364 THE CHEMISTRY OF THE SUN. [CHAP. 



preferably that part between F and D, which has been most 

 closely watched in prominences and spots by Tacchini and 

 myself. 



The observations in 1886 were made by Mr. Turner, chief- 

 assistant at the Greenwich Observatory, and although they are 

 not yet published in extenso, it is known that they confirm in 

 the main the Egyptian results. Nearly the same lines were 

 seen as in Egypt in 1882, short and bright and long and thin. 



It will be clear, then, that the new hypothesis has borne this 

 test in a very satisfactory manner. 



Hence a consideration of variations of temperature alone 

 is sufficient to explain all the phenomena observed. We do 

 not want to introduce an appeal to varying pressures and 

 densities, and other molecular behaviour about which, at the 

 sun, we practically know nothing, and about which, therefore, 

 we may assume anything we choose, while it is certain that no 

 controlling experiments are available. This is not a good basis 

 on which to build, or from which to attack, any hypothesis. 



I next pass to another point, concerning which eclipses, and 

 eclipses alone, enable us to bring yet another test into the 

 field. 



In Fig. 104 we considered the sun's atmosphere, taking the 

 simplest case, that of one element ; when the sun cools it will 

 be a very complex mass chemically. If the laws of evolution 

 hold we need not expect that this will largely increase the com- 

 plexity of the hottest layers A and B, but higher up, say at 

 H L, the complexity of chemical forms produced by evolution 

 along the fittest lines will be very considerable. 



These strata H L may be taken to represent the corona. 

 Its spectrum, therefore, should not be a continuous one, but 

 should consist of an integration of all the radiations and 

 absorptions of these excessively complex layers. 



The earliest spectroscopic observations of the corona recorded 



