president's address — SECTION A. 85 



position with another taken on the same scale a few years 

 hence, point out at once any change of position due to proper 

 motion, kc. 



When, on December 13th, 1885, the new star (Nova Orionis) 

 was discovered by ]Mr. Gore*"*, Professor Pickering's photographic 

 star charts, showing all the stars, became at once aA'ailable, and 

 one taken on November 9th, 1885, affords unmistakable evidence 

 that this star was then much fainter than it was five weeks later 

 when he discovered it. 



On the 15th March, 1885"^ a very brilliant am-ora at Christiana 

 was photographed by Mr. Sophus Tromholt. He used Viogtlander's 

 euroscopic No. 1 lens and rapid dry plates. Exposure of from two 

 to four minutes gave nothing, but one of eight and a half minutes 

 showed the light in the sky, with buildings outlined on it. This 

 M-as the first time an aurora had been photographed. 



On May 11th, 1885, Admiral Mouchez"^ at a meeting of the 

 Academic of Sciences, at Paris, stated the first experiment made 

 by MM. Paul and Prosper Henry with a camera, objective 6}in. 

 diameter, had proved so successful that a new instrument had been 

 Cunstructed, which had a star camera with objective of 13Jin., and 

 another telescope for a pointei' alongside of it for watching the clock 

 motion, and although it was not quite complete it had already yielded 

 some remarkable results, and seemed to solve the question how to 

 use photogi'aphy in mapping the heavens, taking in stars down to 

 the fourteenth or fifteenth magnitude. As we have already seen, it 

 was thought just twenty years before this that Rutherford's 

 star camera had solved this question, and so it had ; but the 

 astronomical world was not ready for such a gigantic step forward, 

 and therefore it had to wait vmtil the general progress in astrono- 

 mical photography had cleared the way for its adoption in 

 recording star positions. 



It was found by Professor Pickering in 1885 that photographs 

 of star spectra can be obtained by simply placing a large prism on 

 the outside of the object glass of the telescope"^ and he adopted 

 this method v/ith a star camera of short focus, and thus in an 

 exposure of five minutes the spectra of all stars down to the 

 sixth magnitvide, and included in an area 10° square, are recorded; 

 and arrangements have been made to photograph in this way the 

 spectra of all stars down to the sixth magnitude, and it is found 

 that the spectra of stars down to the tenth magnitude can in the 

 same way be got in one hour. 



In 1886 Professor Harkness** 2>i"oposed to get over the difficulty 

 caused by the heat of the sun on transit instruments by arranging 

 it so that a sensitive plate could be put near the wires, and a 

 momentary flash of light let in just enough to photograph the sun 

 and show the wires. 



Several others had proposed to photograph the stars in transit, 

 but nothing important has yet been done in this direction; but I 



