EXPENDITURE AND SUPPLY. 25 



be estimated. Nothing of the kind can, however, be dis- 

 cerned. We are obviously only looking at vast masses of 

 glowing cloud suspended in gaseous matter. The solar 

 vapours have but little more permanence than the unstable 

 clouds of our own atmosphere. 



Our knowledge of the interior of the sun is necessarily 

 very imperfect, but there seems no reason to think that 

 the luminary is, even in any part, what may be regarded 

 as a solid body. There is, in fact, a strong presumption 

 in the opposite direction. To explain this it is necessary 

 to contrast certain characteristics of our earth with the 

 corresponding characteristics of the sun. Our globe, for 

 instance, is constituted from materials which are on the 

 whole so heavy that the earth weighs over five times as 

 much as would a globe of water of the same size ; whereas 

 the sun is hardly one and a half times as heavy as a globe 

 of water of equal \olume. Thus we learn that the sun 

 is composed of materials which have about one-fourth of 

 the density of those of the earth. This points to the con- 

 clusion that the materials of the sun are much less closely 

 compressed, and that even the sun's interior can hardly 

 be regarded as consisting of solid substance. 



When, therefore, we discuss the loss of heat from the 

 sun by radiation we ought not to compare it with that of 

 radiation from a solid globe ; we must rather take it to 

 resemble radiation from a gaseous globe. At first, per- 

 haps, the profound difference between the two cases may 

 escape attention. Indeed it is only in comparatively 

 recent times that the remarkable laws by which a globe 

 of gaseous matter parts with its heat have been thoroughly 

 explained. 



