474 REPLY OF MR. GILMAN TO MR. SYNGLEMAN, reason why these approaches should be improved, it could form no reason for taking down the bridge itself. If, then, the promoters of a new bridge could neither have shown that the old bridge was in a state of decay, nor have urged that it was inadequate to the traffic over it; and if they had, at the same time, admitted that the losses occasioned by the fall under the bridge were more than compensated by the advantages arising from the head of water maintained above bridge, what pretext could they have left for calling on the legislature to sanction its demolition? Evidently none whatever. Foreseeing well the hopeless predicament in which such an admission would have left them, they carefully avoided touch. ing at all on the state of the river above bridge, or adverting to any thing which, like the utility of sluice-gates, might point attention in that direction; they dwelt only on the dangers and disasters of the great fall" at the bridge, as they were pleased to style a rapid, such as an American would laugh at, and in the teeth of their own witnesses, exaggerated these dangers and disasters most abominably: shut their eyes, in short, to every thing in favour of the bridge, while they applied a magnifyingglass, of prodigious powers, to the smallest particle of evidence adduced against it. The loss of one drunken waterman and one crazy coal-barge per annum, formed the whole of the notable case which served in this instance to procure an Act of Parliament, which has put in jeopardy the subsistence and the fortunes of thousands. That a project, resting on such shallow and delusive grounds, should have succeeded so well, is, of course, only to be accounted for on the supposition of the existence of a state of the public mind exceedingly favourable to it. The project of a new bridge was, it must be confessed, a popular one. There was almost as great a readiness in most people to be deceived on the subject, as on the part of the projectors to deceive them. The recent erection, on every hand, of new bridges, greatly superior in architectural beauty to the old Lon don, had combined with the natural fondness of all multitudes for novelty and embellishment, to excite a spirit of emulation in the City Proper part of the metropolis which disdained to descend to such vulgar considerations as mere prudence and economy suggested. It is due to the Corporation of London to state, that they were far from parti cipating in the feelings of their constituents in this matter. They opposed the measure of a new bridge most resolutely, through many stages of its progress, and only gave way at last, when the influence of Government united with popular opinion to make resistance unavailing. Well; the people, and the Government, and the jobbers have had their way, and it is to be hoped that they will at length suffer the wise, and the reflecting, and the disinterested to have a little of theirs. The taste for magnificence has had ample indulgence, and it is but reasonable, that some care should now be had for those who are liable to be sufferers by the event. Much as the erection of the new bridge and the formation of the approaches to it may cost the public, that cost, we apprehend, will be found but trifling, compared with the amount of permanent damage which will be sustained by the trade and navigation of the upper part of the Thames, should the old bridge be taken down, and no steps be taken to avert those effects, which, it has been shown, must naturally result from such an alteration in the channel of the river. The talk will not then be of the million or couple of millions which this splendid improvement cost; the answer to enquirers will be, that it cost half the trade of the metropolis. In a future paper we shall enter into a full examination of the means of averting so ruinous a result. REPLY OF MR. GILMAN TO MR. SYN Mr. Editor,-In my last communication, I stated it to be my intention to reply to the "Practical Engineer's" analysis, contained in your 354th humber, so soon as opportunity offered: hitherto, however, uncontrolable cir cumstances have interposed, and prevented me; but I hope to be prepared for the next or following number. In the mean time, please to allow me a small space in the Magazine for a word or two to Mr. J. Syngleman. I am exceedingly obliged to him for having introduced Mr. Hall's patent to the more particular attention of your subscribers, as it happens to be the only one with which I am acquainted, either directly or indirectly, among those patents which the "Practical Engineer" charges me with pirating, and the knowledge of which I derived from the same Source as J. Syngleman, "The Register of Arts." REPLY OF MR. GILMAN TO MR. SYNGLEMAN. Had Mr. Syngleman, however, been really actuated by the good old English principle" he professes to be, and abso lutely wished to see fuir play," I apprehend he would not have been so sparing of his labour, but would have taken a little more trouble," and transcribed the remainder of the paragraphs which describe the real object of the patent in question, in which case I should not have had occasion to trouble you with any remark. I will now, take leave to state, most distinctly, that this patent neither sug-1 gested the principle nor influenced the arrangement of the generator described: in my narrative in the smallest degree. But admitting that it did, for argument sake, it is casy to show that the objects of the two plans are as different and as dis-s tinct as it is possible for two plans to be; indeed, they are wide as the poles asunder" in principle. To prove this, I will furnish the remainder of the specification from the " Register of Arts," and which the respectable Editor of that work affirms to be a verbatim copy. The second and third paragraphs do not, however, bear much upon the question; but, in order that I may not be charged with furnishing a garbled account, I think it best to transcribe the whole. "When the water in the boiler," continues the specification, "" is in a state of ebullition, the steam therefrom passes down the pipe (the stop-cock in it being opened for that purpose), and enters the furnace through the hopper-formed grate; there ascending through the fuel, under intense ignition, it is for the most part decomposed; certain elastic gases are thus generated, which, together with the undecomposed portion of the steam, proceed along the curved pipe i, into the strong receiver or reservoir C. In this vessel it is kept under any required pressure by the safety-valvej, or other usual means for supplying the working cylinder of the engine, by a conducting pipe and cock at k. "From the upper and lower parts of the water-cistern B, proceed to horizontal pipes, which enter the upper and, lower parts of the boilers, preserving the water in both upon the same level, the height of which may be regulated by a float, and a force-pump is fixed at h, for injecting water into the cistern, to supply the loss by evapora tion. "In order to regulate the pressure of the elastic vapours in the several vessels described, a communication is opened 475 between the reservoir C and the cistern B, by means of a short bent tube r, which is furnished with a stop-cock, to cut off that communication whenever required. "In setting this apparatus to work, the cistern" (not shown in your 340th number)" and boiler should be filled up to the pipe l, as shown in the engraving; the apertures at the upper and lower part of the furnace opened, when ignited coke, or other fuel, is to be thrown in through the upper one (d), the bellows set to work, and fuel supplied at intervals, until the fire is raised to its proper intensity. When the steam has acquired the right degree of force, which is indicated by the guage, the apertures in the top and bottom of the furnace are closed by their stop-cocks, also those in pipes ƒ and (supposed to be previously open); the valve or cock in the tube is then opened," (this is the curved tube connecting the fire chamber with the reservoir C), " along which the steam and gases pass into the reser voir C, and from thence to the engine. When the vapour has continued to pass through the furnace for a certain time, the fire becomes incapable of decomposing a further quantity; the communication with the reservoir C is there fore closed, and the fire replenished by additional fuel and the aid of the bellows while this is going forward in one of the furnaces, the other is proceeding uninterruptedly in the generation of steam and gaseous vapour, in the same manner as that already described: the pressure in the reservoir is thus, by the alternate working of the two boilers, kept under an uniform pressure, and the supply from thence to the engine ren◄ dered equable and unremitting." After a perusal of these paragraphs, Mr. Editor, I think every one of your readers conversant with such matters will readily perceive the distinction; but we will contrast the object of each plan more minutely. 476 DR, LARDNER'S LECTURES ON MECHANICS. ring this operation the upper and lower apertures of the furnace are open, and, consequently, the products of combustion escape into the atmosphere, But Again, "When the fire has acquired sufficient intensity, and the steam the right degree of force, the apertures d and e, at the top and bottom of the furnace, are closed." Also, and at the same time, the communication with the bellows is cut off, by means of the cock g in the blast-pipe f" consequently, the fuel is no longer supplied with air: hence Mr. Hall does not use the decomposed at mospheric air (or the nitrogen) with the high-pressure steam, as Mr. J. Syngleman' asserts, nor the products of com bustion arising from the decomposition of atmospheric air and of fuel. this is what Mr. Hall does.-After enclosing the fuel in a state of intense ignition, as just described, "the steam being at the right degree of force, is allowed to pass down the pipe A (the stop-cock being opened for that pur pose), and enters the hopper-formed grate; there ascending through the fuel, under intense ignition, it is for the most part decomposed; certain gases are thus generated, which, together with the undecomposed portion of steam, proceed along the curved pipe i, into the strong reservoir C, and from thence to the working cylinder of the engine." Now, Mr. Editor, I force the products of combustion directly into the water; not, however, for the purpose, or with the expectation of deriving power from the gases, &c. that result from the decomposition of the fuel, as is evident by my endeavour to show that there is little or no loss of power in performing the operation, but with the view to take from such gases, &c. the heat with which they are supercharged, more readily, more effectually, and in smaller compass than by the usual method of external application in flues. Thus the sole object of the apparatus, or generator, described in my narrative, is to secure every atom of heat possible that is evolved during combustion; while Mr. Hall's sole object is, as he states in the commencement of his specification, and as I have proved it to be, in tracing the operation of his apparatus, to decompose steam, by passing it through a mass of fuel in a state of intense ignition. Hence the two objects are as different and distinct as light and darkness. I will now conclude, Mr. Editor, by observing that these public censors for so, I suppose, I must designate them→→ do not appear very remarkable either for candour or veracity, although they are so ready to charge others with a want of both. Of course, it must not be supposed but that they are perfect masters of the subject, otherwise they would not have assumed the critic ; and, therefore, I will leave your readers to infer for what purpose Mr. J. Syngleman has omitted the only paragraphs that are explanatory of the patentee's object: why it is that he has stated "that the patentee lets in only a portion of steam under the grate," when the sole object and purpose of the plan is to pass the whole through the fuel and decompose it if possible; and, finally, why it is he states, "that Mr. Hall uses the decomposed atmospheric air (or nitrogen) with high-pressure steam," which is manifestly an untruth, as he does no such thing. I am, Sir, yours, &c. UNIVERSITY. (Concluded from page 447.) In all the last cases, the weight of the pulleys must be taken into account, which is often found to be very considerable. This inconvenience, however, is remedied in the system represented in fig. 1, where the weight of the pulleys assists the power. The proportion the weight bears to the power is thus found:-If the power, be equal to 1 lb., it will bear a weight, suspended at the end of a string over the pulley D, equal to itself, or 1 lb. These two pounds together will bai lance a weight, suspended at the end of a string over the pulley C, equal to 2 lbs., which, added to the 1 lb. be fore, is equal to 3 lbs. Again, these 3 lbs., added to the power 1 lb. (viz. 4 lbs.), will balance the same weight over the pulley B, and which together with the former weight (3 lbs.) gives: 7 lbs. for the weight; and thus bymeans of the other pulley A, may be increased to 15 lbs., which will be ba lanced by a power, P, equal to l-lb.It will be plainly perceived that the pulleys here assist the power in rais ing the weight. The next figure (2) is called a Spanish Burton, the power of which is to the weight as i to 5. One inconvenience attending pulleys with several strings is, that dies ropes are not equally stretched, as is evident from what has been already mentioned. The results that would be obtained in practice would differ from those before given, on account of the friction which attends the number of pulleys which are used; but the investigation of the precise amount would require more mathematical science than the present Lectures will allow of. The next class to be considered is the inclined plane, which is a plane raised at a certain angle to the horizon, or to the force intended to be resisted. If that force be gravity, it is at an angle to the horizon. The screw and wedge are both machines of this class, but will be de scribed hereafter. Let fig. 3 be the inclined plane. The weight is generally applied at B, while the power acts in the direction BD, by means usually of a string BDP passing over a pulley D. The CE question then is, What must be the proportion between these two for them to be in equilibrium? It has been before mentioned, that three forces acting on a body will be in equili brium where the three sides of a triangle drawn parallel to the direction of those forces are proportional to them. In this case there are three forces acting on the body B: viz. its gravity, re presented by the line BC; the reaction of the plane, represented by BE. at right angles to that plane; and the tension of the string, acting in the direction of the power BD, and repre sented by the parallel line CF: consequently, the three forces are represented by the triangle BCF; Or, what is the same thing, if the weight be in the same proportion to ab as the power is to bC, the resistance will be in the same proportion to aC. Thus, in any inclined plane the weight will be to, the hypothenuse as the power is to the perpendicular, and as the resistance is to the base. Two inclined planes are sometimes used, as at fig. 4; the one to support Fig. 4. 478 DR. LARDNER'S LECTURES ON MECHANICS. by and equal to the common perpendicular BD. The screw, which is the next mechanical power, is only a variety of the inclined plane; a little consideration will explain this. A hill is an inclined plane, but if that hill be wound round a pillar, it will still be an inclined plane, but it has then become the variety called a screw. A straight staircase is an inclined plane, but a spiral one is a screw. In this machine, contrary to most others, the power acts in a direction parallel to the base, and the proportion is as follows; the weight is to the power as the circumference described by the power is to the distance between the threads of the screw. The mechanical efficacy of this machine depends upon two things; viz. the closeness of the thread, and the size of the circumference of the action of the power. In theory there may be no limits to the range of the power or to the fineness of the screw, but there are practical limits. The range of the power is limited, as in the case of the wheel and axle, by the unwieldiness of it, if very large-while the fineness of the screw is limited by its strength. There is a very ingenious machine called, from its inventor, "Hunter's Screw," represented at fig. 5. A B Fig. 5. In this case there are two screws made use of; the one, A, is a hollow cylinder, the interior of which is a nut adapted to receive the second screw B. The former one, A, works in a fixed nut e, and the other one, B, is attached to the moveableboard D. When the screw A is turned once round, it advances through the nut e, through a space equal to the distance between two contiguous threads, and (if the screw B were not supposed to act) the board D would descend the same space. But while the screw A advances through the nut e, the very same revolution causes the other screw B to move downwards through a space equal to the distance between two of its contiguous threads; consequently, if the threads of the screw A be wider apart than those of B, the combined effect will be, that the board D will descend through a space equal to the difference of these intervals. The mechanical efficacy is, therefore, increased by diminishing the difference of the distances between the threads of the screws. If the circumference described by the power be 20 inches, and one screw have 20 threads to an inch, and the other 21, the power will be to the weight as the difference between and, or sit is to the circumference of the action of the power (20), or as 1 to 8400. If, however, one screw has 30 and the other 31 threads to an inch, then the power is to the weight as is to 20, or as 1 is to 18,600. A screw bears this remarkable difference to other machines-that in this machine the friction assists the power; indeed, it would otherwise be useless, for it is the friction which prevents it from recoiling. One of the most curious applications of the screw is the instrument called a micrometer, which is used for measuring small spaces. A very fine wire is divided into parts, and placed parallel to the space to be measured. This wire is moved forward by means of a fine screw, being attached to the end of it, and at the other end of which is fastened an index, against which a fixed hand acts. The index is a circle divided into 100 equal parts. A screw can easily be constructed with the distance between its threads equal to only 1-100th part of an inch; consequently, in one revolution of the screw it will be moved forward that distance, and when the index is moved one part, the screw |