eparated, and a wire connects the two outside of
the cell. Now you will notice that within the cell the current flows, as
shown by the dart E, from the positive to the negative plate, but
outside of the battery the current flows through the wires F from the
negative to the positive plate."

"I can understand it now. The current from the battery will always go
from the negative to the positive pole."

"You are mistaken. I am glad you referred to that. It shows the
importance of using correct terms. You must not confound the terms
'negative plate' with 'negative pole.' All currents leave the battery or
dynamo from the negative plate, but that negative plate is called the
positive pole of the dynamo."

"It seems to me that is a curious way to do it."

"Such is the case, however; but there is no real positive or negative in
the alternating current, so that either side may be termed positive or
negative."

Work on the battery continued for some days, as lack of fine tools made
much of the work difficult, and in doing this work, as in everything
else, a certain amount of preparation was necessary. They had no screws,
and no facilities for making them, so a substitute had to be devised,
but the difficult part now to encounter was the preparation of the wire.

"A battery is of no use unless we can have wire, and it will be a big
job to beat out wire long enough for our purposes," Harry observed as
the battery neared completion.

"Then we must draw some wire?"

"From what?"

"From the copper?"

"Is that better than iron?"

"Copper should be used for several reasons; first, because electricity
travels through a copper wire more easily than through iron, and second,
for the reason that copper is more ductile than iron, and can be drawn
into a wire with greater facility."

"Doesn't electricity flow through different substances at the same rate
of speed?"

"Yes; but it retards the amount or the force."

"You say, 'Amount' or 'Force.' I can understand that if applied to
water, that there might be a large or small quantity of water, or a
greater or less pressure, but I do not see how this applies to
electricity."

"In measuring the pressure of water, calculation is made by taking the
height of the water in the tank. For every 28 inches in height a column
one inch square weighs one pound. This represents the force of the water
when it issues from the orifice below. Now the orifice may be large or
it may be small. T