$4 



ILLUSTRATIONS OF THE 



only effeds of heat are fafion and expanfion - 

 and that which forms the nucleus of the globe 

 may therefore be a fluid mafs, melted, but 

 changed by the a£lion of heat. 



un 



go. If, from th 



nfines of 



in 



iceive certain fiifures and openings to traverfe 

 : folid crufl, and to iiTue at the furface of the 

 th, the vapours afcending through thefe may 



through 



me heat the fides of 



the 



tubes 



which they pafs to a vail diflance from the 

 lower extremities. It is, indeed, difficult to fix 



the limit to which 



diflance may extend 



hich 



vehici 



of the great difference between the i 



t moves Vv^hen it has a fluid for 

 when it is left to make its 



and 



way 



alone through a folid body. In the prefent cafe 

 the fupply of heat is rapid, as being made by i 

 vapour afcending through a tube of folid rock; 

 and the diflipation of it flow, as arifmg from its 



fmiflion through 



th 



roc 



1 



I'i.ly 



The wafte of 



heat is therefore fmall, compared with the fup 



ply, a I 

 longer 

 nued to fl 



d grows fmailer at every given poi 



of heated vapour has 



the ft ream 



and 



Such a ftream, therefore, though 

 may at firft be condenfed within a fmall di- 



fource, will in time reach higher 



may at laft be able to carry its 



ftance of 



gh 



d 



heat to an immenfe dift 



a 



g 



de 



from the place of 



Thus, it is eafy 



ceive, 



^ 



4 



