The steady motion of electrons from atom to atom along a wire, or other conductor, constitutes the well-known "electric current." The moving electrons disturb the æther around the wire and produce what we know as a "magnetic field." The electron explains why it is necessary to have a complete circuit before any electric current can take place. Also how one length of wire may be used to connect two distant places provided the two extremities of the wire are buried in the earth. CHAPTER VII A STEADY MARCH Personally I knew nothing about marching until quite recently. Indeed, none of my fellow-electrons seem to have had definite ideas of regular marches previous to last century. That century is prominent in our history as well as in man's. There is no doubt that before then we must have made more or less regular marches through the crust of the earth and elsewhere; but for myself I have no such recollection previous to the following occasion. The experience was not a very exciting one. I found myself passing along from atom to atom in a copper wire. But what was of special interest to us was that it became evident that these enforced marches were being deliberately controlled by man. Of course you will understand that man knew nothing of our existence at that time. All he knew was that when he placed a piece of zinc and a piece of copper in a chemical solution, there were certain effects produced in some mysterious fashion. For instance, when he connected the top of the two metals in this chemical cell or "battery" by a piece of wire, he got what he described as an _electric current_. Now all that happened really was this. The chemical action in this battery which man had devised caused a rearrangement among the atoms composing the metals and the solution, with the result that we poor electrons had to rearrange our domiciles. As an accumulation of electrons gathered on the zinc, some of us were forced along the connecting wire towards the copper. As long as the chemical action in the battery was kept up, so long were we kept on the march from the zinc to the copper by way of the wire. Man tried increasing the length of this wire bridge across which we had to pass, but we had no difficulty in making our way along. But you must not run away with the idea that we rush along the wire with lightning speed. Although we can fly through the æther at a prodigious speed, our progress from atom to atom in a wire is more like a snail-pace. As a matter of fact, our rate of march is much less than the walking pace of a man; indeed it may be stated conveniently as so many yards per hour.