238 Proceedings of the Royal Physical Society. 



I. On the Natural Agencies at present in operation, to which the 

 Phenomena of the Glacial Epoch may be ascribed. By the Rev. 

 James Brodie, Monimail, Fife. 



Of all the discoveries which geologists have made, there 

 are none that have excited greater interest, or given rise to 

 more varied discussion, than those which relate to the glacial 

 epoch. 



Confining our view to the British Islands, we find that, 

 after the lapse of many ages, during which the temperature 

 seems to have been as warm, or even warmer, than that 

 which now prevails, the country had been subjected for a 

 lengthened period to all the rigours of a polar climate. 

 This severity of climate had again been gradually amelio- 

 rated, till at last it gave place to the equable warmth which 

 we now enjoy. 



We need not, therefore, wonder that a lively interest has 

 been excited in the various endeavours that have been 

 made to discover the causes to which these phenomena are 

 to be attributed. 



In the following observations, it is our object to show 

 that the changes to which we have alluded may all be ex- 

 plained by a reference to the varying effect of the natural 

 agencies by which the solar heat, communicated to the in- 

 tertropical regions, is afterwards distributed over the earth ; 

 and we hope, by a little careful consideration, to establish 

 the accuracy of our views. 



These agencies are three in numbers — I. The air which 

 covers the land ; II. The air that covers the sea ; and III. The 

 surface water of the ocean. 



I. The first of the natural agencies by which the equato- 

 rial heat is distributed over the globe, is that of the air which 

 covers the land within the torrid zone. 



A part of the heat communicated to the intertropical 

 lands passes by radiation into space. Another part is com- 

 municated by contact to the air which lies above them. 

 This latter part we know to be very considerable, though it 

 is difficult to determine the proportion it bears to - that 

 which is given off by radiation. The air, thus warmed and 



