Temperature of the Terrestrial Globe. 3 



If other causes hitherto unknown, can explain the same facts, and 

 if there exist other sources of terrestrial heat, either general or acci- 

 dental, they will be discovered by comparing the results of this theory 

 with those of observation. 



The rays of heat which are continually proceeding from the sun 

 to the earth, produce upon its surface two very distinct effects : one is 

 periodical, and reaches no farther than the exterior crust. The other 

 is constant. It is observed at great depths, say thirty meters, from 

 the surface. The temperature of these places undergoes no sensible 

 change in the course of the year ; it is fixed. But it is very differ- 

 ent in different climates ; it results from the continual action of the 

 solar rays, and from the unequal exposure of different parts of the 

 surface between the equator and the poles. We can determine the 

 time which must pass before the effect of the sun's rays could produce 

 that difference in climate which now exists. All these results agree 

 with those of the dynamic theories which have proved to us the sta- 

 bility of the axis of the earth. 



The periodical effects of the solar heat, arise from the diurnal or 

 annual variations. This order of facts is explained exactly, and in 

 all its details, by the theory. The comparison of the results with 

 the observations will serve to measure the conducting power of those 

 substances of which the crust of the globe is composed. 



The jiressure of the atmosphere and bodies of water, has the gen- 

 eral effect to render the distribution of heat more uniform. In the 

 ocean and in the lakes, the coldest particles, or rather those whose 

 density is the greatest, are continually tending downwards, and the 

 motion of heat depending on this cause is much more rapid than that 

 which takes place in solid masses in consequence of their connecting 

 power. The mathematical examination of this effect would require 

 exact and numerous observations. These would enable us to under- 

 stand how this internal motion prevents the internal heat of the globe 

 from becoming sensible in deep waters. 



Liquids are very poor conductors of heat ; but they have, like 

 aeriform media, the property of carrying it rapidly in certain direc- 

 tions. This is the same property which, combining with the centri- 

 fugal force, displaces and mingles all parts of the atmosphere as 

 well as the ocean, and maintains in them regular and immense cur- 

 rents. 



The interposition of the air very much modifies the effects of the 

 heat upon the surface of the globe. The solar rays traversing the 



