200 Transactions of the Boijal Societu of South Africa. 
transit circle and equatorial. He also found time to visit Hamburg, 
Pulkova, Hanover, and most of the leading European observatories. 
" In this way," he says in his History of the Cape Observatory, " I 
made the acquaintance of the leading continental and some of the 
American astronomers, obtaining at the same time a very complete 
insight into the working and organization of large observatories." 
In 1874 the w^ell-known expedition to Mauritius took place, the object 
of which was, as far as Lord Lindsay and David Gill were concerned, to 
determine the distance of the sun from morning and evening observations 
of the minor planet Juno. The instrument used was the heliometer. 
Although it became afterwards Gill's favourite instrument, in 1874 he had 
had very little experience of the use of it. We mention this to exhibit 
his extraordinary aptitude and skill in the use of the most difficult 
instruments. 
There is some doubt as to whom the credit of the Mauritius expedition 
is due, but it has always seemed to the writer that, while the pecuniary 
burden naturally fell on Lord Lindsay, and that the inception of the 
expedition perhaps was his, the organization, spirit, and success of it 
belonged entirely to Gill. 
Through a number of accidents, adverse winds and calms delaying the 
arrival of Lord Lindsay's yacht, and clouds and bad weather hindering 
observations, the programme had to be considerably curtailed. In 1874 
Juno was in opposition on November 5th. It was intended that observa- 
tions should be begun on October 10th, thus giving nearly a month before 
and a month after the most favourable position of the minor planet But 
it was not till November 12fch, seven days after opposition, that observa- 
tions were begun, and then only twelve evening and eleven morning 
positions were obtained. 
The quality of the observations, however, and the originality and 
thoroughness of the mode of reduction, secured a result far away in 
advance of any previous determination. For all time the question of 
the sun's distance was lifted from out the uncertainties of science. 
Gill's Mauritius determination of the solar parallax gave a value, 
8-77" + 0-04". 
Besides this important service to science, the expedition also determined, 
by chronometer comparisons, the longitude of various points along the East 
Coast of Africa, thus ultimately linking up Greenwich with Cape Town. 
The chain of stations used in this determination was Greenwich — Berlin — 
Malta — Alexandria — Suez — x\den — Durban — Port Elizabeth — Cape Obser- 
vatory, and the resulting difference in longitude between Greenwich and 
the Cape Observatory, 
Ih. 13m. 54-70s. ; 
