It was now within two hours of sunset, and the "Aphrodite" had to find a suitable berth in order to carry out the plans Captain Restronguet had suggested for the safeguarding of his crew.

The confiscated boat had been securely lashed down amidships. It was too large to be taken below through the hatchway, but in order that it would not burst its lashings as the submarine sank Mylor bored four fairly large holes in the garboards so that the water could easily make its way out. The holes could be plugged when the whaler was required for service afloat, and as Hythe remarked an additional washing would do a lot of good to a boat that had been left lying on the wharf of that malodorous and inhospitable town.

Fortunately a fairly deep and extensive hole was discovered in the bed of the river, the soundings giving ten fathoms. Being the rainy season the river was three or four feet higher than its normal level, a circ.u.mstance greatly in the favour of the submarine's voyage of exploration and retribution.

The night pa.s.sed fairly quietly, the air within the submarine being perfectly clear. Looking through the observation scuttle the crew could see that the so-called fresh water was of a deep brown colour, while the full moon, shining through the miasmic mists looked like a ball of greenish yellow copper. Occasionally a crocodile would alight upon the deck of the "Aphrodite" and drag its armoured body over the metal plating with a dull metallic sound. Once a couple of hippopotami in their moonlight gambols brushed against the side of the conning-tower, the shock being distinctly felt by the men on watch.

In the morning the detector registered the position of the "Vorwartz" at eighty-five miles, which was precisely the same distance as it gave overnight.

Not until the mists had disappeared did Captain Restronguet order the "Aphrodite" to be brought to the surface and the hatchways opened. He would not risk the health of his crew by exposing them to the fever-laden atmosphere. Almost as far as the eye could reach the water extended, for being in flood the river, wide under ordinary circ.u.mstances, now resembled a vast lake.

Proceeding at twelve knots, that took her over the ground against the current at barely nine miles an hour, the submarine held steadily on her course, literally feeling her way between the shoals of loathsome black mud.

Just before noon a motor-launch manned by Portuguese pa.s.sed, downward bound. In reply to a signal to close, the little craft ran alongside the "Aphrodite" without the faintest hesitation. Two of her crew who could speak French were interrogated by Hythe. They had neither seen nor heard anything of a vessel resembling the "Vorwartz" although they had come from Tete, a few miles below the limit for navigation. In reply to a request that one of their number should accompany the submarine as far as Sena, to act as a pilot, the Portuguese resolutely refused, saying that a qualified man could be obtained at Molonho, ten miles further up the river.

"What does the detector say, Mr. Kenwyn?" asked Captain Restronguet for the tenth time that morning.

"Eighty-three miles, sir."

"H'm; two gained. But it's very strange that that motor-boat should not have noticed the 'Vorwartz.' Perhaps the river is deeper, and Karl von Harburg took the precaution to run submerged."

"It is wide enough for a large craft to pa.s.s unnoticed," said Devoran.

"Not the actual channel; if we went half a mile to port or starboard we would be hard and fast aground."

"Is it likely that the 'Vorwartz' has taken to a backwater?" asked Hythe.

"By Jove! I hope not," exclaimed Captain Restronguet; then in a confident tone he added, "No matter, our detector will locate her. One thing we know, she hasn't ascended the Shire--a tributary that drains Lake Nya.s.sa. I almost wish she had, for I would like to see the final act take place in British waters."

To guard against the tropical heat awnings had been spread fore and aft, extending the whole length and breadth of the deck. Under this the officers and crew not on duty "stood easy," the former seated in deck-chairs brought from the cabins.

To Hythe the voyage seemed more like a pleasure trip than a mission of destruction. He and Kenwyn amused themselves by shooting at crocodiles and hippopotami that frequently came within a hundred yards of the "Aphrodite," while Captain Restronguet did a more practical act by bringing down a bird resembling a turkey, which, falling on the awning, was received as a welcome change to the menu.

Captain Restronguet was in high spirits, but his enthusiasm received a set-back when the "Aphrodite" ran full tilt upon a shoal. It was through no fault of the leadsman. The depth gave six fathoms but a few moments before. The discolouration of the water prevented any indication of the shoaling of the depth from being noticed. It was simply a case of sheer bad luck.

"Empty the reserve tanks," ordered Captain Restronguet, for the "Aphrodite" was now drawing ten feet for'ard and twelve aft. Quickly the foremost tank was emptied, but the after one, in spite of the action of the powerful pumps, refused to be discharged. Consequently the draught for'ard decreased while the submarine's stern sank lower into the slimy mud.

"Full speed astern," was the next order, but beyond churning up the brownish black ooze the propellers failed to do the slightest good.

"Lay out an anchor, Mr. Devoran," exclaimed his superior officer. "Be sharp, for the tide is falling."

Hastily the boat was lowered, the heaviest anchor slung underneath, and laid out a hundred yards astern. The stout hempen hawser was led to the motor capstan, but as the powerful machinery made it revolve it simply "walked home" with the anchor. The soft mud offered little or no resistance to its broad palm.

The "Aphrodite" seemed doomed to remain hard and fast for another ten hours. Night with all its terrors would envelop her ere the next tide was at its height, and to work in the germ-laden mists was to court the deadly fever.

"Can the ballast tank be got at from the inside, sir?" asked Hythe, struck by an inspiration.

"Not without flooding one of the sub-divisions of Number Three Platform," replied Captain Restronguet. "But why do you ask?"

"I thought perhaps I might put on a diving-dress, and enter the tank and examine the valves."

"It's feasible," observed Captain Restronguet. "If you attempt it and succeed I shall be still more indebted to you."

"Then I have your permission?"

"Certainly."

"Look here, Hythe," exclaimed Kenwyn. "If you tackle the job I'm with you."

"Thanks," replied the sub. "The sooner we start the better."

Donning their diving-suits and equipping themselves with brushes, spanners, rubber-sheeting for the valves, and an electric lamp each, the two men entered No. 4a compartment, as the subdivision was designated.

As soon as the water-tight doors were shut they began unbolting the man-hole cover that gave access to the faulty ballast-tank, guided in their self-imposed task solely by the rays of the lamps.

Presently the water began to ooze between the partially removed cover and side of the tank, increasing in volume till the whole of the compartment was flooded with a liquid resembling thick pea-soup. It was only by the concentrated rays of the two lamps and by keeping his helmeted head within six inches of the metal lid that Hythe was able to complete the work of opening a means of communication with the ballast-tank.

As soon as this was done the sub squeezed through the manhole. His feet touched a thick layer of stiff mud on the floor of the tank. Bringing his lamp down he carefully examined the outlet valve. The secret of the defect was his: when the "Aphrodite" had been submerged by the side of the wharf at Marromea the inrush of water had brought with it a quant.i.ty of sediment sufficiently plastic to form a layer over the outlet valve and thus prevent its action.

For an hour Hythe toiled. He had neglected to bring anything of the nature of a spade, and had to recourse to his bare hands. Handful after handful of the noxious mud he scooped up and pa.s.sed through the manhole into the compartment without, till the interior of the tank was perfectly free from anything of the nature to r.e.t.a.r.d the action of the pumps.

After a lapse of two hours and a half from the time of entering the compartment the two men, their diving-dresses covered in slime, gave the pre-arranged signal to start the pumps. Ten minutes later both the compartment and the tank were emptied of water, and the task of replacing the cover was proceeded with.

But even then Hythe, nothing if not practical, refused to come on deck.

He asked for a couple of buckets full of strong disinfectant fluid to be sent down, and, using a mop vigorously, he thoroughly scrubbed out the interior of the compartment, finishing up by mopping his companion's dress with the liquid, while Kenwyn performed the same office for him.

Thus the risk of fever from the river-mud was entirely obviated.

"I would like a cold bath," exclaimed Kenwyn as the two officers rejoined their comrades.

"You jolly well won't, then," replied Hythe emphatically. "At least unless you wish to pay an indefinite visit to Davy Jones. Why, man, you are as warm as you can possibly be. Have a hot bath, if you like. I will, with plenty of disinfectant in it."

By this time the "Aphrodite," her draught aft considerately lessened, was afloat and resuming her voyage. Kenwyn had had his hot bath and foolishly sat in the fairly strong breeze to cool himself afterwards.

Before night he was lying unconscious in his bunk, prostrate with blackwater fever.

CHAPTER XXIX.

THE "PRIDE OF RHODESIA."

Kenwyn's serious illness was a source of anxiety and perplexity to his chief. Captain Restronguet was loath to leave him ash.o.r.e in an unhealthy district where medical comforts were of a most primitive nature, while to keep the patient on board was undoubtedly detrimental to the health of the rest of the crew and consequently a stumbling-block to the success of the expedition.

Finally he compromised the difficulty. Kenwyn was to be isolated from the rest of the crew, Mylor and Lancarrow volunteering to act as nurses, until the "Aphrodite" entered the gorge through which the Zambezi flows.

Here the patient was to be landed, placed in a tent and left in charge of the two men till the "Aphrodite's" return.

Just below the town of Kaira, where the Shire River joins the Zambezi, definite news came to hand concerning the "Vorwartz." A large canoe, laden with millet, arrived the same day as the "Aphrodite." Her crew reported, through a Portuguese interpreter who spoke indifferent English, that they had pa.s.sed a strange-looking vessel, somewhat resembling the "Aphrodite," four days up the river, and that it was hard aground at the mouth of a tributary known as the Zampa.