226 Fluids in the Cavities of Minerals. 
portion A. In order to determine this, an accurate drawing 
of ail the phenomena was taken at a temperature of 50°, as 
represented in fig. 6, and the changes carefully watehed which 
took place, by raising the temperature to 83°. The new flu- 
id at A gradually expanded itself, till it filled all the four 
cavities V, X, Y, Z; but as the portions B, C, had no cavi- 
ties for this purpose, they could only expand themselves, by 
pushing back the supposed second fluid DEF. This actual- 
ly happened. The second fluid quitted entirely the edge of 
the cavity at F, The two portions of new fluid B, C, were 
immediately united into one; and the second fluid having re- 
treated to its new limit m nn’ v, and being itself but slightly 
expansible, like common fluids, its other limit necessarily ad- 
vanced to p qr. his experiment, which has often been re- 
peated and shewn to others, involves one of those rare combi- 
nations of circumstances, which Nature sometimes presents to 
us, in order to lay open some of the most mysterious of her 
operations. Had the portions B, C, of the new fluid. been 
companied, as is usual, with their vacuities, the interposed 
second fluid would have remained immoveable between the 
two equal and opposite expansions: but, from the accidental 
circumstance of these vacuities having passed over into the 
other branch A of the cavity, the second fluid is placed in a 
sort of unstable equilibrium, and, like the arms of a lever, it 
yields to every variation of the power and of the resistance. 
If any additional evidence were wanted on this subject, we 
have only to examine the mode in which the two portions of 
the new fluid B, C, are united into one, by a disunion of the 
second fluid at g h, and again separated by its reunion. 
on the application of heat, the summits g h become more 
acute, and gradually approach to each other, till they sudden- 
ly unite, and force back the surface of the second fluid into 
the line mnn'o. A portion of the second fluid, however, is 
retained by capillary attraction, in the angular meeting of t 
planes, between ¢ and F, and between d and F, and also a 
smal! portion at f, a phenomenon which affords an ocular ex- 
planation of the immobility of the second flnid im the termina- 
tions and angles of cavities. When the fluids again cool, t 
Surface 7 n! approaches to ¢ d, and when n is near c, the two 
surfaces nn’, and those of the same fluid in c F and d F, sud- 
ueny Start into union, in virtue of their mutual attraction, 
and the portions B and C are again separated. 
