“The two telegraph instruments communicating with India and America, which stood on two tables, side by side, in Mr Pender’s house, were supplied by two batteries in the basement of the building. Eighty cells of Daniel’s battery were used upon the Penzance circuit for India, and 100 cells on the Brest circuit for America. The ordinary water-pipes of the house served to connect the batteries with the earth, so as to enable them to pump their electricity from that inexhaustible reservoir.”
“I was not aware that electricity had to be pumped up through pipes like water,” interrupted Mrs Wright, on whose mild countenance a complication of puzzled expressions was gradually gathering.
“It is not so pumped up,” said Sam. “The pipes were used, not because they were pipes, but because they were metal, and therefore good conductors.”
“But you haven’t told us about the beautiful experiments yet,” murmured Letta, a little impatiently.
“I’m coming to them, little one,” said Sam. “One battery exhibited the power as well as the beauty of that mysterious force which we call electricity. It was the large Grove battery. A current passed from it to copper wires, in a certain manner, produced a dazzling green light, and the copper melted like wax. With silver a still brighter and purer green flame was the result. With platinum an intense white light was given off, and the molten metal fell in globules of exceeding brilliancy. With iron lovely coruscations were exhibited, the boiling vapour flying and burning in all directions; and a platinum wire three feet long was in an instant melted into thousands of minute globules. All this showed the power of electricity to produce intense heat when resistance is opposed to its passage.”
“It is remarkably human-like in that respect,” said Captain Rik, in an under-tone.
“Then its power to produce magnetism,” continued Sam, “was shown by Lord Lindsay’s huge electro-magnet. This magnet, you must know, is nothing but a bit of ordinary metal until it is electrified, when it becomes a most powerful magnet. But the instant the current is cut off from it, it ceases to be a magnet. If you understood much about electricity,” said Sam, looking round on his rapt audience, “I might tell you that it is upon this power of making a piece of iron a magnet or not at pleasure, that depend the Morse and Digné telegraph instruments; but as you don’t understand, I won’t perplex you further. Well, when a piece of sheet copper was passed between the poles of Lord Lindsay’s giant magnet, it was as difficult to move as if it had been sticking in cheese—though it was in reality touching nothing!—influenced only by attraction.” (“That beats your power over Sam, Madge,” whispered Robin. “No it doesn’t,” whispered Madge in reply.) “Then, one most beautiful experiment I could not hope to get you to understand, but its result was, that a ten-gallon glass jar, coated inside and out with perforated squares of tinfoil, was filled with tens of thousands of brilliant sparks, which produced so much noise as completely to drown the voices of those who described the experiment. A knowledge of these and other deep things, and of the laws that govern them, has enabled Sir William Thomson and Mr Cromwell F. Varley to expedite the transmission of messages through very long submarine cables in an enormous degree. Then the aurora borealis was illustrated by a large long exhausted tube—”
“I say, Sam,” interrupted Rik, “don’t you think there’s just a possibility of our becoming a large long-exhausted company if you don’t bring this interesting lecture to a close?”
“Shame! shame! uncle Rik,” cried Robin.
As the rest of the company sided with him, the captain had to give way, and Sam went on.