Properties of the Tivo New Fluids in Minerals. 415 



a variety of cavities of different lengths and sizes, bounded by 

 parallel lines, and communicating by narrow channels, which al- 

 most escape the cognisance of the microscope. In these cavi- 

 ties thus curiously combined, the two new fluids are arranged 

 in the most remarkable manner, the dense fluid occupying 

 all the necks, and angles, and narrow channels, while the ex- 

 pansible one is left in the open and less capillary spaces. When 

 the heat of the hand is applied to the specimen, the fluids in 

 the cavities are all set in motion. The dense fluid quits its 

 corners, and assumes new localities ; and the different portions 

 of the expansible fluid either unite into one, or are subdivided 

 by the interposition of some portion of the dense fluid, which 

 has been expelled from its primitive situation, and drawn into 

 its new position by capillary action. When the specimen is 

 allowed to cool, the two fluids quit their new position ; and, as 

 if they were endowed with vitality, they invariably resume the 

 same positions which they occupied at the commencement of 

 the experiment. 



Another form of the cavities still more remarkable occurs in 

 a very fine specimen belonging to Mr SIVRIGHT. These cavities 

 resemble a number of parallel cylinders, as shewn at AB in 

 Fig. 7. Plate XX ; but, owing to some cause which it is difficult 

 to conjecture, a number of them have been afterwards turned 

 aside towards C, so as to be open at one of their extremities. 

 From these extremities, which terminate in the surface ACB, 

 the fluids have made their escape, and have left the interior of 

 the cavities lined with a black and brown powdery residue, which 

 always remains after their evaporation. When the cavities thus 

 inflected and deprived of their fluids are submitted to the mi- 

 croscope, they exhibit the most extraordinary shapes ; some of 

 which are represented in Figs. 1, 2, 3, 4, 5, and 6, of Plate XX. 

 They have the appearance of having been formed by a turning 



VOL. x. P. ii. 3 G 



