234 HISTORY OF COLD AND THE ABSOLTTTE ZERO. 



eleven may be reasonabl}^ ascril)cd to aroon, krypton, and xenon, one 

 to more volatile gas of the neon class, and the brightest ray ol" all is 

 but a very Uttle less refrangi))le than the characteristic auroral ray, 

 and coincides with a strong- ray of calcium, but also lies between, and 

 close to, an argon and a neon ra}'^, neither of them weak rays. There 

 ma}" be some doubt about the identification of the spectral rays of 

 auroras because of the wide limits of the proba1)le errors in measuring 

 wave lengths so faint as most of them are, but there is no such dou])t 

 about the wave lengths of the ra3^s in solar protuberances measured 

 by Deslandres and Hale. Stassano found that these rays, forty-four 

 in number, lying between the Fraunhofer line i'^and 3148 in the ultra- 

 violet agree very closely with rays which Professor Liveing and' 

 myself measured in the spectra of the most volatile atmospheric gases. 

 It will be remembered that one of the earliest suggestions as to the 

 nature of solar prominences was that they were solar auroras. This 

 supposition helped to explain the marvelous rapidity of their changes, 

 and the apparent suspension of l)rilliant self-luminous clouds at enor- 

 mous heights above the sun's surface. Now, the identification of the 

 rays of their spectra with those of the most volatile gases, which also 

 furnish many of the auroral rays, certainly supports that suggestion. 

 A stronger support, however, seems to be given to it by the results 

 obtained at the total eclipse of May, 1901, by the American expedition 

 to Sumatra. In the Astrophysical Journal for June last is a list of 

 339 lines in the spectrum of the corona photographed by Humphre^^s, 

 during totality, with a very large concave grating. Of these no fewer 

 than 209 do not differ from lines we have measured in the most volatile 

 gases of the atmosphere, or in krypton or xenon, by more than one 

 unit of wave length on Armstrong\s scale, a quantity within the limit 

 of probable error. Of the remainder, a good many agree to a like 

 degree with argon lines, a very few with oxygen lines, and still fewer 

 with nitrogen lines; the characteristic green auroral ray, which is not 

 in the range of Humphreys's photograj^hs, also agrees within a small 

 fraction of a unit of wave length with oiie of the rays emitted by the 

 most volatile atmospheric gas. Taking into account the Fraunhofer 

 lines iT, /r, and G^ usually ascribed to calcium, there remain only 55 

 lines of the 339 unaccounted for to the degree of probability indicated. 

 Of these considerably more than half are very weak lines which have 

 not depicted themselves on more than one of the six films exposed, 

 and extend but a very short distance into the sun's atmosphere. There 

 are, however, seven which are stronger lines, and reach to a consid- 

 erable height above the sun's rim, and all have depicted themselves on 

 at least four of the six films. If there be no considerable error in 

 the wave lengths assigned (and such is not likel}^ to be the case), these 

 lines may perlfaps be due to some volatile element which may yet be 

 discovered in our atmosphere. However that may be, the ver}' great 



