BY PRESSURE IN THE MOLECULES OF BODIES. 
95 
like manner it will be found that in sulphate of lime and glauberite the ex- 
pansions and contractions will be so related to the three axes, as to explain the 
conversion of the biaxal into the uniaxal structure, and the subsequent reappear- 
ance of the biaxal structure in a plane at right angles to that in which the axes 
are found at ordinary temperatures. 
The phenomena exhibited by fluids under the influence of heat and pressure, 
and those of doubly refracting crystals, exposed to compressing or dilating 
forces, are in perfect conformity with the above views ; so that even without 
the fundamental experiment described in this paper, we might have been en- 
titled to conclude that the forces of double refraction are not resident in the 
molecules themselves, but are the immediate result of those mechanical forces 
by which these molecules constitute solid bodies. 
Allerly, October 5th, 1829. 
