July 21, 1881] 



NATURE 



273 



also fouad that other substances be-ides hydrogen, some of 

 which at present we know nothing of, others of whiijh we now 

 think we know a great deil of, also appear side by side with the 

 1 nes of hydrogen. I hive already stated that other substances 

 besides hydro^'en have been deter amed to exist in this lower 



cliro jiospheric layer. In almost all cases, however, we find that 

 these lines are never so lonj as the hylrogen line, from which 

 we leather that the iragnesium sea, to take a ease, is a much 

 shallower one than the hydrogen sea. I should further add 

 here that when the sun is moderately active and can be well 



o'lierved, as in a fin? clima'e like that in Italy, this magnesium 

 sea can be detected all roun 1 the sun, so that we have in the 

 chrom ispheric layer, first of all, a sea of hydrogen with its 

 irojiinences, and then at the bottom of this sea another sea 

 of magnesium, which wells up sometimes where the prominences 

 are strongest 



The different forms which these prominences assume are very 

 striking. You will have no difficulty in seeing that there is 

 really a fundamental difference between them, .and that all 

 present us with indications of movement, and these movements 

 enable us to apply a test to the theories of the firmali-m of 

 spots and prominences to whicli Prof. Stokes referred. Prof. 



Fig. :5.— Diagram showing how the prominences are daily recorded (Respighi). 



Stokes pointed out that a great many phenomena require 

 that the sun-spot shall consist of descending currents, and that 

 these prominences, which when we can see them are fed by the 

 incandescent matter of th^ -un, sh >uld not be descending cur- 

 rints like those in spots, bu' should be j,ascending currents, — in 



fact masses of incandescent vapour shot out from the very 

 bowels of the sun itself. The drawings, ^^hich we owe to the 

 skill of Prof. Respigi, drawn by the simple contrivance of 

 opening the slit after we have got the image of the prominence 

 carefully upon it, give us a great many cases of upward move- 



