THE SUN'S TRUE ATMOSPHERE. Ill 



conversant with the corresponding groups of dark lines. 

 It follows, then, beyond all possibility of question, that 

 the source of light was a highly complex atmosphere, 

 formed of those very vapours which, by their absorptive 

 power, produce the dark lines formed, that is, of the 

 vapours of iron and of copper, of zinc, sodium, magne- 

 sium, and of all those elements whose presence in the 

 sun's substance had been inferred from the study of 

 the solar spectrum. 



Here, then, at length we have the true solar atmo- 

 sphere, an atmosphere of a highly complex nature, and 

 doubtless exceedingly dense near the visible surface of 

 the sun, because subject to a pressure so enormous. 

 The upper limit of this atmosphere cannot lie very far 

 above the sun's surface, at least not very far compared 

 with the sun's dimensions. Supposing the actual time 

 during which the line-spectrum was visible to have been 

 two seconds, then it is easy to tell how deep the atmo- 

 sphere is. For in two seconds the moon must have 

 traversed a space corresponding to about three hun- 

 dred miles at the sun's distance. An atmosphere three 

 hundred miles deep is, therefore, indicated by Pro- 

 fessor Young's observations. It need hardly be said, 

 however, that in the excitement of eclipse observation, 

 the estimate of minute intervals of time can scarcely 

 be relied upon, unless checked by instrumental arrange- 

 ments, which was not the case in the present instance. 

 We may fairly conclude that the depth of the solar 

 atmosphere lies between some such limits as a hundred 

 miles and five hundred miles. 



