374 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT 
them all from one and the same formula, which comprises the — 
whole without ever failing, an agreement so extensive and so 
constant offers the most convincing proof of the accuracy of the 
indications which the optical characters furnish, and thus esta- 
blishes the deductions drawn from them as to the molecular 
state of systems in which such characters may be observed. 
For the tartaric solutions in particular, it evidently results that 
the acid, however weak in quantity, affects the whole mass of 
water presented to it, since it produces in the whole of this mass 
a rotatory power which it did not itself possess; as we have 
already been led to conclude in discussing the course of the den- 
sities of solutions thus formed. Now, an influence so unlimited 
necessarily supposes the alternative of an action exercised im- 
mediately at a sensible distance, or communicated from particle 
to particle at every distance with a decreasing energy, in the 
same way as a natural magnet, or a bar of steel rendered mag- 
netic, communicates its power to the soft and non-magnetic iron 
placed in contact with it. I leave to physicists to decide which 
of these two modes is the most probable. 
In the memoir on some points of chemical mechanics which I 
have inserted in vol. xvi. of the collection of the Academy, I 
have described a great number of facts which lead to the same 
conclusion. They are founded on the complex reactions which 
are exercised in liquid systems, in which tartaric acid is asso- 
ciated with water and other bodies, alkaline or earthy, under 
the influence of their mutual affinities. I content myself with 
referring to them, and I proceed to add here some new proofs — 
of the same kind which have been carried much further. 
Section IV.—On the reactions which take place in the ter- 
nary systems formed by tartaric acid, boracic acid and water, at 
a constant temperature. 
61. Many celebrated chemists have expressed very different 
opinions on the nature of the combinations which tartaric acid 
forms with boracic acid in the presence of water, and the exist- 
ence, or at least the stability, of such a combination has even 
been called into doubt *. 
Optical observations leave no uncertainty in this respect. 
They prove that systems composed of these three bodies may 
* Thenard, 7raité de Chimie, 6th edition, tome iv. p. 35; Dumas, 7raité de 
Chimie, appliquée aux Aris, vol. v. p. 304. 
