402 Celestial Chemistry. 



less, due to the minute solid or liquid nucleus, and, perhaps, 

 is crossed by dark lines. The engraving could not possibly 

 represent this spectrum of sufficient faintness, and it is, there- 

 fore, not attempted. 



The significance of this discovery is invaluable. Terrestrial 

 physics show us that only liquid and solid bodies give a con- 

 tinuous spectrum, while gases alone, when rendered luminous 

 by heat, give out light which, after dispersion by the prism, 

 is found to consist of certain degrees of refrangibility only, 

 which appear as bright lines on a dark ground. Here there 

 was clear and unimpeachable evidence, according to the pre- 

 sent state of our knowledge, that large masses of gas exist ; and 

 these may be the nebulous matter of Herschel and Laplace, 

 which then is no fiction, and that we may yet fairly speculate on 

 the process of the origin of worlds from such a primal form. 



But other nebulae were to be tested. A very similar pla- 

 netary nebula, % 6, in Taurus Poniatowski, when examined, 

 gave precisely the same bright lines, with the merest suspi- 

 cion of a faint spectrum. 78 H. 1Y. Cygni gave the same three 

 bright lines, with a stronger continuous spectrum than the 

 nebula in Draco, extending from about D to Gr of the solar 

 spectrum. This nebula has a distinct 11th magnitude star 

 in the middle, which evidently produces the continuous 

 spectrum, and this opinion was confirmed by a most crucial 

 experiment. The cylindrical lens being removed from the 

 apparatus, it was found that the three bright lines still re- 

 mained of considerable length, corresponding to the diameter 

 of the telescopic image of the nebula, while the faint spectrum 

 became a narrow line, showing that the object producing it was 

 a point in the focus of the object-glass. 51 H. IV. Sagittarii is a 

 fainter planetary nebula, and the two brighter lines were seen, 

 and the third by glimpses. 1 H. IV. Aquarii had the three 

 bright lines sharp and distinct, but the indications of the faint 

 spectrum were mere suspicions. Though brighter than the hist . 

 this nebula probably contains very little matter in the liquid or 

 solid form. 



