The agitation here really seems, as M.Gouy has remarked, to be produced and continued indefinitely, regardless of any difference in temperature; and we seem to witness the incessant motion, in an isothermal medium, of the particles which constitute matter.

Perhaps, however, we find ourselves already in conditions where the too great simplicity of the distribution of the molecules deprives the principle of its value.
M.Lippmann has in the same way shown that, on the kinetic hypothesis, it is possible to construct such mechanisms that we can so take cognizance of molecular movements that _vis viva_ can be taken from them.

The mechanisms of M.Lippmann are not, like the celebrated apparatus at one time devised by Maxwell, purely hypothetical.

They do not suppose a partition with a hole impossible to be bored through matter where the molecular spaces would be larger than the hole itself.

They have finite dimensions.