428 Dr. J. R. Mayer on Celestial Dynamics. 



The continual cooling of the earth cannot be without an 

 influence on the temperature of its surface, and consequently on 

 the climate; scientific men, led by Buffon, in fact, have ad- 

 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 foundation, for 

 the warmth of the earth's surface is even now much more de- 

 pendent on the rays of the sun than on the heat which reaches 

 us from the interior. According to Pouillet's measurements, 

 mentioned in Chapter III., the earth receives 8000 cubic miles 

 of heat a day from the sun, whereas the heat which reaches 

 the surface from the earth's interior may be estimated at 200 

 cubic miles per diem. The heat therefore obtained from the 

 latter source every day is but small in comparison to the diurnal 

 heat received from the sun. 



If we imagine the solar radiation to be constant, and the heat 

 we receive from the store in the interior of the earth to be cut 

 off, we should have as a consequence various changes in the 

 physical constitution of the surface of our globe. The tempe- 

 rature of hot springs would gradually sink down to the mean tem- 

 perature 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 

 parts of the world. Especially it may be presumed that 

 Western Europe, with its present favourable climate, 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 we can pre- 

 dict no diminution of the temperature of the surface of our 

 globe as a consequence of the cooling of its interior mass; and, 

 as far as historic records teach, the climates, the temperatures 

 of thermal springs, and the intensity and frequency of volcanic 

 eruptions are now the same as they were in the far past. 



It was different in prehistoric times, when for centuries the 

 earth's surface was heated by internal fire, when mammoths 

 lived in the now uninhabitable polar regions, and when the tree- 

 ferns and the tropical shell-fish whose fossil remains are now 

 especially preserved in the coal-formation were at home in all 

 parts of the world. 



