On the Compressibility of Solids 387 



trouble of replacing it, because the construction of the instru- 

 ment enables air to be completely excluded from it, and the 

 quantity of water in it to be kept within such limits that it- 



ience is of no account. When a tube bursts it usually 

 splits longitudinally up the middle into two slabs. One of 



e almost always remains entire, the other is sometimes 

 broken into fragments, but there is never any projection of 

 material unless the instrument has been carelessly put together 

 and air admitted. 



Microscismic Effects. In a research like the present where 

 the primary object is the numerical determination of a physical 

 constant, the secondary' phenomena which reveal themselves 

 are often of equal and sometimes of greater interest, because 

 they generally affect preferentially the natural history side of 

 physics. To this class belong the phenomena observed in 

 connection with the behaviour of ice under the relief of high 

 pressure in my earlier investigation 1 . In the present case the 

 frequent bursting of the glass terminals afforded the oppor- 

 tunity of observing another and very interesting phenomenon. 

 It is illustrated in Fig. 2. It was first noticed when copper 

 was being experimented with. The pressure had been 

 raised to 300 atmospheres, and had begun to fall when the tul>< 

 gave On proceeding to replace the broken tube with 



another I was astonished to find the copper wire twi-ud int. 

 a regular spiral in the tube. It made three complete tun; 



length of an inch, and the undulatory form WU \ i-ibK 

 throughout one-half of the length of the wire. Instead of 

 fixing new glass trnninaN. I cut <>ft the end of the copper 

 which showed this curious seismic effert. anl put UMri 



lace. An exactly similar effect was produced on 

 the magn.-iuin wire, \\ln-n a glass terminal l>ur-t ; <ml\ 

 effect was even more marked. The spiral produced in 

 glas- loser, and, indeed, the win- h.<l Urn >h. 



over itself ami lpik-n. for magnesium \ 



ions of greater amphtu led thr<" 



whole lei i there were maxima at distances of 



Trans., \ p. 598. 



25-2 



