore, depended upon the
ability, energy, and character of the actual director.
There was no large organized staff, established
routine, or official tradition, to keep the institution
moving on certain lines, irrespective of the personal
qualities of the chief. It was specially fortunate,
therefore, that the first four Astronomers Royal,
Flamsteed, Halley, Bradley, and Maskelyne (for Bliss,
the immediate successor of Bradley, reigned for so
short a time that he may be practically left out of the
count), were all men of the most conspicuous ability.</p>
<p>It will be convenient to divide the history of the
first seven Astronomers Royal into three sections.
In the first, we have the founder, John Flamsteed, a
pathetic and interesting figure, whom we seem to
know with especial clearness, from the fulness of the
memorials which he has left to us. He was succeeded
by the man who was, indeed, best fitted to succeed<span class="pagenum"><a name="Page_26" id="Page_26">[26]</a></span>
him, but whom he most hated. The second to the
sixth Astronomers Royal formed what we might
almost speak of as a dynasty, each in turn nominating
his successor, who had entered into more or less
close connection with the Observatory during the
lifetime of the previous director; and the lives of
these five may well form the second section. The
line was interrupted after the resignation of the sixth
Astronomer Royal, and the third section will be
devoted to the seventh director, Airy, under whom
the Observatory entered upon its modern period of
expansion.</p>
<blockquote>
<p>'God suffers not man to be idle, although he swim in
the midst of delights; for when He had placed His own
image (Adam) in a paradise so replenished (of His goodness)
with varieties of all things, conducing as well to his
pleasure as sustenance, that the earth produced of itself
things convenient for both,—He yet (to keep him out of
idleness) commands him to till, prune, and dress his
pleasant, verdant habitation; and to add (if it might be)
some lustre, grace, or conveniency to that place, which, as
well as he, derived its original from his Creator.'</p></blockquote>
<p>In these words <span class="smcap">John Flamsteed</span> begins the first
of several autobiographies which he has handed down
to us; this particular one being written before he
attained his majority, 'to keep myself from idleness
and to recreate myself.'</p>
<blockquote>
<p>'I was born,' he goes on, 'at Denby, in Derbyshire, in
the year 1646, on the 19th day of August, at 7 hours 16
minutes after noon. My father, named Stephen, was the
third son of Mr. William Flamsteed, of Little Hallam; my
mother, Mary, was the daughter of Mr. John Spateman, of
Derby, ironmonger. From these two I derived my beginning,
whose parents were of known integrity, honesty, and<span class="pagenum"><a name="Page_27" id="Page_27">[27]</a></span>
fortune, as they [were] of equal extraction and ingenuity;
betwixt whom I [was] tenderly educated (by reason of my
natural weakness, which required more than ordinary care)
till I was aged three years and a fortnight; when my
mother departed, leaving my father a daughter, then not
a month old, with me, then weak, to his fatherly care and
provision.'</p></blockquote>
<p>The weakly, motherless boy became at an early
age a voracious reader. At first, he says—</p>
<blockquote>
<p>'I began to affect the volubility and ranting stories of
romances; and at twelve years of age I first left off the
wild ones, and betook myself to read the better sort of
them, which, though they were not probable, yet carried no
seeming impossibility in the fiction. Afterwards, as my
reason increased, I gathered other real histories; and by
the time I was fifteen years old I had read, of the ancients,
Plutarch's <cite>Lives</cite>, Appian's and Tacitus's <cite>Roman Histories</cite>,
Holingshed's <cite>History of the Kings of England</cite>, Davies's
<cite>Life of Queen Elizabeth</cite>, Saunderson's of <cite>King Charles the
First</cite>, Heyling's <cite>Geography</cite>, and many others of the moderns;
besides a company of romances and other stories, of which
I scarce remember a tenth at present.'</p></blockquote>
<p>Flamsteed received his education at the free school
at Derby, where he continued until the Whitsuntide
of 1662, when he was nearly sixteen years of age.
Two years earlier than this, however, a great misfortune
fell upon him.</p>
<blockquote>
<p>'At fourteen years of age,' he writes, 'when I was nearly
arrived to be the head of the free-school, [I was] visited
with a fit of sickness, that was followed with a consumption
and other distempers, which yet did not so much hinder me
in my learning, but that I still kept my station till the form
broke up, and some of my fellows went to the Universities;
for which, though I was designed, my father thought it
not advisable to send me, by reason of my distemper.'</p></blockquote>
<p><span class="pagenum"><a name="Page_28" id="Page_28">[28]</a></span></p>
<p>This was a keen disappointment to him, but
seems to have really been the means of determining
his career. The sickly, suffering boy could not be
idle, though 'a day's short reading caused so violent
a headache;' and a month or two after he had left
school, he had a book lent to him—Sacrobosco's
<cite>De Sphæra</cite>, in Latin—which was the beginning of
his mathematical studies. A partial eclipse of the
sun in September of the same year seems to have
first drawn his attention to astronomical observation,
and during the winter his father, who had himself a
strong passion for arithmetic, instructed him in that
science.</p>
<p>It was astonishing how quickly his appetite for
his new subjects grew. The <cite>Art of Dialling</cite>, the
calculation of tables of the sun's altitudes for all
hours of the day, and for different latitudes, and the
construction of a quadrant—'of which I was not
meanly joyful'—were the occupations of this winter
of illness.</p>
<p>In 1664 he made the acquaintanceship of two
friends, Mr. George Linacre and Mr. William
Litchford; the former of whom taught him to
recognize many of the fixed stars, whilst the latter
was the means of his introduction to a knowledge of
the motions of the planets.</p>
<blockquote>
<p>'I had now completed eighteen years, when the winter
came on, and thrust me again into the chimney; whence
the heat and dryness of the preceding summer had happily
once before withdrawn me.'</p></blockquote>
<p>The following year, 1665, was memorable to him
'for the appearance of the comet,' and for a journey<span class="pagenum"><a name="Page_29" id="Page_29">[29]</a></span>
which he made to Ireland to be 'stroked' for his
rheumatic disorder by Valentine Greatrackes, a kind
of mesmerist, who had the repute of effecting wonderful
cures. The journey, of which he gives a full and
vivid account, occupied a month; but though he was
a little better, the following winter brought him no
permanent benefit.</p>
<p>But, ill or well, he pressed on his astronomical
studies. A large partial eclipse of the sun was due
the following June; he computed the particulars of it
for Derby, and observed the eclipse itself to the best
of his ability. He argued out for himself 'the
equation of time'; the difference, that is, between
time as given by the actual sun, or 'apparent time,'
and that given by a perfect clock, or 'mean time.'
He drew up a catalogue of seventy stars, computing
their right ascensions, declinations, longitudes, and
latitudes for the year 1701; he attempted to determine
the inclination of the ecliptic, the mean length of the
tropical year, and the actual distance of the earth
from the sun. And these were the recreations of a
sickly, suffering young man, not yet twenty-one years
of age, and who had only begun the study of
arithmetic, such as fractions and the rule of three,
four years previously!</p>
<p>His next attempt was almanac-making, in the
which he improved considerably upon those current
at the time. His almanac for 1670 was rejected,
however, and returned to him, and, not to lose his
whole labour, he sent his calculations of an eclipse of
the sun, and of five occultations of stars by the moon,
which he had undertaken for the almanac, to the<span class="pagenum"><a name="Page_30" id="Page_30">[30]</a></span>
Royal Society. He sent the paper anonymously, or,
rather, signed it with an anagram, 'In mathesi a sole
fundes,' for 'Johannes Flamsteedius.' His covering
letter ends thus:—</p>
<blockquote>
<p>'Excuse, I pray you, this juvenile heat for the concerns
of science and want of better language, from one who, from
the sixteenth year of his age to this instant, hath only
served one bare apprenticeship in these arts, under the discouragement
of friends, the want of health, and all other
instructors except his better genius.'</p></blockquote>
<p>This letter was dated November 4, 1669, and on
January 14, Mr. Oldenburg, the secretary of the
Society, replied to him in a letter which the young
man cannot but have felt encouraging and flattering
to the highest degree.</p>
<blockquote>
<p>'Though you did what you could to hide your name from
us,' he writes, 'yet your ingenious and useful labours for
the advancement of Astronomy addressed to the noble
President of the Royal Society, and some others of that
illustrious body, did soon discover you to us, upon our
solicitous inquiries after their worthy author.'</p></blockquote>
<p>And after congratulating him upon his skill, and
encouraging him to furnish further similar papers,
he signs himself, 'Your very affectionate friend and
real servant'—no unmeaning phrase, for the friendship
then commenced ceased only with Oldenburg's life.</p>
<p>The following June, his father, pleased with the
notice that some of the leading scientific men of the
day were taking of his son, sent him up to London,
that he might be personally acquainted with them;
and he then was introduced to Sir Jonas Moore, the
Surveyor of the Ordnance, who made him a present<span class="pagenum"><a name="Page_31" id="Page_31">[31]</a></span>
of Townley's micrometer, and promised to furnish him
with object-glasses for telescopes at moderate rates.</p>
<p>On his return journey he called at Cambridge,
where he visited Dr. Barrow and Newton, and
entered his name in Jesus College.</p>
<p>It was not until the following year, 1671, that he
was enabled to complete his own observatory, as he
had had to wait long for the lenses which Sir Jonas
Moore and Collins had promised to procure for him.
He still laboured under several difficulties, in that he
had no good means for measuring time, pendulum
clocks not then being common. He, therefore, with
a practical good sense which was characteristic,
refrained from attempting anything which lay out of
his power to do well, and he devoted himself to such
observations as did not require any very accurate
knowledge of the time. At the same time, he was
careful to ascertain the time of his observations as
closely as possible, by taking the altitudes of the stars.</p>
<p>The next four years seem to have passed
exceedingly pleasantly to him. The notes of ill-health
are few. He was making rapid progress in
his acquaintanceship with the work of other astronomers,
particularly with those of the three marvellously
gifted young men—Horrox, Crabtree, and Gascoigne—who
had passed away shortly before his own
birth. He was making new friends in scientific
circles, and, in particular, Sir Jonas Moore was evidently
esteeming him more and more highly. In
1674 he became more intimate with Newton, the
occasion which led to this acquaintanceship being
the amusing one, that his assistance was asked by<span class="pagenum"><a name="Page_32" id="Page_32">[32]</a></span>
Newton, who had found himself unable to adjust a
microscope, having forgotten its object-glass—not
the only instance of the great mathematician's
absent-mindedness.</p>
<p>The same year he took his degree of A.M. at
Cambridge, designing to enter the Church; but Sir
Jonas Moore was extremely anxious to give him
official charge of an observatory, and was urging the
Royal Society to build an astronomical observatory
at Chelsea College, which then belonged to that body.
He therefore came up to London, and resided some
months with Sir Jonas Moore at the Tower. But
shortly after his coming up to London, 'an accident
happened,' to use his own expression, that hastened,
if it did not occasion, the building of Greenwich
Observatory.</p>
<blockquote>
<p>'A Frenchman that called himself Le Sieur de St. Pierre,
having some small skill in astronomy, and made an interest
with a French lady, then in favour at Court, proposed no
less than the discovery of the Longitude, and had procured
a kind of Commission from the King to the Lord Brouncker,
Dr. Ward (Bishop of Salisbury), Sir Christopher Wren, Sir
Charles Scarborough, Sir Jonas Moore, Colonel Titus, Dr.
Pell, Sir Robert Murray, Mr. Hook, and some other ingenious
gentlemen about the town and Court, to receive his
proposals, with power to elect, and to receive into their
number, any other skilful persons; and having heard them,
to give the King an account of them, with their opinion
whether or no they were practicable, and would show what
he pretended. Sir Jonas Moore carried me with him to one
of their meetings, where I was chosen into their number;
and, after, the Frenchman's proposals were read, which were:</p>
<p>'(1) To have the year and day of the observations.</p>
<p>'(2) The height of two stars, and on which side of the
meridian they appeared.</p>
<p><span class="pagenum"><a name="Page_33" id="Page_33">[33]</a></span></p>
<p>'(3) The height of the moon's two limbs.</p>
<p>'(4) The height of the pole—all to degrees and minutes.</p>
<p>'It was easy to perceive, from these demands, that the
sieur understood not that the best lunar tables differed from
the heavens; and that, therefore, his demands were not
sufficient for determining the longitude of the place where
such observations were, or should be, made, from that to
which the lunar tables were fitted, which I represented immediately
to the company. But they, considering the
interests of his patroness at Court, desired to have him
furnished according to his demands. I undertook it; and
having gained the moon's true place by observations made
at Derby, February 23, 1672, and November 12, 1673, gave
him observations such as he demanded. The half-skilled
man did not think they could have been given him, and
cunningly answered "<em>They were feigned</em>." I delivered them
to Dr. Pell, February 19, 1674-5, who, returning me his
answer some time after, I wrote a letter in English to the
commissioners, and another in Latin to the sieur, to assure
him they were not feigned, and to show them that, if they
had been, yet if we had astronomical tables that would give
us the two places of the fixed stars and the moon's true
places, both in longitude and latitude, nearer than to half
a minute, we might hope to find the longitude of places by
lunar observations, but not by such as he demanded. But
that we were so far from having the places of the fixed stars
true, that the Tychonic Catalogues often erred ten minutes
or more; that they were uncertain to three or four minutes,
by reason that Tycho assumed a faulty obliquity of the
ecliptic, and had employed only plain sights in his observations:
and that the best lunar tables differ one-quarter,
if not one-third, of a degree from the heavens; and lastly,
that he might have learnt better methods than he proposed,
from his countryman Morin, whom he had best
consult before he made any more demands of this nature.'</p></blockquote>
<p>This was in effect to tell St. Pierre that his
proposal was neither original nor practicable. If
St. Pierre had but consulted Morin's writings (Morin<span class="pagenum"><a name="Page_34" id="Page_34">[34]</a></span>
himself had died more than eighteen years before),
he would have known that practically the same
proposal had been laid before Cardinal Richelieu
in 1634, and had been rejected, as quite impracticable
in the then state of astronomical knowledge. Possibly
Flamsteed meant further to intimate that St. Pierre
had simply stolen his method from Morin, hoping to
trade it off upon the government of another country;
in which case he would no doubt regard Flamsteed's
letter as a warning that he had been found out.</p>
<p>Flamsteed continues:—</p>
<blockquote>
<p>'I heard no more of the Frenchman after this; but was
told that, my letters being shown King Charles, he startled
at the assertion of the fixed stars' places being false in the
catalogue; said, with some vehemence, "He must have
them anew observed, examined, and corrected, for the use
of his seamen;" and further (when it was urged to him how
necessary it was to have a good stock of observations taken
for correcting the motions of the moon and planets), with
the same earnestness, "he must have it done." And when
he was asked Who could, or who should do it? "The
person (says he) that informs you of them." Whereupon
I was appointed to it, with the incompetent allowance aforementioned;
but with assurances, at the same time, of such
further additions as thereafter should be found requisite for
carrying on the work.'</p></blockquote>
<div class="figcenter bord" style="width: 600px;"><a name="sextant" id="sextant"></a>
<img src="images/i_036.jpg" width="600" height="369" alt="sextant" />
<div class="caption"><p class="center">FLAMSTEED'S SEXTANT.<br />
(<em>From an engraving in the 'Historia Cœlestis.'</em>)</p></div>
</div>
<p>Thus, in his twenty-ninth year, John Flamsteed
became the first Astronomer Royal. In many ways
he was an ideal man for the post. In the twelve
years which had passed since he left school he had
accomplished an amazing amount of work. Despite
his constant ill-health and severe sufferings, and the
circumstance—which may be inferred from many
expressions in his autobiographies—that he assisted<span class="pagenum"><a name="Page_35" id="Page_35"> </a><br /><a name="Page_36" id="Page_36"> </a><br /><a name="Page_37" id="Page_37">[37]</a></span>
his father in his business, he had made himself master,
perhaps more thoroughly than any of his contemporaries,
of the entire work of a practical astronomer
as it was then understood. He was an indefatigable
computer; the calculation of tables of the motions of
the moon and planets, which should as faithfully as
possible represent their observed positions, had had
an especial attraction for him, and, as has been
already mentioned, some years before his appointment
he had drawn up a catalogue of stars, based
upon the observations of Tycho Brahe. More than
that, he had not been a merely theoretical worker,
he had been a practical observer of very considerable
skill, and, in the dearth of suitable instruments, had
already made one or two for himself, and had contemplated
the making of others. In his first letter
to Sir Jonas Moore he asks for instruction as to the
making of object-glasses for telescopes, for he was
quite prepared to set about the task of making his own.
In addition to his tireless industry, which neither illness
nor suffering could abate, he was a man of singularly
exact and business-like habits. The precision
with which he preserves and records the dates of all
letters received or sent is an illustration of this. On
the other hand, he had the defects of his circumstances
and character. His numerous autobiographical
sketches betray him, not indeed as a conceited man, in
the ordinary sense of the word, but as an exceedingly
self-conscious one. Devout and high-principled he
most assuredly was, but, on the other hand, he shows
in almost every line he wrote that he was one who
could not brook anything like criticism or opposition.</p>
<p><span class="pagenum"><a name="Page_38" id="Page_38">[38]</a></span></p>
<p>Such a man, however efficient, was little likely to be
happy as the first incumbent of a new and important
government post; but there was another circumstance
which was destined to cause him greater unhappiness
still.</p>
<p>If we believe, as surely we must, that not only
the moral and the physical progress of mankind is
watched over and controlled by God's good Providence,
but its intellectual progress as well, then there
can be no doubt that John Flamsteed was raised
up at this particular time, not merely to found
Greenwich Observatory, and to assist the solution
of the problem of the longitude at sea, but also, and
chiefly, to become the auxiliary to a far greater mind,
the journeyman to a true master-builder. But for the
founding of Greenwich Observatory, and for John
Flamsteed's observations made therein, the working
out of Newton's grand theory of gravitation must
have been hindered, and its acceptance by the men of
science of his time immensely delayed. We cannot
regard as accidental the combination, so fortunate for
us, of Newton, the great world-genius, to work out the
problem, of Flamsteed, the painstaking observer, to
supply him with the materials for his work, and of
the newly-founded institution, Greenwich Observatory,
where Flamsteed was able to gather those materials
together. This is the true debt that we owe to Flamsteed,
that, little as he understood the position in
which he had been placed from the standpoint from
which we see it to-day, yet, to the extent of his ability,
and as far as he conceived it in accordance with his
duty, he gave Newton such assistance as he could.</p>
<p><span class="pagenum"><a name="Page_39" id="Page_39">[39]</a></span></p>
<p>This is how we see the matter to-day. It wore
a very different aspect in Flamsteed's eyes; and the
two following documents, the one, the warrant founding
the Observatory and making him Astronomer
Royal; the other, the warrant granting him a salary,
will go far to explain his position in the matter. He
had a high-sounding, official position, which could
not fail to impress him with a sense of importance;
whilst his salary was so insufficient that he naturally
regarded himself as absolute owner of his own
work.</p>
<blockquote>
<p class="center"><em>'Warrant for the Payment of Mr. Flamsteed's Salary.</em></p>
<p class="center">'Charles Rex.</p>
<p>'Whereas, we have appointed our trusty and well-beloved
John Flamsteed, Master of Arts, our astronomical
observator, forthwith to apply himself with the most exact
care and diligence to the rectifying the tables of the motions
of the heavens, and the places of the fixed stars, so as to
find out the so-much-desired longitude of places for the
perfecting the art of navigation, Our will and pleasure is,
and we do hereby require and authorize you, for the support
and maintenance of the said John Flamsteed, of whose
abilities in astronomy we have very good testimony, and
are well satisfied, that from time to time you pay, or cause
to be paid, unto him, the said John Flamsteed, or his
assigns, the yearly salary or allowance of one hundred
pounds per annum; the same to be charged and borne
upon the quarter-books of the Office of the Ordnance, and
paid to him quarterly, by even and equal portions, by the
Treasurer of our said office, the first quarter to begin and
be accompted from the feast of St. Michael the Archangel
last past, and so to continue during our pleasure. And for
so doing, this shall be as well unto you, as to the Auditors
of the Exchequer, for allowing the same, and all other our<span class="pagenum"><a name="Page_40" id="Page_40">[40]</a></span>
officers and ministers whom it may concern, a full and
sufficient warrant.</p>
<p>'Given at our Court at Whitehall, the 4th day of March,
1674-5.</p>
<p class="cenetr">
'By his Majesty's Command,</p>
<p class="sig">
'<span class="smcap">J. Williamson</span>.
</p>
<p>'To our right-trusty and well-beloved Counsellor,
Sir Thomas Chichely, Knt., Master of our
Ordnance, and to the Lieutenant-General of our
Ordnance, and to the rest of the Officers of our
Ordnance, now and for the time being, and to all
and every of them.'</p></blockquote>
<blockquote>
<p class="center"><em>'Warrant for Building the Observatory.</em></p>
<p class="center">'Charles Rex.</p>
<p>'Whereas, in order to the finding out of the longitude of
places for perfecting navigation and astronomy, we have
resolved to build a small observatory within our park at
Greenwich, upon the highest ground, at or near the place
where the Castle stood, with lodging-rooms for our
astronomical observator and assistant, Our will and pleasure
is, that according to such plot and design as shall be given
you by our trusty and well-beloved Sir Christopher Wren,
Knight, our surveyor-general of the place and scite of the
said observatory, you cause the same to be fenced in, built
and finished with all convenient speed, by such artificers
and workmen as you shall appoint thereto, and that you
give order unto our Treasurer of the Ordnance for the
paying of such materials and workmen as shall be used and
employed therein, out of such monies as shall come to your
hands for old and decayed powder, which hath or shall be
sold by our order of the 1st of January last, provided that
the whole sum, so to be expended or paid, shall not exceed
five hundred pounds; and our pleasure is, that all our
officers and servants belonging to our said park be assisting
to those that you shall appoint, for the doing thereof, and
for so doing, this shall be to you, and to all others whom it
may concern, a sufficient warrant.</p>
<p><span class="pagenum"><a name="Page_41" id="Page_41">[41]</a></span></p>
<p>'Given at our Court at Whitehall, the 22nd day of June,
1675, in the 27th year of our reign.</p>
<p class="center">
'By his Majesty's Command,</p>
<p class="sig">
<span class="smcap">'J. Williamson</span>.
</p>
<p>'To our right-trusty and well-beloved Counsellor,
Sir Thomas Chichely, Knt., Master-General of our
Ordnance.'</p></blockquote>
<p>The first question that arose, when it had been
determined to found the new Observatory, was where
it was to be placed. Hyde Park was suggested,
and Sir Jonas Moore recommended Chelsea College,
where he had already thought of establishing
Flamsteed in a private observatory. Fortunately,
both these localities were set aside in favour of one
recommended by Sir Christopher Wren. There was
a small building on the top of the hill in the Royal
Park of Greenwich belonging to the Crown, and
which was now of little or no use. Visible from the
city, and easily accessible by that which was then
the best and most convenient roadway, the river
Thames, it was yet so completely out of town as
to be entirely safe from the smoke of London. In
Greenwich Park, too, but on the more easterly hill,
Charles I. had contemplated setting up an observatory,
but the pressure of events had prevented
him carrying out his intention. A further practical
advantage was that materials could be easily transported
thither. The management of public affairs
under Charles II. left much to be desired in the
matter of efficiency and economy, and it was not
very easy to procure what was wanted for the erection
of a purely scientific building. However, the matter<span class="pagenum"><a name="Page_42" id="Page_42">[42]</a></span>
was arranged. A gate-house demolished in the Tower
supplied wood; iron, and lead, and bricks were supplied
from Tilbury Fort, and these could be easily
brought by water to the selected site. The sum of
£500, actually £520, was further allotted from the
results of a sale of spoilt gunpowder; and with these
limited resources Greenwich Observatory was built.</p>
<p>The foundation-stone was laid August 10, 1675,
and Flamsteed amused himself by drawing the horoscope
of the Observatory, a fact which—in spite of
his having written across the face of the horoscope
<i lang="la" xml:lang="la">Risum teneatis amici?</i> (Can you keep from laughter,
my friends?), and his having two or three years before
written very severely against the imposture of astrology—has
led some modern astrologers to claim
him as a believer in their cult. He actually entered
into residence July 10, 1676.</p>
<div class="figcenter bord" style="width: 600px;"><a name="engraving" id="engraving"></a>
<img src="images/i_044.jpg" width="600" height="335" alt="engraving" />
<div class="caption"><p class="center">THE ROYAL OBSERVATORY IN FLAMSTEED'S DAY.<br />
(<em>From an engraving in the 'Historia Cœlestis.'</em>)</p></div>
</div>
<p>His position was not a bright one. The Government
had, indeed, provided him with a building for
his observatory, and a small house for his own
residence, but he had no instrument and no assistant.
The first difficulty was partly overcome for the
moment by gifts or loans from Sir Jonas Moore, and
by one or two small loans from the Royal Society.
The death of this great friend and patron, four years
after the founding of the Observatory, and only three
years after his entering into residence, deprived him
of several of these; it was with difficulty that he
maintained against Sir Jonas' heirs his claim to the
instruments which Sir Jonas had given him. There
was nothing for him to do but to make his instruments
himself, and in 1683 he built a mural quadrant<span class="pagenum"><a name="Page_43" id="Page_43"> </a><br /><a name="Page_44" id="Page_44"> </a><br /><a name="Page_45" id="Page_45">[45]</a></span>
of fifty inches radius. His circumstances improved
the following year, when Lord North gave him the
living of Burstow, near Horley, Surrey, Flamsteed
having received ordination almost at the time of his
appointment to the Astronomer Royalship. We
have little or no account of the way in which he
fulfilled his duties as a clergyman. Evidently he
considered that his position as Astronomer Royal
had the first claim upon him. At the same time, comparatively
early in life he had expressed his desire
to fill the clerical office, and he was a man too
conscientious to neglect any duty that lay upon him.
That in spite of his feeble health he often journeyed
to and fro between Burstow and Greenwich we know;
and we may take it as certain that at a time when
the standard of clerical efficiency was extremely low,
he was not one of those who</p>
<div class="poem"><div class="stanza">
<span class="i16">'For their bellies' sake,<br /></span>
<span class="i0">Creep and intrude and climb into the fold.'<br /></span>
</div></div>
<p>His chief source of income, however, seems to
have been the private pupils whom he took in
mathematics and astronomy. These numbered in
the years 1676 to 1709 no fewer than 140; and as
many of them were of the very first and wealthiest
families in the kingdom, the gain to Flamsteed in
money and influence must have been considerable.
But it was most distasteful work. It was in no sense
that which he felt to be his duty, and which he had
at heart. It was undertaken from sheer, hard necessity,
and he grudged bitterly the time and strength
which it diverted from his proper calling.</p>
<p><span class="pagenum"><a name="Page_46" id="Page_46">[46]</a></span></p>
<p>How faithfully he followed that, one single circumstance
will show. In the thirteen years ending
1689, he made 20,000 observations, and had revised
single-handed the whole of the theories and tables of
the heavenly bodies then in use.</p>
<p>In 1688 the death of his father brought him a
considerable accession of means, and, far more important,
the assistance of Abraham Sharp,<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> the first
and most distinguished of the long list of Greenwich
assistants, men who, though far less well known than
the Astronomers Royal, have contributed scarcely
less in their own field to the high reputation of the
Observatory.</p>
<p>Sharp was not only a most careful and indefatigable
calculator, he was what was even more
essential for Flamsteed—a most skilful instrument-maker;
and he divided for him a new mural arc of
140° and seven feet radius, with which he commenced
operations on December 12, 1689. Above all, Sharp
became his faithful and devoted friend and adherent,
and no doubt his sympathy strengthened Flamsteed
to endure the trouble which was at hand.</p>
<p>That trouble began in 1694, when Newton visited
the Royal Observatory. At that time Flamsteed,
though he had done so much, had published nothing,
and Newton, who had made his discovery of the
laws of gravitation some few years before, was then
employed in deducing from them a complete theory
of the moon's motion. This work was one of
absolutely first importance. In the first place and<span class="pagenum"><a name="Page_47" id="Page_47">[47]</a></span>
chiefly, upon the success with which it could be
carried out, depended undoubtedly the acceptance
of the greatest discovery which has yet been made
in physical science. Secondarily—and this should,
and no doubt did, appeal to Flamsteed—the perfecting
of our knowledge of the movements of the moon
was a primary part of the very work which he was
commissioned to do as Astronomer Royal. Newton
was, therefore, anxious beyond everything to receive
the best possible observations of the moon's places,
and he came to Flamsteed, as to the man from whom
he had a right to expect to receive a supply of them.
At first Flamsteed seems to have given these as fully
as he was able; but it is evident that Newton
chafed at the necessity for these frequent applications
to Flamsteed, and to the constant need of putting
pressure upon him. Flamsteed, on the other hand,
as clearly evidently resented this continual demand.
Feeling, as he keenly did, that, though he had been
named Astronomer Royal, he had been left practically
entirely without support; his instruments
were entirely his own, either made or purchased by
himself; his nominal salary of £100 was difficult to
get, and did not nearly cover the actual current
expenses of his position, he not unnaturally regarded
his observations as his own exclusive property. He
had a most natural dislike for his observations to
be published, except after such reduction as he
himself had carried through, and in the manner
which he himself had chosen. The idea which was
ever before him was that of carrying out a single
great work that should not only be a monument to<span class="pagenum"><a name="Page_48" id="Page_48">[48]</a></span>
his own industry and skill, but should also raise the
name of England amongst scientific nations. He
complained of it, therefore, both as a personal wrong
and an injury to the country when some observations
of Cassini's were combined with some observations
of his own in order to deduce a better orbit for a
comet.</p>
<p>Unknown to himself, therefore, he was called upon
to decide a question that has proved fundamental to
the policy of Greenwich Observatory, and he decided
it wrongly—the question of publication. Newton
had urged upon him as early as 1691 that he should
not wait until he had formed an exhaustive catalogue
of all the brighter stars, but that he should publish
at once a catalogue of a few, which might serve as
standards; but Flamsteed would not hear of it. He
failed to see that his office had been created for a
definite practical purpose, not for the execution of
some great scheme, however important to science.
All his work of thirty years had done nothing to
forward navigation so long as he published nothing.
But if, year by year, he had published the places of
the moon and of a few standard stars, he would have
advanced the art immensely and yet have not
hindered himself from eventually bringing out a
great catalogue. No doubt the little incident of
Newton's difficulty with the microscope, of which he
had forgotten the object-glass, had given Flamsteed
a low opinion of Newton's qualifications as a practical
astronomer. If so, he was wrong, for Newton's insight
into practical matters was greater than Flamsteed's
own, and his practical skill was no less, though<span class="pagenum"><a name="Page_49" id="Page_49">[49]</a></span>
his absent-mindedness might occasionally lead him
into an absurd mistake.</p>
<p>The following extract from Flamsteed's own
'brief History of the Observatory' gives an account
of his view of Newton's action towards him in
desiring the publication of his star catalogue, and
at the same time it illustrates Flamsteed's touchy
and suspicious nature.</p>
<blockquote>
<p>'Whilst Mr. Flamsteed was busied in the laborious work
of the catalogue of the fixed stars, and forced often to watch
and labour by night, to fetch the materials for it from the
heavens, that were to be employed by day, he often, on Sir
Isaac Newton's instances, furnished him with observations
of the moon's places, in order to carry on his correction of
the lunar theory. A civil correspondence was carried on
between them; only Mr. Flamsteed could not but take
notice that as Sir Isaac was advanced in place, so he raised
himself in his conversation and became more magisterial.
At last, finding that Mr. Flamsteed had advanced far in his
designed catalogue by the help of his country calculators,
that he had made new lunar tables, and was daily advancing
on the other planets, Sir Isaac Newton came to see him
(Tuesday, April 11, 1704); and desiring, after dinner, to be
shown in what forwardness his work was, had so much of
the catalogue of the fixed stars laid before him as was then
finished; together with the maps of the constellations, both
those drawn by T. Weston and P. Van Somer, as also his
collation of the observed places of Saturn and Jupiter, with
the Rudolphine numbers. Having viewed them well, he
told Mr. Flamsteed he would (<em>i.e.</em> he was desirous to)
recommend them to the Prince <em>privately</em>. Mr. Flamsteed
(who had long been sensible of his partiality, and heard
how his two flatterers cried Sir Isaac's performances up,
was sensible of the snare in the word <em>privately</em>) answered
that would not do; and (upon Sir Isaac's demanding "why
not?") that then the Prince's attendants would tell him
these were but curiosities of no great use, and persuade<span class="pagenum"><a name="Page_50" id="Page_50">[50]</a></span>
him to save that expense, that there might be the more for
them to beg of him: and that the recommendation must
be made <em>publicly</em>, to prevent any such suggestions. Sir
Isaac apprehended right, that he was understood, and his
designs defeated: and so took his leave not well satisfied
with the refusal.</p>
<p>'It was November following ere Mr. Flamsteed heard
from him any more: when, considering with himself that
what he had done was not well understood, he set himself
to examine how many folio pages his work when printed
would fill; and found upon an easy computation that they
would at least take up 1400. Being amazed at this, he set
himself to consider them more seriously; drew up an
estimate of them; and, to obviate the misrepresentations
of Dr. S[loane] and some others, who had given out that
what he had was inconsiderable, he delivered a copy of the
estimate to Mr. Hodgson, then lately chosen a member of
the Royal Society, with directions to deliver it to a friend,
who he knew would do him justice; and, on this fair
account, obviate those unjust reports which had been
studiously spread to his prejudice. It happened soon after,
Mr. Hodgson being at a meeting, spied this person there,
at the other side of the room; and therefore gave the paper
to one that stood in some company betwixt them, to be
handed to him. But the gentleman, mistaking his request,
handed to the Secretary [Dr. Sloane], who, being a
Physician, and not acquainted with astronomical terms,
did not read it readily. Whereupon another in the
company took it out of his hands; and, having read it
distinctly, desired that the works therein mentioned might
be recommended to the Prince; the charge of printing
them being too great either for the author or the Royal
Society. Sir Isaac closed in with this.'</p></blockquote>
<div class="figcenter bord" style="width: 600px;"><a name="stellata" id="stellata"></a>
<img src="images/i_052.jpg" width="600" height="382" alt="stellata" />
<div class="caption"><p class="center">THE 'CAMERA STELLATA' IN FLAMSTEED'S TIME.<br />(<em>From an engraving in the 'Historia Cœlestis.'</em>)</p></div>
</div>
<p>The work was in consequence recommended to
Prince George of Denmark, the Queen's Consort;
but it was not till November 10, 1705, that the
contract for the printing was signed. Two years
later, the observations which he had made with<span class="pagenum"><a name="Page_51" id="Page_51"> </a><br /><a name="Page_52" id="Page_52"> </a><br /><a name="Page_53" id="Page_53">[53]</a></span>
his sextant in his first thirteen years of office
were printed. Then came the difficulty of the
catalogue. It was not complete to Flamsteed's
satisfaction, and he was most unwilling to let it
pass out of his hands. However, two manuscripts,
comprising some three-quarters of the whole, were
deposited with referees, the first of these being sealed
up. The seal was broken with Flamsteed's concurrence;
but the fact that it had been so broken
was made by him the subject of bitter complaint
later. At this critical juncture Prince George died,
and a stop was put to the progress of the printing.
Two years more elapsed without any advance being
made, and then, in order to check any further
obstruction, a committee of the Royal Society was
appointed as a Board of Visitors to visit and inspect
the Observatory, and so maintain a control over the
Astronomer Royal. This was naturally felt by so
sensitive a man as Flamsteed as a most intolerable
wrong, and when he found that the printing of his
catalogue had been placed in the hands of Halley as
editor, a man for whom he had conceived the most
violent distrust, he absolutely refused to furnish the
Visitors with any further material. This led to,
perhaps, the most painful scene in the lives either
of Newton or Flamsteed. Flamsteed was summoned
to meet the Council of the Royal Society at their
rooms in Crane Court. A quorum was not present,
and so the interview was not official, and no record
of it is preserved in the archives. Flamsteed has
himself described it with great particularity in more
than one document, and it is only too easy to<span class="pagenum"><a name="Page_54" id="Page_54">[54]</a></span>
understand the scene that took place. Newton was
a man who had an absolutely morbid dread of
anything like controversy, and over and over again
would have preferred to have buried his choicest
researches, rather than to have encountered the
smallest conflict of the kind. He was perhaps,
therefore, the worst man to deal with a high-principled,
sensitive, and obstinate man who was
in the wrong, and yet who had been so hardly dealt
with that it was most natural for him to think himself
wholly in the right. Flamsteed adhered absolutely
to his position, from which it is clear it would have
been extremely difficult for the greatest tact and
consideration to have dislodged him. Newton, on
his part, simply exerted his authority, and, that
failing, was reduced to the miserable extremity of
calling names. The scene is described by Flamsteed
himself, in a letter to Abraham Sharp, as follows:—</p>
<blockquote>
<p>'I have had another contest with the President<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> of the
Royal Society, who had formed a plot to make my
instruments theirs; and sent for me to a Committee, where
only himself and two physicians (Dr. Sloane, and another
as little skilful as himself) were present. The President
ran himself into a great heat, and very indecent passion.
I had resolved aforehand his kn—sh talk should not
move me; showed him that all the instruments in the
Observatory were my own; the mural arch and voluble
quadrant having been made at my own charge, the rest
purchased with my own money, except the sextant and
two clocks, which were given me by Sir Jonas Moore, with
Mr. Towneley's micrometer, his gift, some years before
I came to Greenwich. This nettled him; for he has got
a letter from the Secretary of State for the Royal Society<span class="pagenum"><a name="Page_55" id="Page_55">[55]</a></span>
to be Visitors of the Observatory, and he said, "<em>as good
have no observatory as no instruments</em>." I complained
then of my catalogue being printed by Raymer, without my
knowledge, and that I was <em>robbed of the fruit of my labours</em>.
At this he fired, and called me all the ill names, puppy,
etc., that he could think of. All I returned was, I put him
in mind of his passion, desired him to govern it, and keep
his temper: this made him rage worse, and he told me
how much I had received from the Government in thirty-six
years I had served. I asked what he had done for the
£500 per annum that he had received ever since he had
settled in London. This made him calmer; but finding
him going to burst out again, I only told him my catalogue,
half finished, was delivered into his hands, on his own
request, sealed up. He could not deny it, but said Dr.
Arbuthnott had procured the Queen's order for opening it.
This, I am persuaded, was false; or it was got after it had
been opened. I said nothing to him in return; but, with
a little more spirit than I had hitherto showed, told them
that God (who was seldom spoken of with due reverence in
that meeting) had hitherto prospered all my labours, and
I doubted not would do so to a happy conclusion; took
my leave and left them. Dr. Sloane had said nothing all
this while; the other Doctor told me I was proud, and
insulted the President, and ran into the same passion with
the President. At my going out, I called to Dr. Sloane,
told him he had behaved himself civilly, and thanked him
for it. I saw Raymer after, drank a dish of coffee with
him, and told him, still calmly, of the villany of his conduct,
and called it <em>blockish</em>. Since then they let me be quiet;
but how long they will do so I know not, nor am I
solicitous.'</p></blockquote>
<p>The Visitors continued the printing, Halley being
the editor, and the work appeared in 1712 under the
title of <em>Historia Cœlestis</em>. This seemed to Flamsteed
the greatest wrong of all. The work as it appeared
seemed to him so full of errors, wilfully or accidentally
inserted, as to be the greatest blot upon his fair<span class="pagenum"><a name="Page_56" id="Page_56">[56]</a></span>
fame, and he set himself, though now an old man, to
work it out <i lang="la" xml:lang="la">de novo</i> and at his own expense. To
that purpose he devoted the remaining seven years
of his life. Few things can be more pathetic than
the letters which he wrote in that period referring to
it. He was subject to the attacks of one of the
cruelest of all diseases—the stone; he was at all
times liable to distracting headaches. He had been,
from his boyhood, a great sufferer from rheumatism,
and yet, in spite of all, he resolutely pushed on his
self-appointed task. The following extract from one
of his letters will give a more vivid idea of the brave
old man than much description:—</p>
<blockquote>
<p>'I can still, I praise God for it, walk from my door to
the Blackheath gate and back, with a little resting at some
benches I have caused to be set up betwixt them. But I
found myself so tired with getting up the hill when I return
from church, that at last I have bought a sedan, and am
carried thither in state on Sunday mornings and back; I
hope I may employ it in the afternoons, though I have not
hitherto, by reason of the weather is too cold for me.'</p></blockquote>
<p>After the death of Queen Anne, a change in the
ministry enabled him to secure that three hundred
copies of the total impression of four hundred of the
<cite>Historia Cœlestis</cite> were handed over to him. These,
except the first volume, containing his sextant
observations (which had received his own approval),
he burned, 'as a sacrifice to heavenly truth.' His
own great work had advanced so far that the first
volume was printed, and much of the second, when
he himself died, on the last day of 1719. He was
buried in the chancel of Burstow Church.</p>
<p><span class="pagenum"><a name="Page_57" id="Page_57">[57]</a></span></p>
<p>The completion of his work took ten years more;
a work of piety and regard on the part of his assistant,
Joseph Crosthwait.</p>
<p>When compared with the catalogues that have
gone before, it was a work of wonderful accuracy.
Nevertheless, as Caroline Herschel showed, nearly a
century later, not a few errors had crept into it.
Some of the stars are non-existent, others have been
catalogued in more than one constellation; important
stars have been altogether omitted. Perhaps the
most serious fault arises from the neglect of
Flamsteed to accept from Newton a practical hint,
namely, to read the barometer and thermometer at
the time of his observations. Nevertheless, the work
accomplished was not only wonderful under the
untoward conditions in which Flamsteed was placed;
it was wonderful in itself, winning from Airy the
following high encomium:—</p>
<blockquote>
<p>'In regard not only to accuracy of observation, and to
detail in publication of the methods of observing, but also
to steadiness of system followed through many years, and
to completeness of calculation of the useful results deduced
from the observations, this work may shame any other
collection of observations in this or any other country.'</p></blockquote>
<p>This catalogue was not Flamsteed's only achievement.
He had determined the latitude of the Observatory,
the obliquity of the ecliptic, and the position of the
equinoctial points. He thought out an original
method of obtaining the absolute right ascensions of
stars by differential observations of the places of the
stars and the sun near to both equinoxes. He had
revised and improved Horrox's theory of the lunar<span class="pagenum"><a name="Page_58" id="Page_58">[58]</a></span>
motions, which was by far the best existing in
Flamsteed's day. He showed the existence of the
long inequality of Jupiter and Saturn; that is to say,
the periodic influence which they exercise upon each
other. He determined the time in which the sun
rotates on its axis, and the position of that axis.
He observed an apparent movement of the stars
in the course of a year, which he ascribed, though
erroneously, to the stellar parallax, and which
was explained by the third Astronomer Royal,
Bradley.</p>
<p>Flamsteed not only met with harsh treatment
during his lifetime; he has not yet received, except
from a few, anything like the meed of appreciation
which is his just due; but, at least, his successors in
the office have not forgotten him. They have been
proud that their official residence should be known
as Flamsteed House, and his name is inscribed over
the main entrance of the latest and finest of the
Observatory buildings, and his bust looks forth from
its front towards the home where he laboured so
devotedly for nearly fifty years. But he has received
little honour, save at Greenwich, and—in spite of the
proverb—in his other home, the village of Burstow,
in Surrey, of which he was for many years the rector.
Here a stained glass window representing, appropriately,
the Adoration of the Magi, has been
recently set up to his memory, largely through
the interest taken in his history by an amateur
astronomer of the neighbourhood, Mr. W. Tebb,
F.R.A.S.</p>
<p>No instrument of Flamsteed's remains in the<span class="pagenum"><a name="Page_59" id="Page_59">[59]</a></span>
Observatory, his wife removing them after his death.
But we may consider his principal instrument, the
mural quadrant made for him by Abraham Sharp,
as represented by the remains of a quadrant by the
same artist, which was presented to the Observatory
by the Rev. N. S. Heineken, in 1865, and now hangs
over the door of the transit room.</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_60" id="Page_60">[60]</a></span></p>
<h2>CHAPTER III</h2>
<h3>HALLEY AND HIS SUCCESSORS</h3>
<blockquote>
<p>There is no need to give the lives of the succeeding
Astronomers Royal so fully as that of Flamsteed.
Not that they were inferior men to him; on the
contrary, there can be little doubt that we ought to
reckon some of them as his superiors, but, in the
case of several, their best work was done apart from
Greenwich Observatory, and before they came to it.</p></blockquote>
<p>This was particularly the case with <span class="smcap">Edmund
Halley</span>. Born on October 29, 1656, he was ten
years the junior of Flamsteed. Like Flamsteed, he
came of a Derbyshire family, though he was born at
Haggerston, in the parish of St. Leonard's, Shoreditch.
He was educated at St. Paul's School, where
he made very rapid progress, and already showed
the bent of his mind. He learnt to make dials; he
made himself so thoroughly acquainted with the
heavens that it is said, 'If a star were displaced in
the globe he would presently find it out,' and he
observed the changes in the direction of the mariner's
compass. In 1673 he went to Queen's College,
Oxford, where he observed a sunspot in July and
August, 1676, and an occultation of Mars. This was
not his first astronomical observation, as, in June,<span class="pagenum"><a name="Page_61" id="Page_61"> </a><br /><a name="Page_62" id="Page_62"> </a><br /><a name="Page_63" id="Page_63">[63]</a></span>
1675, he had observed an eclipse of the moon from
his father's house in Winchester Street.</p>
<div class="figcenter bord" style="width: 450px;"><a name="halley" id="halley"></a>
<img src="images/i_061.jpg" width="450" height="494" alt="halley" />
<div class="caption"><p class="center">EDMUND HALLEY.<br />
(<em>From an old print.</em>)</p></div>
</div>
<p>A much wider scheme of work than such merely
casual observations now entered his mind, possibly
suggested to him by Flamsteed's appointment to the
direction of the new Royal Observatory. This was
to make a catalogue of the southern stars. Tycho's
places for the northern stars were defective enough,
but there was no catalogue at all of stars below the
horizon of Tycho's observatory. Here, then, was a
field entirely unworked, and young Halley was so
eager to enter upon it that he would not wait at
Oxford to obtain his degree, but was anxious to
start at once for the southern hemisphere.</p>
<p>His father, who was wealthy and proud of his
gifted son, strongly supported him in his project. The
station he selected was St. Helena, an unfortunate
choice, as the skies there were almost always more
or less clouded, and rain was frequent during his stay.
However, he remained there a year and a half, and
succeeded in making a catalogue of 341 stars. This
catalogue was finally reduced by Sharp, and included
in the third volume of Flamsteed's <cite>Historia Cœlestis</cite>.</p>
<p>In 1678 he was elected Fellow of the Royal
Society, and the following year he was chosen to
represent that society in a discussion with Hevelius.
The question at issue was as to whether more accurate
observations of the place of a star could be obtained
by the use of sights without optical assistance, or by
the use of a telescope. The next year he visited the
Paris Observatory, and, later in the same tour, the
principal cities of the Continent.</p>
<p><span class="pagenum"><a name="Page_64" id="Page_64">[64]</a></span></p>
<p>Not long after his return from this tour, Halley
was led to that undertaking for which we owe him
the greatest debt of gratitude, and which must be
regarded as his greatest achievement.</p>
<p>Some fifty years before, the great Kepler had
brought out the third of his well-known laws of
planetary motion. These laws stated that the planets
move round the sun in ellipses, of which the sun
occupies one of the foci; that the straight line
joining any planet with the sun moves over equal
areas of space in equal periods of time; and, lastly,
that the squares of the times in which the several
planets complete a revolution round the sun are
proportional to the cubes of their mean distances
from it. These three laws were deduced from actual
examination of the movements of the planets. Kepler
did not work out any underlying cause of which these
three laws were the consequence.</p>
<p>But the desire to find such an underlying cause
was keen amongst astronomers, and had given rise
to many researches. Amongst those at work on the
subject was Halley himself. He had seen, and been
able to prove, that if the planets moved in circles
round the sun, with the sun in the centre, then the
law of the relation between the times of revolution
and the distances of the planets would show that the
attractive force of the sun varied inversely as the
square of the distance. The actual case, however, of
motion in an ellipse was too hard for him, and he
could not deal with it. Halley therefore went up to
Cambridge to consult Newton, and, to his wonder and
delight, found that the latter had already completely<span class="pagenum"><a name="Page_65" id="Page_65">[65]</a></span>
solved the problem, and had proved that Kepler's
three laws of planetary motion were summed up in
one, namely, that the sun attracted the planets to it
with a force inversely proportional to the square of
the distance.</p>
<p>Halley was most enthusiastic over this great discovery,
and he at once strongly urged Newton to
publish it. Newton's unwillingness to do so was
great, but at length Halley overcame his reluctance;
and the Royal Society not being able at the time
to afford the expense, Halley took the charges
upon himself, although his own resources had been
recently seriously damaged by the death of his
father.</p>
<p>The publication of Newton's <cite>Principia</cite>, which, but
for him, might never have seen the light, and most
certainly would have been long delayed, is Halley's
highest claim to our gratitude. But, apart from this,
his record of scientific achievement is indeed a noble
one. Always, from boyhood, he had taken a great
interest in the behaviour of the magnetic compass,
and he now followed up the study of its variations
with the greatest energy. For this purpose it was
necessary that he should travel, in view of the great
importance of the subject to navigation. King
William III. gave him a captain's commission in the
Royal Navy—a curious and interesting illustration
of the close connection between astronomy and the
welfare of our navy—and placed him in command of
a 'pink,' that is to say, a small vessel with pointed
stern, named the Paramour, in which he proceeded to
the southern ocean. His first voyage was unfortunate,<span class="pagenum"><a name="Page_66" id="Page_66">[66]</a></span>
but the Paramour was recommissioned in 1699, and
he sailed in it as far as south latitude 52°.</p>
<p>In 1701 and the succeeding year he made further
voyages in the Paramour, surveying the tides and
coasts of the British Channel and of the Adriatic,
and helping in the fortification of Trieste. He
became Savilian Professor of Geometry at Oxford in
1703, having failed twelve years previously to secure
the Savilian Professorship of Astronomy, mainly
through the opposition of Flamsteed, who had already
formed a strong prejudice against him, which some
writers have traced to Halley's detection of several
errors in one of Flamsteed's tide-tables, others to
Halley's supposed materialistic views. Probably the
difference was innate in the two men. There was
likely to be but little sympathy between the strong,
masterful man of action and society and the secluded,
self-conscious, suffering invalid. At any rate, in the
contest between Newton and Flamsteed, which has
been already described, Halley took warmly the
side of the former, and was appointed to edit the
publication of Flamsteed's results, and, on the death
of the latter, to succeed him at the Royal Observatory.</p>
<p>The condition of things at Greenwich when
Halley succeeded to the post of Astronomer Royal
in 1720 was most discouraging. The instruments
there had all belonged to Flamsteed, and therefore,
most naturally, had been removed by his widow.
The Observatory had practically to be begun <i lang="la" xml:lang="la">de novo</i>,
and Halley had now almost attained the age at
which in the present day an Astronomer Royal
would have to retire. More fortunate, however, than<span class="pagenum"><a name="Page_67" id="Page_67">[67]</a></span>
his predecessor, he was able to get a grant for
instruments, and he equipped the Observatory as
well as the resources of the time permitted, and his
transit instrument and great eight-foot quadrant still
hang upon the Observatory walls.</p>
<p>As Astronomer Royal his great work was the
systematic observation of the positions of the moon
through an entire <em>saros</em>. As is well known, a period
of eighteen years and ten or eleven days brings the
sun and moon very nearly into the same positions
relatively to the earth which they occupied at the
commencement of the period. This period was well
known to the ancient Chaldeans, who gave it its name,
since they had noticed that eclipses of the sun or
eclipses of the moon recurred at intervals of the above
length. It was Halley's desire to obtain such a set
of observations of the moon through an entire <em>saros</em>
period as to be able to deduce therefrom an improved
set of tables of the moon's motion. It was an
ambitious scheme for a man so much over sixty
to undertake, nevertheless he carried it through
successfully.</p>
<p>His desire to complete this scheme, and to found
upon it improved lunar tables, hindered him from
publishing his observations, for he feared that others
might make use of them before he was in a position to
complete his work himself. This omission to publish
troubled Newton, who, as President of the Royal
Society—the Greenwich Board of Visitors having
lapsed at Queen Anne's death—drew attention at a
meeting of the Royal Society, March 2, 1727, to
Halley's disobedience of the order issued under Queen<span class="pagenum"><a name="Page_68" id="Page_68">[68]</a></span>
Anne, for the prompt communication of the Observatory
results. That Newton should thus have put
public pressure upon Halley, the man to whom he
was so much indebted, and with whom there was so
close an affection, is sufficient proof that his similar
attitude towards Flamsteed was one of principle and
not of arbitrariness. Halley, on his side, stood firm,
as Flamsteed had done, urging the danger that, by
publishing before he had completed his task, he
might give an opportunity to others to forestall his
results. It is said—probably without sufficient
ground—that this refusal broke Newton's heart and
caused his death. Certainly Halley's writings in
that very year show his reverence and affection for
Newton to have been as keen and lively as ever.</p>
<p>Halley's work at the Observatory went on
smoothly, on the lines he had laid down for himself,
for ten years after Newton's death; but in 1737 he
had a stroke of paralysis, and his health, which had
been remarkably robust up to that time, began to
give way. He died January 14, 1742, and was buried
in the cemetery of Lee Church.</p>
<p>As an astronomer, his services to the science
rank higher than those of his predecessor; but as
Astronomer Royal, as director, that is to say, of
Greenwich Observatory, he by no means accomplished
as much as Flamsteed had done. Professor Grant, in
his <cite>History of Physical Astronomy</cite>, says that he seems
to have undervalued those habits of minute attention
which are indispensable to the attainment of a high
degree of excellence in the practice of astronomical
observation. He was far from being sufficiently<span class="pagenum"><a name="Page_69" id="Page_69">[69]</a></span>
careful as to the adjustment of his instruments,
the going of his clocks, or the recording of his
own observations. The important feature of his<span class="pagenum"><a name="Page_70" id="Page_70">[70]</a></span>
administration was that under him the Observatory
was first supplied with instruments which belonged
to it.</p>
<div class="figcenter bord" style="width: 450px;"><a name="quadrant" id="quadrant"></a>
<img src="images/i_069.jpg" width="450" height="591" alt="quadrant" />
<div class="caption"><p class="center">HALLEY'S QUADRANT.<br />
(<em>From an old print.</em>)</p></div>
</div>
<p>His astronomical work apart from the Observatory
was of the first importance. He practically
inaugurated the study of terrestrial magnetism, and
his map giving the results of his observations during
his voyage in the Paramour introduced a new and
most useful style of recording observations. He
joined together by smooth curves places of equal
variation, the result being that the chart shows at
a glance, not merely the general course of the variation
over the earth's surface, but its value at any spot
within the limits of the chart.</p>
<p>Another work which has justly made his name
immortal was the prediction of the return of the
comet which is called by his name, to which reference
will be made later. Another great scheme, and one
destined to bear much fruit, was the working out of
a plan to determine the distance of the sun by
observations of the transit of Venus.</p>
<p>Of attractive appearance, pleasing manners, and
ready wit, loyal, generous, and free from self-seeking,
he probably was one of the most personally engaging
men who ever held the office.</p>
<p>The salary of the Astronomer Royal remained
under Halley at the same inadequate rate which it
had done under Flamsteed—£100, without provision
for an assistant. But in 1729 Queen Caroline, learning
that Halley had actually had a captain's commission
in the Royal Navy, secured for him a post-captain's
pay.</p>
<p><span class="pagenum"><a name="Page_71" id="Page_71"> </a><br /><a name="Page_72" id="Page_72"> </a></span></p>
<div class="figcenter bord" style="width: 450px;"><a name="bradley" id="bradley"></a>
<img src="images/i_072.jpg" width="450" height="522" alt="bradley" />
<div class="caption"><p class="center">JAMES BRADLEY.<br />
(<em>From the painting by Hudson.</em>)</p></div>
</div>
<p><span class="pagenum"><a name="Page_73" id="Page_73">[73]</a></span></p>
<p>Halley's work is represented at the Observatory
by two of his instruments which are still preserved
there, and which hang on the west wall of the present
transit room: the Iron Quadrant afterwards made
famous by the observations of Bradley, and 'Halley's
Transit,' the first of the great series of instruments
upon which the fame of Greenwich chiefly rests.
This transit instrument seems to have been set up
in a small room at the west end of what is now known
as the North Terrace. His quadrant was mounted on
the pier which is now the base of the pier of the
astrographic telescope. This pier was the first extension
which the Observatory received from the original
building.</p>
<p>On the breakdown of his health Halley nominated
as his successor, James Bradley; indeed, it is stated
that he offered to resign in his favour. He had
known him then for over twenty years, and that keen
and generous appreciation of merit in others which
was characteristic of Halley had led him very early
to recognize Bradley's singular ability.</p>
<hr class="tb" />
<p><span class="smcap">James Bradley</span> was born in 1692 or 1693, of
an old North of England family. His birthplace was
Sherbourne, in Gloucestershire, and he was educated
at North Leach Grammar School and at Baliol
College, Oxford. During the years of his undergraduateship
he resided much with his uncle, the
Rev. James Pound, Rector of Wanstead, Essex, an
ardent amateur astronomer, a frequent visitor at the
Observatory in Flamsteed's time, and one of the
most accurate observers in the country. From him,<span class="pagenum"><a name="Page_74" id="Page_74">[74]</a></span>
no doubt, he derived his love of the science, and
possibly some of his skill in observation.</p>
<p>Bradley's earliest observations seem to have been
devoted to the phenomena of Jupiter's satellites and
to the measures of double stars. The accuracy with
which he followed up the first drew the attention of
Halley, and so began a friendship which lasted
through life. His observations of double stars,
particularly of Castor, only just failed to show him
the orbital movement of the pair, because his attention
was drawn to other subjects before it had become
sufficiently obvious.</p>
<p>In 1719 Bradley and his uncle made an attempt
to determine the distance of the sun through observations
of Mars when in opposition, observations which
were so accurate that they sufficed to show that the
distance of the sun could not be greater than 125
millions of miles, nor less than about 94 millions.
The lower limit which they thus found has proved to
be almost exactly correct, our best modern determinations
giving it as 93 millions. The instrument
with which the observations were made was a novel
one, being 'moved by a machine that made it to
keep pace with the stars;' in other words, it was the
first, or nearly the first, example of what we should
now call a clock-driven equatorial.</p>
<p>That same year he was offered the Vicarage of
Bridstow, near Ross, in Monmouthshire, where, having
by that time taken priest's orders, he was duly
installed, July, 1720. To this was added the sinecure
Rectory of Llandewi-Velgry; but he held both livings
only a very short time. In 1721 the death of Dr.<span class="pagenum"><a name="Page_75" id="Page_75">[75]</a></span>
John Keill rendered vacant the Savilian Professorship
of Astronomy at Oxford, for which Bradley became
a candidate, and was duly elected, and resigned his
livings in consequence.</p>
<p>It was whilst he was Savilian Professor that
Bradley made that great discovery which will always
be associated with his name. Though professor at
Oxford, he had continued to assist his uncle, Mr.
Pound, at his observations at Wanstead, and after
the death of the latter he still lived there as much
as possible, and continued his astronomical work.
But in 1725 he was invited by Mr. Samuel Molyneux,
who had set up a twenty-four-foot telescope made by
Graham as a zenith tube at his house on Kew Green,
to verify some observations which he was making.
These were of the star Gamma Draconis, a star which
passes through the zenith of London, and which,
therefore, had been much observed both by Flamsteed
and Hooke, inasmuch as by fixing a telescope in an
absolutely vertical position—a position which could
be easily verified—it was easy to ascertain if there
was any minute change in the apparent position of
the star. Dr. Hooke had declared that there was
such a change, a change due to the motion of the
earth in its orbit, which would prove that the star
was not an infinite distance from the earth, the
seeming change of its place in the sky corresponding
to the change in the place of the earth from which
the observer was viewing it.</p>
<p>Bradley found at once that there was such a
change—a marked one. It amounted to as much
as 1´´ of arc in three days; but it was not in the<span class="pagenum"><a name="Page_76" id="Page_76">[76]</a></span>
direction in which the parallax of the star would have
moved it, but in the opposite. Whether, therefore,
the star was near enough to show any parallax or not,
some other cause was giving rise to an apparent displacement
of the star, which entirely masked and
overcame the effect of parallax.</p>
<p>So far, Bradley had but come to the same point
which Flamsteed had reached. Flamsteed had
detected precisely the same apparent displacement
of stars, and, like Hooke, had ascribed it to parallax.
Cassini had shown that this could not be the case, as
the displacement was in the wrong direction; and
there the matter had rested. Bradley now set to
follow the question up. Other stars beside Gamma
Draconis were found to show a displacement of the
same general character, but the amount varied with
their distance from the plane of the ecliptic, the
earth's orbit. The first explanation suggested was
that the axis of the earth, which moves very nearly
parallel to itself as the earth moves round the sun,
underwent a slight regular 'wobble' in the course of
a year. To check this, a star was observed on the
opposite side of the pole from Gamma Draconis;
then Bradley investigated as to whether refraction
might explain the difficulty, but again without
success. He now was most keenly interested in the
problem, and he purchased a zenith telescope of his
own, made, like that of Molyneux, by Graham, and
mounted it in his aunt's house at Wanstead, and
observed continuously with it. The solution of the
problem came at last to him as he was boating on the
Thames. Watching a vane at the top of the mast,<span class="pagenum"><a name="Page_77" id="Page_77"> </a><br /><a name="Page_78" id="Page_78">[78]</a></span>
he saw with surprise that it shifted its direction every
time that the boat was put about. Remarking to the
boatmen that it was very odd that the wind should
change just at the same moment that there was a
shift in the boat's course, they replied that there was
no change in the wind at all, and that the apparent
change of the vane was simply due to the change of
direction of the motion of the boat.</p>
<div class="figcenter bord" style="width: 366px;"><a name="zenith" id="zenith"></a>
<img src="images/i_077.jpg" width="366" height="600" alt="zenith" />
<div class="caption"><p class="center">GRAHAM'S ZENITH SECTOR.<br />
(<em>From an old print.</em>)</p></div>
</div>
<p>This supplied Bradley with a key to the solution
of the mystery that had troubled him so long. It
had been discovered long before this that light does
not travel instantaneously from place to place, but
takes an appreciable time to pass from one member
of the solar system to another. This had been discovered
by Römer from observations of the satellites
of Jupiter. He had noted that the eclipses of the
satellites always fell late of the computed time, when
Jupiter was at his greatest distance from the earth;
and Bradley's own work in the observation of those
satellites had brought the fact most intimately under
his own acquaintance. The result of the boating
incident taught him, then, that he might look upon
light as analogous to the wind blowing on the boat.
As the wind, so long as it was steady, would seem to
blow from one fixed quarter so long as the boat was
also in rest, but as it seemed to shift its direction
when the boat was moving and changed its direction,
so he saw that the light coming from a particular star
must seem to slightly change the direction in which
it came, or, in other words, the apparent position of
the star, to correspond with the movement of the
earth in its orbit round the sun.</p>
<p><span class="pagenum"><a name="Page_79" id="Page_79">[79]</a></span></p>
<p>This was the celebrated discovery of the Aberration
of Light, a triumph of exact observation and of
clear insight. As to the exactness of Bradley's
observations, it is sufficient to say that his determination
of the value of the 'Constant of Aberration' gave
it as 20·39´´; the value adopted to-day is 20·47´´.</p>
<p>On the death of Halley, in 1742, Bradley was
appointed to succeed him. He found the Observatory
in as utterly disheartening a condition as his predecessors
had done. As already mentioned, Halley
had not the same qualifications as an observer that
Flamsteed had. He was, further, an old man when
appointed to the post, he had no assistant provided
for him, and the last five years of his life his health
and strength had entirely given way. Under these circumstances,
it was no wonder that Bradley found the
instruments of the Observatory in a deplorable state.
Nevertheless, he set to work most energetically, and
in the year of his appointment he made 1500 observations
in the last five months of the year. He was
particularly earnest in examining the condition and
the errors of his instruments; and as their defects
became known to him, he was more and more anxious
for a better equipment. He moved the Royal
Society, therefore, to apply on his behalf for the
instruments he required; and a petition from that
body, in 1748, obtained what in those days must
be considered the generous grant of £1000, the
proceeds of the sale of old Admiralty stores. The
principal instruments purchased therewith were a
mural quadrant and a transit instrument, both eight
feet in focal length, still preserved on the walls of the<span class="pagenum"><a name="Page_80" id="Page_80">[80]</a></span>
transit-room. It is interesting also to note that,
following in the steps of Halley, and forecasting, as it
were, the magnetic observatory which Airy would
found, he devoted £20 of the grant to purchasing
magnetic instruments.</p>
<p>Meantime he had continued his observations on
aberration, and had discovered that the aberration
theory was not sufficient entirely to account for the
apparent changes in places of stars which he had
discovered. A second cause was at work, a movement
of the earth's axis, a 'wobble' in its inclination,
technically known as Nutation, which is due to the
action of the moon, and goes through its course in a
period of nineteen years.</p>
<p>Beside these two great discoveries of aberration
and nutation, Bradley's reputation rests upon his
magnificent observations of the places of more than
three thousand stars. This part of his work was done
with such thoroughness, that the star-places deduced
from them form the basis of most of our knowledge
as to the actual movements of individual stars. In
particular, he was careful to investigate and to correct
for the errors of his instrument, and to determine
the laws of refraction, introducing corrections for
changes in the readings of thermometer and barometer.
His tables of refraction were used, indeed,
for seventy years after his death. Of his other labours
it may be sufficient to refer to his determination of
the longitudes of Lisbon and of New York, and to his
effort to ascertain the parallax of the sun and moon,
in combination with La Caille, who was observing at
the Cape of Good Hope.</p>
<p><span class="pagenum"><a name="Page_81" id="Page_81">[81]</a></span></p>
<p>As Astronomer Royal, Bradley's great achievement
was the high standard to which he raised the
practical work of observation. From his day onwards,
also, there was always at least one assistant.
His first assistant was his own nephew, John Bradley,
who received the munificent salary of ten shillings a
week. Still, this was not out of proportion to the
then salary of the Astronomer Royal, which practically
amounted only to £90. However, in 1752,
Bradley was awarded a Crown pension of £250 a
year. He refused the living of Greenwich, which was
offered him in order to increase his emoluments, on
the ground that he could not suitably fulfil the
double office. Bradley's later assistants were Charles
Mason and Charles Green.</p>
<p>Bradley's last work was the preparation for the
observations of the transit of Venus of 1761, according
to the lines laid down by his predecessor, Halley.
His health gave way, and he became subject to
melancholia, so that the actual observations were
taken by the Rev. Nathaniel Bliss, who succeeded
him in his office after his death, in 1762. He was
buried at Minchinhampton.</p>
<p>So far as we know Bradley's character, he seems
to have been a gentle, modest, unassuming man,
entirely free from self-seeking, and indifferent to
personal gain. He was in many ways an ideal
astronomer, exact, methodical, and conscientious to
the last degree. His skill as an observer was his
chief characteristic; and though his abilities were not
equal as a mathematician or a mechanician, yet, on
the one hand, he had a very clear insight into the<span class="pagenum"><a name="Page_82" id="Page_82">[82]</a></span>
meaning of his observations, and, on the other, he was
skilful enough to himself adjust, repair, and improve
his instruments.</p>
<p>Of Bradley's instruments, there are still preserved
his famous twelve-and-a-half-foot zenith sector, with
which he made his two great discoveries; his brass
quadrant, which in 1750 he substituted for Halley's
iron quadrant; his transit instrument, and equatorial
sector. Bradley added to the buildings of the
Observatory that portion which is now represented
by the upper and lower computing rooms, and the
chronometer room, which adjoins the latter. This
room—the chronometer room—was his transit room,
and the position of the shutters is still marked by
the window in the roof.</p>
<hr class="tb" />
<p>The Rev. <span class="smcap">Nathaniel Bliss</span>, who succeeded
Bradley, only held the office for a couple of years,
and during that time was much at Oxford. He,
therefore, has left no special mark behind him as
Astronomer Royal.</p>
<p>He was born November 28, 1700. His father,
like himself, Nathaniel Bliss, was a gentleman, of
Bisley, Gloucestershire.</p>
<div class="figcenter bord" style="width: 450px;"><a name="bliss" id="bliss"></a>
<img src="images/i_083.jpg" width="450" height="532" alt="bliss" />
<div class="caption"><p class="center">NATHANIEL BLISS.<br />
(<em>From an engraving on an old pewter flagon.</em>)</p></div>
</div>
<p>Bliss graduated at Pembroke College, Oxford, as
B.A. in 1720, and M.A. in 1723. He became the
Rector of St. Ebb's, Oxford, in 1736, and on Halley's
death succeeded him as Savilian Professor of Geometry.
He supplied Bradley with his observations
of Jupiter's satellites, and from time to time, at his
request, rendered him some assistance at the Royal
Observatory. This was particularly the case, as has<span class="pagenum"><a name="Page_83" id="Page_83"> </a><br /><a name="Page_84" id="Page_84"> </a><br /><a name="Page_85" id="Page_85">[85]</a></span>
been already mentioned, with respect to the transit
of Venus of 1761, the observations of which were
carried out by Bliss, owing to Bradley's ill-health.
It was natural, therefore, that on Bradley's death he
should succeed to the vacant post; but he held it too
short a time to do any distinctive work. Such
observations as he made seem to have been entirely
in continuation of Bradley's. He took a great
interest, however, in the improvement of clocks, a
department in which so much was being done at this
time by Graham, Ellicott, and others.</p>
<hr class="tb" />
<p><span class="smcap">Nevil Maskelyne</span>, the fifth Astronomer Royal,
was, like Bliss, a close friend of Bradley's. He was
the third son of a wealthy country gentleman,
Edmund Maskelyne, of Purton, in Wiltshire. Maskelyne
was born in London, October 6, 1732, and was
educated at Westminster School. Thence he proceeded
to Cambridge, where he graduated seventh
Wrangler in 1754. He was ordained to the curacy
of Barnet in 1755, and, twenty years later, was presented
by his nephew, Lord Clive, to the living of
Shrawardine, in Shropshire. In 1782 he was presented
by his college to the Rectory of North
Runcton, Norfolk.</p>
<p>The event which turned his thoughts in the
direction of astronomy was the solar eclipse of July
25, 1748; and about the time that he was appointed
to the curacy of Barnet he became acquainted with
Bradley, then the Astronomer Royal, to whom he
gave great assistance in the preparation of his table
of refractions.</p>
<p><span class="pagenum"><a name="Page_86" id="Page_86">[86]</a></span></p>
<p>Like Halley before him, he made an astronomical
expedition to the island of St. Helena. This was
for the special purpose of observing the transit of
Venus of June 6, 1761, Bradley having induced the
Royal Society to send him out for that purpose.
Here he stayed ten months, and made many
observations. But though the transit of Venus was
his special object, it was not the chief result of
the expedition: not because clouds hindered his
observations, but because the voyage gave him the
especial bent of his life.</p>
<p>Halley had actually held a captain's commission in
the Royal Navy, and commanded a ship; Maskelyne,
more than any of the Astronomers Royal before or
since, made the improvement of the practical business
of navigation his chief aim. None of all the incumbents
of the office kept its original charter—'To find the
so much desired Longitude at Sea, for the perfecting
the Art of Navigation,' so closely before him.</p>
<p>The solution of the problem was at hand at this
time—its solution in two different ways. On the one
hand, the offer by the Government of a reward of
£20,000 for a clock or watch which should go so
perfectly at sea, notwithstanding the tossing of the
ship and the wide changes of temperature to which
it might be exposed, that the navigator might at any
moment learn the true Greenwich time from it, had
brought out the invention of Harrison's time-keeper;
on the other hand, the great improvement that had
now taken place in the computation of tables of the
moon's motion, and the more accurate star-catalogues
now procurable, had made the method of 'lunars,'<span class="pagenum"><a name="Page_87" id="Page_87"> </a><br /><a name="Page_88" id="Page_88"> </a><br /><a name="Page_89" id="Page_89">[89]</a></span>
suggested a hundred and thirty years before by the
Frenchman, Morin, and others, a practicable one.</p>
<div class="figcenter bord" style="width: 450px;"><a name="nevil" id="nevil"></a>
<img src="images/i_087.jpg" width="450" height="557" alt="nevil" />
<div class="caption"><p class="center">NEVIL MASKELYNE.</p></div>
</div>
<p>In principle, the method of finding the longitude
from 'lunars,' that is to say, from measurements of
the distances between the moon and certain stars, is
an exceedingly simple one. In actual practice, it
involves a very toilsome calculation, beside exact
and careful observation. The principle, as already
mentioned, is simply this: The moon travels round
the sky, making a complete circuit of the heavens
in between twenty-seven and twenty-eight days. It
thus moves amongst the stars, roughly speaking, its
own diameter, in about an hour. When once its
movements were sufficiently well known to be exactly
predicted, almanacs could be drawn up in which the
Greenwich time of its reaching any definite point of
the sky could be predicted long beforehand; or, what
comes to the same thing, its distances from a number
of suitable stars could be given for definite intervals
of Greenwich time. It is only necessary, then, to
measure the distances between the moon and some of
these stars, and by comparing them with the distances
given in the almanac, the exact time at Greenwich
can be inferred. As has been already pointed out,
the determination of the latitude of the ship and of
the local time at any place where the ship is, is not
by any means so difficult a matter; but the local
time being known and the Greenwich time, the
difference between these gives the longitude; and
the latitude having been also ascertained, the exact
position of the ship is known.</p>
<p>There are, of course, difficulties in the way of<span class="pagenum"><a name="Page_90" id="Page_90">[90]</a></span>
working out this method. One is, that whilst it takes
the sun but twenty-four hours to move round the sky
from one noon to the next, and consequently its
movements, from which the local time is inferred, are
fairly rapid, the moon takes nearly twenty-eight days
to move amongst the stars from the neighbourhood
of one particular star round to that particular star
again. Consequently, it is much easier to determine
the local time with a given degree of exactness than
the Greenwich time; it is something like the difference
of reading a clock from both hands and from the
hour hand alone.</p>
<p>There are other difficulties in the case which
make the computation a long and laborious one, and
difficult in that sense; but they do not otherwise
affect its practicability.</p>
<p>During this voyage to St. Helena, both when
outward bound and when returning, Maskelyne gave
the method of 'lunars' a very thorough testing, and
convinced himself that it was capable of giving the
information required. For by this time the improvement
of the sextant, or quadrant as it then was, by
the introduction of a second mirror, by Hadley, had
rendered the actual observation at sea of lunar distances,
and of altitudes generally, a much more exact
operation.</p>
<p>This conclusion he put at once to practical effect,
and, in 1763, he published the <cite>British Mariner's
Guide</cite>, a handbook for the determination of the
longitude at sea by the method of lunars.</p>
<p>At the same time, the other method, that by the
time-keeper or chronometer, was practically tested<span class="pagenum"><a name="Page_91" id="Page_91">[91]</a></span>
by him. The time-keeper constructed by John
Harrison had been tested by a voyage to Jamaica
in 1761, and now, in 1763, another time-keeper was
tested in a voyage to Barbadoes. Charles Green, the
assistant at Greenwich Observatory, was sent in
charge of the chronometer, and Maskelyne went with
him to test its performance, in the capacity of
chaplain to his Majesty's ship Louisa.</p>
<div class="figcenter bord" style="width: 450px;"><a name="hadley" id="hadley"></a>
<img src="images/i_091.jpg" width="450" height="368" alt="hadley" />
<div class="caption"><p class="center">HADLEY'S QUADRANT.<br />
(<em>From an old print.</em>)</p></div>
</div>
<p>The position which Maskelyne had already won
for himself as a practical astronomer, and the intimate
relations into which he had entered with Bradley
and Bliss, made his appointment to the Astronomer
Royalship, on the death of the latter, most suitable.<span class="pagenum"><a name="Page_92" id="Page_92">[92]</a></span>
At once he bent his mind to the completion of the
revolution in nautical astronomy which his <cite>British
Mariner's Guide</cite> had inaugurated, and in the year
after his appointment he published the first number
of the <cite>Nautical Almanac</cite>, together with a volume
entitled, <cite>Tables Requisite to be Used with the Nautical
Ephemeris</cite>, the value of which was so instantly
appreciated, that 10,000 copies were sold at once.</p>
<p>The <cite>Nautical Almanac</cite> was Maskelyne's greatest
work, and it must be remembered that he carried
it on from this time up to the day of his death—truly
a formidable addition to the routine labours of an
Astronomer Royal who had but a single assistant on
his staff. The <cite>Nautical Almanac</cite> was, however, in
the main not computed at the Observatory; the
calculations were effected by computers living in
different parts of the country, the work being done
in duplicate, on the principle which Flamsteed had
inaugurated in the preparation of his <cite>Historia Cœlestis</cite>.</p>
<p>Maskelyne's next service to science was almost
as important. He arranged that the regular and
systematic publication of the observations made at
Greenwich should be a distinct part of the duties of an
Astronomer Royal, and he procured an arrangement
by which a special fund was set apart by the Royal
Society for printing them. His observations covering
the years 1776 to 1811 fill four large folio volumes,
and though, as already stated, he had but one
assistant, they are 90,000 in number. Thus it was
Maskelyne who first rendered effective the design
which Charles II. had in the establishment of the
Observatory. Flamsteed and Halley had been too<span class="pagenum"><a name="Page_93" id="Page_93">[93]</a></span>
jealous of their own observations to publish; Bradley's
observations—though he himself was entirely free
from this jealousy—were made, after his death, the
subject of litigation by his heirs and representatives,
who claimed an absolute property in them, a claim
which the Government finally allowed. None of the
three, however much their work ultimately tended
to the improvement of the art of navigation, made
that their first object. Whereas Maskelyne set this
most eminently practical object in the forefront, and
so gave to the Royal Observatory, which under
his predecessors somewhat resembled a private
observatory, its distinctive characteristics of a public
institution.</p>
<p>It fell to Maskelyne to have to advise the
Government as to the assignment of their great
reward of £20,000 for the discovery of the longitude
at sea. Maskelyne, while reporting favourably of
the behaviour of Harrison's time-keeper, considered
that the method of 'lunars' was far too important to
be ignored, and he therefore recommended that half
the sum should be given to Harrison for his watch,
whilst the other half was awarded for the lunar tables
which Mayer, before his death, had sent to the Board
of Longitude. This decision, though there can be
no doubt it was the right one, led to much dissatisfaction
on the part of Harrison, who urged his claim
for the whole grant very vigorously; and eventually
the whole £20,000 was paid him. The whole question
of rewards to chronometer-makers must have
been one which caused Maskelyne much vexation.
He was made the subject of a bitter and most<span class="pagenum"><a name="Page_94" id="Page_94">[94]</a></span>
voluminous attack by Thomas Mudge, for having preferred
the work of Arnold and Earnshaw to his own.</p>
<p>Otherwise his reign at the Observatory seems to
have been a singularly peaceful one, and there is little
to record about it beyond the patient prosecution,
year by year, of an immense amount of sober, practical
work. To Maskelyne, however, we owe the practice
of taking a transit of a star over five wires instead
of over one, and he provided the transit instrument
with a sliding eye-piece, to get over the difficulty
of the displacement which might ensue if the star
were observed askew when out of the centre of the
field. To Maskelyne, too, we owe in a pre-eminent
degree the orderly form of recording, reducing, and
printing the observations. Much of the work in this
direction which is generally ascribed to Airy was
really due to Maskelyne. Indeed, without a wonderful
gift of organization, it would have been impossible
to plan and to carry the <cite>Nautical Almanac</cite>.</p>
<p>Beside the editing of various works intended for
use in nautical astronomy or in general computation,
the chief events of his long reign at Greenwich were
the transit of Venus in 1769, which he himself
observed, and for which he issued instructions in the
<cite>Nautical Almanac</cite>; and his expedition in 1774 to
Scotland, where he measured the deviation of the
plumb-line from the vertical caused by the attraction
of the mountain Schiehallion, deducing therefrom
the mean density of the earth to be four and a half
times that of water.</p>
<div class="figcenter bord" style="width: 450px;"><a name="pond" id="pond"></a>
<img src="images/i_096.jpg" width="450" height="523" alt="pond" />
<div class="caption"><p class="center">JOHN POND.<br />
(<em>From an old engraving.</em>)</p></div>
</div>
<p>He died at the Observatory, February 9, 1811,
aged 79, leaving but one child, a daughter, who<span class="pagenum"><a name="Page_95" id="Page_95"> </a><br /><a name="Page_96" id="Page_96"> </a><br /><a name="Page_97" id="Page_97">[97]</a></span>
married Mr. Anthony Mervin Story, to whom she
brought the family estates in Wiltshire, inherited by
Maskelyne on the deaths of his elder brothers, and,
in consequence, Mr. Story added the name of
Maskelyne to his own.</p>
<p>Maskelyne's character and policy as Astronomer
Royal have been sufficiently dwelt upon. His private
character was mild, amiable, and generous. 'Every
astronomer, every man of learning, found in him a
brother;' and, in particular, when the French Revolution
drove some French astronomers to this country
to find a refuge, they received from the Astronomer
Royal the kindest reception and most delicate
assistance.</p>
<p>Maskelyne added no instrument to the Observatory
during his reign, though he improved Bradley's transit
materially. He designed the mural circle, but it was
not completed until after his death. His additions
to the Observatory buildings consisted of three new
rooms in the Astronomer Royal's house, and the
present transit circle room.</p>
<hr class="tb" />
<p><span class="smcap">John Pond</span> was recommended by Maskelyne
as his successor at Greenwich. At the time of his
succession he was forty-four years of age, having
been born in 1767. He was educated at Trinity
College, Cambridge, and then spent some considerable
time travelling in the south of Europe and Egypt.
On his return home he settled at Westbury, where
he erected an altazimuth by Troughton, with a two-and-a-half-foot
circle. A born observer, his observations
of the declinations of some of the principal<span class="pagenum"><a name="Page_98" id="Page_98">[98]</a></span>
fixed stars showed that the instrument which
Maskelyne was using at Greenwich—the quadrant by
Bird—could no longer be trusted. Maskelyne, in
consequence, ordered a six-foot mural circle from
Troughton, but did not live to see it installed, and
in 1816 this was supplemented by Troughton's transit
instrument of five inches aperture and ten feet focal
length.</p>
<p>The introduction of these two important instruments,
and of other new instruments, together with
new methods of observation, form one of the chief
characteristics of Pond's administration. Under this
head must be specially mentioned the introduction
of the mercury trough, both for determining the
position of the vertical, and for obtaining a check
upon the flexure of the mural circle in different
positions; and the use in combination of a pair of
mural circles for determining the declinations of
stars.</p>
<p>Another characteristic of his reign was that under
him there was the first attempt to give the Astronomer
Royal a salary somewhat higher than that of a
mechanic, and to support him with an adequate staff
of assistants. His salary was fixed at £600 a year,
and the single assistant of Maskelyne was increased
to six.</p>
<p>This multiplication of assistants was for the purpose
of multiplying observations, for Pond was the
first astronomer to recognize the importance of greatly
increasing the number of all observations upon which
the fundamental data of astronomy were to be
based.</p>
<p><span class="pagenum"><a name="Page_99" id="Page_99">[99]</a></span></p>
<p>In 1833 he finished his standard catalogue of
1113 stars, at that time the fullest of any catalogue
prepared on the same scale of accuracy. 'It is not
too much to say,' was the verdict of the Royal
Astronomical Society, 'that meridian sidereal observation
owes more to him than to all his countrymen
put together since the time of Bradley.'</p>
<p>A yet higher testimony to the exactness of his
work is given by his successor, Airy.</p>
<blockquote>
<p>'The points upon which, in my opinion, Mr. Pond's
claims to the gratitude of astronomers are founded, are
principally the following. <em>First</em> and chief, the accuracy
which he introduced into all the principal observations.
This is a thing which, from its nature, it is extremely difficult
to estimate now, so long after the change has been made;
and I can only say that, so far as I can ascertain from
books, the change is one of very great extent; for certainty
and accuracy, astronomy is quite a different thing from
what it was, and this is mainly due to Mr. Pond.'</p></blockquote>
<p>The same authority eulogizes him further for his
laborious working out of every conceivable cause or
indication of error in his declination instruments, for
the system which he introduced in the observation
of transits, for the thoroughness with which he determined
all his fundamental data, and for the regularity
which he infused into the Greenwich observations.</p>
<p>One result of this great increase of accuracy was
that Pond was able at once authoritatively to discard
the erroneous stellar parallaxes that had been announced
by Brinkley, Royal Astronomer for Ireland.</p>
<p>But Pond's administration was open, in several
particulars, to serious censure, and the Board of<span class="pagenum"><a name="Page_100" id="Page_100">[100]</a></span>
Visitors, which had been for many years but a committee
of the Royal Society, but which had recently
been reconstituted, proved its value and efficiency by
the remonstrances which it addressed to him, and
which eventually brought about his resignation. His
personal skill and insight as an observer were of the
highest order; but either from lack of interest or
failing health, he absented himself almost entirely
from the Observatory in later years, visiting it only
every ninth or tenth day. He had caused the staff
of assistants to be increased from one to six, but had
stipulated that the men supplied to him should be
'drudges.' His minute on the subject ran—</p>
<blockquote>
<p>'I want indefatigable, hard-working, and, above all,
obedient drudges (for so I must call them, although they
are drudges of a superior order), men who will be contented
to pass half their day in using their hands and eyes in the
mechanical act of observing, and the remainder of it in
the dull process of calculation.'</p></blockquote>
<p>This was a fatal mistake, and one which it is very
hard to understand how any one with a real interest
in the science could have made. Men who had the
spirit of 'drudges,' to whom observation was a mere
'mechanical act,' and calculation a 'dull process,'
were not likely to maintain the honour of the Observatory,
particularly under an absentee Astronomer
Royal. Pond tried to overcome the difficulty by
devising rules for their guidance of iron rigidity.
The result was that after his resignation, in 1835, the
First Lord and the Secretary of the Admiralty expressed
their feeling to Airy, Pond's successor, 'that
the Observatory had fallen into such a state of<span class="pagenum"><a name="Page_101" id="Page_101">[101]</a></span>
disrepute that the whole establishment should be
cleared out.' A further evil was the excessive development
of chronometer business, so as practically to
swamp the real work of the Observatory, whilst the
prices paid for the chronometers at this time were
often much larger than would have been the case
under a more business-like administration.</p>
<p>With all his merits, therefore, as an observer, the
administration of Pond was, in some respects, the least
satisfactory of all that the Observatory has known,
and he alone of all the Astronomers Royal retired
under pressure. He did not long survive his resignation,
dying in September, 1836. He was buried
by the side of Halley, in the churchyard at Lee.</p>
<p>Of Pond's instruments, the Observatory retains
the fine transit instrument which was constructed by
Troughton at his direction, and the mural circle,
designed by Maskelyne, but which Pond was the
first to use. Both of these have, of course, long been
obsolete, and now hang on the walls of the transit
room. The small equatorial, called, after its donor,
the Shuckburgh equatorial, was also added in Pond's
day, and though practically never used, still remains
mounted in its special dome.</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_102" id="Page_102">[102]</a></span></p>
<h2>CHAPTER IV</h2>
<h3>AIRY</h3>
<blockquote>
<p>One hundred and sixty years from the day when
Flamsteed laid the foundation stone of the Observatory,
the Royal Warrant under the sign manual
was issued, appointing the seventh and strongest
of the Astronomers Royal, August 11, 1835. He
actually entered on his office in the following October,
but did not remove to the Observatory until the end
of the year.</p></blockquote>
<p><span class="smcap">George Biddell Airy</span> was born at Alnwick, in
Northumberland, on July 27, 1801. His father was
William Airy, of Luddington, in Lincolnshire, a
collector of excise; his mother was the daughter of
George Biddell, a well-to-do farmer, of Playford, near
Ipswich. He was educated at the Grammar School,
Colchester, and so distinguished himself there that
although his father was at this time very straitened
in his circumstances, it was resolved that young Airy
should go to Cambridge. Here he was entered as
sizar at Trinity College, and his robust, self-reliant
character was seen in the promptness with which he
rendered himself independent of all pecuniary help
from his relatives. In 1823 he graduated as Bachelor<span class="pagenum"><a name="Page_103" id="Page_103"> </a><br /><a name="Page_104" id="Page_104"> </a><br /><a name="Page_105" id="Page_105">[105]</a></span>
of Arts, being Senior Wrangler and Smith's prizeman,
entirely distancing all other men of his year.
He had already begun to pay attention to astronomy,
at first from the side of optics, to the study of which
he had been very early attracted; a paper of his
on the achromatism of eye-pieces and microscopes,
written in 1824, being one of especial value. In 1826
he attempted to determine 'the diminution of gravity
in a deep mine'—that of Dolcoath, in Cornwall.
In the winter of 1823-24 he was invited to London
by Mr. (afterwards Sir) James South, who took him,
amongst other places, to Greenwich Observatory,
and gave him his first introduction to practical
astronomy. In 1826 he was appointed Lucasian
Professor at Cambridge, and in 1828, Plumian Professor,
with the charge of the new University Observatory.
Prior to his election he had definitely told
the electors that the salary proposed was not sufficient
for him to undertake the responsibility of the
Observatory. He followed this up by a formal
application for an increase, which created not a little
commotion at the time, the action being so unprecedented;
and after a delay of a little over a year
he obtained what he had asked for. The delay gave
rise, however, to the remark of a local wit, that
the University had given 'to Airy, nothing, a local
habitation and a name.'</p>
<div class="figcenter bord" style="width: 450px;"><a name="airy" id="airy"></a>
<img src="images/i_103.jpg" width="450" height="567" alt="airy" />
<div class="caption"><p class="center">GEORGE BIDDELL AIRY.</p></div>
</div>
<p>The seven years which he spent in the Cambridge
Observatory were the best possible preparation for
that greater charge which he was to assume later.
When he entered on his duties the Observatory had
been completed four years, but no observations had<span class="pagenum"><a name="Page_106" id="Page_106">[106]</a></span>
been published; there was no assistant, and the only
instruments were a couple of good clocks and a
transit instrument. But Airy set to work at once
with so much energy that the observations for 1828
were published early in the following year, and he
had very quickly worked out the best methods for
correcting and reducing his observations. In 1829 an
assistant was granted to him, in 1833 a second, and
in the latter year Mr. Baldrey, the senior assistant,
observed about 5000 transits, and Mr. Glaisher, the
junior, about the same number of zenith distances.</p>
<p>A syndicate had been appointed at Cambridge
for the purpose of visiting the Observatory once in
each term, and making an annual report to the
senate. A smaller-minded and less acute man than
Airy might have resented such an arrangement. He,
on the contrary, threw himself heartily into it, and
made such formal written reports to the syndicate as
best helped them in the performance of their duty,
and at the same time secured for the Observatory
the support and assistance which from time to time
it required. On his appointment to Greenwich, he
at once entered into the same relations to the Board
of Visitors of that Observatory, and from that time
forth the friction that had occasionally existed
between the Board and the Astronomer Royal in
the past entirely ceased. The Board was henceforth
no longer a body whose chief function was to reprove,
to check, or to quicken the Astronomer Royal, but
rather a company of experts, before whom he might
lay the necessities of the Observatory, that they in
turn might present them to the Government.</p>
<p><span class="pagenum"><a name="Page_107" id="Page_107">[107]</a></span></p>
<p>Such representations were not likely to be in
vain. For, as Mr. Sheepshanks has left on record—</p>
<blockquote>
<p>'When Mr. Airy wants to carry anything into effect by
Government assistance, he states, clearly and briefly, why
he wants it; what advantages he expects from it; and
what is the probable expense. He also engages to direct
and superintend the execution, making himself personally
responsible, and giving his labour gratis. When he has
obtained permission (which is very seldom refused), he
arranges everything with extraordinary promptitude and
foresight, conquers his difficulties by storm, and presents
his results and his accounts in perfect order, before men
like ... or myself would have made up our minds about
the preliminaries. Now, men in office naturally like persons
of this stamp. There is no trouble, no responsibility, no
delay, no inquiries in the House; the matter is done, paid
for, and published, before the seekers of a grievance can
find an opportunity to be heard. This mode of proceeding
is better relished by busy statesmen than recommendations
from influential noblemen or fashionable ladies.'</p></blockquote>
<p>His first action towards the Board was, however,
a very bold and independent one. He made strong
representations on the subject of the growth of the
chronometer business, which proved displeasing to
the Hydrographer, Captain Beaufort, who was one of
the official visitors, and by his influence the report
was not printed. Airy 'kept it, and succeeding
reports, safe for three years, and then the Board of
Visitors agreed to print them, and four reports were
printed together, and bound with the Greenwich
Observations of 1838.'</p>
<p>With the completion of arrangements which put
the chronometer business in proper subordination to
the scientific charge of the Observatory, Airy was<span class="pagenum"><a name="Page_108" id="Page_108">[108]</a></span>
free to push forward its development on the lines
which he had already marked out for himself. To
go through these in detail is simply to describe the
Observatory as he left it. Little by little he entirely
renovated the equipment. Greatly as Pond had
improved the instruments of the Observatory, Airy
carried that work much further still. Though he did
not observe much himself, and was not Pond's equal
in the actual handling of a telescope, he had a great
mechanical gift, and the detail in its minutest degree
of every telescope set up during his long reign was
his own design.</p>
<p>In the work of reduction he introduced the use of
printed skeleton forms, to which Pond had been a
stranger. The publication of the Greenwich results
was carried on with the utmost regularity; and, in
striking contrast to the reluctance of Flamsteed and
Halley, he was always most prompt in communicating
any observations to every applicant who could show
cause for his request for them.</p>
<p>It is most difficult to give any adequate impression
of his far-reaching ability and measureless activity.
Perhaps the best idea of these qualities may be
obtained from a study of his autobiography, edited
and published some four years after his death by his
son. The book, to any one who was not personally
acquainted with Airy, is heavy and monotonous,
chiefly for the reason that its 400 pages are little but
a mere catalogue of the works which he undertook
and carried through; and catalogues, except to the
specialist, are the dullest of reading. To enter into
the details of his work might fill a library.</p>
<p><span class="pagenum"><a name="Page_109" id="Page_109"> </a><br /><a name="Page_110" id="Page_110"> </a></span></p>
<div class="figcenter bord" style="width: 600px;"><a name="royal" id="royal"></a>
<img src="images/i_110.jpg" width="600" height="447" alt="royal" />
<div class="caption"><p class="center">THE ASTRONOMER ROYAL'S ROOM.</p></div>
</div>
<p><span class="pagenum"><a name="Page_111" id="Page_111">[111]</a></span></p>
<p>As Astronomer Royal he seems to have inherited
and summed up all the great qualities of his predecessors:
Flamsteed's methodical habits and
unflagging industry; Halley's interest in the lunar
theory; Bradley's devotion to star observation and
catalogue making; Maskelyne's promptitude in
publishing, and keen interest in practical navigation;
Pond's refinement of observation. Nor did he allow
this inheritance to be merely metaphorical; he made
it an actual reality. He discussed, reduced, and
published, in forms suitable for use and comparison
to-day, the whole vast mass of planetary and lunar
observations made at the Royal Observatory from
the year 1760 to his own accession, a work of
prodigious labour, but of proportionate importance.
Airy has been accused—and with some reason—of
being a strong, selfish, aggressive man; yet nothing
can show more clearly than this great work how
thoroughly he placed the fame and usefulness of the
Observatory before all personal considerations.
With far less labour he could have carried on a dozen
investigations that would have brought him more
fame than this great enterprise, the purpose of which
was to render the work of his predecessors of the
highest possible use. The light in which he regarded
his office may best be expressed in his own words:—</p>
<blockquote>
<p>'The Observatory was expressly built for the aid of
astronomy and navigation, for promoting methods of
determining longitude at sea, and (as the circumstances
that led to its foundation show) more especially for determination
of the moon's motions. All these imply, as their
first step, the formation of accurate catalogues of stars,
and the determination of the fundamental elements of the<span class="pagenum"><a name="Page_112" id="Page_112">[112]</a></span>
solar system. These objects have been steadily pursued
from the foundation of the Observatory; in one way by
Flamsteed; in another way by Halley, and by Bradley in
the earlier part of his career; in a third form by Bradley
in his later years; by Maskelyne (who contributed most
powerfully both to lunar and to chronometric nautical
astronomy), and for a time by Pond; then with improved
instruments by Pond, and by myself for some years; and
subsequently, with the instruments now in use. It has
been invariably my own intention to maintain the principles
of the long-established system in perfect integrity; varying
the instruments, the modes of employing them, and the
modes of utilizing the observations of calculation and publication,
as the progress of science might seem to require.'</p></blockquote>
<p>The result of this keen appreciation of the essential
continuity of the Astronomer Royalship has been
that it is to Airy, more than to any of his predecessors,
or than to all of them put together, that the high
reputation of Greenwich Observatory is due. Professor
Newcomb, the greatest living authority on the subject
outside our own land—and other great foreign
astronomers have independently pronounced the
same verdict—has said:—</p>
<blockquote>
<p>'The most useful branch of astronomy has hitherto been
that which, treating of the positions and motions of the
heavenly bodies, is practically applied to the determination
of geographical positions on land and at sea. The Greenwich
Observatory has, during the past century, been so far the
largest contributor in this direction as to give rise to the
remark that, if this branch of astronomy were entirely lost,
it could be reconstructed from the Greenwich observations
alone.'</p></blockquote>
<p>Early in 1836 Airy proposed to the Board of
Visitors the creation of the Magnetic and Meteorological
department of the Observatory, and in 1840<span class="pagenum"><a name="Page_113" id="Page_113">[113]</a></span>
a system of regular two-hourly observations was set
on foot. This was the first great enlargement of
programme for the Observatory beyond the original
one expressed in Flamsteed's warrant. It was followed
in 1873 with the formation of the Solar Photographic
department, to which the Spectroscope was added a
little later.</p>
<p>Though he had objected strongly on his first
coming to the Observatory to the excessive time
devoted to the merely commercial side of the care of
chronometers, yet the perfecting of these instruments
was one that he had much at heart, and many recent
appliances are either of his own invention or are due
to suggestions which he threw out.</p>
<p>Much work lying outside the Observatory, and yet
intimately connected with it, was carried out either
by him or in accordance with his directions. The
transit of Venus expeditions of 1874, the delimitation
of the boundary line between Canada and the United
States, and, later, that of the Oregon boundary; the
determination of the longitudes of Valencia, Cambridge,
Edinburgh, Brussels, and Paris; assistance
in the determination of the longitude of Altona—all
came under Airy's direction. Nor did he neglect
expeditions in connection with what we would now
call the physical side of astronomy. On three
occasions, 1842, 1851, and 1860, he himself personally
took part in successful eclipse expeditions. The
determination of the increase of gravity observable
in the descent of a deep mine was also the subject
of another expedition, to the Harton Colliery, near
South Shields.</p>
<p><span class="pagenum"><a name="Page_114" id="Page_114">[114]</a></span></p>
<p>But with all these, and many other inquiries—for
he was the confidential adviser of the Government
in a vast number of subjects: lighthouses, railways,
standard weights and measures, drainage, bridges—he
yet always kept the original objects of the
Observatory in the very first place. It was in order
to get more frequent observations of the moon that
he had the altazimuth erected, which was completed
in May, 1847. This was followed, in 1851, by the
transit circle, as he had long felt the need for more
powerful light grasp in the fundamental instrument
of the Observatory. The transit circle took the
place both of the old transit instrument and of the
mural circle. Above all, he arranged for the observations
of moon and stars to be carried out with
practical continuity. The observations were made
and reduced at once, and published in such a way
that any one wishing to discuss them afresh could
for himself go over every step of the reduction from
the commencement, and could see precisely what
had been done.</p>
<p>The greatest addition made to the equipment
of the Observatory in Airy's day was the erection of
the 12<small><sup>3</sup>/<sub>4</sub></small>-inch Merz equatorial, which proved of great
service when spectroscopy became a department of
the Observatory.</p>
<div class="figcenter bord" style="width: 409px;"><a name="tower" id="tower"></a>
<img src="images/i_115.jpg" width="409" height="550" alt="tower" />
<div class="caption"><p class="center">THE SOUTH-EAST TOWER.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>So strong and gifted a man as Airy was bound to
make enemies, and at different times of his life bitter
attacks were made on him from one quarter or
another. One of these, curiously enough, was from
Sir James South, the man who, as he said, first
introduced him to practical astronomy. Later came<span class="pagenum"><a name="Page_115" id="Page_115">[115]</a></span>
the discovery of Neptune, and Airy was subjected to
much bitter criticism, since, as it appeared on the
surface, it was owing to his supineness that Adams<span class="pagenum"><a name="Page_116" id="Page_116">[116]</a></span>
missed being held the sole discoverer of the new planet,
and narrowly missed all credit for it altogether. Last
of all was the vehement attack made upon him by
Richard Anthony Proctor, in connection with his
preparations for the transit of Venus. All such
attacks, however, simply realized the old fable of
the viper and the file. Attacks which would have
agonized Flamsteed's every nerve, and have called
forth full and dignified rejoinders from Maskelyne,
were absolutely and entirely disregarded by Airy.
He had done his duty, and in his own estimation—and,
it should be added, in the estimation of those
best qualified to judge—had done it well. He was
perfectly satisfied with himself, and what other
people thought or said about him influenced him
no more than the opinions of the inhabitants of
Saturn.</p>
<p>But great as Airy was, he had the defects of his
qualities, and some of these were serious. His love
of method and order was often carried to an absurd
extreme, and much of the time of one of the greatest
intellects of the century was often devoted to doing
what a boy at fifteen shillings a week could have
done as well, or better. The story has often been
told, and it is exactly typical of him, that on one
occasion he devoted an entire afternoon to himself
labelling a number of wooden cases 'empty,' it so
happening that the routine of the establishment kept
every one else engaged at the time. His friend Dr.
Morgan jocularly said that if Airy wiped his pen on
a piece of blotting-paper he would duly endorse the
blotting-paper with the date and particulars of its<span class="pagenum"><a name="Page_117" id="Page_117">[117]</a></span>
use, and file it away amongst his papers. His mind
had that consummate grasp of detail which is characteristic
of great organizers, but the details acquired
for him an importance almost equal to the great
principles, and the statement that he had put a new
pane of glass into a window would figure as prominently
in his annual report to the Board of Visitors
as the construction of the new transit circle. His
son remarks of him that 'in his last days he seemed
to be more anxious to put letters which he received
into their proper place for reference than even to
master their contents,' his system having grown with
him from being a means to an end, to becoming the
end itself.</p>
<p>So, too, his regulation of his subordinates was,
especially in his earlier days, despotic in the extreme—despotic
to an extent which would scarcely be
tolerated in the present day, and which was the
cause of not a little serious suffering to some of his
staff, whom, at that time, he looked upon in the true
spirit of Pond, as mere mechanical 'drudges.' For
thirty-five years of his administration the salaries of
his assistants remained discreditably low, and his
treatment of the supernumerary members of his staff
would now probably be characterized as 'remorseless
sweating.' The unfortunate boys who carried out
the computations of the great lunar reductions were
kept at their desks from eight in the morning till eight
at night, without the slightest intermission, except an
hour at midday. As an example of the extreme
detail of the oversight which he exercised over his
assistants, it may be mentioned that he drew up for<span class="pagenum"><a name="Page_118" id="Page_118">[118]</a></span>
each one of those who took part in the Harton
Colliery experiment, instructions, telling them by
what trains to travel, where to change, and so forth,
with the same minuteness that one might for a child
who was taking his first journey alone; and he himself
packed up soap and towels with the instruments,
lest his astronomers should find themselves, in Co.
Durham, out of reach of these necessaries of
civilization.</p>
<p>A regime so essentially personal may indeed have
been necessary after Pond's administration, and to
give the Observatory a fresh start. But it would not
have been to the advantage of the Observatory, had
it become a permanent feature of its administration,
as it militated—was almost avowedly intended to
militate—against the growth of real zeal and intelligence
in the staff, and necessarily occasioned labour
and discomfort out of proportion to the results
obtained. Fortunately, in Airy's later years, the
extension of the work of the Observatory, a slight
failing in his own powers, and the efforts he was
devoting to the working out of the lunar theory,
compelled him to relax something of that microscopic
imperiousness which had been the chief characteristic
of his rule for so long.</p>
<p>Airy had, in the fullest degree, the true spirit of
the public servant; his sense of duty to the State was
very high. He was always ready to undertake any
duty which he felt to be of public usefulness, and
many of these he discharged without fee or reward.</p>
<p>So great an astronomer was necessarily most
highly esteemed by astronomers. He was President<span class="pagenum"><a name="Page_119" id="Page_119">[119]</a></span>
of the Royal Society for two years; he was five times
President of the Royal Astronomical Society, and
twice received its gold medal, beside a special testimonial
for his reduction of the Greenwich lunar
observations. From the Royal Society he received
the Copley medal and the Royal medal, beside
honorary titles from the Universities of Oxford,
Cambridge, and Edinburgh. So invaluable a public
servant, he received the distinction of a Knight
Commandership of the Bath in 1872. He had been
repeatedly offered knighthood before, but had not
thought it well to receive it. He was in the receipt
of decorations also from a great number of foreign
countries; for, for many years, he was looked up to,
not only by English astronomers, but by scientific
men in all countries, as the very head and representative
of his science.</p>
<p>And he also received a more popular appreciation—and
most justly so. For whilst no one could
have less of the arts of the ordinary popularizer
about him, no one has ever given popular lectures
on astronomy which more fully corresponded to the
ideal of what such should be than Airy's six lectures
to working men, delivered at Ipswich. And we
may count the bestowal upon him of the honorary
freedom of the City of London, in 1875, as one of the
tokens that his services in this direction had not
been unappreciated.</p>
<p>During the last seven years of his official career
he undertook the working out of a lunar theory, and,
to allow himself more leisure for its completion, he
resigned his position August 15, 1881, after forty-six<span class="pagenum"><a name="Page_120" id="Page_120">[120]</a></span>
years of office. He was now eighty years of age,
and he took up his residence at the White House,
just outside Greenwich Park. He resided there till
his death, more than ten years later—January 2, 1892.</p>
<hr class="tb" />
<p>Airy was succeeded in the Astronomer Royalship
by the present and eighth holder of the office,
<span class="smcap">W. H. M. Christie</span>. He was born at Woolwich, in
1845, his father having been Professor Samuel Hunter
Christie, F.R.S. He was educated at King's College,
London, and Trinity College, Cambridge, graduating
as fourth Wrangler in 1868. In 1870 he was
appointed chief assistant at Greenwich, in succession
to Mr. Stone, who had become her Majesty's
astronomer at the Cape, and in 1881 he succeeded
Airy as Astronomer Royal.</p>
<div class="figcenter bord" style="width: 417px;"><a name="christie" id="christie"></a>
<img src="images/i_121.jpg" width="417" height="600" alt="christie" />
<div class="caption"><p class="center">W. H. M. CHRISTIE, ASTRONOMER ROYAL.<br />
(<em>From a photograph by Elliott and Fry.</em>)</p></div>
</div>
<p>During Mr. Christie's office, the two new departments
of the Astrographic Chart and Double-star
observations have come into being. The following
buildings have been erected under his administration:
the great New Observatory in the south
ground, the New Altazimuth, the New Library,
nearly opposite to it, the Transit Pavilion, the
porter's lodge, and the Magnetic Pavilion out in
the Park. Whilst in the old buildings the Astrographic
dome has been added, and the Upper and
Lower Computing rooms have been rebuilt and enlarged.
As to the instruments, the 28-inch refractor,
the astrographic twin telescope, the new altazimuth,
the 26-inch and 9-inch Thompson photographic refractors,
and the 30-inch reflector are all additions
during the present reign. Roughly speaking, therefore,<span class="pagenum"><a name="Page_121" id="Page_121"> </a><br /><a name="Page_122" id="Page_122"> </a><br /><a name="Page_123" id="Page_123">[123]</a></span>
we may say that three-fourths of the present Observatory
has been added during the nineteen years
of the present Astronomer Royal. One exceedingly
important improvement should not be overlooked.
Airy observed little himself whilst at Greenwich,
and had an inadequate idea of the necessity for
room in a dome and breadth in a shutter-opening.
With the sole exception, perhaps, of the
transit circle, every instrument set up by Airy was
crammed into too small a dome or looked out
through too narrow an opening. The increase of
shutter-opening of the newer domes may be well seen
by contrasting, say, the old altazimuth or the Sheepshanks
dome with that of the astrographic. This
reform has had much to do with the success of later
work.</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_124" id="Page_124">[124]</a></span></p>
<h2>CHAPTER V</h2>
<h3>THE OBSERVATORY BUILDINGS</h3>
<p>Like a living organism, Greenwich Observatory bears
the record of its life-history in its structure. It was
not one of those favoured institutions that have sprung
complete and fully equipped from the liberality of
some great king or private millionaire. As we have
seen, it was originally established on the most modest—not
to say meagre—scale, and has been enlarged
just as it has been absolutely necessary. To quote
again from Professor Newcomb—</p>
<blockquote>
<p>'Whenever any part of it was found insufficient for its
purpose, new rooms were built for the special object in
view, and thus it has been growing from the beginning by
a process as natural and simple as that of the growth of a
tree. Even now the very value of its structure is less than
that of several other public observatories, though it eclipses
them all in the results of its work.'</p></blockquote>
<p>Entering the courtyard—an enclosure some eighty
feet deep by ninety feet in extreme breadth—by the
great gate, we see before us Flamsteed House, the
original building of the Observatory. Flamsteed's
little domain was only some twenty-seven yards
wide by fifty deep, and for buildings comprised little
beyond a small dwelling-house on the ground floor,
and one fine room above it. This room—the original<span class="pagenum"><a name="Page_125" id="Page_125">[125]</a></span>
Greenwich Observatory—still remains, and is used
as a council room by the official Board of Visitors,
who come down to the Observatory on the first
Saturday in June, to examine into its condition and
to receive the Astronomer Royal's report. The room
is called, from its shape, the Octagon Room, and is
well known to Londoners from the great north
window which looks out straight over the river
between the twin domes of the Hospital.</p>
<p>In Bradley's time, about 1749, the first extension
of the domains of the Observatory took place to the
south and east of the original building, the direction
in which, on the whole, all subsequent extensions
have taken place, owing to the fact that the original
building was constructed at the extremity of what
Sir George Airy was accustomed to call a 'peninsula'—a
projecting spur of the Blackheath plateau, from
which the ground falls away very sharply on three
sides and on part of the fourth.</p>
<p>The Observatory domain at present is fully two
hundred yards in greatest length, with an average
breadth of about sixty. Nearly the whole of this
accession took place under the directorates of Pond
and Airy. The present instruments are, therefore,
as a rule, the more modern in direct proportion to
their distance from the Octagon Room—the old
original Observatory. There is one notable exception.
The very first extension of the Observatory buildings,
made in the time of Halley, the second Astronomer
Royal, consisted in the setting up of a strong pier,
to carry two quadrant telescopes. The pier still
remains, but now forms the base of the support of<span class="pagenum"><a name="Page_126" id="Page_126">[126]</a></span>
the twin telescopes devoted to the photographic
survey of the heavens for the International Chart.</p>
<p>Standing just within the gate of the courtyard,
and looking westward, that is toward Flamsteed
House, we have immediately on our right hand the
porter's lodge; a little farther forward, also on the
right, the Transit Pavilion, a small building sheltering
a portable transit instrument; and farther forward,
still on the right, the entrance to the Chronograph
Room. Above the Chronograph Room is a little,
inconveniently-placed dome, containing a small equatorially-mounted
telescope, known as the Shuckburgh.
Beyond the Chronograph Room a door opens on to
the North Terrace, over which is seen the great north
window of the Octagon Room. Close by the door of the
Chronograph Room a great wooden staircase rises to
the roof of the main building. It is not an attractive-looking
ascent, as the steps overlap inconveniently.
Still, there is no record of an accident upon them,
and those who venture on the climb to the roof,
where are placed the anemometers and the turret
carrying the time-ball, which is dropped daily at
1 p.m., will be well repaid by the splendid view of
the river which is there afforded to them.</p>
<p>Passing under this staircase, on the wall by its
side is seen the following inscription:—</p>
<p class="center">
<span class="smcap">Carolus II<sup>s</sup> Rex Optimus<br />
Astronomiæ et Nauticæ artis<br />
Patronus Maximus<br />
Speculam hanc in utriusque commodum<br />
fecit<br />
Anno D<sup>NI</sup> MDCLXXVI. Regni sui XXVIII.</span><br />
</p>
<p class="sig">
Curante Iona Moore milite<br />
R. T. S. G.
</p>
<p><span class="pagenum"><a name="Page_127" id="Page_127">[127]</a></span></p>
<div class="figcenter bord" style="width: 400px;"><a name="astro" id="astro"></a>
<img src="images/i_127.jpg" width="400" height="469" alt="astro" />
<div class="caption"><p class="center">THE ASTRONOMER ROYAL'S HOUSE.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>In the extreme angle of the courtyard is the
entrance to the mean solar clock cupboard, and to
the staircase leading up to the Octagon Room. At
the head of this staircase in a small closet is the
winch for winding up the time-ball.</p>
<p><span class="pagenum"><a name="Page_128" id="Page_128">[128]</a></span></p>
<p>Coming back into the courtyard, and crossing the
face of the Astronomer Royal's private house, the
range of buildings is reached which form the left
hand or south side of the enclosure. Entering the
first of these, we find ourselves in the Lower Computing
Room, which is devoted to the 'Time Department.'
The next room which opens out of it, as
we turn eastwards, was Bradley's Transit Room, but
is now used for the storage of chronometers. Passing
through Bradley's Transit Room, we come to the
present Transit Room, which brings us close to the
great gate. The range of buildings is, however, continued
somewhat farther, containing on the ground
floor some small sitting-rooms and a fire-proof room
for records.</p>
<div class="figcenter bord" style="width: 600px;"><a name="court" id="court"></a>
<img src="images/i_130.jpg" width="600" height="443" alt="court" />
<div class="caption"><p class="center">THE COURTYARD.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>Turning back to the Lower Computing Room,
we notice in it the stone pier, already alluded to,
which was set up by Halley, and formed the first
addition to the original Observatory of Flamsteed.
The Lower Computing Room itself and Bradley's
Transit Room were due to the Astronomer after
which the latter is named. An iron spiral staircase
in the middle of the Lower Computing Room leads
up to the Upper Computing Room, and above that
to the Astrographic dome, so called because the
twin telescope housed therein is devoted to the work
of the Astrographic Chart—a chart of the entire sky
to be made by eighteen co-operating observatories
by means of photography. In this way it is intended
to secure a record of the places of far more stars than
could be done by the ordinary methods, and in this
project Greenwich has necessarily taken a premier<span class="pagenum"><a name="Page_129" id="Page_129"> </a><br /><a name="Page_130" id="Page_130"> </a><br /><a name="Page_131" id="Page_131">[131]</a></span>
place. This is a work which, whilst it is the legitimate
and natural outcome of the original purpose of the
Observatory, is yet pushed beyond what is necessary
for any mere utilitarian assistance to navigation. For
the sailor it will always be sufficient to know the
places of a mere handful of the brightest stars, and
the vast majority of those in the great photographic
map will never be visible in the little portable telescope
of the sailor's sextant. But it will be freely
admitted that in the case of an enterprise of this
nature, in which the observatories of so many different
nations were uniting, and which was so precisely on
the lines of its original charter, though an extension
of it, it was impossible for Greenwich to hold back
on the plea that the work was not entirely utilitarian.</p>
<p>Descending again to the Lower Computing Room,
and passing through it, not to the east, into Bradley's
Transit Room, but through a little lobby to the south,
we come upon an inconvenient wooden staircase
winding round a great stone pillar with three rays.
This pillar is the support of Airy's altazimuth, and
very nearly marks the place where Flamsteed set up
his original sextant.</p>
<p>Returning again to the Lower Computing Room,
and passing out to the east, just in front of the Time
Superintendent's desk, we enter a small passage
running along the back of Bradley's Transit Room,
and from this passage enter the present Transit
Room near its south end. Just before reaching the
Transit Room, however, we pass the Reflex Zenith
Tube, a telescope of a very special kind.</p>
<p><span class="pagenum"><a name="Page_132" id="Page_132">[132]</a></span></p>
<p>Immediately outside the Transit Room is a staircase
leading on the first floor to two rooms long used
as libraries, and to the leads above them, on which
is a small dome containing the Sheepshanks equatorial.
These libraries are over the small sitting-rooms
already referred to. The fire-proof Record
Rooms, two stories in height, terminate this range
of buildings.</p>
<p>Beyond the Record Rooms the boundary turns
sharply south, where stands a large octagonal building
surmounted by a dome of oriental appearance, a
'circular versatile roof,' as the Visitors would have
called it a hundred years ago. This dome—which
has been likened, according to the school of æsthetics
in which its critics have been severally trained, to
the Taj at Agra, a collapsed balloon, or a mammoth
Spanish onion—houses the largest refractor in England,
the 'South-east Equatorial' of twenty-eight
inches aperture. But, though the largest that England
possesses, it would appear but as a pigmy beside some
of the great telescopes for which America is famous.</p>
<p>Beyond this dome the hollow devoted to the
Astronomer Royal's private garden reduces the
Observatory ground to a mere 'wasp's waist,' a
narrow, inconvenient passage from the old and north
observatory to the younger southern one.</p>
<p>The first building, as the grounds begin to widen
out to the south, contains the New Altazimuth, a
transit instrument which can be turned into any
meridian. A library of white brick and a low wooden
cruciform building—the Magnetic Observatory—follow
it closely.</p>
<p><span class="pagenum"><a name="Page_133" id="Page_133">[133]</a></span></p>
<p>This latter building houses the Magnetic Department,
a department which, though it lies aside from
the original purposes of the Observatory, as defined
in the warrant given to Flamsteed, is yet intimately
connected with navigation, and was founded by Airy
very early in his period of office. This deals with
the observation of the changes in the force and
direction of the earth's magnetism, an inquiry which
the greater delicacy of modern compasses, and, in
more recent times, the use of iron instead of wood
in the construction of ships, has rendered imperative.</p>
<p>Closely associated with the Magnetic Department
is the Meteorological. Weather forecasts, so necessary
for the safety of shipping round our coasts, are not
issued from Greenwich Observatory, any more than
the <cite>Nautical Almanac</cite> is now issued from it. But just
as the Observatory furnishes the astronomical data
upon which the almanac is based, so also a considerable
department is set apart for furnishing observations
to be used by the Meteorological Office at
Westminster for their daily predictions.</p>
<p>So far, the development of the Observatory had
been along the central line of assistance to navigation.
But the 'Magnetic Department' led on to a new one,
which had but a secondary connection with it. It
had been discovered that the extent of the daily
range of the magnetic needle, and the amount of the
disturbances to which it was subjected, were in close
connection with the numbers and size of the spots
on the sun's surface. This led to the institution of
a daily photographic record of the state of the sun's<span class="pagenum"><a name="Page_134" id="Page_134"> </a><br /><a name="Page_135" id="Page_135">[135]</a></span>
surface, a record of which Greenwich has now the
complete monopoly.</p>
<div class="figcenter bord" style="width: 421px;"><a name="plan" id="plan"></a>
<img src="images/i_134.jpg" width="421" height="600" alt="plan" />
<div class="caption"><p class="center">PLAN OF OBSERVATORY AT PRESENT TIME.<br />
(For key to plan, see p. 135.)</p></div>
</div>
<p class="center"><span class="smcap">Key to the Plan of the Observatory on Page 134.</span></p>
<p class="noin">
<span style="margin-left: 0.5em;">1. Chronograph Room.</span><br />
<span style="margin-left: 0.5em;">2. Old Altazimuth Dome.</span><br />
<span style="margin-left: 0.5em;">3. Safe Room.</span><br />
<span style="margin-left: 0.5em;">4. Computing Room.</span><br />
<span style="margin-left: 0.5em;">5. Bradley's Transit Room.</span><br />
<span style="margin-left: 0.5em;">6. Transit Circle Room.</span><br />
<span style="margin-left: 0.5em;">7. Assistants' Room.</span><br />
<span style="margin-left: 0.5em;">8. Chief Assistant's Room.</span><br />
<span style="margin-left: 0.5em;">9. Computers' Room.</span><br />
10. Record Rooms.<br />
11. Chronometer Rooms and South-east Dome.<br />
12. Greenhouse and Outbuildings.<br />
14. New Library.<br />
15. Magnetic Observatory.<br />
16. Offices.<br />
19. Sheds.<br />
23. Winch Room for Time-ball.<br />
24. Porter's Lodge.<br />
25. New Transit Pavilion.<br />
26. New Altazimuth Pavilion.<br />
27. Museum: New Building.<br />
28. South Wing "<br />
29. North Wing "<br />
30. West Wing "<br />
31. East Wing "<br />
<br />
F. Rooms built for Flamsteed.<br />
H. Added by Halley.<br />
B. " Bradley.<br />
M. " Maskelyne.<br />
A. " Airy.<br />
F'F'. Flamsteed's boundaries.<br />
M'M'. Maskelyne's " 1790.<br />
P'P'. Pond's " 1814.<br />
A'A'. Airy's " 1837.<br />
A"A". Airy's " 1868.<br />
</p>
<p>Beyond the Magnetic Observatory the ground
widens out into an area about equal to that of the
northern part, and the new building just completed,
and which is now emphatically 'The Observatory,'
stands clear before us. The transfer to this stately
building of the computing rooms, libraries, and store
rooms has been aptly described as a shift in the
latitude of Greenwich Observatory, which still preserves
its longitude. It may be noted that the only two
buildings of any architectural pretensions in the whole
range are—Flamsteed's original observatory, built
by Sir Christopher Wren, and containing little beyond
the octagon room, in the extreme north; and this
newest building in the extreme south.</p>
<p><span class="pagenum"><a name="Page_136" id="Page_136">[136]</a></span></p>
<p>This 'New Observatory,' like the old, and like
the great South-eastern tower, is an octagon in its
central portion. But whilst the two other great
buildings are simply octagonal, here the octagon
serves only as the centre from which radiate four
great wings to the four points of the compass. The
building is by far the largest on the ground, but in
little accord with the popular idea of an astronomer
as perpetually looking through a telescope, carries
but a single dome; its best rooms being set apart
as 'computing rooms,' for the use of those members
of the staff who are employed in the calculations and
other clerical work, which form, after all, much the
greater portion of the Observatory routine.</p>
<p>An observer with the transit instrument, for
instance, will take only three or four minutes to make
a complete determination of the place of a single
star. But that observation will furnish work to the
computers for many hours afterwards. Or, to take
a photograph of the sun will occupy about five
minutes in setting the instrument, whilst the actual
exposure will take but the one-thousandth part of a
second. But the plate, once exposed, will have to
be developed, fixed, and washed; then measured, and
the measures reduced, and, <em>on the average</em>, will provide
one person with work for four days before the final
results have been printed and published.</p>
<p>It is easy to see, then, that observing, though the
first duty of the Observatory, makes the smallest
demand on its time. The visitor who comes to the
Observatory by day (and none are permitted to do
so by night) finds the official rooms not unlike those<span class="pagenum"><a name="Page_137" id="Page_137">[137]</a></span>
of Somerset House or Whitehall, and its occupants
for the most part similarly engaged in what is,
apparently, merely clerical work. An examination
of the big folios would of course show that instead of
being ledgers of sales of stamps, or income-tax
schedules, they referred to stars, planets, and sun-spots;
but for one person actively engaged at a
telescope, the visitor would see a dozen writing or
computing at a desk.</p>
<p>The staff, like the building, is the result of a
gradual development, and bears traces of its life
history in its composition. First comes the Astronomer
Royal, the representative and successor of the
original 'King's Astronomer,' the Rev. John Flamsteed.
But the 'single surly and clumsy labourer,'
which was all that the 'Merry Monarch' could grant
for his assistance, is now represented by a large and
complex body of workers; each varied class and
rank of which is a relic of some stage in the progress
of the Observatory to its present condition.</p>
<p>The following extract from the Annual Report of
the Astronomer Royal to the Board of Visitors, June,
1900, describes the present <em>personnel</em> of the establishment:—</p>
<blockquote>
<p>'The staff at the present time is thus constituted, the
names in each class being arranged in alphabetical
order:—</p>
<p>'Chief assistants—Mr. Cowell, Mr. Dyson.</p>
<p>'Assistants—Mr. Hollis, Mr. Lewis, Mr. Maunder, Mr.
Nash, Mr. Thackeray.</p>
<p>'Second-class assistants—Mr. Bryant, Mr. Crommelin.</p>
<p>'Clerical assistant—Mr. Outhwaite.</p>
<p>'Established computers—Mr. Bowyer, Mr. Davidson,
Mr. Edney, Mr. Furner, Mr. Rendell, and one vacancy.</p>
<p><span class="pagenum"><a name="Page_138" id="Page_138">[138]</a></span></p>
<p>'The two second-class assistants will be replaced by
higher grade established computers as vacancies occur.</p>
<p>'Mr. Dyson and Mr. Cowell have the general superintendence
of all the work of the Observatory. Mr. Maunder
is charged with the heliographic photography and reductions,
and with the preparation of the Library Catalogue.
Mr. Lewis has charge of the time-signals and chronometers,
and of the 28-inch equatorial. Mr. Thackeray
superintends the miscellaneous astronomical computations,
including the preparation of the new Ten-Year
Catalogue. Mr. Hollis has charge of the photographic
mapping of the heavens, the measurement of the plates,
and the computations for the Astrographic Catalogue.
Mr. Crommelin undertakes the altazimuth and Sheepshanks
equatorial reductions, and Mr. Bryant the transit
and meridian zenith distance reductions and time-determinations.
In the magnetic and meteorological branch,
Mr. Nash has charge of the whole of the work. Mr. Outhwaite
acts as responsible accountant officer; has charge of
the library, records, manuscripts, and stores, and conducts
the official correspondence. As regards the established
computers, Mr. Bowyer, Mr. Furner, Mr. Davidson, and
Mr. Rendell assist Mr. Lewis, Mr. Thackeray, Mr. Hollis,
and Mr. Bryant respectively, and Mr. Edney assists Mr.
Nash.</p>
<p>'There are at the present time twenty-four supernumerary
computers employed at the Observatory, ten being
attached to the astronomical branch, two the chronometer
branch, six to the astrographic, one to the heliographic,
four to the magnetic and meteorological, and one to the
clerical.</p>
<p>'A foreman of works, with two carpenters, and two
labourers; a skilled mechanic with an assistant; a gate
porter, two messengers, a watchman, a gardener, and a
charwoman, are also attached to the Observatory.</p>
<p>'The whole number of persons regularly employed at
the Observatory is fifty-three.'</p></blockquote>
<p>The day work, as said before, is by far the
greatest in amount, the 'office hours' being from<span class="pagenum"><a name="Page_139" id="Page_139">[139]</a></span>
nine till half-past four, with an hour's interval. The
arrangements for the night watches present some
complications.</p>
<p>For many years the instruments in regular use
were two only, the transit circle and the altazimuth.
The arrangements for observing were simple. Four
assistants divided the work between them thus: an
assistant was on duty with the transit circle one day,
his watch beginning about six a.m. or a little later,
and ending about three the following morning;
a watch of twenty-one hours in maximum length.
The second day his duties were entirely computational,
and were only two or three hours in length.
The third day he had a full day's work on the
calculations, followed by a night duty with the altazimuth.
The latter instrument might give him a very
easy watch or a terribly severe one. If the moon
were a young one it was easy, especially if the night
was clear, as in that case an hour was enough to
secure the observations required.</p>
<p>Very different was the case with a full moon,
especially in the long, often cloudy, nights of winter.
Then a vigilant watch had to be kept from sunset to
sunrise, so that in case of a short break in the clouds
the moon might yet be observed. Such a watch was
the severest (with one exception) that an assistant
had to undergo.</p>
<p>His fourth day would then resemble his second,
and with the fifth day a second cycle of his quartan
fever would commence, the symptoms following each
other in the same sequence as before.</p>
<p>Such a routine carried on with iron inflexibility<span class="pagenum"><a name="Page_140" id="Page_140">[140]</a></span>
was exceedingly trying, as it was absolutely impossible
for an observer to keep any regularity in his
hours of rest or times for meals.</p>
<p>This routine has been considerably modified by
the present Astronomer Royal, partly because the
instruments now in regular daily use are five instead
of two, and partly because a less stringent system has
proved not merely far less wearing to the observers,
but also much more prolific of results. It was impossible
for a man to be at his best for long under
the old <em>régime</em>, and from forty-six to forty-seven has
been an ordinary age for an assistant to break down
under the strain.</p>
<p>One point in which the observing work has been
lightened has been in the discontinuance of the
altazimuth observations at the full of the moon,
another in the shortening of the hours of the transit
circle watch; and a further and most important one
in the arrangement that the observers with the larger
instruments should have help at their work. The
net result of these changes has been a most striking
increase in the amount of work achieved. Thus,
whilst in the year ending May 20, 1875, 3780 transits
were taken with the transit circle, and 3636 determinations
of north polar distance; in that ending
May 10, 1895, the numbers had risen to 11,240 and
11,006 respectively, the telescope remaining precisely
the same.</p>
<p>One principle of Airy's rule still remains. So far
as possible no observer is on duty for two consecutive
days, but a long day of desk work and observing is
followed by a short day of desk work without
observing.</p>
<p><span class="pagenum"><a name="Page_141" id="Page_141">[141]</a></span></p>
<p>It will be readily understood that with five
principal telescopes in constant work and one or two
minor ones, some demanding two observers, others
only one, each telescope having its special programme
and its special hours of work, whilst by no means
every member of the staff is authorized to observe
with all instruments indifferently, it becomes a somewhat
intricate matter to arrange the weekly <i lang="la" xml:lang="la">rota</i> in
strict accordance with the foregoing principle, and
with the further one, that whilst a considerable
amount of Sunday observing is inevitable, the average
duty of an observer should be three days a week,
not seven days a fortnight. There is a story, received
with much reserve at Cambridge, that there
was once a man at that university who had mastered
all the colours and combinations of shades and
colours of the various colleges and clubs. If so
gifted a being ever existed, he may be paralleled by
the Greenwich assistant who can predict for any
future epoch the sequence of duties throughout the
entire establishment. At any rate, one of the first
items in the week's programme is the preparation of
the <i lang="la" xml:lang="la">rota</i> for the week, or rather, to use an ecclesiastical
term, for the 'octave,' <em>i.e.</em> from the Monday
to the Monday following.</p>
<p>The special work to be carried out on any telescope
is likewise a matter of programme. For the
transit circle a list of the most important objects to
be observed is supplied for the observer's use, and
the general lines upon which the other stars are to
be selected from a huge 'Working Catalogue' are
well understood. With some of the other telescopes<span class="pagenum"><a name="Page_142" id="Page_142">[142]</a></span>
the principles upon which the objects are to be
selected are laid down, but the actual choice is left to
the discretion of the observer at the time. There is
no time for the watcher to spend in what the outsider
would regard as 'discovery'; such as sweeping
for comets or asteroids, hunting for variable stars,
sketching planets, and so forth. Indeed, there is a
story current in the Observatory that some fifty
years ago, when the tide of asteroid discovery
first set in, Airy found an assistant, since famous,
working with a telescope on his 'off-duty' night.
That stern disciplinarian asked what business the
assistant had to be there on his free night, and on
being told he was 'searching for new planets,' he
was severely reprimanded and ordered to discontinue
at once. A similar energy would not meet so gruff
a discouragement to-day; but the routine work so
fully occupies both staff and telescopes that an
assistant may be most thoroughly devoted to his
science, and yet pass a decade at the Observatory
without ever seeing those 'show places' of the sky
which an amateur would have run over in the first
week after receiving his telescope. For example,
there is no refractor in the British Isles so competent
to bring out the vivid green light of the great Orion
nebula—that marvellous mass of glowing, curdling,
emerald cloud—or the indescribable magnificence
of the myriad suns that cluster like swarming bees
or the grapes of Eshcol in the constellation of
Hercules; yet probably most of the staff have
never seen either spectacle through it. The professional
astronomer who is worth his salt will find<span class="pagenum"><a name="Page_143" id="Page_143">[143]</a></span>
abundance of charm and interest in his work, but he
will not,</p>
<div class="poem"><div class="stanza">
<span class="i16">'Like a girl,<br /></span>
<span class="i0">Valuing the giddy pleasures of the eyes,'<br /></span>
</div></div>
<p class="noin">consider the charm to lie mainly in the occasional
sight of wonderful beauty which his work may bring
to him, nor the interest in some chance phenomenon
which may make his name known.</p>
<p>It is not every field of astronomy that is cultivated
at Greenwich. The search for comets and for 'pocket
planets' forms no part of its programme; and the
occupation so fascinating to those who take it up, of
drawing the details on the surfaces of the moon,
Mars, Jupiter, or Saturn, has been but little followed.
Such work is here incidental, not fundamental, and
the same may be said of certain spectroscopic
observations of new or variable stars, and of many
similar subjects. Work such as this is most interesting
to the general public, and is followed with much
devotion by many amateur astronomers. For that
very reason it does not form an integral part of the
programme of our State observatory. But work
which is necessary for the general good, or for the
advancement of the science, and which demands
observations carried on continuously for many years,
and strict unity of instruments and methods, cannot
possibly be left to chance individual zeal, and is
therefore rightly made the first object at Greenwich.</p>
<p>Those striking discoveries which from time to
time appeal strongly to the popular imagination,<span class="pagenum"><a name="Page_144" id="Page_144">[144]</a></span>
and which have rendered so justly famous some of
the great observatories of the sister continent, have
not often been made here.</p>
<p>Its work has, none the less, been not only useful
but essential. A century ago, when we were engaged
in the hand-to-hand struggle with Napoleon, by far
the most brilliant part of that naval war which we
waged against the French, and the most productive
of prize-money, was carried on by our cruisers, who
captured valuable prizes in every sea. But a much
greater service, indeed an absolutely vital one, was
rendered to the State by those line-of-battle ships
which were told off to watch the harbours wherein
the French fleet was taking refuge. This was a
work void of the excitement, interest, and profit of
cruising. It was monotonous, wearing, and almost
inglorious, but absolutely necessary to the very
existence of England. So the continuance for more
than two centuries of daily observations of places
of moon, stars, and planets is likewise 'monotonous,
wearing, and almost inglorious;' the one compensation
is that it is essential to the life of astronomy.</p>
<p>The eight Astronomers Royal have, as already
said, kept the Observatory strictly on the lines
originally laid down for it, subject, of course, to that
enlargement which the growth of the science has
inevitably brought. But had they been inclined to
change its course, the Board of Visitors has been
specially appointed to bring them back to the right
way. As already mentioned in the account of
Flamsteed, the Board dates from 1710, when it
practically consisted of the President and Council<span class="pagenum"><a name="Page_145" id="Page_145">[145]</a></span>
of the Royal Society. Its Royal warrant lapsed on
the death of Queen Anne, and was not renewed at
the accession of the two following sovereigns; but
in the reign of George III. a new warrant was issued
under date February 22, 1765; and this was renewed
at the accession of George IV. When William IV.
came to the throne, the constitution of the Board
was extended, so as to give a representation to the
new Royal Astronomical Society, founded in 1820.
The President of the Royal Society is still chairman
of the Board, but the Admiralty, of which the
Observatory is a department, the two Universities
of Oxford and Cambridge, and the Royal Astronomical
Society are all represented on it by <i lang="la" xml:lang="la">ex
officio</i> members, and twelve other members are
contributed by the Royal and Royal Astronomical
Societies respectively, six by each. The first Saturday
in June is the appointed day for the annual
inspection by the Board, and for the presentation
to it of the Astronomer Royal's Report. To this
all-important business meeting has been added
something of a social function, by the invitation of
many well-known astronomers and the leading men
of the allied sciences to inspect the results of the
year, and to partake of the chocolate and cracknels,
which have been the traditional refreshments offered
on these occasions for a period 'whereof the memory
of man runneth not to the contrary.'</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_146" id="Page_146">[146]</a></span></p>
<h2>CHAPTER VI</h2>
<h3>THE TIME DEPARTMENT</h3>
<p>One day two Scotchmen stood just outside the main
entrance of Greenwich Observatory, looking intently
at the great twenty-four-hour clock, which is such an
object of attention to the passers through the Park.
'Jock,' said one of them to the other, 'd'ye ken whaur
ye are?' Jock admitted his ignorance. 'Ye are at
the vara ceentre of the airth.'</p>
<p>Geographers tell us that there is a sense in which
this statement as it stands may be accepted as true.
For if the surface of the globe be divided into two
hemispheres, so related to each other that the one
contains as much land as possible, and the other as
little, then London will occupy the centre or thereabouts
of the hemisphere with most land.</p>
<p>This was not, however, what the Scotchman
meant. He meant to tell his companion that he was
standing on the prime meridian of the world, the
imaginary base line from which all distances, east or
west, are reckoned; in short, that he was on 'Longitude
Nought.'</p>
<p>He was not absolutely correct, however, for the
great twenty-four-hour clock does not mark the exact<span class="pagenum"><a name="Page_147" id="Page_147">[147]</a></span>
meridian of Greenwich. To find the instrument
which marks it out and defines it we must step inside
the Observatory precincts, and just within the gate
we see before us on the left hand a door which leads
through a little lobby straight into the most important
room of the whole Observatory—the Transit Room.</p>
<div class="figcenter bord" style="width: 450px;"><a name="clock" id="clock"></a>
<img src="images/i_147.jpg" width="450" height="473" alt="clock" />
<div class="caption"><p class="center">THE GREAT CLOCK AND PORTER'S LODGE.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>This room is not well adapted for representation
by artist or photographer. Four broad stone pillars<span class="pagenum"><a name="Page_148" id="Page_148">[148]</a></span>
occupy the greater part of the space, and leave little
more than mere passage room beside. Two of these
pillars are tall, as well as broad and massive, and
stand east and west of the centre of the room,
carrying between them the fundamental instrument
of the Observatory, the transit circle. The optical
axis of this telescope marks 'Longitude Nought,'
which is further continued by a pair of telescopes,
one to the north of it, the other to the south, mounted
on the third and fourth of the pillars alluded to
above.</p>
<p>This room has not always marked the meridian
of Greenwich, for it stands outside the original
boundary of the Observatory. But it is only a few
feet to the east of the first transit instrument which
was set up by Halley, the second Astronomer Royal,
in the extreme N.-W. corner of the Observatory
domain, a distance equivalent to very much less than
one-tenth of a second of time, an utterly insensible
quantity with the instruments of two hundred years
ago.</p>
<p>It would be a long story to tell in detail how the
Greenwich transit room has come to define one of
the two fundamental lines that encircle the earth.
The other, the equator, is fixed for us by the earth
itself, and is independent of any political considerations,
or of any effort or enterprise of man. But of
all the infinite number of great circles which could be
drawn at right angles to the equator, and passing
through the north and south poles, it was not easy to
select one with such an overwhelming amount of
argument in its favour as to obtain a practically<span class="pagenum"><a name="Page_149" id="Page_149">[149]</a></span>
universal acceptance. The meridians of Jerusalem
and of Rome have both been urged, upon what we
may call religious or sentimental grounds; that of
the Great Pyramid at Ghizeh has been pressed in
accordance with the fantastic delusion that the
Pyramid was erected under Divine inspiration and
direction; that of Ferro, in the Canaries, as being an
oceanic station, well to the west of the Old World,
and as giving a base line without preference or
distinction for one nation rather than another.</p>
<p>The actual decision has been made upon no such
grounds as these. It has been one of pure practical
convenience, and has resulted from the amazing
growth of Great Britain as a naval and commercial
power. Like Tyre of old, she is 'situate at the entry
of the sea, a merchant of the people for many isles,'
and 'her merchants are the great men of the earth.'
To tell in full, therefore, the steps by which the
Greenwich meridian has overcome all others is
practically to tell again, from a different standpoint,
the story of the 'expansion of England.' The need
for a supreme navy, the development of our empire
beyond the seven seas, the vast increase of our
carrying trade—these have made it necessary that
Englishmen should be well supplied with maps and
charts. The hydrographic and geographic surveys
carried on, either officially by this country, or by
Englishmen in their own private capacity, have been
so numerous, complete, and far-reaching as not only
to outweigh those of all other countries put together,
but to induce the surveyors and explorers of not a
few other countries to adopt in their work the same<span class="pagenum"><a name="Page_150" id="Page_150">[150]</a></span>
prime meridian as that which they found in the
British charts of regions bordering on those which they
were themselves studying. Naturally, the meridian
of Greenwich has not only been adopted for Great
Britain, but also for the British possessions over-sea,
and, from these, for a large number of foreign countries;
whilst our American cousins retain it, an historic relic
of their former political connection with us. The
victories of Clive at Arcot and Plassy, of Nelson at
the Nile and Trafalgar, the voyages and surveys of
Cook and Flinders, and many more; the explorations
of Bruce, Park, Livingstone, Speke, Cameron, and
Stanley; these are some of the agencies which have
tended to fix 'Longitude Nought' in the Greenwich
Transit Room.</p>
<p>There are two somewhat different senses in which
the meridian of Greenwich is the standard meridian
for nearly the entire world. The first is the sense
about which we have already been speaking; it
constitutes the fundamental line whence distances
east and west are measured, just as distances north
and south are measured from the equator. But there
is another, though related sense, in which it has
become the standard. <em>It gives the time to the world.</em></p>
<p>There are few questions more frequently put than,
'What time is it?' 'Can you tell me the true
time?' A stickler for exactitude might reply, 'What
kind of time do you mean?' 'Do you mean solar
or sidereal time?' 'Apparent time or mean time?'
'Local time or standard time?' There are all these
six kinds of time, but it is only within the last two
generations, within, indeed, the reign of our Sovereign,<span class="pagenum"><a name="Page_151" id="Page_151">[151]</a></span>
Queen Victoria, that the subject of the differences of
most of these kinds of time has become of pressing
importance to any but theorists.</p>
<p>In one of the public gardens of Paris a little
cannon is set up with a burning-glass attached to it
in such a manner that the sun itself fires the cannon
as it reaches the meridian. This, of course, is the
time of Paris noon—apparent noon—but it would be
exceedingly imprudent of any traveller through Paris
who wished, say, to catch the one o'clock express,
to set his watch by the gun. For if it happened to
be in February, he would find when he reached the
railway station that the station clock was faster than
the sun by nearly a full quarter of an hour, and that
his train had gone; whilst towards the end of October
or the beginning of November, he would find himself
as much too soon.</p>
<p>Until machines for accurately measuring time
were invented, apparent time—time, that is to say,
given by the sun itself, as by a sun-dial—was the
only time about which men knew or cared. But
when reasonably good clocks and watches were made,
it was very soon seen that at different times in the
year there was a marked difference between sun-dial
time and that shown by the clock, the reason being
simply that the apparent rate of motion of the sun
across the sky was not always quite the same, whilst
the movement of the clock was, of course, as regular
as it could be made.</p>
<p>This difference between time as shown by the
actual sun and by a perfect clock is known as the
'equation of time.' It is least about April 15, June 15,<span class="pagenum"><a name="Page_152" id="Page_152">[152]</a></span>
August 31, and December 25. It is greatest, the sun
being after the clock, about February 11; and the sun
being before the clock, about November 2. Flamsteed,
before he became Astronomer Royal, investigated the
question, and so clearly demonstrated the existence,
cause, and amount of the equation of time as entirely
to put an end to controversy on the subject.</p>
<p>We had thus, early in the century, the two kinds
of time in common use, apparent time and mean time,
or clock time. But as the sun can only be on one
particular meridian at any given instant, the time as
shown by the clocks in one particular town will differ
from that of another town several miles to the east
or west of it. It is thus noon at Moscow 1 hr. 36 min.
before it is noon at Berlin, and noon at Berlin 54 min.
before it is noon in London.</p>
<p>This was all well enough known, but occasioned
no inconvenience until the introduction of railway
travelling; then a curious difficulty arose. Suppose
an express train was running at the rate of sixty
miles an hour from London to Bristol. The guard
of the train sets his watch to London time before he
leaves Paddington, but if the various towns through
which the train passes, Reading, Swindon, etc., each
keep their own local time, he will find his watch
apparently fast at each place he reaches; but on his
return journey, if he sets to Bristol time before starting,
he will in a similar way find it apparently slow by
the Swindon, Reading, and Paddington clocks as he
reaches them in succession.</p>
<p>It became at once necessary to settle upon one
uniform system of time for use in the railway guides.<span class="pagenum"><a name="Page_153" id="Page_153">[153]</a></span>
Apart from this, a passenger taking train, say, at
Swindon, might have been very troubled to know
whether the advertised time of his train was that of
Exeter, the place whence it started, or Swindon, the
station where he was getting in, or London, its
destination. 'Railway time,' therefore, was very
early fixed for the whole of Great Britain to be the
same as London time, which is, of course, time as
determined at Greenwich Observatory. At first it
was the custom to keep at the various stations two
clocks, one showing local time, the other 'railway,' or
Greenwich time, or else the clocks would be provided
with a double minute hand, one branch of which
pointed to the time of the place, the other to the time
of Greenwich.</p>
<p>It was soon found, however, that there was no
sufficient reason for keeping up local time. Even in
the extreme West of England the difference between
the two only amounted to twenty-three minutes, and
it was found that no practical inconvenience resulted
from saying that the sun rose at twenty-three minutes
past six on March 22, rather than at six o'clock.
The hours of work and business were practically put
twenty-three minutes earlier in the day, a change of
which very few people took any notice.</p>
<p>Other countries besides England felt the same
difficulty, and solved it in the same way, each country
as a rule taking as its standard time the time of its
own chief city.</p>
<p>There were two countries for which this expedient
was not sufficient—the United States and Canada.
The question was of no importance until the iron<span class="pagenum"><a name="Page_154" id="Page_154">[154]</a></span>
road had linked the Atlantic to the Pacific in both
countries. Then it became pressing. No fewer than
seventy different standards prevailed in the United
States only some twenty years ago. The case was
a very different one here from that of England, where
east and west differed in local time by only a little
over twenty minutes. In North America, in the
extreme case, the difference amounted to four hours,
and it seemed asking too much of men to call eight
o'clock in their morning, or it might be four o'clock
in their afternoon, their noonday.</p>
<p>The device was therefore adopted of keeping the
minutes and seconds the same for all places right
across the continent, but of changing the hour at
every 15° of longitude. The question then arose
what longitude should be adopted as the standard.
The Americans might very naturally have taken their
standard time from their great national observatory
at Washington, or from that of their chief city, New
York, or of their principal central city, Chicago. But,
guided partly no doubt by a desire to have their
standard times correspond directly to the longitudes
of their maps, and partly from a desire to fall in, if
possible, with some universal time scheme, if such
could be brought forward, they fixed upon the
meridian of Greenwich as their ultimate reference
line, and defined their various hour standards as
being exactly so many hours slow of Greenwich mean
time.</p>
<p>The decision of the United States and of Canada
brought with it later a similar decision on the part of
all the principal States of Europe; and Greenwich is<span class="pagenum"><a name="Page_155" id="Page_155">[155]</a></span>
not only 'Longitude Nought' for the bulk of the
civilized world, but Greenwich mean time, increased
or decreased by an exact number of hours or half-hours,
is the standard time all over the planet.</p>
<p>No; the statement requires correction. Two
countries hold out, both close to our own doors.
France, instead of adopting Greenwich time as such,
adopts <em>Paris time less</em> 9 m. 21 s. (that being the precise
difference in longitude between the two national
observatories). Ireland disdains even such a veiled
surrender, and Dublin time is the only one recognized
from the Hill of Howth to far Valentia. So the
distressful country preserves her old grievance, that
she does not even get her time until after England
has been served.</p>
<p>The alteration in national habits following on the
adoption of this European system has had a very
perceptible effect in some cases. Thus, Switzerland
has adopted Mid-European time, one hour fast of
Greenwich; the true local time for Berne being just
half an hour later. The result of putting the working
hours this thirty minutes earlier in the day has had
such a noticeable effect on the consumption of gas, as
to lead the gas company to contemplate agitating for
a return to the old system.</p>
<p>Thus, Greenwich time, as well as the Greenwich
meridian, has practically been adopted the world over.</p>
<p>It follows, then, that the determination of time is
the most important duty of the Royal Observatory;
and the Time Department, the one to which is
entrusted the duty of determining, keeping, and
distributing the time, calls for the first attention.</p>
<p><span class="pagenum"><a name="Page_156" id="Page_156">[156]</a></span></p>
<p>Entering the transit room, the first thing that
strikes the visitor is the extreme solidity with which
the great telescope is mounted. It turns but in one
plane, that of 'longitude nought,' and its pivots are
supported by the pair of great stone pillars which we
have already spoken of as occupying the principal
part of the transit-room area, and the foundations
of which go deep down under the surface of the hill.
On the west side of the telescope, and rigidly
connected with it, is a large wheel some six feet in
diameter, and with a number of wooden handles
attached to it, resembling the steering-wheel of a large
steamer. This wheel carries the setting circle, which
is engraved upon a band of silver let into its face
near its circumference, a similar circle being at the
back of the wheel nearer the pillar. Eleven microscopes,
of which only seven are ordinarily used,
penetrate through the pier, and are directed on to
this second circle.</p>
<p>The present transit is the fourth which the
Observatory has possessed, and its three predecessors,
known as Halley's, Bradley's, and Troughton's,
respectively, are still preserved and hang on the walls
of the transit room, affording by their comparison
an interesting object-lesson in the evolution of a
modern astronomical instrument.</p>
<p>The watcher who wishes to observe the passing of
a star must note two things: he must know in what
direction to point his telescope, and at what time to
look for the star. Then, about two minutes before
the appointed time, he takes his place at the eyepiece.
As he looks in he sees a number of vertical<span class="pagenum"><a name="Page_157" id="Page_157">[157]</a></span>
lines across his field of view. These are spider-threads
placed in the focus of the eye-piece. Presently,
as he looks, a bright point of silver light, often
surrounded by little flashing, vibrating rays of colour,
comes moving quickly, steadily onward—'swims
into his ken,' as the poet has it. The watcher's hand
seeks the side of the telescope till his finger finds a
little button, over which it poises itself to strike. On
comes the star, 'without haste, without rest,' till it
reaches one of the gleaming threads. Tap! The
watcher's finger falls sharply on the button. Some
three or four seconds later and the star has reached
another 'wire,' as the spider-threads are commonly
called. Tap! Again the button is struck. Another
brief interval and the third wire is reached, and so on,
until ten wires have been passed, and the transit is
over. The intervals are not, however, all the same,
the ten wires being grouped into three sets, two of
three apiece, and the third of four.</p>
<div class="figcenter bord" style="width: 428px;"><a name="graph" id="graph"></a>
<img src="images/i_158.jpg" width="428" height="600" alt="graph" />
<div class="caption"><p class="center">THE CHRONOGRAPH.</p></div>
</div>
<p>Each tap of the observer's finger completed for an
instant an electric circuit, and recorded a mark on the
'chronograph.' This is a large metal cylinder covered
with paper, and turned by a carefully-regulated clock
once in every two minutes. Once in every two
seconds a similar mark was made by a current sent
by means of the standard sidereal clock of the
Observatory. The paper cover of the chronograph
after an hour's work shows a spiral trace of little dots
encircling it some thirty times. These dots are at
regular intervals, about an inch apart, and are the
marks made by the clock. Interspersed between
them are certain other dots, in sets of ten; and these<span class="pagenum"><a name="Page_158" id="Page_158">[158]</a></span>
are the signals sent from the telescope by the transit
observer. If, then, one of the clock dots and one of
the observer's dots come exactly side by side, we<span class="pagenum"><a name="Page_159" id="Page_159">[159]</a></span>
know that the star was on one of the wires at a given
precise second. If the observer's dot comes between
two clock dots, it is easy, by measuring its distance
from them with a divided scale, to tell the instant the
star was on the wire to the tenth of a second, or even
to a smaller fraction. Whilst, since the transit was
taken over ten wires, and the distance of each wire
from the centre of the field of view is known, we have
practically ten separate observations, and the average
of these will give a much better determination of the
time of transit than a single one would.</p>
<p>But let the watcher be ever so little too slow in
setting his telescope, or ever so little late in placing
himself at his eye-piece, and the star will have passed
the wire, and as it smoothly, resistlessly moves on its
inexorable way, will tell the tardy watcher in a
language there is no mistaking, 'Lost moments can
never be recalled.' The opportunity let slip, not
until twenty-four hours have gone by will another
chance come of observing that same star.</p>
<p>It is the stars that are chiefly used in this determination,
partly because the stars are so many, whilst
there is but one sun. If, therefore, clouds cover the
sun at the important moment of transit, the astronomer
may well exclaim, so far as this observation is
concerned, 'I have lost a day!' The chance will not
be offered him again until the following noon. But
if one star is lost by cloud, there are many others,
and the chance is by no means utterly gone. Beside,
the sun enables us to tell the time only at noon; the
stars enable us to find it at various times throughout
the entire night; indeed, throughout both day and<span class="pagenum"><a name="Page_160" id="Page_160">[160]</a></span>
night, since the brighter stars can be observed in a
large telescope even during the day.</p>
<p>There are two great standard clocks at the
Observatory: the mean solar clock and the sidereal
clock. The latter registers twenty-four hours in the
precise time that the earth rotates on its axis. A
'day' in our ordinary use of the term is somewhat
longer than this; it is the average time from one
noon to the next, and as the earth whilst turning
round on its axis is also travelling round the sun, it
has to rather more than complete a rotation in order
to bring the sun again on to the same meridian. A
solar day is therefore some four minutes longer than
an actual rotation of the earth, <em>i.e.</em> a sidereal day, as
it is called, since such rotation brings a star back
again to the same meridian.</p>
<p>The sidereal clock can therefore be readily checked
by the observation of star transits, for the time when
the star ought to be on the meridian is known. If,
therefore, the comparison of the transit taps on the
chronograph with the taps of the sidereal clock show
that the clock was not indicating this time at the
instant of the transit, we know the clock must be so
much fast or slow. Similarly, the difference which
should be shown between the sidereal and solar
clocks at any moment is known; and hence when the
error of the sidereal clock is known, that of the solar
can be readily found.</p>
<p>It is often quite sufficient to know how much a
clock is wrong without actually setting its hands
right; but it is not possible to treat the Greenwich
clock so, for it controls a number of other clocks<span class="pagenum"><a name="Page_161" id="Page_161">[161]</a></span>
continually, and sends hourly signals out over the
whole country, by which the clocks and watches all
over the kingdom are set right.</p>
<p>In the lower computing room, below the south
window, we find the Time-Desk, the head-quarters of
the Time Department. This is a very convenient
place for the department, since one of the chronometer
rooms, formerly Bradley's transit room, opens
out of the lower computing room; the transit instrument
is just beyond; it is close to the main gate of
the Observatory, and so convenient for chronometer
makers or naval officers bringing chronometers or
coming for them, whilst just across the courtyard is
the chronograph room, with the Battery Basement, in
which the batteries for the electric currents are kept,
and the Mean Solar Clock lobby, with the winch for
the winding of the time-ball at the head of the stairs
above it. These rooms do not exhaust the territory
of the department, since it owns two other chronometer
rooms on the ground floor and first floor
respectively of the S.-E. tower.</p>
<p>At the time-desk means are provided for setting
the clock right very easily and exactly. Just above
the desk are a range of little dials and bright brass
knobs, that almost suggest the stops of a great
organ.</p>
<p>Two of these little dials are clock faces, electrically
connected with the solar and sidereal standard
clocks, so that, though these clocks are themselves a
good way off, in entirely different parts of the Observatory,
the time superintendent, seated here at the
time-desk, can see at once what they are indicating.<span class="pagenum"><a name="Page_162" id="Page_162">[162]</a></span>
Between the two is a dial labelled 'Commutator.'
From this dial a little handle usually hangs vertically
downwards, but it can be turned either to the right
or to the left, and when thus switched hard over, an
electric current is sent through to the mean solar
clock. If now we leave the computing room and
cross the courtyard to the extreme north-west corner,
we find the Mean Solar Clock in a little lobby, carefully
guarded by double doors and double windows
against rapid changes of temperature. Opening the
door of the clock case, we see that the pendulum
carries on its side a long steel bar, and that this bar
as the pendulum swings passes just over the upper
end of an electro-magnet. When the current is
switched on at the commutator, this electro-magnet
attracts or repels the steel bar according to the
direction of the current, and the action of the clock
is accordingly quickened or retarded. To put the
commutator in action for one minute will alter the
clock by the tenth of a second. As the error of the
clock is determined twice a day, shortly before ten
o'clock in the morning, and shortly before one o'clock
in the afternoon, its error is always small, usually
only one or two tenths. These two times are chosen
because, though time-signals are sent over the metropolitan
area every hour from the Greenwich clock
through the medium of the Post Office, at ten and at
one o'clock signals are also sent to all the great provincial
centres. Further, at one o'clock the time
balls at Greenwich and at Deal are dropped, so that
the captains of ships in the docks, on the river, or in
the Downs may check their chronometers.</p>
<p><span class="pagenum"><a name="Page_163" id="Page_163">[163]</a></span></p>
<p>The Time-Ball is dropped directly by the mean
solar clock itself. It is raised by means of a windlass
turned by hand-power to the top of its mast just
before one o'clock. Connected with it is a piston
working in a stout cylinder. When the ball has
reached the top of the mast, the piston is lightly
supported by a pair of catches. These catches are
pulled back by the hourly signal current, and the
piston at once falls sharply, bringing the ball with it.
But after a fall of a few feet, the air compressed by
the piston acts as a cushion and checks the fall, the
ball then gently and slowly finishing its descent.
The instant of the beginning of the fall is, of course,
the true moment to be noted.</p>
<p>The other dials on the time-desk are for various
purposes connected with the signals. One little
needle in a continual state of agitation shows that
the electric current connecting the various sympathetic
clocks of the Observatory is in full action.
Another receives a return signal from various places
after the despatch of the time-signal from Greenwich,
and shows that the signal has been properly received
at the distant station, whilst all the many electric
wires within the Observatory or radiating from it are
made to pass through the great key-board, where
they can be at once tested, disconnected, or joined
up, as may be required.</p>
<div class="figcenter bord" style="width: 450px;"><a name="desk" id="desk"></a>
<img src="images/i_164.jpg" width="450" height="403" alt="desk" />
<div class="caption"><p class="center">THE TIME-DESK.</p></div>
</div>
<p>The distribution of Greenwich time over the
island in this way is thus a simple matter. The far
more important one of the distribution of Greenwich
time to ships at sea is more difficult. The difficulty
lay in the construction of a clock or watch, the rate<span class="pagenum"><a name="Page_164" id="Page_164">[164]</a></span>
of which would not be altered by the uneasy motion
of a ship, or by the changes of temperature which are
inevitable on a voyage. Two hundred years ago it
was not deemed possible to construct a watch of
anything like sufficient accuracy. They would not
even keep going whilst they were being wound, and
would lose or gain as much as a minute in the day
for a fall or rise of 10° in temperature. This was
owing to the extreme sensitiveness of the balance
spring—which takes the place in a watch of a pendulum
in a clock—to the effects of temperature.
The British Government, therefore, in 1714 offered a<span class="pagenum"><a name="Page_165" id="Page_165">[165]</a></span>
prize of the amount of £20,000 for a means of finding
the longitude at sea within half a degree, or, in other
words, for a watch that would keep Greenwich time
correct to two minutes in a voyage across the
Atlantic. In 1735, James Harrison, the son of a
Yorkshire carpenter, succeeded in solving the problem.
His method was to attach a sort of automatic
regulator to the spring which should push the
regulator over in one direction as the temperature
rose, and bring it back as it fell. This he effected by
fastening together two strips of brass and steel. The
brass expanded with heat more rapidly than the
steel, and hence with a rise of temperature the strip<span class="pagenum"><a name="Page_166" id="Page_166">[166]</a></span>
bent over on the steel side. This was the first germ
of the idea of making watches 'compensated for
temperature;' watches, that is, which maintain practically
the same rate whether they are in heat or
cold, an idea now brought to great perfection in the
modern chronometer.</p>
<div class="figcenter bord" style="width: 400px;"><a name="harrison" id="harrison"></a>
<img src="images/i_165.jpg" width="400" height="438" alt="harrison" />
<div class="caption"><p class="center">HARRISON'S CHRONOMETER.</p></div>
</div>
<p>The great reward the Government had offered
stimulated many men to endeavour to solve the
problem. Of these, Dr. Halley, the second Astronomer
Royal, and Graham, the inventor of the
astronomical clock, were the most celebrated. But
when Harrison, then poor and unknown, came to
London in 1735, and laid his invention before them,
with an utter absence of self-seeking, and in the true
scientific spirit, they gave him every assistance.</p>
<p>Harrison's first four time-keepers are still preserved
at the Royal Observatory. He did not,
however, receive his reward until a facsimile of the
fourth had been made by his apprentice, Larcum
Kendall. The latter is preserved at the Royal
Observatory. There is a Larcum Kendall at the
Royal Institution which is said to have been used by
Captain Cook. Harrison's chronometer was sent on
a trial voyage to Jamaica in 1761, and on its return
to Portsmouth in the following year it was found that
its complete variation was under the two minutes for
which the Government had stipulated.</p>
<p>Since Harrison's day the improvement of the
chronometer has been carried on almost to perfection,
and now the care and rating of chronometers for the
Royal Navy is one of the most important duties of
the Observatory.</p>
<p><span class="pagenum"><a name="Page_167" id="Page_167"> </a></span></p>
<div class="figcenter bord" style="width: 600px;"><a name="room" id="room"></a>
<img src="images/i_167.jpg" width="600" height="397" alt="room" />
<div class="caption"><p class="center">THE CHRONOMETER ROOM.</p></div>
</div>
<p><span class="pagenum"><a name="Page_168" id="Page_168"> </a><br /><a name="Page_169" id="Page_169">[169]</a></span></p>
<p>A visitor who should make the attempt to compare
a single chronometer with a standard clock
would probably feel very disheartened when, after
many minutes of comparison, he had got out its
error to the nearest second, were he told that it was
his duty to compare the entire army here collected,
some five hundred or more, and to do it not to
the second, but to the nearest tenth of a second.
Practice and system make, however, the impossible
easy, and one assistant will quietly walk round the
room calling out the error of each chronometer as he
passes it, as fast as a second assistant seated at the
table can enter it at his dictation in the chronometer
ledgers. The seconds beat of a clock sympathetic
with the solar standard, rings out loud and clear
above the insect-like chatter of the ticking of the
hundreds of chronometers, and wherever the assistant
stands, he has but to lift his eyes to see straight
before him, if not a complete clock-face, at least a
seconds dial moving in exact accordance with the
solar standard.</p>
<p>The test to which chronometers are subjected is
not merely one of rate, but one of rate under carefully
altered conditions. Thus they may be tried
with the XII pointing in succession to the four
points of the compass, or, in the case of chronometer
watches, they may be laid flat down on the table or
hung from the ring or pendant, or with the ring right
or left, as it would be likely to be when carried in
the waistcoat pocket. But the chief test is the performance
of a chronometer when subjected to considerable
heat for a long period. This is a matter of<span class="pagenum"><a name="Page_170" id="Page_170">[170]</a></span>
great consequence, since a chronometer travelling
from England to India, Australia, or the Cape, would
necessarily be subjected to very different conditions
of temperature from those to which it would be exposed
in England. They are therefore kept for eight
weeks in a closed stove at a temperature of about
85° or 90°. At one time a cold test was also applied,
and Sir George Airy, the late Astronomer Royal, in
one of his popular lectures, drew a humorous comparison
between the unhappy chronometers thus
doomed to trial, now in heat and now in frost, and
the lost spirits whom Dante describes as alternately
plunged in flame and ice. The cold test has, however,
been done away with. It is perfectly easy
on the modern ship to keep the chronometer comfortably
warm even on an Arctic expedition. The
elaborate cold testing applied to Sir George Nares'
chronometers before he started on his polar journey
was found to have been practically quite superfluous;
the chronometers were, if anything, kept rather too
warm. The exposure of the chronometer in the
cooling box, moreover, was found to be attended
with a risk of rusting its springs.</p>
<div class="figcenter bord" style="width: 600px;"><a name="oven" id="oven"></a>
<img src="images/i_171.jpg" width="600" height="429" alt="oven" />
<div class="caption"><p class="center">THE CHRONOMETER OVEN.</p></div>
</div>
<p>Once the determination of the longitude at sea
became possible, it was clearly the next duty to fix
with precision the position of the principal places,
cities, ports, capes, islands, the world over. Of all the
work done in this department none has ever been done
better, in proportion to the means at command, than
that accomplished by Captain Cook in his celebrated
three voyages. As has already been pointed out, it
is the extent and thoroughness of the hydrographic<span class="pagenum"><a name="Page_171" id="Page_171"> </a><br /><a name="Page_172" id="Page_172"> </a><br /><a name="Page_173" id="Page_173">[173]</a></span>
surveys of the British Admiralty which have largely
contributed to the honour done to England by the
international selection of the English meridian, and
of English standard time, as in principle those for the
whole civilized world. The generosity and public
spirit therefore which led the second Astronomer
Royal to help forward and support his rival, has
almost directly led to this great distinction accruing
to the Observatory of which he was the head.</p>
<p>Three different methods have successively been
used in the determination of longitudes of distant
places. In each case the problem required was to
ascertain the time at the standard place, say Greenwich,
at the same time that it was being determined in the
ordinary way at the given station. One method of
ascertaining Greenwich time when at a distance from
it was, as stated in Chapter I., to use the moon, as it
were, as the hand of a vast clock, of which the sky
was the face and the stars the dial figures. This is
the method of 'lunar distances,' the distances of the
moon from a certain number of bright stars being
given in the <cite>Nautical Almanac</cite> for every three hours
of Greenwich time.</p>
<p>As chronometers were brought to a greater point
of perfection, it was found easier and better in many
cases to use 'chronometer runs,' that is, to carry backwards
and forwards between the two stations a
number of good chronometers, and by constant comparison
and re-comparison to get over the errors
which might attach to any one of them.</p>
<div class="figcenter bord" style="width: 450px;"><a name="transit" id="transit"></a>
<img src="images/i_174.jpg" width="450" height="359" alt="transit" />
<div class="caption"><p class="center">THE TRANSIT PAVILION.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>But of late years another method has proved
available. Distant nations are now woven together<span class="pagenum"><a name="Page_174" id="Page_174">[174]</a></span>
across thousands of miles of ocean by the submarine
telegraph. The American reads in his morning paper
a summary of the debates of the previous night in
the House of Commons at Westminster. The
Londoner watches with interest the scores of the
English cricket team in Australia. It is now therefore
possible for an astronomer in England to record,
should he so desire, the time of the transit of a star
across the wires of his instrument, not only on his
own chronograph, but upon that of another observatory,
it may be 2000 miles away. Or, much more
conveniently, each observer may independently determine
the error of his own clock, and then bring his<span class="pagenum"><a name="Page_175" id="Page_175">[175]</a></span>
clock into the current, so that it may send a signal
to the chronograph of the other station.</p>
<p>In one way or another this work of the determination
of geographical longitudes has been an
important part of the extra-routine work at Greenwich,
part of the work which has built up and sustained its
claim to define 'longitude nought'; and many
distinguished astronomers, especially from the leading
observatories of the Continent, have come here from
time to time to obtain more accurately the longitude
of their own cities. The traces of their visits may be
seen here and there about the Observatory grounds
in flat stones which lie level with the surface, and
bear a name and date like the gravestones in some
old country churchyard. These are not, as one might
suppose, to mark the burial-places of deceased astronomers,
but record the sites where, on their visits
for longitude purposes, different foreign astronomers
have set up their transit instruments. Now, however,
a permanent pier has been erected in the courtyard,
and a neat house—the Transit Pavilion—built
over it, so that in all probability no fresh additions
will be made to these sepulchral-looking little monuments.</p>
<p>It might be asked, What reason is there for a
foreign observer to come over to England for such
a purpose? Would it not be sufficient for the clock
signals to be exchanged? But a curious little fact
has come out with the increase of accuracy of transit
observation, and that is, that each observer has his
own particular habit or method of observation. A
hundred years ago, Maskelyne, the fifth Astronomer<span class="pagenum"><a name="Page_176" id="Page_176">[176]</a></span>
Royal, was greatly disturbed to find that his assistant,
David Kinnebrook, constantly and regularly observed
a star-transit a little later than he did himself. The
offender was scolded, warned, exhorted, and finally,
when all proved useless to bring his observations into
exact agreement with the Astronomer Royal's, dismissed
as an incompetent observer. As a matter of
fact, poor Kinnebrook has a right to be regarded as
one of the martyrs of science, and Maskelyne, by this
most natural but mistaken judgment, missed the
chance of making an important discovery, which was
not made until some thirty years later. Astronomers
now would be more cautious of concluding that
observations were bad simply because they differed
from what had been expected. They have learnt
by experience that these unexpected differences are
the most likely hunting-ground in which to look for
new discoveries.</p>
<p>In a modern transit observation with the use of
the chronograph it will be seen at once that before
the observer can register a star-transit on the chronograph,
he has to perceive with his eye that the star
has reached the wire, he has to mentally recognize
the fact, and consciously or unconsciously to exert
the effort of will necessary to bring his finger down
on the button. A very slight knowledge of character
will show that this will require different periods of
time for different people. It will be but a fraction
of a second in any case, but there will be a distinct
difference, a constant difference, between the eager,
quick, impulsive man who habitually anticipates,
as it were, the instant when he sees star and wire<span class="pagenum"><a name="Page_177" id="Page_177">[177]</a></span>
together, and the phlegmatic, slow-and-sure man who
carefully waits till he is quite sure that the contact
has taken place, and then deliberately and firmly
records it. These differences are so truly personal
to the observer that it is quite possible to correct
for them, and after a given observer's habit has
become known, to reduce his transit times to those
of some standard observer. It must, of course, be
remembered that this 'personal equation' is an
exceedingly minute quantity, and in most cases is
rather a question of hundredths of seconds than of
tenths.</p>
<p>It will be seen from the foregoing description how
little of what may be termed the picturesque or
sensational side of astronomy enters into the routine
of the Time Department, the most important of all
the departments of the Observatory. The daily
observation of sun and of many stars—selected from
a carefully chosen list of some hundreds, and known
as 'clock stars'—the determination of the error of
the standard clock to the hundredth of a second if
possible, and its correction twice a day, the sending
out of time signals to the General Post Office and
other places, whence they are distributed all over the
country; the care, winding, and rating of hundreds
of chronometers and chronometer watches, and from
time to time the determination of the longitude of
foreign or colonial cities, make up a heavy, ceaseless
routine in which there is little opportunity for the
realization of an astronomer's life as it is apt to be
popularly conceived.</p>
<p>Yet there is interest enough in the work. There<span class="pagenum"><a name="Page_178" id="Page_178">[178]</a></span>
is the charm which always attaches to work of
precision, the delight of using delicate and exact
instruments, and of obtaining results of steadily
increasing perfection. It may be akin to the sporting
passion for record-breaking, but surely it is a
noble form of it which has led the assistants, in
recent years, to steadily increase the number of
observations in a normal night's work up to the
very limit, taking care the while that their accuracy
has in no degree suffered. In longitude work also
'the better is the enemy of the good,' and there is
the ambition that each fresh determination shall be
markedly more precise than all that have preceded it.
The constant care of chronometers soon reveals a
kind of individuality in them which forms a fresh
source of interest, whilst if a man has but a spark
of imagination, how easily he will wrap them round
with a halo of romance!</p>
<p>Glance through the ledgers, and you will see how
some of them have heard the guns at the siege of
Alexandria, others have been carried far into the
frozen north, others have wandered with Livingstone
or Cameron in the trackless forests of equatorial
Africa.</p>
<p>More striking still are those pages across which
the closing line has been drawn; never again will the
time-keeper there scheduled return to the kindly
inquisition of Flamsteed Hill. This sailed away in
the Wasp, and was swallowed up in the eastern
typhoon; that went down in the sudden squall that
smote the Eurydice off the Isle of Wight; these
foundered with the Captain. The last fatal journey<span class="pagenum"><a name="Page_179" id="Page_179">[179]</a></span>
of Sir John Franklin to find the North-West Passage
leaves its record here; the chronometers of the
Erebus and Terror will never again appear on the
Greenwich muster roll. Land exploration claims
its victims too. Sturt's ill-fated expedition across
Australia, and Livingstone's last wandering, are
represented.</p>
<div class="figcenter bord" style="width: 450px;"><a name="lost" id="lost"></a>
<img src="images/i_179.jpg" width="450" height="321" alt="lost" />
<div class="caption"><p class="center">'LOST IN THE BIRKENHEAD.'</p></div>
</div>
<p>Sometimes an amusing entry interrupts the silent
pathos of these closed pages. 'Lost by Mr. Smith
on the coast of Africa,' reads at first sight like a
rather thin attempt of some one to shift the responsibility
of his own carelessness on to the broad
shoulders of Mr. Nobody. In reality it probably
gives a hint of the necessary, dangerous, and exciting
work of slave-dhow chasing which gives employment<span class="pagenum"><a name="Page_180" id="Page_180">[180]</a></span>
to our ships on the African coast. 'Mr. Smith' was
no doubt a petty officer who was told off to carry
the chronometer for a boat's crew sent to search for
a slave-dhow up some equatorial estuary. Probably
the dhow was found, and the Arabs who manned it
gave so stout a resistance that 'Mr. Smith' and his
men had other things to do than take care of
chronometers before they could overcome them.
We may take it that the real story outlined here was
one of courage and hard fighting, not of carelessness
and shirking.</p>
<p>Stories of higher valour and nobler courage yet
are also hinted: the calm discipline of the crew of
the Victoria as she sank from the ram of the Camperdown,
the yet nobler devotion of the men of the
Birkenhead, as they formed up in line on deck and
cheered the boats that bore away the women and
children to safety, whilst they themselves went down
with the ship into the shark-crowded sea.</p>
<div class="poem"><div class="stanza">
<span class="i0">'There rose no murmur from the ranks, no thought<br /></span>
<span class="i2">By shameful strength, unhonoured life to seek;<br /></span>
<span class="i0">Our post to quit we were not trained, nor taught<br /></span>
<span class="i2">To trample down the weak.<br /></span>
</div><div class="stanza">
<span class="i0">'What followed, why recall? The brave who died<br /></span>
<span class="i2">Died without flinching in that bloody surf.<br /></span>
<span class="i0">They sleep as well beneath that purple tide<br /></span>
<span class="i2">As others under turf.'<br /></span>
</div></div>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_181" id="Page_181">[181]</a></span></p>
<h2>CHAPTER VII</h2>
<h3>THE TRANSIT AND CIRCLE DEPARTMENTS</h3>
<p>The determination of time is a duty the importance
of which readily commends itself to the general
public. It is easy to see that in any civilized country
it is very necessary to have an accurate standard of
time. Our railways and telegraphs make it quite
impossible for us to be content with the rough-and-ready
sun-dial which satisfied our forefathers. But
it should be remembered that it was neither to
establish a 'longitude nought,' nor to create a system
of standard time, that Greenwich Observatory was
founded in 1675. It was for 'The Rectifying the
Tables of the Motions of the Heavens and the Places
of the Fixed Stars, in order to find out the so-much-desired
Longitude at Sea for the perfecting the Art
of Navigation.'</p>
<p>The two related departments, therefore, those of
the Transit and the Circle, which are concerned in
the work of making star-catalogues, come next in
order to the Time Department. Though both
departments deal with the same instrument, the
transit circle, they are at present placed at opposite
ends of the Observatory domain; the Circle Department
being lodged in the upper computing room<span class="pagenum"><a name="Page_182" id="Page_182">[182]</a></span>
of the old building; the Transit Department in the
south wing of the New Observatory in the south
ground.</p>
<p>It may be asked why, if this were the purpose of
the Observatory at its foundation, two and a quarter
centuries ago; if, as was the case, the work was set
on foot from the beginning and was carried out with
every possible care, how comes it that it is still the
fundamental work of the Observatory, and, instead of
being completed, has assumed greater proportions at
the present day than ever before?</p>
<p>The answer to this inquiry may be found in a
special application of the old proverb, originally
directed against the discontent of man: 'The more
he has, the more he wants.' For, however paradoxical
it may seem, it is true that the fuller a star-catalogue
is, and the more accurate the places of the stars that
it contains, the greater is the need for a yet fuller
catalogue, with places more accurate still.</p>
<p>It is worth while following up this paradox in
some detail, as it affords a very instructive example
of the way in which a work started on purely utilitarian
grounds extends itself till it crosses the undefined
boundary and enters the region of pure science.</p>
<p>We have no idea who made the earliest census of
the sky. It is written for us in no book; it is not
even engraved on any monument. And yet no small
portion of it is in our hands to-day, and, strangest of
all, we are able to fix fairly closely the time at which
it was made, and the latitude in which its compiler
lived. The catalogue is very unlike our star-catalogues
of to-day. The places of the stars are very<span class="pagenum"><a name="Page_183" id="Page_183">[183]</a></span>
roughly indicated; and yet this catalogue has left a
more enduring mark than all those that have succeeded
it. The catalogue simply consists of the star
names.</p>
<p>An old lady who had attended a University
Extension lecture on astronomy was heard to exclaim:
'What wonderful men these astronomers are!
I can understand how they can find out how far off
the stars are, how big they are, and what they weigh—that
is all easy enough; and I think I can see how
they find out what they are made of. But there is
one thing that I can't understand—I don't know how
they can find out what are their names!' This same
difficulty, though with a much deeper meaning than
the old lady in her simplicity was able to grasp, has
occurred to many students of astronomy. Many
have wished to know what was the meaning of, and
whence were derived, the sonorous names which are
found attached to all the brighter stars on our celestial
globes: Adhara, Alderamin, Betelgeuse, Denebola,
Schedar, Zubeneschamal, and many more. The
explanation lies here. Some 5000 years ago, a man,
or college of men, living in latitude 40° north, in
order that they might better remember the stars,
associated certain groups of them with certain fancied
figures, and the individual star names are simply
Arabic words designed to indicate whereabouts in
its peculiar figure or constellation that special star
was situated. Thus Adhara means 'back,' and is
the name of the bright star in the back of the great
Dog. Alderamin means 'right arm,' and is the
brightest star in the right arm of Cepheus, the king.<span class="pagenum"><a name="Page_184" id="Page_184">[184]</a></span>
Betelgeuse is 'giant's shoulder,' the giant being
Orion; Denebola is 'lion's tail.' Schedar is the
star on the 'breast' of Cassiopeia, and Zubeneschamal
is 'northern claw,' that is, of the Scorpion. So far is
clear enough. The names of the stars for the most
part explain themselves; but whence the constellations
derived their names, how it was that so many snakes
and fishes and centaurs were pictured out in
the sky, is a much more difficult problem, and one
which does not concern us here.</p>
<p>One point, however, these old constellations do
tell us, and tell us plainly. They show that the axis
of the earth, which, as the earth travels round the sun,
moves parallel with itself, yet, in the course of ages,
itself rotates so as in a period of some 26,000 years
to trace out a circle amongst the stars. This is the
cause of what is called 'precession,' and explains how
it is that the star we call the pole-star to-day was
not always the pole-star, nor will always remain so.
We learn this fact from the circumstance that the
old constellations do not cover the entire celestial
sphere. They leave a great circular space of 40°
radius unmapped in the southern heavens. This
simply means that the originators of the constellations
lived in 40° north latitude, and stars within 40°
of their south pole never rose above their horizon,
and consequently were never seen, and could not be
mapped, by them. In like manner, the star census
taken at Greenwich Observatory does not include
the whole sky, but leaves a space some 52° in radius
round our south pole. Since the latitude of Greenwich
is nearly 52° north, stars within that distance of<span class="pagenum"><a name="Page_185" id="Page_185">[185]</a></span>
the south pole do not rise above our horizon, and are
never seen here. But if we compare the vacant space
left by the old original constellations with the vacant
space left by a Greenwich catalogue of to-day, we
see that the centre of the first space, which must
have been the south pole of that time, is a long way
from the centre of the second space—our south pole
of to-day. The difference tells us how far the pole
has moved since those old forgotten astronomers did
their work. We know the rate at which the pole
appears to move, by comparing our more modern
catalogues one with another; and so we are able
to fix pretty nearly the time when lived those old
first census-takers of the stars, whose names have
perished so completely, but whose work has proved
so immortal.</p>
<p>These old workers gave us the constellation
groupings and names which still remain to us, and
are still in common, every-day use. Their work
affords us the most striking illustration of the result
of precession, but precession itself was not recognized
till nearly 3000 years after their day, when a marvellous
genius, Hipparchus, established the fact, and
'built himself an everlasting name' by the creation
of a catalogue of over 1000 stars prepared on modern
principles. That catalogue formed the basis of one
which survives to us at the present time, and was
made some 1750 years ago by Claudius Ptolemy,
the great astronomer of Alexandria, whose work,
which still bears the proud name of <cite>Almagest</cite>, 'The
Greatest,' remained for fourteen centuries the one
universal astronomical text-book.</p>
<p><span class="pagenum"><a name="Page_186" id="Page_186">[186]</a></span></p>
<p>A modern catalogue contains, like that of Ptolemy,
four columns of entry. The first gives the star's
designation; the second an indication of its brightness;
the third and fourth the determinations of its
place. These are expressed in two directions, which,
in modern catalogues, not in Ptolemy's, correspond
on the celestial sphere to longitude and latitude on
the terrestrial. Distance north or south of the
celestial equator is termed 'declination,' corresponding
to terrestrial latitude. Distance in a direction
parallel to the equator is termed 'right ascension,'
corresponding to terrestrial longitude. For geographical
purposes we conceive the earth to be
encircled by two imaginary lines at right angles to
each other—the one, the equator, marked out for us
by the earth itself; the other, 'longitude nought,' the
meridian of Greenwich, fixed for us by general consent,
after the lapse of centuries, by a kind of historical
evolution. On the celestial globe in like manner
we have two fundamental lines—one, the celestial
equator, marked out for us by nature; the other at
right angles to it, and passing through the poles of
the sky, adopted as a matter of convenience. But a
difficulty at once confronts us—Where can we fix
our 'right ascension nought'? What star has the
right to be considered the Greenwich of the sky?</p>
<p>The difficulty is met in the following manner:
For six months of the year, the summer months, the
sun is north of the celestial equator; for the other
six months of the year, the months of winter, it is
south of it. It crosses the equator, therefore, twice
in the year—once when moving northward at the<span class="pagenum"><a name="Page_187" id="Page_187">[187]</a></span>
spring equinox; once when moving southward at
the equinox of autumn. The point where it crosses
the equator at the first of these times is taken as the
fundamental point of the heavens, and the first sign
of the zodiac, Aries the Ram, is said to begin here,
and it is called, therefore, 'the first point of Aries.'</p>
<p>One of the very first facts noticed in the very
early days of astronomy was that, as the stars seemed
to move across the sky night by night, they seemed
to move in one solid piece, as if they were lamps
rigidly fixed in one and the same solid vault. Of
course it has long been perfectly understood that this
apparent movement was not in the least due to any
motion of the stars, but simply to the rotation of the
earth on its axis. This rotation is the smoothest,
most constant, and regular movement of which we
know. It follows, therefore, that the interval of time
between the passage of one star across the meridian
of Greenwich and that of any other given star is
always the same. This interval of time is simply the
difference of their right ascension. If we are able,
then, to turn our transit instrument to the sun, and
to a number of stars, each in its proper turn, and by
pressing the tapping-piece on the instrument as the
sun or star comes up to each of the ten wires in
succession, to record the times of its transit on the
chronograph, we shall have practically determined
their right ascensions—one of the two elements of
their places.</p>
<p>The other element, that of declination, is found in
a different manner. The celestial equator, like the
terrestrial, is 90° from the pole. The bright star<span class="pagenum"><a name="Page_188" id="Page_188">[188]</a></span>
Polaris is not exactly at the north pole, but describes
a small circle round it. Twice in the twenty-four
hours it transits across the meridian—once when
going from east to west it passes above the pole,
once when going from west to east below the pole.
The mean between these two altitudes of Polaris
above the horizon gives the position of the true
pole.</p>
<div class="figcenter bord" style="width: 357px;"><a name="circle" id="circle"></a>
<img src="images/i_189.jpg" width="357" height="600" alt="circle" />
<div class="caption"><p class="center">THE TRANSIT CIRCLE.</p></div>
</div>
<p>A complete transit observation of a star consists
therefore of two operations. The observer, as we
have already described, sees a star entering the field
of the telescope, and as it swims forward, he presses
the galvanic button, which sends a signal to the
chronograph as the star comes up to each of the ten
vertical wires in succession. But, beside the ten wires,
there are others. Two vertical wires lie outside the
ten of which we have already spoken, and there is
also a horizontal wire. The latter can be moved by
a graduated screw-head just above the eye-piece, and
as the star comes in succession to these two vertical
wires, this horizontal wire is moved by the screw-head,
so as to meet the star at the moment it is
crossing the vertical wire, and the observer presses
a second little button, which records the position of
the horizontal wire on a small paper-covered drum.
Then, the transit over, the observer leaves the telescope
and comes round to the outside of the west
pier. Here he finds seven large microscopes, which
pierce the whole thickness of the pier, and are directed
towards the circumference of a large wheel which is
rigidly attached to the telescope and revolves with it.
This wheel is six feet in diameter, and has a silver<span class="pagenum"><a name="Page_189" id="Page_189"> </a><br /><a name="Page_190" id="Page_190"> </a><br /><a name="Page_191" id="Page_191">[191]</a></span>
circle upon both faces. Each circle is divided
extremely carefully into 4320 divisions—these
divisions, therefore, being about the one-twentieth of
an inch apart. There are, therefore, twelve divisions
to every degree (12 × 360 = 4320), and each division
equals five minutes of arc. The lowest microscope is
the least powerful, and shows a large part of the
circle, enabling the observer to see at once to what
degree and division of a degree the microscope is
pointing. The other six microscopes are very carefully
placed 60° apart—as equally placed as they
possibly can be. These microscopes are all fitted
with movable wires—wires moved by a very fine and
delicate screw; the screw-head having divisions upon
it so that the exact amount of its movement can be
told. Each of the six screw-heads will read to the
one five-thousandth part of a division of the circle;
in other words, to the one hundred thousandth part
of an inch. Using all six microscopes, and taking
their mean, we are able to <em>read</em> to the one-hundredth
of a second of arc. If, therefore, the observations
could be made with perfect certainty down to the
extremest nicety of reading which the instrument
supplies, we should be able to read the declination of
a star to this degree of refinement. It may be added
that a halfpenny, at a distance of three miles, appears
to be one second of arc in diameter; at three hundred
miles it would be one-hundredth of a second. It
need scarcely be said that we cannot observe with
quite such refinement of exactness as this would
indicate. Nevertheless, this exactness is one after
which the observer is constantly striving, and tenths,<span class="pagenum"><a name="Page_192" id="Page_192">[192]</a></span>
even hundredths, of seconds of arc are quantities
which the astronomer cannot now neglect.</p>
<p>The observer has then to read the heads of all
these seven microscopes on the pier side, and also
two positions of the horizontal wire on the screw-head
at the eye-piece. The following morning he will also
read off from the chronograph-sheet the times when
he made the ten taps as the star passed each of the
ten vertical wires. There are, therefore, nine entries
to make for one position of a star in declination, and
ten for one position of a star in right ascension. The
observer will also have to read the barometer to get
the pressure of the air at the time of observation, and
one thermometer inside the transit room, and another
outside, to get the temperature of the air. In some
cases thermometers at different heights in the room
are also read. A complete observation of a single
star means, therefore, the entry of two-and-twenty
different numbers.</p>
<p>It may be asked, What is the use of reading the
barometer and thermometer? The answer to the
question can only be given by contradicting a statement
made above, that the true pole lay midway
between the position of the telescope when pointing
to the pole-star at its upper transit, and its position
when pointing to it at its lower transit. The pole
being very high in the heavens in this country, there
are a great number of stars that, like the pole-star,
cross the meridian twice in the twenty-four hours—once
when they pass above the pole, moving from
east to west, once when they pass below it, moving
from west to east As the real distance of a star<span class="pagenum"><a name="Page_193" id="Page_193">[193]</a></span>
from the true pole does not alter, it follows that we
ought to get the position of the pole from the mean
of the two transits of any of these stars, and they
ought all to exactly agree with each other. But
they do not. So, too, I said that the stars all appeared
to move as in a single piece. If, then, we constructed
an instrument with its axis parallel to the axis of the
earth, and fixed a telescope to it, pointing to any
particular star, if we turn the telescope round as fast
from east to west as the earth itself is turning from
west to east—if we built an equatorial, that is to
say—we ought to find that the star once in the centre
of the field would remain there. As a matter of fact,
when the star got near the horizon it would soon be
a long way from the centre of the field.</p>
<p>Sir George Airy, the seventh Astronomer Royal,
makes, with reference to this very point, the following
remarks:</p>
<blockquote>
<p>'Perhaps you may be surprised to hear me say the rule
is established as true, and yet there is a departure from it.
This is the way we go on in science, as in everything else;
we have to make out that something is true, then we find
out under certain circumstances that it is not quite true;
and then we have to consider and find out how the
departure can be explained.'</p></blockquote>
<p>In this particular case, the disturbing cause is
found in the action of our own atmosphere. The
rays of light from the star are bent out of a perfectly
straight course as they pass through the various
layers of that atmosphere, layers which necessarily
become denser the closer we get to the actual surface
of the earth. Every celestial body therefore appears<span class="pagenum"><a name="Page_194" id="Page_194">[194]</a></span>
to be a little higher in the sky than it really is. This
action is most noticeable at the horizon, where it
amounts to about half a degree. As both sun and
moon are about half a degree in diameter, it follows
that when they have really just entirely sunk below
the horizon they appear to be just entirely above it.
It happens, in consequence, on rare occasions, that an
eclipse of the moon will take place when both sun
and moon are together seen above the horizon.</p>
<p>It was a great matter to discover this effect of
refraction. It was soon seen that it was not constant,
that it varied with both temperature and pressure.
It is, indeed, the most troublesome of all the hindrances
to exact observation with which the astronomer has
to contend; partly because of its large amount—half
a degree, as has been already said, in the extreme
case—and partly because it is difficult in many cases
to determine its exact effect.</p>
<p>The double observation with the transit circle
gives us, then, the place in the sky where the star
<em>appeared</em> to be at the moment of observation, not its
true place; to find that true place we have to calculate
how much refraction had displaced the star
at the particular height in the sky, and at the
particular temperature and atmospheric pressure at
which the observation was made.</p>
<div class="figcenter bord" style="width: 436px;"><a name="mural" id="mural"></a>
<img src="images/i_195.jpg" width="436" height="600" alt="mural" />
<div class="caption"><p class="center">THE MURAL CIRCLE.</p></div>
</div>
<p>The transit circle is a comparatively recent instrument.
In earlier times the two observations of right
ascension and declination were entrusted to perfectly
separate instruments. The transit instrument was
mounted as the transit circle is, between two solid
stone piers, and moved in precisely the same way.<span class="pagenum"><a name="Page_195" id="Page_195">[195]</a></span>
But the great six-foot wheel, which was made as stiff
as it possibly could be, was mounted on the face of
a great stone pier or wall, from which circumstance
it was called the 'mural circle,' and a light telescope
was attached to it which turned about its centre.
This arrangement had a double disadvantage—that
the two observations had to be made separately, and<span class="pagenum"><a name="Page_196" id="Page_196">[196]</a></span>
the mural circle, not being a symmetrical instrument,
was liable to small errors which it was difficult to
detect. Thus, being supported on one side only, a
flexure or bending outwards of either telescope or
circle, or both, might be feared.</p>
<p>It was for this reason that Pond set up a pair of
mural circles, one on the east side of its supporting
pier and the other on the west.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> His plan was not
only to have each star observed simultaneously in
the two instruments, a plan by which, at the cost of
some additional labour, he would have got rid, to a
large extent, of the individual errors of the two
separate instruments, inasmuch as, on the whole, it
might have been expected that the errors of the two
instruments would have been very nearly equal in
amount, but of opposite character. The differences,
too, between the two instruments would have afforded
the means for tracing these small errors to their
respective causes, and so ascertaining the laws to
which they were subject.</p>
<p>Pond went further still. He added to the mural
circle a simple instrument, the extreme value of
which every astronomer recognizes to-day—the mercury
trough. Not only was the star to be observed
by both circles when the two telescopes were pointing
directly to it, it was also to be observed by reflection;
the telescopes were to be pointed down towards a
basin of mercury, in which the image of the star
would be seen reflected. The mercury being a<span class="pagenum"><a name="Page_197" id="Page_197">[197]</a></span>
liquid, its surface is perfectly horizontal; and, since
the law of reflection is that the angle of incidence is
equal to the angle of reflection, it follows that the
telescope, when pointed down toward the mercury
trough, points just at as great an angle below the
horizon as, when it is set directly on the star, it
points above it. If the circle, therefore, be carefully
read at both settings, half the difference between the
two readings will give the angular elevation of the
star above the horizon. A combination, therefore, of
all four observations, that is to say, one reflection and
one direct with each of the telescopes, would give
an exceedingly exact value for the star's altitude.
The conception of this method gives a striking idea
of Pond's thoroughness and skill as a practical
observer, and it is a distinct blot upon Airy's justly
high reputation in the same line that he discontinued
the system upon his accession to office.</p>
<p>However, in 1851, as already mentioned, Airy
substituted for the two separate instruments—the
transit and mural circle—the transit circle, which,
unlike the mural circle, is equally supported on both
sides. This, however, does not free it from the
liability to some minute flexure in the direction of
its length, from the weight of its two ends, and the
mercury trough is used for the detection of such
bending, should it exist. The present practice is to
observe a star both by reflection and directly in the
course of the same transit. The observer sets the
telescope carefully before ever the star comes into the
field of view, and reads his seven microscopes. Then
he climbs up a narrow wooden staircase and watches<span class="pagenum"><a name="Page_198" id="Page_198">[198]</a></span>
the star transit nearly half across the field. Then
comes a rush, the observer swings himself down the
ladder, unclamps the telescope, turns it rapidly up to
the star itself, clamps it again, flings himself on his
back on a bench below the telescope, and does it so
quickly that he is able to observe the star across the
second half of the field. There is no time for
dawdling, no room for making any mistakes; the
stars never forgive; 'they haste not, they rest not;'
and if the unfortunate observer is too slow, or makes
some slip in his second setting, the star, cold and
inexorable, takes no pity, and moves regardless on.</p>
<p>It will be seen that a considerable amount of work
is involved in taking a single observation of a star-place.
But in making a star-catalogue it is always
deemed necessary to obtain at least three observations
of each star; and many are observed much more
frequently.</p>
<p>A modern star-catalogue contains, like Ptolemy's,
four columns. It contains also several more. Of
these the principal are devoted to the effect of precession.
As precession is caused by a movement of
the earth's axis making the pole of the sky seem to
describe a circle in the heavens, it follows that the
celestial poles, and the celestial equator with them
are slowly, but continually, changing their place with
respect to the stars, and therefore that the declinations
of the stars are always undergoing change, and as
the equator changes, the point where the sun crosses
it in spring—the first point of Aries—changes also,
and with it the stars' right ascensions.</p>
<p>To make one determination of a star's place<span class="pagenum"><a name="Page_199" id="Page_199">[199]</a></span>
comparable with another made at another time, it is
clear that we must correct for the effects of precession
in the interval of time between the two observations,
and for the effects of refraction. But observations
made with the transit circle must also be corrected
for errors in the instrument itself. The astronomer
will see to it that his instrument is made and is set
up as perfectly as possible. The pivots on which it
turns must be exactly on the same level; they must
point exactly east and west, and the axis of the
telescope must be exactly at right angles to the line
joining the pivots in all positions of the instrument.
These conditions are very nearly fulfilled, but never
absolutely. Day by day, therefore, the astronomer
has to ascertain just how much his instrument is in
error in each of these three matters. Were his
instrument absolutely without error to-day, he could
not assume that it would remain so, nor, if he had
measured the amount of its errors yesterday, would
it be safe to assume that those errors would not
change to-day.</p>
<p>In the examination of these sources of error the
mercury trough comes again into use. The transit
circle is turned directly downwards, and the mercury
trough brought below it. A light is so arranged as
to illuminate the field of the telescope, and the
observer, looking in, sees the ten transit wires and
the one declination wire, and also sees their images
reflected from the surface of the mercury. If the
telescope be pointing <em>exactly</em> down towards the surface
of the mercury, then the image of the declination
wire will fall exactly on the declination wire itself,<span class="pagenum"><a name="Page_200" id="Page_200">[200]</a></span>
and by reading the circle we can tell where the
zenith point of the circle is. Similarly, if the pivots
of the telescope are precisely on the same level, the
centre wire of the right ascension series would
coincide with its reflected image. A third point is
determined by looking through the eye-piece of the
north collimator telescope—that is to say, the telescope
mounted in a horizontal position at the north
end of the room—at the spider lines in the focus of
the south collimator. In order to get this view, the
transit telescope has either to be lifted up out of its
usual position, or else the middle of the tube has to
be opened. The spider lines in the north collimator
are then made to coincide with the image of the
wires of the south collimator. The transit telescope
is then turned first to one collimator, then to the
other, and the central wire of the right ascension
series is turned till it coincides with the wire of the
collimator; the amount by which it has to be moved
giving an index of the error of collimation; that is
to say, of the deviation of the optical axis of the
telescope from perpendicularity to the line joining
the pivots.</p>
<p>I have said enough to show that the making of
an observation is a small matter as compared with
those corrections which have to be made to it afterwards,
before it is available for use. But I have only
mentioned some of the reductions and corrections
which have to be made. There are several more,
and it is a just pride of Greenwich that her third
ruler, Bradley, as has been already told in the notice
of his life, discovered two of the most important.<span class="pagenum"><a name="Page_201" id="Page_201">[201]</a></span>
The one, aberration, is due to the fact that light,
though it moves so swiftly—186,000 miles per second—yet
does not move with an infinitely greater velocity
than that of the earth. The other, nutation, might
be called a correction to precession, inasmuch as,
moved by the moon's attraction, the earth's axis does
not swing round smoothly, but with a slight nodding
or staggering motion.</p>
<p>But when these observations of the places of a star
have been made, and have been properly 'reduced,'
even then we do not find an exact correspondence
between two different determinations. Little differences
still remain. Some of these are to be accounted
for by changes in the actual crust of the earth, which,
solid and stable as we think it, is yet always in
motion. Professor Milne, our greatest authority on
earth movements, says, 'The earth is so elastic that
a comparatively small impetus will set it vibrating;
why, even two hills tip together when there is a
heavy load of moisture in the valley between them.
And then, when the moisture evaporates in a hot
sun, they tip away from each other.' So there is
a perceptible rocking to and fro even of the huge
stone piers of a transit circle, as seasons of rain and
drought, heat and cold, follow each other. More
than that, the earth is so sensitive to pressure that
it was found, at the Oxford University Observatory,
that there was a distinct swaying shown by a horizontal
pendulum when the whole of a party of
seventy-six undergraduates stood on one side of the
instrument and close up to it, from the position it
had when the party stood ninety feet away. More<span class="pagenum"><a name="Page_202" id="Page_202">[202]</a></span>
wonderful still, a comparison of the star-places,
obtained at a number of observatories, including
Greenwich, has shown that the earth is continually
changing her axis of rotation. And so the star-places
determined at Greenwich have shown that
the north pole of the earth, 2600 miles away, moves
about in an irregular curve about thirty feet in radius.</p>
<p>Nothing is stable, nothing is immovable, nothing
is constant. The astronomer even finds that his
own presence near the instrument is sufficient to
disturb it.</p>
<p>The great interest attaching to transit-circle work
is this striving after ever greater and greater precision,
with the result of bringing out fresh little discordances,
which, at first sight, appear purely accidental, but
which, under further scrutiny, show themselves to be
subject to some law. Then comes the hunt for this
new unknown law. Its discovery follows. It explains
much, but when it is allowed for, though the observations
now come much closer together, little deviations
still remain, to form the subject of a fresh inquiry.
Astronomy has well been called the exact science,
and yet exactitude ever eludes its pursuer.</p>
<p>If it be asked, 'What is the use of this ever-increasing
refinement of observation?' no better
answer can be given than the words of Sir John
Herschel in one of his Presidential addresses to the
Royal Astronomical Society:—</p>
<blockquote>
<p>'If we ask to what end magnificent establishments are
maintained by States and sovereigns, furnished with masterpieces
of art, and placed under the direction of men of
first-rate talent and high-minded enthusiasm, sought out for
those qualities among the foremost in the ranks of science,<span class="pagenum"><a name="Page_203" id="Page_203">[203]</a></span>
if we demand, <i lang="la" xml:lang="la">cui bono?</i> for what good a Bradley has toiled,
or a Maskelyne or a Piazzi has worn out his venerable age
in watching?—the answer is, Not to settle mere speculative
points in the doctrine of the universe; not to cater for the
pride of man by refined inquiries into the remoter mysteries
of nature; not to trace the path of our system through
space, or its history through past and future eternities.
These, indeed, are noble ends, and which I am far from any
thought of depreciating; the mind swells in their contemplation,
and attains in their pursuit an expansion and a
hardihood which fit it for the boldest enterprise. But the
direct practical utility of such labours is fully worthy of
their speculative grandeur. The stars are the landmarks
of the universe; and, amidst the endless and complicated
fluctuations of our system, seem placed by its Creator as
guides and records, not merely to elevate our minds by the
contemplation of what is vast, but to teach us to direct our
actions by reference to what is immutable in His works.
It is, indeed, hardly possible to over-appreciate their value
in this point of view. Every well-determined star, from the
moment its place is registered, becomes to the astronomer,
the geographer, the navigator, the surveyor, a point of
departure which can never deceive or fail him, the same
for ever and in all places; of a delicacy so extreme as to
be a test for every instrument yet invented by man, yet
equally adapted for the most ordinary purposes; as
available for regulating a town clock as for conducting a
navy to the Indies; as effective for mapping down the
intricacies of a petty barony as for adjusting the boundaries
of Transatlantic empires. When once its place has been
thoroughly ascertained and carefully recorded, the brazen
circle with which that useful work was done may moulder,
the marble pillar may totter on its base, and the astronomer
himself survive only in the gratitude of posterity; but the
record remains, and transfuses all its own exactness into
every determination which takes it for a groundwork,
giving to inferior instruments—nay, even to temporary
contrivances, and to the observations of a few weeks or
days—all the precision attained originally at the cost of so
much time, labour, and expense.'</p></blockquote>
<p><span class="pagenum"><a name="Page_204" id="Page_204">[204]</a></span></p>
<p>But for these strictly utilitarian purposes a comparatively
small number of stars would meet our
every requisite. In the narrow sense of which Sir
John Herschel is here speaking, we have no use for
anything beyond the smallest of catalogues; and if
the question before us is, 'Why are we continually
extending our catalogues?' the following words of a
more recent writer<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> on the subject will set forth the
real explanation:—</p>
<blockquote>
<p>'A word in conclusion, suggested by the history of star-catalogues.
We have no difficulty in understanding that it
is necessary to study the planets, and a reasonable number
of the brighter stars, for the purpose of determining the
figure of the earth, and the positions of points upon its
surface; but the use for a catalogue of ten thousand stars,
such as La Caille compiled, is not just so apparent. Nay,
what did Ptolemy want with a thousand stars, or Tamerlane's
grandson, born, reared, and destined to die amidst
a horde of savages, however splendid in their trappings?
There is not, and there never was, any real, practical use
for the great volumes of star-catalogues that weigh down
the shelves of our libraries. The navigator and explorer
need never see them at all. Why, then, were these pages
compiled? Why have astronomers, from Hipparchus's
time to the present, spent their lives in the weary routine-work
of observing the places of tiny points in the stellar
depths? Does it not seem that there is something in the
mind of man that impels him to seek after knowledge—truly—for
its own sake? something heaven-born, heaven-nurtured,
God-given ... that there is something in man
common to him and his Creator, and therefore eternal ...
in beautiful accord with the plain statement that "God
made man in His own image?"'</p></blockquote>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_205" id="Page_205">[205]</a></span></p>
<h2>CHAPTER VIII</h2>
<h3>THE ALTAZIMUTH DEPARTMENT</h3>
<p>The determining of the places of the fixed stars
which Flamsteed carried out so efficiently in his
<cite>British Catalogue of Stars</cite>—the first 'Census of the
Sky' made with the aid of a telescope—was but half
of the work imposed upon him. The other half,
equally necessary for the solution of the problem of
the longitude at sea, was the 'Rectifying the Tables
of the Motions of the Heavens.'</p>
<p>This second duty was not less necessary than the
other, for, if we may again use the old simile of the
clock-face, the fixed stars may be taken to represent
the figures on the vast dial of the sky, whilst the
moon, as it moves amongst them, corresponds to the
moving hand of the timepiece. To know the places
of the stars, then, without being able to predict the
place of the moon, would be much like having a clock
without its hands. But if not less necessary, it was
certainly more difficult. The secret of the movements
of the moon and planets had not then been
grasped, and the only tables which had been calculated
were based upon observations made before the
days of telescopes.</p>
<p><span class="pagenum"><a name="Page_206" id="Page_206">[206]</a></span></p>
<p>It is one of the most fortunate and remarkable
coincidences in the whole history of science, that at
the very time that Greenwich Observatory was being
called into existence, the greatest of all astronomers
was working out his demonstration of the great fundamental
law of the material universe—the law that
every particle of matter attracts every other particle
with a force which varies directly with the mass and
inversely with the square of the distance.</p>
<p>Several other of the great minds of that time, in
particular Dr. Hooke, the Gresham Professor of
Astronomy, had seen that it was possible that some
such law might supply the secret of planetary motion;
but it is one thing to make a suggestion, and a very
different matter indeed to be able to demonstrate it;
and the latter was in Newton's power alone. He did
much more than demonstrate it—he brought out a
whole series of most important and far-reaching consequences.
He showed that the ebb and flow of the
tides was due to the attraction of both sun and moon,
especially the latter, upon the waters of our oceans.
He pointed out certain irregularities which must take
place in the motion of our moon, due to the influence
of the sun upon it. He showed, too, what was the
cause of that swinging of the axis of the earth which
gives rise to precession. He deduced the relative
weights of the earth, the sun, and of Jupiter and
Saturn, the planets with satellites. He proved also
that comets, which had seemed hitherto to men as
perfectly lawless wanderers, obeyed in their orbits the
self-same law which governed the moon and planets.
The whole vast system of celestial movements, which<span class="pagenum"><a name="Page_207" id="Page_207">[207]</a></span>
had long seemed to men irregular and uncontrolled,
now fell, every one of them, into its place, as but
the necessary manifestations of one grand, simple
order.</p>
<p>This great discovery gave a new and additional
importance to the regular observation of the moon
and planets. They were needed now, not only to
assist in the practical work of navigation, but for the
development of questions of pure science. Halley,
the second Astronomer Royal, and Maskelyne, the
fifth, devoted themselves chiefly to this department
of work, to the partial neglect of the observation of
the places of stars. Airy, the seventh, whilst making
catalogue-work a part of the regular routine of the
Observatory, developed the observation of the members
of the solar system, and especially of the moon,
in a most marked degree, and collected and completely
reduced the vast mass of material which the
industry of his predecessors had gathered. It is
pre-eminently of the work of Airy that the memorable
words quoted before of Professor Newcomb, the great
American mathematician and astronomer, are applicable:
'that if this branch of astronomy were entirely
lost, it could be reconstructed from the Greenwich
observations alone.'</p>
<p>A most important step taken by Airy was the
construction of an altazimuth. An altazimuth is
practically a theodolite on a large scale. Its purpose
is to determine, not the declination and right ascension
of some celestial body, as is the case with the
transit circle, but its altitude, <em>i.e.</em> its height above the
horizon, and its azimuth, <em>i.e.</em> the angle measured on<span class="pagenum"><a name="Page_208" id="Page_208">[208]</a></span>
the horizontal plane from the north point. The
altazimuth, then, like the transit circle, consists of a
telescope revolving on a horizontal axis, but, unlike
the transit circle, both the telescope and the piers
which carry its pivots can be rotated so as to point
not merely due north and south, but in any direction
whatsoever.</p>
<div class="figcenter bord" style="width: 450px;"><a name="alta" id="alta"></a>
<img src="images/i_208.jpg" width="450" height="454" alt="alta" />
<div class="caption"><p class="center">AIRY'S ALTAZIMUTH.</p></div>
</div>
<p>The observations with the altazimuth are rather
more complicated than those with the transit circle.<span class="pagenum"><a name="Page_209" id="Page_209">[209]</a></span>
Looking in the telescope, the observer sees a double
set of spider threads or 'wires'; and when a star or
other heavenly body enters the field, it will generally
be observed to move obliquely across both sets of
wires. The observer usually determines to make an
observation either in altitude or azimuth. In the
former case he presses the little contact button, which,
as in the transit circle, is provided close to the eyepiece,
as the star reaches each of the horizontal wires
in succession. If in azimuth, it is the times of crossing
the vertical wires that are in like manner telegraphed
to the chronograph. The transit over, the
appropriate circle is read; for the telescope itself is
rigidly attached to a vertical wheel having a carefully
engraved circle on its face and read by four microscopes,
whilst the entire instrument carries another
set of microscopes, pointing to a fixed horizontal
circle, and upon which the azimuth can be read.
A complete observation involves four such transits
and sets of circle readings, two of altitude, and two
of azimuth; for after one of altitude and one of
azimuth the telescope is turned round, and a second
observation is taken in each element.</p>
<p>The observation gives us the altitude and azimuth
of the star. These particulars are of no direct value
to us. But it is a mere matter of computation,
though a long and laborious one, to convert these
elements into right ascension and declination.</p>
<p>The usefulness of the altazimuth will be seen at
once. It will be remembered that with the transit
circle any particular object can only be observed as it
crosses the meridian. If the weather should be<span class="pagenum"><a name="Page_210" id="Page_210">[210]</a></span>
cloudy, or the observer late, the chance of observation
is lost for four and twenty hours, and in the case of
the moon, for which the altazimuth is specially used,
it is on the meridian only in broad daylight during
that part of the month which immediately precedes
and follows new moon. At such times it is practically
impossible to observe it with the transit circle;
with the altazimuth it may be caught in the twilight
before sunrise or after sunset; and at other times in
the month, if lost on the meridian in the transit circle,
the altazimuth still gives the observer a chance of
catching it any time before it sets. But for this
instrument, our observations of the moon would have
been practically impossible over at least one-fourth
of its orbit.</p>
<p>Airy's altazimuth was but a small instrument of
three and three-quarter inches aperture, mounted in a
high tower built on the site of Flamsteed's mural
arc; and, after a life history of about half a century,
has been succeeded by a far more powerful instrument.
The 'New Altazimuth' has an aperture of eight
inches, and is housed in a very solidly constructed
building of striking appearance, the connection of the
Observatory with navigation being suggested by a
row of circular lights which strongly recall a ship's
portholes. This building is at the southern end of the
narrow passage, 'the wasp's waist,' which connects
the older Observatory domain with the newer. It is
the first building we come to in the south ground.
The computations of the department are carried on
in the south wing of the new Observatory.</p>
<p>It will be seen from the photograph that the<span class="pagenum"><a name="Page_211" id="Page_211">[211]</a></span>
instrument is much larger, heavier, and less easy to
move in azimuth than the old altazimuth. It is,
therefore, not often moved in azimuth, but is set in
some particular direction, not necessarily north and
south, in which it is used practically as a transit
circle.</p>
<div class="figcenter bord" style="width: 450px;"><a name="zimuth" id="zimuth"></a>
<img src="images/i_211.jpg" width="450" height="467" alt="zimuth" />
<div class="caption"><p class="center">NEW ALTAZIMUTH BUILDING.</p></div>
</div>
<p>There is quite another way of determining the
place of the moon, which is sometimes available, and
which offers one of the prettiest of observations to<span class="pagenum"><a name="Page_212" id="Page_212">[212]</a></span>
the astronomer. As the moon travels across the sky,
moving amongst the stars from west to east, it
necessarily passes in front of some of them, and
hides them from us for a time. Such a passage,
or 'occultation,' offers two observations: the 'disappearance,'
as the moon comes up to the star and
covers it; the 'reappearance,' as it leaves it again,
and so discloses it.</p>
<div class="figcenter news" style="width: 600px;"><a name="news" id="news"></a>
<img src="images/i_213.jpg" width="600" height="449" alt="news" />
<div class="caption"><p class="center">THE NEW ALTAZIMUTH.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>Except at the exact time of full moon, we do not
see the entire face of our satellite; one edge or 'limb'
is in darkness. As the moon therefore passes over
the star, either the limb at which the star disappears,
or that at which it reappears, is invisible to us. To
watch an occultation at the bright limb is pretty; the
moon, with its shining craters and black hollows, its
mountain ranges in bright relief, like a model in
frosted silver, slowly, surely, inevitably comes nearer
and nearer to the little brilliant which it is going to
eclipse. The movement is most regular, most smooth,
yet not rapid. The observer glances at his clock,
and marks the minute as the two heavenly bodies
come closer and closer to each other. Then he counts
the clock beats: 'five, six, seven,' it may be, as the
star has been all but reached by the advancing moon.
'Eight,' it is still clear; ere the beat of the clock rings
to the 'nine,' perhaps the little diamond point has
been touched by the wide arch of the moon's limb,
and has gone! Less easy to exactly time is a
reappearance at the bright limb. In this case the
observer must ascertain from the <cite>Nautical Almanac</cite>
precisely where the star will reappear; then a little
before the predicted time he takes his place at the<span class="pagenum"><a name="Page_213" id="Page_213"> </a><br /><a name="Page_214" id="Page_214"> </a><br /><a name="Page_215" id="Page_215">[215]</a></span>
telescope, watches intently the moon's circumference
at the point indicated, and, listening for the clock-beats,
counts the seconds as they fly. Suddenly,
without warning, a pin-point of light flashes out at
the edge of the moon, and at once draws away from
it. The star has 'reappeared.'</p>
<p>Far more striking is a disappearance or reappearance
at the 'dark limb.' In this case the limb of the
moon is absolutely invisible, and it may be that no
part of the moon is visible in the field of the telescope.
In this case the observer sees a star shining brightly
and alone in the middle of the field of his telescope.
He takes the time from his faithful clock, counting
beat after beat, when suddenly the star is gone! So
sudden is the disappearance that the novice feels
almost as astonished as if he had received a slap in
the face, and not unfrequently he loses all count or
recollection of the clock beats. The reappearance at
the dark limb is quite as startling; with a bright star
it is almost as if a shell had burst in his very face,
and it would require no very great imagination to
make him think that he had heard the explosion.
One moment nothing was visible; now a great star
is shining down serenely on the watcher. A little
practice soon enables the observer to accustom
himself to these effects, and an old hand finds no
more difficulty in observing an occultation of any
kind than in taking a transit.</p>
<p>Such an observation is useful for more purposes
than one. If the position of the star occulted is
known—and it can be determined at leisure afterwards—we
necessarily know where the limb of the moon<span class="pagenum"><a name="Page_216" id="Page_216">[216]</a></span>
was at the time of the observation. Then the time
which the moon took to pass over the star enables us
to calculate the diameter of our satellite; the different
positions of the moon relative to the star, as seen
from different observatories, enable us to calculate its
distance.</p>
<p>But if the disappearance takes place at the bright
limb, the reappearance usually takes place at the
dark, and <i lang="la" xml:lang="la">vice versâ</i>; and the two observations are
not quite comparable. There is one occasion, however,
when both observations are made under similar
circumstances, namely, at the full. And if the moon
happens also to be totally eclipsed, the occultations
of quite faint stars can be successfully observed, much
fainter than can ordinarily be seen close up to the
moon. Total eclipses of the moon, therefore, have
recently come to be looked upon as important events
for the astronomer, and observatories the world over
usually co-operate in watching them. October 4,
1884, was the first occasion when such an organised
observation was made; there have been several since,
and on these nights every available telescope and
observer at Greenwich is called into action.</p>
<p>It may be asked why these different modes of
observing the moon are still kept up, year in and
year out. 'Do we not know the moon's orbit
sufficiently well, especially since the discovery of
gravitation?' No; we do not. This simple and
beautiful law—simple enough in itself, gives rise to
the most amazing complexity of calculation. If the
earth and moon were the only two bodies in the
universe, the problem would be a simple one. But<span class="pagenum"><a name="Page_217" id="Page_217">[217]</a></span>
the earth, sun, and moon are members of a triple
system, each of which is always acting on both of the
others. More, the planets, too, have an appreciable
influence, and the net result is a problem so intricate
that our very greatest mathematicians have not
thoroughly worked it out. Our calculations of the
moon's motions need, therefore, to be continually
compared with observation, need even to be
continually corrected by it.</p>
<p>There is a further reason for this continual
observation, not only in the case of the sun, which
is our great standard star, since from it we derive
the right ascensions of the stars, and it is also our
great timekeeper; not only in that of the moon, but
also in the case of the planets. Their places as computed
need continually to be compared with their
places as observed, and the discordances, if any, inquired
into. The great triumph which resulted to
science from following this course—to pure science,
since Uranus is too faint a planet to be any help to
the sailor in navigation—is well known. The observed
movements of Uranus proved not to be in
accord with computation, and from the discordances
between calculation and observation Adams and
Leverrier were able to predicate the existence of a
hitherto unseen planet beyond—</p>
<blockquote>
<p>'To see it, as Columbus saw America from Spain. Its
movements were felt by them trembling along the far-reaching
line of their analysis, with a certainty hardly
inferior to that of ocular demonstration.'<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a></p></blockquote>
<p><span class="pagenum"><a name="Page_218" id="Page_218">[218]</a></span></p>
<p>The discovery of Neptune was not made at
Greenwich, and Airy has been often and bitterly
attacked because he did not start on the search for
the predicted planet the moment Adams addressed
his first communication to him, and so allowed
the French astronomer to engross so much of the
honour of the exploit. The controversy has been
argued over and over again, and we may be content
to leave it alone here. There is one point,
however, which is hardly ever mentioned, which must
have had much effect in determining Airy's conduct.
In 1845, the year in which Adams sent his provisional
elements of the unseen disturbing planet to Airy, the
largest telescope available for the search at Greenwich
was an equatorial of only six and three-quarter inches
aperture, provided with small and insufficient circles
for determining positions, and housed in a very
small and inconvenient dome; whilst at Cambridge,
within a mile or so of Adams' own college, was the
'Northumberland' equatorial, of nearly twelve inches
aperture, under the charge of the University Professor
of Astronomy, Professor Challis, and which was then
much the largest, best mounted and housed equatorial
in the entire country. The 'Northumberland' had
been begun from Airy's designs and under his own
superintendence, when he was Professor of Astronomy
at Cambridge. Naturally, then, knowing how much
superior the Cambridge telescope was to any which
he had under his care, he thought the search should
be made with it. He had no reason to believe that
his own instrument was competent for the work.</p>
<div class="figcenter bord" style="width: 600px;"><a name="observe" id="observe"></a>
<img src="images/i_219.jpg" width="600" height="395" alt="observe" />
<div class="caption"><p class="center">THE NEW OBSERVATORY AS SEEN FROM FLAMSTEED'S OBSERVATORY.</p></div>
</div>
<p>On the other hand, it is hard for the ordinary
<span class="pagenum"><a name="Page_219" id="Page_219"> </a><br /><a name="Page_220" id="Page_220"> </a><br /><a name="Page_221" id="Page_221">[221]</a></span>man to understand how it was that Adams not only
left unnoticed and unanswered for three-quarters of
a year, an inquiry of Airy's with respect to his
calculations, but also never took the trouble to visit
Challis, whom he knew well, and who was so near at
hand, to stir him up to the search. But, in truth,
the whole interest of the matter for Adams rested
in the mathematical problem. The irregularities in
the motion of Uranus were interesting to him simply
for the splendid opportunity which they gave him
for their analysis. A purely imaginary case would
have served his purpose nearly as well. The actuality
of the planet which he predicted was of very little
moment; the <i lang="fr" xml:lang="fr">éclat</i> and popular reputation of the
discovery was less than nothing; the problem itself
and the mental exercise in its solution, were what
he prized.</p>
<p>But it was not creditable to the nation that the
Royal Observatory should have been so ill-provided
with powerful telescopes; and a few years later Airy
obtained the sanction of the Government for the
erection of an equatorial larger than the 'Northumberland,'
but on the same general plan and in a much
more ample dome. This was for thirty-four years the
'Great' or 'South-East' equatorial, and the mounting
still remains and bears the old name, though the
original telescope has been removed elsewhere. The
object-glass had an aperture of twelve and three-quarter
inches and a focal length of eighteen feet,
and was made by Merz of Munich, the engineering
work by Ransomes and Sims of Ipswich, and the
graduations and general optical work by Simms, now<span class="pagenum"><a name="Page_222" id="Page_222">[222]</a></span>
of Charlton, Kent. The mounting was so massive
and stable that the present Astronomer Royal has
found it quite practicable and safe to place upon it
a telescope (with its counterpoises) of many times
the weight, one made by Sir Howard Grubb, of
Dublin, of twenty-eight inches aperture and twenty-eight
feet focal length, the largest refractor in the
British Empire, though surpassed by several American
and Continental instruments.</p>
<p>The stability of the mounting was intended to
render the telescope suitable for a special work.
This was the observation of 'minor planets.' On
the first day of the present century the first of these
little bodies was discovered by Piazzi at Palermo.
Three more were discovered at no great interval afterwards,
and then there was an interval of thirty-eight
years without any addition to their number. But
from December 8, 1845, up to the present time, the
work of picking up fresh individuals of these 'pocket
planets' has gone on without interruption, until now
more than 400 are known. Most of these are of no
interest to us, but a few come sufficiently near to
the earth for their distance to be very accurately
determined; and when the distance of one member
of the solar system is determined, those of all the
others can be calculated from the relations which
the law of gravitation reveals to us. It is a matter
of importance, therefore, to continue the work of
discovery, since we may at any time come across an
interesting or useful member of the family; and that
we may be able to distinguish between minor planets
already discovered and new ones, their orbits must<span class="pagenum"><a name="Page_223" id="Page_223">[223]</a></span>
be determined as they are discovered, and some sort
of watch kept on their movements.</p>
<p>A striking example of the scientific prizes which
we may light upon in the process of the rather dreary
and most laborious work which the minor planets
cause, has been recently supplied by the discovery
of Eros. On August 13, 1898, Herr Witt, of the
Urania Observatory, Berlin, discovered a very small
planet that was moving much faster in the sky than
is common with these small bodies. The great
majority are very much farther from the sun than
the planet Mars, many of them twice as far, and
hence, since the time of a planet's revolution round
the sun increases, in accordance with Kepler's law,
more rapidly than does its distance, it follows that
they move much more slowly than Mars. But this
new object was moving at almost the same speed as
Mars; it must, therefore, be most unusually near to
us. Further observations soon proved that this was
the case, and Eros, as the little stranger has been
called, comes nearer to us than any other body of
which we are aware except the moon. Venus when
in transit is 24<small><sup>1</sup>/<sub>2</sub></small> millions of miles from us, Mars at
its nearest is 34<small><sup>1</sup>/<sub>2</sub></small> millions, Eros at its nearest approach
is but little over 13 millions.</p>
<p>The use of such a body to us is, of course, quite
apart from any purpose of navigation, except very
indirectly. But it promises to be of the greatest
value in the solution of a question in which astronomers
must always feel an interest, the determination of
the distance of the earth from the sun. We know
the <em>relative</em> distances of the different planets, and,<span class="pagenum"><a name="Page_224" id="Page_224">[224]</a></span>
consequently if we could determine the absolute
distance of any one, we should know the distances
of all. As it is practically impossible to measure our
distance from the sun directly, several attempts have
been made to determine the distances of Venus,
Mars, or such of the minor planets as come the
nearest to us. Three of these in particular, the little
planets Iris, Victoria, and Sappho, have given us the
most accurate determinations of the sun's distance
(92,874,000 miles) which we have yet obtained; but
Eros at its nearest approach will be six times as near
to us as either of the three mentioned above, and
therefore should give us a value with only one-sixth
of the uncertainty attaching to that just mentioned.</p>
<p>The discovery of minor planets has lain outside
the scope of Greenwich work, but their observation
has formed an integral part of it. The general
public is apt to lay stress rather on the first than
on the second, and to think it rather a reproach to
Greenwich that it has taken no part in such explorations.
Experience has, however, shown that they
may be safely left to amateur activity, whilst the
monotonous drudgery of the observation of minor
planets can only be properly carried out in a permanent
institution.</p>
<p>The observation of these minute bodies with the
transit circle and altazimuth is attended with some
difficulties; but precise observations of various objects
may be made with an equatorial; indeed, comets are
usually observed by its means.</p>
<p>The most ordinary way of observing a comet with
an equatorial is as follows: Two bars are placed in<span class="pagenum"><a name="Page_225" id="Page_225">[225]</a></span>
the eye-piece of the telescope, at right angles to each
other, and at an angle of forty-five degrees to the
direction of the apparent daily motion of the stars.
The telescope is turned to the neighbourhood of the
comet, and moved about until it is detected. The
telescope is then put a little in front of the comet,
and very firmly fixed. The observer soon sees the
comet entering his field, and by pressing the contact
button he telegraphs to the chronograph the time
when the comet is exactly bisected by each of the
bars successively. He then waits until a bright star,
or it may be two or three, have entered the telescope
and been observed in like manner. The telescope
is then unclamped, and moved forward until it is
again ahead of the comet, and the observations are
repeated; and this is done as often as is thought
desirable. The places of the stars have, of course,
to be found out from catalogues, or have to be
observed with the transit circle, but when they are
known the position of the comet or minor planet can
easily be inferred.</p>
<p>Next to the glory of having been the means of
bringing about the publication of Newton's <cite>Principia</cite>,
the greatest achievement of Halley, the second
Astronomer Royal, was that he was the first to
predict the return of a comet. Newton had shown
that comets were no lawless wanderers, but were as
obedient to gravitation as were the planets themselves,
and he also showed how the orbit of a comet
could be determined from observations on three
different dates. Following these principles, Halley
computed the orbits of no fewer than twenty-four<span class="pagenum"><a name="Page_226" id="Page_226">[226]</a></span>
comets, and found that three of them, visible at
intervals of about seventy-five years, pursued practically
the same path. He concluded, therefore, that
these were really different appearances of the same
object, and, searching old records, he found reason
to believe that it had been observed frequently earlier
still. It seems, in fact, to have been the comet which
is recorded to have been seen in 1066 in England at
the time of the Norman invasion; in <small>A.D.</small> 66, shortly
before the commencement of that war which ended
in the destruction of Jerusalem by Titus; and earlier
still, so far back as <small>B.C.</small> 12. Halley, however, experienced
a difficulty in his investigation. The period
of the comet's revolution was not always the same.
This, he concluded, must be due to the attraction of
the planets near which the comet might chance to
travel. In the summer of 1681 it had passed very
close to Jupiter, for instance, and in consequence he
expected that instead of returning in August 1757,
seventy-five years after its last appearance, it would
not return until the end of 1758 or the beginning of
1759. It has returned twice since Halley's day, a
triumphant verification of the law of gravitation; and
we are looking for it now for a third return some
ten years hence, in 1910.</p>
<p>Halley's comet, therefore, is an integral member
of our solar system, as much so as the earth or
Neptune, though it is utterly unlike them in appearance
and constitution, and though its path is so
utterly unlike theirs that it approaches the sun
nearer than our earth, and recedes farther than
Neptune. But there are other comets, which are<span class="pagenum"><a name="Page_227" id="Page_227">[227]</a></span>
not permanent members of our system, but only
passing visitors. From the unfathomed depths of
space they come, to those depths they go. They
obey the law of gravitation so far as our sight can
follow them, but what happens to them beyond?
Do they come under some other law, or, perchance,
in outermost space is there still a region reserved to
primeval Chaos, the 'Anarch old,' where no law at
all prevails? Gravitation is the bond of the solar
system; is it also the bond of the Universe?</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_228" id="Page_228">[228]</a></span></p>
<h2>CHAPTER IX</h2>
<h3>THE MAGNETIC AND METEOROLOGICAL
DEPARTMENTS</h3>
<p>Passing out of the south door of the new altazimuth
building, we come to a white cruciform erection,
constructed entirely of wood. This is the Magnet
House or Magnetic Observatory, the home of a
double Department, the Magnetic and Meteorological.</p>
<p>This department does not, indeed, lie within the
original purpose of the Observatory as that was
defined in the warrant given to Flamsteed, and yet
is so intimately connected with it, through its bearing
on navigation, that there can be no question as to
its suitability at Greenwich. Indeed, its creation is
a striking example of the thorough grasp which Airy
had upon the essential principles which should govern
the great national observatory of an essentially
naval race, and of the keen insight with which he
watched the new development of science. The
Magnetic Observatory, therefore, the purpose of which
was to deal with the observation of the changes in
the force and direction of the earth's magnetism—an
inquiry which the greater delicacy of modern compasses,
and, in more recent times, the use of iron<span class="pagenum"><a name="Page_229" id="Page_229">[229]</a></span>
instead of wood in the construction of ships has
rendered imperative—was suggested by Airy on the
first possible occasion after he entered on his office,
and was sanctioned in 1837. The Meteorological
Department has a double bearing on the purpose of
the Observatory. On the one side, a knowledge of
the temperature and pressure of the atmosphere is, as
we have already seen, necessary in order to correct
astronomical observations for the effect of refraction.
On the other hand, meteorology proper, the study of
the movements of the atmosphere, the elucidation of
the laws which regulate those movements, leading to
accurate forecasts of storms, are of the very first
necessity for the safety of our shipping. It is true
that weather forecasts are not issued from Greenwich
Observatory, any more than the <cite>Nautical Almanac</cite> is
now issued from it; but just as the Observatory
furnishes the astronomical data upon which the
Almanac is based, so also it takes its part in furnishing
observations to be used by the Meteorological
Office at Westminster for its daily predictions.</p>
<p>Those predictions are often made the subject of
much cheap ridicule; but, however far short they
may fall of the exact and accurate predictions which
we would like to have, yet they mark an enormous
advance upon the weather-lore of our immediate
forefathers.</p>
<div class="poem"><div class="stanza">
<span class="i0">'He that is weather wise<br /></span>
<span class="i0">Is seldom other wise,'<br /></span>
</div></div>
<p class="noin">says the proverb, and the saying is not without a
shrewd amount of truth. For perhaps nowhere can
we find a more striking combination of imperfect<span class="pagenum"><a name="Page_230" id="Page_230">[230]</a></span>
observation and inconsequent deduction than in the
saws which form the stock-in-trade of the ordinary
would-be weather prophet. How common it is to
find men full of the conviction that the weather must
change at the co-called 'changes of the moon,'
forgetful that</p>
<div class="poem"><div class="stanza">
<span class="i0">'If we'd no moon at all—<br /></span>
<span class="i2">And that may seem strange—<br /></span>
<span class="i0">We still should have weather<br /></span>
<span class="i2">That's subject to change.'<br /></span>
</div></div>
<p>They will say, truly enough, no doubt, that they have
known the weather to change at 'new' or 'full,' as
the case may be, and they argue that it, therefore,
must always do so. But, in fact, they have only
noted a few chance coincidences, and have let the
great number of discordances pass by unnoticed.</p>
<p>But observations of this kind seem scientific and
respectable compared with those numerous weather
proverbs which are based upon the mere jingle of
a rhyme, as</p>
<div class="poem"><div class="stanza">
<span class="i0">'If the ash is out before the oak,<br /></span>
<span class="i0">You may expect a thorough soak'—<br /></span>
</div></div>
<p class="noin">a proverb which is deftly inverted in some districts
by making 'oak' rhyme to 'choke.'</p>
<p>Others, again, are based upon a mere childish fancy,
as, for example, when the young moon 'lying on her
back' is supposed to bode a spell of dry weather,
because it looks like a cup, and so might be thought
of as able to hold the water.</p>
<p>During the present reign, however, a very different
method of weather study has come into action, and<span class="pagenum"><a name="Page_231" id="Page_231">[231]</a></span>
the foundations of a true weather wisdom have been
laid. These have been based, not on fancied analogies
or old wives' rhymes, or a few forechosen coincidences,
but upon observations carried on for long periods
of time and over wide areas of country, and discussed
in their entirety without selection and bias. Above
all, mathematical analysis has been applied to the
motions of the air, and ideas, ever gaining in precision
and exactness, have been formulated of the general
circulation of the atmosphere.</p>
<p>As compared with its sister science, astronomy,
meteorology appears to be still in a very undeveloped
state. There is such a difference between the power
of the astronomer to foretell the precise position of
sun, moon, and planets for years, even for centuries,
beforehand, and the failure of the meteorologist to
predict the weather for a single season ahead, that
the impression has been widely spread that there is
yet no true meteorological science at all. It is forgotten
that astronomy offered us, in the movements
of the heavenly bodies, the very simplest and easiest
problem of related motion. Yet for how many thousands
of years did men watch the planets, and speculate
concerning their motions, before the labours of
Tycho, Kepler, and Newton culminated in the revelation
of their meaning? For countless generations
it was supposed that their movements regulated the
lives, characters, and private fortunes of individual
men; just as quite recently it was fancied that a
new moon falling on a Saturday, or two full moons
coming within the same calendar month, brought
bad weather!</p>
<p><span class="pagenum"><a name="Page_232" id="Page_232">[232]</a></span></p>
<p>It is still impossible to foresee the course of weather
change for long ahead; but the difference between
the modern navigator, surely and confidently making
a 'bee-line' across thousands of miles of ocean to his
destination, and the timid sailor of old, creeping from
point to point of land, is hardly greater than the
contrast between the same two men, the one watching
his barometer, the other trusting in the old wives'
rhymes which afforded him his only indication as to
coming storms.</p>
<p>It is still impossible to foresee the weather change
for long ahead, but in our own and in many other
countries, especially the United States, it has been
found possible to predict the weather of the coming
four-and-twenty hours with very considerable exactness,
and often to forecast the coming of a great
storm several days ahead. This is the chief purpose
of the two great observatories of the storm-swept
Indian and Chinese seas, Hong Kong and Mauritius;
and the value of the work which they have done in
preventing the loss of ships, and the consequent loss
of lives and property, has been beyond all estimate.</p>
<p>The Royal Observatory, Greenwich, is a meteorological
as well as an astronomical observatory, but, as
remarked above, it does not itself issue any weather
forecasts. Just as the Greenwich observations of the
places of the moon and stars are sent to the <cite>Nautical
Almanac</cite> Office, for use in the preparation of that ephemeris;
just as the Greenwich determinations of time
are used for the issue of signals to the Post Office,
whence they are distributed over the kingdom, so the
Greenwich observations of weather are sent to the<span class="pagenum"><a name="Page_233" id="Page_233">[233]</a></span>
Meteorological Office, there to be combined with
similar records from every part of the British Isles,
to form the basis of the daily forecasts which the
latter office publishes. To each of these three offices,
therefore, the Royal Observatory, Greenwich, stands
in the relation of purveyor. It supplies them with
the original observations more or less in reduced and
corrected form, without which they could not carry
on most important portions of their work.</p>
<p>Let it be noted how closely these three several
departments, the <cite>Nautical Almanac</cite> Office, the Time
Department, and the Meteorological Office, are related
to practical navigation. Whatever questions of pure
science—of knowledge, that is, apart from its useful
applications—may arise out of the following up of
these several inquiries, yet the first thought, the first
principle of each, is to render navigation more sure
and more safe.</p>
<p>The first of all meteorological instruments is the
barometer, which, under its two chief forms of mercurial
and aneroid, is simply a means of measuring
the pressure exerted by the atmosphere.</p>
<p>There are two important corrections to which its
readings are subject. The first is for the height of
the station above the level of the sea; the second is
for the effect of temperature upon the mercury in the
barometer itself, lengthening the column. To overcome
these, the height of the standard barometer at
Greenwich above sea-level has been most carefully
ascertained, and the heights relative to it of the other
barometers of the Observatory, particularly those in
rooms occupied by fundamental telescopes, have also<span class="pagenum"><a name="Page_234" id="Page_234">[234]</a></span>
been determined, whilst the self-recording barometer
is mounted in a basement, where it is almost
completely protected from changes of temperature.</p>
<p>Next in importance to the barometer as a meteorological
instrument comes the thermometer. The great
difficulty in the Observatory use of the thermometer
is to secure a perfectly unexceptionable exposure, so
that the thermometer may be in free and perfect
contact with the air, and yet completely sheltered
from any direct ray from the sun. This is secured
in the great thermometer shed at Greenwich by a
double series of 'louvre' boards, on the east, south,
and west sides of the shed, the north side being open.
The shed itself is made a very roomy one, in order
to give access to a greater body of air.</p>
<p>A most important use of the thermometer is in
the measurement of the amount of moisture in the air.
To obtain this, a pair of thermometers are mounted
close together, the bulb of one being covered by
damp muslin, and the other being freely exposed.
If the air is completely saturated with moisture, no
evaporation can take place from the damp muslin,
and consequently the two thermometers will read
the same. But if the air be comparatively dry, more
or less evaporation will take place from the wet bulb,
and its temperature will sink to that at which the
air would be fully saturated with the moisture which
it already contained. For the higher the temperature,
the greater is its power of containing moisture. The
difference of the reading of the two thermometers is,
therefore, an index of humidity. The greater the
difference, the greater the power of absorbing moisture,
<span class="pagenum"><a name="Page_235" id="Page_235"> </a><br /><a name="Page_236" id="Page_236"> </a><br /><a name="Page_237" id="Page_237">[237]</a></span>or, in other words, the dryness of the air. The great
shed already alluded to is devoted to these companion
thermometers.</p>
<div class="figcenter bord" style="width: 396px;"><a name="self" id="self"></a>
<img src="images/i_235.jpg" width="396" height="600" alt="self" />
<div class="caption"><p class="center">THE SELF-REGISTERING THERMOMETERS.</p></div>
</div>
<p>Very closely connected with atmospheric pressure,
as shown us by the barometer, is the study of the
direction of winds. If we take a map of the British
Isles and the neighbouring countries, and put down
upon them the barometer readings from a great
number of observing stations, and then join together
the different places which show the same barometric
pressure, we shall find that these lines of equal
pressure—technically called 'isobars'—are apt to run
much nearer together in some places than in others.
Clearly, where the isobars are close together it means
that in a very short distance of country we have a
great difference of atmospheric pressure. In this
case we are likely to get a very strong wind blowing
from the region of high pressure to the region of low
pressure, in order to restore the balance.</p>
<p>If, further, we had information from these various
observing stations of the direction in which the
wind was blowing, we should soon perceive other
relationships. For instance, if we found that the
barometer read about the same in a line across the
country from east to west, but that it was higher in
the north of the islands than in the south, we should
then have a general set of winds from the east, and
a similar relation would hold good if the barometer
were highest in some other quarter; that is, the
prevailing wind will come from a quarter at right
angles to the region of highest barometer, or, as it
is expressed in what is known as 'Buys Ballot's law,'<span class="pagenum"><a name="Page_238" id="Page_238">[238]</a></span>
'stand with your back to the wind, and the barometer
will be lower on your left hand than on your right.'
This law holds good for the northern hemisphere
generally, except near to the equator; in the southern
hemisphere the right hand is the side of low barometer.</p>
<p>The instruments for wind observation are of two
classes: vanes to show its direction, and anemometers
to show its speed and its pressure. These may be
regarded as two different modes in which the strength
of the wind manifests itself. Pressure anemometers
are usually of two forms: one in which a heavy plate
is allowed to swing by its upper edge in a position
fronting the wind, the amount of its deviation from
the vertical being measured; and the other in which
the plate is supported by springs, the degree of
compression of the springs being the quantity
registered in that case. Of the speed anemometers,
the best known form is the 'Robinson,' in which four
hemispherical cups are carried at the extremities of
a couple of cross bars.</p>
<p>For the mounting of these wind instruments the
old original Observatory, known as the Octagon
Room, has proved an excellent site, with its flat roof
surmounted by two turrets in the north-east and
north-west corners, and raised some two hundred
feet above high-water mark.</p>
<div class="figcenter bord" style="width: 424px;"><a name="anemone" id="anemone"></a>
<img src="images/i_240.jpg" width="424" height="600" alt="anemone" />
<div class="caption"><p class="center">THE ANEMOMETER ROOM, NORTH-WEST TURRET.</p></div>
</div>
<p>The two chief remaining instruments are those
for measuring the amount of rainfall and of full
sunshine. The rain gauge consists essentially of a
funnel to collect the rain, and a graduated glass to
measure it. The sunshine recorder usually consists
of a large glass globe arranged to throw an image<span class="pagenum"><a name="Page_239" id="Page_239"> </a><br /><a name="Page_240" id="Page_240"> </a><br /><a name="Page_241" id="Page_241">[241]</a></span>
of the sun on a piece of specially prepared paper.
This image, as the sun moves in the sky, moves along
the paper, charring it as it moves, and at the end
of the day it is easy to see, from the broken, burnt
trace, at what hours the sun was shining clear, and
when it was hidden by cloud.</p>
<p>An amusing difficulty was encountered in an
attempt to set on foot another inquiry. The
Superintendent of the Meteorological Department at
the time wished to have a measure of the rate at
which evaporation took place, and therefore exposed
carefully measured quantities of water in the open
air in a shallow vessel. For a few days the record
seemed quite satisfactory. Then the evaporation
showed a sudden increase, and developed in the most
erratic and inexplicable manner, until it was found
that some sparrows had come to the conclusion that
the saucer full of water was a kindly provision for
their morning 'tub,' and had made use of it accordingly.</p>
<p>A large proportion of the meteorological instruments
at Greenwich and other first-class observatories
are arranged to be self-recording. It was early felt
that it was necessary that the records of the barometer
and thermometer should be as nearly as possible
continuous; and at one time, within the memory
of members of the staff still living, it was the duty
of the observer to read a certain set of instruments
at regular two-hour intervals during the whole
of the day and night—a work probably the most
monotonous, trying, and distasteful of any that the
Observatory had to show.</p>
<p>The two-hour record was no doubt practically<span class="pagenum"><a name="Page_242" id="Page_242">[242]</a></span>
equivalent to a continuous one, but it entailed a
heavy amount of labour. Automatic registers were,
therefore, introduced whenever they were available.
The earliest of these were mechanical, and several
still make their records in this manner.</p>
<p>On the roof of the Octagon Room we find, beside
the two turrets already referred to, a small wooden
cabin built on a platform several feet above the
roof level. This cabin and the north-western turret
contain the wind-registering instruments. Opening
the turret door, we find ourselves in a tiny room
which is nearly filled by a small table. Upon this
table lies a graduated sheet of paper in a metal frame,
and as we look at it, we see that a clock set up close
to the table is slowly drawing the paper across it.
Three little pencils rest lightly on the face of the
paper at different points. One of these, and usually
the most restless, is connected with a spindle which
comes down into the turret from the roof, and which
is, in fact, the spindle of the wind vane. The gearing
is so contrived that the motion on a pivot of the vane
is turned into motion in a straight line at right angles
to the direction in which the paper is drawn by the
clock. A second pencil is connected with the wind-pressure
anemometer. The third pencil indicates
the amount of rain that has fallen since the last
setting, the pencil being moved by a float in the
receiver of the rain gauge.</p>
<div class="figcenter bord" style="width: 450px;"><a name="trace" id="trace"></a>
<img src="images/i_243.jpg" width="450" height="586" alt="trace" />
<div class="caption"><p class="center">THE ANEMOMETER TRACE.</p></div>
</div>
<p>An objection to all the mechanical methods of
continuous registration is that, however carefully the
gearing between the instrument itself and the pencil
is contrived, however lightly the pencil moves over<span class="pagenum"><a name="Page_243" id="Page_243">[243]</a></span>
the paper, yet some friction enters in and affects the
record: this is of no great moment in wind registration,
when we are dealing with so powerful an agent as
the wind, but it becomes a serious matter when the<span class="pagenum"><a name="Page_244" id="Page_244">[244]</a></span>
barometer is considered, since its variations require
to be registered with the greatest minuteness. When
photography, therefore, was invented, meteorologists
were very prompt to take advantage of this new ally.
A beam of light passing over the head of the column
of mercury in a thermometer or barometer could
easily be made to fall upon a drum revolving once in
the twenty-four hours, and covered with a sheet of
photographic paper. In this case, when the sensitive
paper is developed, we find its upper half blackened,
the lower edge of the blackened part showing an
irregular curve according as the mercury in the
thermometer or barometer rose or fell, and admitted
less or more light through the space above it.</p>
<p>Here we have a very perfect means of registration:
the passage of the light exercises no friction or check
on the free motion of the mercury in the tube, or on
the turning of the cylinder covered by the sensitive
paper, whilst it is easy to obtain a time scale on the
register by cutting off the light for an instant—say
at each hour. In this way the wet and dry bulb
thermometers in the great shed make their registers.</p>
<p>The supply of material to the Meteorological
Office is not the only use of the Greenwich meteorological
observations. Two elements of meteorology,
the temperature and the pressure of the atmosphere,
have the very directest bearing upon astronomical
work. And this in two ways. An instrument is
sensible to heat and cold, and undergoes changes of
form, size, or scale, which, however absolutely minute,
yet become, with the increased delicacy of modern
work, not merely appreciable, but important. So too<span class="pagenum"><a name="Page_245" id="Page_245">[245]</a></span>
with the density of the atmosphere: the light from a
distant star, entering our atmosphere, suffers refraction;
and being thus bent out of its path, the star appears
higher in the heavens than it really is. The amount
of this bending varies with the density of the layers
of air through which the light has to pass. The two
great meteorological instruments, the thermometer
and barometer, are therefore astronomical instruments
as well.</p>
<p>In the arrangements at Greenwich the Magnetic
Department is closely connected with the Meteorological,
and it is because the two departments have
been associated together that the building devoted
to both is constructed of wood, not brick, since
ordinary bricks are made of clay which is apt to be
more or less ferruginous. Copper nails have alone
been employed in the construction of the buildings.
The fire-grates, coal-scuttles, and fire-irons are all of
the same metal.</p>
<p>The growth of the Observatory has, however,
made it necessary to set up some of the new telescopes,
into the mounting of which much iron enters,
very close to the magnetic building. The present
Astronomer-Royal has therefore erected a Magnetic
Pavilion right out in the park at an ample distance
from these disturbing causes.</p>
<p>The double department is, therefore, the most
widely scattered in the whole Observatory. It is
located for computing purposes in the west wing of
the New Observatory; many of its magnetic instruments
are in the old Magnet House, others are
across the park in the new Magnetic Pavilion; the<span class="pagenum"><a name="Page_246" id="Page_246">[246]</a></span>
anemometers are on the roof of the Octagon Room,
Flamsteed's original observatory, and the self-registering
thermometers are in the south ground between
the old Magnet House and the New Observatory.</p>
<div class="figcenter bord" style="width: 450px;"><a name="ext" id="ext"></a>
<img src="images/i_246.jpg" width="450" height="410" alt="ext" />
<div class="caption"><p class="center">MAGNETIC PAVILION—EXTERIOR.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>The object of the Magnetic Observatory is to
study the movements of the magnetic needle. The
quaintest answer that I ever received in an examination
was in reply to the question, 'What is meant by
magnetic inclination and declination?' The examinee
replied:</p>
<p><span class="pagenum"><a name="Page_247" id="Page_247">[247]</a></span></p>
<blockquote>
<p>'To make a magnet, you take a needle, and rub it on a
lodestone. If it refuses or <em>declines</em> to become a magnet,
that is magnetic declination; if it is easily made a
magnet, or is <em>inclined</em> to become one, that is magnetic
inclination.'</p></blockquote>
<p>One greatly regretted that it was necessary to
mark the reply according to its ignorance, and not,
as one would have wished, in proportion to its
ingenuity. Magnetic declination, however, as everybody
knows, measures the deviation of the 'needle'
from the true geographical north and south direction;
the inclination or dip is the angle which a 'needle'
makes with the horizon.</p>
<p>At one time the only method of watching the
movements of the magnetic needles was by direct
observation, just precisely as it was wont to be in the
case of the barometer and thermometer. But the
same agent that has been called in to help in their
case has enabled the magnets also to give us a direct
and continuous record of their movements. In principle
the arrangement is as follows: A small light
mirror is attached to the magnetic needle, and a
beam of light is arranged to fall upon the mirror,
and is reflected away from it to a drum covered
with sensitive paper. If, then, the needle is perfectly
at rest, a spot of light falls on the drum and blackens
the paper at one particular point. The drum is made
to revolve by clockwork once in twenty-four hours,
and the black dot is therefore lengthened out into
a straight line encircling the drum. If, however, the
needle moves, then the spot of light travels up or
down, as the case may be.</p>
<p><span class="pagenum"><a name="Page_248" id="Page_248">[248]</a></span></p>
<p>Now, if we look at one of these sheets of photographic
paper after it has been taken from the drum,
we shall see that the north pole of the magnet has
moved a little, a very little, towards the west in the
early part of the day, say from sunrise to 2 p.m., and
has swung backwards from that hour till about 10 p.m.,
remaining fairly quiet during the night. The extent
of this daily swing is but small, but it is greater in
summer than in winter, and it varies also from year
to year.</p>
<div class="figcenter bord" style="width: 450px;"><a name="int" id="int"></a>
<img src="images/i_248.jpg" width="450" height="334" alt="int" />
<div class="caption"><p class="center">MAGNETIC PAVILION—INTERIOR.<br />
(<em>From a photograph by Mr. Lacey.</em>)</p></div>
</div>
<p>Besides this daily swing, there occasionally happen
what are called 'magnetic storms;' great convulsive
twitchings of the needle, as if some unseen operator<span class="pagenum"><a name="Page_249" id="Page_249">[249]</a></span>
were endeavouring, whilst in a state of intense excitement,
to telegraph a message of vast importance, so
rapid and so sharp are the movements of the needle
to and fro. These great storms are felt, so far as we
know, simultaneously over the whole earth, and the
more characteristic begin with a single sharp twitch
of the needle towards the east.</p>
<p>Besides the movements of the magnetic needle,
the intensity of the currents of electricity which are
always passing through the crust of the earth are also
determined at Greenwich; but this work has been
rendered practically useless for the last few years by
the construction of the electric railway from Stockwell
to the City. Since it was opened, the photographic
register of earth currents has shown a broad blurring
from the moment of the starting of the first train in
the morning to the stopping of the last train at night.
As an indication of the delicacy of modern instruments,
it may be mentioned that distinct indications
of the current from this railway have been detected
as far off as North Walsham, in Norfolk, a distance
of more than a hundred miles. A further illustration
of the delicacy of the magnetic needles was afforded
shortly after the opening of the railway referred to.
On one occasion the then Superintendent of the
Magnetic Department visited the Generating Station
at Stockwell, and on his return it was noticed
day after day that the traces from the magnets
showed a curious deflection from 9 a.m. to 3 p.m.,
the hours of his attendance. This gave rise to some
speculation, as it did not seem possible that the
gentleman could himself have become magnetized.<span class="pagenum"><a name="Page_250" id="Page_250">[250]</a></span>
Eventually, the happy accident of a fine day solved
the mystery. That morning the Superintendent left
his umbrella at home, and the magnets were undisturbed.
The secret was out. The umbrella had
become a permanent magnet, and its presence in the
lobby of the magnetic house had been sufficient to
influence the needles.</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_251" id="Page_251">[251]</a></span></p>
<h2>CHAPTER X</h2>
<h3>THE HELIOGRAPHIC DEPARTMENT</h3>
<p>So far the development of the Observatory had been
along the central line of assistance to navigation.
But the Magnetic Department led on to one which
had but a very secondary connection with it.</p>
<p>A greatly enhanced interest was given to the
observations of earth magnetism, when it was found
that the intensity and frequency of its disturbances
were in close accord with changes that were in
progress many millions of miles away. That the
surface of the sun was occasionally diversified by the
presence of dark spots, had been known almost from
the first invention of the telescope; but it was not
until the middle of the present century that any
connection was established between these solar
changes and the changes which took place in the
magnetism of the earth. Then two observers, the
one interesting himself entirely with the spots on
the sun, the other as wholly devoted to the study of
the movements of the magnetic needle, independently
found that the particular phenomenon which each
was watching was one which varied in a more or less
regular cycle. And further, when the cycles were<span class="pagenum"><a name="Page_252" id="Page_252">[252]</a></span>
compared, they proved to be the same. Whatever
the secret of the connection, it is now beyond dispute
that as the spots on the sun become more and more
numerous, so the daily swing of the magnetic needle
becomes stronger; and, on the other hand, as the
spots diminish, so the magnetic needle moves more
and more feebly.</p>
<p>This discovery has given a greatly increased
significance to the study of the earth's magnetism.
The daily swing, the occasional 'storms,' are seen to
be something more than matters of merely local
interest; they have the closest connection with
changes going on in the vast universe beyond; they
have an astronomical importance.</p>
<p>And it was soon felt to be necessary to supplement
the Magnetic Observatory at Greenwich by one
devoted to the direct study of the solar surface; and
here again that invaluable servant of modern science,
photography, was ready to lend its help. Just as,
by the means of photography, the magnets recorded
their own movements, so even more directly the sun
himself makes register of his changes by the same
agency, and gives us at once his portrait and his
autograph.</p>
<p>This new department was again due to Airy, and
in 1873 the 'Kew' photo-heliograph, which had been
designed by De la Rue for this work, was installed
at Greenwich.</p>
<div class="figcenter bord" style="width: 600px;"><a name="helio" id="helio"></a>
<img src="images/i_254.jpg" width="600" height="389" alt="helio" />
<div class="caption"><p class="center">THE DALLMEYER PHOTO-HELIOGRAPH.</p></div>
</div>
<p>In order to photograph so bright a body as the
sun, it is not in the least necessary to have a very
large telescope. The one in common use at Greenwich
from 1875 to 1897, is only four inches in aperture<span class="pagenum"><a name="Page_253" id="Page_253"> </a><br /><a name="Page_254" id="Page_254"> </a><br /><a name="Page_255" id="Page_255">[255]</a></span>
and even that is usually diminished by a cap to three
inches, and its focal length is but five feet. This is
not very much larger than what is commonly called
a 'student's telescope,' but it is amply sufficient for
its work.</p>
<p>This 'Dallmeyer' telescope, so called from the
name of its maker, is one of five identical instruments
which were made for use in the observation of the
transit of Venus of 1874, and which, since they are
designed for photographing the sun, are called 'photo-heliographs.'</p>
<p>The image of the sun in the principal focus of this
telescope is about six-tenths of an inch in diameter;
but a magnifying lens is used, so that the photograph
actually obtained is about eight inches. Even with
this great enlargement, the light of the sun is so
intense that with the slowest photographic plates
that are made the exposure has to be for only a very
small fraction of a second. This is managed by
arranging a very narrow slit in a strip of brass. The
strip is made to run in a groove across the principal
focus. Before the exposure, it is fastened up so as to
cut off all light from entering the camera part of the
telescope. When all is ready, it is released and drawn
down very rapidly by a powerful spring, and the slit,
flying across the image of the sun, gives exposure to
the plate for a very minute fraction of a second—in
midsummer for less than a thousandth of a second.</p>
<p>Two of these photographs are taken every fine
day at Greenwich; occasionally more, if anything
specially interesting appears to be going on. But in
our cloudy climate at least one day in three gives no<span class="pagenum"><a name="Page_256" id="Page_256">[256]</a></span>
good opportunity for taking photographs of the sun,
and in the winter time long weeks may pass without
a chance. The present Astronomer-Royal, Mr.
Christie, has therefore arranged that photographs
with precisely similar instruments should be taken in
India and in the Mauritius, and these are sent over
to Greenwich as they are required, to fill up the
gaps in the Greenwich series. We have therefore at
Greenwich, from one source or another, practically a
daily record of the state of the sun's surface.</p>
<p>More recently the 'Dallmeyer' photo-heliograph,
though still retained for occasional use, has been
superseded generally by the 'Thompson'; a photographic
refractor of nine inches aperture, and nearly
nine feet focal length, presented to the Observatory
by Sir Henry Thompson. The image of the sun
obtained after enlargement in the telescope, with this
instrument, is seven and a half inches in diameter.
The 'Thompson' is mounted below the great twenty-six-inch
photographic refractor,—also presented to the
Observatory by Sir Henry Thompson,—in the dome
which crowns the centre of the New Observatory.</p>
<p>A photograph of the sun taken, it has next to
be measured, the four following particulars being
determined for each spot: First, its distance from
the centre of the image of the sun; next, the angle
between it and the north point; thirdly, the size of
the spot; and fourthly, the size of the umbra of the
spot, that is to say, of its dark central portion. The
size or area of the spot is measured by placing a thin
piece of glass, on which a number of cross-lines have
been ruled one-hundredth of an inch apart, in contact<span class="pagenum"><a name="Page_257" id="Page_257">[257]</a></span>
with the photograph. These cross-lines make up a
number of small squares, each the ten-thousandth
(<small><sup>1</sup>/<sub>10000</sub></small> in.) part of a square inch in area. When the
photograph and the little engraved glass plate are
nearly in contact, the photograph is examined with
a magnifying glass, and the number of little squares
covered by a given spot are counted. It will give
some idea of the vast scale of the sun when it is
stated that a tiny spot, so small that it only just
covers one of these little squares, and which is only
one-millionth of the visible hemisphere of the sun in
area, yet covers in actual extent considerably more
than one million of square miles.</p>
<p>The dark spots are not the only objects on the
sun's surface. Here and there, and especially near
the edge of the sun, are bright marks, generally in
long branching lines, so bright as to appear bright
even against the dazzling background of the sun itself.
These are called 'faculæ,' and they, like the spots,
have their times of great abundance and of scarcity,
changing on the whole at the same time as the spots.</p>
<p>After the solar photographs have been measured,
the measures must be 'reduced,' and the positions
of the spots as expressed in longitude and latitude on
the sun computed. There is no difficulty in doing
this, for the position of the sun's equator and poles
have long been known approximately, the sun revolving
on its axis in a little more than twenty-five
days, and carrying of course the spots and faculæ
round with him.</p>
<p>There are few studies in astronomy more engrossing
than the watch on the growth and changes of the<span class="pagenum"><a name="Page_258" id="Page_258">[258]</a></span>
solar spots. Their strange shapes, their rapid movements,
and striking alterations afford an unfailing
interest. For example, the amazing spectacle is
continually being afforded of a spot, some two, three,
or four hundred millions of square miles in area,
moving over the solar surface at a speed of three
hundred miles an hour, whilst other spots in the same
group are remaining stationary. But a higher interest
attaches to the behaviour of the sun as a whole than
to the changes of any particular single spot; and the
curious fact has been brought to light, that not only
do the spots increase and diminish in a regular cycle
of about eleven years in length, but they also affect
different regions of the sun at different points of the
cycle. At the time when spots are most numerous
and largest, they are found occupying two broad
belts, the one with its centre about 15° north of the
equator, the other about as far south, the equator
itself being very nearly free from them. But as the
spots begin to diminish, so they appear continually
in lower and lower latitudes, until instead of having
two zones of spots there is only one, and this one
lies along the equator. By this time the spots have
become both few and small. The next stage is that
a very few small spots are seen from time to time in
one hemisphere or the other at a great distance from
the equator, much farther than any were seen at the
time of greatest activity. There are then for a little
time three sun-spot belts, but the equatorial one soon
dies out. The two belts in high latitude, on the other
hand, continually increase; but as they increase, so
do they move downwards in latitude, until at length
<span class="pagenum"><a name="Page_259" id="Page_259"> </a><br /><a name="Page_260" id="Page_260"> </a><br /><a name="Page_261" id="Page_261">[261]</a></span>they are again found in about latitude 15° north or
south, when the spots have attained their greatest
development.</p>
<div class="figcenter bord" style="width: 600px;"><a name="spots" id="spots"></a>
<img src="images/i_259.jpg" width="600" height="353" alt="spots" />
<div class="caption"><p class="center">PHOTOGRAPH OF A GROUP OF SUN-SPOTS.<br />
(<em>From a photograph taken at the Royal Observatory, Greenwich, April, 1882, 20 d. 10 h. 6 m.</em>)</p></div>
</div>
<p>The clearest connection between the magnetic
movements and the sun-spot changes is seen when
we take the mean values of either for considerable
periods of time, as, for instance, year by year. But
occasionally we have much more special instances of
this connection. Some three or four times within the
last twenty years an enormous spot has broken out
on the sun, a spot so vast that worlds as great as our
own could lie in it like peas in a breakfast saucer,
and in each case there has been an immediate and a
threefold answer from the earth. One of the most
remarkable of these occurred in November, 1882. A
great spot was then seen covering an area of more
than three thousand millions of square miles. The
weather in London happened to be somewhat foggy,
and the sun loomed, a dull red ball, through the haze,
a ball it was perfectly easy to look at without specially
shading the eyes. So large a spot under such circumstances
was quite visible to the naked eye, and
it caught the attention of a great number of people,
many of whom knew nothing about the existence of
spots on the sun.</p>
<p>This great disturbance, evidently something of
the nature of a storm in the solar atmosphere,
stretched over one hundred thousand miles on the
surface of the sun. The disturbance extended
farther still, even to nearly one hundred millions of
miles. For simultaneously with the appearance of
the spot the magnetic needles at Greenwich began<span class="pagenum"><a name="Page_262" id="Page_262">[262]</a></span>
to suffer from a strange excitement, an excitement
which grew from day to day until it had passed
half-way across the sun's disc. As the twitchings
of the magnetic needle increased in frequency and
violence, other symptoms were noticed throughout
the length of the British Isles. Telegraphic communication
was greatly interfered with. The telegraph
lines had other messages to carry more urgent
than those of men. The needles in the telegraph
instruments twitched to and fro. The signal bells
on many of the railway lines were rung, and some
of the operators received shocks from their instruments.
Lastly, on November 17, a superb aurora
was witnessed, the culminating feature of which was
the appearance, at about six o'clock in the evening,
of a mysterious beam of greenish light, in shape
something like a cigar, and many degrees in length,
which rose in the east and crossed the sky at a pace
much quicker than but nearly as even as that of sun,
moon, or stars, till it set in the west two minutes
after its rising.</p>
<p>So far we have been dealing only with effects.
Their causes still rest hidden from us. There is
clearly a connection between the solar activity as
shown by the spots and the agitation of the magnetic
needles. But many great spots find no answer in
any magnetic vibration, and not a few considerable
magnetic storms occur when we can detect no great
solar changes to correspond.</p>
<p>Thus even in the simplest case before us we have
still very much to explain. Two far more difficult
problems are still offered us for solution. What is<span class="pagenum"><a name="Page_263" id="Page_263">[263]</a></span>
the cause of these mysterious solar spots? and have
they any traceable connection with the fitful vagaries
of earthly weather? It was early suggested that
probably the first problem might find an answer in
the ever-varying combinations and configurations of
the various planets, and that the sun-spots in their
turn might hold the key of our meteorology. Both
ideas were eagerly followed up—not that there was
much to support either, but because they seemed to
offer the only possible hope of our being able to
foretell the general current of weather change for any
long period in advance. So far, however, the first
idea may be considered as completely discredited.
As to the second, there would appear to be, in the
case of certain great tropical and continental countries
like India, some slight but by no means conclusive
evidence of a connection between the changes in the
annual rainfall and the changes in the spotted surface
of the sun. Dr. Meldrum, the late veteran Director
of the great Meteorological Observatory in Mauritius,
has expressed himself as confident that the years of
most spots are the years of most violent cyclones in
the Indian Ocean. But this is about as far as real
progress has been made, and it may be taken as
certain that many years more of observation will be
required, and the labours of many skilful investigators,
before we can hope to carry much farther our knowledge
as to any connection between storm and sun.</p>
<p>A further relation of great interest has come to
light within the last few years. The year 1868
opened a new epoch in the study of eclipses of the
sun. These, perhaps, scarcely lie within the scope<span class="pagenum"><a name="Page_264" id="Page_264">[264]</a></span>
of a book on the Royal Observatory, since Greenwich
has seen but one in all its history. That fell in the
year 1715; for the next it must wait many centuries.
Yet, as the late Astronomer Royal conducted three
expeditions to see total eclipses, and as the present
Astronomer Royal has undertaken a like number,
and members of the staff have been sent on other
occasions, it may not be deemed quite a digression
to refer to one feature which they have brought to
light.</p>
<p>When the dark body of the moon has entirely
hidden the sun, we have revealed to us, there and
then only, that strange and beautiful surrounding of
the sun which we call the corona. The earlier
observations of the corona seem to reveal it as a
body of the most weird and intricate form, a form
which seemed to change quite lawlessly from one
eclipse to another. But latterly it has been abundantly
clear that the forms which it assumes may be
grouped under a few well-defined types. In 1878
the corona was of a particularly simple and striking
character. Two great wings shot out east and west
in the direction of the sun's equator; round either
pole was a cluster of beautiful radiating 'plumes.'
It was then recollected that the corona of 1867 had
been of precisely the same character, both years
being years when sun-spots were at their fewest.
The coronæ, on the other hand, seen at times when
sun-spots are more abundant, were of an altogether
different character, the streamers being irregularly
distributed all round the sun. Other types also have
been recognized, and it is perfectly apparent that the<span class="pagenum"><a name="Page_265" id="Page_265">[265]</a></span>
corona changes its shape in close accordance with
the eleven-year period. The eclipses of 1889 and
1900, for example, showed coronæ that bore the very
closest resemblance to those of 1878 and 1866, the
interval of eleven years bringing a return to the same
form.</p>
<p>The further problem, therefore, now confronts us:
Does the corona produce the sun-spots, or do the
sun-spots produce the corona, or are both the result
of some mysterious magnetic action of the sun, an
action powerful enough on occasion to thrill through
and through this world of ours, ninety-three millions
of miles away?</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_266" id="Page_266">[266]</a></span></p>
<h2>CHAPTER XI</h2>
<h3>THE SPECTROSCOPIC DEPARTMENT</h3>
<p>Another department was set on foot by Airy at the
same time as the Heliographic Department, and in
connection with it; and it is the department which
has the greatest of interest for the general public.
This deals with astronomical physics, or astrophysics,
as it is sometimes more shortly called; the astronomy,
that is, which treats of the constitution and condition
of the heavenly bodies, not with their movements.</p>
<p>The older astronomy, on the other hand, confined
itself to the movements of the heavens so entirely
that Bessel, the man whose practical genius revolutionized
the science of observation, and whose
influence may be traced throughout in Airy's great
reconstitution of Greenwich Observatory, denied that
anything but the study of the celestial movements
had a right to the title of astronomy at all. Hardly
more than sixty years ago he wrote:</p>
<blockquote>
<p>'What astronomy is expected to accomplish is evidently
at all times the same. It may lay down rules by which
the movements of the celestial bodies, as they appear to
us upon the earth, can be computed. All else which we
may learn respecting these bodies, as, for example, their<span class="pagenum"><a name="Page_267" id="Page_267">[267]</a></span>
appearance, and the character of their surfaces, is, indeed,
not undeserving of attention, but possesses no proper astronomical
interest. Whether the mountains of the moon are
arranged in this way or in that is no further an object of
interest to astronomers than is a knowledge of the mountains
of the earth to others. Whether Jupiter appears with dark
stripes upon its surface, or is uniformly illuminated, pertains
as little to the inquiries of the astronomer; and its four
moons are interesting to him only for the motions they
have. To learn so perfectly the motions of the celestial
bodies that for any specified time an accurate computation
of these can be given—that was, and is, the problem which
astronomy has to solve.'</p></blockquote>
<p>There is a curious irony of progress which seems
to delight in falsifying the predictions of even master
minds as to the limits beyond which it cannot
advance. Bessel laid down his dictum as to the true
subjects of astronomical inquiry, Comte declared that
we could never learn what were the elements of
which the stars were composed, at the very time that
the first steps were being taken towards the creation
of a research which should begin by demonstrating
the existence in the heavenly bodies of the elements
with which we are familiar on the earth, and should
go on to prove itself a true astronomy, even in
Bessel's restricted sense, by supplying the means for
determining motion in a direction which he would
have thought impossible—that is to say, directly to
or from us.</p>
<p>The years that followed Kirchhoff's application
of the spectroscope to the study of the sun, and his
demonstration that sodium and iron existed in the
solar atmosphere, were crowded with a succession of
brilliant discoveries in the same field. Kirchhoff,<span class="pagenum"><a name="Page_268" id="Page_268">[268]</a></span>
Bunsen, Angström, Thal·n, added element after
element to the list of those recognized in the sun.
Huggins and Miller carried the same research into
a far more difficult field, and showed us the same
elements in the stars. Rutherfurd and Secchi grouped
the stars according to the types of their spectra, and
so laid the foundations of what may be termed stellar
comparative anatomy. Huggins discovered true
gaseous nebulæ, and so revived the nebular theory,
which had been supposed crushed when the great
telescope of Lord Rosse appeared to have resolved
several portions of the Orion nebula into separate
stars. The great riddle of 'new stars'—which still
remains a riddle—was at least attacked, and glowing
hydrogen was seen to be a feature in their constitution.
Glowing hydrogen, again, was, in the observation of
total eclipses, seen to be a principal constituent
of those surroundings of our own sun which we
now call prominences and chromosphere. Then the
method was discovered of observing the prominences
without an eclipse, and they were found to wax and
wane in more or less sympathy with the solar spots.
Sun-spots, planets, comets, meteors, variable stars, all
were studied with the new instrument, and all yielded
to it fresh and valuable, and often unexpected,
information.</p>
<div class="figcenter bord" style="width: 352px;"><a name="orion" id="orion"></a>
<img src="images/i_269.jpg" width="352" height="600" alt="orion" />
<div class="caption"><p class="center">THE GREAT NEBULA IN ORION.<br />
(<em>From a photograph taken at the Royal Observatory Greenwich,
December 1, 1899, with an exposure of 2<small><sup>1</sup>/<sub>4</sub></small> hours.</em>)</p></div>
</div>
<p>In this activity Greenwich Observatory practically
took no part. Airy, ever mindful of the original
purpose of the Observatory, and deeply imbued with
views similar to those which we have quoted from
Bessel, considered that the new science lay outside
the scope of his duties, until in Mr., now Sir William,<span class="pagenum"><a name="Page_269" id="Page_269"> </a><br /><a name="Page_270" id="Page_270"> </a><br /><a name="Page_271" id="Page_271">[271]</a></span>
Huggins's skilful hands the spectroscope showed itself
not only as a means for determining the condition
and constitution of the stars, but also their movements—until,
in short, it had shown itself as an astronomical
instrument even within Bessel's narrow definition.</p>
<p>The principle of this inquiry is as follows: If a
source of light is approaching us very rapidly, then
the waves of light coming from it necessarily appear
a little shorter than they really are, or, in other words,
that light appears to be slightly more blue—the blue
waves being shorter than the red—than it really is.
A similar thing with regard to the waves of sound is
often noticed in connection with a railway train. If
an express train, the whistle of which is blowing the
whole time, dashes past us at full speed, there is a
perceptible drop in the note of the whistle after it has
gone by. The sound waves as it was coming were a
little shortened, and the whistle therefore appeared to
have a sharper note than it had in reality. And in
the same way, when it had gone by, the sound waves
were a little lengthened, making the note of the
whistle appear a very little flatter.</p>
<p>Such a change of colour in a star could never
have been detected without the spectroscope; but
since when light passes through a prism the shorter
waves are refracted more strongly, that is to say, are
more turned out of their course than the longer, the
spectroscope affords us the means of detecting and
measuring this change. Let us suppose that the
lines of hydrogen are recognized in a given star. If
we compare the spectrum of this star with the
spectrum of a tube containing hydrogen and through<span class="pagenum"><a name="Page_272" id="Page_272">[272]</a></span>
which the electric spark is passing, we shall be able
to see whether any particular hydrogen line occupies
the same place as shown by the two spectra. If the
line from the star is a little to the red of the line from
the tube, the star must be receding from us; if to the
blue, approaching us. The amount of displacement
may be measured by a delicate micrometer, and the
rate of motion concluded from it.</p>
<div class="figcenter bord" style="width: 600px;"><a name="prism" id="prism"></a>
<img src="images/i_273.jpg" width="600" height="389" alt="prism" />
<div class="caption"><p class="center">THE HALF-PRISM SPECTROSCOPE ON THE SOUTH-EAST EQUATORIAL.</p></div>
</div>
<p>The principle is clear enough. The actual working
out of the observation was one of very great difficulty.
The movements of the stars towards us, or away from
us, are, in general, extremely slow as compared with
the speed of light itself; and hence the apparent
shift in the position of a line is only perceptible when
a very powerful spectroscope is used. This means
that the feeble light of a star has to be spread out
into a great length of spectrum, and a very powerful
telescope is necessary. The work of observing the
motions of stars in the line of sight was started at
Greenwich in 1875, the 'Great Equatorial' being
devoted to it. This telescope, of 12<small><sup>3</sup>/<sub>4</sub></small> inches aperture,
was not powerful enough to do much more than
afford a general indication of the direction in which
the principal stars were moving, and to confirm in a
general way the inference which various astronomers
had found, from discussing the proper motions of
stars, that the sun and the solar system were moving
towards that part of the heavens where the constellations
Hercules and Lyra are placed. In 1891,
therefore, the work was discontinued, and as already
mentioned, the 12<small><sup>3</sup>/<sub>4</sub></small> telescope by Merz was removed
to make room for the present much larger instrument<span class="pagenum"><a name="Page_273" id="Page_273"> </a><br /><a name="Page_274" id="Page_274"> </a><br /><a name="Page_275" id="Page_275">[275]</a></span>
by Sir Howard Grubb, upon the same mounting.
The new telescope being much larger than the one
for which mounting and observing room were
originally built, it was not possible to put the
spectroscope in the usual position, in the same
straight line as the great telescope. It was therefore
mounted under it, and parallel to it, and the light of
the star was brought into it after two reflections.
The observer therefore stood with his back to the
object and looked down into the spectroscope. It
had, however, become apparent by this time that this
most delicate field of work was one for which photography
possessed several advantages, and as Sir
Henry Thompson had made the munificent gift to
the Observatory of a great photographic equatorial, it
was resolved to devote the 28-inch telescope chiefly
to double-star work, and to transfer the spectroscope
to the 'New Building.'</p>
<p>The 'New Observatory' in the south ground is
crowned indeed with the dome devoted to the great
Thompson photographic refractor, but this is not its
chief purpose. Its principal floor contains four fine
rooms which are used as 'computing rooms'—for the
office work, that is to say, of the Observatory. Of
these the principal is in the north wing, where the
main entrance is placed, and is occupied by the
Astronomer Royal and the two chief assistants.
The basement contains the libraries and the workshops
of the mechanics and carpenters. The upper floor
will eventually be used for the storage of photographs
and manuscripts, and the terrace roofs of the four
wings will be exceedingly convenient for occasional<span class="pagenum"><a name="Page_276" id="Page_276">[276]</a></span>
observations, as, for example, of meteor showers.
The central dome, which rises high above the level of
the terraces, is the only room in the building devoted
to telescopic work. As in the New Altazimuth
building, a ring of circular lights just below the
coping of the wall recalls the portholes of a ship, and
again reminds us of the connection of the Observatory
with navigation.</p>
<div class="figcenter bord" style="width: 450px;"><a name="workshop" id="workshop"></a>
<img src="images/i_276.jpg" width="450" height="319" alt="workshop" />
<div class="caption"><p class="center">THE WORKSHOP.</p></div>
</div>
<p>Here the spectroscope is now placed, but not, as
it happens, on the Thompson refractor. The equatorial
mounting in this new dome is a modification of
what is usually called the 'German' form of mounting—that
is to say, there is but one pier to support the
telescope, and the telescope rides on one side of the
pier and a counterpoise balances it on the other
<span class="pagenum"><a name="Page_277" id="Page_277"> </a><br /><a name="Page_278" id="Page_278"> </a><br /><a name="Page_279" id="Page_279">[279]</a></span>The 'Great Equatorial,' on the other hand, is an
example of the English mounting, and has two piers,
one north and the other south, whilst the telescope
swings in a frame between them. In the new dome
three telescopes are found rigidly connected with each
other on one side of the pier, the telescopes being (1)
the great Thompson photographic telescope, double
the aperture and double the focal length of the
standard astrographic telescope used for the International
Photographic Survey; (2) the 12<small><sup>3</sup>/<sub>4</sub></small> telescope by
Merz, that used to be in the great South-East dome,
but which is now rigidly connected with the Thompson
refractor as a guide telescope; and (3) a photographic
telescope of 9 inches aperture, already described as
the 'Thompson' photo-heliograph, and used for
photographing the sun or in eclipse expeditions.
The counterpoise to this collection of instruments is
not a mere mass of lead, but a powerful reflector of
30 inches' aperture, and it is to this telescope that the
spectroscope is now attached. At the present time,
however (August, 1900), regular work has not been
commenced with it.</p>
<div class="figcenter bord" style="width: 449px;"><a name="reflect" id="reflect"></a>
<img src="images/i_278.jpg" width="449" height="600" alt="reflect" />
<div class="caption"><p class="center">THE 30-INCH REFLECTOR WITH THE NEW SPECTROSCOPE
ATTACHED.</p></div>
</div>
<p>Beside this attempt to determine the motions of
the stars as they approach us or retreat from us,
on rare occasions the spectroscope has been turned
on the planets. As these shine by reflected light,
their spectra are normally the same as that of the
sun. Mars appeared to the writer, as to Huggins
and others, to show some slight indication of the
presence of water vapour in its atmosphere. Jupiter
and Saturn show that their atmospheres contain some
absorbing vapour unknown to ours. And Uranus<span class="pagenum"><a name="Page_280" id="Page_280">[280]</a></span>
and Neptune, faint and distant as they are, not only
show the same dark band given by the two nearer
planets, but several others. More attractive has been
the examination of the spectra of the brighter comets
that have visited us. The years 1881 and 1882 were
especially rich in these. The two principal comets of
1881 were called after their respective discoverers,
Tebbutt's and Schaeberle's. They were not bright
enough to attract popular attention, though they
could be seen with the naked eye, and both gave
clear indications of the presence of carbon, their
spectra closely resembling that of the blue part of a
gas or candle flame. There was nothing particularly
novel in these observations, since comets usually show
this carbon spectrum, though why they should is still
a matter for inquiry; but the two comets of the
following year were much more interesting. Both
comets came very near indeed to the sun. The earlier
one, called from its discoverer Comet Wells, as it drew
near to the sun, began to grow more and more yellow,
until in the first week of June it looked as full an
orange as even the so-called red planet, Mars. The
spectroscope showed the reason of this at a glance.
The comet had been rich in sodium. So long as it
was far from the sun the sodium made no sign, but as
it came close to it the sodium was turned into glowing
vapour under the fierce solar heat. And as the writer
saw it in the early dawn of June 7, the comet itself
was a disc of much the same colour as Mars, whilst
its spectrum resembled that of a spirit lamp that has
been plentifully fed with carbonate of soda or common
salt. The 'Great Comet' of the autumn of the same<span class="pagenum"><a name="Page_281" id="Page_281">[281]</a></span>
year, and which was so brilliant an object in the early
morning, came yet nearer to the sun, and the heating
process went on further. The sodium lines blazed
up as they had done with Comet Wells, but under the
fiercer stress of heat to which the Great Comet was
subjected, the lines of iron also flashed out, a significant
indication of the tremendous temperature to which it
was exposed.</p>
<p>There are two other departments of spectroscopic
work which it was attempted for a time to carry on as
part of the Greenwich routine. These were the daily
mapping of the prominences round the sun, and the
detailed examination of the spectra of sun-spots.
Both are almost necessary complements of the work
done in the heliographic department—that is to say,
the work of photographing the appearance of the
sun day by day, and of measuring the positions and
areas of the spots. For the spots afford but one index
out of several, of the changes in the sun's activity.
The prominences afford another, nor can we at the
present moment say authoritatively which is the more
significant. Then again, with regard to the spots
themselves, it is not certain that either their extent
or their changes of appearance are the features which
it is most important for us to study. We want, if
possible, to get down to the soul of the spot, to find
out what makes one spot differ from another; and
here the spectroscope can help us. Great sun-spots
are often connected with violent agitation of the
magnetic needles, and with displays of auroræ. But
they are not always so, and the inquiry, 'What makes
them to differ?' has been made again and again,<span class="pagenum"><a name="Page_282" id="Page_282">[282]</a></span>
without as yet receiving any unmistakable answer. The
great spot of November, 1882, which was connected with
so remarkable an aurora and so violent a magnetic
storm, was as singular in its spectrum as in its earthly
effects. The sun was only seen through much fog,
and the spectrum was therefore very faint, but shooting
up from almost every part of its area, except the
very darkest, were great masses of intensely brilliant
hydrogen, evidently under great pressure. The
sodium lines were extremely broadened, and on
November 20 a broad bright flame of hydrogen was
seen shooting up at an immense speed from one edge
of the nucleus. A similar effect—an outburst of
intensely luminous hydrogen—has often been observed
in spots which have been accompanied by great
magnetic storms; and it may even be that it is this
violent eruption of intensely heated gas which has
the directest connection with the magnetic and
auroral disturbances here upon earth.</p>
<p>This sun-spot work was not carried on for very
long, as only one assistant could be spared for the
entire solar work of whatever character. Yet in that
time an interesting discovery was made by the writer—namely,
that in the green part of the spectrum of
certain spots a number of broad diffused lines or
narrow bands made their appearance from time to
time, and especially when sun-spots were increasing
in number, or were at their greatest development.</p>
<p>The prominence work had also to be dropped,
partly for the same reason, but chiefly because the
atmospheric conditions at Greenwich are not suitable
for these delicate astrophysical researches. When<span class="pagenum"><a name="Page_283" id="Page_283">[283]</a></span>
the Observatory was founded 'in the golden days'
of Charles II., Greenwich was a little country town
far enough removed from the great capital, and no
interference from its smoke and dust had to be feared
or was dreamt of. Now the 'great wen,' as Cobbett
called it, has spread far around and beyond it, and
the days when the sky is sufficiently pure round the
sun for successful spectrum work on the spots or
prominences are few indeed.</p>
<p>Whether in the future it will be thought advisable
for the Royal Observatory to enter into serious
competition in inquiries of this description with the
great 'astrophysical' observatories of the Continent
and of America—Potsdam, Meudon, the Lick, and
the Yerkes—we cannot say. That would involve a
very considerable departure from its original programme,
and probably also a departure from its
original site. For the conditions at Greenwich tend
to become steadily less favourable for such work, and
it would most probably be found that full efficiency
could only be secured by setting up a branch or
branches far from the monster town.</p>
<p>With the older work it is otherwise. So long as
Greenwich Park and Blackheath are kept—as it is
to be hoped they always will be—sacred from the
invasion of the builder; so long as no new railways
burrow their tunnels in the neighbourhood of the
Observatory, so long the fundamental duties laid
upon Flamsteed, 'of Rectifying the Tables of the
Motions of the Heavens and the Places of the Fixed
Stars,' will be carried out by his successors on
Flamsteed Hill.</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_284" id="Page_284">[284]</a></span></p>
<h2>CHAPTER XII</h2>
<h3>THE ASTROGRAPHIC DEPARTMENT</h3>
<p>The two last departments mentioned, the heliographic
and spectroscopic, lie clearly and unmistakably
outside the terms of the original warrant of the
Observatory, though the progress of science has led
naturally and inevitably to their being included in
the Greenwich programme. But the Astrographic
Department, though it could no more have been
conceived in the days of Charles II. than the
spectroscopic, does come within the terms of the
warrant, and is but an expansion of that work of
'Rectifying the Places of the Fixed Stars,' which
formed part of the programme enjoined upon Flamsteed,
the first Astronomer Royal, at the first foundation
of the Observatory, and which was so diligently
carried out by him, the first Greenwich catalogue,
containing about 3000 stars, being due to his labours.</p>
<div class="figcenter bord" style="width: 431px;"><a name="plate" id="plate"></a>
<img src="images/i_286.jpg" width="431" height="600" alt="plate" />
<div class="caption"><p class="center">'CHART PLATE' OF THE PLEIADES.<br />
(<em>From a photograph taken at the Royal Observatory, Greenwich, with an
exposure of forty minutes.</em>)</p></div>
</div>
<p>His immediate successors did much less in this
field, though Bradley's observations were published,
long after his death, as a catalogue of 3222 stars, in
some aspects the most important ever issued. Pond,
the sixth Astronomer Royal, restored catalogue-making
to a prominent place in the Greenwich routine,<span class="pagenum"><a name="Page_285" id="Page_285"> </a><br /><a name="Page_286" id="Page_286"> </a><br /><a name="Page_287" id="Page_287">[287]</a></span>
and his precedent is sedulously followed to-day. But
each of these was confined to about 3000 stars. The
necessity has long been felt for a much ampler census,
and Argelander, at the Bonn Observatory, brought
out a catalogue of 324,000 stars north of South
declination 2°, a work which has been completed by
Schönfeld, who carried the census down to South
declination 23°, and by the two great astronomers of
Cordoba, South America, Dr. Gould and Dr. Thome,
by whom it was extended to the South Pole.</p>
<p>These last three catalogues embrace stars of all
magnitudes down to the 9th or 10th; but certain
astronomers had endeavoured to go much lower, and
to make charts of limited portions of the sky down to
even the 14th magnitude.</p>
<p>From the very earliest days that men observed
the stars, they could not help noticing that 'one star
differeth from another star in glory,' and consequently
they divided them into six classes, according to their
brightness—classes which are commonly spoken of
now as magnitudes. The ordinary 6th magnitude
star is one which can be clearly seen by average sight
on a good night, and it gives us about one-hundredth
the light of an average 1st magnitude star. Sirius,
the brightest of all the fixed stars, is called a 1st
magnitude star, but is really some six or seven times
as bright as the average. It would take, therefore,
more than two and a half million stars of the 14th
magnitude to give as much light as Sirius.</p>
<p>It is evident that so searching a census as to
embrace stars of the 14th magnitude would involve
a most gigantic chart. But the work went on in<span class="pagenum"><a name="Page_288" id="Page_288">[288]</a></span>
more than one Observatory for a considerable time,
until at last the observers entered on to the region
of the Milky Way. Here the numbers of the stars
presented to them were so great as to baffle all
ordinary means of observation. What could be
done?</p>
<p>Just at this time immense interest was caused in
the astronomical world by the appearance of the great
comet of 1882. It was watched and observed and
sketched by countless admirers, but more important
still, it was photographed, and some of its photographs,
taken at the Royal Observatory, Cape of Good Hope,
showed not only the comet with marvellous beauty
of detail, but also thousands of stars, and the success
of these photographs suggested to her Majesty's
Astronomer at the Cape, Dr. Gill, that in photography
we possessed the means for making a complete sky
census even to the 14th magnitude.</p>
<p>The project was thought over in all its bearings,
and in 1887 a great conference of astronomers at
Paris resolved upon an international scheme for
photographing the entire heavens. The work was to
be divided between eighteen Observatories of different
nationalities. It was to result in a photographic
chart extending to the 14th magnitude, and probably
embracing some forty million stars, and a catalogue
made from measures of the photographs down to
the 11th magnitude, which would probably include
between two and three million stars.</p>
<div class="figcenter bord" style="width: 437px;"><a name="pendulum" id="pendulum"></a>
<img src="images/i_289.jpg" width="437" height="600" alt="pendulum" />
<div class="caption"><p class="center">THE CONTROL PENDULUM AND THE BASE OF THE
THOMPSON TELESCOPE.</p></div>
</div>
<p>The eighteen Observatories all undertook to use
instruments of the same capacity. This was to be
a photographic refractor, with an object-glass of 13<span class="pagenum"><a name="Page_289" id="Page_289">[289]</a><br /><a name="Page_290" id="Page_290">[290]</a></span>
inches aperture and 11 feet focus. At Greenwich
this telescope is mounted equatorially—that is, so as
to follow the stars in their courses—and is mounted
on the top of the pier that once supported Halley's
quadrant. The telescope is driven by a most efficient
clock, whose motive power is a heavy weight. The
rate of the weight in falling is regulated by an
ingenious governor, which brings its speed very nearly
indeed to that of the star, and any little irregularities
in its motion are corrected by the following device.
A seconds pendulum is mounted in a glass case on
the wall of the Observatory, and a needle at the
lower end of the pendulum passes at each swing
through a globule of mercury. On one of the wheels
of the clock are arranged a number of little brass
points, at such intervals apart that the wheel, when
going at the proper rate, takes exactly one second
to move through the distance between any pair. A
little spring is arranged above the wheel, so that
these points touch it as they pass. If this occurs
exactly as the pendulum point passes through the
mercury nothing happens, but if the clock is ever
so little late or early, the electric current from the
pendulum brings into action a second wheel, which
accelerates or retards the driving of the clock, as the
case may be. The total motion, therefore, is most
beautifully even.</p>
<div class="figcenter bord" style="width: 450px;"><a name="telescope" id="telescope"></a>
<img src="images/i_291.jpg" width="450" height="530" alt="telescope" />
<div class="caption"><p class="center">THE ASTROGRAPHIC TELESCOPE.<br />
(<em>Reproduced from 'Engineering' by permission.</em>)</p></div>
</div>
<p>But even this is not quite sufficient, especially as
the plates for the great chart have to be exposed
for at least forty minutes. Rigidly united with the
13-inch refractor, so that the two look like the two
barrels of a huge double-barrelled gun, is a second<span class="pagenum"><a name="Page_291" id="Page_291">[291]</a></span>
telescope for the use of the observer. In its eyepiece
are fixed two pairs of cross spider lines,
commonly called wires, and a bright star, as near as<span class="pagenum"><a name="Page_292" id="Page_292">[292]</a></span>
possible to the centre of the field to be photographed,
is brought to the junction of two wires. Should the
star appear to move away from the wire, the observer
has but to press one of two buttons on a little plate
which he carries in his hand, and which is connected
by an electric wire with the driving clock, to bring it
back to its position.</p>
<p>The photographs taken with this instrument are
of two kinds. Those for the great chart have but
a single exposure, but this lasts for forty minutes.
Those for the great catalogue have three exposures
on them, the three images of a star being some
20 seconds of arc apart. These exposures are of
six minutes', three minutes', and twenty seconds'
duration, and the last exposure is given as a test,
since, if stars of the 9th magnitude are visible with
an exposure of twenty seconds, stars of the 11th
magnitude should be visible with three minutes'
exposure.</p>
<p>Thus it will be seen that in three minutes an
impression is got of many scores of stars, whose
places it would require many hours to determine at
the transit instrument. But the positions of these
stars on the plate still remain to be measured. For
this purpose a net-work of lines, at right angles to
each other, is printed on the photograph before its
development, and, after it has been developed, washed
and dried, the distances of the stars from their
nearest cross-lines are measured in the measuring
machine.</p>
<div class="figcenter bord" style="width: 358px;"><a name="driving" id="driving"></a>
<img src="images/i_294.jpg" width="358" height="600" alt="driving" />
<div class="caption"><p class="center">THE DRIVING CLOCK OF THE ASTROGRAPHIC TELESCOPE.<br />
(<em>Reproduced from 'Engineering' by permission.</em>)</p></div>
</div>
<p>The measuring machine is constructed to hold
two plates, one half its breadth higher than the other.<span class="pagenum"><a name="Page_293" id="Page_293"> </a><br /><a name="Page_294" id="Page_294">[294]</a><br /><a name="Page_295" id="Page_295">[295]</a></span>
In fact, in each of the two series of photographs the
whole sky is taken twice, but the two photographs
of any region are not simply duplicates of each
other. The centre of each plate is at a corner of
four other plates, and in the micrometer the stars
on the quarter common to two plates are measured
simultaneously.</p>
<p>In this way will be carried out a great census of
the sky that will exceed Flamsteed's ten thousand
fold. And just as Flamsteed's was but the first of
many similar catalogues, so, no doubt, will this be
followed by others—not superseded, for its value will
increase with its age and the number of those that
follow it, by comparison with which it will prove
an inexhaustible mine of information concerning
the motions of the stars and the structure of the
universe.</p>
<p>There is a great difference between the work of
the observer with the 'Astrographic Telescope,' as
this great twin photographic instrument is called,
and the work of the transit observer. The latter
sees the star gliding past him, and telegraphs the
instant that the star threads itself on each of the
ten vertical wires in succession. The astrographic
observer, on the other hand, sees his star shining
almost immovably in the centre of his field, threaded
on the two cross wires placed there, for the driving-clock
moves the telescope so as to almost exactly
compensate for the rotation movement of the earth.
The observer's duty in this case is to telegraph to
his driving-clock, when it has in the least come short
of or exceeded its duty, and so to bring back the<span class="pagenum"><a name="Page_296" id="Page_296">[296]</a></span>
'guiding star' to its exact proper place on the cross
wires.</p>
<p>So far, the work of the Astrographic Department
has been, as mentioned above, a development on an
extraordinary scale, but a development still, of the
original programme of the Observatory. But the
munificent gift of Sir Henry Thompson has put it
within the power of the Astronomer Royal to push
this work of sidereal photography a stage further.
Sir Henry Thompson gave to the Observatory, not
merely the photographic refractor of 9 inches' aperture,
now used for solar photography, and known as
the 'Thompson photo-heliograph,' but also one of 26
inches' aperture and 22<small><sup>1</sup>/<sub>2</sub></small> feet focal length. This
instrument was specially designed of exactly double
the dimensions of the standard astrographic telescope
used for the International Photographic Survey, the
idea being that, in the case of a field of special interest
and importance, a photograph could be obtained
with the larger instrument on exactly double the
scale given by the smaller. It has rather, however,
found its usefulness in a slightly different field. The
observation of the satellites of Jupiter was suggested
by Galileo as a means of determining the longitude
at sea. As already pointed out, the suggestion did
not prove to be a practical one for that purpose, but
observations of the satellites have been made none
the less with a view simply to improving our knowledge
of their movements, and of the mass of Jupiter.
The utilitarian motive for the work having fallen
through, it has been carried on as a matter of pure
science.</p>
<p><span class="pagenum"><a name="Page_297" id="Page_297">[297]</a></span></p>
<p>And the work has not stopped with the satellites
of Jupiter; eight satellites were in due time discovered
to Saturn, four to Uranus, and two to Mars; and
though these could give not the remotest assistance
to navigation, they too have been made the subjects
of observation for precisely the same reason as those
of Jupiter have been.</p>
<div class="figcenter bord" style="width: 450px;"><a name="thompson" id="thompson"></a>
<img src="images/i_297.jpg" width="450" height="364" alt="thompson" />
<div class="caption"><p class="center">THE THOMPSON TELESCOPE IN THE NEW DOME.</p></div>
</div>
<p>In just the same way, when the discovery
of Neptune was followed by that of a solitary
companion to it, this also had to be followed. The
difficulties in the way of observing the fainter of all
these satellites were considerable, and the work has<span class="pagenum"><a name="Page_298" id="Page_298">[298]</a></span>
been mostly confined to two or three observatories
possessing very large telescopes. As the largest
telescope at Greenwich was only 7 inches in aperture
up to 1859, and only 12<small><sup>3</sup>/<sub>4</sub></small> inches up to 1893, it is only
very recently that it has been able to take any very
substantial part in satellite measures. But since the
Thompson photographic telescope was set up, it has
been found that a photograph of Neptune and its
satellite can be taken in considerably less time than
a complete set of direct measures can be made, whilst
the photograph, which can be measured at leisure
during the day, gives distinctly the more accurate
results.</p>
<p>So, too, the places of the minor planets can be
got more accurately and quickly by means of photographs
with this great telescope than by direct
observation, and photographs of the most interesting
of them all, the little planet Eros, have been very
successfully obtained. So that, though doing
nothing directly to improve the art of navigation, or
to find the longitude at sea, the great photographic
refractor takes its share in the work of 'Rectifying
the Tables of the Planets.'</p>
<div class="figcenter bord" style="width: 600px;"><a name="neb" id="neb"></a>
<img src="images/i_300.jpg" width="600" height="359" alt="neb" />
<div class="caption"><p class="center">THE NEBULÆ OF THE PLEIADES.<br />
(<em>From a photograph taken at the Royal Observatory, Greenwich, December 3, 1899, with an exposure of three hours.</em>)</p></div>
</div>
<p>The reflector of 30 inches' aperture, which acts
as a counterpoise to the sheaf of telescopes of the
Thompson, is intended for use with the spectroscope,
the quality which mirrors possess of bringing all
rays, whatever their colour, to the same focus being
of great importance for spectroscopic work. But the
experiments which have been made with it in celestial
photography have proved so extremely successful as
to cause the postponement of the recommencement<span class="pagenum"><a name="Page_299" id="Page_299"> </a><br /><a name="Page_300" id="Page_300"> </a><br /><a name="Page_301" id="Page_301">[301]</a></span>
of the spectroscopic researches. Chief amongst these
photographs are some good ones of the moon, and
more recently some exceedingly fine photographs
of the principal nebulæ.</p>
<p>In no department of astronomy has photography
brought us such striking results as in regard to the
nebulæ. Dr. Roberts' photograph of the great
nebula in Andromeda converted the two or three
meaningless rifts—which some of the best drawings
had shown—into the divisions between concentric
rings; and what had appeared a mere shapeless cloud
was seen to be a vast symmetrical structure, a great
sidereal system in the making. The great nebula in
Orion has grown in successive photographs in detail
and extent, until we have a large part of the constellation
bound together in the convolutions of a
single nebula of the most exquisite detail and most
amazing complexity. The group of the Pleiades has
had a more wonderful record still. Manifestly a
single system even to the naked eye, and showing
some faint indications of nebulosity in the telescope,
the photographs have revealed its principal stars
shining out from nebulous masses, in appearance like
carded wool, and have shown smaller stars threaded
on nebulous lines like pearls upon a string.</p>
<p>Such photographs are, of course, of no utilitarian
value, and at present they lead us to no definite
scientific conclusions. They lie, therefore, doubly
outside the limits of the purely practical, but they
attract us by their extreme beauty, and by the
amazing difficulty of the problems they suggest.
How are these weird masses of gas retained in such<span class="pagenum"><a name="Page_302" id="Page_302">[302]</a></span>
complex form over distances which must be reckoned
by millions of millions of miles? By what agency
are they made to glow so as to be visible to us here?
What conceivable condition threads together suns on
a line of nebula? What universes are here in the
making, or perhaps it may be falling into ruin and
decay?</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_303" id="Page_303">[303]</a></span></p>
<h2>CHAPTER XIII</h2>
<h3>THE DOUBLE-STAR DEPARTMENT</h3>
<p>The foregoing chapters will have shown that though
the original purpose of the Observatory has always
been kept in view, yet the progress of science has
caused many researches to be undertaken which
overstep its boundaries. Thus in the present transit
room, beside the successive transit instruments we
find upon the wall two long thin tubes, labelled
respectively Alpha Aquilæ and Alpha Cygni.
These were two telescopes set up by Pond for a
special purpose. Dr. Brinkley, Royal Astronomer
for Ireland, had announced that he had found that
several stars shifted their apparent place in the sky
in the course of a year, due to the change in the
position of the earth from which we view them, by an
amount which would show that they were only about
six to nine billions of miles distant from us; or, in
other words, they showed a parallax of from two to
three seconds of arc. Pond was not able to confirm
these parallaxes from his observations, and to decide
the point he set up these two telescopes, the Alpha
Aquilæ telescope being rigidly fixed on the west side
of the pier of Troughton's mural circles; the Alpha<span class="pagenum"><a name="Page_304" id="Page_304">[304]</a></span>
Cygni telescope on another pier, the one which now
forms the base of the pier of the astrographic telescope.
Pond's method was to compare the position
of these two stars with that of a star almost exactly
the same distance from the pole, but at a great
distance from it in time of crossing the meridian; in
other words, of almost the same declination, but
widely different right ascension. The result proved
that Brinkley was wrong, and vindicated the delicacy
and accuracy of Pond's observations.</p>
<p>These two telescopes, therefore, had their day and
ceased to be. Others have followed them. An
ingenious telescope was set up by Sir George Airy in
order to ascertain if the speed of light were different
when passing through water than when passing
through air. Or, in other words, if the aberration
of light would give the same value as at present if
we observed through water. The water telescope, as
it was called, is kept on the ground floor of the
central octagon of the new observatory. The observations
obtained with it were hardly quite satisfactory,
but gave on the whole a negative result.</p>
<p>Turning back to the transit room, and leaving it
by the south-west door, we come into the little
passage which leads at the back of Bradley's transit
room into the lower computing room. Just inside
this passage, on the left-hand side, there is a little
room of a most curious shape, the 'reflex zenith
room.' Here is fixed a telescope pointing straight
upwards, the eye-piece being fixed by the side of the
object-glass. The light from a star—the star Gamma
Draconis—which passes exactly over the zenith of<span class="pagenum"><a name="Page_305" id="Page_305">[305]</a></span>
Greenwich, enters the object-glass, passes downwards
to a basin of mercury, and is reflected upwards from
the surface of the mercury to a little prism placed
over the centre of the object-glass, from which it is
reflected again into the eye-piece. By means of this
telescope the distance of the star Gamma Draconis
from the zenith could be measured very exactly, and,
consequently, the changes in the apparent position
of the star due to aberration, parallax, and other
causes could be very exactly followed, and the corrections
to be applied on account of these causes
precisely determined.</p>
<p>This particular telescope was devised by Airy, and
the observations with it were continued to the end of
his reign. The germ of the idea may be traced back,
however, to the time of Flamsteed, who would seem
to have occasionally observed Gamma Draconis from
the bottom of a deep well; the precise position of the
well is not, however, now known. Later, Bradley set
up his celebrated 12<small><sup>1</sup>/<sub>2</sub></small>-foot zenith sector, still preserved
in the transit room, first at Wanstead and
then at Greenwich, for the determination of the
amount of aberration. Later, a zenith tube by
Troughton, of 25 feet focus, was used by Pond in
conjunction with the mural circle for observations of
Gamma Draconis in order to determine the zenith
point of the latter instrument.</p>
<p>These telescopes for special purposes have passed
out of use. Observations with the spectroscope have
been suspended for some years. The work of the
Astrographic Department will come to an end, in the
ordinary course of events, when the programme<span class="pagenum"><a name="Page_306" id="Page_306">[306]</a></span>
assigned to Greenwich in the International Scheme
is completed.</p>
<p>Within the last few years a new department
has come into being at Greenwich—a department
which has been steadily worked at many foreign
public observatories, but only recently here.</p>
<p>This is the Department of Double-Star Observation.
The first double star, Zeta Ursæ Majoris, was
discovered 250 years ago. Bradley discovered two
exceedingly famous double stars whilst still a young
man observing with his uncle at Wanstead—Gamma
Virginis and Castor. Bradley made also other discoveries
of double stars after his appointment to
Greenwich, and Maskelyne succeeded him in the
same line, but the great foundation of double-star
astronomy was laid by Sir William Herschel.</p>
<p>At first it was supposed that double stars were
double only in appearance; one star comparatively
near us 'happened' to lie in almost exactly the
same direction as another star much further off. It
was, indeed, in the very expectation that this would
prove to be the case, that the elder Herschel first
took up their study. But he was soon convinced
that many of the objects were true double stars—members
of the same system of which the smaller
revolved round the larger—not merely apparently
double, one star appearing by chance to be close to
another with which it had no connection—but real
double stars. The discovery of these has led to the
establishment of a new department of astronomy,
again scientific rather than utilitarian.</p>
<div class="figcenter bord" style="width: 600px;"><a name="star" id="star"></a>
<img src="images/i_308.jpg" width="600" height="428" alt="star" />
<div class="caption"><p class="center">DOUBLE-STAR OBSERVATION WITH THE SOUTH-EAST EQUATORIAL.<br />
(<em>From a photograph by Mr. Edney.</em>)</p></div>
</div>
<p>As mentioned above, it is only recently that
<span class="pagenum"><a name="Page_307" id="Page_307"> </a><br /><a name="Page_308" id="Page_308"> </a><br /><a name="Page_309" id="Page_309">[309]</a></span>Greenwich has taken any appreciable part in this
work. Under Airy, the largest equatorial of the
time had been furnished with a good micrometer,
and observations of one or two double stars been
made now and again; but Airy's programme of work
was far too rigid, and kept the staff too closely
engaged for such observations to be anything but
extremely rare. And, indeed, when the micrometers
of the equatorials were brought into use, they were
far more generally devoted to the satellites of Saturn
than to the companions of stars. In the main, double-star
astronomy has been in the hands of amateurs, at
least in England. But the discovery in recent years
of many pairs so close that a telescope of the largest
size is required for their successful observation, has
put an important section of double stars beyond the
reach of most private observers, and therefore the
great telescope at Greenwich is now mainly devoted
to their study. The Astronomer Royal, therefore,
soon after the completion of the great equatorial of
28-inches aperture placed in the south-east dome,
added this work to the Observatory programme.</p>
<p>The 28-inch equatorial is a remarkable-looking
instrument, its mounting being of an entirely different
kind to that of the other equatorials in the Observatory,
with the solitary exception of the Shuckburgh,
which is set up in a little dome over the chronograph
room. The Shuckburgh was presented to the
Observatory in the year 1811, by Sir G. Shuckburgh.
It was first intended to be mounted as an altazimuth,
but proved to be unsteady in that position, and was
then converted into an equatorial without clockwork,<span class="pagenum"><a name="Page_310" id="Page_310">[310]</a></span>
and mounted in its present position. The position is
about as hopelessly bad a one as a telescope could well
have, completely overshadowed as it is by the trees
and buildings close at hand. The dome is a small
one, and the arrangements for the shutters and for
turning the dome are as bad as they could possibly be.
It has practically been useless for the last forty years.</p>
<p>Its only interest is that the method of mounting
employed is a small scale model of that of the
great telescope in the S.-E. dome. In the German
or Fraunhofer form of mounting for an equatorial
there is but a single pillar, which carries a comparatively
short polar axis. At the upper end of the
polar axis we find the declination axis, and at one
end of the declination axis is the telescope, whilst at
the other end is a heavy weight to counterpoise it.
The German mounting has the advantage that the
telescope can easily point to the pole of the heavens;
its drawbacks are that, except in certain special forms,
the telescope cannot travel very far when it is on the
same side of the meridian as the star to which it is
pointed, the end of the telescope coming into contact
under such circumstances with the central pier, whilst
the introduction of mere deadweight as the necessary
counterpoise, is not economical. It has been already
pointed out that the present Astronomer Royal has
not only considerably modified the German mounting
in the great collection of telescopes in the Thompson
dome, but has used a powerful reflector as a counterpoise
to the sheaf of refractors at the other end of
the declination axis.</p>
<p>The English equatorial requires two piers.<span class="pagenum"><a name="Page_311" id="Page_311">[311]</a></span>
Between these two piers is a long polar axis. Both
in the little Shuckburgh and in the great 28-inch
equatorial the frame of the polar axis consists of six
parallel rods disposed in two equilateral triangles,
with their bases parallel to each other, the telescope
swinging in the space between the two bases. The
construction of this form of equatorial, therefore, is
expensive, as it requires two piers. It takes much
more room than the German form, and the telescope
cannot be directed precisely to the pole. But the instrument
is symmetrical, there is no deadweight, and
the telescope can follow a star from rising to setting
without having to be reversed on crossing the meridian.</p>
<p>The great stability of the English form of mounting,
therefore, commended it very highly to Airy, and
he designed the great Northumberland equatorial of
the Cambridge Observatory on that plan, as well as
one for the Liverpool Observatory at Bidston, and in
1858 the S.-E. equatorial at Greenwich.</p>
<p>The telescope at first mounted upon it had an
object-glass of 12<small><sup>3</sup>/<sub>4</sub></small> inches' aperture, and 18 feet focal
length. That was dismounted in 1891, and is now
used as the guiding telescope of the Thompson 26-inch
photographic refractor. Its place was taken by an
immensely heavier instrument, the present refractor
of 28 inches' aperture, and 28 feet focal length; and
that this change was effected safely was an eloquent
testimony to the solidity of the original mounting.</p>
<p>The clock that drives this great instrument, so
that it can follow a star or other celestial object in
its apparent daily motion across the sky, is in the
basement of the S.-E. tower. It is a very simple<span class="pagenum"><a name="Page_312" id="Page_312">[312]</a></span>
looking instrument, a conical pendulum in a glass
case. The pendulum makes a complete revolution
once in two seconds. Below it in a closed case is a
water turbine. A cistern on the roof of the staircase
supplies this turbine with water, having a fall of about
thirty feet. The water rushing out of the arms of the
turbine forces it backward, and the turbine spins
rapidly round, driving a spindle which runs up into
the dome, and gears through one or two intermediate
wheels with the great circle of the telescope; the
extremely rapid rotation of the spindle, four times
in a second, being converted by these intermediate
wheels into the exceedingly slow one of once in
twenty-four hours. Just above the centre of motion
of the turbine is a set of three small wheels, all of
exactly the same size, and of the same number of
teeth. Of these the bottom wheel is horizontal, and
is turned by the turbine. The top wheel is also
horizontal, and is turned by the pendulum. The
third wheel gears into both these, and is vertical. If
the top and bottom wheels are moving exactly at the
same rate, the intermediate wheel simply turns on its
axis, but does not travel; but if the turbine and
pendulum are moving at different rates, then the
vertical wheel is forced to run in one direction or
the other, and, doing so, it opens or closes a throttle
valve, which controls the supply of water to the
turbine, and so speedily brings the turbine into
accord with the pendulum. The control of the
motion of the great telescope is therefore almost as
perfect as that of the astrographic and Thompson
equatorials, though the principle employed is very<span class="pagenum"><a name="Page_313" id="Page_313">[313]</a></span>
different. And the control needs to be perfect, for,
as said above, the great telescope is mostly devoted
to the observation of double stars, and there can be
no greater hindrance to this work than a telescope
which does not move accurately with the star.</p>
<p>There is a striking contrast between the great
telescope and all the massive machinery for its
direction and movement, and the objects on which
it is directed—two little points of light separated by
a delicate hair of darkness.</p>
<p>The observation is very unlike those of which we
have hitherto spoken. The object is not to ascertain
the actual position in the sky of the two stars, but
their relative position to each other. A spider's
thread of the finest strands is moved from one star
to the other by turning an exquisitely fine screw;
this enables us to measure their distance apart.
Another spider thread at right angles to the first is
laid through the centres of both stars, and a divided
circle enables us to read the angle which this line
makes to the true east and west direction. Such
observations repeated year after year on many stars
have enabled the orbits of not a few to be laid down
with remarkable precision; and we find that their
movements are completely consistent with the law of
gravitation. Further, just as Neptune was pre-recognized
and discovered from noting the irregularities in
the motion of Uranus, so the discordances in the place
of Sirius led to the belief that it was attracted by a
then unseen companion, whose position with respect to
the brighter star was predicted and afterwards seen.</p>
<div class="figcenter bord" style="width: 450px;"><a name="shutter" id="shutter"></a>
<img src="images/i_314.jpg" width="450" height="547" alt="shutter" />
<div class="caption"><p class="center">THE SOUTH-EAST DOME WITH THE SHUTTER OPEN.</p></div>
</div>
<p>Gravitation thus appears, indeed, to be the Bond<span class="pagenum"><a name="Page_314" id="Page_314">[314]</a></span>
of the Universe, yet it leaves us with several weighty
problems. The observation of the positions of stars
shows that though we call them fixed they really
have motions of their own. Of these motions, a great
part consists of a drift away from one portion of the<span class="pagenum"><a name="Page_315" id="Page_315">[315]</a></span>
heavens towards a point diametrically opposite to it,
a drift such as must be due, not to a true motion of
the individual stars, but to a motion through space
of our sun and its attendant system. The elder
Herschel was the first to discover this mysterious
solar motion. Sir George Airy and Mr. Edwin
Dunkin, for forty-six years a member of the Greenwich
staff, and from 1881-1884 the Chief Assistant,
contributed important determinations of its direction.</p>
<p>What is the cause of this motion, what is the law
of this motion, is at present beyond our power to
find out. Many years ago a German astronomer
made the random suggestion that possibly we were
revolving in an orbit round the Pleiades as a centre.
The suggestion was entirely baseless, but unfortunately
has found its way into many popular works,
and still sometimes is brought forward as if it were
one of the established truths of astronomy. We can
at present only say that this solar motion is a mystery.</p>
<p>There is a greater mystery still. The stars have
their own individual motions, and in the case of a
few these are of the most amazing swiftness. The
earth in its motion round the sun travels nearly
nineteen miles in a second, say one thousand times
faster than the quickest rush of an express train.
The sun's rate of motion is probably not quite so
swift, but Arcturus, a sun far larger than our own,
has a pace some twenty times as swift as the orbital
motion of the earth. This is not a motion that we
can conceive of as being brought about by gravitation,
for if there were some unseen body so vast as
to draw Arcturus with this swiftness, other stars too<span class="pagenum"><a name="Page_316" id="Page_316">[316]</a></span>
would be hurtling across the sky as quickly. Such
'runaway stars' afford a problem to which we have
as yet no key, and, like Job of old, we are speechless
when the question comes to us from heaven, 'Canst
thou guide Arcturus and his sons?'</p>
<p>It will be seen then that, fundamentally, Greenwich
Observatory was founded and has been maintained
for distinctly practical purposes, chiefly for
the improvement of the eminently practical science
of navigation. Other inquiries relating to navigation,
as, for instance, terrestrial magnetism and
meteorology, have been added since. The pursuit
of these objects has of necessity meant that the
Observatory was equipped with powerful and accurate
instruments, and the possession of these again
has led to their use in fields which lay outside
the domain of the purely utilitarian, fields from
which the only harvest that could be reaped was that
of the increase of our knowledge. So we have been
led step by step from the mere desire to help the
mariner to find his way across the trackless ocean, to
the establishment of the secret law which rules the
movements of every body of the universe, till at
length we stand face to face with the mysteries
of vast systems in the making, with the intimate
structure of the stellar universe, with the apparently
aimless, causeless wanderings of vast suns in lightning
flight; with problems that we cannot solve, nor hope
to solve, yet cannot cease from attempting, problems
to which the only answer we can give is the confession
of the magicians of Egypt—'This is the
finger of God.'</p>
<hr class="chap" />
<p><span class="pagenum"><a name="Page_317" id="Page_317">[317]</a></span></p>
<h2>INDEX</h2>
<div>
Aberration of light, <a href="#Page_79">79</a><br />
<br />
Adams, John C., his discovery of Neptune, <a href="#Page_217">217</a><br />
<br />
Adhara, <a href="#Page_183">183</a><br />
<br />
Airy, George Biddell, seventh Astronomer Royal, his early life, <a href="#Page_102">102</a>;<br />
<span style="margin-left: 1em;">his work at Cambridge, <a href="#Page_105">105</a>;</span><br />
<span style="margin-left: 1em;">comes to Greenwich, <a href="#Page_105">105</a>;</span><br />
<span style="margin-left: 1em;">his relations with the Visitors, <a href="#Page_106">106</a>;</span><br />
<span style="margin-left: 1em;">his autobiography, <a href="#Page_108">108</a>;</span><br />
<span style="margin-left: 1em;">his character, <a href="#Page_111">111</a>;</span><br />
<span style="margin-left: 1em;">his labours, <a href="#Page_113">113</a>;</span><br />
<span style="margin-left: 1em;">attacks on, <a href="#Page_114">114</a>;</span><br />
<span style="margin-left: 1em;">his distinctions, <a href="#Page_118">118</a>;</span><br />
<span style="margin-left: 1em;">his resignation, <a href="#Page_119">119</a>;</span><br />
<span style="margin-left: 1em;">his death, <a href="#Page_120">120</a>;</span><br />
<span style="margin-left: 1em;">anecdote of, <a href="#Page_142">142</a>;</span><br />
<span style="margin-left: 1em;">his conduct <em>re</em> Adams, <a href="#Page_217">217</a>;</span><br />
<span style="margin-left: 1em;">his water telescope, <a href="#Page_304">304</a></span><br />
<br />
Alderamin, <a href="#Page_183">183</a><br />
<br />
<cite>Almagest</cite>, <a href="#Page_185">185</a><br />
<br />
Almanac making, <a href="#Page_29">29</a><br />
<br />
Alpha Aquilæ, telescope for, <a href="#Page_303">303</a><br />
<br />
—— Cygni, telescope for, <a href="#Page_303">303</a><br />
<br />
Altazimuth the, <a href="#Page_114">114</a>;<br />
<span style="margin-left: 1em;">description and work of, <a href="#Page_207">207</a>, <em>et seq.</em></span><br />
<br />
Altazimuth Department, <a href="#Page_205">205</a>, <em>et seq.</em><br />
<br />
American time, <a href="#Page_153">153</a><br />
<br />
Andromeda nebula, <a href="#Page_301">301</a><br />
<br />
Anemometer, use of, <a href="#Page_238">238</a>;<br />
<span style="margin-left: 1em;">trace of, <a href="#Page_242">242</a></span><br />
<br />
Angström, <a href="#Page_268">268</a><br />
<br />
Anson, Commodore, <a href="#Page_17">17</a><br />
<br />
Apparent time, <a href="#Page_152">152</a><br />
<br />
Arcturus, motion of, <a href="#Page_315">315</a><br />
<br />
Argelander, star catalogue of, <a href="#Page_287">287</a><br />
<br />
<cite>Art of Dialling</cite>, the, <a href="#Page_28">28</a><br />
<br />
Assistants, position of the, <a href="#Page_98">98</a>, <a href="#Page_100">100</a>, <a href="#Page_117">117</a>, <a href="#Page_137">137</a><br />
<br />
Astrographic chart, <a href="#Page_128">128</a><br />
<br />
—— Department, <a href="#Page_284">284</a>, <em>et seq.</em><br />
<br />
—— dome, <a href="#Page_128">128</a><br />
<br />
—— telescope, <a href="#Page_289">289</a>, <em>et seq.</em><br />
<br />
Astronomers Royal, the, <a href="#Page_25">25</a><br />
<br />
Astrophysical researches, <a href="#Page_282">282</a><br />
<br />
Auroræ, <a href="#Page_281">281</a><br />
<br />
Automatic register, <a href="#Page_241">241</a><br />
<br />
Axis of the earth, precession of, <a href="#Page_184">184</a><br />
<br />
<br />
Ball, Time, <a href="#Page_162">162</a><br />
<br />
Barometer, use of the, <a href="#Page_192">192</a>, <a href="#Page_233">233</a><br />
<br />
Battery basement, <a href="#Page_161">161</a><br />
<br />
Beaufort, Captain, <a href="#Page_107">107</a><br />
<br />
Bessel quoted, <a href="#Page_266">266</a><br />
<br />
Betelgeuse, <a href="#Page_184">184</a><br />
<br />
Birkenhead, wreck of the, <a href="#Page_180">180</a><br />
<br />
Bliss, Nathaniel, fourth Astronomer Royal, history of, <a href="#Page_82">82</a><br />
<br />
Bradley, James, third Astronomer Royal, his life, <a href="#Page_73">73</a>;<br />
<span style="margin-left: 1em;">his ordination, <a href="#Page_74">74</a>;</span><br />
<span style="margin-left: 1em;">Vicar of Bridstow, <a href="#Page_74">74</a>;</span><br />
<span style="margin-left: 1em;">Savilian Professor of Astronomy, <a href="#Page_75">75</a>;</span><br />
<span style="margin-left: 1em;">discovers Aberration of Light, <a href="#Page_75">75</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">becomes Astronomer Royal, <a href="#Page_79">79</a>;</span><br />
<span style="margin-left: 1em;">labours of, <a href="#Page_80">80</a>;</span><br />
<span style="margin-left: 1em;">character of, <a href="#Page_81">81</a></span><br />
<br />
Bradley's transit room, <a href="#Page_128">128</a><br />
<br />
Brinkley, Dr., <a href="#Page_303">303</a><br />
<br />
<cite>British Mariner's Guide</cite>, the, <a href="#Page_90">90</a><br />
<br />
Bunsen, <a href="#Page_268">268</a><br />
<br />
Buys Ballot's law, <a href="#Page_237">237</a><br />
<br />
<br />
Canadian time, <a href="#Page_153">153</a><br />
<br />
Castor, <a href="#Page_74">74</a>, <a href="#Page_306">306</a><br />
<br />
Catalogues, star, <a href="#Page_182">182</a>, <a href="#Page_185">185</a>, <em>et seq.</em>, <a href="#Page_198">198</a>, <a href="#Page_284">284</a><br />
<br />
Cepheus, <a href="#Page_183">183</a><br />
<br />
Charles II., warrants of, <a href="#Page_39">39</a>, <a href="#Page_40">40</a><br />
<br />
Christie, W. H. M., eighth Astronomer Royal, work of, <a href="#Page_120">120</a><br />
<br />
Chromosphere of the sun, <a href="#Page_268">268</a><br />
<br />
Chronograph, the, <a href="#Page_157">157</a><br />
<br />
—— room, <a href="#Page_126">126</a><br />
<br />
Chronometer business, <a href="#Page_101">101</a>, <a href="#Page_107">107</a><br />
<br />
Chronometers, Harrison's improvements in, <a href="#Page_165">165</a>, <em>et seq.</em>;<br />
<span style="margin-left: 1em;">tests of, <a href="#Page_169">169</a>;</span><br />
<span style="margin-left: 1em;">'runs' of, <a href="#Page_173">173</a>;</span><br />
<span style="margin-left: 1em;">romance of, <a href="#Page_178">178</a></span><br />
<br />
Circle Department, <a href="#Page_181">181</a>, <em>et seq.</em><br />
<br />
Clock, Astrographic driving, <a href="#Page_290">290</a>;<br />
<span style="margin-left: 1em;">driving 28-inch telescope, <a href="#Page_312">312</a></span><br />
<br />
Clocks, standard, <a href="#Page_160">160</a><br />
<br />
Columbus, aim of voyage of, <a href="#Page_18">18</a><br />
<br />
Comet, appearance of a, <a href="#Page_28">28</a><br />
<br />
—— Wells, <a href="#Page_280">280</a><br />
<br />
Comets, observation of, <a href="#Page_224">224</a>;<br />
<span style="margin-left: 1em;">spectra of, <a href="#Page_280">280</a></span><br />
<br />
Commutator, the, <a href="#Page_162">162</a><br />
<br />
Comte, assertion of, <a href="#Page_267">267</a><br />
<br />
Constant of Aberration, <a href="#Page_79">79</a><br />
<br />
Cook, Captain, work of, <a href="#Page_170">170</a><br />
<br />
Copper, use of in Observatory, <a href="#Page_245">245</a><br />
<br />
Corona of the sun, <a href="#Page_264">264</a><br />
<br />
Crabtree, James, <a href="#Page_31">31</a><br />
<br />
<span class="pagenum"><a name="Page_318" id="Page_318">[318]</a></span>Crosthwait, Joseph, <a href="#Page_57">57</a><br />
<br />
<br />
Dallmeyer telescope, <a href="#Page_252">252</a><br />
<br />
Declination, <a href="#Page_186">186</a>, <em>et seq.</em><br />
<br />
Denebola, <a href="#Page_184">184</a><br />
<br />
Distances of planets, <a href="#Page_223">223</a>;<br />
<span style="margin-left: 1em;">of sun, <a href="#Page_224">224</a></span><br />
<br />
Double-Star Department, <a href="#Page_303">303</a>, <em>et seq.</em><br />
<br />
Double Stars, <a href="#Page_306">306</a><br />
<br />
Dublin time, <a href="#Page_155">155</a><br />
<br />
Dunkin, Edwin, <a href="#Page_315">315</a><br />
<br />
<br />
Earth, the, movements of, <a href="#Page_201">201</a><br />
<br />
Eclipses of the moon, <a href="#Page_216">216</a>;<br />
<span style="margin-left: 1em;">of the sun, July 25, 1748...85;</span><br />
<span style="margin-left: 1em;">other eclipses of the sun, <a href="#Page_263">263</a>, <em>et seq.</em></span><br />
<br />
Electric Railway, influence of, <a href="#Page_249">249</a><br />
<br />
Equation of Time, the, <a href="#Page_29">29</a>, <a href="#Page_151">151</a><br />
<br />
Equatorial, Shuckburgh's, <a href="#Page_101">101</a><br />
<br />
——, the great 28-inch, <a href="#Page_221">221</a><br />
<br />
——, the Merz, 12<small><sup>3</sup>/<sub>4</sub></small>-inch, <a href="#Page_114">114</a><br />
<br />
——, 28-inch, driving clock of, <a href="#Page_309">309</a>;<br />
<span style="margin-left: 1em;">use of, <a href="#Page_313">313</a></span><br />
<br />
——, clock-driven, <a href="#Page_74">74</a><br />
<br />
Eros, discovery of, <a href="#Page_223">223</a>;<br />
<span style="margin-left: 1em;">photographs of, <a href="#Page_298">298</a></span><br />
<br />
Errors in observations, noting of, <a href="#Page_199">199</a>, <em>et seq.</em><br />
<br />
Evaporation, <a href="#Page_241">241</a><br />
<br />
<br />
Faculæ of the sun, <a href="#Page_257">257</a><br />
<br />
Flamsteed, John, his report on Saint-Pierre's proposal, <a href="#Page_23">23</a>, <a href="#Page_32">32</a>;<br />
<span style="margin-left: 1em;">appointed first Astronomer Royal, <a href="#Page_23">23</a>, <a href="#Page_34">34</a>;</span><br />
<span style="margin-left: 1em;">his autobiography, <a href="#Page_26">26</a>;</span><br />
<span style="margin-left: 1em;">his studies, <a href="#Page_29">29</a>;</span><br />
<span style="margin-left: 1em;">his almanac, <a href="#Page_29">29</a>;</span><br />
<span style="margin-left: 1em;">sent to London, <a href="#Page_30">30</a>;</span><br />
<span style="margin-left: 1em;">enters Jesus College, Cambridge, <a href="#Page_31">31</a>;</span><br />
<span style="margin-left: 1em;">completes his observatory, <a href="#Page_31">31</a>;</span><br />
<span style="margin-left: 1em;">acquaintance with Newton, <a href="#Page_31">31</a>;</span><br />
<span style="margin-left: 1em;">takes his degree, <a href="#Page_32">32</a>;</span><br />
<span style="margin-left: 1em;">his work, <a href="#Page_34">34</a>;</span><br />
<span style="margin-left: 1em;">warrant for his salary, <a href="#Page_39">39</a>;</span><br />
<span style="margin-left: 1em;">position of, <a href="#Page_42">42</a>;</span><br />
<span style="margin-left: 1em;">his ordination, <a href="#Page_45">45</a>;</span><br />
<span style="margin-left: 1em;">his pupils, <a href="#Page_45">45</a>;</span><br />
<span style="margin-left: 1em;">his trouble with Newton, <a href="#Page_46">46</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">his catalogue, <a href="#Page_53">53</a>;</span><br />
<span style="margin-left: 1em;">his letter to Sharp, <a href="#Page_54">54</a>;</span><br />
<span style="margin-left: 1em;">his death, <a href="#Page_56">56</a>;</span><br />
<span style="margin-left: 1em;">his labours, <a href="#Page_57">57</a></span><br />
<br />
Flamsteed House, <a href="#Page_126">126</a><br />
<br />
Fraunhofer mounting, <a href="#Page_310">310</a><br />
<br />
French time, <a href="#Page_155">155</a><br />
<br />
<br />
Galileo, his discovery of Jupiter's satellites, <a href="#Page_19">19</a><br />
<br />
Gamma Draconis, <a href="#Page_75">75</a>, <a href="#Page_304">304</a><br />
<br />
—— Virginis, <a href="#Page_306">306</a><br />
<br />
Gascoigne, William, <a href="#Page_31">31</a><br />
<br />
Gemma Frisius, plan of, <a href="#Page_22">22</a><br />
<br />
George of Denmark, Prince, <a href="#Page_50">50</a><br />
<br />
German mounting, <a href="#Page_276">276</a>, <a href="#Page_310">310</a><br />
<br />
Gould, Dr., <a href="#Page_287">287</a><br />
<br />
Graham, <a href="#Page_166">166</a><br />
<br />
Gravitation, the bond of the universe, <a href="#Page_313">313</a><br />
<br />
Great comet of 1882, the, <a href="#Page_280">280</a>, <a href="#Page_288">288</a><br />
<br />
Greatrackes, Valentine, <a href="#Page_29">29</a><br />
<br />
Green, Charles, <a href="#Page_91">91</a><br />
<br />
Greenwich time, <a href="#Page_153">153</a>;<br />
<span style="margin-left: 1em;">distribution of, <a href="#Page_163">163</a></span><br />
<br />
<br />
Halley, Edmund, his life, <a href="#Page_60">60</a>;<br />
<span style="margin-left: 1em;">his early work, <a href="#Page_60">60</a>;</span><br />
<span style="margin-left: 1em;">his catalogue of stars, <a href="#Page_63">63</a>;</span><br />
<span style="margin-left: 1em;">elected F.R.S., <a href="#Page_63">63</a>;</span><br />
<span style="margin-left: 1em;">his work on Kepler's laws, <a href="#Page_64">64</a>;</span><br />
<span style="margin-left: 1em;">becomes captain, <a href="#Page_65">65</a>;</span><br />
<span style="margin-left: 1em;">Savilian Professor of Geometry, <a href="#Page_66">66</a>;</span><br />
<span style="margin-left: 1em;">Astronomer Royal, <a href="#Page_66">66</a>;</span><br />
<span style="margin-left: 1em;">observations on saros of the moon, <a href="#Page_67">67</a>;</span><br />
<span style="margin-left: 1em;">pressed by Newton, <a href="#Page_68">68</a>;</span><br />
<span style="margin-left: 1em;">his death, <a href="#Page_68">68</a>;</span><br />
<span style="margin-left: 1em;">his services to science, <a href="#Page_68">68</a>;</span><br />
<span style="margin-left: 1em;">his pay, <a href="#Page_70">70</a>;</span><br />
<span style="margin-left: 1em;">nominates his successor, <a href="#Page_73">73</a>;</span><br />
<span style="margin-left: 1em;">his transit instrument, <a href="#Page_73">73</a></span><br />
<br />
Halley's comet, <a href="#Page_225">225</a><br />
<br />
Harrison, James, timekeepers of, <a href="#Page_86">86</a>, <a href="#Page_91">91</a>, <a href="#Page_93">93</a>, <a href="#Page_165">165</a><br />
<br />
Heineken, Rev. N. S., <a href="#Page_59">59</a><br />
<br />
Heineken quadrant, <a href="#Page_59">59</a><br />
<br />
Heliographic Department, <a href="#Page_251">251</a>, <em>et seq.</em><br />
<br />
Herschel, Caroline, <a href="#Page_57">57</a><br />
<br />
Hipparchus, catalogue of, <a href="#Page_185">185</a><br />
<br />
Hodgson, Mr., <a href="#Page_50">50</a><br />
<br />
Hooke, Robert, <a href="#Page_75">75</a>, <a href="#Page_206">206</a><br />
<br />
Horrox, Jeremiah, <a href="#Page_31">31</a><br />
<br />
Huggins, Sir W., his use of spectroscope, <a href="#Page_268">268</a><br />
<br />
<br />
Inscription, an, <a href="#Page_126">126</a><br />
<br />
International Photographic Survey, <a href="#Page_296">296</a><br />
<br />
Ireis, <a href="#Page_224">224</a><br />
<br />
Iron quadrant, <a href="#Page_73">73</a><br />
<br />
Isobars, <a href="#Page_237">237</a><br />
<br />
<br />
Jupiter, satellites of, <a href="#Page_19">19</a>, <a href="#Page_296">296</a>;<br />
<span style="margin-left: 1em;">atmosphere of, <a href="#Page_279">279</a></span><br />
<br />
<br />
Keill, John, <a href="#Page_74">74</a><br />
<br />
Kendall, Larcum, <a href="#Page_166">166</a><br />
<br />
Kepler, laws of, <a href="#Page_64">64</a><br />
<br />
Kew, photo-heliograph, the, <a href="#Page_252">252</a><br />
<br />
Kinnebrook, David, <a href="#Page_176">176</a><br />
<br />
Kirchhoff's use of spectroscope, <a href="#Page_267">267</a><br />
<br />
<br />
Latitude, finding the, <a href="#Page_18">18</a><br />
<br />
Ledgers, chronometer, romance of, <a href="#Page_176">176</a><br />
<br />
Leverrier, his discovery of Neptune, <a href="#Page_217">217</a><br />
<br />
Libraries, <a href="#Page_132">132</a><br />
<br />
Linacre, G., <a href="#Page_28">28</a><br />
<br />
Lindsay, Thomas, quoted, <a href="#Page_204">204</a><br />
<br />
Litchford, W., <a href="#Page_28">28</a><br />
<br />
Local apparent time, <a href="#Page_22">22</a><br />
<br />
Longitude, finding the, <a href="#Page_18">18</a>;<br />
<span style="margin-left: 1em;">at sea, problem of, <a href="#Page_86">86</a>;</span><br />
<span style="margin-left: 1em;">determination of, <a href="#Page_173">173</a></span><br />
<br />
Longitude nought, <a href="#Page_148">148</a><br />
<br />
Lower computing room, <a href="#Page_128">128</a><br />
<br />
Lunars, method of, <a href="#Page_86">86</a><br />
<br />
<br />
Magnetic Department, work of, <a href="#Page_133">133</a>;<br />
<span style="margin-left: 1em;">description of, <a href="#Page_228">228</a>, <em>et seq.</em></span><br />
<br />
Magnetic inclination and declination, <a href="#Page_246">246</a><br />
<br />
—— needles, movements of, <a href="#Page_247">247</a>, <a href="#Page_262">262</a><br />
<br />
—— observatory, <a href="#Page_132">132</a><br />
<br />
—— pavilion, <a href="#Page_245">245</a><br />
<br />
—— storms, <a href="#Page_248">248</a>, <a href="#Page_262">262</a><br />
<br />
Mars, distance of, <a href="#Page_223">223</a>;<br />
<span style="margin-left: 1em;">atmosphere of, <a href="#Page_279">279</a>;</span><br />
<span class="pagenum"><a name="Page_319" id="Page_319">[319]</a></span><span style="margin-left: 1em;">satellites of, <a href="#Page_296">296</a></span><br />
<br />
Maskelyne, Nevil, fifth Astronomer Royal, <a href="#Page_85">85</a>;<br />
<span style="margin-left: 1em;">practical work of, <a href="#Page_86">86</a>;</span><br />
<span style="margin-left: 1em;">Astronomer Royal, <a href="#Page_91">91</a>;</span><br />
<span style="margin-left: 1em;">his work, <a href="#Page_92">92</a>;</span><br />
<span style="margin-left: 1em;">his publications, <a href="#Page_92">92</a>;</span><br />
<span style="margin-left: 1em;">his observations and work, <a href="#Page_92">92</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">his death, <a href="#Page_94">94</a>;</span><br />
<span style="margin-left: 1em;">his character, <a href="#Page_97">97</a>;</span><br />
<span style="margin-left: 1em;">recommends his successor, <a href="#Page_97">97</a>;</span><br />
<span style="margin-left: 1em;">his mural circle, <a href="#Page_101">101</a></span><br />
<br />
Mean solar clock, <a href="#Page_160">160</a><br />
<br />
Mean time, <a href="#Page_152">152</a><br />
<br />
Meldrum, Dr., on sun spots, <a href="#Page_263">263</a><br />
<br />
Meridian, the, <a href="#Page_149">149</a><br />
<br />
Merz telescope, <a href="#Page_279">279</a><br />
<br />
Meteorological Department, work of, <a href="#Page_133">133</a>;<br />
<span style="margin-left: 1em;">description of, <a href="#Page_228">228</a>, <em>et seq.</em></span><br />
<br />
Micrometers, use of, <a href="#Page_309">309</a><br />
<br />
Microscopes, use of, <a href="#Page_188">188</a><br />
<br />
Milky Way, <a href="#Page_288">288</a><br />
<br />
Miller, Professor, <a href="#Page_268">268</a><br />
<br />
Milne, Professor, on earth movements, <a href="#Page_201">201</a><br />
<br />
Minor planets, <a href="#Page_222">222</a><br />
<br />
Molyneux, Samuel, <a href="#Page_75">75</a><br />
<br />
Moon, observation of the, <a href="#Page_212">212</a>, <em>et seq.</em>;<br />
<span style="margin-left: 1em;">eclipses of, <a href="#Page_266">266</a></span><br />
<br />
Moore, Sir Jonas, <a href="#Page_30">30</a>;<br />
<span style="margin-left: 1em;">death of, <a href="#Page_42">42</a></span><br />
<br />
Morin, <a href="#Page_33">33</a><br />
<br />
Mounting telescopes, modes of, <a href="#Page_310">310</a><br />
<br />
Mudge, Thomas, <a href="#Page_94">94</a><br />
<br />
Mural arc, 7-feet, <a href="#Page_46">46</a><br />
<br />
Mural circles, <a href="#Page_101">101</a>, <a href="#Page_196">196</a><br />
<br />
<br />
Names of stars, origin of, <a href="#Page_183">183</a><br />
<br />
Nares, Sir George, <a href="#Page_170">170</a><br />
<br />
<cite>Nautical Almanac</cite>, the, <a href="#Page_22">22</a>, <a href="#Page_23">23</a>, <a href="#Page_92">92</a><br />
<br />
Navigation, state of primitive, <a href="#Page_17">17</a><br />
<br />
Neptune, discovery of, <a href="#Page_217">217</a>;<br />
<span style="margin-left: 1em;">atmosphere of, <a href="#Page_280">280</a>;</span><br />
<span style="margin-left: 1em;">satellite of, <a href="#Page_298">298</a></span><br />
<br />
New altazimuth, the, <a href="#Page_132">132</a>, <a href="#Page_210">210</a><br />
<br />
New Observatory, the, <a href="#Page_136">136</a>, <a href="#Page_275">275</a><br />
<br />
New stars, <a href="#Page_268">268</a><br />
<br />
Newcomb, Professor, on growth of Observatory, <a href="#Page_124">124</a>;<br />
<span style="margin-left: 1em;">on Greenwich observations, <a href="#Page_207">207</a></span><br />
<br />
Newton, Sir I., his absent-mindedness, <a href="#Page_31">31</a>;<br />
<span style="margin-left: 1em;">his trouble with Flamsteed, <a href="#Page_46">46</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">on Kepler's laws, <a href="#Page_65">65</a>;</span><br />
<span style="margin-left: 1em;">his <cite>Principia</cite>, <a href="#Page_65">65</a>;</span><br />
<span style="margin-left: 1em;">his pressure on Halley, <a href="#Page_68">68</a>;</span><br />
<span style="margin-left: 1em;">his discovery of gravitation, <a href="#Page_206">206</a></span><br />
<br />
North terrace, the, <a href="#Page_126">126</a><br />
<br />
Northumberland equatorial, <a href="#Page_218">218</a><br />
<br />
Nutation of the earth, <a href="#Page_80">80</a><br />
<br />
<br />
Observation, modes of, <a href="#Page_156">156</a>, <a href="#Page_176">176</a>, <a href="#Page_188">188</a>;<br />
<span style="margin-left: 1em;">by reflection, <a href="#Page_196">196</a>;</span><br />
<span style="margin-left: 1em;">of comets, <a href="#Page_224">224</a></span><br />
<br />
Observatory, Greenwich, work of, <a href="#Page_13">13</a>;<br />
<span style="margin-left: 1em;">foundation of, <a href="#Page_23">23</a>;</span><br />
<span style="margin-left: 1em;">warrant for building, <a href="#Page_40">40</a>;</span><br />
<span style="margin-left: 1em;">position of, <a href="#Page_41">41</a>;</span><br />
<span style="margin-left: 1em;">foundation stone laid, <a href="#Page_42">42</a>;</span><br />
<span style="margin-left: 1em;">condition of, <a href="#Page_79">79</a>;</span><br />
<span style="margin-left: 1em;">enlargement of, <a href="#Page_112">112</a>;</span><br />
<span style="margin-left: 1em;">recent extensions of, <a href="#Page_120">120</a>;</span><br />
<span style="margin-left: 1em;">description of, <a href="#Page_124">124</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">staff of, <a href="#Page_137">137</a>;</span><br />
<span style="margin-left: 1em;">work of, <a href="#Page_139">139</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">visitors to, <a href="#Page_175">175</a>;</span><br />
<span style="margin-left: 1em;">new altazimuth building, <a href="#Page_211">211</a>;</span><br />
<span style="margin-left: 1em;">magnet house, <a href="#Page_228">228</a>;</span><br />
<span style="margin-left: 1em;">magnetic pavilion, <a href="#Page_245">245</a>;</span><br />
<span style="margin-left: 1em;">new Observatory, <a href="#Page_275">275</a>;</span><br />
<span style="margin-left: 1em;">future of, <a href="#Page_283">283</a>;</span><br />
<span style="margin-left: 1em;">reflex zenith room, <a href="#Page_304">304</a>;</span><br />
<span style="margin-left: 1em;">objects of, <a href="#Page_316">316</a></span><br />
<br />
Occultations by the moon, <a href="#Page_212">212</a>, <em>et seq.</em><br />
<br />
Octagon room, <a href="#Page_125">125</a>, <a href="#Page_238">238</a>, <a href="#Page_242">242</a><br />
<br />
Oldenburg, Mr., <a href="#Page_30">30</a><br />
<br />
Orion nebula, <a href="#Page_268">268</a>, <a href="#Page_301">301</a><br />
<br />
<br />
Parallax of stars, <a href="#Page_303">303</a><br />
<br />
Paramour, the, <a href="#Page_65">65</a><br />
<br />
Paris, conference at, <a href="#Page_288">288</a><br />
<br />
——, noon at, <a href="#Page_151">151</a><br />
<br />
Philip III., offer of, <a href="#Page_19">19</a><br />
<br />
Photographic registration, <a href="#Page_244">244</a>, <a href="#Page_247">247</a>, <a href="#Page_252">252</a>, <a href="#Page_255">255</a>;<br />
<span style="margin-left: 1em;">refractors, <a href="#Page_288">288</a></span><br />
<br />
Photographs, star, <a href="#Page_290">290</a><br />
<br />
Photo-heliographs, <a href="#Page_252">252</a>, <em>et seq.</em>, <a href="#Page_279">279</a><br />
<br />
Piazzi, discovery of, <a href="#Page_222">222</a><br />
<br />
Pleiades, the, <a href="#Page_301">301</a><br />
<br />
Polar plumes of the corona, <a href="#Page_264">264</a><br />
<br />
Polaris, <a href="#Page_188">188</a><br />
<br />
Pole-star, variation of, <a href="#Page_184">184</a><br />
<br />
Pond, John, sixth Astronomer Royal, his life, <a href="#Page_97">97</a>;<br />
<span style="margin-left: 1em;">his reign, <a href="#Page_98">98</a>;</span><br />
<span style="margin-left: 1em;">his salary, <a href="#Page_98">98</a>;</span><br />
<span style="margin-left: 1em;">his assistants, <a href="#Page_98">98</a>;</span><br />
<span style="margin-left: 1em;">his observations, <a href="#Page_99">99</a>;</span><br />
<span style="margin-left: 1em;">censured by Visitors, <a href="#Page_99">99</a>;</span><br />
<span style="margin-left: 1em;">his observations of stars, <a href="#Page_303">303</a></span><br />
<br />
Pound, James, <a href="#Page_73">73</a><br />
<br />
Precession of earth's axis, <a href="#Page_184">184</a><br />
<br />
<cite>Principia</cite>, publication of, <a href="#Page_65">65</a><br />
<br />
Proctor, R. A., attack of, <a href="#Page_116">116</a><br />
<br />
Ptolemy, Claudius, catalogue of, <a href="#Page_185">185</a><br />
<br />
Publication, the problem of, <a href="#Page_48">48</a>, <a href="#Page_92">92</a><br />
<br />
<br />
Quadrant, Heineken, <a href="#Page_59">59</a><br />
<br />
——, the iron, <a href="#Page_73">73</a><br />
<br />
<br />
Railway time, <a href="#Page_152">152</a><br />
<br />
Rain gauge, <a href="#Page_238">238</a><br />
<br />
Record rooms, <a href="#Page_132">132</a><br />
<br />
Reflection, observation by, <a href="#Page_196">196</a><br />
<br />
Reflex zenith room, <a href="#Page_304">304</a><br />
<br />
—— —— tube, <a href="#Page_131">131</a><br />
<br />
Refraction, effects of, <a href="#Page_194">194</a><br />
<br />
Right ascension, <a href="#Page_186">186</a>, <em>et seq.</em><br />
<br />
Roberts, Dr. Isaac, <a href="#Page_301">301</a><br />
<br />
Römer, discovery of, <a href="#Page_78">78</a><br />
<br />
Rosse, Lord, <a href="#Page_268">268</a><br />
<br />
Royal Society and Flamsteed, <a href="#Page_46">46</a>, <em>et seq.</em><br />
<br />
<br />
Saint-Pierre, Le Sieur de, proposal of, <a href="#Page_23">23</a>, <a href="#Page_32">32</a><br />
<br />
Sappho, <a href="#Page_224">224</a><br />
<br />
Saros of the moon, <a href="#Page_67">67</a><br />
<br />
Satellites, discovery of, <a href="#Page_296">296</a><br />
<br />
Saturn, atmosphere of, <a href="#Page_279">279</a>;<br />
<span style="margin-left: 1em;">satellites of, <a href="#Page_296">296</a></span><br />
<br />
Schaeberle's comet, <a href="#Page_280">280</a><br />
<br />
Schedar, <a href="#Page_184">184</a><br />
<br />
Schiehallion, attraction of, <a href="#Page_94">94</a><br />
<br />
Schönfeld, <a href="#Page_287">287</a><br />
<br />
Scotchmen, anecdote of, <a href="#Page_146">146</a><br />
<br />
Sharp, Abraham, <a href="#Page_46">46</a><br />
<br />
Sheepshanks, Rev. James, on Airy, <a href="#Page_107">107</a><br />
<br />
Shuckburgh equatorial, <a href="#Page_309">309</a><br />
<br />
<span class="pagenum"><a name="Page_320" id="Page_320">[320]</a></span>Sidereal clock, <a href="#Page_160">160</a><br />
<br />
Sirius, <a href="#Page_287">287</a><br />
<br />
Sloane, Dr., <a href="#Page_50">50</a><br />
<br />
'Smith, Mr.,' his chronometer, <a href="#Page_179">179</a><br />
<br />
Solar photographs, <a href="#Page_257">257</a><br />
<br />
—— storms, <a href="#Page_261">261</a>, <a href="#Page_282">282</a><br />
<br />
Sound waves, <a href="#Page_271">271</a><br />
<br />
South, Sir James, <a href="#Page_105">105</a>, <a href="#Page_114">114</a><br />
<br />
South-east equatorial, the, <a href="#Page_132">132</a>, <a href="#Page_221">221</a><br />
<br />
Spectroscope, use of, <a href="#Page_267">267</a><br />
<br />
Spectroscopic Department, <a href="#Page_266">266</a>, <em>et seq.</em><br />
<br />
Spots, sun, <a href="#Page_251">251</a>, <em>et seq.</em>, <a href="#Page_281">281</a><br />
<br />
Staff of Observatory, <a href="#Page_137">137</a>;<br />
<span style="margin-left: 1em;">work of, <a href="#Page_139">139</a>, <em>et seq.</em></span><br />
<br />
Standard time, <a href="#Page_21">21</a><br />
<br />
Stars, observations of, <a href="#Page_156">156</a>, <a href="#Page_176">176</a>, <a href="#Page_188">188</a>;<br />
<span style="margin-left: 1em;">origin of names of, <a href="#Page_183">183</a>;</span><br />
<span style="margin-left: 1em;">movements of, <a href="#Page_187">187</a>;</span><br />
<span style="margin-left: 1em;">catalogues of, <a href="#Page_198">198</a>, <a href="#Page_284">284</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">composition of, <a href="#Page_268">268</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">colour of, <a href="#Page_271">271</a>;</span><br />
<span style="margin-left: 1em;">classes of, <a href="#Page_287">287</a>;</span><br />
<span style="margin-left: 1em;">census of, <a href="#Page_287">287</a>;</span><br />
<span style="margin-left: 1em;">photographs of, <a href="#Page_288">288</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">motions of, <a href="#Page_303">303</a>, <a href="#Page_315">315</a></span><br />
<br />
Story, Mr. A. M., <a href="#Page_97">97</a><br />
<br />
Sun, distance of the, <a href="#Page_74">74</a>, <a href="#Page_224">224</a>;<br />
<span style="margin-left: 1em;">spots on, <a href="#Page_251">251</a>, <em>et seq.</em>, <a href="#Page_281">281</a>;</span><br />
<span style="margin-left: 1em;">eclipses of, <a href="#Page_263">263</a>, <em>et seq.</em>;</span><br />
<span style="margin-left: 1em;">chromosphere of, <a href="#Page_268">268</a>;</span><br />
<span style="margin-left: 1em;">motions of, <a href="#Page_315">315</a></span><br />
<br />
Sunshine recorder, <a href="#Page_238">238</a><br />
<br />
Swiss time, <a href="#Page_155">155</a><br />
<br />
<br />
Tebb, Mr. W., <a href="#Page_58">58</a><br />
<br />
Tebbutt's comet, <a href="#Page_280">280</a><br />
<br />
Telescope, the great transit, <a href="#Page_156">156</a><br />
<br />
——, 28-inch, <a href="#Page_275">275</a><br />
<br />
——, astrographic, <a href="#Page_289">289</a><br />
<br />
——, Shuckburgh, <a href="#Page_309">309</a><br />
<br />
——, Thompson, <a href="#Page_256">256</a>, <a href="#Page_279">279</a>, <a href="#Page_296">296</a><br />
<br />
Thalèn, <a href="#Page_268">268</a><br />
<br />
Thermometer, use of, <a href="#Page_192">192</a>, <a href="#Page_234">234</a><br />
<br />
Thome, Dr., <a href="#Page_287">287</a><br />
<br />
Thompson photo-heliograph, <a href="#Page_256">256</a>, <a href="#Page_279">279</a>, <a href="#Page_296">296</a><br />
<br />
Time ball, <a href="#Page_162">162</a><br />
<br />
—— Department, the, <a href="#Page_146">146</a>, <em>et seq.</em><br />
<br />
—— desk, <a href="#Page_161">161</a><br />
<br />
——, foreign, <a href="#Page_153">153</a><br />
<br />
—— signals, <a href="#Page_162">162</a><br />
<br />
—— standard, <a href="#Page_21">21</a><br />
<br />
Transit, Halley's, <a href="#Page_73">73</a><br />
<br />
Transit circle, the, <a href="#Page_114">114</a>;<br />
<span style="margin-left: 1em;">mode of observation with, <a href="#Page_188">188</a>, <em>et seq.</em></span><br />
<br />
Transit circle, Troughton's, <a href="#Page_98">98</a><br />
<br />
—— Department, <a href="#Page_181">181</a>, <em>et seq.</em><br />
<br />
—— observations, number of, <a href="#Page_140">140</a><br />
<br />
—— pavilion, <a href="#Page_126">126</a>, <a href="#Page_175">175</a><br />
<br />
—— room, <a href="#Page_128">128</a>, <a href="#Page_147">147</a><br />
<br />
Troughton's transit circle, <a href="#Page_98">98</a><br />
<br />
<br />
Uranus, discovery of, <a href="#Page_217">217</a>;<br />
<span style="margin-left: 1em;">atmosphere of, <a href="#Page_279">279</a>;</span><br />
<span style="margin-left: 1em;">satellites of, <a href="#Page_296">296</a></span><br />
<br />
<br />
Vanes, use of, <a href="#Page_238">238</a><br />
<br />
Venus, distance of, <a href="#Page_223">223</a><br />
<br />
Victoria, <a href="#Page_224">224</a><br />
<br />
Visitors, the Board of, <a href="#Page_53">53</a>;<br />
<span style="margin-left: 1em;">censures Pond, <a href="#Page_99">99</a>;</span><br />
<span style="margin-left: 1em;">work of, <a href="#Page_106">106</a>;</span><br />
<span style="margin-left: 1em;">constitution of, <a href="#Page_144">144</a></span><br />
<br />
Visitors to Observatory, <a href="#Page_175">175</a><br />
<br />
<br />
Warrant for Flamsteed's salary, <a href="#Page_39">39</a><br />
<br />
Water telescope, <a href="#Page_304">304</a><br />
<br />
Weather predictions, <a href="#Page_229">229</a>, <em>et seq.</em><br />
<br />
Winds, study of, <a href="#Page_237">237</a><br />
<br />
Witt, Herr, discovery of, <a href="#Page_223">223</a><br />
<br />
Working Catalogue, the, <a href="#Page_142">142</a><br />
<br />
<br />
Zenith sector, <a href="#Page_82">82</a>, <a href="#Page_305">305</a><br />
<br />
—— tube, <a href="#Page_75">75</a>, <a href="#Page_305">305</a><br />
<br />
Zeta Ursæ Majoris, <a href="#Page_306">306</a><br />
<br />
Zubeneschamal, <a href="#Page_184">184</a><br />
</div>
<hr class="chap" />
<p> </p>
<p class="center space-above">
LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,<br />
STAMFORD STREET AND CHARING CROSS.
</p>
<hr class="chap" />
<div class="footnotes"><h3>FOOTNOTES:</h3>
<div class="footnote">
<p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> Abraham Sharp had been with Flamsteed earlier than
this—in 1684 and 1685.</p></div>
<div class="footnote">
<p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> Sir Isaac Newton.</p></div>
<div class="footnote">
<p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> The second circle was intended for the Cape Observatory,
but Pond obtained leave to retain it. In 1851 it was transferred
to the Observatory of Queen's College, Belfast.</p></div>
<div class="footnote">
<p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> Mr. Thomas Lindsay, <cite>Transactions of the Astronomical
and Physical Society of Toronto</cite>, 1899, p. 17.</p></div>
<div class="footnote">
<p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> From Sir John Herschel's address to the British Association,
September 10, 1846, thirteen days before Galle's first observation
of the planet.</p></div></div>
<p> </p>
<p> </p>
<div class="tn"><h3>Transcriber's note:</h3>
<p>Minor typographical errors have been corrected without
note. Irregularities and inconsistencies in the text have been retained as printed.</p>
<p>The illustrations have been moved so that they do not break up paragraphs, thus the page number of the illustration might not match the page number in the List of Illustrations.</p>
<p>Mismatched quotation marks were not corrected if it was not clear
where the missing quotation mark should be placed.</p>
<p>Missing page numbers are page numbers that were not shown
in the original text.</p>
</div>
<p> </p>
<p> </p>
<div>*** END OF THE PROJECT GUTENBERG EBOOK 44167 ***</div>
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