"The fellow was pretty sharp to slip by," Ned observed.

"The stockade is no mean barrier, especially with the rows of barbed
wire at the top," said Mr. Swift.

"Barbed wire! That's it!" exclaimed Tom. It was just here that Mr.
Damon's idea for guarding his prize buff Orpingtons came into play in
Tom's scheme of things. "Barbed wire doesn't seem to keep out spies,"
he added slowly. "But believe me, something else will!"

For Tom to think of a thing was to start action without delay.
Immediately he called a gang from the shops and set them to work
stringing copper wire along the top of the stockade.

He was sure that the man who had set the time bomb in place had got
into the enclosure over the fence. If he tried the same trick again he
was very apt to have the surprise of his life!

Each night when the shops closed and the watchmen went on duty, a
current of electricity was turned into those copper wires entwined with
the barbed wire entanglement at the top of the stockade that would
certainly double up any marauder who sought to get over the top.

However, no further attempt was made against Tom's peace of mind and
against his invention during the immediate weeks that followed. The
young inventor was so closely engaged in his work that he scarcely left
the house or the confines of the shops. Even Mary Nestor saw very
little of him.

But Mary realized fully that at such a time as this Tom must give all
his thought and energy to the task in hand. She was proud of Tom's
ability and took a deep interest in his inventions.

"I want to see the test when you try the locomotive, Tom," she told
him, when she came to the shops the first time to look at the monster
locomotive. "What a wonderful thing it is!"

"Its wonder is yet to be proved," rejoined the young inventor. "I
believe I've got the right idea; but nothing is sure as yet."

In addition to his mechanical contrivances inside the locomotive, Tom
had to arrange for an increased supply of electric power to drive the
huge machine around the track that was being built inside the stockade.

A regular station had to be built for receiving the electricity in a
100,000-volt alternating current and delivering it to the locomotive in
a 3,000-volt direct current. Therefore, this station had two functions
to perform--reducing the voltage and changing the current from
alternating to direct.

The reduction of the voltage was accomplished as follows: The
100,000-volt a