12 DR BREWSTER on the Existence of Two New Fluids 



might, in virtue of the elasticity of the stone, have closed up 

 completely, so as to transmit the light as freely as if it had never 

 existed. This process is by no means a hypothetical one. I 

 have repeatedly formed these fissures in glass, and have some- 

 times seen them close up in a few minutes, without leaving a 

 trace of their existence behind. When they are wide, a day, a 

 week, and sometimes a month was necessary, to effect the re- 

 union of their sides *. 



These circumstances enable us to give a satisfactory expla- 

 nation of the remarkable phenomenon represented in Fig. 5. 

 When the expansive force of the imprisoned fluid was sufficient 

 to make it penetrate the stone, it would probably escape at the 

 weakest point of the cavity, and pass to the surface through a 

 narrow channel, which the elasticity of the stone would imme- 

 diately close up. These fissures would probably he in the di- 

 rection of the cleavage, and this seemed to be the path which 

 the globules took in their oblique ascent, as represented in 

 Fig. 5, 



4. Amethyst from Siberia. 



The greatest quantity of the new fluid which I have yet 

 seen, exists in a specimen of Amethyst belonging to THOMAS 

 ALLAN, Esq. This very interesting specimen is represented in 

 Fig. 7., where a, b, c, d, e, represent five cavities parallel to each 

 other. The largest of these is |f of an inch in length, and ^yth 

 of an inch in breadth ; and the vacuity is about one-fourth part 

 of the whole cavity. By the heat of the hand the fluid swells, 

 and fills all the cavities, and when the vacuity has been consi- 

 derably reduced by heat, it moves from one end of the cavity to 

 the other, with a degree of volubility truly surprising. By a 



* A full account of these experiments will be found in the Philosophical Trmt- 

 sactwns for 1816, p. 73. 



