of the grand staircase (in which direction lay the sleeping apartments, bath-rooms, and domestic offices) they found themselves at the head of another staircase much narrower than the former. The one now before them was only about four feet wide, winding cork-screw fashion round the tube which encased the communications between the pilot-house and the engine-room, etcetera, and it was in its turn encased in a cylindrical bulk-head, in which, on their way below, they passed several doors giving access, as the professor explained, to the different decks.

Winding their way downward for a considerable distance they at length reached the foot of the staircase and passed at once through a doorway marked “Engine Room.” The first sensation of those who now visited this apartment for the first time was disappointment. The room, though full of machinery, was small, absurdly so, it seemed to them. So also with the machinery itself. The main engines, consisting of a pair of three-cylinder compound engines, though made throughout of aethereum, and consequently presenting an exceedingly handsome appearance, suggested more the idea of an exquisite model in silver than anything else, the pair occupying very little more space than those of one of the larger Thames river steamers. The impression of diminutiveness and inadequacy of power passed away, however, when the professor informed his companions that the vapour would enter the high-pressure cylinder at the astounding pressure of five thousand pounds to the square inch, and that, though the engines themselves would only make fifty revolutions per minute, the propeller, would be made, by means of speed-multiplying gear, to revolve at the rate of one thousand times per minute in air of ordinary atmospheric pressure.

“But how on earth do you manage to get your vapour up to that tremendous pressure?” asked the colonel.

“Oh!” answered the professor, “that is a mere matter of mixing. According to the proportions in which the crystals and the acid are mingled together, so is the pressure of the vapour.”

“And how do you mingle them together?” asked the lieutenant.

“This,” said the professor, leading them up to a small boiler-like vessel, “is the generator. The crystals are placed in a hopper at one end, and the acid in that small tank at the other, from whence they are respectively conducted along tubes into a small well in the bottom of the generator, where, their proportions being regulated by the size of the tubes through which they pass, they mingle and generate a vapour having a pressure of five thousand pounds on the square inch. See, there is the gauge, and it is now registering a pressure of five thousand pounds.”

“Good Heavens, man!” exclaimed the baronet, starting back; “you don’t mean to say that your generator is now, at this moment, subjected to that enormous pressure of more than two tons per square inch? Supposing it exploded, what would become of us?”

“We should be consumed in an instant by the fierce heat of the liberated vapour,” replied the professor calmly. “But,” he continued, “you need have no apprehension of an explosion. When that generator was being made I had a second one constructed at the same time, precisely similar in every respect, and this second one I tested to destruction, with the satisfactory result that it endured without distress a pressure of thirty-five tons per square inch, showed the first signs of weakness when it became subjected to a pressure of thirty-eight tons, and burst at a joint when under a pressure of forty-three tons per square inch. You may therefore feel quite satisfied that the generator is fully equal to a continuous pressure of at least fifteen tons, instead of the trifle over two which it will have to sustain.”

The remainder of the machinery possessing no very startling or novel features, it was passed by with merely an admiring glance at its exquisite finish; and the quartette, leaving the engine-room, passed round on the other side of the spiral staircase to a room marked “Diving Room.”

Entering this they found themselves in an apartment about twenty feet square, one side of which was wholly occupied by four cupboards labelled respectively “Sir Reginald Elphinstone,” “Colonel Lethbridge,” “Lieutenant Mildmay,” and “Von Schalckenberg.”

“This,” explained the professor, “is the room wherein we shall equip ourselves for our submarine rambles; and here,” opening one of the cupboards, “are the costumes which we shall wear upon such occasions.”

The opened cupboard contained an ordinary indiarubber diving-dress, a sort of double knapsack, a number of heterogeneous articles, and, lastly, a suit of armour.

“Why, professor, what, in the name of all that is comical, is the meaning of this? Are we to walk forth among the fishes equipped like the knights of old?” asked the baronet, pointing to the armour.

“I will explain,” said the professor. “In an ordinary diving-dress a man can only descend to a depth of something like fifteen fathoms. Instances have certainly occurred where this depth has been exceeded, a Liverpool diver named Hooper having descended as far as thirty-four fathoms, if my information is correct; but this was quite an exceptional circumstance; and, as I have said, fifteen fathoms may be taken as the average depth at which a man can move about and work in comfort. The reason for this limit is that beyond it the pressure of the water on the exposed hands is so great as to drive the blood to the head and bring on a fainting fit, if nothing worse; besides which, the volume of air inside the dress necessary to counteract the outside pressure of the water would be so great as to speedily result in suffocation. Now, if our explorations were limited to a depth of fifteen fathoms only they would hardly be worth the undertaking; so I have devised these suits of armour, in which we may safely explore the profoundest depths of the ocean to which the Flying Fish can penetrate. The armour is, as you see, composed of a number of small scales or plates of aethereum, and is so constructed that, whilst it is perfectly flexible, permitting the utmost freedom of movement to the wearer, it is also absolutely water-tight and incompressible, no matter how great the exterior pressure to which it is subjected. The wearer of it will consequently be perfectly protected at all points from the enormous water pressure; and he will be able to breathe in comfort, his air being supplied to him at the normal atmospheric pressure. In equipping himself the diver will first don the india-rubber diving-dress in the usual way. Then he will assume this double-haversack, the larger chamber of which, worn on the back, will contain a supply of air, whilst the smaller of the two, worn on the chest, is charged with a supply of chemicals for the purification of the air after it has been breathed. The two are connected together by a pair of flexible tubes, as you may perceive, and the mere expansion and contraction of the chest, in the act of breathing, sets in motion the simple apparatus which produces the necessary circulation of air between the two chambers. Having secured this haversack in position the diver next dons his body armour, and straps about his waist this belt, with its electric lamp and its dagger. The dagger, as you see, is double-bladed; it has a haft of insulating material, and the blades have connected to them this insulated wire at the point where the blades and the handle unite. You thus have a weapon which, on being plunged into the body of a foe, not only inflicts a severe wound, but also administers an electric shock of such terrible intensity as must result in instant death. The last portion of the armour to be assumed is the helmet, on the top of which is securely fixed an electric lamp, which, with the aid of the one at the belt, will give us, I imagine, as much light as we are likely to need.

“Having donned our armour we pass out of this chamber into the