300 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT 
6. Now, it may be asked how material particles should be 
constituted to produce thus a total effect sensibly constant, in 
all the relative positions which a mechanical agitation imparts to 
them when they are altogether liquid, and in those probably not 
less variable which result from their internal vibrations, when 
they compose a coagulated or solid mass, the parts of which ap- 
pear to be in repose relative to our gross senses? It is easy to 
form a conception of this, if not absolutely certain, at least me- 
chanically admissible, without framing any hypothesis on the 
nature of light. It suffices for this to transfer to the constituent 
molecules of the active masses the same properties which these 
masses present to us, and which we see to be in them indepen- 
dent of their accidental state of aggregation; just as we refer 
also to these molecules, according to similar characters, the pro- 
perty of weight which is observed in sensible masses. Imagine, 
in fact, an active mass, without losing its homogeneity, to be se- 
parated in idea into similar parts of a minuteness imperceptible 
to our senses, and having for example the figure of spheres or of 
ellipsoids with two or three axes, or in any intermediate form 
imaginable. Suppose then that each kind of these particles is 
assembled and maintained in continuous systems of sensible 
dimension, by repulsive forces, calorific or others, which should 
balance their mutual attractions, or by diffusing them in dia- 
phanous fluid media incapable of modifying them by a chemical 
action, or exercising any peculiar action of deviation upon the 
polarized light,—I say that all the material systems thus formed 
would present optical properties similar to those of the active 
liquids under consideration* ; that is to say, that each one of 
them would impress on the planes of polarization of luminous 
rays deviations in the same direction with all thicknesses in 
which they may be observed; that the magnitude of these de- 
viations would be proportional to the total mass of the active 
particles, traversed either in continuity or in succession; and 
that, lastly, these pheenomena would be produced in them with- 
out perceptible variation, either in a state of agitation or of re- 
pose. This is evident, first, for systems of spherical molecules. 
* T specify here, as a condition, the /iguid state, to avoid the intervention in 
this statement of the polarizing properties, which the regularity of aggregation 
developes in solid crystallized bodies,—properties which modify the observable 
phenomena of deviations produced by molecular action when they coexist with 
it in one and the same material system, as I shall show hereafter. 
