IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 335 
colour. Lastly, beyond a certain inclination, which varies with 
the thickness of the plate, the portion of light contained in the 
image E becomes insensible, and the whole of the transmitted 
light appears to have passed into the image O, as if the rotatory 
power had disappeared. But the progress of the phenomenon 
proves that it continues to exist even then, and that its influence 
has only become too weak, relatively to the increasing energy 
of the double refraction, to remove from the latter an appreciable 
portion of the transmitted light. This division of the interior 
ray between two powers of polarization distinct in their cause, 
and in the laws, both absolute and relative, of their action, would 
doubtless be a very curious phenomenon to study. For the un- 
equal susceptibility which it indicates among the elements of the 
same luminous ray, to yield to or escape from one or the other 
action, appears to be connected with their most intimate nature. 
33. But the foregoing fact already warns us that the molecular 
rotatory power can only be observed in solid bodies, under cer- 
tain conditions, dependent on the mode of aggregation of their 
mass. If this mass is not crystallized, nor stratified in distinct 
layers among which special phenomena of polarization are de- 
veloped, the rotatory power proper to the chemical groups which 
constitute it are indistinctly manifested in all directions, with the 
peculiarities of direction and of energy which belong individually 
to those groups, in the physical state in which they then are. 
If, on the contrary, the mass is regularly crystallized, its inter- 
nal structure will be symmetrical around a point, a right line 
ora plane. Let us admit, moreover, that no effects of lamellar 
polarization are there developed, which disguise or conceal those 
which we now wish to consider*. Then, in the case of sym- 
* This class of phenomena is observed in certain crystallized bodies whose 
masses are formed of distinct layers, stratified in continuous systems, where they 
are respectively parallel. Each of these systems produces effects upon polarized 
light in part analogous to those of piles of glass plates, but which are related 
by other characters to those of crystalline laminz, possessing double refraction. 
They are, however, independent of this latter property, for they have hitherto 
been observed solely in bodies which are deprived of it. If it may occasionally 
exist in combination with them, which is very probable, it must render them 
more difficult to be perceived, by impressing on the polarized light different 
directions of polarization, and more energetically established or more fixed, 
which would weaken their proper effects, or entirely conceal them. They may, 
without doubt, be likewise associated with the rotatory power in solid crystal- 
lized bodies, although they have not hitherto been observed in such a state. 
For this reason I have comprised this physical possibility in the general state- 
ment of the circumstances which may mask the rotatory properties. If the 
reader desires to know in detail the phenomena produced by this kind of 
Sag which I have called Jamellar, he may consult vol. xviii. of the 
émoires de ? Académie des Sciences, in which I have expounded them. 
Dao 
