414 J. R. Mayer on Celestial Dynamics. 
circumstances which, according to mathematical analysis, would 
tend to lengthen the duration of this period of the earth’s ex- 
istence. 
The historical times of mankind are, according to Laplace's 
calculation, to be placed in this period. Whether we are at the 
vanced the supposition that the loss of heat sustained by our 
globe must at some time render it an unfit habitation for organic 
life. Such an apprehension has evidently no meer aa for 
the warmth of the earth’s surface is even now muc e de- 
pendent on the rays of the sun than on the heat which eal 
ior ma. 
miles per diem. The heat therefore obtained from the latter 
source every day is but so in comparison to the diurnal heat 
sy te from the sun. 
e imagine the solar radiation to be constant, and the heat 
we Bak from the store in the interior of the earth to be cut 
es we should have as a consequence various changes in the 
physical constitution of the surface of our globe. The tempe 
lane of hot springs would gradually sink down to the mean 
temperature of the earth’s crust, volcanic eruptions would cease, 
earthquakes would no longer be felt, and the temperature of the 
water of the ocean would be sensibly altered in many places— 
circumstances which would doubtless affect the climate In many 
es of the world. Especially, it may be presumed that Western 
urope, with its pleasant favorable tat would become colder, 
and thus perhaps the seat of the power and culture of our race 
transferred to the milder parts of North America. 
_Be this as it may, for thousands of years to come W 
an 
so far as historic records teach, the climates, the temperatures of 
thermal springs, and the intensity and frequency of volcanic 
; a aig are now the same as they were in the far past. 
_ It was different in proreetons aver when for centuries the 
_ earth’s surface was by internal fire, when mammoths 
lived in the now sninhabitabla lvoe regions, and vn the tree- 
ferns and the tropica -fish, whose oman — are now 
char 1 at home in all 
