150 



Mr. W. N. Hartley on the 



[Apr. 12, 



IV, " On the Constant Vibration of Minute Bubbles.*' By 

 Walter Noel Hartley, F.B.S.E., King's College, London. 

 Communicated by Prof. Stokes, Sec. U.S. Received March 3, 

 1877. 



Those who have given great attention to the study of fluid-cavities in 

 minerals have occasionally met with vibrating particles which are appa- 

 rently bubbles. 



I first became acquainted with these at the close of last year, 1875, 

 when Mr. P. J. Butler was kind enough to show me a ruby containing 

 a cavity partially filled with liquid carbonic acid, the bubble in which, 

 when of small size, was in constant motion. I was much struck with 

 this, and immediately connected it with the motions caused by heat which 

 have just been described, but which at that time had not been so fully 

 studied. 



During this last summer I have had' the opportunity of examining a 

 specimen of felstone from Snowdon, for the loan of which and for a 

 section of the same stone I am much indebted to Mr. J. C. Young, E.G-.S. 

 This contained portions of quartz with many cavities. The majority of 

 these were water-cavities, but others appeared to be empty ; and in one 

 of them Mr. Young had noticed a moving particle, supposed to be a 

 bubble, which made its appearance only in a cold atmosphere. By drop- 

 ping a little ether on the object, the evaporation cooled it sufficiently to 

 condense a liquid in the cavity, and the moving particle was easily seen 

 with a magnifying-power of 400 diameters. By immersion in iced 

 water, the temperature of which was 3 0, 5 C, the cavity has the appear- 

 ance of being two thirds filled with a liquid, the gas-bubble of course 

 occupying the remaining space and having a sort of trembling motion. 

 The bubble decreased in size, and the motion became more and more 

 rapid as the size became smaller, until it rushed up and down and across 

 the space in which it was confined. The cavity and the bubble are 

 represented in fig. 7 (p. 139) by A, and the course of the bubble during 

 rapid motion by C. The thought immediately occurred that this was not 

 a gas-bubble, but a liquid in the spheroidal condition — in all proba- 

 bility carbon dioxide in a perfectly dry condition, and perhaps mixed 

 with some incondensable gas, so that its critical point was lowered. A 

 considerable number of experiments was necessary in order to arrive 

 at a judgment as to whether the moving particle was liquid or gaseous ; 

 for if it were the former the particle would diminish by rise of tempera- 

 ture through evaporation, if the latter through contraction of the bubble 

 consequent on expansion of the surrounding liquid. Variations in tem- 

 perature caused the following changes : — 



