and aeriform matter in cavities found in certain crystals. 375 
APPENDIX. 
Since the foregoing pages were communicated to the Royal 
Society, I have made some new experiments on the same 
subject ; all of them, except two, offered results of the same 
kind as those I have detailed, and upon such I shall not enter : 
but these two, from their peculiarity, will not, I trusty be 
thought unworthy of a particular notice. 
In examining, with Mr. Heuland, the beautiful specimens 
of rock crystals in the collection of Charles Hampden 
Turner, Esq. I observed one crystal which, Mr. Heuland 
informed me, was from La Gardette, in Dauphin^, that con- 
tained a considerable cavity, in which there was a viscid 
brownish liquid, resembling in its appearance and consistence 
linseed oil. As the void space or cavity filled with aeriform 
matter appeared considerable in proportion to the fluid, I ex- 
pressed a desire to pierce the crystal ; and Mr. Turner, 
hearing of my wish, was so kind as to gratify it in the most 
polite and liberal manner, by presenting to me the specimen. 
With Mr. Newman’s assistance I made the usual experiments 
upon it. The cavity was pyramidal, and nearly the third of 
an inch in diameter. I soon ascertained that the fluid was 
not water, as it congealed and became opaque at a tempera- 
ture of 56°. When the crystal was pierced under distilled 
water, the water rushed in and entirely filled the cavity, so 
that no other aeriform matter but the vapour of the substance 
could have been present ; the water was rendered white and 
cloudy, apparently by the substance. I endeavoured to col- 
lect some of it for chemical examination, but it was too small 
in quantity (not equalling in volume i of the volume of the 
cavity,) to be submitted to analysis. It swam on the water, had 
