1 873-1 Colours and their Relations. jj 



are separate from each other, and that only those atoms 

 yielding this particular bright line are in sufficient quantity 

 to originate a light of such intensity as to penetrate through 

 so great a distance as that at which these nebulas are placed. 



This particular phenomenon it has been sought to explain 

 by the fact, observed by Messrs. Frankland and Lockyer, 

 that when attenuated hydrogen is illuminated by the elec- 

 trical discharge, and the spectrum produced is viewed at a 

 considerable distance, all the bright lines disappear, save 

 that corresponding to F. But this explanation is incon- 

 sistent with the fact that all the four hydrogen lines are 

 distinguishable in the spectrum of the solar chromosphere. 

 Moreover, the disappearance of all the lines but F from the 

 spectrum of attenuated hydrogen, when viewed at a distance, 

 is a fact which itself requires explanation; and the simplest 

 is afforded by the supposition that, in each ultimate of 

 hydrogen, the atoms which vibrate in unison with the line F 

 considerably exceed in number those which give rise to the 

 other three bright lines. It appears very unlikely that, 

 were all the ultimates of hydrogen themselves individual 

 atoms of the same bulk and weight, a greater number of 

 them should elect to vibrate in unison with the F line than 

 with the three other bright lines ; while we should be left 

 without any assignable reason why such atoms, if all exactly 

 alike, should not, every one of them, vibrate in exactly the 

 same time, and so give rise to only one bright line. 



It has been recently pointed out by Mr. G. Johnston Stoney 

 that the wave-lengths of the ist, 2nd, and 4th hydrogen 

 lines stand to each other approximately in the following 

 relation — 2oH I = 27H 2 = 32H 4 ; whence he infers that these 

 three may be harmonics derived from one and the same 

 fundamental vibration (Phil. Mag., Aug., 1868). To this 

 conclusion, however, is opposed the fact of the preponder- 

 ance of H 2 or F over all the others; and still more the 

 phenomenon already noted that, in two distinct observations 

 on the solar prominences, the line H 2 or F was violently 

 agitated, while H z or C remained unaffected. These two 

 facts it appears impossible to explain, except on the supposi- 

 tion that C and F have their origin in two distinct sets of 

 atoms, capable of existing either separately, constituting 

 different gases, or united into one ultimate — that of hydrogen 

 gas. In the sequel it will be shown on other grounds to be 

 extremely improbable that these two have their wave- 

 lengths in the exact ratio of 2oC = 27F. There remains, 

 moreover, the fact that the vibrations corresponding to the 

 line H 3 have no such numerical relations to the other three 



