"In the primary battery that is the case; but when electricity is generated and sent over the wires, the natural current flows in both directions—that is, it goes in one direction as much as in the other."
"I do not understand what you mean by that."
"The current alternates. What is meant by that is this: For an instant the current flows from the positive to the negative, and the next instant it flows from the negative to the positive, and so on, making the alternate current."
"Then the primary battery we are going to make will be another kind of current?"
"We shall make what is called the direct current which goes in one direction only—that is, within the battery it moves from the positive plate, the zinc, to the copper plate, or negative, and outside of the battery it moves from the negative to the positive plate."
"Why does it do so?"
"In order that you may understand, I shall make a drawing so Harry will not have so much trouble in arranging the parts. So if you will examine the sketch (Figure 25), you will see that the clay cell, which we are to make, has in it the two electrodes, A and B. That is what they are called when they are spoken of together; but the positive one (A), the zinc, is called the anode, and the negative (B), or copper, is called the cathode. You should keep these terms in mind.
