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[1] 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, employed the dark lines in the solar spectrum as his guides. Judge of his astonishment 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 identical with Fraunhofer's lines, so for each of the iron lines, of which Kirchhoff and Ångström have mapped no less than 460, a dark solar line was seen to correspond. Not only had each line its dark representative in the solar spectrum, but the breadth and degree of shade of the two sets of lines were seen to agree in the most perfect manner, the brightest iron lines corresponding to the darkest solar lines.
This statement was 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, lithium, 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 Professor 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.
