296 



Mr. J. Y. Buchanan. 



[Feb. 11, 



"On the Compressibility of Solids." By J. Y. Buchanan, F.B.S. 

 Received February 11, — Bead February 25, 1904. 



The solids dealt with in this research are the metals platinum, gold, 

 copper, aluminium, and magnesium. Their absolute linear compressi- 

 bilities were directly determined at pressures of from 200 — 300 

 atmospheres at temperatures between 7° and 11° C. The determina- 

 tions were made by the same method, and with the same instrument 

 which I used for the determination of the compressibility of glass in 

 1880.* As nearly a quarter of a century has passed since then it will 

 fee 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 

 '8 days later, on March 29, when, however, the depth was only 

 -2450 fathoms (4410 metres). The observations which I was making 

 during the voyage on the compressibility of water, sea-water, and 

 mercury, were of little value without a knowledge of the compressi- 

 bility 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 

 faulty. 



The idea of utilising the linear compressibility of glass in order to 

 arrive at its cubic compressibility had occurred to me, as it had, no 

 doubt, occurred to many others, before. The difficulty lay in giving 

 the idea experimental expression. It was clear that the 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 liquid, 

 and this I had recognised to be fatal to absolute measurements. The 

 problem had, therefore, come to be : to design a piezometer which 

 should contain no liquid ; and it was the solution of this problem 

 which occurred to me on the evening of March 23, 1875. 



The form which the instrument took was very simple. In my 

 laboratory outfit I had included some lengths of tubing suitable for the 

 stems of piezometers, of which I had to make a number during the 

 voyage. In order to be able to use the indices of broken deep-sea 

 thermometers, the tubes had the same internal diameter as the stems 

 of these instruments, about 1 mm. On the -outside of the tubes a 

 scale of millimetres was etched. I took the greatest available length 

 of this tube, namely 60 cms. I then drew out a wire of the same 

 glass and passed it into the tube until it appeared at the other end of 

 * 'Roy. Soc. Edin. Trans.,' vol. 39, p. 589. 



