168 ..-HrM-.*' 3 ^ CHEMISTRY OF THE SUN. [CHAP. 



composition of the solar atmosphere as one went down into it got 

 more and more complex ; nothing was left behind, but a great 

 many things were added. We had, dealing with known 

 elements, 



Highest . . Hydrogen. 



Medium . . Magnesium, calcium, sodium. 



Lowest / ' Y . Iron, nickel, manganese, chromium, 

 cobalt, barium, copper, zinc, tita- 

 nium, and aluminium. 



One word about the hydrogen. 



We may have hydrogen, in a large globe, at such a pressure 

 that we can make it luminous with a feeble current. If we exa- 

 mine it with the spectroscope we find it gives the F line alone, 

 there is nothing red about it. Now there is a region around 

 the sun which gives us something very like that in colour, and 

 something absolutely like it, so far as the result of spectro- 

 scopic observation is concerned. Again, we may have hydrogen 

 in a narrow tube in a condition to be considerably agitated ; 

 instead of allowing the current to act throughout a globe, 

 it has to pass through a fine capillary space in which 

 the gas is confined. That is a condition which is supposed 

 to give us the effect of high temperature. It really does 

 give us something like what we see in the next lower solar 

 region. As we pass from few encounters of molecules to many, 

 the gas is very much more luminous, and it is red. The 

 level which gives such a spectrum as is got from the capillary 

 tube is considerably lower than the one which gives us the 

 F line alone (Fig. 69). 



We may go more into detail with regard to the lower reaches. 

 Further down, as has been already pointed out, we got all 

 round the sun at certain periods of the solar activity some lines 

 seen in the spectrum of magnesium. Underneath this again we 

 got a layer in which lines seen in the case of sodium and 

 calcium are almost as constantly seen. Still a lower depth 



