he entered Trinity College, Cambridge, as a sizar, meaning that
he paid a reduced fee but essentially worked as a servant to make
good the fee reduction. Here he had a brilliant career, and seems
to have been almost immediately recognized as the leading man of
his year. In 1822 he was elected scholar of Trinity, and in the
following year he graduated as senior wrangler and obtained first
Smith's prize. On October 1, 1824 he was elected fellow of Trinity,
and in December 1826 was appointed Lucasian professor of mathematics
in succession to Thomas Turton. This chair he held for little more
than a year, being elected in February 1828 Plumian professor of
astronomy and director of the new Cambridge observatory.
idea of his activity as a writer on mathematical and physical
subjects during these early years may be gathered from the fact
that previous to this appointment he had contributed no less than
three important memoirs to the Philosophical Transactions of the
Royal Society, and eight to the Cambridge Philosophical Society.
At the Cambridge observatory Airy soon showed his power of organization.
The only telescope in the establishment when he took charge was
the transit instrument, and to this he vigorously devoted himself.
By the adoption of a regular system of work, and a careful plan
of reduction, he was able to keep his observations up to date,
and published them annually with a punctuality which astonished
his contemporaries. Before long a mural circle was installed,
and regular observations were instituted with it in 1833. In the
same year the Duke of Northumberland presented the Cambridge observatory
with a fine object-glass of 12 in. aperture, which was mounted
according to Airy's designs and under his superintendence, although
construction was not completed until after he moved to Greenwich
writings during this time are divided between mathematical physics
and astronomy. The former are for the most part concerned with
questions relating to the theory of light arising out of his professorial
lectures, among which may be specially mentioned his paper "On
the Diffraction of an Object-Glass with Circular Aperture,"
and his enunciation of the complete theory of the rainbow. In
1831 the Copley Medal of the Royal Society was awarded to him
for these researches. Of his astronomical writings during this
period the most important are his investigation of the mass of
Jupiter, his report to the British Association on the progress
of astronomy during the 19th century, and his work On an Inequality
of Long Period in the Motions of the Earth and Venus.
of the sections of his able and instructive report was devoted
to "A Comparison of the Progress of Astronomy in England
with that in other Countries," very much to the disadvantage
of England. This reproach was subsequently to a great extent removed
by his own labours.
discovery of a new inequality in the motions of Venus and the
earth is in some respects his most remarkable achievement. In
correcting the elements of Delambre's solar tables he had been
led to suspect an inequality overlooked by their constructor.
The cause of this he did not long seek in vain; Eight times the
mean motion of Venus is so nearly equal to thirteen times that
of the earth that the difference amounts to only a small fraction
of the earth's mean motion, and from the fact that the term depending
on this difference, although very small in itself, receives in
the integration of the differential equations a multiplier of
about 2,200,000, Airy was led to infer the existence of a sensible
inequality extending over 240 years (Phil. Trans. cxxii. 67).
The investigation was probably the most laborious that had been
made up to Airy's time in planetary theory, and represented the
first specific improvement in the solar tables effected in England
since the establishment of the theory of gravitation. In recognition
of this work the Gold Medal of the Royal Astronomical Society
was awarded to him in 1833 (he would win it again in 1846).
June 1835 Airy was appointed Astronomer Royal in succession to
John Pond, and began his long career at the national observatory
which constitutes his chief title to fame. The condition of the
observatory at the time of his appointment was such that Lord
Auckland, the first lord of the Admiralty, considered that "it
ought to be cleared out," while Airy admitted that "it
was in a queer state." With his usual energy he set to work
at once to reorganize the whole management. He remodelled the
volumes of observations, put the library on a proper footing,
mounted the new (Sheepshanks) equatorial and organized a new magnetic
observatory. In 1847 an altazimuth was erected, designed by Airy
to enable observations of the moon to be made not only on the
meridian, but whenever it might be visible. In 1848 Airy invented
the reflex zenith tube to replace the zenith sector previously
employed. At the end of 1850 the great transit circle of 8 inch
(203 mm) aperture and 11 ft 6 inch (3.5 m) focal length was erected,
and is still the principal instrument of its class at the observatory.
The mounting in 1859 of an equatorial of 13 inch (330 mm) aperture
evoked the comment in his journal for that year, "There is
not now a single person employed or instrument used in the observatory
which was there in Mr Pond's time"; and the transformation
was completed by the inauguration of spectroscopic work in 1868
and of the photographic registration of sun-spots in 1873.
formidable undertaking of reducing the accumulated planetary observations
made at Greenwich from 1750 to 1830 was already in progress under
Airy's supervision when he became Astronomer Royal. Shortly afterwards
he undertook the further laborious task of reducing the enormous
mass of observations of the moon made at Greenwich during the
same period under the direction, successively, of James Bradley,
Nathaniel Bliss, Nevil Maskelyne and John Pond, to defray the
expense of which a large sum of money was allotted by the Treasury.
As the result, no less than 8,000 lunar observations were rescued
from oblivion, and were, in 1846, placed at the disposal of astronomers
in such a form that they could be used directly for comparison
with the theory and for the improvement of the tables of the moon's
this work Airy received in 1848 a testimonial from the Royal Astronomical
Society, and it at once led to the discovery by P.A. Hansen of
two new inequalities in the moon's motion. After completing these
reductions, Airy made inquiries, before engaging in any theoretical
investigation in connection with them, whether any other mathematician
was pursuing the subject, and learning that Hansen had taken it
in hand under the patronage of the king of Denmark, but that,
owing to the death of the king and the consequent lack of funds,
there was danger of his being compelled to abandon it, he applied
to the admiralty on Hansen's behalf for the necessary sum. His
request was immediately granted, and thus it came about that Hansen's
famous Tables de la Lune were dedicated to La Haute Amirauté
de sa Majesté la Reine de la Grande Bretagne et d'Irlande.
of the most remarkable of Airy's researches was his determination
of the mean density of the earth. In 1826 the idea occurred to
him of attacking this problem by means of pendulum experiments
at the top and bottom of a deep mine. His first attempt, made
in the same year, at the Dolcoath mine in Cornwall, failed in
consequence of an accident to one of the pendulums; a second attempt
in 1828 was defeated by a flooding of the mine, and many years
elapsed before another opportunity presented itself. The experiments
eventually took place at the Harton pit near South Shields in
1854. Their immediate result was to show that gravity at the bottom
of the mine exceeded that at the top by 1918 6th of its amount,
the depth being 1,256 ft (383 m) From this he was led to the final
value of 6.566 for the mean density of the earth as compared with
that of water (Phil. Trans. cxlvi. 342). This value, although
considerably in excess of that previously found by different methods,
was held by Airy, from the care and completeness with which the
observations were carried out and discussed, to be "entitled
to compete with the others on, at least, equal terms."
1872 Airy conceived the idea of treating the lunar theory in a
new way, and at the age of seventy-one he embarked on the prodigious
toil which this scheme entailed. A general description of his
method will be found in the Monthly Notices of the Royal Astronomical
Society, vol. xxxiv, No. 3. It consisted essentially in the adoption
of Delaunay's final numerical expressions for longitude, latitude
and parallax, with a symbolic term attached to each number, the
value of which was to be determined by substitution in the equations
this mode of treating the question the order of the terms is numerical,
and though the amount of labour is such as might well have deterred
a younger man, yet the details were easy, and a great part of
it might be entrusted to "a mere computer". (Note that
at the time that this was written, the term "computer"
referred to a human being who performed calculating work, either
manually or with mechanical aids).
work was published in 1886, when its author was eighty-five years
of age. For some little time previously he had been harassed by
a suspicion that certain errors had crept into the computations,
and accordingly he addressed himself to the task of revision.
But his powers were no longer what they had been, and he was never
able to examine sufficiently into the matter. In 1890 he tells
us how a grievous error had been committed in one of the first
steps, and pathetically adds, "My spirit in the work was
broken, and I have never heartily proceeded with it since."
In 1881 Sir George Airy resigned the office of Astronomer Royal
and resided at the White House, Greenwich, not far from the Royal
Observatory, until his death.
complete list of Airy's printed papers, numbering no less than
518, will be found in his Autobiography, edited in 1896 by his
son, Wilfrid Airy, B. A., M. Inst.C.E. Amongst the most important
of his works not already mentioned may be named the following:
Tracts (1826) on the Lunar Theory,
Figure of the Earth, Precession and Nutation, and Calculus of
Variations, to which, in the second edition of 1828, were added
tracts on the Planetary Theory and the Undulatory Theory of Light;
Experiments on Iron-built Ships, instituted for the purpose of
discovering a correction for the deviation of the Compass produced-by
the Iron of the Ships (1839).
On the Algebraical and Numerical Theory of Errors of Observations
and the Combination of Observations (1861).
crater Airy on Mars is named in honor of George Biddell Airy.
Within that crater lies another smaller crater called Airy-0 whose
location defines the prime meridian of that planet, as does the
location of Airy's 1850 telescope for Earth. There is also an
Airy crater on the Moon named in his honor.