70 Lord Kelvin on the Age of the 



my mind to this day. We had been hearing a brilliant and 

 suggestive lecture by Professor (now Sir Archibald) Geikie 

 on the geological history of the actions by which the existing 

 scenery of Scotland was produced. I asked Ramsay how long 

 a time he allowed for that history. He answered that he 

 could suggest no limit to it. I said, " You don't suppose 

 things have been going on always as they are now ? You 

 don't suppose geological historvhas run through 1,000,000,000 

 years?" "Certainly I do/' " 10,000,000,000 years V } ' ; Yes." 

 " The sun is a finite body. You can tell how many tons it is. 

 Do you think it has been shining on for a million million 

 years ? " "I am as incapable of estimating and under- 

 standing the reasons which you physicists have for limiting 

 geological time as you are incapable of understanding the 

 geological reasons for our unlimited estimates." I answered, 

 " You can understand physicists' reasoning perfectly if you 

 give your mind to it." I ventured also to say that physicists 

 were not wholly incapable of appreciating geological diffi- 

 culties ; and so the matter ended, and we had a friendly 

 agreement to temporarily differ. 



§ 9. In fact, from about the beginning of the century till 

 that time (1867), geologists had been nurtured in a philosophy 

 originating with the Huttonian system: much of it substantially 

 very good philosophy, but some of it essentially unsound and 

 misleading : witness this, from Playfair, the eloquent and able 

 expounder of Hutton : — 



"How often these vicissitudes of decay arid renovation have been 

 repeated is not for us to determine ; they constitute a series of which as 

 the author of this theory has remarked, we neither see the beginning nor 

 the end ; a circumstance that accords well with what is known concerning 

 other parts of the economy of the world. In the continuation of the 

 different species of animals and vegetables that inhabit the earth, we 

 discern neither a beginning nor an end : in the planetary motions where 

 geometry has carried the eye so far both into the future 'and the past we 

 discover no mark either of the commencement or the termination of the 

 present order." 



§ 10. Led by Hutton and Playfair, Lyell taught the 

 doctrine of eternity and uniformity in geologv : and to 

 explain plutonic action and underground heat, invented a 

 thermo-electric " perpetual " motion on which, in the vear 

 1862, in my paper on the " Secular Cooling of the Earth"* 

 published in the " Transactions of the Royal Societv of Edin- 

 burgh/ I commented as follows : — 



* Reprinted in Thomson and Tait, ' Treatise on Natural Philosophy,' 

 1st and 2nd Editions, Appendix D (g). 



