78 WARD'S ESSAY ON THE LEVER. To these errors in principle, we think we might add not a few defects in the Essay before us; but having no desire to hunt about for faults, where we really wish to commend and to serve, we shall merely mention two of the more prominent sins of omission which have forced themselves on our attention. The first is, that the author has not shown, as he ought to have done, how the weight of a lever may have an effect on its equilibrium, and how that effect may be allowed for in a computation. The second, that there is no explanation given of the method of obtaining, by means of a false balance, the true weight. The Essay, as a whole, however, is one of rare merit, and confers equal honour on Mr. Ward, and on the Institu tution to which he has been indebted for bis scientific education. We heartily wish we could separate the Essay itself from the official eulogium with which it has been ushered into the world by the learned President of that Institution; for, excellent as the Essay is, it would require to be doubly so to justify all the praise which Dr. Birkbeck has indiscreetly lavished upon it. "Taken as whole," says that learned gentleman," as an historical, mathematical, and practical dissertation on the lever, I will venture to assert, that it stands unrivalled." A bold "venture," indeed! Unrivalled as "" an historical" dissertation? Ample, indeed, the his torical materials on this subject are, for many are the theories of the lever celebrated in the history of mechanics; but which of them all does Mr. W. describe, or criticise, or illustrate ? That of Archimedes? No. That of Galileo? No. That of De la Hire? No. That of Newton? No. That of Landen? No. That of Hamilton? No. That of Vince? No. That of Prony? No. The plain matter of fact is, that there is not one historical sentence in the Essay from the beginning to the end! Aguin: as to its being "unrivalled" as a mathematical" dissertation, we wonder where the good Doctor found those "mathematical" displays on which he confers this pre-eminence. We suspect it must have been on the other side of the same missing leaf which contains the historical beauties of the Essay; for though we have examined the pamphlet diligently, we can discover nothing of mathematics in it, saving some traces of its first rudiments. A pupil of that excellent mathematician, John Dawson, should have known better than to confound, as Dr. B. appears to have done, a profusion of diagrams, signs, and symbols, with the spirit of mathematical investigation. Mr. Ward's Essay is a "" practical dissertation;" and so far it is excellent, though not even in that respect "uarivalled;" but it is neither an "historical" nor a "mathematical" one, in any sense in which these terms are usually employed. Not content with thus generally exalting Mr. Ward above all the philosophers who have ever written on the subject of the lever, Dr. Birkbeck has made a further" venture," and pointed out by name those individuals of the present day whose reputations are most placed in jeopardy by the appearance of this "mathematical" prodigy amongst them. "If the detection of current and oftrepeated errors," he goes on to say, "be evidence of more accurate, and therefore of more profound investigation, it must be granted that Mr. Ward has proved himself to be less superficial than some individuals of considerable renown, who have been instructed in schools for the more favoured classes, and who are, ut this time, occupying distinguished stations in important literary and scientific establishments." The "individuals of considerable renown" who are thus admonished to "hide their diminished heads" before the humble "journeyman machine maker" are Dr. Lardner, Professor of Natural Philosophy and Astronomy in the London University, and Dr. Gregory, Professor of Mathematics in the Royal Military Academy at Woolwich. We shall say nothing of the strong sense of propriety which shines forth in this comparison-nothing of its wholesome tendency to repress every thing like self-conceit and arrogance in the minds of the many young persons (all young, at least, in science) under Dr. Birkbeck's presidential careall this we shall pass over as too obvious to escape any one's notice, and proceed at once to probe the Doctor's "most exquisite reason." According to the worthy President, Dr. Lardner has committed an error respecting the ratios of toothed wheels in the second Treatise on Mechanics published by the Society for the Diffusion of Useful Knowledge (a Treatise generally attributed to Dr. L.)-and Dr. Gregory has committed an error respecting an alleged property of a modification of the wheel and axle in his Treatise of Me. chanics and Mr. Ward has detected these supposed errors (a single error in each writer!)-argol, Mr. Ward is a "" more accurate," and "more profound" investigator than either of the two learned Doctors!! Was there ever a WARD'S ESSAY ON THE LEVER. more convincing piece of reasoning? "Why," as Parolles says, touching philosophical persons who " ensconce themselves into seeming knowledge," "it is the rarest argument of wonder that hath shot out in our later times!" Only to be matched by that famous one of the College of Dunces, who declared (strange to say, almost in the same words now used by Dr. Birkbeck) that "since there can be no stronger proof of a good taste in arts, than a man's detecting blunders which have escaped the notice of all the world beside, the tailor who first discovered that the buttons in the statue of Ben Jonson in Westminster Abbey are on the wrong side of the coat, was, all to nothing, the first connoisseur of his age." But have Doctors Lardner and Gregory really committed the errors ascribed to them? Are the buttons really on the wrong side of the coat? As regards Dr. Lardner, we are inclined to think that he actually has been guilty of the oversight imputed to him; but we cannot so readily yield our assent to the validity of the charge brought against his brother Professor. The matter stands thus:-Mr. Ward, referring to Dr. Gregory's account of Eckhardt's double barrelled axis in peritrochio, affirms that the Doctor is quite in error when he says, "This windlass has like. wise the peculiar property of holding the weight at any part of its rise or fall, without needing a ratchet wheel and catch;" and because Mr. Ward says so, Dr. Birkbeck takes it for granted that he is in the right. Had the worthy President, instead of indulging his fondness for high-sounding assumptions, directed Mr. W., or some other pupil of the Institution, to make a model, and to try an experiment with that model, he would have found that Dr. Gregory is perfectly correct in his assertion with regard to all such cases as are likely to occur in practice. We have seen a machine of this kind, in which the diameters of the two parts of the barrel were in the ratio of 10 to 9, and the radius of the winch handle six times the radius of the larger part of the barrel, The machine, therefore, gave a mechanical advantage of 120 to 1; and yet, when the hand which drew up the weight was withdrawn, the weight did not descend, although there was no ratchet wheel and catch. The reason is very evident. The difference in the tendencies of the weight to draw down the counteracting portions of the cord, which fold in contrary directions upon the two cylinders, 19 is more than overcome by the friction of the pulley, and by the strain upon the two points, at the ends of the axle occasioned by the oblique position of the cord; the latter of which points is well explained by Mr. Ward at page 30. It is true that in a case like that assumed by Mr. Ward (p. 28), in which the radii of the two portions of the axle are as 2 to 1, the weight would run down when the action of the power was remitted. But who would employ this mode of con struction in a case where it would be so useless? Who would think of having recourse to the double barrel, to gain a mechanical advantage of 2 to 1 (instead of 120 to 1, as in the case of the machine which came under our observation), when that advantage could be obtained by a single additional pulley? The peculiarity of Eckhardt's contrivance seems to us to consist in this-that the greater the mechanical advantage obtained by the construction, the less is the tendency of the weight to run down when the application of the power is remitted. We hope Mr. Ward will understand distinctly, that we are far from identifying him with the extravagant representations of the merits of his Essay given by Dr. Birkbeck. He could not, in publishing his Essay, well avoid prefixing to it the Address which accompanied the delivery of the prize with which it was honoured; but the tone of the Essay itself is modest and becoming. Mr. W. obtrudes neither "historical" nor mathematical" pretensions; and when he differs with such authorities as Dr. Gregory and Dr. Lardner, states, without chuckling, the grounds of his difference.. After all, perhaps, we have regarded in too serious a light the commendations of the worthy President. The excessive affection of foster nurses is a matter of (natural) history; and it is rather, therefore, a thing of course, that Dr. Birkbeck should take an exaggerated view of the Mechanics' Institution, and of every thing arising out of, or connected with, it. Why should we stare at his discovering another Archimedes in one of his pupils, when, in the same address, he gravely tells us that the London Mechanicss' Institution is the father of the London University, and grandfather of the King's College.* And The idea of the London University is at least as old as the London Institution, which was, in fact, originally in. tended to serve all the purposes of a Metropolitan University; and was only not 80 MINOR CORRESPONDENCE. when he moreover warns both child and grandchild to take heed how they behave themselves, since grandpapa is resolved "to watch," and "even to correct," them, should they chance to go astray? It were best, perhaps, when old gentlemen talk so, "to be sad, and say nothing." MINOR CORRESPONDENCE. Sir,-A constant reader of your invaluable work begs to point out two trifling errors in your Magazine of the 21st inst. 1. The dimensions of Elephant and Imperial are reversed. 2. You state that laid papers are never made larger than Imperial, whereas Double Elephant is made, and kept by two or three wholesale stationers.-I am, &c.-G. F. J.-Feb. 23, 1829. Sir,-Amongst the number of inquiries in Vol. x. Part 71, I see one for a method to raise water by the pressure of the atmospheric air. I am well acquainted with an old correspondent to your publication, who has an original invention to raise water from any depth, beyond the reach of the most powerful engines, by the pressure of the atmosphere; and I am authorized to say, should this notice engage the attention of engineers, or other persons possessing the means, and willing to reduce this scheme to the test of experiment, he will, upon honourable terms, undertake to lay the plan before them.-I am, &c.-A Constant Reader. "R. N.," who desires to learn where the most approved machine for sweeping chimneys can be obtained, and what is the price," will find, in our 9th vol.!p, 181, a description of Glass's Machine, which has been recommended by the Society for Superseding the Use of Climbing Boys, as the best which has yet come under their notice. Mr. Glass's address is No. 2, Moor-lane, Forestreet, Cripplegate. We are glad to perceive, from the public papers, that Mr. Peel has directed that it shall be employed in all the public buildings in his department. Mr. Peel should go a step farther, and bring a Bill into Parliament, prohibiting altogether the use of climbing boys. Postscript to the Question in Number 290, p. 45.-Sir,-It may be as well to observe that this question must be confined within certain limits, which must be determined by the common sense of the thing. It would be absurd to suppose that a hog could be of more value than a cow, or eight quarts of honey dearer than either; there fore, I think we must suppose a cow to have been worth at least from two to three times as much as a hog, and a hog three times as much as a sextary of honey, or thereabouts. I doubt not, most of your intelligent readers will have anticipated me in these remarks; but I have thought it as well to send them by way of supplement, that all unnecessary cavilling may be prevented.-I am, &c.- Glevum. Compound Interest, Dimensions of the Earth, &c.-Sir,-Allow me to make a few remarks ou the compound question,-which will certainly close my correspondence on the subject. The price of gold employed in the original computation (vol. x.-page 42), was greater, as I before remarked, than its present value; and, consequently, the number of globes less than at the called one (as the reader will find by consulting the records of its establishment), from deference to those preju dices, which even at the present day it is found so difficult to overcome. present time. Standard gold is now exact par, or 467. 14s. 6d. per lb. troy; whence, pure gold is 507. 19s. 4 d. (deducting for the value of the copper), which gives 792,105,700 globes of gold, for the value of one penny, at 5 per cent. compound interest for 1828 years. The value employed in the original computation was 547. 12s 3d. per lb. troy; taking the earth's diameter at 7917 miles, the diameter of a sphere equal to the earth in solidity, considered as an oblate spheroid. The value of pure gold was,at one time during the late war, as high as about 707. per lb. troy! If, however, instead of 1828 years, the time be taken at 1826, or, more correctly, 1826 years 1933 days, the original calculation (vol. x. page 42) will then stand correct, according to the value of pure gold at the present time. In respect to what your correspondent (without a name) says in reference to my pretended knowledge of the arithmetic of logarithms, I am not aware that I made any pretensions to superior, or, in fact, to any knowledge whatever, either as to their construction or application. I have, however, had as much practice in logarithmic arithmetic as most persons; having computed nearly one fourth part of the Tables contained in the first volume of Dr. Pearson's Introduction to Practical Astronomy," as well as many other Tables in manuscript,-not to say anything about computations made for amusement. My labours have had a view to the improvement of science; and in respect to periodical communications, they have been made to elicit truth, and not, as some may, perhaps, imagine, from any motive of vanity. The applause of a few critics is but a sorry compensation for such laborious computations. Your correspondent is very liberal in giving advice, notwithstanding what he recommends is contrary to his own practice. As to my attack on Mr. Squire, it is hardly necessary for me to inform your readers, that this gentleman first attacked me. In concluding with your (nameless) correspondent, I am ready to meet him, if he come forward in a manly and honourable way,-not otherwise. I shall, therefore, take no further notice of his past communications, he having pronounced his own elegy!! (vol. xi. page 32).-I am, &c.-J. Utting.-Lynn Regis, Feb. 1829. Our correspondent O. C. F." wishes us "to inform Mr. Foord, that the angles of his new triangle C B D (page 41, No. 290), are 80 deg. 50 m. 52 sec., 41 deg. 10 min., and 60 deg.; and that, therefore, two of his new results are erroneous. He hopes that that ingenious gentleman will, hence, be induced to relinquish his own method, and adopt some process that will always furnish correct results." For a farther exposition of these errors, see a communication from « G. S.," in a preceding part of this Number. INTERIM NOTICES. The Supplement to Vol. X., which has been unavoidably delayed, will be published early next r week. Communications received from Mr. BarnardHenry D--; An Occasional Reader- Mr. Alexander Mr. Baddeley-A-C. H. R.—A Constant Reader-Mr. Shires-Mr. Joseph Hall -Mr. J. Walker-Mr. Hopwood-and Mr. Bailey This remark is not intended to apply to such persons as know the value of such computations. Communications (post paid) to be addressed to Printed by G. Duckworth, 76, Fleet-street, Mechanics Magazine, MUSEUM, REGISTER, JOURNAL, AND GAZETTE. Sir, It is a serious consideration, that during every winter season a greater or less number of persons lose their lives for want of due caution, in venturing to skate on the ice before it has become sufficiently strong. There are also many other causes to which these accidents might be traced; but it cannot be necessary to enlarge upon them here. Certain it is, that these fatal occurrences are far more numerous than would be supposed, considering the various methods of recovery resorted to, and seldom wanting wherever skating is much practised. VOL. XI. d One thing, however, may be remarked of the means here alluded to: they are not intended for the sufferer's use, previous to an accident; and whether they may be available afterwards is always dependent upon the prompt exertions of the bystanders. As I am not aware that anything of the same kind has yet been offered, I trust a safeguard I am about to describe will possess sufficient ingenuity and simplicity to recommend its being very generally adopted. The engraving prefixed represents a young person in the act of falling G 82 BUSTON'S FIRE-ESCAPE. amongst broken ice. His hat is thrown off, and from the inside of it proceeds a small line, fastened both to his hat and to his dress. Of this part, a, b, c, d, e, is an enlarged view. A small piece of stout cord a, about fifteen inches long, has both its ends attached to the leather of a hat; a ball of strong twine or whipcord c, when its two ends are drawn out, b, one of them, is tied to the loop a, and d, the other, is knotted to a piece of narrow black ribbon e. The whole ball of twine is to be placed inside the hat, and covered with a handkerchief, to prevent its getting entangled. The ribbon only hangs outside; and when the hat is on the head, this ribbon may very conveniently be placed behind the coat collar, and secured in two or three of the waistcoat button-holes. The intention of this extremely simple guard must at once appear evident. It affords a ready and certam means of withdrawing the individual from under the ice,-the hat serving as a buoy, to discover the running line. The assistance, too, of more than one person, together with the use of poles, ropes, grapples, and the like, may be dispensed with. I am, Sir, HENRY D. Finsbury March, 1829. BUSTON'S FIRE-ESCAPE. Sir, It will, doubtless, be gratitifying to your numerous readers to know, that the fire-escape invented by the late Samuel Buston, which I described and recommended at pages 213 and 310 of your 9th volume, has been adopted by the benevolent and spirited Directors of the Protector Fire Office. Although this mode of escape is by no means so pleasant as many that have been suggested, yet in point of efficacy it is inferior to none; while, on the score of simplicity, economy, and portability, it is even superior to most others. Its efficiency was fully established, by experiment, about a week since; when a fireman belonging to the above Office, named Stocks, precipitated himself, three several times, from the second floor window of a house in the Southwark Bridge Road, near the Protector Engine Station. The weight of this man was stated to be about thirteen stone, and the distance fallen about thirty feet. The canvas was upheld by ten persons. Both the weight of the person, and the distance fallen, are somewhat beyond the range of general occurrence; but I think there is little doubt that both may be increased, or the number of the holders decreased, without the least fear of danger; and I feel convinced, that these fire-escapes, properly distri buted, would supersede all other more complex and expensive apparatus. I am happy to learn that some of the other Fire Offices have it in contemplation to adopt this simple but useful article in their several establishments. Whether I have overrated the merits of this invention or not, yet I think all will agree with me when I state, that as an addition to the ordinary equipment of a fire-engine, this is by far the most convenient yet laid before the public, and one which, with proper activity, may be the means of saving not only human life (the first and greatest consideration), but also property to a great extent, from what would otherwise be inevitable destruction. The weight of this escape is about 30lbs. One of them was exhibited by Mr. Wix, of Stockwell, at the late meeting of the Society for Preventing Loss of Life by Fire. I remain, Sir, March 6, 1829. CHEMICAL INQUIRIES. What are the respective strengths of sulphuric, nitric, and muriatic acids, in the salts formed by their union with alkaline, earthy, and metallic bases? Platina, when exposed to a jet of hydrogen gas, becomes red-hot. Does the same effect take place when sulphuretted, phosphorated, |