Meanwhile no time was lost in getting to the root of the mischief.

The danger could not be averted by switching off the power altogether at the various electrical stations of the metropolis. At intervals along the tubes were immense accumulators which for the present could not be touched. It was these accumulators that rendered the streets such a ghastly peril.

It was the electrical expert to the County Council—Alton Rossiter—who first got on the track of the disaster. More than once before, the contact between gas and electricity had produced minor troubles of this kind. Gas that had escaped into man-holes and drains had been fired from the sparks caused by a short-circuit current wire. For some time, even as far back as 1895, instances of this kind had been recorded.

But how could the gas have leaked into the tube, seeing that it was a steel core with a solid bedding of concrete beyond? Unless an accident had happened when the tube was under repair, this seemed impossible.

The manager of the associated tubes was quite ready to afford every information to Mr. Rossiter. The core had corroded in Bond Street in consequence of a settling of the earth caused by a leaky water-main. The night before, this had been located and the steel skin stripped off for the necessary repairs.

Mr. Alton Rossiter cut the speaker short.

"Will you come to Bond Street with me, Mr. Fergusson?" he said; "we may be able to get into the tunnel there."

Fergusson was quite ready. The damage in Bond Street was not so great, though the lift shaft was filled with débris, and it became necessary to cut a way into the station before the funnel was reached.

For a couple of hundred yards the tube was intact; beyond that point the fumes of gas were overpowering. A long strip of steel hung from the roof. Just where it was, a round, clean hole in the roadway rendered it possible to work and breathe there in spite of the gas fumes.

"We shall have to manage as best we can," Rossiter muttered. "For a little time, at any rate, the gas of London must be cut off entirely. With broken mains all over the place the supply is positively dangerous. Look here."

He pointed to the spot where the gas main had trended down and where a short-circuit wire had fused it. Here was the whole secret in a nutshell. A roaring gas main had poured a dense volume into the tube for hours; mixed with the air it had become one of the most powerful and deadly of explosives.

"What time does your first train start?" Rossiter asked.

"For the early markets, four o\'clock," Fergusson replied. "In other words, we s............