squadron watching the Gallo-Batavian flotilla off the ports of
Boulogne, Ambleteuse and Calais; and the occasion of her dropping
anchor off Portsmouth on the way was a special and somewhat singular
one; yet no more singular than the crisis with which Great Britain
had then to cope.

Behind the sandhills from Ostend around to Etaples lay a French army
of 130,000 men, ready to invade us if for a few hours it could catch
our fleets napping. To transport them Napoleon had collected in the
ports of Ostend, Dunkirk, Calais, Ambleteuse, Vimereux, Boulogne and
Etaples, 954 transports and 1339 armed vessels--gun-brigs, schooners,
luggers, schuyts and prames; and all these light vessels lay snug in
their harbours, protected by shoals and sandbanks which our heavier
ships of war, by reason of their draught, could not approach.

In particular, a double tier of vessels--one hundred and fifty in
all--which were moored outside the pier of Boulogne, and protected by
heavy shore batteries, excited while it baulked the rage of our
gallant seamen manoeuvring in the deep waters of the Channel.

Strange diseases suggest strange remedies. Our Admiralty, in the
spring of the year, had been approached by an ingenious gentleman
with the model of an invention by which he professed himself able to
reach these hundred and fifty ships in Boulogne and blow them in air
without loss or even danger to our fleet. This machine consisted of
a box, about twenty feet long by three feet wide, lined with lead,
caulked, tarred, ballasted and laden almost to the water's edge with
barrels of powder and other combustibles. In the midst of the
inflammable matter was placed a clockwork mechanism which, on the
withdrawal of a peg, would in a fixed time (within some ten minutes
or thereabouts) ignite and explode the vessel.

A dozen of these engines, claimed the inventor, if towed within range
and released, to be swept down upon Boulogne pier by the tide, would
within a few minutes shatter and dispel the nightmare of invasion.

The Admiralty sanctioned the experiment, news of which had awakened
some interest not unmixed with derision throughout the British Fleet;
and the business which called the _Vesuvius_ to Portsmouth was to
take in tow the first of these catamarans (as our sailors called
them) and convey it across to the squadron watching Boulogne.

On the morning after the _Vesuvius's_ arrival, two dockyard boats
arrived with the hull of the machine i