6io THE POPULAR SCIENCE MONTHLY, 



garded as the basis of all subsequent work, he is careful to state that 

 the sixty iron lines in the sun, to which he referred, only agree " as a 

 rule " in intensity with those observed in the electric spark. Those who 

 have given an account of his work have not always been so cautious. 

 Indeed, I find Professor Roscoe ' running far beyond the record in the 

 following sentence : 



In order to map and determine the positions of the bright lines found in the 

 electric spectra of the various metals, Kirchhoff, as I have already stated, em- 

 ployed the dark lines in the solar spectrum as his guides. Judge of his aston- 

 ishment when he observed that dark solar lines occur in positions connected 

 with those of all the bright iron lines ! Exactly as the sodium lines were iden- 

 tical with Fraunhofer's lines, so for each of the iron lines, of which KirchhoflE 



o 



and Angstrom have mapped no less than 460, a dark solar line was seen to cor- 

 respond. Not only had each line its dark representative in the solar spectrum, 

 hut the 'breadth and degree of shade of the tico sets of lines icere seen to agree in 

 the most perfect manner, the brightest iron lines corresponding to the darkest solar 

 lines. 



This statement w-as made to prove the absolutely identical nature 

 of the iron vapor in the sun's atmosphere and in the electric spark. As 

 the statement is not true, the vapors can hardly be identical. 



Such, then, is the reasoning on which I base the two counts in the 

 indictment against the simple nature of the elementary bodies. 



First, the common lines visible in the spectra of different elements 

 at high identical temperatures point to a common origin. Secondly, 

 the different lines visible in the spectra of the same substance at high 

 and low temperatures indicate that at high temperatures dissociation 

 goes on as continuously as it is generally recognized to do at all lower 

 temperatures. 



In my paper I attempt to show that if we grant that the highest 

 temperatures produce common bases — in other words, if the elements 

 are really compounds — all the phenomena so difficult to account for on 

 the received hypothesis find a simple and sufficient explanation. And, 

 with regard to the second count, I discuss the cases of calcium, iron, lith- 

 ium, and hydrogen. I might have brought, and shall subsequently bring, 

 other cases forward. In all these I show that the lines most strongly 

 developed at the highest temperatures are precisely those which are 

 seen almost alone in the spectra of the hottest stars, and which are 

 most obviously present in the spectrum of our own sun. Now, if it be 

 true that the temperature of the arc breaks up the elements, then the 

 higher temperature of the sun should do this in a still more effective 

 manner. Here, then, we have a test. 



I have put this question to the sun, and I have sent in a second 

 paper to the Royal Society embodying a preliminary discussion of Pro- 

 fessor Young's work at Sherman, Tacchini's observations, and my own. 

 In this paper I state my grounds for the belief that all the solar phe- 

 ^ "Spectrum Analysis," third edition, p. 240. 



