tive positions of the molecules, we call
the body a solid. In a liquid, cohesion is greatly reduced, and any part
of it may be deformed without materially changing the form of the rest.
The molecules are free to move about each other, and there is no
definite position which any need assume or keep. With gases, the
molecules are without any cohesion, each one is independent of every
other one, collides with and bounds away from others as free elastic
particles do. Between impacts it moves in what is called its free path,
which may be long or short as the density of the gas be less or greater.

These differing degrees of cohesion depend upon temperature, for if the
densest and hardest substances are sufficiently heated they will become
gaseous. This is only another way of saying that the states of matter
depend upon the amount of molecular energy present. Solid ice becomes
water by the application of heat. More heat reduces it to steam; still
more decomposes the steam molecules into oxygen and hydrogen molecules;
and lastly, still more heat will decompose these molecules into their
atomic state, complete dissociation. On cooling, the process of
reduction will be reversed until ice has been formed again.

Cohesive strength in solids is increased by reduction of temperature,
and metallic rods become stronger the colder they are.

No distinction is now made between cohesion and chemical affinity, and
yet at low temperatures chemical action will not take place, which
phenomenon shows there is a distinction between molecular cohesion and
molecular structure. In molecular structure, as determined by chemical
activity, the molecules and atoms are arranged in definite ways which
depend upon the rate of vibrations of the components. The atoms are set
in definite positions to constitute a given molecule. But atoms or
molecules may cohere for other reasons, gravitative or magnetic, and
relative positions would be immaterial. In the absence of temperature, a
solid body would be solider and stronger than ever, while a gaseous mass
would probably fall by gravity to the floor of the containing vessel
like so much dust. The molecular structure might not be changed, for
there would be no agency to act upon it in a disturbing way.

THE ETHER HAS NO CORRESPONDING STATES.

Degrees of density have already been excluded, and the homogeneity and
continuity of the ether would also exclude the possibility of different
states at all comparab