ductor, and Mister Electricity has an irresistible desire to bolt into the earth, like a mole."
"Naughty fellow!" murmured Madge.
"But," continued Robin impressively, "if I fix little lumps of glass with a hole in them to the posts, and fix my wires to these. Electricity cannot bolt, because the glass lumps are non-conductors, and won't let him pass."
"How good of them!" said Madge.
"Yes, isn't it? So, you see," continued Robin, "the glass lumps are insulators, for they cut the electricity off from the earth as an island is, or, at all events, appears to be, cut off from it by water; and Mister Electricity must go along the wires and do what I tell him. Of course, you know, I must make my electricity first in a battery, which, as I have often and often told you, is a trough containing a mixture of acid and water, with plates or slices of zinc and copper in it, placed one after the other, but not touching each other. How, if I fix a piece of wire to my first copper slice or plate, and the other end of it to my last zinc slice or plate, immediately electricity will begin to be made, and will fly from the copper to the zinc, and so round and round until the plates are worn out or the wire broken. D'ee see?"
"No, Robin, I don't see; I 'm blinder than the blindest mole."
