in 1824, but in 1828, when Airy entered on the discharge of his
duties as Director, the establishment was still far from completion,
in so far as its organisation was concerned. Airy commenced his work
so energetically that in the next year after his appointment he was
able to publish the first volume of "Cambridge Astronomical
Observations," notwithstanding that every part of the work, from the
making of observations to the revising of the proof-sheets, had to be
done by himself.
It may here be remarked that these early volumes of the publications
of the Cambridge Observatory contained the first exposition of those
systematic methods of astronomical work which Airy afterwards
developed to such a great extent at Greenwich, and which have been
subsequently adopted in many other places. No more profitable
instruction for the astronomical beginner can be found than that
which can be had by the study of these volumes, in which the Plumian
Professor has laid down with admirable clearness the true principles
on which meridian work should be conducted.
[PLATE: SIR GEORGE AIRY.
From a Photograph by Mr. E.P. Adams, Greenwich.]
Airy gradually added to the instruments with which the observatory
was originally equipped. A mural circle was mounted in 1832, and in
the same year a small equatorial was erected by Jones. This was made
use of by Airy in a well-known series of observations of Jupiter's
fourth satellite for the determination of the mass of the great
planet. His memoir on this subject fully expounds the method of
finding the weight of a planet from observations of the movements of
a satellite by which the planet is attended. This is, indeed, a
valuable investigation which no student of astronomy can afford to
neglect. The ardour with which Airy devoted himself to astronomical
studies may be gathered from a remarkable report on the progress of
astronomy during the present century, which he communicated to the
British Association at its second meeting in 1832. In the early
years of his life at Cambridge his most famous achievement was
connected with a research in theoretical astronomy for which
consummate mathematical power was required. We can only give a brief
account of the Subject, for to enter into any full detail with regard
to it would be quite out of the question.
Venus is a planet of about the same size and the same weight as the
earth, revolving in an orbit which lies within that described by our
globe. Venus, consequently, takes less time than the earth to
accomplish one revolution round the sun, and it happens that the
relative movements of Venus and the earth are so proportioned that in
the time in which our earth accomplishes eight of her revolutions the
other planet will have accomplished almost exactly thirteen. It,
therefore, follows that if the earth and Venus are in line with the
sun at one date, then in eight years later both planets will again be
found at the same points in their orbits. In those eight years the
earth has gone round eight times, and has, therefore, regained its
original position, while in the same period Venus has accomplished
thirteen complete revolutions, and, therefore, this planet also has
reached the same spot where it was at first. Venus and the earth, of
course, attract each other, and in consequence of these mutual
attractions the earth is swayed from the elliptic track which it
would otherwise pursue. In like manner Venus is also forced by the
attraction of the earth to revolve in a track which deviates from
that which it would otherwise follow. Owing to the fact that the sun
is of such preponderating magnitude (being, in fact, upwards of
300,000 times as heavy as either Venus or the earth), the
disturbances induced in the motion of either planet, in consequence
of the attraction of the other, are relatively insignificant to the
main controlling agency by which each of the movements is governed.
It is, however, possible under certain circumstances that the
disturbing effects produced upon one planet by the other can become
so multiplied as to produce peculiar effects which attain measurable
dimensions. Suppose that the periodic times in which the earth and
Venus revolved had no simple relation to each other, then the points
of their tracks in which the two planets came into line with the sun
would be found at different parts of the orbits, and consequently the
disturbances would to a great extent neutralise each other, and
produce but little appreciable effect. As, however, Venus and the
earth come back every eight years to nearly the same positions at the
same points of their track, an accumulative effect is produced. For
the disturbance of one planet upon the other will, of course, be
greatest when those two planets are nearest, that is, when they lie
in line with the sun and on the same side of it. Every eight years a
certain part of the orbit of the earth is, therefore, disturbed by
the attraction of Venus with peculiar vigour. The consequence is
that, owing to the numerical relation between the movements of the
planets to which I have referred, disturbing effects become
appreciable which would otherwise be too small to permit of
recognition. Airy proposed to himself to compute the effects which
Venus would have on the movement of the earth in consequence of the
circumstance that eight revolutions of the one planet required almost
the same time as thirteen revolutions of the other. This is a
mathematical inquiry of the most arduous description, but the Plumian
Professor succeeded in working it out, and he had, accordingly, the
gratification of announcing to the Royal Society that he had detected
the influence which Venus was thus able to assert on the movement of
our earth around the sun. This remarkable investigation gained for
its author the gold medal of the Royal Astronomical Society in the
year 1832.
In consequence of his numerous discoveries, Airy's scientific fame
had become so well recognised that the Government awarded him a
special pension, and in 1835, when Pond, who was then Astronomer
Royal, resigned, Airy was offered the post at Greenwich. There was
in truth, no scientific inducement to the Plumian Professor to leave
the comparatively easy post he held at Cambridge, in which he had
ample leisure to devote himself to those researches which specially
interested him, and accept that of the much more arduous observatory
at Greenwich. There were not even pecuniary inducements to make the
change; however, he felt it to be his duty to accede to the request
which the Government had made that he would take up the position
which Pond had vacated, and accordingly Airy went to Greenwich as
Astronomer Royal on October 1st, 1835.
He immediately began with his usual energy to organise the systematic
conduct of the business of the National Observatory. To realise one
of the main characteristics of Airy's great work at Greenwich, it is
necessary to explain a point that might not perhaps be understood
without a little explanation by those who have no practical
experience in an observatory. In the work of an establishment such
as Greenwich, an observation almost always consists of a measurement
of some kind. The observer may, for instance, be making a
measurement of the time at which a star passes across a spider line
stretched through the field of view; on another occasion his object
may be the measurement of an angle which is read off by examining
through a microscope the lines of division on a graduated circle when
the telescope is so pointed that the star is placed on a certain mark
in the field of view. In either case the immediate result of the
astronomical observation is a purely numerical one, but it rarely
happens, indeed we may say it never happens, that the immediate
numerical result which the observation gives expresses directly the
quantity which we are really seeking for. No doubt the observation
has been so designed that the quantity we want to find can be
obtained from the figures which the measurement gives, but the object
sought is not those figures, for there are always a multitude of
other influences by which those figures are affected. For example,
if an observation were to be perfect, then the telescope with which
the observation is made should be perfectly placed in the exact
position which it ought to occupy; this is, however, never the case,
for no mechanic can ever construct or adjust a telescope so perfectly
as the wants of the astronomer demand. The clock also by which we
determine the time of the observation should be correct, but this is
rarely if ever the case. We have to correct our observations for
such errors, that is to say, we have to determine the errors in the
positions of our telescopes and the errors in the going of our
clocks, and then we have to determine what the observations would
have been had our telescopes been absolutely perfect, and had our
clocks been absolutely correct. There are also many other matters
which have to be attended to in order to reduce our observations so
as to obtain from the figures as yielded to the observer at the
telescope the actual quantities which it is his object to determine.
The work of effecting these reductions is generally a very intricate
and laborious matter, so that it has not unfrequently happened that
while observations have accumulated in an observatory, yet the
tedious duty of reducing these observations has been allowed to fall
into arrear. When Airy entered on his duties at Greenwich he found
there an enormous mass of observations which, though implicitly
containing materials of the greatest value to astronomers, were, in
their unreduced form, entirely unavailable for any useful purpose.
He, therefore, devoted himself to coping with the reduction of the
observations of his predecessors. He framed systematic methods by
which the reductions were to be effected, and he so arranged the work
that little more than careful attention to numerical accuracy would
be required for the conduct of the operations. Encouraged by the
Admiralty, for it is under this department that Greenwich Observatory
is placed, the Astronomer Royal employed a large force of computers
to deal with the work. BY his energy and admirable organisation he
managed to reduce an extremely valuable series of planetary
observations, and to publish the results, which have been of the
greatest importance to astronomical investigation.
The Astronomer Royal was a capable, practical engineer as well as an
optician, and he presently occupied himself by designing astronomical
instruments of improved pattern, which should replace the antiquated
instruments he found in the observatory. In the course of years the
entire equipment underwent a total transformation. He ordered a
great meridian circle, every part of which may be said to have been
formed from his own designs. He also designed the mounting for a
fine equatorial telescope worked by a driving clock, which he had
himself invented. Gradually the establishment at Greenwich waxed
great under his incessant care. It was the custom for the
observatory to be inspected every year by a board of visitors, whose
chairman was the President of the Royal Society. At each annual
visitation, held on the first Saturday in June, the visitors received
a report from the Astronomer Royal, in which he set forth the
business which had been accomplished during the past year. It was on
these occasions that applications were made to the Admiralty, either
for new instruments or for developing the work of the observatory in
some other way. After the more official business of the inspection
was over, the observatory was thrown open to visitors, and hundreds
of people enjoyed on that day the privilege of seeing the national
observatory. These annual gatherings are happily still continued,
and the first Saturday in June is known to be the occasion of one of
the most interesting reunions of scientific men which takes place in
the course of the year.
Airy's scientific work was, however, by no means confined to the
observatory. He interested himself largely in expeditions for the
observation of eclipses and in projects for the measurement of arcs
on the earth. He devoted much attention to the collection of magnetic
observations from various parts of the world. Especially will it be
remembered that the circumstances of the transits of Venus, which
occurred in 1874 and in 1882, were investigated by him, and under his
guidance expeditions were sent forth to observe the transits from
those localities in remote parts of the earth where observations most
suitable for the determination of the sun's distance from the earth
could be obtained. The Astronomer Royal also studied tidal
phenomena, and he rendered great service to the country in the
restoration of the standards of length and weight which had been
destroyed in the great fire at the House of Parliament in October,
1834. In the most practical scientific matters his advice was often
sought, and was as cheerfully rendered. Now we find him engaged in
an investigation of the irregularities of the compass in iron ships,
with a view to remedying its defects; now we find him reporting on
the best gauge for railways. Among the most generally useful
developments of the observatory must be mentioned the telegraphic
method for the distribution of exact time. By arrangement with the
Post Office, the astronomers at Greenwich despatch each morning a
signal from the observatory to London at ten o'clock precisely. By
special apparatus, this signal is thence distributed automatically
over the country, so as to enable the time to be known everywhere
accurately to a single second. It was part of the same system that a
time ball should be dropped daily at one o'clock at Deal, as well as
at other places, for the purpose of enabling ship's chronometers to
be regulated.
Airy's writings were most voluminous, and no fewer than forty-eight
memoirs by him are mentioned in the "Catalogue of Scientific
Memoirs," published by the Royal Society up to the year 1873, and
this only included ten years out of an entire life of most
extraordinary activity. Many other subjects besides those of a
purely scientific character from time to time engaged his attention.
He wrote, for instance, a very interesting treatise on the Roman
invasion of Britain, especially with a view of determining the port
from which Caesar set forth from Gaul, and the point at which he
landed on the British coast. Airy was doubtless led to this
investigation by his study of the tidal phenomena in the Straits of
Dover. Perhaps the Astronomer Royal is best known to the general
reading public by his excellent lectures on astronomy, delivered at
the Ipswich Museum in 1848. This book has passed through many
editions, and it gives a most admirable account of the manner in
which the fundamental problems in astronomy have to be attacked.
As years rolled by almost every honour and distinction that could be
conferred upon a scientific man was awarded to Sir George Airy. He
was, indeed, the recipient of other honours not often awarded for
scientific distinction. Among these we may mention that in 1875 he
received the freedom of the City of London, "as a recognition of his
indefatigable labours in astronomy, and of his eminent services in
the advancement of practical science, whereby he has so materially
benefited the cause of commerce and civilisation."
Until his eightieth year Airy continued to discharge his labours at
Greenwich with unflagging energy. At last, on August 15th, 1881, he
resigned the office which he had held so long with such distinction
to himself and such benefit to his country. He had married in 1830
the daughter of the Rev. Richard Smith, of Edensor. Lady Airy died
in 1875, and three sons and three daughters survived him. One
daughter is the wife of Dr. Routh, of Cambridge, and his other
daughters were the constant companions of their father during the
declining years of his life. Up to the age of ninety he enjoyed
perfect physical health, but an accidental fall which then occurred
was attended with serious results. He died on Saturday, January 2nd,
1892, and was buried in the churchyard at Playford.
HAMILTON.
William Rowan Hamilton was born at midnight between the 3rd and 4th
of August, 1805, at Dublin, in the house which was then 29, but
subsequently 36, Dominick Street. His father, Archibald Hamilton,
was a solicitor, and William was the fourth of a family of nine. With
reference to his descent, it may be sufficient to notice that his
ancestors appear to have been chiefly of gentle Irish families, but
that his maternal grandmother was of Scottish birth. When he was
about a year old, his father and mother decided to hand over the
education of the child to his uncle, James Hamilton, a clergyman of
Trim, in County Meath. James Hamilton's sister, Sydney, resided with
him, and it was in their home that the days of William's childhood
were passed.
In Mr. Graves' "Life of Sir William Rowan Hamilton" a series of
letters will be found, in which Aunt Sydney details the progress of
the boy to his mother in Dublin. Probably there is no record of an
infant prodigy more extraordinary than that which these letters
contain. At three years old his aunt assured the mother that William
is "a hopeful blade," but at that time it was his physical vigour to
which she apparently referred; for the proofs of his capacity, which
she adduces, related to his prowess in making boys older than himself
fly before him. In the second letter, a month later, we hear that
William is brought in to read the Bible for the purpose of putting to
shame other boys double his age who could not read nearly so well.
Uncle James appears to have taken much pains with William's
schooling, but his aunt said that "how he picks up everything is
astonishing, for he never stops playing and jumping about." When he
was four years and three months old, we hear that he went out to dine
at the vicar's, and amused the company by reading for them equally
well whether the book was turned upside down or held in any other
fashion. His aunt assures the mother that "Willie is a most sensible
little creature, but at the same time has a great deal of roguery."
At four years and five months old he came up to pay his mother a
visit in town, and she writes to her sister a description of the
boy;--
"His reciting is astonishing, and his clear and accurate knowledge of
geography is beyond belief; he even draws the countries with a pencil
on paper, and will cut them out, though not perfectly accurate, yet
so well that a anybody knowing the countries could not mistake them;
but, you will think this nothing when I tell you that he reads Latin,
Greek, and Hebrew."
Aunt Sydney recorded that the moment Willie got back to Trim he was
desirous of at once resuming his former pursuits. He would not eat
his breakfast till his uncle had heard him his Hebrew, and he
comments on the importance of proper pronunciation. At five he was
taken to see a friend, to whom he repeated long passages from
Dryden. A gentleman present, who was not unnaturally sceptical about
Willie's attainments, desired to test him in Greek, and took down a
copy of Homer which happened to have the contracted type, and to his
amazement Willie went on with the greatest ease. At six years and
nine months he was translating Homer and Virgil; a year later his
uncle tells us that William finds so little difficulty in learning
French and Italian, that he wishes to read Homer in French. He is
enraptured with the Iliad, and carries it about with him, repeating
from it whatever particularly pleases him. At eight years and one
month the boy was one of a party who visited the Scalp in the Dublin
mountains, and he was so delighted with the scenery that he forthwith
delivered an oration in Latin. At nine years and six months he is
not satisfied until he learns Sanscrit; three months later his thirst
for the Oriental languages is unabated, and at ten years and four
months he is studying Arabic and Persian. When nearly twelve he
prepared a manuscript ready for publication. It was a "Syriac
Grammar," in Syriac letters and characters compiled from that of
Buxtorf, by William Hamilton, Esq., of Dublin and Trim. When he was
fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid a
visit to Dublin, and, as a practical exercise in his Oriental
languages, the young scholar addressed to his Excellency a letter in
Persian; a translation of which production is given by Mr. Graves.
When William was fourteen he had the misfortune to lose his father;
and he had lost his mother two years previously. The boy and his
three sisters were kindly provided for by different members of the
family on both sides.
It was when William was about fifteen that his attention began to be
turned towards scientific subjects. These were at first regarded
rather as a relaxation from the linguistic studies with which he had
been so largely occupied. On November 22nd, 1820, he notes in his
journal that he had begun Newton's "Principia": he commenced also the
study of astronomy by observing eclipses, occultations, and similar
phenomena. When he was sixteen we learn that he had read conic
sections, and that he was engaged in the study of pendulums. After
an attack of illness, he was moved for change to Dublin, and in May,
1822, we find him reading the differential calculus and Laplace's
"Mecanique Celeste." He criticises an important part of Laplace's
work relative to the demonstration of the parallelogram of forces. In
this same year appeared the first gushes of those poems which
afterwards flowed in torrents.
His somewhat discursive studies had, however, now to give place to a
more definite course of reading in preparation for entrance to the
University of Dublin. The tutor under whom he entered, Charles
Boyton, was himself a distinguished man, but he frankly told the
young William that he could be of little use to him as a tutor, for
his pupil was quite as fit to be his tutor. Eliza Hamilton, by whom
this is recorded, adds, "But there is one thing which Boyton would
promise to be to him, and that was a FRIEND; and that one proof he
would give of this should be that, if ever he saw William beginning
to be UPSET by the sensation he would excite, and the notice he would
attract, he would tell him of it." At the beginning of his college
career he distanced all his competitors in every intellectual
pursuit. At his first term examination in the University he was
first in Classics and first in Mathematics, while he received the
Chancellor's prize for a poem on the Ionian Islands, and another for
his poem on Eustace de St. Pierre.
There is abundant testimony that Hamilton had "a heart for friendship
formed." Among the warmest of the friends whom he made in these
early days was the gifted Maria Edgeworth, who writes to her sister
about "young Mr. Hamilton, an admirable Crichton of eighteen, a real
prodigy of talents, who Dr. Brinkley says may be a second Newton,
quiet, gentle, and simple." His sister Eliza, to whom he was
affectionately attached, writes to him in 1824:--
"I had been drawing pictures of you in my mind in your study at
Cumberland Street with 'Xenophon,' &c., on the table, and you, with
your most awfully sublime face of thought, now sitting down, and now
walking about, at times rubbing your hands with an air of
satisfaction, and at times bursting forth into some very heroical
strain of poetry in an unknown language, and in your own internal
solemn ventriloquist-like voice, when you address yourself to the
silence and solitude of your own room, and indeed, at times, even
when your mysterious poetical addresses are not quite unheard."
This letter is quoted because it refers to a circumstance which all
who ever met with Hamilton, even in his latest years, will remember.
He was endowed with two distinct voices, one a high treble, the other
a deep bass, and he alternately employed these voices not only in
ordinary conversation, but when he was delivering an address on the
profundities of Quaternions to the Royal Irish Academy, or on
similar occasions. His friends had long grown so familiar with this
peculiarity that they were sometimes rather surprised to find how
ludicrous it appeared to strangers.
Hamilton was fortunate in finding, while still at a very early age, a
career open before him which was worthy of his talents. He had not
ceased to be an undergraduate before he was called to fill an
illustrious chair in his university. The circumstances are briefly
as follows.