Franco-Italian armies which had been faced about to oppose their
progress while the other halves were making their assault on London.

As soon as news reached the Tsar that the blockade of the river had
been broken, he had ordered twelve of his remaining war-balloons to
destroy the ships that were swarming below London Bridge. Their fuel
and cargoes of explosives had been renewed, and they rose into the
air to execute the Autocrat's command just as Natasha had taken leave
of Arnold on her errand of mercy. He fathomed their design at once,
swung the _Ithuriel_ rapidly round to the northward, and said to his
lieutenant, who had just come on deck--

"Mr. Marston, those fellows mean mischief. Put a three-minute time
fuze on a couple of No. 3 fire-shell, and load the bow guns."

The order was at once executed. He trained one of the guns himself,
giving it an elevation sufficient to throw the shell over the rising
balloons. As the sixtieth second of the first minute passed, he
released the projectile. It soared away through the air, and burst
with a terrific explosion about fifty feet over the ascending
aerostats.

The rain of fire spread out far and wide, and showered down upon the
gas-holders. Then came a concussion that shook the air like a
thunder-clap as the escaping gas mixed with the air, took fire, and
exploded. Seven of the twelve aerostats instantly collapsed and
plunged back again to the earth, spending the collective force of
their explosives on the slopes of Muswell Hill. Meanwhile the second
gun had been loaded and fired with the same effect on the remaining
five.

Arnold then ran the _Ithuriel_ up to within a mile of Muswell Hill,
and found the remaining thirteen war-balloons in the act of making
off to the northward.

"Two more time-shells, quick!" he cried. "They are off to take part
in the battle to the north, and must be stopped at once. Look lively,
or they'll see us and rise out of range!"

Almost before the words were out of his mouth one of the guns was
ready. A moment later the messenger of destruction was speeding on
its way, and they saw it explode fairly in the midst of the squadron.
The second followed before the glare of the first explosion had
passed, and this was the last shot fired in the aerial warfare
between the air-ships and the war-balloons.

[Illustration: "The rain of fire spread out far and wide."

_See page 344._]

The effects of these two shots were most extraordinary. Th