176 Tlxe Nebular Hypothesis : Its Present Condition. 



that they exist in a state of very low tension ; facts as I have already 

 t«tated, which are fatal to the hypothesis. It is, of course, possible 

 that similarly as the numerous lines of the sjDCCtra of nitrogen and 

 hydrogen are reduced to two or three in the nebular spectrum, in con- 

 sequence of the faintness of the light operated upon, to may the 

 width of the lines be diminished from a like cause ; but with this I 

 have nothing to do. It is my object merely to show at present, so ftir 

 as the spectroscope has afforded us increased knowledge of the state of 

 these bodies, it is fatal to the theory, and it remains for those who 

 uphold it in its integrity to establish by experiment that the spectrum 

 of a dense gas, when very faint, not only is reduced to a single line, 

 but that that line itself is narrow when the slit is narrow, as in the 

 case of rarefied gases. Unless the proposition can be established, 

 there remains no alternative but to reject the hypothesis, as an invit- 

 mg but fallacious guide to the explanation of the origin of the solar 

 system, and to look for some new theory, or for some modification of 

 the old one, for the solution of those problems which it would other- 

 wise afford. 



There are still further reasons for believing that the nebular 

 hypothesis in its old form is not altogether trustworthy, and though 

 of less weight, may help to turn the scale, at the same time that they 

 prepare the ground for an altered conception of it, free from thest^^ 

 objections. It has been necessary hitherto to assume that the nebul- 

 ous matter existed originally at a great heat, without suggesting, it 

 seems to me, any sufficient force by which this high temperature was 

 reached. This is, at least wanting in completeness, especially as there 

 is at hand, as I hope to show, the means by which the matter may 

 have been thus raised in temperature. But a still more fatal objection 

 would appear to be, that the glass which have been identified in the 

 nebulae do not seem to be, in themselves, adequate to form a system 

 such as our own, unless by the addition of foreign matter from with- 

 out. Probably no advocate of Mr. Lockyer's theory of the disassocia- 

 tion of the material molecules into their primary or truly elementary 

 components by enormous heat, will go so far as to imagine that the 

 two known gaseous constitutents of the nebula?, together with one 

 other unknown substance, is all that is essential to form a globe such 

 as our own sun, especially when it has been proved that the actual 

 materials required are known to exist in the immediate neighborhood-, 

 and appear to have no other use in the economy of the universe than 

 that of forming with the nebulee suns and systems such as our own. 



It is, perhaps, scarcely necessary to point out that it is to the 

 cometary system that I allude as capable of supplying the necesearj 



