MAN THE INTERPRETER OF NATURE. 193 



either causing them to be entirely overlooked, or veiling the as- 

 sunnptions on which they are based. Thus Mr. Lockyer speaks as 

 confidently of the sun's chromosphere of incandescent hydrogen, 

 and of the local outbursts which cause it to send forth projections 

 tens of thousands of miles high, as if he had been able to capture 

 a flask of this gas, and had generated water by causing it to unite 

 with oxygen. Yet this confidence is entirely based on the as- 

 sumption, that a certain line which is seen in the spectrum of a 

 hydrogen flame, means hydrogen also when seen in the spectrum 

 of the sun's chromosphere ; and high as is the probability of that 

 assumption, it cannot be regarded as a demonstrated certainty, 

 since it is by no means inconceivable that the same line fiiight be 

 produced by some other substance at present unknown. And so 

 when Dr. Huggins deduces from the different relative positions 

 of certain lines in the spectra of different stars, that these stars 

 are moving from or towards us in space, his admirable train of 

 reasoning is based on the assumption that these lines have the same 

 meaning — that is, that they represent the same elements — in every 

 luminary. That assumption, like the preceding, may be regarded 

 as possessing a sufficiently high probability to justify the reasoning 

 based upon it ; more especially since, by the other researches of 

 that excellent observer, the same chemical elements have been 

 detected as vapours in those filmy cloudlets which seem to be 

 stars in an early stage of consolidation. But when Frankland and 

 Lockyer, seeing in the spectrum of the yellow solar prominences 

 a certain bright line not identifiable with that of any known ter- 

 restrial flame, attribute this to a hypothetical new substance which 

 they propose to call Helium, it is obvious that their assump- 

 tion rests on a far less secure foundation ; until it shall have 

 received that verification, which, in the case of Mr. Crookes's 

 researches on Thallium, was afforded by the actual discovery 

 of the new metal, whose presence had been indicated to him by 

 a line in the spectrum not attributable to any substance then 

 known. 



In a large number of other cases, moreover, our scientific inter- 

 pretations are clearly matters of yW-,'-;//^///; and this is eminently 

 d. personal act, the value of its results depending in each case upon 

 the qualifications of the individual for arriving at a correct decision. 



