IO4 LIGHT SCIENCE FOR LEISURE HOURS. 



common thermometer (in which one hundred and eighty 

 degrees above freezing represents the heat of boiling 

 water). On the other hand, we have a theory main- 

 tained by Faye, St. Claire Deville, Fizeau, and many 

 others, according to which the sun's heat does not 

 greatly exceed that obtained in the electric light, and 

 is certainly comparable with the heat obtained in many 

 processes of manufacture. Indeed, according to some 

 of the most satisfactory investigations which this 

 subject has received, the actual heat at the sun's 

 surface does not very greatly exceed that at which iron 

 melts ; while St. Claire Deville even asserts his belief 

 that a degree of heat not greatly beyond that which 

 our physicists have obtained cannot possibly be exceeded 

 under any circumstances, either in our own sun or in 

 any of his fellow suns. 



Above the glowing photosphere, or light surface of 

 the sun, there extends to a depth of several hundred 

 miles the most wonderful atmospheric envelope known 

 to astronomers. In dealing with this envelope, I am 

 touching on the work of the recent eclipse, because, 

 although the envelope had been recognised theoretically 

 two years ago, and its existence demonstrated during 

 the eclipse of December 1870, yet doubts had continued 

 to be entertained by a few respecting the reality of this 

 relatively shallow atmosphere. I can now, however, 

 speak of it unquestioningly, since scarcely one of those 

 who sought for it during the late eclipse failed to 

 recognise its existence. 



Let it be premised that, at the sun's distance, a 



