t
semicircle of daylight came into view. "There's the other end."

"Stop a minute," cried Jack, emboldened by the prospect of soon being
once more in the fresh air; "let's see if we can make an echo."

The little party halted for a moment, but instead of hearing the shrill
yell for the production of which Jack had just filled his lungs, their
ears were greeted with a far more terrible sound, which caused their
hearts to stop beating. There was, it seemed, a sudden boom, followed
by a long, continuous roar. Diggory turned his head, to find the
far-off patch of light replaced by a spark of fiery red, and the
terrible truth flashed across his mind that in the excitement of the
moment he could not remember for certain which was the down line.

It was well for the Triple Alliance that at least one of their number
was blessed with the faculty of quick decision and prompt action, or the
history of their friendship might have had a tragic ending.

Diggory wheeled round, and catching hold of Mugford, cried in a voice
loud enough to be heard above the ever-increasing din, "Quick! get into
the six-foot way, and lie down!"

What followed even those who underwent the experience could never
clearly describe. They flung themselves upon the ground: there were the
thundering roar of an earthquake, coupled with a deafening clatter, as
though the whole place were falling about their ears, and a whirling
hurricane of hot air and steam.

In ten seconds, which seemed like ten minutes, the whole thing had come
and gone, and Diggory, scrambling to his feet in the dense darkness of
the choking atmosphere, inquired in a shaky voice, "Are you all right,
you chaps?"

There was a reply in the affirmative, and the three boys proceeded to
grope their way along in silence, until the broad archway of the
tunnel's mouth appeared through a fog of steam and smoke.

"I say, you fellows," cried Diggory, as they emerged into the fresh air,
"I wouldn't go through there again for something."

"It was a good thing you gave me that shove," said Mugford; "I felt as
though I couldn't move. And we were standing on the very line it went
over."

"Yes: I couldn't remember for the moment which was 'up' and which was
'down.' I thought, too, we should be safer lying flat on the ground
when it passed; had we stood up in the six-foot way, we might have got
giddy and fallen under the wheels."

The conversation was suddenly interrupted by a strange voice s