the kind of explosive I want one that will deal a
succession of constant blows at the hard rock instead of one great big
blast."

"Can you make it, Tom?"

"Well, I don't know. I'll do the best I can."

From then on Tom was busy with his experiments.

Work on the tunnel did not cease while he was searching for a new
explosive. There was plenty of the old explosive left and charges of
this were set off as fast as holes could be drilled to receive it. But
comparatively little was accomplished. Sometimes more rock would be
loosed than at others, and the native laborers, now seemingly perfectly
contented, would be kept busy. Again, when a heavy blast would be set
off hardly a dozen dump cars could be filled.

But the work must go on. Already the time limit was getting perilously
close, and the contractors did not doubt that their rivals were only
waiting for a chance to step in and take their places.

Nothing more had been seen or heard of the bearded man, Waddington, or
Blakeson & Grinder. But that the rival firm had not given up was
evidenced by the efforts made in New York to cripple, financially, the
firm in which Tom was interested. In fact, at one time the Titus
brothers were so tied up that they could not get money enough to pay
their men. But Tom cabled his father, who was quite wealthy, and Mr.
Swift loaned the contractors enough to proceed with until they could
dispose of some securities.

It might be mentioned that Tom was to get a large sum if the tunnel
were completed on time, so it was to his interest and his father's, to
bring this about if he could.

Tom kept on with his powder experiments. Mr. Damon helped him, for that
gentleman had succeeded in putting the affairs of the wholesale drug
business on a firm foundation, and there was no more trouble about
getting the supplies of cinchona bark to market. The natives seemed to
have taken kindly to the eccentric man, or perhaps it was the
reputation of Tom Swift and his electric rifle that induced them to
work hard.

It must not be supposed that Professor Bumper was idle all this while.

He came and went at odd times, accompanied by his little retinue of
Indians, a guide and a native cook. He would come back to the tunnel
camp, where he made his headquarters, travel stained, worn and weary,
with disappointment showing on his face.

"No luck," he would report. "The hidden city of Pelone is still lost."

Then he would retire to his tent, to pour ove