determining the Thermal Conductibility of Bodies. 141 



tained by Peclet for the conducting-power of the two metals be 

 expressed in the same units, namely, 1 grm., 1 minute, and 

 1 centimetre, we get for 



Copper . 11*4 



Iron 4*35 



values which materially differ from the above. 



§6. 



As it may not be uninteresting to know also the conductibility 

 of different soils, I have endeavoured to use the results obtained 

 from the observations made in Upsala with the earth thermo- 

 meter to ascertain the conductibility of those layers in which 

 the thermometer was sunk. 



From the observations* were obtained 



/c_ ro-07 



0282 with 4 and 6 feet thermometer 

 068996 with 6 and 10 feet thermometer. 



In this case the Swedish foot and the year are taken as units ; if 

 instead of them the centimetre and minute are introduced, we get 



k _ f 0-269521 

 ~ 1 0-271 



S" 10-27958 J * 



The highest layer in which the thermometers were immersed, 

 consisted of a mixture of sand and clay ; the lower (5 to 10 feet) 

 of moist clay, which, on being heated, lost 19 per cent, of its 

 weight. The specific gravity and specific heat w r ere found by a 

 determination to be 



6\ c. c8. 



Argillaceous sand . 1-725 0*4416 0*7618 



Moist clay . . . 1*821 0*4448 0*8100 



from which 



£ = 0*2053 for argillaceous sand, 

 = 0-2264 for moist clay. 



If it be assumed that the mean temperature of the earth's layers 

 decreases about 1° C. for 30 metres of depth, and the con- 

 ducting-power is equal to the value obtained for k, we can easily 

 calculate the loss of heat of the earth's surface during a year. 

 Suppose the earth covered with a layer of water 282*5 millims. in 

 height, the heat communicated to it by the internal layers during 

 a year would be enough to raise the temperature of this aqueous 

 layer by 1° C. 



Postscript. — The above experiments on the conductibility of 



* " Mem. sur la Temperature de la Terre," &c., Act. Reg. Soc. Scient. 

 Upsala, S. 3. vol. i. p. 211. 



