PKESIDENT S ADDRESS SECTION A. »< 



sets of photographs — one including stars down to the fourteenth 

 magnitude, the other set to take stars to the eleventh magnitude 

 only. These are to be measured and catalogued for reference, and 

 the heavens have been divided into eighteen portions as nearly equal 

 as possible. 



On March loth, 1888, Professor Vogel*'" announced in a paper 

 read before the Royal Prussian Academy that he had found in 

 taking photographs of the spectra of stars that the vibrations of 

 our atmosphere, which are so exceedingly troublesome to the eye, 

 rendering it oftentimes impossible to make a measure, do not affect 

 the definition of a photograph of the spectrum at all. 



Dr. Huggins, as we have seen, was the first to use the spectro- 

 scope to determine the motion of stars in the line of sight, and 

 Professor VogeF' was the first to apply photography to recording 

 spectra in order to determine star motions in the line of sight. 

 For this purpose he used the 12in. equatorial at Potsdam to carry 

 the very fine spectrograph which he had designed. The work 

 was begun in September, 1888, and by May, 1891, all the stars 

 in the northern heavens, fifty-one in all, bright enough for the 

 purpose had been examined with this instrument, and their velo- 

 cities in the line of sight accurately determined. 



On December 29th, 1888, Dr. Isaac Roberts succeeded in 

 making a very fine photograph of the great nebula in Andromeda, 

 which is a startling revelation of its extent and complex character. 



At a meeting of the Royal Astronomical Society, March 8th, 

 1889, Captain Abney"**, the highest authority, replied, in answer to 

 a question, that •' I have made experiments and can say distinctly 

 there is, as far as I know, no light so feeble that an accumulation 

 of it will not give an image upon a photographic plate." And not 

 long since we were told, upon other authority, that a good photo- 

 graph of a dark interior of a building has been taken and required 

 seven whole days' exposure. There seems then no reason why 

 exposures should not be continued night after night, reaching 

 fainter and fainter lights. 



Professor Pickering®" had a startling report to make in the fact 

 that the work of photographing the spectra of all stars down to 

 the sixth magnitude, between 25° south declination and the North 

 Pole, was completed in May, 1889, and that it contained 10,800 

 stars and '28,600 spectra ; that in practice it was found that 

 planetary spectra are readily distinguished from those of stars, and 

 it had been decided to take the Bache telescope to Arequipa, and 

 continue this survey to the South Pole, and Mrs. Draper has 

 enlarged her original gift in order to determine the spectra of all 

 stars down to the tenth magnitude ; the original 28in. reflector 

 made by Dr. Draper for star spectrum work is to be used. In 

 1888 and 1889 Dr. Huggins secured photographs of the spectra 

 of the nebula in Orion, confirming his results obtained in 1882, 

 only altering the wave length of one line from 3,730 to 3,724, and 



