No. 25. [From Trans. Roy. Soc. Edin. 1880, Vol. xxix. p. 589.] 



PRELIMINARY NOTE ON THE 

 COMPRESSIBILITY OF GLASS 



THE following experiments were undertaken with a view 

 to determine by actual observation the effect produced on 

 solids by hydraulic pressure. 



. The instrument was constructed according to my directions 

 by Mr Milne of Milton House, about two years ago, but it is 

 only now that I have been able to devote myself to its applica- 

 tion to the purposes for which it was designed. It consists 

 of a hydraulic pump, which communicates with a steel receiver 

 capable of holding instruments of considerable size, and also 

 with a second receiver of peculiar form. This receiver consists 

 essentially of a steel tube, terminated at each end by thick 

 glass tubes fitted tightly. It is tapped at the centre with two 

 holes, the one to establish connection with the pump, and the 

 other to admit a pressure gauge or manometer. The steel 

 tube may be of any length, being limited only by the extent 

 of laboratory accommodation at disposal. The tube which 

 I am using at present has a length of a little over six feet, and 

 an internal diameter of about three-tenths of an inch. The 

 solid to be experimented on must be in the form of a rod or 

 wire, and must, at the ends at least, be sufficiently small to 

 be able to enter the terminal glass tubes, which have a bore 

 of O'o8" and an external diameter of 0-42". The length of the 

 solid is such that when it rests in the steel tube its ends are 

 visible in the glass terminations. 



When the joints have all been made tight, the experiment 

 is conducted as follows: A microscope, with micrometer eye- 

 piece, is brought to bear on each end of the rod or wire. These 

 microscopes stand on substantial platforms altogether inde- 



