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of Edinburgh, Session 1863 - 64 . 
maintaining, that they have their origin in physical dissymmetry 
only, and that the existence of the vaunted chemical dissymmetry 
is at least very problematical. The reason, therefore, why chlorate 
of soda and its congeners lose the property of circular polarisation 
during the act of solution must be sought in differences of tempera- 
ture and the altered state of aggregation, both of which conspire 
in restoring the physical symmetry, while the process of crystalli- 
sation tends to produce the opposite effect. I may add, moreover, 
that the discovery of a substance exhibiting the same optical de- 
portment as chlorate of soda, while these physical processes are 
reversed, would prove a powerful argument in support of my view, 
but utterly subversive of Monsieur Pasteur’s mode of reasoning. 
The theory here advocated naturally leads us to suspect the 
existence of another set of equivalents, namely, the volume equi- 
valents ; their numerical expression would correspond to the 
highest degree of repulsive energy, and to the greatest amount of 
vibratory movements, of which the various species of elementary 
molecules are susceptible. They would, however, differ materially 
from the weight equivalents, which are constant, whereas they 
would, on the contrary, be subject to a peculiar law of variations, 
which enables them to pass through a series of values from a given 
maximum down to zero. I am not at present prepared to enter 
into details, but a careful comparison of facts has convinced me 
that the variations in the specific volumes of the molecules, or, 
what comes to the same thing, the variations in the volume- equi- 
valents of their component elements, are genetically connected, and 
run parallel with the modifications of their various physical pro- 
perties. If, then, all the chemical and physical properties of matter 
are due to the simultaneous agency of two essentially distinct 
principles, it follows that chemistry, both as an art and as a 
science, rests not on a simple but on a complex foundation. On the 
one hand, it is the purely chemical principle which determines the 
various forms of molecular arrangement, and it is the ponderable 
portion alone of the various kinds of atoms, which, in their con- 
stant weight-equivalents, furnishes the basis of calculation. On 
the other hand, it is the purely physical principle which deter- 
mines the specific volume of the molecules, and it is the imponder- 
able portion alone of the various kinds of atoms, which, in their 
