Fluids in the Cavities of Minerals. 215 
Sect. 3. On the phenomena of two immiscible Fluids, 
without a vacuity, in the cavities of minerals: 
Sect. 4. On the changes which these fluids have under- 
gone in particular crystals. 
Sect. 5. On the vaporisation and decomposition of the 
new fluid at low temperatures, when enclosed in the cavities 
of minerals. : 
Sect. 6. On the phenomena of the two new fluids when 
taken ont of the cavities. 
Sect. 7. On the existence of moveable crystals in a fluid 
cavity of quartz. * 
ect. 8. On the phenomena of a single fluid in the cavities 
of minerals and artificial crystals. 
Sect. I.—On the existence of a new fluid in the cavities of — 
Minerals. 
While examining the cavities of crystallised bodies, our 
author observed such remarkable differences in the pheno- 
mena of the fluids which they enclosed, that he found it im- 
possible to explain them upoh the supposition of their being 
fluids possessing the ordinary properties of that class of -bo- 
dies. Hence he was led, by the following train of reasoning, 
to ascribe these phenomena to new fluids, possessing new 
physical properties. 
In examining the topazes from New-Holland, Scotland and 
Brazil, he observed the cavities arranged in strata. These 
cavities are sometimes beautifully crystallised, and sometimes 
amorphous, sometimes extremely shallow, and at other times 
deep. ae 
e so . 
Trey are filled with a colourless and trans fluid, as 
shown at ABCD, fig. 1, plate 2, and have almc st always a 
vacuity V, of a circular form, which moves by an inclination 
of the plate to different parts of the cavity. The depth of 
the cavity may be easily estimated by the breadth of its 
bounding line ABCD, which, in the flat cavities, 1s generally 
the same as that of the circle V. In very s cavities, 
this boundary is a narrow line, scarcely visible, and in deep 
Ones it is broad, with a penumbral termination inwards, aris~ 
ing from the deviation of the light at the separating surfaces 
of the fluid, and the topaz, and at that of the fluid and the 
vacuity. = 
“When the hand is applied to the crystal, the heat of it 
gradually expands the fluid. The vacuity V conseq 
