IMPROVED STEAM-BOAT PADDLE IN ACTUAL USE. those of Smeaton just quoted. He said he was decidedly of opinion that, after the removal of the old bridge, the bed of the river between its site and Westminster Bridge would often, at and near low-water be dry, and the navigation completely at a stand. On being asked if he could suggest any remedy for so great an evil, he replied there was an obvious and effectual remedy which he trusted would be adopted. His proposal, if I correctly understood him, was to the following effect: That the new bridge, instead of having five arches, as was proposed, should have seven; and that under each arch there should be sluicegates of a kind into the minutiae of which I cannot enter, but which, he said, were well known in Hollandthat there should be similar sluicegates at Westminster Bridge, and perhaps at Blackfriars Bridge; the whole of the river between London and Westminster Bridges being thus converted into a large wet-dockthat the river should be contracted by extending the wharfs and quays farther upon the present bed, both on the Surry and the Middlesex sides*. that in these operations all sudden projections and bold sinuosities in the river should, as far as possible, be softened down-that by the judicious shutting and opening of some, or of all, of the sluice-gates at the three bridges, and by the employment of temporary aprons or water-turners, so as to direct the stream upon deposits of mud, &c., under the constant superintendence of proper officers appointed by the Conservators of the Thames, the evils which would otherwise inevitably result from taking down the old bridge might be greatly diminished, if not altogether prevented, and the navigation above bridge considerably improved. I well remember hearing Mr. Telford (who was then employed by the City of London to oppose the new bridge) say to Dr. Gregory, as he quitted the committee-room," If they adopt your hints, I shall advise the This proposal was, if I rightly recollect, several months before the announcement of Col. Trench's plan. 339 City to withdraw their opposition." The plan, however, has not been adopted; and the erection of a bridge of five instead of seven arches will evidently render it more difficult of execution. But I am one of those who think that unless some such plan be carried into operation, a very few years will transfer all the business now done at wharfs above bridge to widely-different localities. Yet, Sir, I am no croaker; and rather mean, by the previous detail, as well as what follows, to suggest what is useful than to indulge in dismal forebodings. I shall, therefore, with your permission, employ the remainder of this communication in briefly describing the nature and use of the aprons and water-turners alluded to in Dr. Gregory's evidence. (To be concluded in our next.) IMPROVED STEAM-BOAT ACTUAL USE. PADDLE IN In the last Number of "The Register of Arts," there is a letter from a Mr. Merryweather, of Lincoln Castle, containing an account of an improved paddle-wheel, which is stated to have been recently invented by a smith of that place of the name of Poole, and adopted with great advantage in the steam-vessels navigating the River Witham. The Editor of the "Register" introduces the letter of his correspondent by congratulating "the public that an apparatus has been at length not merely devised, but brought extensively into actual and beneficial operation, by which the inconvenience and waste of power attending the use of the common paddle-wheel are completely obviated." And the correspondent himself observes-“Having paid very particular attention to whatever has appeared on that head, I think I may venture to say, that to this time there are none that have answered the expectations entertained of them, nor is there one in actual and beneficial practice; a sufficient proof of the entire failure up to this period." That none of the many other "improved" paddle-wheels which have of late years been brought under public notice has yet been brought into 340 IMPROVED STEAM-BOAT PADDLE IN ACTUAL USE. "actual and beneficial practice," is, we believe, quite true; but that this is "a sufficient proof of the (their) entire failure," is, we presume to think, rather a hasty conclusion. Can a thing be said to have entirely failed, that has never been fairly tried? Or to have failed at all, that has never been tried at all? We have heard of various experiments with new paddle-wheels, and have recorded some which furnished very promising results; but we question much whether any of them even those which seemed most likely to succeed -have as yet had a fair trial; such a trial, for instance, as it has been the good fortune of Mr. Poole to obtain. We know too of some very ingenious schemes of wheels which have but existed on paper or in models, and to which, of course, Mr. Merryweather's "sufficient proof" cannot possibly have any application. There is a case of the latter description, which we feel it to be our duty to submit very specially to Mr. Merryweather's consideration, that will at once convince him that a scheme may be extremely good, and yet pass unheeded even by such as flatter themselves that they "have paid very particular attention to whatever has appeared" on the subject. We refer to the design of a paddle-wheel, which he will find described by Chelmeriensis in our 276th Number (October, 1828), which was afterwards (No. 298, p. 173) stated to be the invention of Mr. Joel Lean, of Fishponds, near Bristol, and a moIdel of which has been exhibited for several months past at our office. We invite Mr. Merryweather to compare the construction of that wheel with the construction of the wheel of his protegée, Mr. Poole, and to state in what material respect the one differs from the other. To us they appear to be substantially identical; but that our readers may be enabled to judge for themselves, we subjoin Mr. Merryweather's description of Mr. Poole's wheel, as it appears the "Register." It is, of course, possible that in this, as in other the two parties may have hit on the same invention, without the one being aware of the other's proceedings. Be this however as it may-be the wheel cases, in in question the invention of Mr. Lean or Mr. Poole-we join with the Editor of the "Register" in congratulating the public on its being adopted with such beneficial effect as the following letter describes : "The object of this communication is chiefly to introduce to your notice, and thereby to the public, another candidate for an improved paddle-wheel, in a Mr. Poole, a smith of this town, who is possessed of considerable mechanical invention, and is also a superior operative, and to whom I have frequently made known whatever has been offered to the public on this subject, either in models, or attempts in practice. Mr. Poole has recently patented his invention, and I believe it will be found to surpass every other of the same kind hitherto offered to the public. The wheel is a common one, to be suited to the size of the vessel it may be designed for, except that the float or paddle is not fixed to the radii, but vibrates on its axis in the rims of the wheel. On the side of the vessel is placed, very securely, two concentric circles of iron, placed vertically edgeways, with a space of about one inch and a half between them, forming thereby, what may be called a railroad, on the side of the vessel for a guide-pin, fixed on the end of a lever, attached to the paddle-axle to travel in. The concentric circles before-mentioned are placed excentric to the axle of the wheel, and the paddles are thereby carried round, so as to enter and leave the water in such angles as to avoid the splash at entering and the lift at coming out. This wheel allows advantageously of a deeper immersion in the water than the radial paddle, obtaining a greater power by being brought to a leverage on a denser medium than the surface water, and thereby adding most materially to the propelling power of the wheel it is equally efficacious in its back stroke. It should seem however that one-third of the diameter of the wheel, from present experience, is the best dip; and as this may allow of the lowering of the main axle, and probably the reducing of the wheel, in consequence of the greater extent of paddle surface that can be employed, the paddle-boxes may be considerably lowered. The angle formed by Mr. Poole's arrangement, we know, has been obtained before by Mr. Steenstrup, Mr. Oldham, and others; but it has hitherto been the result of intricate trains of wheels, endless chains, &c. &c.: the expense of making which, the loss by friction, the DR. LARDNER'S LECTURES ON MECHANICS. liability to injury, and the difficulty of reparation in complex machinery, are very sufficient reasons why their inventions have not been carried into practice. The same beneficial angle, however, is got by Mr. Poole's excentric railroad, and is obtained by a mere lever connecting the paddle-axis and the railroad, which is traversed as the wheel is driven round by a guide-pin at right angles to the end of the lever; and to prevent the noise, which was found to proceed from friction-wheels, pieces of thick sole leather, cut round with a hole in the centre, are kept upon the guide-pin, and screwed together upon it so tight and hard as to bear the friction of the railroad circles, without injury, for a great length of time, and which quickly assume a hardness and polish with use that will almost defy wear. I am well aware that models are very fallacious, and that they have often deceived the most knowing mechanics when put into practice: I am therefore most happy in being enabled to show the effects of Mr. Poole's wheels in practice, as they have been placed in succession on three different steampackets, that are regularly plying between Lincoln and Boston, a distance of more than 31 miles, on one of them 341 for a period of five months; the particulars of which, with the size of the boats, &c., are given below, and the new wheels are certainly effecting much more than has hitherto been obtained by any other; and when they can be used with a different description of boat, in which the condensing-engines must give way to the superior high-pressure engines, and patent tube-boilers of Mr. W. H. James, (which I have had the pleasure of seeing on board their "Safety Steam-Boat, at Vauxhall, and which I believe to be decidedly superior to any other hitherto offered to the public, both for security against accident, as well as lightness with power,) many of the objections at present existing against the introduction of steam navigation on rivers and canals must be removed. This being a subject in which I am much interested, being one of the Committee of Management of the River Witham, who are most anxious to give every facility in their power to steamvessels navigating the Witham, though they are compelled from the present structure of the vessels to limit the rate of speed to 4 miles per hour in the first nine miles from Lincoln, for fear of injury to the banks, in consequence of the reduced scale of that part of the river. Description of Steam-Vessels navigating the River Witham, "N. B.-The average speed in the above table must not be looked upon as what only can be accomplished, the limit of speed before mentioned being the occasion of it. In the lower part of the river, where the width is from 90 to 100 feet at surface, and 7 feet to 10 deep, the Countess of Warwick can go eight miles per hour well on still water. The Witham, when put down by loading to four feet, which she has been, goes surprisingly better; thereby showing the advantage derived by a deeper 93 3 13 Bush. 6 40 32 32 45 48 40 leverage. The consumption of coals stated, is in going down to Boston one day, and returning the next." NOTES OF DR. LARDNER'S LECTURES ON MECHANICS, AT THE LONDON UNIVERSITY. (Continued from page 319.) There are some experiments which may be shown, by which the centre of gravity may seem actually to as 342 DR. LARDNER'S LECTURES ON MECHANICS. cend rather than descend. It is a general idea, that the centre of gravity lies in the centre of magnitude; and this is true, when the body is composed of the same substance throughout. But let ABC be a circle of any light substance, as wood, &c.; and let there be part of it, as a hole D, filled with lead. Now the centre of gravity has been moved to F, in consequence of the weight D being applied, while the centre of magnitude is at E, the centre of the circle. If the body be so placed that the centre of gravity be above the centre of magnitude (or rather a little to one side), it will roll towards that side, even although the plane on which it rolls be so inclined as to form a slight ascent. Yet, notwithstanding that the centre of gravity may appear to ascend, yet in reality it descends, as may be thus proved. Measure the height of the centre of gravity from the horizontal line CC, also its height when it shall have arrived at the top of the plane; at which place it will be found to be lower than it was at first, although the centre of magnitude is higher. The centre of gravity is not always a real point in a body: thus that of a ring is at an imaginary point, as is also that of an arch. When a body which rests upon a base is liable to disturbance, its stability depends upon the position of the centre of gravity. Let ABCD be a horizon. Now to turn this body over on the point B, it is evident that the centre of gravity must be moved from E, along EF, or, what is the same thing, must be raised the height of GF. Again, let the body be twice the height, but on the same base: let ABCD be the figure, (see fig. 3.) draw lines in the same manner as the last, when it will be seen that the line GF is shorter than in the last case; consequently it will be more liable to turn over. It may be shown in exactly the same way, why waggons, &c. are more dangerous when the load is placed high than when it is lower. It is also on this principle that the stability of the different positions of the human body depends: the degree in which it exists may be determined by drawing lines joining the toes and heels of the feet. Thus, it is evident Fig. 4. All the various inflections of the body are governed by this principle. But there are some curious instances of the effects produced, which may be amusing. When a person is setting on a chair, PURIFYING OIL-BRIGHT'S SHADOWLESS LAMP. if he attempts to get up, he will find it impossible, if he keeps his body erect; but if he stoops forward, he can easily do so, which may be thus explained. Let A B represent the body, BC the upper, and CD the lower parts of the legs of a person when seated. Now the centre of gravity being at E, it is plain that there is no support for it except the stool; but when he throws his body forward in the direction Ba, then the centre of gravity, e, is above his feet; consequently, the only force required will be in a perpendicular direction. It may have been observed, that when a man, a horse, &c. is turning a corner, the body is inclined towards that corner. This is most visible in the feats of horsemanship effected in a ring. Let AB represent the diame ter of a ring, round which the horse is to run, and the centre of which is at C. Now when a body is turning round rapidly, there is a certain force generated which is called a centrifugal force; the effect of which is to make the body endeavour to fly away from the centre. Let the line G H be the direction and quantity of that force, then the line of direction of the centre of gravity will be in the line HA. Now by making a parallelogram on the lines GH and GF (GF being substituted for HA), the diagonal GA will be the resultent, and which is the direction of the horse's body. The same effect is observable in a carriage; which shows the danger of turning a corner rapidly, particularly when the weight is placed high. A rope-dancer uses a pole, by means of which he shifts the centre of gra 343 vity from one side to another, according as he finds himself leaning on the opposite side. PURIFYING (To be continued.) OIL-BRIGHT'S SHADOW- Sir, I am inclined to think that purifying oil by filtration through charcoal, (respecting which "A West Countryman" makes inquiry in your 329th Number, p. 254,) is the French method of extracting humid particles from the "huile de colse," after being agitated with sulphuric acid, which is used in purifying it for burning; but our oil used for illumination, which is almost entirely obtained from fish, is not so treated, and would, I presume, not be benefited by a similar remedy. Should your Correspondent have faith in the advantage of filtering through charcoal, he can easily try so very simple a process. He should have stated what sort of oil his is; and if it has been frozen for merely a twelvemonth's keep, would not so deteriorate it as he mentions. Considering the immense consumption of the better sorts of lamp oil, it is extraordinary we know so little about chemicising it. The French certainly have the start of us in the preparation of their seed-oils. Bright's lamp is on the principle of Hero's fountain: though all hitherto made on that plan have been so constructed, that when a leak occurred, it was very uncertain if it could be stopped, on account of the number of tubes and chambers enclosed by one case. The pneumatic lamp, a French and most ingenious application of Hero's principle, was formerly very generally used both here and on the Continent, and when properly manufactured succeeded admirably; but it was often impossible to repair it. In Bright's lamp the reservoirs are only connected by tubes, and there are fewer of them than in the old lamps-consequently they are easily repaired. I know of one having been used for more than a year, which still acts perfectly well. Your obedient servant, |