CAVITIES IN MINERALS. 



335 



acting upon each other, induced many persons to 

 whom I showed the phenomenon to consider the 

 lines in n, o p, Fig. 80, 81, as a partition in the 

 cavity, or the spaces Am H, op C, either as filled 

 with solid matter, or as corners into which the 

 expanding fluid would not penetrate. The 

 regular curvature, however, of the boundary line 

 m w, op, and other facts, rendered these sup- 

 positions untenable. 



This difficulty was at last entirely removed by 



the discovery of a cavity of the form shown in 



the annexed figure, where A, B, and C are three 



portions of the expansible fluid separated by the 



Fig. 83. 



interposition of the second fluid DEF. The first 

 portion A of the expansible fluid had four vacui- 

 ties V, X, Y, Z, while the other two portions 

 B, C, had no vacuity. In order to determine if 

 the vacuities of the portions B, C, had passed 

 o\er to A, I took an accurate drawing of the 

 appearances at a temperature of 50, as shown 

 in the figure, and I watched the changes which 

 took place in raising the temperature to 83. 

 The portion A gradually expanded itself till it 

 filled up all the four vacuities V, X, Y, and Z, 

 but as the portions B, C, had no vacuities, they 

 could expand themselves only by pushing back 



