Page:Ballantyne--The Battery and the Boiler.djvu/93

 from the shore, as well as every message sent by us in reply, has to travel through the entire length of the cable, namely about 2400 miles, and as every mile of distance increases this unwillingness, or resistance, we have to increase the electrical power in the batteries in proportion to the distance to which we want to send our message. D' you understand ?"

"I think I do, sir; but how is the exact amount of resistance tested?"

Mr. Smith smiled as he looked at the earnest face of his young questioner.

"My boy," said he, "you would require a more fully educated mind to understand the answer to that question. The subtleties of electrical science cannot be explained in a brief conversation. You 'll have to study and apply to books for full light on that subject. Nevertheless, although I cannot carry you into the subject just now, I can tell you something about it. You remember the testing-room which I showed you yesterday—the darkened room between the captain's state-room and the entrance to the grand saloon?" Yes, sir, I remember it well," responded Robin,—"the room into which the conducting-wires from the ends of the cable are led to the testing-tables, on which are the curious-looking galvanometers and other testing machines."

"Just so," returned Smith, pleased with his