TELESCOPIC TESTS NEBULA. 



Fig, 



in fig. 10, a faint and rather indistinct indication of minute stars 



being perceptible ; but when a still higher power is brought to 



bear upon it, the object will be 



seen as what it really is, a 



dense mass consisting of countless 



numbers of separate stars, as 



shown in fig. 11. 



18. Different nebulae require 

 telescopes of different powers, and 

 many have never been yet re- 

 solved, even by the greatest 

 powers that scientific art has yet 

 produced. In proportion, how- 

 ever, as the telescopic power has 

 been increased, more and more 

 of these objects have been re- 

 solved. A remarkable illustration 

 of this state of progressive discovery is supplied in the case of a 

 well-known nebula, first observed and drawn by Sir John 

 Herschel, as seen in a twenty-foot reflector. Sir John 



Fig. 10. 



Fig. 11. 



describes it as an object shaped like a dumb-bell, double-headed 

 shot, or hour-glass ; the elliptic outline being filled up by a more 

 feeble and nebulous light, as shown in fig. 12, copied from the 

 drawing of Sir John Herschel. 



Such was the form and character assigned to this object until 

 Lord Rosse had constructed larger and more powerful instruments, 

 and when he directed upon it a twenty-seven foot reflector witli 

 three feet aperture, it assumed the appearance shown in fig. 13y 

 where a faint indication of stars can be seen ; subsequently r 



57 



