Dr. J. R. Mayer on Celestial Dynamics. 425 



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 re- 

 collect that in 1783 Skaptar-Jokul, a volcano in Iceland, 

 emitted sufficient lava in the space of six weeks to cover 60 

 square miles of country to an average depth of 200 metres, or, 

 in other words, about 1\ cubic mile 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 1000 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 resnlt, produces a 

 sum which evidently does not agree with the assumption that 

 the volume of our earth has remained unchanged. 



In the investigation of the cooling of our globe, the iufluence 

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

 calculations are based on the observations of the increase of the 

 temperature of the crust of our earth, from the surface towards 

 the centre. But two- thirds 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 increases most probably in a greater ratio from the 

 bottom of the sea towards the interior of the globe, than it does 

 in our observations on the land. Secondly, we have to con- 

 sider that the whole bottom of the sea is covered by a layer of 

 ice-cold water, which moves constantly from the poles to the 

 equator, and which, in its passage over sand-banks, causes, as 

 Humboldt aptly remarks, the low temperatures which arc 

 generally observed in shallow places. That the water near the 

 bottom of the sea, on account of its great specific heat and its 

 low temperature, is better fitted than the atmosphere to with- 

 draw the heat from the earth, is a point which requires no 

 further discussion. 



