he amount or quantity which flows out is dependent on
the size of the opening. Electricity is measured in a somewhat similar
manner. What is called 'Volts' is the same as the force in the
tank--that is, voltage means the pressure. Amperage, on the other hand,
refers to the amount of current which is passing, and a greater quantity
will pass over a large wire just the same as a greater amount of water
will flow through a large than a small pipe. Is this perfectly clear to
you?"

"Yes; I understand the difference, now."

The drawing of wire is not a difficult task where facilities are at
hand, but it must be remembered that all their tools were of the crudest
kind. Harry had prepared a number of bars of copper, each having been
beaten out to form pieces about ten inches long and a half inch thick. A
steel plate about three-eighths of an inch thick, two inches wide, and
six inches long, had a number of holes bored through it, the largest
hole being a half inch in diameter, and gradually increasing in size,
the smallest being about a sixteenth of an inch in diameter.

[Illustration: _Fig. 26. Template for Drawing Wire._]

When all was ready Harry was instructed to hammer out one end, so it
would go through the largest hole. The projecting end was then grasped
by a pair of heavy pliers, and pulled through, so that the bar was
formed the size and shape of the first hole, and of course the bar was
lengthened. The end was then hammered out so that it would go through
the next smaller hole, and the same process was repeated, and when the
wire got larger they had a tool which pushed the wire in at the same
time it was being pulled out at the other side.

It was laborious work, and a long time was consumed in fully drawing out
each bar. In this way a quantity of serviceable wire was prepared.

"Why does this plate get so hot when we pull the wire through?"

"Why do you make a fire by rubbing together two substances?" replied the
Professor.

"On account of the friction."

"For that same reason you are making the heat in drawing the copper
through the die."

"But I notice that if I hammer a piece of cold iron it will get hot.
There is not any rubbing motion there to make friction."

"Do you think not? You have by that means made the most intense
friction. The iron is composed of tiny particles, called atoms, and
molecules. When you strike a piece of iron you force these particles in
among themselves, and the friction ca