When the hole is circular, the rings will be found circular also, but if the hole is square, then the rings will be irregular in shape. One remarkable 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 give the basis to the combining properties of atomic weights.

The Vortex Atom theory is simple in character, as it does not postulate any extravagant hypothesis, but makes use of the Aether as the common basis for all matter, simply stating that this property of rotation may be the basis of all that we call matter. We shall further consider the relation of the Vortex Atom to matter, when we deal with the constitution of matter and the unity of the universe.

Art. 35. Elements of Matter.--As is well known, modern chemistry has succeeded in reducing all the complex forms of matter in Nature into a number of simple substances, which are called elements. Of these elements about seventy are at present known, some of which, however, are very rare. An element therefore is a simple substance which cannot be decomposed by any known force or process, as heat or electricity, into other elements.

There are, however, only about fourteen of these elements that enter largely into the constitution of the earth, the most common being oxygen and silicon. By the use of the spectroscope, it has been proved that many of these elements, as for example oxygen, hydrogen, sodium and calcium, exist in the sun and stars, as well as in the most distant nebulae. Most of the elementary bodies are to be found in a gaseous form as hydrogen, oxygen, fluorine and chlorine, though it has been found possible to liquefy even these gases. Thus we see that matter may be roughly divided into three states, viz. solid, liquid, or gaseous.

The condition in which the substance is found depends upon its temperature and pressure. An example of matter in its three stages is best shown in the case of water, where in the solid condition we have it as ice, in the liquid condition as water, and in the gaseous condition as steam.