ADDRESS SECTION A, n.A. 1876. 241 



in observations of underground temperature is 

 scarcely one kilometre ; and that if a ten per 

 cent, diminution of the rate of augmentation of 

 underground temperature downwards were found 

 at a depth of one kilometre, this would demon- 

 strate l that within the last 100,000 years the 

 upper surface of the earth must have been at a 

 higher temperature than that now found at the 

 depth of one kilometre. Such a result is no 

 doubt to be found by observation in places 

 which have been overflown by lava in the memory 

 of man or a few thousand years further back ; 

 but if, without going deeper than a kilometre, a 

 ten per cent, diminution of the rate of increase 

 of temperature downwards were found for the 

 whole earth, it would limit the whole of geological 

 history to within 100,000 years, or, at all events, 

 would interpose an absolute barrier against the 

 continuous descent of life on the earth from earlier 

 periods than 100,000 years ago. Therefore, al- 



1 For proof of this and following statements regarding under- 

 ground heat, I refer to "Secular Cooling of the Earth," Transac- 

 tions of the Royal Society of Edinburgh, 1862 ; and Thomson and 

 Tait's Natural Philosophy, Appendix D. 



VOL. II. R 



