le plasticity.

Let us note that the question of the continuity of the liquid and
solid states is not quite the same as the question of knowing whether
there exist bodies intermediate in all respects between the solids and
liquids. These two problems are often wrongly confused. The gap
between the two classes of bodies may be filled by certain substances
with intermediate properties, such as pasty bodies and bodies liquid
but still crystallized, because they have not yet completely lost
their peculiar structure. Yet the transition is not necessarily
established in a continuous fashion when we are dealing with the
passage of one and the same determinate substance from the liquid to
the solid form. We conceive that this change may take place by
insensible degrees in the case of an amorphous body. But it seems
hardly possible to consider the case of a crystal, in which molecular
movements must be essentially regular, as a natural sequence to the
case of the liquid where we are, on the contrary, in presence of an
extremely disordered state of movement.

M. Tamman has demonstrated that amorphous solids may very well, in
fact, be regarded as superposed liquids endowed with very great
viscosity. But it is no longer the same thing when the solid is once
in the crystallized state. There is then a solution of continuity of
the various properties of the substance, and the two phases may
co-exist.

We might presume also, by analogy with what happens with liquids and
gases, that if we followed the curve of transformation of the
crystalline into the liquid phase, we might arrive at a kind of
critical point at which the discontinuity of their properties would
vanish.

Professor Poynting, and after him Professor Planck and Professor
Ostwald, supposed this to be the case, but more recently M. Tamman has
shown that such a point does not exist, and that the region of
stability of the crystallized state is limited on all sides. All along
the curve of transformation the two states may exist in equilibrium,
but we may assert that it is impossible to realize a continuous series
of intermediaries between these two states. There will always be a
more or less marked discontinuity in some of the properties.

In the course of his researches M. Tamman has been led to certain very
important observations, and has met with fresh allotropic
modifications in nearly all substances, which singularly complicate
the question. In the case of water, fo