aeriform matter in cavities found in certain crystals. 3 69 
> & 
included, and the elastic fluid confined with it, supposing it 
non-absorbable, ought to be in the same state of density. On 
the contrary, if the earthy matter and the fluid separated 
from each other under a much higher temperature than that 
now belonging to the surface, a certain vacuum might be ex- 
pected in the cavity from the contraction of the fluid, and if 
any gas were present, a considerable rarefaction of it ; and 
though, supposing a much higher temperature on the surface 
of the globe, the atmosphere formed by aqueous vapour must 
have had much greater absolute weight, which, as liquids 
are compressible , must have influenced the volume of the 
fluid at the time it was inclosed, a circumstance which would 
render it impossible to draw any conclusion as to the exact 
temperature, yet still the experiments appeared to offer, on 
any view, interesting results ; and I was the more desirous 
of performing them, as I believe the nature of the fluid and 
aeriform matters included in rock crystals and other siliceous 
stones, has never been accurately ascertained. 
Having purchased some crystals, and having had others 
committed to my care by the liberality of my Brother Trustees 
of the British Museum, and of my friend Professor Buckland, 
I proceeded to make the necessary experiments upon them. 
It will be improper for me to take up the time of the Society 
by a minute description of my manipulations. Holes were 
drilled in the crystals by the use of diamonds, generally by 
Mr. Newman, under distilled water, or mercury, the gas was 
expelled by the introduction of wires, and the fluids included 
in the cavities were drawn out by means of fine capillary tubes, 
and experiments were afterwards made to determine the space 
they occupied, which had been accurately measured and 
MDCCCXXII 0 3 B 
