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rising above the tube increases its diameter, becoming bell shaped. The dome has a diameter across its mouth or base equal to the greatest diameter of the collar, and when in place it is supported a short distance above and directly over the collar, leaving an opening all the way around between them. The band is somewhat broader than this opening and of greater diameter than the collar. so that in position it encircles the opening but does not come in contact with the main structure except at the points where it is secured.

In operation the "cap" works as an aspirator. and the external air currents, no matter in which direction they move, whether vertically, diagonally or horizontally, produce a tendency to vacuum in the tube, and consequently an upward and outflowing current. This process continues as long as there is any agitation of the external air, and the velocity of the exhaust current is increased as the wind increases, Applied to an apartment, its tendency to exhaust the air creates the desired circulation.

The correct principle of ventilation being to supply means for lifting or pumping the impure air out, as then fresh air will take its place, it would seem that the device described is well adapted to accomplish this process. Fitted to a vessel, in suitable sizes for the different locations, they would occupy, and with proper connections, they would insure an almost continuous circulation through its holes, bilges, store rooms and apartments. In selecting situations for them, advantage can be taken of their power to act whether they are placed right side up, up side down or sidewise; and for this reason they could be run along underneath the hammock rail, on the outside of the ship, and project only a few inches. These would serve to ventilate the holds. bilges, et cetera, while others of greater capacity could be distributed about the decks, and one of sufficient size to cap the smoke stack would do good service, not only in the process of ventilation and in exciting a strong draft for the fire, but in protecting the interior of the smoke stack and its dependencies from the weather.

P. A. Eng. ROELKER: Mr. Chairman, I wish to call attention to that portion of Mr. Baird's paper which gives an account of experiments made by him on the velocity of air currents in ventilating shafts temporarily fitted to openings in the deck. These experiments show how large a quantity of air may be discharged through such improvised air ducts, or by making use of the annular space between the chimney and its outer casing, as proposed by Mr. Baird, when the temperature below decks exceeds by but a few degrees the temperature of the outside air. Such means of ventilation are, of course, purely auxiliary, and are not intended to take the place of systematic mechanical ventilation; but, in the absence of the latter, means may be found in nearly every vessel for improvising temporary ventilating shafts which will exhaust large quantities of the vitiated air below decks. Since the majority of our naval vessels will remain, necessarily, without mechanical ventilation, for years to come, it is to be hoped that the facts presented by Mr. Baird will induce others to apply in a similar manner the means at hand to the ventilation of our vessels, and I have no doubt that Mr. Baird will feel rewarded for his labors if the interesting paper read by him tonight produces this immediate practical result.

Lieutenant TANNER: It will, perhaps, be of interest to those present if I give a short account of my own experience with ventilators in sea going ships. When I took command of the Pacific mail steamer City of Peking, I found that she had been fitted with ventilating apparatus which extended to all parts of the ship except the main passenger saloons, which, being light and well up above the water, where air could circulate naturally, were considered not to require artificial ventilation. The draught was furnished by large blowers in the fire rooms, connected to circulating pipes, having at proper intervals small ports fitted with shutters. Particular attention had been paid to the ventilation of the cargo and passenger decks; the latter requiring a very frequent change of air, owing to the number of Chinese

that were transported each trip. On my arrival in Yokohama on my first trip I found a couple of Italian merchants who were in great trouble with regard to the transportation of a heavy invoice of silk-worm eggs. Hitherto the Pacific Mail company had refused to take this sort of freight, on account of the risk of losing a great part of it on the long passage to San Francisco. It is absolutely necessary that silk-worm eggs shall be kept in a cool place, where air can circulate freely about them: otherwise, if the temperature rises above a certain point, the eggs will hatch and the cocoons are spoiled. Having tested the ventilating apparatus thoroughly on the trip. I was very confident that it fully answered all that could be required of it. I therefore made overtures to the merchants, and succeeded in underbidding rival lines, and secured the cargo, which was valued at over half a million of dollars. This cargo I transported with absolute safety to San Francisco. Every morning on my round of inspection through the ship I would start the blowers and open the connections on the cargo deck, and in twenty minutes I could bring down the temperature 10°. It was only necessary to ventilate for about ten minutes three or four times in the twenty-four hours, and the temperature of my cargo would be kept at a constant point. Thus in one trip this apparatus paid a dozen times over the cost of putting it in the vessel. The Chinese passengers were frequently very much annoyed by the draught when their bunks happened to be in the vicinity of the ventilating ports, and, as they could not close the shutters, they resorted to stuffing their hats or clothing into the ports. The draught was so strong that no amount of jamming would hold their things in position, and every thing they put in would be drawn straight to the fire-room. Showers of hats, pantaloons and shirts were not infrequent in the stoke hole. Notwithstanding the airy position of the passenger saloons, the lack of proper ventilation was readily noticeable at sea. Passing from one of the ventilated apartments to the saloon, its "stuffiness" was quite appreciable, although, compared with the apartments of our men-of-war, these saloons were extremely well ventilated.

Lieutenant VERY: In going over H. M. ironclad Dreadnought, I was especially struck with the excellence of the ventilating apparatus, which was apparently of the same type as that mentioned by Lieut. Tanner. The circulating pipes ran along under the shelf pieces of the main deck so as to be just above the head, and in the state rooms just over the bunks. The ports, of which there was one to each room besides a number elsewhere, throughout the storerooms, engine rooms, berth deck and holds, were closed by shutters. so that the draught at any one place could be regulated. Another feature noticeable on this ship was the absence of engine room bulkheads. The heat from engine and fire rooms was forcibly drawn straight up through the uptake jacket apparently, at any rate it could not distribute itself about the decks. I noticed this same feature on the Russian ironclad frigate Minin, and I also remember that whilst a midshipman on the Asiatic squadron I commented on the absence of fire and engine room bulkheads on the French ironclad Belliqueuse, remarking that it must be very hot on the berth deck and in the steerages, owing to the escape of hot air. I was corrected by one of the French officers, who told me that on the contrary the deck was better ventilated. This of course was not due to the absence of the bulk head, but to the arrangement overhead by which the hot air was drawn straight up, taking with it the vitiated atmosphere below decks. With our present system of fire room ventilation, cold air is forced down the ventilators and rushes immediately to the fires, leaving the vitiated air to grow and spread itself throughout the ship. Bulkheads are of but little service, as the heat is refracted from their outer surface and vitiates what little fresh air there may be circulating. As for wind-sails, they are simply a God-send to the officer who is able to point the muzzle into his stateroom door. Beyond a small radius their effects are so diminished as to amount to almost nothing.

P. A. Eng. BAIRD: I have had some experience in automatic ventilators, but have never seen the exact device sketched by Mr. Sullivan. We had a very smoky galley pipe on board the Trenton, and it was effectually cured by an aspirating hood which I made on the principle of the air injector which I had previously patented for my distilling apparatus, and which is probably well known to all the gentlemen present. So far as the history of the principles of ventilation are concerned, and to whom the original invention is due, I must admit that I was not well posted, and have, therefore, to thank our chairman for his able chronological arrangements of the dates of those inventions. My part in this matter commenced in 1863, and has been the part of an engineer and not that of an inventor. I have not been able to find recorded the experiments of anybody, except myself, upon the velocities due to difference of temperature in the smoke pipe jacket, nor has any person, so far as I can find, ever attempted to combine the carbonic acid analyses taken on ship board with the experimental draught of the wind-sails, and to put the same to any practical use. Nor is there published, to my knowledge, any data which will guide our mechanics in the proportioning of exhaust fans and tubes for ships. I have viewed this problem from an engineering stand point, and have sought to put it in a practical shape. The paper I wrote on this subject in 1873 (vide Sanitary and Medical Report III, Bureau of Medicine and Surgery for 1873 and 1874, and also the Report of the Secretary of the Navy for 1873,) has been favorably received by the officers of the Navy, and I do not hesitate to say that the ventilating machinery on board the Richmond is an indifferent imitation of that proposed by myself.

BOSTON BRANCH.

APRIL 30th, 1880.

COM'DR O. A. BATCHELLER U. S. N., in the chair.

THE WANT OF DOCKING FACILITIES IN OUR NAVY

YARDS.

BY CIVIL ENG. U. S. G. WHITE U. S. N.

MR. CHAIRMAN, AND GENTLEMEN :

If there is any one thing in which we are deficient in our navy yard appointments it is in the matter of docks. We have not to-day a navy yard at which it can be said that there are any docking facilities.

We have at Boston, New York and Norfolk one stone dry dock each; at Kittery there is an old and cumbersome lifting dock, as also one at Mare Island. Each of these docks is in bad condition and it was but a short time since that the Mare Island dock failed with a foreign man-of-war, very nearly producing disastrous results. There is now building for the Pensacola yard an iron, floating, sectional dock, two sections being already at the yard. This work being new is probably in good working order and is also, probably, supplied with such appliances as modern requirements may have suggested.

At the yard now building at League Island there are contemplated numerous stone dry docks, and also a lifting dock with marine railways, but it is very doubtful whether any means will be provided for the docking of a ship in such a near future as to interest any one here present. The same may be said of the dockage embraced in the proposed plan of development of the station at New London Conn.

Of all systems of docking it is conceded that the stone dock is the best. Although costing more in the first place, it possesses the advantage of greatest economy of maintenance, while, once within it, a ship is subjected to less strain. The most marked disadvantage is that a very limited space is provided in which to work, and during the heated term the men working in the lower part of the structure suffer somewhat from the heat, being almost entirely cut off from any air that may be stirring. Again a stone dock is limited in its capacity; but as it is not probable that in the future naval vessels will have the great length which

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