406 Captain F.W. Hutton on the Phenomena of the 



Baron Fourier has calculated that the earth decreases in 

 temperature 1° F. in 3,000,000 years. Now a hollow shell 

 one mile thick surrounding the earth is to the rest as 1 : 1316; 

 if, therefore, this shell collected all the heat radiated outward, it 

 would be raised in temperature 1316° F. in 3,000,000 years. If, 

 now, we suppose the total amount of this heat to be spread 

 out through a shell of rock in such a manner that it decreased 

 outward -^° F. for every foot until it was zero on the outside, 

 a simple calculation will show that this shell would have to be 

 26,364 feet in thickness ; so that if the earth were enclosed in a 

 shell of this thickness, the internal heat would reach the surface 

 in 3^000,000 years ; consequently it would have travelled out- 

 ward at the rate of '1 inch per year. Sir W. Thomson (Proc. 

 Roy. Soc. of Edinb. 1864, p. 200, and 1865, p. 512), basing his 

 calculations on the experiments on the conductivity of rocks 



made by Forbes, Glaisher, Angstrom, and Peclet, concludes that 

 the earth decreases in temperature 1° C. in 2,000,000 years, or 

 2°-7 F. in 3,000,000, which gives an outward conduction of -27 

 inch per year. These experiments, however, were made on dry 

 rocks, while newly formed deposits would be saturated with 

 water ; and if we suppose that the thermal capacity of mud and 

 sand saturated with water is the same as that of water, his cal- 

 culations will have to be reduced by one half, which would make 

 the outward conduction '135 inch per year. Peclet^s experi- 

 ments show that the conductivity of marble is only two fifths of 

 the average taken by Sir W. Thomson ; so that in limestone the 

 conduction outwards might only be "1 inch per year. These 

 calculations, therefore, although founded on but few experiments, 

 agree so closely with the results arrived at by Baron Fourier, 

 that we may place considerable confidence in their accuracy; 

 and if we assume that the internal heat is conducted outward 

 through limestone at the rate of '1 inch per year, and through 

 wet sand and mud at the rate of '13 inch per year, we shall pro- 

 bably be not very far from the truth. 



Prof. Dana (Manual of Geology, p. 386) estimates that lime- 

 stone grows at the rate of '125 inch per year, and sedimentary 

 rocks from five to ten times as fast, or from -62 to 1*25 inch per 

 year. The Mississippi delta has been estimated to increase in 

 thickness '17 inch per year, and that of the Ganges '26 inch per 

 year. The mean of these estimates is '6 per year ; and if we 

 assume that in a formation one third consists of limestone, the 

 average rate for the whole would be '4 inch per annum ; so that 

 the rate of deposition would be more than three times as fast as 

 the rate of heating. 



From this it follows that when the internal temperature in- 

 creased three times as fast as it does now, or at the rate of jt^° F. 



