Fluids in the Cavities of Minerals. : 217 
vould be estimated = — accuracy, and it may be 
stated in general, from the estimates and measures taken by 
different persons, to Whom the eatites were shown, that the 
fluid expands fully one-fourth of its size, by an increment of 
30° of heat; and that it is nearly 32 times more expansible 
than water, by an increment of 30° of heat at the tempera- 
ture of 50°, 
This extraordinary result proved beyond a doubt, that the 
substance contained in the cavity was a new fluid, differing 
from all known fluids in its high expansibility, arid resem- 
bling in this respect 4 gaseous more than a fluid body. 
In order to confirm this result, our author was desirous of 
cuneate the other physical properties of ‘this remarkable 
substance. He noticed, in the deep cavities especially, the 
singular volubility of the fluid, and its slight adherence to the 
sides of the cavity, as indicated by the motion of the vacuity 
VY. In small cavities containing water, the adhesion of the 
fluid to the stone is so strong, that the air-bubble moves with 
extreme difficulty, and even when very large, it often changes 
its place by starts, and remains stationary at the Paci or 
in the middle of the cavity. In the present case, howeve 
the vacuity moved about with great facility, and in the pee = 
zy of an inch long, by 3's and 3; of an inch wide and deep, 
the slightest tap of the finger on 1 the mic roscope, caused the 
air-bubble to tremble and oscillate in this microscopic level. 
ence the new fluid is distinguished by a second physical 
property, no less remarkable than the first. 
Although no doubt was now entertained of the accuracy 
of the conclusion, that the fluid was a new one, yet it was 
conceived ible to obtain an approximate measure of its 
refute power, and thus to put its novelty beyond the reach 
of adoubt. In order to do this, it became necessary to ob- 
serve the manner in which the total reflexion of the upper 
surface of the cavity was modified by the contact of the fluid, 
and to measure the angle at which total reflexion was effect- 
ed, by the separating surface of the fiuid and the solid. For 
this purpose, our author took a plate of topaz AB, fig. 2, 
with a stratum of cavities mn, perfectly parallel to the natural 
surface of the plate. He then placed upon each surface the 
rectangular prisms ABC, ABD, and introduced between 
them a thin film of oil of cassia. Rays of light RS, RS 
were then allowed to fall upon the stratum of the cavities mn, 
so that the rays reflected from the upper surface of the cavity 
VOL. XII. No. 2. 28 
