SIR DAVID GILL. 883 



SIR DAVID GILL (1843-1914) 



Foreign Honorary Member in Class I, Section 1, 1910. 



David Gill was born at Aberdeen, Scotland, on June 12, 1843. 

 His higher education was received in Marischal College and Univer- 

 sity, Aberdeen. There he came under the inspiring influence of 

 James Clerk Maxwell. Gill's tastes had developed along the lines 

 of physics and chemistry, but his father, who was a prosperous horol- 

 ogist, influenced the son to enter the clock business. David Gill 

 mastered both the commercial and the technical sides of the work, 

 but he did not cease to dream about a career in pure science. Such 

 time as could be spared from business, beginning with 1863, he devoted 

 to re-establishing the observatory of King's College in Aberdeen 

 University, as a basis for supplying accurate time signals to the 

 university and city. In the years 1868-73 he gave much spare time 

 to the construction and use of his own observatory in Aberdeen. 

 He designed the mounting for a 12-inch reflecting telescope, and with 

 his own hands constructed the excellent driving clock of the telescope. 

 His observations related mostly to double stars and nebulae. 



In 1872 he gave up his well established and prosperous business in 

 order to devote his talents exclusively to astronomical science. He 

 accepted the invitation of .the Earl of Crawford and his son. Lord 

 Lindsay, to take charge of the splendid private observatory which 

 they had decided to construct at Dun Echt. Lord Lindsay's plans 

 included an expedition to the Island of Mauritius to observe the 

 transit of Venus, in 1874. Lindsay and Gill took advantage of the 

 trip to determine the longitude of Mauritius, by means of telegraphic 

 signals sent between Greenwich and Aden, and thence by transport 

 of clxronometers between Aden and Mauritius. While at Mauritius 

 Gill made heliometer observations of the minor planet Juno, for a 

 new determination of the value of the solar parallax. This was the 

 beginning of a long series of heliometer observations by Gill to improve 

 our knowledge of the Sun's distance from the Earth. 



On the return journey from Mauritius Gill accepted the invitation 

 of the Government of Egypt to measure a primary base line near the 

 Pyramids of Gizeh for the projected geodetic survey of Egypt. 



Gill's expedition to the Island of Ascension to observe Mars at the 

 especially close approach of that planet in 1877, to determine anew 

 the solar parallax, was a memorable event in his career. The success 



