216 Refrigeration of the Earth. 



his own on the world. But no, he kept by his demonstrations, 

 his measurements, and his proofs." 



Gentlemen, let us, as far as is consistent with the nature of 

 geological investigation, show the strength and soundness of our 

 philosophy in the same manner. 



That heat of considerable intensity prevails occasionally, in 

 certain places, at some depth, is all that we have as yet clearly 

 established. Whether that heat is permanent, whether it is ge- 

 nerally diffused, whether it is central, are questions of mere 

 speculation. 



Intimately connected with the hypothesis of central heat is 

 that of refrigeration. 



It has been observed by one of our members, that " the re- 

 mains, both of the animal and vegetable kingdom, preserved in 

 strata of different ages, indicate that there has been a great di- 

 minution of temperature throughout the northern hemisphere, 

 in the latitudes now occupied by Europe, Asia, and America ; 

 the change has extended to the arctic circle as well as to the 

 temperate zone ; the heat and humidity of the air, and the uni- 

 formity of climate, appear to have been most remarkable when 

 the oldest strata hitherto discovered were formed. The ap- 

 proximation of a climate similar to that now enjoyed in these 

 latitudes, does not commence till the aera of the formations 

 termed tertiary ; and while the different tertiary rocks were de- 

 posited in succession, the temperature seems to have been still 

 further lowered, and to have continued to diminish gradually 

 even after the appearance of a great portion of existing species 

 upon the earth."*' The little knowledge we have of the fossil 

 productions of countries south of the temperate zone, induces 

 me to believe that these observations are as applicable to the 

 southern hemisphere as to the northern. 



This refrigeration, one of the most undoubted facts in geo- 

 logy, is supposed by the Huttonians, and, if I mistake not, by 

 M. Elie de Beaumont and others, to arise from a decrease of 

 the central heat ; an opinion, however, which cannot I think be 

 supported. 



We know of one method only by which central heat, if it 

 exists, can pass from the earth, viz. by radiation. It cannot 

 pass by conduction. Conduction implies conductors, which in 



