76 president's address — section a. 



photographs of the bright stars Castor and Vega, and now with 

 more sensitive collodion he was able to take the companion of 

 Zeta Urste Majoi'is, which is fifth magnitude and emerald green 

 in color, so would photograph in normal conditions. The time 

 required was eight seconds. Now the Brothers Henry photograph 

 such a star with a 13in. star camera in one-fifth of a second. 

 Bond's objective reduced to 13in. would take 10-7' to photograph 

 this star, and therefore fifty-three and a half times longer than it 

 does now. 



Hartnuj), in Liverpool, 1864, took 124 times longer for the moon 

 than it does in Sydney to-day. 



Mr. De La Rue's''' work in 1852 has already been mentioned, 

 and the photographs then taken without clock movement were so 

 promising that he determined to have a proper clock. This was not 

 finished till 1857, and he then devoted his whole energy and his 

 observatory to the study and practice of astronomical photography, 

 and everyone is aware of his pre-eminent success — success eclipsing 

 all that had been done before ; and even in the present day his work 

 must still be classed as good, but not equal to the best modern 

 efforts. 



At the British Association, in September, 1859, he exhibited two 

 original negatives of the moon, which would bear considerable 

 magnifying power — two enlargements from these Sin. in diameter, 

 other enlargements 3^in. diameter; photographs of Jupiter, showing 

 his belts and satellites ; and one of the Moon with Saturn near the 

 limb taken in fifteen seconds. 



From the same source I learn that experiments in lunar 

 photography were made by Lord Rosse with his 6ft. reflector. 

 Having no clock motion for the telescope, he applied to it a 

 sliding plate holder of the kind used by De La Rue in his first 

 experiments, but this is said not to have met all the exigencies of the 

 case. The telescope was wanted for other purposes, and from the fact 

 that no photographs with the great reflector were published, it is 

 probable they were not so good as it was hoped they would be. In 

 his best photographs of the moon'-" De La Rue claimed to have 

 recorded in a picture of the moon 1-roin. diameter details so small 

 that any subsequent change over a space measuring two miles each 

 way must be detected, and claimed^' to be able, with best weather 

 and chemicals, to get a photograph of dark parts of crescent moon 

 in from twenty to thirty seconds which would show all the parts 

 visible near the dark limb. 



Having made a new driving clock in 1857, Bond devoted the 

 great refractor at Harvard College to a series of experiments, 

 which lasted to 1858'--, making photographs of stars with various 

 apertures from the full 15in. down to lin., to ascertain the 

 possibility of classifying the stars by their photographic images 

 on the plate, which, being suitable for accurate measurement, he 



