No. 26. [From Proc. Roy. Soc. 1904, Vol. LXXIII. pp. 296 310]. 



ON THE COMPRESSIBILITY OF SOLIDS 



THE solids dealt with in this research are the metals plati- 

 num, gold, copper, aluminium, and magnesium. Their absolute 

 linear compressibilities were directly determined at pressures 

 of from 200 300 atmospheres at temperatures between 7 and 

 11 C. The determinations were made by the same method, 

 and with the same instrument which I used for the deter- 

 mination of the compressibility of glass in i860 1 . As nearly a 

 quarter of a century has passed since then it will be expedient 

 to recall the principal features of the instrument, and of the 

 method. 



The idea of it occurred to me on the evening of March 23, 

 1875, the day on which the "Challenger" made her deepest 

 sounding, namely, 4475 fathoms (8055 metres), and I was able 

 to put it in practice six days later, on March 29, when, however, 

 the depth was only 2450 fathoms (4410 metres). The obst ; 

 tions which I was making during the voyage on the compressi- 

 bility of water, sea-water, and mercury, were of little value 

 without a knowledge of the compressibility of the envelope 

 which contained them. It was a matter to which I had given 

 much thought. I had studied all the methods which had been 

 used up to that date, but they had all turned out to be fault v. 



The idea of utilising the linear compressibility of glass in 

 order to arrive at its cubic compressibility had occurred to in< . 

 as it had, no doubt, occurred to many others, before. The 

 difficulty lay in giving the idea experimental expression. It 

 was clear that tli instrument would fall to be classed as a 

 piezometer, and would have to be a self-registering one, because 

 what takes place in the depths of the sea is removed from 

 observation. All my piezometers contained a li|uil, and this 



1 Roy. S<< /'raw. vol. p. 589, and this volume, paper 



5, P- 35. 



242 



