15G ANNUAL OF SCIENTIFIC DISCOVERY. 



Fourier can bring to our knowledge only one part of the heat which 

 is annually lost by the earth ; lor simple conduction through terra, 

 firma is not the only way by which heat escapes from our globe. 



In the first place, we may make mention of the aqueous deposits of 

 our atmosphere, which, as far as they penetrate our earth, wash away, 

 so to speak, a portion of the heat, and thus accelerate the cooling of 

 the globe. The whole quantity of water which fails from the atmos- 

 phere upon the land in one day, however, cannot be assumed to be 

 much more than half a cubic mile in volume, hence the cooling effect 

 produced by this water may be neglected in our calculation. The 

 heat carried off by all the thermal springs in the world is very small 

 in comparison with the quantities which we have to consider here. 



Much more important is the effect produced by active volcanos. As 

 the heat which accompanies the molten matter to the surface is de- 

 rived from the store in the interior of the earth, their action must 

 influence considerably the diminution of the earth's heat. And we 

 have not only to consider here actual eruptions which take place in 

 succession or simultaneously at different parts of the earth's surface, 

 but also volcanos in a quiescent state, which continually radiate 

 large quantities of heat abstracted from the interior of the globe. If 

 we compare the earth to an animal body, we may regard each volcano 

 as a place where the epidermis has been torn off, leaving the interior 

 exposed, and thus opening a door for the escape of heat. Of the 

 whole of the heat which passes away through these numerous outlets, 

 too low an estimate must not be made. To have some basis for the 

 estimation of this loss, we have to recollect that in 1783, &kaptar-Jo- 

 kul, a volcano in Iceland, emitted sufficient lava in the space of six 

 weeks to cover GO square miles of country to an average depth of 200 

 meters, or, in other words, about 1% cubic miles of lava. The amount 

 of heat lost by this one eruption of one volcano must, when the high 

 temperature of the lava is considered, be estimated to be more than 

 1,000 cubic miles of heat ; and the whole loss resulting from the 

 action of all the volcanos amounts, therefore, in all probability, to 

 thousands of cubic miles of heat per annum. This latter number, 

 when added to Fourier's result, produces a sum which evidently does 

 not agree with the assumption that the volume of our earth has re- 

 mained unchanged. 



In the investigation of the cooling of our plol.e, the influence of the 

 water of the ocean has to be taken into account. Fourier's calcula- 

 tions are based on the observations of the increase of the temperature 

 of the crust of our earth, from the surface toward the center. But f 

 of the surface of our globe are covered with water, and we cannot 

 assume a priori that this large area loses heat at the same rate as the 

 solid parts; on the contrary, various circumstances indicate that the 

 cooling of our globe proceeds more quickly through the waters of the 

 ocean resting on it than from the solid parts merely in contact with 

 the atmosphere. 



In the first place, we have to remark that the bottom of the ocean 

 is, generally speaking, nearer to the store of heat in the interior of 

 the earth than the dry land is, and hence that the temperature in- 

 creases most probably in a greater ratio from the bottom of the sea 

 toward the interior of the globe, than it does in our observations on 



