know not whether this plan has been suggested before, but I think it would answer. Nor am I skilful enough to decide whether an Archimedes' screw would be the best kind of engine to work by such a power; but a clever mechanic would soon form a judgment on that I remain, Sir, J. E. ALLOYS, SOLDERS, AND AMALGAMS, USED IN THE ARTS. (From the Journal of the Franklin Institute.) The following table of the alloys and amalgams used in the arts, has been prepared by Mr. Chaudet, a distinguished and experienced assayer in the Mint of Paris, from actual analysis of carefully selected samples. In a few instances, the proportions of the composing metals are not given, for reasons that, in one instance at least, are obvious. This deficiency is more than compensated by the addition of several others, particularly that of the alloys of Palladium, which I have added, in the full persuasion that the whole will be found useful. FRANKLIN PEALE. The medals made from this alloy are cast; they have the advantage of being struck by a few blows of the press, and of wearing a long time. The standard here indicated is the best; a second is composed of 800 of silver, and 200 of copper, in the 1000. This alloy is the Packfond of the Chinese. Alloy used to make Ductile Gold of 18 carats, or 950 milliemes.tt— In this alloy small quantities of lead and zinc are often found, but they are present by accident. The proportions here indicated are the result of an analysis of the beautiful bronze statues of the garden of Versailles, which were cast by the Brothers Kellers, celebrated founders employed by Louis XIV. This alloy is very hard; it is annealed by dipping, while red-hot, into water, and is then malleable; whilst, if suffered to cool gradually, it is excessively hard: this important fact is due to M. d'Arcet, who has thus furnished the means of fabricating, in France, cymbals, &c., formerly imported, at great cost, from China. The proportions here indicated having been found by analysis, it is evident that the tin is present by accident. This alloy of brass is important, and is due to Mr. Chaudet. Sometimes a small quantity of copper is added to these two metals. ** This alloy may be prepared with a smaller proportion of mercury; it melts at 65° of the centigrade scale. The previous combination of the alloy is found to produce ductile gold, when the same metals would prove the contrary, if mixed directly. Among the twenty-three metals that are not enumerated in the foregoing list, there are 'several that enter into alloys, but they are without utility in the arts; we should not, how. ever, include in the remark, the native alloy of Osmiun and Rhodium, which is excessively hard, and is at present used for the nibs of metallic pens. Care has been taken in the arrangement to name those metals first which enter in the largest quantities in the alloy. This alloy is extremely important; it is used for all those purposes in the fabrication of philosophical instrument, for which platinum was formerly applied, being superior to it in hardness and colour, and yet inoxidable under all the usual circumstances. + An extremely useful alloy, having a degree of elasticity only exceeded by steel, with all the advan tages of superior lightness and hardness over platinum; this, and the preceding, are due to Mr. Percival N. Johnson, of London. The copper and zinc ought to be taken in the form of brass; for two parts of silver, take one part of brass. This amalgam is hard, and melts at a low heat; it was used by the French police, under the adminis tration of the celebrated Fouché, for the purpose of opening and resealing the letters that passed through their hands. MR. HERAPATH'S LOCOMOTIVE THEO REMS. Sir, Mr. Herapath very kindly informs me, p. 22, No. 12 of his series, that if I will attentively read what he has written, I will find that his theorems on railway transit are based on the principle that the opposing forces, namely, gravity and friction on the one side, and steam-power on the other one in equilibrio;" and, therefore, that this acceleration and retardation which, I" presume," have "no existence." Now, in the first place, I beg leave to inform Mr. Herapath, that it is not my custom to presume to give an opinion upon any subject before having first considered it with attention; errors, no doubt, I have often fallen into, but never for the purpose of misleading. Nor do I wish to insinuate that Mr. H. has had any intention of misleading the readers of the Mechanics' Magazine. But from his vaunted attainments in mathematical and physical science, he seems to wish to convince us that he can at once jump to a conclusion which I, Iver M'Iver, a canny Scotchman," will not implicitly believe before I have carefully examined the premises. 66 Secondly, with regard to the acceleration and retardation, which he says have no existence," I would ask Mr. Herapath if he means to disown his own. handiwork? Mr. H.'s theorems, for determining the speed on ascending` and descending planes, are recorded in the Mechanics' Magazine, and no sophistry on my side, nor shuffling on his, can now alter them. Again, Mr. Herapath informs me, "that his formulæ are not given as ma thematically but practically true!" This, no doubt, is a singular concession; but I am almost sure, that had I been a practical man—a humble stoker, for example -and had urged similar objections to the prodigious velocity which his theorems produce, he would have found it conve nient to reverse the above expression. Take it in either sense, however, I will ask him how he can reconcile such an expression with No. 2 of his series, in which we meet with the following memorable observations:-"Obloquy I know is frequently endeavoured to be thrown on scientific opinions by the ignorant and designing, from the vulgar prejudice that theory and practice are usually at variance. But I can assure my readers, that in no instance did I find experiments on the points I went last year to examine on the Liverpool and Manchester Railway, at the request of one of the Companies, differ sensibly from the results I had anticipated and computed previous to my going. Theory, indeed, as applied to any particular art, is no more than experiment generalised, and cannot, therefore, when managed with honesty and skill, materially differ from practice." If I chose to adopt the language which Anti-H. has used towards the strong-ofhand H., or which Anti-Carper has used against myself, I could retort upon all three with a vengeance, but for the present I shall forbear. I would just ask Mr. H. what proof has he given that his theorems are practically true? I may venture, I think, without much fear of contradiction, to answer the question myself-none whatever. They have never yet, by his own admission, been tested by any experiments. "There are," he states, matters to be investigated to render the subject complete, and which, had not various causes interposed (the old story), I should before now have taken up, I admit," &c. Mr. H. has very little cause to com plain of want of time. The first number of his series appeared in the Mechanics' Magazine on May 30th, and week after week he was allowed to go on without any interference at a galloping pace, until he had absolutely attained a velocity (down a gentle descent) of 1,320 miles an hour, and by a little slight-of-handtrick, he has shown us how a greater velocity may be attained by moving up an ascent!!! But, Mr. Editor, I am afraid Mr. H. has done himself great injustice, by denying that his theorems were not intended to be mathematically true. On this subject, however, I shall not at present enter, but reserve it for my next communication. I am, Sir, yours, &c., Nov. 30, 1835. The strong-of-hand Mr. "H." supposes that Mr. Herapath and Anti-H. are the same person;→ might I ask him who he supposes Anti-Carper to be? THE PRINCIPLES OF LOCOMOTION. Sir,-In p. 124, Iver M'Iver supposes the "force of steam applied so as to overcome friction ;" and as the resistance of the atmosphere has not, to the best of my recollection, been noticed in the observations of any of the parties, I thought the retarding forces were left out of consideration, in which case he will find the numbers I have given as correct as they were stated to be. But Anti-Carper, in his last letter, blames Iver M'Iver for not taking the magnitude of the load, the power of the engine, and the mode of heating the boiler, into consideration; from which I think it is fair to infer, that the results derived from the rival theorems of Mr. Herapath are intended, in some way or other, to depend upon those matters; will Anti. Carper point out any of that gentleman's theorems in which they are introduced? NAVIGATION OF THE TYNE. Sir, I was lately in company with some persons who were talking on the subject of Jarrow Slake, as to its capabilities, &c.; and I stated that if it were cut off or filled in, it would materially improve the navigation of the River Tyne between Shields and Newcastle, but the others strongly dissented from my opinion. That it is the intention of Nature to do what I proposed, seems to me to be clearly proved by the increasing fluvial deposit. It might instruct others, however, as well as myself, if your able correspondents were to discuss the question in a cool way, and still more if they were to elucidate it by experiment, of which it is very capable. It is impossible to dam out the ocean; hence the water let into Jarrow Slake would, if prevented, be carried above Tyne Bridge, and add to the volume and current of the ebb-tide. I attempted to illustrate my argument by the fact of confining the spread of streams by quays, adding ta the depth of the water abreast of the quays; but this was also overborne by my opponents. I admit that the danger of crossing the bar at the last of the ebb would be much increased for a time; but this evil would be cancelled by a greater mean depth at high-water at neap-tides. In 1825, I saw that something similar had been done in the Clyde; and I should think other rivers have had the same operation, that is, cutting off the waste-water and making docks, timberponds, or mill-reservoirs. At this time when railroads are talking of between Newcastle and Shields, it would be as well to consider whether a road could be made across the Slake, saving much distance to South Shields from Gateshead. I have long had a plan for such works as sea-walls, built without cement or lime; which might be of service, and is quite original, having been thought of previous to the metallic caissons noticed in the Mechanics' Magazine some years since. That there are great vested interests at stake upon this question is not to be doubted; yet if the good of many be advanced at the doubtful risk of the few, the merits of the question need not be advocated by your constant reader, KEENAMS. Durham, Nov. 27, 1835. [We would recommend to the notice of our correspondent, and other friends on the Tyne, a very judicious article on regulating the flow of currents, in our 18th vol. p. 227.-ED. M. M.] SLATE RAILWAY PLATFORMS-COAL-TAR A PRESERVATIVE OF STONE-ORGANIC ACTION. Sir, The letter which you did me the honour to insert in your No. 642, in observation on Mr. Jopling's plan of laying a complete platform of slate, instead of isolated blocks or sleepers, as a support to the rails of railroads, was written on the spur of the moment, and, as I now think, without having sufficiently reflected on the subject. My opinion now is, that instead of the slate itself being tapped with a female thread, it would be preferable, with respect to time, expense, and efficiency, to drill a plain hole in the slate, and insert a square nut into its under surface for the screwed end of the bolt. If the difference between the cost of copper or brass nuts and iron ones should be thought at all worthy of consideration, I beg leave to suggest, that iron ones will answer equally well: But to this intent the nuts |