FEBRUARY 5, 1914] 
NATURE 
637 
earth’s revolution carries it to or from them. As 
a corollary to these important researches, the 
mass of the moon was determined from the dis- | 
placement of the observer’s position, arising from 
the movement of the earth about the centre of 
gravity of the earth and moon. 
In 1882 photographs of the great comet were 
taken, under Gill’s auspices, with an ordinary 
camera strapped on an equatorial telescope. Not- 
withstanding its small optical power, a surprising 
number of stars were shown in excellent defini- 
tion over a considerable field. This suggested 
the possibility of employing similar but more 
powerful means for mapping the stars. Gill im- 
mediately took steps to obtain a suitable lens, 
and in January, 1885, having obtained 3ool. from 
the Government Grant Committee, commenced 
a photographic durchmusterung of the southern 
sky. Prof. J. C. Kapteyn, of Groningen, volun- 
teered to measure the photographs, and from the 
cooperation of the two astronomers a compre- 
hensive survey of the sky was made from 19° S. 
declination to the south pole, containing more than 
450,000 stars. 
The photographs of this comet were fruitful 
in another manner. Copies of them, with a short 
explanatory note, were forwarded to Admiral 
Mouchez, the Director of the Paris Observatory, 
and were communicated by him to the French 
Academy. Their excellence led Admiral Mouchez 
to encourage the brothers Henry, who were en- 
gaged in charting the zodiac, to devote their 
attention to the construction of astrographic 
lenses. In this they had signal success, and after 
further correspondence between Gill and Mouchez, 
a conference was called at Paris in 1877 for the 
execution of an international chart and catalogue 
of the whole sky by photographic means. In 
this important work Gill took a keen interest and 
exercised great influence. He attended all the 
meetings of the Comité permanent in Paris, where 
he delighted to discuss with his colleagues the 
details of a great project which has been con- 
stantly advanced by his enthusiasm and energy. 
Soon after Gill’s appointment as H.M. Astro- 
nomer of South Africa, he laid before Sir Bartle 
Frere, who was Governor of Cape Colony and 
High Commissioner for South Africa, a compre- 
hensive scheme for a geodetic survey of the 
country. His recommendations included a grid- 
iron system of principal triangulation extending 
over Cape Colony, the Orange Free State, Natal, 
and the Transvaal. There were considerable 
delays at the start, but little by little the great 
project was carried out always under the unify- 
ing direction of Gill. In 1896 he suggested that 
the progress made in geodetic survey in South 
Africa should be regarded as a first step in a 
chain of triangulation which, approximately 
traversing the thirtieth meridian of east longitude, 
should extend continuously to the mouth of the 
Nile. He never lost any opportunity of forward- 
ing this important geodetic project, and had the 
satisfaction of seeing the great arc of meridian 
measured from latitude 31° 36/ in the extreme 
NO. 2310, VOL. 92] 
south of Africa so far north as Lake Tanganyika 
in lat, 9° 41’. 
Gill remained at the Cape as H.M. Astronomer 
for twenty-eight years. In this period he re- 
modelled the fundamental meridian work of the 
observatory, introduced photographic astronomy, 
and achieved results of the highest importance 
with the heliometer. The generous gift of the 
Victoria telescope by Mr. F. McClean (a 24-in. 
photographic telescope with objective prisms and 
spectroscope) enabled work in astrophysics to be 
added to the activities of the observatory. In 
addition to the staff of the observatory, a number 
of astronomers were attracted to the Cape and 
worked there guided by Gill’s counsel and stimu- 
lated by his enthusiasm. In this connection the 
names of Elkin, de Sitter, Cookson, and Franklin- 
Adams are readily recalled. .In 1905 the British 
Association visited South Africa, and Gill had the 
greatest pleasure in showing them the great 
observatory which owed so much to him. The 
success of this memorable visit was largely due to 
the great respect and admiration entertained for 
Gill by the visitors from Europe and their hosts in 
South Africa. 
He left the Cape in October, 1906, and took 
up his residence in London. His time was very 
fully occupied in writing the history and descrip- 
tion of the Cape Observatory (see Nature, Janu- 
ary 15, p. 556), and in the activities of a number 
of scientific societies into which he entered with 
zest. He served on the council of the Royal 
Society, 1908-9 and 1910-11; on that of the 
Royal Astronomical Society from 1907-13, being 
president from 1910-12, and succeeding Huggins 
as foreign secretary in 1912; and on the council 
of the Royal Geographical Society, 1908-10 and 
1911-12. He was, president of the British Asso- 
ciation at the Leicester meeting in 1907. He was 
constantly consulted by astronomers, particularly 
in the design of instruments. Another subject in 
which he was greatly interested was the manu- 
facture of optical glass for large telescopes. His 
interests embraced not only the practical branches 
of astronomy and geodesy in which his own work 
had been done; he followed the recent researches 
in solar and stellar spectroscopy, in gravitational 
astronomy, and especially those bearing on the 
extent and movements of the sidereal system. 
The signal services which he rendered to science 
were recognised by his creation as Knight Com- 
mander of the Bath, as Knight of the Prussian 
Order Pour le Mévite, and as Commander of the 
Legion of Honour of France. Honorary degrees 
were conferred upon him by the Universities of 
Oxford, Cambridge, Edinburgh, Aberdeen, 
Dublin, and the Cape of Good Hope. He was 
corresponding member of the leading academies 
of Europe and America. He received the Valz 
medal of the Institut of France in 1882, the gold 
medal of the Royal Astronomical Society the same 
year ; the Bruce medal of the Astronomical Society 
of the Pacific in 1900, and the Watson medal of 
the National Academy of the United States in 
the same year; a royal medal of the Royal Society 
