THE ADVICE OF SERKO THE ENGINEER 211

to the Zalinski shell, but a hundred times greater, and
requires no projecting apparatus, since it flies, so to speak,
on its own wings through space.”

I listened, in the hope of detecting a portion of the
secret, but Serk6 said no more than he intended to say.

“Has M. Roch,” I asked, “made known to you the
composition of his explosive ?”

“Yes, Mr. Hart—with your leave—and we shall soon
possess large quantities of it, which will be stored in a safe
place.”

“And is there not danger—perpetual danger in re-
serving -so much of this substance? If there were an
accident, the explosion would destroy the island of—”

Once more the name of Backcup was on the point of
escaping me. Aware at once of the identity of Ker
Karraje, and the situation of the cavern, Simon Hart
would be considered decidedly better informed than was
convenient.

Happily the engineer had not observed my pause, and
he answered,—

“We have nothing to fear. Roch’s explosive can only
be ignited by means of a special defiagrator. Neither
shock nor fire will make it explode.”

“Flas Thomas Roch also sold you the secret of this
deflagrator ?”

“Yes, Mr. Hart,’ replied the engineer, although I
noticed a certain hesitation in his response. “But I re-
peat there is no danger, and you may sleep with perfect
ease! We have no wisli to be blown up with our cavern

P 2