al. His only reasonable course, therefore, would be to sell
the vessel to the Tsar, and leave his Majesty's chemists to discover
and renew the motive power if they could.

These conclusions once arrived at, it was an easy matter for the keen
and subtle intellect of Natas to deduce from them almost the exact
sequence of events that had actually taken place. The _Lucifer_ had a
sufficient supply of power-cylinders and shells for present use, and
these would doubtless be employed at once by the Tsar, who would
trust to his chemists and engineers to discover the nature of the
agents employed.

For this purpose it would be absolutely necessary for him to give
them one or two of the shells, and at least two of the spare
power-cylinders as subjects for their experiments.

Now Natas knew that if there was one man in Russia who could discover
the composition of the explosives, that man was Professor Volnow of
the Imperial Arsenal Laboratory, and therefore the shells and
cylinders would be sent to him at the Arsenal for examination. The
whereabouts of the deserters for the present mattered nothing in
comparison with the possible discovery of the secret on which the
whole power of the Terrorists depended.

That once revealed, the sole empire of the air was theirs no longer.
The Tsar, with millions of money at his command, could very soon
build an aerial fleet, not only equal, but, numerically at least,
vastly superior to their own, and this would practically give him the
command of the world.

Natas therefore came to the conclusion that no measures could be too
extreme to be justified by such a danger as this, and so, after a
consultation with the commanders of the three vessels, it was decided
to, if necessary, destroy the Arsenal at St. Petersburg, on the
strength of the reasoning that had led to the logical conclusion that
within its precincts the priceless secret either might be or had
already been discovered.

As the crow flies, St. Petersburg is thirty degrees of latitude, or
eighteen hundred geographical miles, north of Alexandria, and this
distance the _Ithuriel_ and her consorts, flying at a speed of a
hundred and twenty miles an hour, traversed in fifteen hours,
reaching the Russian capital a few minutes after seven on the evening
of the 27th.

The Rome of the North, basking in the soft evening sunlight of the
incomparable Russian summer, lay vast and white and beautiful on the
islands formed by the Neva and it