loS POPULAR LECTURES AND ADDRESSES. 



Popular Geology." I have no wish to press the 

 charge, merely for the sake of proving myself to 

 have been in the right at the time I made it ; and 

 if it rested solely on the question of geological 

 time, I would willingly avoid repeating it. But in 

 some of the most recent geological writings of the 

 highest character I still find the same tendency to 

 overlook essential principles of thermodynamics, 

 as that to which I called the attention l of the 

 geological section of the British Association, at 

 Manchester in 1861. 



26. In the last edition of The Principles of 

 Geology, 1868, vol. 2, page 242, we find the 

 following statement : " The existence of electrical 

 " currents in the earth's crust, and the changes in 

 " direction which they may undergo after great 

 : ' geological revolutions in the position of mountain 

 " chains, and of land and sea, the connection also 

 " of solar and terrestrial magnetism, and of this 

 " lust with electricity and chemical action, may 



1 In a Communication published afterwards, under the title, 

 "Secular Cooling of the Earth," in the Transactions of the Royal 

 :y of Edinburgh, 1862, and in Thomson and Tail's Natural 

 1'hilosopliy, Appendix D (1867). 



