S62 



CENTRAL HEAT. 



tice, which fs becoming general in that country, of boring for water, 

 to form what are called Artesian wells, has greatly facilitated the in- 

 vestigation.* 



M. Cordier has particularly directed his attention to this subject, 

 and from numerous experiments made by himself and others in mines 

 and Artesian wells, he has drawn the following conclusions : — 1st. 

 that there exists a subterranean heat in the terrestrial globe inde- 

 pendent of solar radiation, and which increases rapidly with the 

 depth : — 2nd. that the increase of heat does not follow the same 

 line in all parts of the earth ; indeed, he supposes the differences 

 may be twice or three times as great in one country as in another : — 

 3rd. these differences are not in constant relation with the longitudes 

 and latitudes of places where the experiments have been made :-— 

 4th. that the heat increases with the increase of depth, in a much 

 greater degree than was previously believed. M. Cordier farther 

 maintains, that there is a source of intense heat in the earth, and that 

 the external crust may be from 50 to 100 miles in thickness, and 

 that all within this crust is a mass of melted matter : that originally 

 the whole globe was an entire mass of melted matter before the ex- 

 ternal crust- became solid, by throwing out its heat into space ; and 

 that, in this manner, the solid crust is constantly growing thicker, 

 and the internal heat diminishing. 



The spheroidal form of the earth indicates an original state of 

 fluidity, and whatever might be the tenacity of the fluid matter, the 

 rapid rotation of the earth on its axis, would swell out the equatorial 

 parts, and form a spheroid of rotation. Intense heal appears to be 

 the only natural agent we are acquainted with, that could retain the 

 mass of the earth in a fluid state : — farther, the granitic crust of the 

 globe most probably owes its crystalline structure to slow refrigeration 

 from a state of igneous fusion. Thus both the form of the earth, 

 and the structure of its crystalline crust, are favorable to the theory 

 of central heat. If this theory can be established, it will offer a sat- 

 isfactory explanation of the former high temperature of the globe, 

 and of its subsequent progressive refrigeration : — also of another cir- 

 cumstance equally remarkable ; for it would appear, from the fossil 

 remains of vegetables in different latitudes, that every part of the 

 globe once enjoyed nearly the same degree of heat ; the cause of 

 this equality must have been independent of solar radiation, and de- 

 rived from the earth itself. There are certainly numerous circum- 

 stances that favour the theory of central heat, but it must be conr- 



* Boring for Artesian wells has become general in many parts of Italy and 

 Germany. In France, it is found that the average increase of heat, above the 

 mean temperature of the surface, is about one degree of Fahrenheit's thermome-^ 

 ter, for every forty-five feet in depth ; or one degree of the centigrade scale, for 

 twenty-five metres: but this is liable to variation of increase or decrease in differ- 

 ent situations. For a further account of the temperature of mines and wells see 

 Appendix. 



