characteristic about these rings is, that when two of the rings
are travelling in the same straight line, the one behind will overtake the
front one, and while so doing, the diameter of the front one is enlarged,
while that of the one behind contracts. The front one will also travel
slower, while the one behind travels faster until it has caught up the
former, and then the latter, having contracted sufficiently, will pass
through the diameter of the former as illustrated in the figure. This
alternation of contraction and expansion is continued as long as the two
rings move in the same plane and until they are destroyed. When, however,
the two rings are moving in opposite directions, and meeting each other in
the same straight line, they will repel one another, instead of attracting
each other.

Their rate of progress is gradually reduced as they approach together,
and they begin to expand and enlarge, but they never touch each other.
Another peculiar feature about the rings consists in the fact, that the
central core of air in the ring remains the same all the time the ring
is in motion through the room, so that it has the same core of air at
the end of its journey as it had when it left the box.

As Lord Kelvin pointed out, if there were no friction of the air, the
ring once created would rotate for ever. If, therefore, there were such
a thing as a perfect fluid, and there were vortex rings in it, nothing
could destroy these rings when once they were created, and this is one
of the most striking suggestions with reference to the Vortex Atom
theory of matter. It remains to be seen whether in the universe we have
such a medium as a perfect fluid.

Sir Wm. Thompson has applied the Vortex Atom theory of matter to the
Aether, but from mathematical calculation he was unable to arrive at a
satisfactory conclusion as to the Aether being composed of vortex atoms.

Another remarkable property belonging to these rings, lies in the fact
that they cannot be cut in two. It will be found that when the knife is
brought near to them, they seem to recoil from the knife. In that sense,
it is literally an atom, a thing which cannot be cut in two.

The Vortex Atom has many recommendations in its favour. Many of the most
important properties of matter are possessed by it, as for example
indestructibility, elasticity, inertia, compressibility, and its
incapability to be cut in two. Further, it may be linked with another
ring, and so giv