66 ; Temperature of the Terrestrial 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 ; and 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. 
* * * * * * * 
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 usin 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. é 
Brn 
