66 Temperature of the TeiTestrial Globe, 



in a vertical direction should really be due to the original heat of 

 the globe, it would follow that, at the present epoch, this primi- 

 tive heat would augment the temperature of the surface itself by 

 a small fraction of a degree ; but, that this small augmentation 

 might reduce itself, for instance, one half, it would be necessary 

 that more than a- thousand millions of centuries elapse ; arid if 

 we desire to retrograde to an epoch at which this may have been 

 sufficient to produce the observed geological phenomena, it would 

 be necessary to ascend the stream of time such an immense num- 

 ber of centuries as would alarm the most fearless imagination, 

 whatever idea may otherwise be entertained of the antiquity of 

 our planet. 



*M, .V, - .U* •U* •If' lit* 



tP tP TT TT t"c* ^W" 



There is reason to believe that, of stellary heat, equal quanti- 

 ties are not transmitted to us from all the various regions of the 

 heavens. If we imagine a cone, extremely pointed, which has 

 its summit in some point of the surface of the earth, and which 

 is prolonged to the fixed stars; by reason of the very great dis- 

 tance of the earth from these stars, this cone would embrace an 

 immense number of them ; and it is the mean of the quantities 

 of heat that they thus emit which I take for the intensity of stel- 

 lary heat in that direction. Now it is out of all probability that 

 this intensity would remain the same, if we suppose this cone 

 moved round its summit, and pointed, successively, in every dif- 

 ferent direction ; or if we remove its summit, and transport it, in 

 succession, from one place to another upon the earth's surface : 

 still the most delicate experiments would alone be able to disclose 

 to us those parts of the heavens from which the stellary radiation 

 is of the greatest or least intensity ; nor has observation hitherto 

 aided us, in the least, upon this subject — one of the most inter- 

 esting of celestial physicks. At the different hours of the day, 

 the total quantity of stellary heat which reaches any point of the 

 earth, emanates from all the celestial bodies situated above the 

 horizon of such point, and it may therefore vary, in any given 

 time, at one place with another, and cannot be the same, for ex- 

 ample, at the equator and at the poles. The quantity of stellary 

 heat which comes to us in the same interval of time must also be 

 very unequal in the two hemispheres ; and this inequality is one 

 of the possible causes of the difference of the mean temperature 

 of the northern and southern hemispheres. 



