336 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT 
metry around a point, the rotatory power proper to the con- 
stituent particles will manifest itself freely and with a uniform 
energy in all directions, as in the state of disaggregation. If the 
symmetry takes place around a right line, the crystal will exer- 
cise uniaxal double refraction, which will be the right line itself. 
Then the rotatory power proper to the constituent molecules 
will not be exercised freely except in that single direction; and 
it will be especially there that we must seek to detect its mani- 
festation. But, since the crystallization will there maintain all 
the molecules in parallel directions, the total rotatory power 
resulting from them collectively may possibly be found different 
from what it would be in the state of disaggregation or of con- 
fused aggregation, which would present them indistinctly turned 
in all directions around the transmitted ray. Lastly, in the 
third mode of symmetrical crystallization around a plane, the 
body will exercise binaxal double refraction, according to which we 
must consequently endeavour, by analogy, to ascertain the phze- 
nomena of molecular rotation, if this system of double refraction, 
in which the transmitted ray is always oblique to one of the two 
axes, allows them to be manifested ; and the parallelism of the con- 
stituent molecules might very well, in this case also, produce total 
resultants different from what they would be if these same disag- 
gregated molecules could present themselves in any direction 
whatsoever to the luminous ray passing through them, or if, re- 
maining aggregated in a solid system, they were there disposed 
according to a mode of arrangement which had nothing regular. 
34. This last state—that of confused aggregation—is the only 
one in which the rotatory power of a solid body has hitherto 
been observed with the uniformity of agglomeration necessary to 
measure its energy, and to compare it to the action of the same 
body disaggregated by solution in an inactive liquid. The sub- 
stance which has furnished the example is cane-sugar, deprived 
of crystallization by fusion, and then solidified by rapid cooling. 
In order to obtain it in transparent masses, it is first dissolved 
in a small quantity of water, and the solution being well-clari- 
fied, a little acetic acid is added. This solution is then brought 
over the naked fire to the consistence of a syrup, sufficiently dense 
that threads drawn from it solidify immediately. It is then 
poured into metallic cases with very thin sides, on a cold marble 
slab, where it immediately solidifies into diaphanous plates, 
generally of a yellowish tint, the less intense the less it was 
heated, and they are sometimes obtained nearly colourless; this 
