64 Temperature of the Ter-restrial Globe, 



ence, closed on every side ; since, from such point, in any direc- 

 tion, whatever, if a right hne be produced, of indefinite extent, 

 it will terminate by encountering a star, either visible or invis- 

 ible. Now, whatever may be its form and its dimensions, if this 

 enclosure had, throughout, the same temperature, that of all space 

 would be the same ; but this is not the case : the heat as well as 

 the light of each star is maintained by some peculiar cause, and 

 these incandescent bodies tend not, therefore, to a uniformity of 

 temperature, by the exchanges of radiant heat. This admitted, 

 it follows that the temperature of space varies, one point with 

 another ; yet by reason of the immensity of the stellary enclo- 

 sure, it is only by comparing the temperature of points greatly 

 distant from each other that this variation would become percep- 

 tible. In distances no greater than that traversed by the earth, 

 in its annual orbit, the temperature of space would be sensibly 

 identical ; but in regions so elongated as are parts of that through 

 which the sun and the planets are carried, in their common move- 

 ment, this would not remain the same ; and the earth, in common 

 with all the other bodies, would experience corresponding varia- 

 tions of temperatm-e. Still, from the magnitude of its mass, it 

 may readily be seen that in passing from a heated to a colder re- 

 gion our globe would not readily lose, in the second, all the heat 

 it had imbibed in the first ; but, like a body of considerable vol- 

 ume that we might transport from the equator to our climate, so 

 the earth, on arriving in a more frigid region, would present, as 

 we see the earth really does, a temperature increasing from the 

 surface towards the centre. The opposite would take place when 

 the earth, by continuation of its movement in space, shall pass 

 from a cold region to one of a temperature more elevated. 



Both the extent and the periods of these variations are unknown 

 to us ; but, like all the inequalities of long periods, like those, for 

 instance, arising from the secular displacement of the ecliptick, 

 if they were sensible, these variations will extend themselves to 

 very great depths, although not to the centre of the earth ; nor, 

 perhaps, to a distance from the surface which will bear any con- 

 siderable proportion to the radius of our globe : still, the increase 

 or decrease of temperature, in a vertical direction, which will ac- 

 company them, will extend far below the utmost depths accessi- 

 ble to us ; where they will attain their maximum, and beyond 

 such point will disappear. We may assume, upon the inequali- 



