In the Cavities of Minerals. 7 



vacuities, which instantly unite into one vacuity, that gradually 

 goes on enlarging as the temperature diminishes. 



In order to determine the expansion which takes place by a 

 given increment of temperature, I measured the relative size of 

 the vacuity, and the cavity at the temperature of 50 and 80, 

 the temperature at which the fluid had expanded so as wholly 

 to fill the cavity. In many cases this could be estimated with 

 tolerable accuracy, and it may be stated in general, from the esti- 

 mates and measures taken by myself, and by others, to whom I 

 shewed the cavities, that the fluid expands fully one-fourth of its 

 size, by an increment of 30 of heat. 



Hence, since water expands ^Vd f its Du lk in passing from 

 41, its state of maximum density, to 212, it will expand -fi^th 

 of its bulk for 30, and T T -r- = 31 ; that is, the fluid con- 

 tained in the cavities is above 30 times more expansible than 

 water, by an increment of 30 of heat at the temperature of 50. 



This extraordinary result proved beyond a doubt, that the 

 substance contained in the cavity was a new fluid, differing from 

 all known fluids in its high expansibility, and resembling in this 

 respect a gaseous more than a fluid body. 



In order to confirm this result, I was desirous of examining 

 the other physical properties of this remarkable substance. I 

 could not fail to notice, in the deep cavities especially, the singu- 

 lar volubility of the fluid, and its slight adherence to the sides of 

 the cavity, as indicated by the motion of the vacuity V. In 

 small cavities containing water, the adhesion of the fluid to the 

 stone is so strong, that the air-bubble moves with extreme diffi- 

 culty, and even when very large, it often changes its place by 

 starts, or remains stationary at the bottom or in the middle of 

 the cavity. In the present case, however, the vacuity moved 

 about with great facili ty, and in the cavity, ^th of an inch long, 

 by T a T th and T Vd of an inch wide and deep, the slightest tap of the 



