386 On the Compressibility of Solids 



which occupy a homologous position. If these facts indi 

 anything more general, we should expect the metals of the 

 palladium and the iron groups to have a low compressibility 

 like platinum, zinc and cadmium to have a very high com- 

 pressibility like magnesium, and thallium an intermediate but 

 still considerable compressibility like aluminium. 



It will be observed that the two kinds of glass mentioned 

 in Table VII are more compressible the greater their density. 

 This may, however, be due to a specific feature of the oxide of 

 lead which enters largely into the composition of the flint glass. 



It is obvious that there is here a great field for interesting 

 research, and fortunately the method is capable of great refine- 

 ment ; only, the successful application of it requires considerable 

 manipulative skill, as well as great patience. The necessity to 

 have, as part of the apparatus, two glass tubes which are 

 exposed to the high pressure on the inside only, introduces an 

 element of chance into the work which is sometimes annoying 

 and sometimes exciting. It is impossible to say beforehand 

 whether a particular glass terminal will stand or not. It is 

 necessary to be provided with a large reserve of them before 

 beginning work, and when one fails another is put in its place 

 without loss of time. Hitherto I have taken no particular 

 care of my glass terminals, because I can always depend on 

 finding plenty of them which will stand from 200 300 atmo- 

 spheres, and there is abundance of work to be done at these 

 pressures. When, however, it is desired to use higher pressures, 

 it will be prudent to take some measures for preventing the 

 points of the wires scratching the internal surfaces of the 

 terminals. When some precaution of this kind has been taken, 

 casualties will be less frequent, and the attainment of higher 

 pressures will be merely a question of how many glass ends the 

 bbserver is prepared to sacrifice in the service. 



In the work connected with this paper, which extended 

 over the greater part of four weeks, fifteen glass terminals gave 

 way ; and oddly enough, the failures were as nearly as possible 

 equally distributed between the two ends; eight of them fell 

 to the left arm and seven of them to the right arm. The 

 bursting of a terminal causes no inconvenience beyond the 



