whirling rings may be seen when an experienced smoker sends out a
dexterous puff of smoke into the still air, but a more evanescent
phenomenon it is difficult to conceive. This evanescence is owing to
the viscosity of the air; but Helmholtz has shewn that in a perfect
fluid such a whirling ring, if once generated, would go on whirling
for ever, would always consist of the very same portion of the fluid
which was first set whirling, and could never be cut in two by any
natural cause. The generation of a ring-vortex is of course equally
beyond the power of natural causes, but once generated, it has the
properties of individuality, permanence in quantity, and
indestructibility. It is also the recipient of impulse and of energy,
which is all we can affirm of matter; and these ring-vortices are
capable of such varied connexions and knotted self-involutions, that
the properties of differently knotted vortices must be as different as
those of different kinds of molecules can be.

If a theory of this kind should be found, after conquering the
enormous mathematical difficulties of the subject, to represent in any
degree the actual properties of molecules, it will stand in a very
different scientific position from those theories of molecular action
which are formed by investing the molecule with an arbitrary system of
central forces invented expressly to account for the observed
phenomena.

In the vortex theory we have nothing arbitrary, no central forces or
occult properties of any other kind. We have nothing but matter and
motion, and when the vortex is once started its properties are all
determined from the original impetus, and no further assumptions are
possible.