98 POPULAR LECTURES AND ADDRESSES. 



that of an equal mass of water under ordinary 

 pressure. A British jury could not, I think, be 

 easily persuaded to disregard my present estimate 

 by being told that I have learned something in 

 fifteen years. 



19. (III.) Referring to my third line of argument 

 founded on a consideration of terrestrial tempera- 

 ture, Professor Huxley asks the question, " But is 

 " the earth nothing but a cooling mass, ' like a 

 " hot-water jar, such as is used in carriages,' or 

 " ' a globe of sand-stone,' and has its cooling been 

 " uniform ? " and says, " An affirmative answer to 

 " both these questions seems to be necessary to 

 " the validity of the calculations on which Sir 

 " W. Thomson lays so much stress." I reply that 

 I have carefully considered the first question, and 

 referred to it in my paper on the " Secular Cooling 

 of the Earth," 9, 1 or Thomson and Tait's Natural 

 Philosophy, Appendix D, i. ; and that the main 

 purport of that paper constitutes a negative answer 

 to the second question. I have distinguished the 



1 " Secular Cooling," 18 ; Transactions of the Royal Society of 

 Edinburgh, 1862; Phil. Mag., 1862; or, Thomson and Tait, 

 Appendix, D, 5. 



