1887.] on the Amplications of Photography in Astronomy. 169 



the focus of his telescope, so sensitive are the plates he has employed, 

 that the detail of the brighter parts has been completely burnt out, 

 but a great deal of new found detail is brought to light. 



Here is another photograph of the same object by Professor 

 Pickering, taken with a four lens objective of eight inches aperture 

 and very short focus, and including a field of 5 degrees square. 

 Exposure 82 min. This shows what can be done with such a com- 

 bination. 



In 1885 the brothers Henry, photographing the Pleiades on Novem- 

 ber 16th, discovered a new nebula, near the bright star Maia in the 

 group. Here on the screen is a co-pj of the original negative by 

 which the discovery was made. You observe the nebula like a filmy 

 projection from one of the stars. 



After the nebula had been discovered by photography it was found 

 to be visible in the great telescope of 30 inches aperture at Pulkowa. 

 But to discover is one thing, to see after discovery is another. 



Strangely enough this new nebula was really photographed a 

 fortnight before its discovery at Paris, by Professor Pickering at 

 Cambridge in America. In exhibiting the photograph to the National 

 Academy of Sciences five days before Henry's discovery, Professor 

 Pickering pointed out the " wing" attached to the star, but there was 

 only one plate shown, the impression was that the mark was due to a 

 defect in the gelatine film. 



Here, however, is another picture of the Pleiades taken at Cam- 

 bridge with the same instrument an^ an exposure of eighty-two 

 minutes, which shows nebulosity about more than one star of the 

 group. 



And here is a copy of a negative by Mr. Eoberts, of Liverpool, 

 with an exposure of three hours. The star discs are of course large 

 and ill defined ; but the quantity of nebula, invisible to the eye in the 

 largest telescopes, is quite surprising. 



These photographs appear to prove conclusively that the nebula 

 and the stars in this group are one system ; the doctrine of chances 

 renders it almost an impossibility to suppose that such a symmetrical 

 arrangement of nebulous matter with respect to the stars could exist 

 by chance, if the stars were projected in front of a far distant back- 

 ground of nebulous matter. 



Here is a photograph of the stars surrounding the celebrated 

 variable star r) Argus, taken at the Cape with the telescope of 9 inches 

 aperture, generously presented to me for such work by Mr. James 

 Nasmyth. The nebula surrounding this star is very faint compared 

 with the Orion nebula, and it seems to be deficient in actinic rays, and 

 besides, the telescope is intended for stellar photography by its long 

 focal length, and not for nebulae, which require a shorter proportional 

 focus — i. e. more intrinsically brilliant image. 



Still there is the nebula, and I believe this is the only existing 

 photograph of the object. The exposure was 2J hours, and yet 

 although the original negative has been enlarged four diameters the 



