WHAT TEE SUN IS MADE OF. 



319 



nebular hypothesis, because to many persons the 

 absence of this important group has presented a 

 considerable difficulty. 



" At first sight it seems rather difficult to be- 

 lieve that an ignited gas in the solar envelope 

 should not be indicated by dark lines in the solar 

 spectrum, and should appear not to act under the 

 law, ' A gas when ignited absorbs rays of the same 

 refrangibility as those it emits.' But, in fact, the 

 substances hitherto investigated in the sun are 

 really metallic vapors, hydrogen probably coming 

 under that rule. The non-metals obviously may 

 behave differently. It is easy to speculate on the 

 causes of such behavior, and it may be suggested 

 that the reason of the non-appearance of a dark 

 line may be that the intensity of the light from a 

 great thickness of ignited oxygen overpowers the 

 effect of the photosphere, just as if a person were 

 to look at a candle-flame through a yard thickness 

 of ignited sodium-vapor, he would only see bright 

 sodium-lines, and no dark absorption-lines. Of 

 course, such an explanation would necessitate the 

 hypothesis that ignited gases, such as oxygen, 

 give forth a relatively large proportion of the solar 

 light. In the outburst of T Coronre Huggins 

 showed that hydrogen could give bright lines on 

 a background of spectrum analogous to that of the 

 sun. 



" However all that may be, I have no doubt of 

 the existence of substances other than oxygen in 

 the sun, which are only indicated by bright lines. 

 Attention may be called to the bright bands near 

 G, from wave-lengths 4307 to 4337, which are 

 only partly accounted for by oxygen. Further in- 

 vestigation in the direction I have thus far pur- 

 sued will lead to the discovery of other elements 

 in the sun, but it is not proper to conceal the 

 principle on which such researches are to be con- 

 ducted for the sake of personal advantage. It is 

 also probable that this research may furnish the 

 key to the enigma of the D 3 or Helium line, and 

 the 1474 K or Corona line. The case of the D 3 

 line strengthens the argument in favor of the ap- 

 parent exemption of certain substances from the 

 common law of the relation of emission and ab- 

 sorption, for, while there can be no doubt of the 

 existence of an ignited gas in the chromosphere 

 giving this line, there is no corresponding dark 

 line in the spectrum of the sobr disk." 



If these observations of Dr. Draper are in- 

 dorsed, it is impossible to overrate their impor- 

 tance, and those studies which teach us what the 

 sun is made of will be considerably advanced. 

 But this is not all. Not only will our present 

 views of the distribution of the various element- 

 al substances in the sun's atmosphere be entirely 

 bouleversed, but, as may have been gathered 

 from the last quotations, a good deal of physical 

 theory will have to go overboard also. 



The existence of oxygen in the sun has hith- 

 erto been negatived, because there was no cor- 

 respondence between its bright lines and the 

 dark ones on the solar spectrum. Dr. Draper 

 not only turns the tables upon us, but suggests 

 that there is one law of absorption for metals, 

 another for metalloids. In the case of most of 

 the molecular stages of the metalloids this cer- 

 tainly is not true, for the absorption phenomena 

 of iodine, chlorine, sulphur, etc., are among the 

 most beautiful in the whole range of spectrum 

 analysis. 



It is unfortunate, too, that Dr. Draper has 

 never read, or has forgotten, what has been long 

 written on the most probable position of the 

 metalloids in the solar economy ; that is, above 

 (outside) the metals, exactly where, as I have 

 already shown, carbon in all probability has 

 been found. 



But my objections do not rest on pure theory. 

 I have gone over the ground as completely as 1 

 have been able, and, as a result, I wish to point 

 out, with regard to this work of Dr. Draper's, 

 that the photograph in which these comparisons 

 with the oxygen-lines have been made is not one 

 which is competent to settle such an extremely 

 important question. 1 Secondly, I do not find 

 the coincidences between bright solar lines and 

 oxygen-lines in that part of the spectrum with 

 which I am most familiar, for the reason that 

 there are no bright lines in this portion of the 

 spectrum, either visible to the eye or in a per- 

 fect photograph. Mr. Rutherfurd's magnificently 

 perfect spectrum, going nearly the whole length 

 from to E, embraces the region included in 



1 The spectrum between the more marked lines 

 suggests ribbed structure ; hence it is important to 

 know whether the photograph was taken by means of 

 one of the silver-on-glass gratings made by Mr. Ruth- 

 erfurd. I find that in these, in consequence of the 

 grating being ruled on the back surface of the glass 

 and the double transmission of the light through the 

 plate, there is a considerable formation of Talbot 

 bands, and the solar spectrum is in some regions en- 

 tirely hidden and absolutely transformed. Lines are 

 made to disappear ; lines are apparently produced, so 

 that, if one compares a part of the spectrum taken 

 with one of these silver-on-glass gratings with an or- 

 dinary refraction-spectrum, the greatest precaution is 

 requisite. Indeed, I think that I am not going beyond 

 the mark when I say that the positions of all lines be- 

 low the third or fourth order of intensity must be re- 

 ceived with very great caution indeed when these 

 gratings are employed. So much is this recognized 

 by Mr. Rutherfurd himself, that he is now generously 

 distributing gratings containing the same number of 

 lines to the inch (17,300, or something like that) en- 

 graved on speculum-metal, in order that these defects 

 may be obviated. 



