Properties of the Two New Fluids in Minerals. 423 



structures of the lower world, where the force of gravity is en- 

 tirely subjected to the more powerful energy of capillary forces, 

 it is extremely probable that the mechanism of immiscible 

 fluids, and fluid valves, is generally adopted. We must leave it, 

 however, to the physiologist to determine the truth of this sup- 

 position. 



In the second, or dense fluid, whose motions we have now de- 

 scribed, there exist frequently black spicular crystals, which may 

 be made to move to different parts of the cavity. Whether or 

 not these crystals are extraneous bodies, or indicate the com- 

 mencement of that induration of the fluids which I have describ- 

 ed in a former paper, is a point which can only be ascertained by 

 observing the progressive changes which the crystals may un- 

 dergo. 



4. On the Condition of the Fluids when taken out of the Cavities. 



I have already described so fully in a former paper the sin- 

 gular movements into which the expansible fluid is thrown, when 

 it first flows out of its cavity upon the surface of the plate of to- 

 paz which contains it, that I have nothing to add upon this sub- 

 ject *. It did not then occur to me that these movements might 

 be owing to electricity, till I read an account of the following expe- 

 riment made both by Professor ERMAN and Mr HERSCHEL. When 

 a globule of water, dropped on the surface of a flat dish of mer- 

 cury, is brought into connexion with the positive pole of a gal- 

 vanic battery, while the mercury is connected with the negative 

 pole, it instantly flattens and spreads to twice its diameter, re- 

 gaining its former sphericity when the circuit is broken. This 

 extension and subsequent re-aggregation of the globule of water, 



* Some of the fluids in quartz seem to be entirely gaseous, while in sulphate of 

 barytes the fluid appears to be the mineral itself in a fluid state ; see p. 4525. and note' 

 on p. 427- 



VOL. X. P. II, 3 H 



