They go out from the positive brush of the dynamo; there is a
ground-connection through the negative brush; the other ends of
the wire return to the cave, and each is grounded independently."
"No, no, that won't do!"
"Why?"
"It's too expensive--uses up force for nothing. You don't want
any ground-connection except the one through the negative brush.
The other end of every wire must be brought back into the cave
and fastened independently, and _without_ any ground-connection.
Now, then, observe the economy of it. A cavalry charge hurls
itself against the fence; you are using no power, you are spending
no money, for there is only one ground-connection till those horses
come against the wire; the moment they touch it they form a
connection with the negative brush _through the ground_, and drop
dead. Don't you see?--you are using no energy until it is needed;
your lightning is there, and ready, like the load in a gun; but
it isn't costing you a cent till you touch it off. Oh, yes, the
single ground-connection--"
"Of course! I don't know how I overlooked that. It's not only
cheaper, but it's more effectual than the other way, for if wires
break or get tangled, no harm is done."
"No, especially if we have a tell-tale in the cave and disconnect
the broken wire. Well, go on. The gatlings?"
"Yes--that's arranged.
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