90.5 gallons of water at starting. 8 gallons of water at stopping. Highest temperature Lowest temperature General Result of First Series with 50 gallons or 500 lbs. water agitated at 88.64 revolutions per minute. Degree, including radiation. Degree per hour. General Result of Second Series with 10 gallons or 100 lbs. of water agitated at First Series.-These were obtained by means of Prony's Friction Break applied to a correctly turned pulley of cast iron, fitted in the upper part of the vertical wooden spindle of the agitator. The friction bracket was carefully equilibriated on the pulley by means of weights, oil, and tallow until it made the same number of revolutions as before; the box having previously been emptied of its water. The following were the results : 1st. That 500 lbs. of water agitated at the rate of 88.64 revolutions per minute were heated 30.38 per hour by an expenditure of 29.000 lbs. per minute. This is equivalent to 1690 lbs. raised one degree. Then 29.000 × 60—174·000 1690 =1030, equivalent to 1 lb. being heated 1° in one hour. Second Series.-That 100 lbs. of water agitated at the rate of 232.67 revolutions per minute were heated 6° 27 per hour by an expenditure of 1.8 H. P., or 59 400 × 60=356 400 lbs. This is equivalent to 621 lbs. raised 1° in one hour. From the preceding result it appears that the mechanical equivalent varies as the quantity of water used in the experiment, and the rate of agitation; the larger quantity of water agitated by 88 64 revolutions giving an equivalent of 1030 lbs., and the smaller quantity giving only 621 lbs. when agitated 232.67 revolutions. Mechanical Structure of the Great Eastern' Steam Ship. The author laid before the Section some of the mechanical details of the construction of the great ship now building at his establishment at Millwall. The first point related to the peculiarity of her great size; the second, on which her merits or demerits as a piece of naval architecture depended, was the general structure or lines of the ship; the third point would be the distribution of materials in the construction of the ship, so as to obtain the safest and strongest possible structure with the minimum of materials; and the last point would be to allude generally to the mechanical arrangements for her propulsion. With respect to size, it was generally supposed that, as a practical shipbuilder, he was an advocate for big ships. The contrary, however, was the fact. There were cases in which big ships were good, and there were certain cases in which big ships were ruinous to their owners. In every case the smallest ship that would supply the convenience of trade was the right ship to build. He came there as an advocate of little ships; and it was the peculiarity of the Great Eastern' that she was the smallest ship capable of doing the work she was intended to do; and he believed that if she answered the purpose for which she was designed, she would continue to be the smallest ship possible for her voyage. It was found by experience that no steam-ship could be worked profitably which was of less size than a ton to a mile of the voyage she was to perform, carrying her own coal. Thus, a ship intended to ply between England and America would not pay permanently unless she were of 2500 or 3000 tons burden. In like manner, if a vessel were intended to go from this country to Australia or India, without coaling on going out, but taking her coals with her, she would require to be 13,000 tons burden. And turning to the case before them, it would be found that the big ship was a little short of the proper size. Her voyage to Australia and back would be 25,000 miles; her tonnage, therefore, should be 25,000 tons, whereas its actual amount was 22,000 tons. The idea of making a ship large enough to carry her own coals for a voyage to Australia and back again was the idea of a man famous for large ideas-Mr. Brunel. He suggested the matter to him (Mr. Russell) as a practical shipbuilder, and the result was the monster vessel which he was about to describe. He had peculiar pleasure in laying a description of the lines of the ship before the present meeting, because the ship, as a naval structure, as far as her lines were concerned, was a child of the British Association. It was twenty-two years since they had the pleasure of meeting together in Dublin. On that occasion he laid before the Mechanical Section a form of construction which had since become well known as the "wave-line." The Section received the idea so well that it appointed a committee to examine into the matter, with the intention, if they found the wave principle to be the true principle, to proclaim it to the world. The committee pursued its investigations, publishing the results in the account of their 'Transactions;' and from that time to the present he had continued to make large and small vessels on the wave principle; and the diffusion of the knowledge of this system through the Transactions of the British Association' had led to its almost universal adoption. Wherever they found a steam-vessel with a high reputation for speed, economy of fuel, and good qualities at sea, he would undertake to say that they would find that she was constructed on the wave principle. ་ He would endeavour to explain what were the principles of the wave-line as distinguished from the older-fashioned modes of building, and how they were carried out in the big ship. All practical men knew that the first thing a shipbuilder had to think of was what was called the midship section of the vessel: that was, the section which would be made if the vessel were cut through the middle, and the spectator saw the cut portions. Mr. Russell here pointed out a diagram of the midship section of the 'Wave,' a small vessel about 7 tons burden, which was the first ever constructed upon that principle. Now the first thing to be done in building a steamvessel was to make a calculation of the size of the midship section in the water. In sailing from one place to another, it was necessary to excavate a canal out of the water large enough to allow the whole body of the ship to pass through. The problem was, how to do that most economically; and this was effected by making the canal as narrow and as shallow as possible, so that there would be the smallest quantity of water possible to excavate. Therefore it was that the shipbuilder endeavoured to obtain as small a midship section as he could; and that had been effected in the case of the big ship, whose midship section was small,-not small absolutely, but small in proportion. In increasing the tonnage of a ship, three things had to be considered, the paying power, the propelling power, and the dimensions. Mr. Russell then entered into a calculation to show that while he doubled the money-earning power of a ship by increasing its size, he only increased its midship section by 50 per cent. For instance, a ship of 2500 tons burden would have 500 feet of excavation through the water to do; the big ship had 2000 feet of excavation; and the lineal dimensions of one were to the lineal dimensions of the other as 1 to 21. The excavation to be done by the big ship in relation to that to be done by the small ship was as 4 to 1, but the carrying power was as 10 to 1. To propel the big ship they had a nominal H.P. of 2500, while to propel the smaller vessel there was a nominal H.P. of 500; so that the big ship would be worked quite as economically as the small one. Referring again to the wave-line, he would suppose that it was given as a problem to any one to design a ship on the wave principle. The first thing to be done was to settle the speed at which the ship was intended to go. If the speed were fixed at 10 miles an hour, a reference to the table of the wave principle would show that, in order to effect that object, the length of the ship's bows ought to be about 60 feet, and that of her stern about 40 feet. If a larger vessel were required, say a ship of 130 feet long, there would be nothing more to do than to put a middle body of 30 feet in length between the bow and the stern. Having then made the width of the ship in accordance with the midship section agreed upon, it would be necessary to draw what was known as the wave-line on both sides of the bow, and the wave-line of the second order on both sides of the stern. Constructed in this manner, and propelled by the ordinary amount of H.P., the ship would sail precisely 10 miles an hour. They could go slower than 10 miles an hour if necessary, and in doing so they would economise fuel, in consequence of the diminished resistance of the water; whereas there would be a vastly increased resistance if an attempt were made to drive the steamer more than 10 miles an hour. For the speed at which it was intended to drive the Great Eastern,' it was found that the length of her bow should be 330 feet, the length of her stern 220 feet, of the middle body 120 feet, and of the screw propeller 10 feet; making in all 680 feet in length. The lines on which she was constructed were neither more nor less than an extended copy of the lines of all the ships which he had built since he first laid the wave principle before the Association. It was his pride that he had not put a single experiment or novelty into the structure of the vessel, with one or two exceptions, which he had adopted on the recommendation of men who had had practical experience of their efficacy. The wave principle had never in a single instance deceived him as to the exact shape a vessel ought to have in order to accomplish a certain rate of speed, and he had therefore adopted it in the construction of the big ship. It He would next refer to the mechanical construction of the big ship, the arrangement of the iron of which she was made, and the object of those arrangements. was much to be desired that our mechanical science should make progress by the simple adoption of what was best, come from where it might; but he was sorry to say that iron shipbuilding did not grow in that manner. They commenced by servilely imitating the construction of wooden ships, thereby incurring a great deal of unnecessary labour and expense. There was this great difference between the strength of iron and of wood, that whilst the latter was weak crossways and strong lengthways, or with the grain of the timber, iron was almost equally strong either way. This had been clearly ascertained by experiments made by Mr. Fairbairn and Mr. E. Hodgkinson, at the request of the British Association, in whose Transactions' the results were published to the world. The consequence was, that the ribs or frames used to strengthen wooden ships were rendered unnecessary in iron shipbuilding; and acting on this principle, the 'Wave' (in the construction of which he was assisted by two Irishmen) was built of iron entirely, with bulkheads, and had not a frame in her from one end to the other. He was ashamed to say he did not always practise what he preached. He was compelled against his will, by the persons for whom he built, to pursue the old system; besides which, there were laws of trade, Acts of Parliament, and Lloyd's rule, to which he was obliged to conform. Thus, if he did not put a certain number of frames in the ship, a black mark would be put upon her, and she would not be allowed to go to sea. But whenever he was allowed to build according to his judgment, he built in what he considered to be the best way. And he believed that in what he was now placing before the Section he was laying the grounds of meeting the British Association that day twenty years, and finding that the mode of mechanical construction which he proposed had been as universally adopted as the wave principle, because of the publications of the British Association. The author then proceeded to give an elaborate description of the old method of constructing an iron ship, contrasting it with the improved style which he pursued at present. Instead of the mass of wooden rubbish, which did not strengthen the ship, and involved enormous expense, he placed inside the iron shell as many complete bulkheads as the owner permitted him to do, and then constructed in the intermediate spaces partial bulkheads, or bulkheads in the centre of which holes had been cut for the purposes of stowage. The deck was strengthened by introducing pieces of angle iron, and other contrivances; and as an iron ship when weak was not weak crossways, but lengthways, he strengthened it in this direction by means of two longitudinal bulkheads; and the result was a strength and solidity which could not be obtained in any other way. The 'Great Eastern' had all these improvements, and, in addition, the cellular system, so successfully applied in the Britannia Bridge, had been introduced all round the bottom and under the deck of the ship, giving the greatest amount of strength to resist crushing that could be procured. As he had already observed, there was nothing new in the ship but her great size and cellular construction. It was true she would be propelled both by screw and paddles, but there was no reason to doubt that they would work harmoniously. He wished he could tell them how fast she would go, but that was the secret of the owners of the ship. On the Importance of Regulating the Speed of Marine Engines. On the Formation of the Entrances to Tidal Basins. By BINDON B. STONEY, M.R.I.A. In the formation of the entrances to tidal basins, two points have to be considered: 1. The shape of the entrance. 2. Its position. In existing docks we find some entrances constructed at right angles to the river, others sloping upwards against the stream, and others again sloping downwards, which latter form not only tends to prevent deposits, but greatly facilitates the entrance and departure of vessels. Even though no downward current does exist in the river, that form of entrance which slopes in the direction of the vessel's course presents obvious advantages, especially in the case of a narrow river, where it is essential that a ship should, both before entering and after leaving the basin, be in the line of the river, and at the same time not far from its centre, where the channel is deep and unobstructed. The usual position of the entrance is at or near the centre of that side of the basin which is parallel to the river. This however is objectionable, since, besides promoting deposit, it makes it necessary that vessels lying within the basin be warped, at no small expense of time and labour, into a suitable position for passing through. The chief considerations to be kept in view in the construction of floating docks or tidal basins are as follows: 1. Facility of ingress and egress. 2. Freedom from silting up. To these may be added, 3. Economy of quay room. 4. Facilities for the land traffic in connexion with the dock. These conditions are, it is believed, in a great measure fulfilled by the form of entrance advocated by the author. The general form of the basin is a lozenge, a trapezium, or a rectangle, whose width is equal to the breadth of two vessels together, with sufficient space between them for another vessel to turn round freely: the entrance, placed at the lower end, is well sloped in the direction of the ebb current, and has its obtuse angles rounded off, so that a ship or steamer can pass from the river into the basin, and take up her berth without warping, or any such annoyance and delay. Similarly, on leaving, a vessel, when once her head is round, can pass out without slacking speed, and therefore without risk of being carried by the current against the pier-heads. The diagram represents a succession of basins formed according to the proposed method, and, if desirable, at different periods to meet the exigencies of the port, yet in such a manner that there is easy communication between each quay and the main road leading into the city or the traffic depôts. These quays are, from the obtuse angles at which they intersect, well adapted for tramways, which may branch off a trunk line laid along the main road. When additional port accommodation is thus obtained the result cannot but be beneficial to the river, since these basins will act as reservoirs, increasing the volume of water which passes through the channel, and thus aiding by its source in maintaining the river at its proper depth. On Machinery for Laying Submarine Telegraph Cables. On Superheated Steam. By J. WETHERHEAD, United States. APPENDIX. On the proposed Ship Canal through the Isthmus of Suez. Although the difficulty at one time supposed to exist in the difference of level between the Mediterranean and Red Seas is now no longer urged, there are other physical difficulties which are of at least equal importance. The canal must not only be made, but must also be maintained in a serviceable condition. Now, it is well known that on the Mediterranean side the sea is not only shallow and sandy, but that its depth is subject to constant variation from the moving character of the sand-banks. It might almost be presumed, à priori, that the same causes which prevent any of the mouths of the Nile from serving as an available ingress or egress for vessels navigating the Nile, would produce and maintain an effectual obstacle to vessels passing in either direction between the Mediterranean Sea and an artificial canal. I had an opportunity of witnessing a strong confirmation of this inference in proceeding from Alexandria to Jaffa. Although we kept out at sea to the distance of some miles, the captain of the steam-boat, which was a much smaller vessel than would be required for Indian or Australian commerce, thought it needful, in broad daylight, to be frequently using the sounding-line as a security against stranding his vessel. The force of this objection is so far admitted by the advocates of the canal as to induce them to allow that it will be necessary to construct piers advancing some miles into the sea, and that at their mouth, and in the channel between them, it will be requisite to keep dredging vessels constantly employed to preserve a practicable passage. It will, perhaps, be asked in what the difficulties consist? The general facts may be safely stated to be-first, a certain amount of elevated land to be cut through; secondly, land considerably lower than either sea, where very substantial embankments must be thrown up to prevent the neighbouring country from being submerged. Throughout this tract, and probably along the greater portion of the line, a very careful and expensive process of puddling will be absolutely necessary to enable the canal to hold water. |