to have been worth while to remove the paddle to the centre in the case of the Lord Dundas, for the sake of dimiany nution of agitation that might possibly be realized; while it must have been quite obvious, that a paddle-trough enclosed all round, and only open at bottom to the water, must be still worse off for an adequate supply of water than a paddletrough open behind, as well as at the bottom. Mr. F. admits that this central trough must be "liable to be choked whenever the vessel moves from the canal into the sea in stormy weather," p. 33. So far, therefore, the removal of the paddle-wheel to the centre is decidedly objectionable. Neither do we find that any thing has been gained by this change in point of speed-the great object aimed at in the construction of the Lord Dundas. The Committee of the Forth and Clyde Canal state in the Report to which we have before referred, that this vessel drag one of the quick passage-boats at the rate of six miles per hour;" but this falls greatly short of the speed realized by means of the gig-boats and horses on the Ardrossan Canal; and does not much exceed that of which the heavy Cyclops is capable. can The new improved steam passage-boat which Mr. Fairbairn was commissioned by the Forth and Clyde Company to construct, "for the double purpose of navigating the canal and the adjoining coasts," and which is by this time we presume completed, will owe what excellence she may possess to being constructed on an entirely different plan from either the Cyclops or the Lord Dundas. We shall first quote Mr. F.'s statement of the general views on which he proceeded in its construction; and then his specification of its different dimensions. "The improvements I suggested were to construct a vessel with two narrow paddles on each side, close to the rudder or stern of the vessel; this would in a great measure obviate the objections urged against the Cyclops; it would remove every impediment to the free access of the water to the paddles, and allow a free and open outlet to the discharge of the wheels on each side; it would also give considerably more bearing to the stern of the vessel; facilitate the working of the rudder; and furnish a large useful hold instead of two comparatively small ones. It may here be urged, that two paddle-wheels, viz. one on each side at the stern, would be liable to get damaged against the locks, bridges, and banks of the canal. This is certainly an objection of some weight; but, on a minute inspection of the plan, it will be found that a remedy is provided by a fender or portcullis sliding down on the outside of the wheels, to protect them from injury during the time they are passing the canal; at other times, when the vessel is in the open sea, the portcullis is drawn up, leaving the whole space open for the free action of the paddles."-P. 42. The engravings on our front-page exhibit a side-view and plan of the steamer constructed by Mr. Fairbairn on this improved plan. Her dimensions are as follow: "Whole length, 68 feet. "Breadth of beam, 15 feet. "Depth from the keel to the deck, 8 feet. "Steam-engine 24-horses' power, having two cylinders on the locomotive principle: "Paddle-wheels, each 11 feet diameter and 3 feet wide. "Computed weight of boat, paddlewheels, engines, &c. : "This vessel will contain a cargo of 50 tons on a draught of water of about 3 feet 9 inches; she is constructed of the best material, with strong iron ribs and plate-sheeting of about inch thick "— P. 90. Mr. F. admits that this vessel will, like the Cyclops, be liable to hang by the stern, from the weight of the machinery being placed there; but he thinks this objection of no moment in the present case, as vessels of this description will seldom sail without some loading, and at all times there is the power to trim the cargo so as to give her the proper bearing on the water." A list is given by Mr. F. of 44 different inland lines of navigation on which steamers of this class might be introduced with as much facility as on the Forth and Clyde. As it may serve to promote the IRON STEAM-BOAT ADAPTED TO CANAL AND COASTING NAVIGATION. extension of canal steam-navigation to make this list more generally known than it can be through the medium of Mr. F.'s book, we shall subjoin it to the present notice. Mr. F. remarks, that "on canals such as the Chesterfield, Cromford, Grand Turk, Huddersfield, Macclesfield, Peak Forrest, &c., little can be gained by the substitution of steam in place of animal power, as on them and similar navigations there are no data or experiments on which to form an opinion as to what, if any, advantage could be obtained by a change in the system of trackage." Mr. F. is perhaps right in this opinion; but he argues in a strange way. He thinks that nothing is to be gained by the employment of steam power on these canals; and his reason is that there are 66 no data or experiments on which to form an opinion!" We humbly submit, that until data for forming an opinion are obtained, it is always very foolish to offer any. The only obstacle that we know of, to employing steam power on such narrow canals, is the difficulty of so reducing the bulk and weight of the requisite machinery, that there shall be room enough for it, in boats of no greater width than six or seven feet in the beam; but surely there have been much greater difficulties than this overcome in the practice of steam navigation. A year or two ago it was thought impracticable to navigate canals at all by steam; and a year or two later it will probably be found that wherever a barge can float, there steam may be employed to propel it, with greater effect than any other power. Mr. F. very properly cautions his readers against supposing that a steam-boat, such as we have just described, though well adapted to canal, river, and coasting navigation, would answer equally well for long voyages at sea. 66 It appears to me that a vessel of this description would be in her machinery exIceedingly ineffective in a gale of wind blowing direct a-head or hard aft, if accompanied with a heavy swell. The position of the paddles in this case is objectionable so far as the working of the wheels would be obstructed by the pitching of the vessel, which is much greater at the prow and stern than at midships; a running sea, fore and aft, would consequently affect the paddles, as they would be alternately raised when the vessel hung on the sea, and deeply immersed 87 when the top of the swell was passing the stern."-P. S4. Mr. F. gives, however, a design for a steam-vessel which he thinks would be free from these objections, and "combine the advantages of a canal-steamer with the practical usefulness of a vessel constructed for general traffic and the navigation of the open sea." The length proposed to be given to this sea-going vessel is 8 feet, the breadth of beam 20 feet, the depth 9 feet. The paddlewheels are to be 12 feet diameter each; and to be kept within the external line of the vessel, but placed much nearer midships than in the boat we have last described. The steam engine is to be a high-pressure one of 60-horses' power. Mr. F. estimates that a vessel of these dimensions, and with machinery of that power, would not weigh more than 46 tons, 4 cwt., 3 qrs., and would be capable, with a draught of 4 feet 6 inches, of carrying a cargo of 116 tons. It remains to be observed of the sort of boat which Mr. F. recommends as of such general application to canals, that it may be either employed to carry goods and passengers by itself, or to tow a train of accompanying flats, or partly as a carrier and partly as a drag. Mr. F. is for combining both sorts of employment, and offers some observations on this head, which seem well worthy the attention of canal proprietors :— 64 I am inclined to think that this mode of trackage would be found the most eligible that could be adopted, particularly on broad canals, navigable rivers, and where there is a long reach, free from the interruption of locks. I am the more convinced of the efficacy of steam trackage above all others, from the circumstance, that the train of boats intended to be towed could follow in each other's wake, as the eddy formed by the leading vessel materially lessens the resistance opposed to the succeeding boats; and, if I may use the expression, sucks the towed boat into the vacuity formed by the vessel's progress through the canal. I am the more induced to recommend this principle from the fact, that all leading boats having a moderate draught of water, and used for the purpose of towing, cause by their own displacement a sufficient inlet for towed vessels to fill up the wake, and to move forward in a ratio equal to the currents as they flow in the direction of the boat's progress."-P. 81. List of Canals capable of admitting the Improved Steam Boat, of the class described in the preceding Notice. MR. RYAN'S SYSTEM OF VENTILATING COAL MINES. 39 MR. RYAN'S SYSTEM OF VENTILATING COAL MINES. Sir,-In the Mechanics' Magazine, No. 423, page 459, vol. xv., Mr. Ryan has given a New System of Clearing Coal Mines of Hydrogen Gas. I fear such a plan would be too troublesome in practice to be adopted; a good steady current of atmospheric air is the thing, and nothing besides will do. Mr. R. illustrates his system by the description of a colliery, which has a site of a mile (does he mean a mile square?). He tells us that this colliery will elucidate the intricate method by which this simple fossil is quarried, and the small portions into which it is cut, in accordance with the existing mode of ventilation. The field, that is the colliery, is said to present 147 roads, each one mile in length, and 12 feet wide, driven on the face of the coal; and at the end of the coal there are 88 drifts, each one mile long and 6 feet wide, making a total of 235 miles of road, in the working of one mile square of coal. The first set of roads will contain, or take up of the mine, one million thirty-four thousand eight hundred and eighty yards superficial. The second set of roads will take up three hundred and nine thousand seven hundred and sixty yards superficial. Now, a superficial mile, contains three millions ninety-seven thousand six hundred yards; therefore, more than a third of the whole colliery is taken up by the roads; and Mr. Ryan says, double the quantity of coal extracted from the mine is left in the pillars, to sink in the floor of the mine (which said sinking is a strange thing to me). But this surely must be a mistake; because, there will not be two thirds of the coal left after even the roads only are made through it. Mr. R. also tells us, only a small portion of the pillars are getable, after being squeezed into the floor of the mine, and that little by virtue of the Davy lamps. There are some other remarkable things belonging to the colliery in question. We are told that on the 235 miles of road through it, there is to be met with at every distance of 34 yards one foot four inches and three quarters, a dam across; for, he says, there are 12,000 such dams in the colliery. The intermediate spaces between the dams are moreover encumbered with board brattissing, doors, trappers, &c.; for I can not perceive, by the description of the colliery, where there is room to put these anywhere else. I beg to ask if there was ever such a colliery seen before, or heard of? Mr. Ryan demands whether if such a coal-field were on the surface, such a method of quarrying would be permitted one day? I answer, no, Not even if it were at the bottom of the sea, need there be so much coal left behind, and wasted, as there appears to have been in the colliery alluded to by Mr. Ryan. If you will have the goodness to find room for this in your useful Magazine, perhaps it may be the means of inducing Mr. Ryan or Mr. Buddle to send to the Mechanics' Magazine a working plan of a colliery, and along with it a description of the manner in which the air is made to circulate through it, so as to We keep it clear of hydrogen gas. shall then be better able to judge what improvements are practicable and expedient. Sir, In the Miscellaneous department of your last number, it is stated that India rubber, moistened with water, will take out ink marks as effectually as a pen-knife, without in the least injuring the fabric. In this there is a slight mistake. The fact is, that moistened Indiarubber will take out ink-marks; but not without injuring the fabric. In using the pen-knife, the ink and paper are both removed in the state of powder, by scraping; in the case of the India-rubber, the paper is peeled off in flakes. In both cases the surface of the paper and the sizing are removed, and therefore the fabric of the paper is in both cases materially injured, which an attempt to write again upon the same place most satisfactorily demonstrates. In scratching out, a sharp knife should DESIGN FOR THE CITY APPROACH TO THE NEW LONDON BRIDGE. 1. 2. D Sir,-The object of the accompanying. design, is not only to furnish a handsome entrance to the New London Bridge (which simply, might have been attained at far less cost) but also to adorn and dignify our city with a magnificient architectural way, which, at present, I be eve, it nowhere possesses. It may be een by the Plan and Elevation that I propose, the formation of a circus (in the modern sense of the word) to contain in its centre, a triumphal arch, and on each side of the same an insulated column, the London Monument being one. A, is the proposed new monument. B, the triumphal arch. C, the London Monument. D, the new bridge road. Yours, &c. J. B. Το [We like this design extremely; but fear there is but little chance of seeing any thing so splendid realized. save room, we have given part of the ground-plan only, but the reader will understand that the circle of which we have exhibited a portion only, is to be completed, and to encompass, as described by our correspondent, the triumphal arch, and the two monuments. Next week we shall give a plan, which has been submitted by Mr. Legg, of Friday-street, to the Court of Common Council, which, if adopted, as it well deserves to be, would, at least, rescue the Monument from the state of obscurity to which it seems, at present, to be consigned.-ED. M. M.] |