34 MACKINTOSH'S IMPROVED PADDLE-WHEEL. MACKINTOSH'S IMPROVED PADDLE- Sir,-At a time like the present, when steam navigation is rapidly extending itself throughout the whole British dominions, whatever tends to its improvement must be deemed a matter of national im portance. Under this impression, the inclosed sketch of an improved paddle wheel is submitted for your consideration, that it may be inserted in the pages of your useful Magazine, if, in your judgment, it shall appear to merit such distinction. I have taken the excentric motion from the outside of the paddlewheel down to a cross-shaft, which moves on its centre, and is placed at a short distance above the paddle-board; from this cross-shaft two rods (instead of one, as in Morgan's) extend to the paddle-board. It is not pretended that this wheel is original—the principle is the same as Morgan's; but by this arrangement the shaft (the principal point of strength in the framing) is allowed to pass entirely through thus all the advantages of the epicycloidal motion of the paddles is retained, whilst the strength of the wheel remains unimpaired. The principle of Morgan's wheel is excellent; but until that can be fitted with a shaft entirely through the centre, it cannot be trusted or deemed seaworthy by any experienced engineer, however strongly it may be supported by written testimonials. Although steam-navigation is of comparatively recent introduction, no less than fifty or sixty patents have been granted for improvements in paddlewheels. This at least shows the importance that is attached to this part of the machinery; but in almost every instance it has, unfortunately, happened, that a great deal has been sacrificed to attain one particular object. It may, therefore, be worth while to inquire what are the essential qualifications of a good paddlewheel. It seems to be allowed on all hands, that that wheel which most perfectly fulfils the three following conditions is the best: 1st. That gives the most effective stroke, or greatest amount of propelling power. 2d. That most effectually clears itself of the back-water, and thereby causes the smallest amount of swell astern of the vessel. 3. That is simple in its construction, durable, and not liable to derangement. There has no paddle-wheel yet been offered to the public which completely satisfies these conditions, although it must be allowed that some have approached much nearer than others to this ideal perfection. Nearly all these fifty or sixty patent wheels are laid aside, or cushioned, as they say in the House of Commons; however, there are a few of the more recent in the construction of which considerable ingenuity is displayed, and which appear, in some respects, well calculated to obviate the evils that have been complained of in the common wheel, and upon these I will venture to offer a few observations—taking them in the order in which they have appeared in the Mechanics' Magazine. Morgan's wheel has been already noticed; it appears to give a most effective stroke, to clear itself of the back-water admirably-but is wofully deficient in strength and durability, and therefore until this defect is remedied, cannot come into general use. Symington's wheel appears to give a less effective stroke than Morgan's, but is well calculated to destroy the swell in the wake of the vessel, because as the two floats of which the paddle is composed cause the back-water to recede in opposite directions, the one portion acts as a check upon the other; and thus the effect is neutralised, and the evil consequences arising from the undulations obviated. These wheels are, therefore, well adapted for river work; and were they in more general use, might be the means of preventing a great and unnecessary loss of human life. But the manner of working the floats, or causing them to revolve, is decidedly bad. The friction upon a roller working in a groove is very great when the angle is sufficiently acute to give the proper direction to the paddles, and must, therefore, cause a considerable loss of power, and also occasion the working parts to wear out very rapidly. Seaward's wheel is (whatever the ViceChancellor may say) nothing more or less than a modification of Morgan's; the construction is the same in every particular, except as it is expressed in the affidavit of Messrs. Morgan and Lucena, the excentric is caused to "revolve on an enlarged axis affixed to the side of the MERRYWEATHER'S FIRE-ENGINE BRANCH-PIPE. said steam-boat." It is not here intended to insinuate that Seaward's wheel is an infringement upon Morgan's or Galloway's patent; on the contrary, it is notorious to every one at all acquainted with the subject, that the principle of causing the floats of a paddle-wheel to revolve by means of an excentric was well known and acted upon many years before either Messrs. Galloway, Morgan, or Seaward, -attempted, or possibly even thought of attempting, to accomplish that object by -the same means. All that is meant to be here asserted is, that Morgan's wheel and Seaward's are the same in their mechanical construction, except that in Seaward's the main shaft passes through the wheel, and the excentric works upon an "enlarged axis." In point of strength and durability, when compared with Morgan's, Seaward's wheel has decidedly the advantage. But as regards the excentric action, the friction of the working parts, especially upon the "enlarged axis," is so very excessive, and presents so great a drawback on the working of the wheel, that it is very questionable whether it possesses any superiority, or whether it is, in all respects, even equal to the common paddle-wheel. Carter's wheel is, in principle, a combination of Morgan's and Symington's; there is much ingenuity displayed in its construction, but it is too complicated. It bears evident marks of being the production of an amateur engineer, and may suit very well his amusement or recreation, but appears ill-adapted for the purposes of navigation. And last and least, Galloway's second patent. This wheel has been strongly recommended by the inventor on account of its simplicity and power; and how is this power obtained? The inventor says, in his circular, that of the series of bars of which his paddle is composed, "the lowest bar only encounters a resistance at entering, the other bars following in its wake or path." If this were really the case, a very considerable portion of the power must be lost altogether, as it is by the resistance which the water opposes to the revolving of the paddle-wheel that the vessel is propelled, and, consequently, an increase of speed cannot be obtained under such circumstances. This wheel is calculated, however, to obviate one evil -the tremulous motion or vibration communicated to the vessel by the successive 35 striking of the paddle-boards as they enter the water; but this object might be equally attained by fixing the bars composing the paddles at regular intervals upon the outer rim of the wheel, or by placing them upon steps, as in the patent wheel-in either case, it is simply dividing the heavy and perceptible stroke of one great paddle-board into several lesser, which are not so perceptibly felt. The merit of this wheel certainly lies in its simplicity; and perhaps the inventor himself may be allowed to possess equal merit of the same description. Sir, I have animadverted freely on the several paddle-wheels now before the public, as I conceive I had a right, and was perhaps, in some measure, in duty bound to do; and shall conclude with this observation, that I freely concede the same right to any gentleman who may feel disposed to criticise this which is now submitted to the public. I remain, Sir, yours respectfully, THOS. S. MACKINTOSH. 101, Long-alley, Finsbury, Feb. 25, 1836. Description of the Engravings. Fig. 1, represents my paddle-wheel with stay-braces or outside bearing; and fig. 2, a paddle-wheel without the outside bearing; the former of these arrangements I consider the best. In fig. 1, aa is the wheel; bb, staybraces, fixed firmly into the brass collar c, which collar works freely on the pin g; d, excentric motion; ee, cross-shafts ; ff, paddle-boards; and g, pin to support the outside of the wheel by means of the stay-braces bb. MERRYWEATHER'S FIRE-ENGINE BRANCH PIPE. Sir,-Many circumstances have prevented me from resuming the consideration of certain hydraulic phenomena that were under discussion in your last volume, until a comparatively recent period, when I had an opportunity of repeating the experiment which gave rise to the question, and also of making some other experiments, alluded to in my communication at page 227; the results of which, but for a severe domestic affliction, should ere this have been laid before your readers. On making another trial of the flattopped branch-pipe, described at page 6 of your 23rd volume, I found I had committed the error attributed to me by J. L., MERRYWEATHER'S FIRE-ENGINE BRANCH-pipe. of having overlooked the contraction of the jet during the slow working of the engine, and I thank that gentleman for his correction. The contraction must inevitably have taken place, although it entirely escaped the notice of all the persons present at the first experiment. I subsequently found that the head of water in the engine-cistern (somewhere about three feet) was of itself sufficient to give a slight jet, in which the contraction was as clearly defined as in the higher ones. It is therefore evident, that with the simple orifice, the smallest pres sure that will give a perceptible jet will also cause its contraction. M. Bossut found that when the height of the reservoir was augmented, the contraction of the fluid vein was also increased, and the expense of water diminished; but we were unable to perceive any difference in the amount of contraction, whether the jet was one foot or fifty feet high. Our observations correspond with those of M. Bidone in this respect, although at variance with the opinions of some other experimentalists; one thing is certain, that when the pressure is produced by the working of an hydraulic machine, such as a fire-engine for in-stance, it is quite impossible that the expense of water should be diminished under increased pressure. I have searched several works of repute in vain for a correct delineation of the vena contracta; M. Bossut has dedescribed it as a kind of truncated conoid, whose greatest base was the orifice, having its altitude equal to the radius of the orifice, and its bases in the ratio of three to two. M. Bidone and Sir Isaac Newton considered the greatest contraction of the fluid vein to take place at a distance not more than the greatest diameter of the orifice; it appears to be within the distance of the radius, and of the form represented at page 6 of your last volume. M. Bossut has stated the result of some experiments which he made on jets of various forms, to be, that jets rise to the smallest height when the adjutage is a cylindrical tube; that a conical tube throws the flaid much higher; and that when the adjutage is a simple orifice, the jet rises highest of all! It is possible that this statement led to the employment of the flat-topped branchpipe before alluded to, but the result by no means corroborated M. Bossut's state ment; on the contrary, the jet of water was sadly disfigured, and fell greatly short of the elevation attained with other orifices. Ineligible as the simple orifice has been proved to be for the adjutage of a fireengine, it is not quite the worst that can be employed. Venturi obtained the maximum quantity of water that could be delivered through a given orifice, by making the discharging-pipe in the natural curve of the fluid, and by continuing or rather reversing the curves so as to enlarge the end of the orifice. Accordingly, I procured a branch-pipe of this form, represented in section by fig. 1. Fig. 1. In practice, however, this branch was found much more objectionable than the simple orifice, the stream of water being divided into a fine spray, and thrown about in every direction with a rapid rotatory motion. The best form of adjutage for hydraulic-engines has long been matter of considerable speculation; the general practice hitherto has been, to make the discharging-pipe conical, with a cylin drical space at the end, equal in length to the diameter of the orifice. The London Fire-Establishment being extremely desirous of rendering their excellent engines as efficient as possible, some experiments were recently instituted by Mr. Braidwood, the Superintendent, for the purpose of ascertaining the comparative advantages of nose-pipes of different forms. The flat-topped and trumpet-shaped branch-pipes have already MERRYWEATHER'S FIRE-ENGINE BRANCH-pipe. been noticed as altogether unsuited for this purpose. It having frequently been asserted, that the best form for a discharging-pipe was that of the vena contracta; Mr. Merryweather constructed a branch-pipe terminating in an adjutage or nose-pipe precisely of that form. Mr. Tilley submitted a very pretty branch-pipe, furnished with a nosel about six inches long, in which a more easy curve was employed, conformably to the hypothesis of Newton. Both of these appeared to have an advantage over the common conical branch; but a second nose pipe made by Mr. Merryweather, which was a sort of me dium between his first and that of Mr. Tilley, appeared to have a most decided advantage. With this branch-pipe a very beautiful jet was obtained, the stream of water being delivered in a compact body at a much greater elevation than with any others that were tried. 37. ther's improved branch and nose-pipe, on a scale of two inches to a foot. It consists of a slightly tapering copper tube a; the female-screw b is for attaching it to the hose, a male-screw at the other end receiving the nose-pipe c, the form of which will be at once understood from the sketch. The length of the whole is but 21 inches, and the weight only 4lbs. It will be observed, that in this branch-pipe the stream of water is continued nearly of the full size of the hose, till within less than three inches of the discharging orifice, when the velocity of the water becomes accelerated, and the jet formed under the most favourable circumstances. The importance and great advantage, in all cases of fire, of throwing a jet of water point-blank upon the burning materials, was strongly insisted upon and strikingly exemplified full forty years ago by Mr. Van Marum, some of whose experiments are detailed in one of your But the correctness of early volumes.* this view, and the immense advantage resulting from its practical adoption, have recently been most extensively and successfully demonstrated, particularly in Edinburgh and in London, by the firemen under Mr. Braidwood. For the effectual accomplishment of this most desirable object, the improved short branch-pipe of Mr. Merryweather is peculiarly favourable, as either in standing, kneeling, or lying down, the fireman has the power of throwing a jet of water all around him with a facility before unknown, and into places where no other branch-pipe could be directed. For external operations, where great heights have to be reached, the nose-pipe c can be screwed upon a longer branch without any prejudice to the effect, but for close combat the short branch is unrivalled. Notwithstanding the comparatively recent date of the experiments, which fully established the superiority of this branch, i has already come into very extensive use. Besides being adopted by the London Fire-Establishinen, it has also been employed by the non-conforming fireoffices; the fire-engines of many of the nobility and gentry, as well as those belonging to the Admiralty, the Temple, the Mint, and many other public offices, Vol. iii. p. 184. have been supplied with new branchpipes of this pattern, with uniform advantage, and it seems likely to obtain, as in fact it really merits, universal adoption. I am, Sir, Very respectfully yours, London, April 14, 1836. THE BRITISH MUSEUM. Sir,—I am glad to perceive from the letter of S. S., inserted in your last Number, that he proposes to furnish you with a list of the " permanent and public literary institutions of the kingdom. I hope the catalogue will turn out more lengthy than I anticipated; but to say the truth, in spite of the gallant bearing of S. S., and the chivalrous promptitude with which he has accepted my challenge, I have still my doubts whether in the course of his inquiries he will not find the troop, which he has undertaken to marshal to the public, such a thorough "ragged regiment," that he will decline to "march through Coventry with them" after all. But whatever may become of the "public and permanent "institutions of other parts of England, I cannot but anticipate a general crash of the numerous private and self-supported establishments of a literary nature about London and its neighbourhood, in case the alteration in the management of the British Museum, recommended by your correspondent, F. S. A. (in page 535 of your last volume), should be carried into effect. I am well aware, indeed, that the measure which he advocates-the "erection of a detached fire-proof reading-room for evening visitors"-is a favourite one with many, even of the members of the House of Commons' Committee now sitting on the affairs of the Museum; and I certainly cannot deny that the convenience of it to frequenters of the Museum would be immense; but has it ever been considered what would be its effect on the other London libraries now existing? How many persons, for instance, would be found inclined to pay a not-inconsiderable sum for the privilege of admission to the London, the Royal, the Russell, or other similar institutions, when within five minutes' walk of some of them, might be found a gigantic rival,-compared to them an "Ossa to a wart,"—the price of admission to which would be just nothing at all? At present, the: mass of visitors to these excellent and most useful institutions congregate together in the evening, the great majority having been occupied in business during the day, and merely devoting a few hours to literature for their own private information or amusement. The dayreaders at the Museum, on the other hand, are in general those who are either pursuing literature as a profession, or following out some particular course of study to which they give more than ordinary attention. Some mere devourers of novels and magazines have indeed found their way into that reading-room; and few as these are, there are more than. enough; but compared to the main body of readers, they are "in them but not of them," and must, one would think, be almost ashamed to look the servants, who bring them the volumes, in the face. That reading-room is, as the regulations observe, a place devoted to study." Of course, if open in the evening it would remain so no longer. That impossibility, which is now found to exist, of excluding all but those who derive a real benefit from admission, would then (excuse the bull, if it is one,) be increased tenfold. And it is, I think, a question well worthy of more mature consideration than it hitherto appears to have obtained, whether, under these circumstances, any advantage would be derived to the public sufficient to counterbalance the great additional expenses that would necessarily be incurred, and the destruction or depreciation of the value of the literary institutions of the metropolis, which would be the almost inevitable consequence ? The benefit, as I said before, would certainly be great; but thus accompanied with evils, would it be great enough? There is an improvement in the Museum which might be effected at less expense, which I am aware of no serious objection to, and which would afford gratification to a greater number of persons to all the visitors of the Museum, in fact, and all the inhabitants of London may visit it if they please. This would be to exhibit the medals. The collection is excessively valuable-perhaps, since the late. robbery at the Royal Library of Paristhe most valuable in Europe. There is no reason, I believe, for not exhibiting these, except that, as they are kept at. |