It did not need Ned Newton's story of what he had overheard at the bank to prove that an attempt had been made to blow to pieces Tom Swift's electric locomotive before even it had been tested.

An examination of the water-soaked package in the open yard of the shops of the Swift Construction Company, proved that there was enough explosive in the bomb to blow the shed itself to pieces. But the stopping of the clockwork attachment of course made the bomb harmless.

"The main thing to be explained," Tom said, when he and his father and Ned discussed the particulars of the affair, "is not who did it, or what it was done for. Those are comparatively easy questions to answer."

"Yes," agreed Ned. "O'Malley did it, or caused it to be done; and it was an attempt to balk Mr. Bartholomew and the H, & P. A. rather than a direct attack upon the Swift Construction Company."

"I am afraid, however," remarked Mr. Swift, "that Tom has aroused the personal antagonism of this spy from the West. We must not overlook that."

"I don't," replied the young inventor. "O'Malley has it in for me. No doubt of that. But he could not be sure that I would be hurt by the explosion he arranged for."

"True," said his father.

"The attempt was against my invention. And O'Malley was doubtless urged to destroy the locomotive that I am building because my success will aid Mr. Bartholomew and his railroad."

"Quite agreed," said Ned. "But--"

"But the important question," interrupted Tom, "is this: How did the bomb get into the interior of the electric locomotive? That is the first and most important problem. Its having been done once warns us that it can be done again until our system of guarding the works is changed."

"We have five watchmen on the job at night, and the gates are never opened in the daytime to anybody for any purpose without a pass," declared Ned. "I don't see how that fellow got in here with the time bomb."

"Exactly. It shows that there is a fault in our system somewhere," said Tom grimly. "We cannot surround the place at night with an armed guard. It would cost too much. Even Koku cannot be everywhere. And I have reason to know that he was wandering about the stockade last night as usual."

"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 alternating current was received through an oil switch and was conveyed to a high-tension current distributor made up of three lines of copper tubing, thus forming the source of power for this station.

From the current distributor the current was conducted through other oil switches to the transformers--entering at 100,000 volts and emerging at 2,300 volts. Then the current was conducted from the transformers through switches to the motor-generator sets and became the power employed to operate them.

The motor generator consisted of one alternating current motor driving two direct current generators. The motor Tom established in his station was of the 60-cycle synchronous type, which means that the current changes sixty times each second.

There were two sets, each generating a 1,500 or 2,000 volt direct current; and the two generators being permanently connected, delivered a combined direct current of 3,000 volts--as high a direct voltage current, Tom knew, as had ever been adopted for railroad work. The current voltage for ordinary street railway work is 550 volts.

"I could run even this big machine," Tom explained to Ned Newton, "with a much lighter current. But out there on the Hendrickton & Pas Alos line the transforming stations deliver this high voltage to the locomotives. I want to test mine under similar conditions."

"This is going to be an expensive test, Tom," said Ned, grumbling a little. "The cost-sheets are running high."

"We are aiming at a big target," returned the inventor. "You've got to bait with something bigger than sprats to catch a whale, Ned."

"Humph! Suppose you don't catch the whale after all?"

"Don't lose hope," returned Tom, calmly. "I am going after this whale right, believe me! This is one of the biggest contracts--if not the very biggest--we ever tackled."

"It looks as if the expense account would run the highest," admitted the financial manager.

"All right. Maybe that is so. But I'll spend the last cent I've got to perfect this patent. I am going to beat the Jandels if it is humanly possible to do so."

"I can only hope you will, Tom. Why, this track and the overhead trolley equipment is going to cost a small fortune. I had no idea when you signed that contract with Mr. Bartholomew that so much money would have to be spent in merely the experimental stage of the thing."

Ned Newton possessed traits of caution that could not be gainsaid. That was one thing that made him such a successful financial manager for the Swift Company. He watched expenditures as closely now as he had when the business was upon a much more limited footing.

The rails laid along the inside of the stockade made a two-mile track, as well ballasted as any regular railroad right of way. In addition the overhead equipment was costly.

To eliminate any possibility of the trolley wire breaking, a strong steel cable, called a catenary, was slung just above the trolley wire. To this catenary the trolley wire was suspended by hangers at short intervals.

These cables were strung from brackets so that a single row of poles could be used, save at the curves, at which cross-span construction was used. The trolley wire itself was of the 4/0 size, and was the largest diameter copper wire ever employed for railroad purposes.

Several weeks had now passed since the great locomotive had been assembled in the erection shed and the cab of the locomotive completed. It really was a monster machine, and any stranger coming into the place and seeing it for the first time must have marveled at the grim power suggested by the mere bulk of the structure.

When the day of the first test arrived Tom allowed only his most intimate friends to be present. Mary Nestor accompanied Mr. Swift into the shops at the time appointed, and she was as excited over the outcome of the test as Tom himself.

Ned Newton and the mechanical force of the shops knocked off work to become spectators at the exhibition. The only other outsider was Mr. Damon.

"Bless my alternating current!" cried the eccentric gentleman. "I would not miss this for the world. If you tried to shut me out, Tom, I'd climb over the stockade to get in."

"You'd better not," Tom told him, dryly. "If you tried that you'd get a worse shock than any chicken thief will get that tries to steal your buff Orpingtons."