THE PHOTOGKAPHIC CHAKT OF THE HEAVENS. 65 



(in the photographs) a vast number of stars appearing as of the 

 14th magnitude, which the eye cannot see through the telescope, 

 just as I found in Kappa Crucis. The longer exposure given in 

 order to secure visible 14th magnitude stars, resulted in recording 

 a large number of stars photographically of 14th magnitude, but 

 wholly invisible through the telescope. At the recent meeting of 

 the Committee, it was decided on the evidence given by Dr. 

 Schemer, to extend the time of exposure for 14th magnitude 

 stars to forty minutes, and it is reasonable to expect, since all are 

 interested and working at this difficulty, that it will soon be solved, 

 and times of exposure in different states of the atmosphere agreed 

 upon. At present there seems to be no possibility of dealing with 

 the colour difficulty which is a serious one, as I have already 

 pointed out. Great differences are found also in the sensitive 

 plates, we have tried Swan's, Wratten and Wainwright, Field 

 Dodgsons star plates, M. A. Seed plates (American), and Ilford 

 plates; and so far as I have gone, the Ilford plates are certainly 

 the best for our purpose. 



In my photographs of the Great Magellan Cloud taken with 

 the portrait camera, which I exhibited at the November meet- 

 ing, the stars owing to their countless numbers appear as blurred 

 masses, and the great and remarkable nebula 30 Doradus is only 

 a white spot. With the Star Camera the picture is enlarged 

 eighteen times, and the stars are separated and brought out sharply 

 denned, while the nebula 30 Doradus is revealed in its wonderful 

 complexity, and shewn to be much more extensive than Herschel 

 made it with his great reflector, so that quite a new light is 

 brought out by the Star Camera, and is thrown on the structure 

 of this object. 



There is one thing about this nebula which is very suggestive,, 

 some of its loops are round, and all its features seem to be laid 

 out, as if in a plane at right angles, or nearly so to the line of sight; 

 there are no decided elliptical forms, which so commonly appear in 

 nebulae, owing to their circular forms being oblique to the line of 

 sight, and therefore projected into ellipses. If we look at the main 



E— July 1, 1891. 



