composed of these minute electri-cal units: stone, iron, paper, plant,

animal, and man — each of them is matter, or rather materials, built at bottom of electrons and protons.

Now that we have gained this acquaintance with the structure of matter, we can inquire into electricity.

We said above that the electrons are lighter in motion and more active than the protons. But these electrons move in order within the solar system of the atom: they revolve and revolve, forever and always. If, however, we can isolate these electrons and make them all travel in a defined direc-tion, the result is what we call the electric current. Electricity, then, is nothing but streams of these electrons as they pass from one place to another.

And just as ease of travel depends to a great extent on the roughness or the goodness of the road, so the ease with which the throngs of electrons pass through a given body depends to a great extent on the capacity of that body to facilitate the passage of these throngs. Copper wires, for exam-ple, allow them to pass with great ease, and for that reason they are much used in carrying electric power from one place to another; while air allows the electrons to pass only with great difficulty, and under the influence of an electric force greater than the force these electrons need in order to travel through the copper wire. This difference in the ease with which electricity travels through different bodies, and the light and heat generated as a result of it, is one of the theoretical foundations on which electric lighting rests.

The electric lamp, or "bulb," is composed of a fine wire, usually made of a metal called tungsten. This wire is fixed inside a glass tube of spherical shape, as we all know, and is connected at its end with the source of the electric current outside. The lamp must be tightly sealed and emptied of air, because air contains the element oxygen, which reacts with the tungsten metal and renders it unfit for lighting for any length of time. The air is replaced by a gas called argon, an inactive gas which does not combine with the tungsten but helps to preserve it longer than if the lamp were emptied of all gas; for in that case — the case of absolute vacuum — the tungsten evaporates quickly, and the wire becomes incapable of long service. The presence of argon gas, then, is of double benefit: it reduces the amount of the tungsten's evaporation, and it does not react with it as does the oxygen present in the air.

As for the reason tungsten metal was chosen, it is that it melts only under the influence of a very high temperature — 3,370 degrees centigrade.

Let us now try to picture how electricity runs through the lamp. We said that the electric current is a great multitude of electrons traveling in one direction. When the electric current reaches one of the two ends of the metal wire in the lamp, these electrons try to travel inside it so as to pass out at the other end; and in their attempt to travel through this wire they meet with some difficulty. But they are compelled to travel, because they are all pushed by the electric force drawn from the town's electricity stations. Thus the difficulty of the electrons' passage through

the metal wire generates friction between them and the atoms of tungsten. This friction causes the temperature of the wire to rise, just as one of us feels heat in his palms if he rubs one against the other. The greater the friction between the electrons and the tungsten atoms, the higher the temperature of the metal wire rises, until, when this heat reaches a certain degree, the wire begins to glow. Heat and light are in truth two different expressions of a single principle: any body that sends out a ray, or light, is a body whose heat has reached the degree of incandescence. A piece of cold iron gives no light at all; but if the blacksmith's fire is turned upon it, we see it glow red and send out a shining ray.

Hence, if the tungsten metal, in the state in which it exists inside the lamp, allowed the electrons to pass with great ease, no friction would occur and no light would be generated. And since it is a metal that melts only under very high heat, the heat produced by the friction referred to does not affect this wire as it would affect a wire that melts under low heat.

This has been a very summary inquiry into the theoretical side of electricity and into one practical application of it. My great hope is that this brief exposition may serve as an incentive to the honored readers to try to widen their knowledge of this important subject. For science is a sea of vast horizons: the deeper a man plunges into it, the greater grows his passion for it and his attachment to it.

If this article has been able to spur some readers to widen their knowledge, it will have achieved the essential purpose for which it was written.