542 



of the superincumbent mass through which the transmission takes 

 place (in the previous case the quantity of transmitted heat is 

 independent of. that power). Consequently, whatever may be the 

 cause supplying the heat at depths not much exceeding the general 

 aggregate depth of the sedimentary beds, it must furnish a quantity 

 of heat proportional to the vertical flow of heat, i. e. a quantity pro- 

 portional to the conductive power of the superincumbent mass. 

 Thus the energy of the producing cause must have distinct relations 

 to superficial conditions. Must not, then, the cause itself be at least 

 partly superficial, and not entirely central ? The author is convinced 

 that such must be the case. He does not profess, in this paper, to 

 carry his speculations further. 



It should be remarked that the argument derived from the above 

 investigations is not directly against the theory of a primitive heat, 

 but only against the manifestation of the remains of such heat as the 

 sole cause of existing terrestrial temperatures in the superficial crust 

 of the globe, at depths beyond the sensible effect of the direct solar 

 heat. Whatever may be the weight of the argument in favour of 

 the earth's original fluidity (and therefore of its primitive heat), 

 founded on the oblateness of its form, for example, the cogency of 

 such argument remains unaltered. At the same time, all the colla- 

 teral arguments in favour of primitive heat, founded on the existing 

 temperature of the earth's crust, or the climatal changes which are 

 believed to have taken place on its surface, are deprived, the 

 author conceives, of nearly all their weight. Moreover, admitting 

 only a part of the existing terrestrial heat to be due to superficial 

 causes, the flow of heat from the earth's central portions must be less 

 by that amount than if the whole flow were due to central heat. 

 Consequently the rate of increase of terrestrial temperature due to 

 the flow of central heat must be proportionally diminished, and the 

 depth at which we should arrive at the temperature of fusion pro- 

 portionally increased. The conclusion, therefore, that the earth's 

 solid crust is as thin as some geologists have supposed it to be, as 

 well as all theories based on that conclusion whether of volcanic 

 action, or of elevation and depression of the earth's surface must 

 be deprived of nearly all their force. 



The remainder of this paper contains details of experiments, and 

 descriptions of the apparatus used in making them. 



