METEOROLOGY OF THE SXJN AND EARTH. 79 



the continual disturbances prevent this arrangement from taking place, 

 but in the sun's enormously extended atmosphere (if, indeed, our lumi- 

 nary be not nearly all gaseous) it appears to hold, inasmuch as the 

 upper portion of this atmosphere, dealing with known elements, ap- 

 parently consists entirely of hydrogen. Various other vapors are, 

 however, as we have seen, injected from below the photosphere into 

 the solar atmosphere on the occasion of great disturbances, and Mr. 

 Lockyer has asked the question, whether we have not here a true in- 

 dication of the relative densities of these various vapors derived from 

 the relative heights to which they are injected on such occasions. 



This question has been asked, but it has not yet received a definite 

 solution, for chemists tell us that the vapor densities of some of the 

 gases injected into the sun's atmosphere on the occasion of disturb- 

 ances are, as far as they know from terrestrial observations, difierent 

 from those which would be indicated by taking the relative heights 

 attained in tlie atmosphere of the sun. Mr. Lockyer has attempted to 

 bring this question a step nearer to its solution by showing that the 

 vapors at the temperatures at which their vapor densities have been 

 experimentally determined are not of similar molecular constitution, 

 whereas in the sun we get an indication, from the fact that all the ele- 

 ments give us line spectra, that they are in similar molecular states. 



Without, however, attempting to settle this question, I may remark 

 that we have here an interesting example of how two branches of 

 science physics and chemistry meet together in solar research. 



It had already been observed by KirchholF that sometimes one or 

 more of the spectral lines of an elementary vapor appeared to be re- 

 versed in the solar spectrum, while the other lines did not experience 

 reversal. Mr. Lockyer succeeded in obtaining an explanation of this 

 phenomenon. This explanation was found by means of the method of 

 localization already mentioned. 



Hitherto, when taking the spectrum of the electric spark between 

 the two metallic poles of a coil, the arrangements were such as to give 

 an average spectrum of the metal of these poles ; but it was found that, 

 when the method of localization was employed, difierent portions of 

 the spark gave a different number of lines, the regions near the ter- 

 minals being rich in lines, while the midway regions give compara- 

 tively few. 



If we imagine that in the midway regions the metallic vapor given 

 off by the spark is in a rarer state than that near the poles, we are 

 thus led to regard the short lines which cling to the poles as those 

 which require a greater density or nearness of the vapor-particles be- 

 fore they make their appearance ; while, on the other hand, those which 

 extend all the way between the two poles come to be regarded as 

 those which will continue to make their appearance in vapor of great 

 tenuity. 



Now, it was remarked that these long lines were the very lines 



