means of entrance which the party used upon the present occasion. The professor, to whose genius was due the entire design of the wonderful ship, undertook, at Sir Reginald’s request, to point out to Lady Elphinstone a few of the most remarkable characteristics of the structure; and accordingly, when her ladyship had exhausted her wonder at the enormous proportions of the Flying Fish, Herr von Schalckenberg conducted his hostess forward and into the space between the starboard bilge-keel and the bottom of the ship, where there was just sufficient room for a tall man to stand upright close to the inner face of the bilge-keel. At a certain point in the tunnel-like passage the professor came to a halt, and remarked—

“Now, Lady Olivia, kindly favour me with your attention. Although you cannot distinguish it, there is a trap-door here, giving ingress to the interior of the ship, and as it is possible that you may at some time or other wish to make use of it when none of us are at hand to help you, I should like to show you how the door is to be opened or closed. Now, in the first place, you will observe that there is a vertical and also a horizontal joint in the plating, meeting just here—it is the only junction of the kind in this passage-way, so you cannot possibly mistake it. Now, kindly take notice of these vertical and horizontal rows of rivet-heads, and especially of this particular rivet that is common to both rows. There is nothing whatever to distinguish it from the others, is there? No. But if you will place your finger upon it, thus, and push firmly to the left, thus, you will see what happens.”

And, as the professor spoke, a section of the polished silver-like plating of the ship’s bottom folded gently out until its outer edge rested upon the ground, forming a kind of sloping gangway, by means of which it was easy to enter the yawning aperture that now appeared in the ship’s bottom.

“Supposing, however,” continued the professor, “that you are leaving the ship, and wish to close the trap-door behind you, all that you have to do is to push the rivet back into its original position, and the mechanism operating the door at once responds, closing the flap, thus, and leaving no indication whatever of its existence. Now, Lady Olivia, let me see whether you can open the flap.”

Thus invited, Lady Elphinstone laid her finger upon the rivet-head and gave it a vigorous push to the left, upon which the flap folded out as before, and von Schalckenberg, taking her ladyship’s hand, led her with old-fashioned gallantry up the gangway, the others following.

As well as the party could discern in the obscurity, they now found themselves standing in an apartment some ten feet square by seven feet in height, with no other perceptible means of egress from it than the trap-door by which they had entered; but upon the professor stretching forth his arm and groping for a moment about the wall, the room became suddenly illumined by the radiance of an electric light set in a very thick and strong glass globe let into the ceiling, and it now became apparent that there was a door in the bulkhead opposite them as they entered.

“This small room,” said the professor, “is known as the chamber of egress, because, as is quite obvious, it is from here that one leaves the ship for the outer world. But it has also another purpose besides the mere furnishing of access to the trap-door, as I will endeavour to explain to your ladyship. You are, of course, aware that one of the objects with which the Flying Fish was constructed was to enable her crew to explore the ocean depths, and to examine and, if necessary, operate upon the ocean’s bed. Now, in order to leave the ship and walk out upon the sea floor, an aperture of some kind in the hull is clearly necessary, through which we may pass; and that aperture you see before you in the shape of the trap-door. But you will readily understand that, with the ship sunk to the bottom, the water will pour violently through that trap, if it is opened without the observance of proper precautions; and unless some special means are adopted to prevent such a catastrophe, the water will quickly invade and fill the entire hull. Hence this room. Its use, in actual practice, is this: having donned our diving-suits in the diving-room, we pass into this small chamber by means of the door of communication, which you see in that partition, close the door carefully behind us, and turn on this tap, which admits a small stream of water into the room from outside. The pressure of water being considerable, the room quickly fills; but the partition, with its water-tight door, effectually prevents the water from penetrating any farther into the hull of the ship—and we then throw open the trap-door, and walk forth on to the sea floor. Upon our return we close the trap-door behind us, thus, turn on this air tap, and immediately a stream of densely compressed air rushes into the chamber, expelling the water through this valve in the floor. And when the water is all out, we turn off the stream of compressed air, and open this valve, which allows the compressed air to pass into the habitable portion of the ship, quickly reducing the air-pressure in this room to what it is in the other habitable portion of the ship; then we open this door, and pass into the diving-room.”

The professor then threw open the door and, with a profound bow, stood aside to allow Lady Elphinstone to pass through.

The room in which the party presently found themselves was an apartment about twenty feet square, one side of which was wholly occupied by four cupboards labelled respectively “Sir Reginald Elphinstone,” “Colonel Lethbridge,” “Captain Mildmay,” and “Von Schalckenberg.”

“This,” explained the professor, “is the room wherein we shall equip ourselves for our submarine rambles; and,” throwing open the door of one of the cupboards and disclosing certain articles neatly arranged upon hooks fastened to the walls, “here is a suit of the clothing and armour that we shall wear upon such occasions.”

“Oh yes,” responded Lady Olivia, “I remember having heard Sir Reginald speak of his ‘diving-armour’; what a very handsome suit it is,”—as she touched and thoughtfully opened the folds of a surcoat of scale armour that looked as though made of silver; “but it seems a queer idea to don armour for the purpose of walking about at the bottom of the sea. Yet, what a man of foresight you must be, Professor! My husband has often told Ida the story of your terrible fight with the conger eels, the first time that the party ever sallied forth from the Flying Fish. You appear to have foreseen and provided against every possible danger.”

“No, no!” exclaimed von Schalckenberg, laughingly disclaiming any such prescience; “I am not nearly as clever as that. For instance: the armour was not provided as a protection against the attacks of savage animals or fish, but for quite a different purpose.”

“Indeed!” exclaimed her ladyship; “for what purpose, then, was it provided?”

“For the purpose of protecting the wearer against the enormous pressure of the water to which he would be subjected when moving about on the bed of the ocean at a great depth below the surface,” answered the professor. “You must understand,” he continued, “that water exerts a pressure upon everything immersed in it; and the deeper the water, the greater is the pressure upon the immersed body. So rapidly does this pressure increase, that divers attired in an ordinary diving-dress are only able to descend to a depth of about fifteen fathoms, or ninety feet; there are a few cases where this depth has been exceeded, but they are few and far between. Now I have always held the opinion that to descend into the sea to merely such a trifling depth as this, for the purpose of scientific investigation, is scarcely worth the trouble; so when Sir Reginald was good enough to furnish me with the means to materialise, as it were, in