X. On the Progress of Heat when communicated to Spheri- 

 cal Bodies from their Centres. By John Playfatb, 

 F. R. S. Lond. Sec. R. S. Edin. and Professor of 

 Natural Philosophy in the University of Edinburgh. 



[Read March 6. 1809-] 



I. AN argument againfl the hypothefis of central heat has 

 jlJl been ftated by an ingenious author as carrying with 

 it the evidence of demonflration. 



" The eflential and characteriflic property of the power 

 " producing heat, is its tendency to exilt every where in a flate 

 " of equilibrium, and it cannot hence be preferved without lofs 

 " or without diffuhon, in an accumulated flate. In the theory 

 " of Hutton, the exiftence of an intenfe local heat, acting for 

 " a long period of time, is afTumed. But it is impoflible to pro- 

 " cure caloric in an infulated Hate. Waving every objection 

 " to its production, and fuppofing it to be generated to any ex- 

 tent, it cannot be continued, but mull be propagated to the 

 contiguous matter. If a heat, therefore, exifted in the cen- 

 tral region of the earth, it mull be difTufed over the whole 

 mafs ; nor can any arrangement effectually counteract this 

 " diffufion. It may take place flowly, but it mufl always con- 

 " tinue progreflive, and mull be utterly fubverlive of that fy- 

 " Hem of indefinitely renewed operations which is repre- 

 Vol.VI. P. II. Yy " fented 



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