"Not they. Do you mean to tell me that if they had spotted anything suspicious they would not follow it up. I was----"
The navigating officer's words were interrupted by a heavy detonation, like the report of a fourteen-inch gun fired with a full charge. Beyond the houses of Old Portsmouth, and at an altitude of about five hundred feet, a cloud of yellow smoke hung almost motionless in the still air. The aero-hydroplanes, overtaken by a wave of disturbed atmosphere, lurched violently, although fully a mile from the actual place of the explosion. It required all the efforts at the command of their crew to save the aerial vessels from destruction, but recovering their equilibrium by superb manoeuvring of the planes, the aero-hydroplanes turned and headed towards that portion of Spithead over which they had so lately been reconnoitring.
"By Jove! There's pluck for you!" ejaculated Egmont. "That was Restronguet's signal. If it had been to time those fellows would have been done for; and now they're trying to spot the submarine. You were right after all, Hythe. That paragraph was not a hoax."
Captain Tarfag was in the middle of lunch when the detonation was heard. He rushed on deck, and realizing that it was a case where waiting for orders would be detrimental to success, he ordered the moorings to be slipped.
Within the harbour all was commotion. Nearly a dozen destroyers, two scouts, and three tugs were making for Spithead, while five more aero-hydroplanes and the naval airship "Beresford" were ploughing their way against a stiff south-easterly breeze towards the scene of Captain Restronguet's latest demonstration.
One noticeable result of the explosion was that within a quarter of an hour the weather, hitherto perfectly calm, became changed. Clouds were rapidly banking up, with every appearance of a heavy thunderstorm, while the placid waters of Spithead were now white with foam-crested waves.
For two hours the "Investigator" and her consorts cruised up and down, betwixt the Nab Lightship to the eastward and Cowes to the west. Aloft the aircraft kept anxious watch and ward, till it seemed impossible that any craft could lie at the bottom of that comparatively shallow roadstead without being discovered.
"Nothing to report," came the wireless message from the aircraft with monotonous regularity. Captain Restronguet had outwitted the eyes and ears of the British Fleet.
Upon the "Investigator's" return to Portsmouth Harbour it was possible to obtain details of what had occurred: The sea wall in front of Southsea Castle was crowded with people who, half-doubting, were yet sufficiently curious to see whether the promise in The Times would be redeemed. They saw the two aero-hydroplanes approach and manoeuvre over the pre-arranged area. They heard the clocks chime the hour of twelve. They waited a few moments longer, nothing happened, so with a derisive cheer they began to disperse. Some remained--mostly those of the leisured class who were not restricted by the midday meal that the British workman holds up as an established institution.
Suddenly--it was exactly at eleven minutes past twelve--a column of water leapt vertically upwards at less than four hundred yards from the shore. There was a shrieking sound like the screech of a high velocity projectile, followed by a detonation so powerful that most of the spectators on the sea-front were deaf for days afterwards. The ground trembled, several persons were overthrown; the windows of several houses overlooking the common were broken. Expecting a shower of scraps of metal from the bursting projectile the terror-stricken crowd broke and ran, but curiously enough no one could afterwards be found to report that anything of a solid nature fell to earth. Captain Restronguet's token was merely an explosive rocket of high power.