Sir David Gill. 
213 
much time and thought, that a definite spectrographic determination of 
the sun's parallax should be made. 
In 1908 Dr. Halm, from a series of spectrograms, derived a value of the 
solar parallax, 
8-804" + 0-004:". 
When the minor planet Eros ws^s discovered, Gill saw its importance 
as a stepping-stone to the sun's distance. He accordingly urged that a 
similar combined effort to that made in 1888 and 1889 should be under- 
taken at the planet's opposition during 1900 and 1901. This was done, 
and the observations were discussed by Hinks, of Cambridge, who obtained 
as the mean value of the sun's parallax, 
8-807" + 0-002". 
Although many astronomers would consider the determination of the 
sun's distance, and the improvements he effected in securing and reducing 
observations, as among Gill's most notable achievements, it is on his 
inception and furtherance of the great photographic star map that his 
fame depends with most men. 
His mind was early drawn to the importance of photography as an 
auxiliary to astronomical research, and although the peculiar circum- 
stances of his career compelled his thoughts to run in the direction of 
refined instrumental work, the possibility of one day using photography in 
depicting charting and defining the heavenly bodies never passed from his 
outlook. And thus there is nothing fortuitous in his discovery in 1882 
that it was possible to photograph the stars. Accident has little part in 
the life of a man like Gill. Yet there is always something dramatic about 
the advent of an epoch, be it historical or scientific. Suddenly, through 
some unexpected circumstance, we are hustled out of the old toilsome 
road, out into the newer and better way along which we may travel with 
greater ease and rapidity. The appearance of the southern great comet of 
1882 was the circumstance that ushered in stellar photography. But 
again, we aver, that Gill's mind was unconsciously prepared for the 
epoch-making change that the new discovery brought about. 
The comet was first seen by Finlay on September 8th. Early in 
October tidings reached Gill that the comet had been successfully photo- 
graphed by several people, the modern dry plate making possible what the 
wet plate could not. 
There being no suitable photographic lens at the Cape Observatory, and 
no one of the staff competently acquainted with the more recent methods 
of developing dry plates. Gill called to his aid Mr. Allis, of Mowbray, who 
at once entered most heartily into the enterprise. 
A camera with doublet of 2|-inch aperture and 11-inch focal length, 
was mounted on to the declination counterpoise of the 6-inch equatorial. 
