1909] Experiments at High Temperatures and Pressures. 541 



WEEKLY EVENINCt MEETING, 



Friday, March 19, 1909. 



Geokge Matthey, Esq., F.R.S. F.C.S., Manager, 

 in the Chair. 



RiCHAED Threlfall, Esq., M.A. F.R.S. Assoc.Inst.C.E. F.C.S. 



Experiments at High Temperatures and Pressures. 



Within a few miles of this lecture room there is an unexplored 

 region — to approach it we should have to move vertically downwards. 

 It has been suggested by Mr. Parsons * that it would be worth while 

 to make a short expedition in this direction, but the journey would 

 be slow and the cost high — for instance, to bore a hole 12 miles deep 

 was estimated to be a labour which would occupy eighty-five years 

 and cost 5,000,000/. A well-to-do man desiring to benefit his fellow 

 creatures could not do better than undertake this project, but till he 

 comes forward we must perforce be content to try to imitate in our 

 laboratories the temperature and pressure conditions which would be 

 met with deep down in the earth. 



Information, attainable from experiments under these condi- 

 tions, is essential to the development of any exact concept of the 

 structure and evolution of the earth. One of the most important 

 questions in connection with the study of bodies under high pressures 

 and at various temperatures is, as to whether any particular body is 

 solid or liquid under specified conditions, and, if soHd, whether it is 

 amorphous, glassy or crystalline. That pressure would influence the 

 melting point of solids was clearly put forward by Clapeyron in 1834, 

 but it was not till after the establishment of the mechanical theory of 

 heat in the " forties " of the last century that the exact numerical rela- 

 tions could be established, as was done by Prof. James Thomson in 

 1851, when he calculated for the first time the amount by which the 

 temperature of fusion of ice would be reduced by a given increase of 

 pressure. The ideas underlying such calculations are based on a con- 

 sideration of the way in which heat is converted into mechanical work 

 in any prime mover depending on a heat-supply, and were first formu- 

 lated by Carnot in 18:^4, before the true nature of heat was under- 

 stood. As the matter is fully dealt with in every text-book, I will 

 merely remind you that Prof. James Thomson was able to oljtain an 

 equation between the mechanical work actually produced under stated 

 conditions and the work which, according to Carnot's principle, must 

 be developed by a reversible engine operating between fixed tempera- 

 ture limits upon a given amount of heat. 



* B. A. Eeports, Cambridge, 1904, 672. 



