32 VESTIGES OF THE 



may be that a sufficiency of heat still remains in those 

 planets to make up for their distance from the sun, and 

 the consequent smallness of the heat which they derive 

 from his rays. And it may equally be, since Mercury is 

 twice the density of the earth, that its matter exists 

 under a degree of cold for which that planet's large 

 enjo3'ment of the sun's rays is no more than a comj)ensa- 

 tion. Thus there may be upon the whole a nearly equal 

 experience of heat amongst all these children of the sun. 

 Where, meanwhile, is the heat once diifused through the 

 system over and above what remains in the planets'? 

 May we not rationally presume it to have gone to con- 

 stitute that luminous envelope of the sun, in which his 

 warmth-giving power is now held to reside ] It could 

 not be destroyed — it cannot be supposed to have gone off 

 into space — it must have simply been reserved to con- 

 stitute, at the last, a means of sustaining the many 

 operations of which the planets were destined to be the 

 theatre. 



The tendency of the whole of the preceding considera- 

 tions is to bring the conviction that our globe is a 

 specimen of all the similarly placed bodies of space, as 

 respects its constituent matter and the physical and 

 chemical laws governing it, with only this qualification, 

 that there arc possihhj shades of variation with respect 

 to the component materials, and undouhtedbj with respect 

 to the conditions under which the laws operate, and 

 consequently the effects wdiicli they produce. Thus, 

 there may be substances hei-e which are not in some 

 other bodies, and substances here solid may be elsewhere 

 licjuid or vapoiiform. We ai-e the more entitled to draw 

 such conclusions, seeing that there is nothing at all 

 singular or special in the astronomical situation of the 

 earth. It takes its place third in a series of planets^ 



