forms such as cubes, tetrahedra, hexagonal
prisms and stellate forms, with properties emphasized on certain faces
or ends. Thus quartz will twist a ray of light in one direction or the
other, depending upon the arrangement which may be known by the external
form of the crystal. Calc spar will break up a ray of light into two
parts if the light be sent through it in certain directions, but not if
in another. Tourmaline polarizes light sent through its sides and
becomes positively electrified at one end while being heated. Some
substances will conduct sound or light or heat or electricity better in
one direction than in another. All matter is magnetic in some degree,
and that implies polarity. If one will recall the structure of a
vortex-ring, he will see how all the motion is inward on one side and
outward on the other, which gives different properties to the two sides:
a push away from it on one side and a pull toward it on the other.

THE ETHER IS ISOTROPIC.

That is, its properties are alike in every direction. There is no
distinction due to position. A mass of matter will move as freely in one
direction as in another; a ray of light of any wave-length will travel
in it in one direction as freely as in any other; neither velocity nor
direction are changed by the action of the ether alone.

9. MATTER IS CHEMICALLY SELECTIVE.

When the elements combine to form molecules they always combine in
definite ways and in definite proportions. Carbon will combine with
hydrogen, but will drop it if it can get oxygen. Oxygen will combine
with iron or lead or sodium, but cannot be made to combine with
fluorine. No more than two atoms of oxygen can be made to unite with one
carbon atom, nor more than one hydrogen with one chlorine atom. There is
thus an apparent choice for the kind and number of associates in
molecular structure, and the instability of a molecule depends
altogether upon the presence in its neighbourhood of other atoms for
which some of the elements in the molecule have a stronger attraction
or affinity than they have for the atoms they are now combined with.
Thus iron is not stable in the presence of water molecules, and it
becomes iron oxide; iron oxide is not stable in the presence of hot
sulphur, it becomes an iron sulphide. All the elements are thus
selective, and it is by such means that they may be chemically
identified.

There is no phenomenon in the ether that is comparable with this.
Evidently th