58 



others which have acquired names for themselves, such as the 

 Horse-Shoe and the Dumb-Bell ; another is that in Andromeda, 

 and there is the ring-nebula in Lyra, very well known (represented 

 in diagram). 



In the observations that have been made lately with the 

 best and largest telescopes, in the first instance of Lassell 

 and Lord Rosse, both of which are reflecting telescopes of 

 the largest class, there has come to light a system of nebute 

 called spiral nebute (one is represented in this drawing). 

 They seem to have some bearing on the supposition that the 

 nebulse are contracting and getting into a rotatory state. But these 

 changes go on so slowly that whether human life is long enough to 

 see them we do not know. We have not been able to infer with 

 certainty any of the changes of which I speak ; the whole thing is 

 theoretical, but is in the highest degree probable. Supposing 

 things contracted together in this way, they would get rapid 

 rotation, and in their contraction they would become very hot. 

 Condensation of them would produce enormous heat, and we have 

 there sufficient explanation of the great heat we find in the centre 

 of the earth, or little below the surface of the earth in some 

 places. 



Now there is another circumstance connected not simply 

 with the nebulse but with other stars. We suppose, of course, that 

 the stars have been formed from the condensation of nebulse. A 

 series of scientific inferences, founded upon optical observations, 

 has come to light in late years, which has done more to reveal 

 some of the secrets of nature than anything before, — that is 

 spectroscopy. It is a word not generally understood by many of 

 my audience, and I cannot explain it, on this occasion, so fully as 

 I could wish. Sir Isaac Newton first made extensive use of a 

 prism of glass. Whether he invented the prism or not I cannot 

 say, but he was the first person who made a rational use of it. In 

 looking through a prism at anything, say at a lamp, you will see 

 into what strange colours its appearance is changed. We know 

 that on looking at a brilliant white lamp we see it partly red, and 

 blue, and green. We know it is not a change of the light, because 



