374 Mr. A. A. Common [Feb. 26, 



In a recent pliotograpli of tlie Pleiades, wbicli the MM. Henry 

 have taken, they have obtained a picture of a nebula near Maia that 

 has not been seen before, and which has since been seen with the great 

 telescope at Pulkowa in Russia — a telescope very much larger than 

 that with which the photograph was taken. 



On this plate part of the nebula near Merope is also shown. 



[Photographs of Orion with exposures of from 1 to 80 minutes 

 were shown, and also photographs of the drawings made by the Bonds, 

 Lord Rosse, Trouvelot, and others, for comparison.] 



Of comets, I have here copies of two of the photograi^hs taken 

 at the Cape of Good Hope, in 1882. These pictures may be called 

 I)hotographs of stars from the immense number that have impressed 

 themselves on the plate. 



To others as well as to myself, these photographs came as a revela- 

 tion of the power of photography in this direction, and it is probably 

 to them that the increased attention lately given to stellar photo- 

 graphy is due. 



Thei'e are other applications of photography to the work of the 

 astronomer besides those I have mentioned. 



By the analysis of the light that comes to us from the heavenly 

 bodies the spectroscope tells us what elementary substances exist in 

 those bodies and in this most delicate research photography has 

 played a most important part, especially in dealing with that part of 

 the spectrum that the eye is not able to grasp. 



The fleeting image that requires all the care that the mind can 

 give to interpret is recorded by means of photography, and can then 

 be studied under the most favourable conditions. 



Such photographs cannot be shown in the same way as those I 

 have shown you to-night, nor can they be rendered intelligible except 

 to the very few who have made the consideration their study. 



The recording of the passage of a star past the wires of a transit 

 instrument has always hitherto been done by the eye, but it is quite 

 possible that here photography may come in for this purpose, and 

 render such observations free from personal equation, as the allowance 

 that has to be made for different powers of different brains to record 

 an event is called by astronomers. 



There is also a possibility that photograi^hy will be available to 

 record the paths of meteors and thus aid in a research that is engag- 

 ing more attention every day. 



The discovery of minor planets by means of photography cannot 

 be helped when such photographs of the heavens as those taken by 

 the MM. Henry are produced consecutively, a comparison from time 

 t(j time being sufficient to detect the disi^lacement in position that 

 they must undergo, and it is not too much to say that if Uranus had 

 not been discovered by Herschel, and in consequence of the disagree- 

 ment between the position this planet should have occupied, and those 

 it did occupy owing to the attraction of Neptune, and the subsequent 

 discovery of this planet by the entirely theoretical investigations of 



