NATURE 



\_yuly 28, 1 88 1 



in that part of the spectrum where the dark line would otherwise 

 be. In the brighter portion between the two small spots (Fig. 

 19) the absorption is replaced by an exceedingly brilliant radia- 

 tion, so brilliant indeed that it is quite impossible to draw a 

 diagram so as to give any idea of the intense brilliancy of some 

 of these little spots of light which one sees in the spectroscope ; 

 they fatigue the eye enormously, although they cover such a very 

 small portion of the field of view. 



Accompanying this intense radiation there is a gradual fading 

 away of the absorption line ; it wanes, and fades, and becomes 

 almost invisible ; while, on the other hand, on the other side or 

 in other places, instead of getting a brilliant patch of light of 

 the same width as the "F" line, we get one many times 

 broader. We have also the absorption deflected to the left, 



or red end of the spectrum, and on this side it is gradually 

 fined or eased off, so that it is very difficult to determine ex- 

 actly where this iDroadened, deflected " F " line actually ceased 

 to give us absorption ; whereas at the other side, where it changed 

 its refrangibility towards the blue end of the spectram, we have 

 an enormous patch of light. Now the explanation of that is 

 perfectly ^imple : v\'e have at one part of the spot an enormous 

 up-rush, an ejection of hydrogen so intensely hot that it declines 

 naturally to absorb the light from anything behind it, because 

 it finds nothing hotter. This gradually replaces the absorbing 

 hydrogen which was driven down again with considerable velocity, 

 and so changed its refrangibility towards the the red. 



Enough has been said already to show that this method of 

 studying solar phenomena in situ has really helped us enormously 



Fig. iS.— Motion-forms. 



with regard to the chemical nature of the sun. We can allocate 

 the absorption of the hydrogen, magnesium, and so on ; we can 

 see where they are absorbing, and in the phenomena just referred 

 to, where they cease to absorb, we get bright lines. 



What, then, ^^'as the totality of the knowledge which had been 

 acquired a few years ago %\'ith regard to the chemical nature of 

 the sun's atmosphere taken as a whole — the sun's atmosphere 

 from the upper reaches of the coronal atmo.'phere down to the 

 region where, doubtless, the spot phenomena are located ? 



I have two little glass vessels here which ought to point what 

 I wish to say. I have here hydrogen arranged so that I can make 

 it luminous with a minimum of agitation. If we examined it with 

 the spectroscope, we should find it would give the F line alone, 

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



which gives us something veiy like that in colour, and something 

 absolutely like it, so far as the result of spectroscopic observation 

 is concerned. Now i^e have in this other little tube hydrogen 

 in a condition to be considerably agitated, because instead of 

 allowing it to occupy a globe, it is arranged so that the electric 

 current has to pass through a fine capillary space in which the 

 gas is inclosed. That is a condition which is supposed to give 

 us the effect of higli temperature. This really does give us 

 something like what we see in the next lower solar region. This 

 is exactly the same gas as we have in the globe, but it is treated 

 differently, and the effect is widely different. As we pass from few 

 encounters of molecules to many it is very much more luminous, 

 and it is red. The level which gives such a spectrum as is got 

 from the capillary tube is consider.ably lower than the one which 

 gives us the Fline alone (Fig. 21). 



