SIR DAVID GILL EDDINGTON. 513 



Mauritius that he first began to use the heliometer, an instrument 

 with which his most celebrated researches were afterwards made. 

 The 4-inch heliometer of the Dun Echt Observatory (afterwards pur- 

 chased for the Cape) was made under Gill's superintendence by Rep- 

 sold ; and whilst it was in the course of construction he took the op- 

 portunity to visit Hamburg for the meeting of the Astronomische 

 Gesellschaft in 1873. Besides attending this congress, Gill visited 

 several of the continental observatories, and in this way made the 

 acquaintance of the leading European astronomers, and also obtained 

 an insight into the organization of the large observatories. 



The Mauritius expedition introduced him to two of the great prob- 

 lems, which more especially he made his life's work — ^the determina- 

 tion of the solar parallax and the problems of geodetic measure- 

 ments. Deferring, for the present, consideration of the scientific 

 results of this expedition and of another expedition to Ascension 

 Island in 1877, we pass on to the next great step in his career. 



Early in 1879 David Gill was appointed by the admiralty to be 

 Her Majesty's astronomer at the Cape of Good Hope, in succession 

 to Mr. E. J. Stone. Before sailing for the Cape he made another tour 

 of the European observatories, visiting Paris, Leiden, Groningen, 

 Hamburg, Copenhagen, Helsingfors, and Poulkovo. Perhaps the 

 most important fruit of these visits was his acquaintance with Dr. 

 Auwers and Dr. EUdn, which led to much valuable cooperation be- 

 tween them. 



On the 29th of May, 1879, he arrived at Cape Town and took up 

 his duties at the observatory. The only instruments which he found 

 in use were the Airy transit circle, a 7-inch equatorial, and a photo- 

 heliograph. The observatory, founded in 1820, had fulfilled a useful 

 duty by the regular work of meridian observation, the early Cape 

 Catalogues being a most valuable source for the positions of the 

 southern stars. Its history had also been marked by one conspicuous 

 achievement — Henderson's detection of the parallax of a Centauri, 

 the first proof that the parallax of a fix^d star could amount to a 

 measurable quantity. Whilst the instruments and observations might 

 be open to many criticisms, the work was, for that period, fairly effi- 

 cient. But the standard of precision was being raised, and Gill's 

 standard was the highest of his time. To his mechanical insight the 

 faulty design and unsatisfactory repair of the old instruments was 

 apparent, and he would not rest until the defects were remedied. 

 He was no believer in the Airy type of transit circle, incapable of re- 

 versal, but it was many years before he could obtain an instrument 

 according to his ideals. Meanwhile it was necessary to make the 

 best of the existing telescope. The object glass was deteriorated, the 

 micrometer screws were worn, and the whole instrument was in need 

 18618°— SM 1915 33 



