-1859] WRITINGS OF JOSEPH HENRY. ^53 



Original heat of the earth. — Besides the smaller influence of 

 celestial space, and the governing one of the emanations from 

 the sun, there is another source of terrestrial heat, which, 

 though it at present produces scarcely an appreciable effect 

 upon the temperature of the surface, was once powerfully active 

 in effecting geological changes, and in so modifying the sur- 

 face of our planet as to give rise to the diversities of surface 

 constituting mountains, seas, and continents, which now 

 determine the varieties and peculiarities of our present cli- 

 mates, and may in the future be of vast practical value in 

 its applicability to the wants of life. We allude to the in- 

 ternal heat of the earth. 



That the earth was once at least in a liquid condition by 

 heat, can scarcely be doubted, when all the cumulative evi- 

 dence in favor of the hypothesis is considered. 



First. Self-luminous bodies are met with in every part of 

 the visible universe, and if we follow the strict inductive pro- 

 cess, allowing no more causes than are true and sufficient, 

 we must admit that these bodies are intensely heated. It is 

 therefore not impossible that the earth itself may have been 

 at one time a self-luminous star. 



Second. The surfaceof our moon, though it now gives lit- 

 tle or no indication of heat, appears when viewed through a 

 powerful telescope almost covered with the craters of extinct 

 volcanoes ; and hence we may infer that it has cooled down 

 from a high temperature to its present condition. 



Third. Every portion of the earth's crust exhibits the re- 

 mains of igneous action, and the facts of geology are inex- 

 plicable on any other hypothesis than that of the past high 

 temperature of our globe. 



Fourth. On every part of the earth where the experiment 

 has been made, starting from the point where the sun's 

 influence ceases, there has been found an increase of tem- 

 perature as we descend toward the centre, at the rate of about 

 a degree for every fifty feet. 



Fifth. On different parts of the earth's surface springs oi 

 hot water are found bursting forth. 



Sixth. There are on the surface of the earth several hun- 



