100 Dr Brewster on the Existence of Tim New Fluids 
pass from one branch of a cavity to another branch, our 
author did not doubt that the vacuities of the portions B and 
C had passed over the second fluid into the portion A. In 
order to determine this, an accurate drawing of all the phe- 
nomena was taken at a temperature of 50°, as represented in 
Fig. 6., and the changes carefully watched which took place, 
by raising the temperature to 83°. The new fluid at A gradu- 
ally expanded itself, till it filled all the four cavities Y, X, Y, Z ; 
but as the portions B, C, had no cavities for this purpose, they 
could only expand themselves, by pushing back the suppo- 
sed second fluid DEF, This actually happened. The se- 
cond 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 retreated to its new limit 
m n ?i f o, and being itself but slightly expansible, like common 
fluids, its other limit necessarily advanced to p q r. This ex- 
periment, which has often been repeated, and shewn to others, 
involves one of those rare combinations' of circumstances, 
which Nature sometimes presents to us, in order to lay open 
some of the most mysterious of her operations. Had the por- 
tions B, C, of the new fluid been accompanied, as is usual, with 
their vacuities, the interposed second fluid would have remain- 
ed immoveable between the two equal and opposite expan- 
sions : 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. Upon the ap- 
plication of heat, the summits g h become more acute, and gra- 
dually approach to each other, till they suddenly unite, and force 
back the surface of the second fluid into the line m n n' o. A 
portion of the second fluid, however, is retained by capillary at- 
traction, in the angular meeting of the planes, between c and F, 
and between d and F, and also a small portion at /J a phenomenon 
which affords an ocular explanation of the immobility of the 
