“I see,” said Uncle Jeff; “but what next?”
“I’ll show you directly,” continued Stan, with his forehead puckered up in lines as if it were a mental Clapham Junction. “Now then, this stationery-case is my battery of cells, each charged with acid and stuff.”
“We don’t want to put a dangerous battery on Mr Blunt’s table to blow him up,” said Uncle Jeff. “He’s too useful.”
“Of course he is, uncle; but we couldn’t blow him up, because the battery isn’t dangerous.”
“Then what’s the good of it?”
“Ah! you don’t see yet; you will directly,” cried the boy. “There’s no danger at all till it is connected with the wire; and the wire, you know, is connected with the canister of explosive, uncle. And don’t you see that it will be sunk right away there off the wharf? When we connect the wire with the battery, it is not that which goes off, but the powder in the canister under the junk.”
“Oh, I see!” said Uncle Jeff. “Good; but when it is connected what does it do?”
“Sends a current of electricity along the wire.”
“Of course; I do understand that. Sends an electric spark through the powder and blows it up.”
“That’s right, uncle; only, instead of sending a spark along the wire, it sends a current to the end of the wire, and that end begins to glow till it turns white-hot. But long before that it has set the powder off, and if all goes right we should have a great junk blown all to pieces.”