





XIII.] 



LAYERS. 



[69 



practically there is no end of them in which we got the lines 

 of iron and other substances. There are many lower variable 

 layers depending upon local disturbance. We have by these 

 observations a means of determining the fact that the solar 

 atmosphere consists of what may be very conveniently and 

 justly called a very considerable number of layers ; arid what 

 happens with these layers is this : If the sun is quiet, or 

 if we observe any particular part of it at any time at 

 which it is not agitated, the layers visible at that time, 

 few in number, are nearly concentric (Fig. 69), but the 

 moment there is any agitation in the subjacent photosphere 



H.W/w 



FIG. 69. Imagined stratification of the solar atmosphere (1873). 

 (H = Hydrogen ; Mg = Magnesium ; Na = Sodium ; Fe = Iron.) 



the lower layer shoots up into the next layer above it ; 

 the next shoots up into the one next above that ; and so on 

 (Fig. 70). How far into the very confines of the solar atmo- 

 sphere this sort of action goes we do not know, because it 

 wants more time to observe than is afforded by an eclipse, 

 but it is certainly known that from the very lowest layer to 

 the upper hydrogen one the layers are made to obey this same 

 impulse, and bulge up like so many domes on that part of the 

 sun which is being violently agitated. 



The following extract from a lecture I gave at Cambridge 

 in 1871 refers to an experiment of some interest in this 

 connection : 



