For a few days past the police have had their attention directed to the movements, not of a "long, low, black schooner;" but of an iron submarine boat, to which very extraordinary abilities and infernal propensities were attributed. The Harbor Police, under the direction of Lieutenant Benjamin Edgar, were directed to be especially spry, and they kept their optics wide open for the mysterious stranger. Yesterday afternoon they stumbled upon a queer contrivance which lay at the lower end of Smith's Island, and proved to be the submarine monster of which they were in search. Externally it had the appearance of a section of boiler about twenty feet long, with tapered ends, presenting the shape and appearance of an enormous cigar with a boiler iron wrapper, and for all the world like Winan's celebrated steamer in respect to shape. The after end was furnished with a propeller, which had a contrivance for protecting it from damage from coming in contact with external objects. The forward end was sharkish in appearance, and the shark idea was carried out in other respects, as only the ridge of the back was above water, while the tail and snout were submerged. Near the forward end was a hatchway or "man-hole," through which egress and ingress were obtained. This whole was covered with a heavy iron flap, which was made air tight, and which was secured in its place by numerous powerful screws and hooks. Two tiers of glass bull's eyes along each side of the submarine monster, completed its external features, afforded light to the inside, and gave it a particular wide awake appearance.

But its Angus eyes did not avail to save it from capture. About twelve o'clock last night the harbor policemen saw a skiff loaded with pig lead move off from South street wharf, in charge of two young men, and they paid a visit to the submarine ship, in which a portion of the same description of lead had already been placed. The submarines with their skiff and lead were seized and brought to the city, and at about two o'clock this morning their iron pet was towed to town and moored at Noble street wharf.

The news of the capture soon flew around, and by little after daylight, the rush of people to the spot commenced. All sorts of stories were aloft, and thousands upon thousands gathered at the wharves, scaled the neighboring board piles, and importuned the amphibious policemen, who had the monster in charge, for permission to board her and see how she looked inside. But "no admission" was the rule, and the interior remained invisible to the millions.

The harbor men very courteously offered us a peep inside. After dropping from a high wharf into a skiff and then jumping a few feet, we found ourselves upon the back of the iron mystery. After much unscrewing and unhooking, the top of the man-hole was lifted off, and divesting ourselves of coat and hat, we squeezed into the machine, under the gaze of a curious and admiring multitude of about five thousand people.

We suddenly found ourselves squatting inside of a cigar-shaped iron vessel, about four feet in diameter. There was a crank for the purpose of operating the propeller already described, apparatus for steering, rods, connecting with fins outside, which could be moved at pleasure, and which had something to do with steadying and sinking the craft. There was a large reel of wire which might be intended for galvanic purposes, pumps, brass faucets, pigs of ballast lead, and numerous other things, which might be intended for either infernal or humane purposes for aught we know. The interior was abundantly lighted by means of the double tier of bull's eyes we have described.

By making inquiry in proper quarters, we learned the history of the machine. It seems that it is the invention of a Frenchman named De Villeroi. The cash for building it is said to have been furnished by a relative of the late Stephen Girard. It was constructed in this city about two years ago, and since that time it has been lying at New Castle, Marcus Hook, and Rancocas. It has been tried frequently at those points, and marvelous stories are told of the facility with which it can be sunk beneath the waters, again raised to the surface, and propelled and steered ether beneath the surface or upon it. After visiting the submarine affair, we had an interview at the Central Station. They gave their names as Alexander Rodes, a Frenchman, aged 30, and Henry Kriner, an American, aged 19. In reply to our questions, they told us that the vessel was intended for all submarine purposes. It had been under water for three hours at a time, and could be moved about at pleasure. The persons in it could leave it while under water, as though it was a diving bell. They manufacture, while under water, they said, the supply of air needed for respiration.

They informed us that the vessel had been lying at Rancocas for five months past, and that they brought it away from there on Tuesday last, their object being to test it at the Navy Yard here, for the purpose of obtaining a patent for it. They stated that M. de Villeroi had got permission from the officers of the yard to make the trial. Upon the other hand, we hear from the police, that the authorities at the yard know nothing of the machine, and that no such arrangement has been made. The business will be properly investigated, and if the submarine craft is bound upon any errand that is not friendly to the Union, it will not be likely to reach its destination very speedily. Under any circumstances, its appearance in the river at this time, and its capture, have created an extraordinary excitement.