DR. LARDNER'S LECTURES ON MECHANICS. when it will descend; and, after vibrating, will settle in the former state of equilibrium called the Stable, while the latter is the Unstable, state of equilibrium. However, these are not the exact definitions of the words "stable" and "unstable," as there are instances when they are exactly opposite, which would be the case supposing the body to be a small balloon filled with gas. But the true criterion for distinguishing the different states is this: the tate of equilibrium is stable, when, any disturbing force being applied to it, the body will return to its former position; and it is unstable, when it will move into the other state on being disturbed. (The manner of finding the centre of gravity of a body, is too well known to need description.) When a body rests on a base, its stability depends on the line of direction falling within that base.* Thus Fig. 2. let ABCD be a parallelogram, resting on the base AB. Now the line of direction, drawn from the centre of gravity E, falls within the base; therefore the body will stand securely. Now suppose another parallelogram, DCFG, be placed upon the former one, which together will make the figure ABFG; the line drawn, as before, from the centre of gravity H, will fall exactly at the point B. This position may be called the boundary between the stable and the unstable states of equilibrium: for although it may stand on its base, yet, on the slightest force being applied to it, it 319 will fall over. Again, let a third parallelogram, GFIK, be applied, which will raise the centre of gravity to L: the whole figure ABIK will then fall over, and the line of direction will fall beyond or outside the point B of the base. (To be continued.) WHITE'S EPHEMERIS FOR 1830. The Editor of "White's Ephemeris" presents his best compliments to the Editor of the "Mechanics' Magazine," and will be greatly obliged if he will allow him, through the medium of his extensively circulated publication, to specify a few corrections in that almanac. Speculum Phanom. &c.—Errata. P. 42. Jan. 1.—Sun in perihelio, should be Earth in perihelio. P. 43. July 1. Sun in aphelio, should be Earth in aphelio. P. 42. May 4-Mars in conjunction with Capricorn, dif. lat. 19', should be Mars in conjunction with iota Capricorn, dif. lat. 19'. P. 43. Sept. 2.-Moon eclipsed invisible, should be Moon eclipsed visible. 776 May, 166 May, &c. indicate the stars numbered 776, 166, &c. respectively in Mayer's Catalogue. P. 48.-For Guroa, read Genoa. Perhaps, also, the Editor of the "Mechanics' Magazine" will permit it to be observed, that the elements of slight corrections, in consequence of the planet Ceres have received some the recent observations of foreign astronomers; the result of which was not known in England until after "White's Ephemeris," for 1830, was printed. If these new elements should be accurate, the geometric right ascension of Ceres on the noon of April 30, 1830, the day of the approaching opposition, will be 14h. 44m. 28s., and the declination 4° 10' 13" S. The former differing about a minute in time; the latter, about 7' in arc from what are given at p. 36 of " White." Woolwich, Dec. 16, 1829. 320 MISCELLANEOUS NOTICES. MINOR CORRESPONDENCE. Patents.-Sir, I have observed that the greater number of patents granted for useful improvements continue only for a few months instead of years. I should be glad to learn the cause of this seemning barrier being placed between merit and its reward. I am, Sir, yours, &c. W. (A Constant Reader.) [Our Correspondent has mistaken the meaning of the phrases "2 months," "4 months," and 6 months," usually attached to the announcements of new patents; but he is not the first person, by some scores, we have known to labour under a similar apprehension. A brief explanation may therefore convey information to many of our "Constant Readers," besides the one who addresses us. After a patent is granted, a certain time is allowed to the patentee to lodge a specification of his invention. If the patent is taken out for England alone, the time usually allowed is two months; if for Eugland and Scotland, four months; if for England, Scotland, and Ireland, six mouths. These are the customary periods, but they may be enlarged at the discretion of the Attorney and Solicitorgenerals for the time being. The fixed duration of all patents is fourteen years; but an extension of the period may be obtained by application to Parliament, when it can be shown (as in the case of Watt), that, for particular reasons, the patentee has not had a fair opportunity during the fourteen years of reaping the reward due to his ingenuity.-EDIT.] Sergeants Arabin and Denman.-We are authorised to state that Mr. Common Sergeant Denman, though a Member of the Superintending Committee of the Society for the Diffusion' of Useful Knowledge, never saw The British Almanac for 1829, in which there is the omis sion complained of respecting Mr. Sergeant Arabin, until after its publication. New Mechanical Motion.-Pendulum Power.That Mr. Dixon Vallance is a very valuable Correspondent all who read your Magazine must allow; that there may have been a coincidence of ideas between him and a very old mechanic, I am ready to admit: at the same time it is only just to say that a power of the same kind was applied to an engine for raising water previous to the year 1635; an account of which, with a plate of the machine, I have in a book in my library, which was printed in the above year. HOMO. MISCELLANEOUS. Effects of different Winds on the Colours of Vapours. I wish to know if any of your numerous readers have observed that the particles of vapour, which are at all times floating in the air, refract different rays of light, or rather divide the rays of light differently (like a prism), with each change of wind? I have for a long time noticed (and living in a hilly country, where the views are extensive, I have an opportunity of seeing objects, such as high hills, at a very great distance, and with consequently a large volume of air between me and the object viewed), that with an east wind the air appears of a rosy hue-inclining to purple if north of east-to scarlet if south of east; with a south' wind the hills appear clear and of their natural colour, and the air and sky white or paler blue than usual; with a 'west wind deep blue; with a north wind dark and gloomy, and if any fog with it quite black. The intermediate points of the compass partake of the nature of the more cardinal points between which they stand.-A. French Method of making Mortar for Building. -The method used by the masons in some part of France, is to put the lime in a sort of trough raised on four legs, about 18 inches from the ground, and then to pour in sufficient water to slack the lime, adding, when properly slacked, more water, and stirring it until it is about the consistence of thin milk. At one end of the trough is a hole four inches square, covered with a wire grating, and closed by a wooden slide, or shutter when the lime has been rendered liquid, as above, the shutter or slide is withdrawn, and the fluid runs out through the wire grating into a reservoir, formed on the ground by the well-sifted sand or drift, with which sand or drift the fluid lime is subsequently mixed to make the mortar. Is not this a cleaner way than our clumsy one of sifting the lime in the streets or roads through a coarse sieve, covering with a destructive white powder every thing near, and putting out the eyes of passers-bye? It also makes a better mortar.-A. INTERIM NOTICES. We persist in our refusal. Fidelitas still leaves untouched our representation of the facts, which led us to the painful conclusion that Dr. Birkbeck did not state that which he knew to be the truth, when he described the London Mechanics' Institution as being" triumphant" and prosperous;" and we are resolved not to open our pages to any mere talk on the subject. Fidelitas had better make a speech somewhere, and get the Doctor's man to report it in the newspapers; truth and candour will then be matters of less consequence. H. H.-No. 11. Fact and Nothing Else is quite right. We did at first ascribe to Dr. Birkbeck the honour of "founding the first school in Great Britain for the instruction of mechanics," but we were not then sufficiently informed with respect to all the circunstances of Dr. Birkbeck's connexion with the Glasgow Institution. It has been since established past all doubt, that Dr. Birkbeck was but a Lecturer in "the first school," and that the founder was a very different personage -the justly celebrated John Anderson. There was an address, it is true, got up by some mechanics of Glasgow, in which the honour was transferred from Professor Anderson to Dr. Birkbeck; but thereby hangs another tale of cash lent, of which more anon. Lest any of our readers should think of purchasing Adcock's Engineer's Pocket-Book for 1830, under an impression that the numerous numerical errors which we pointed out in that work for 1829, have been corrected, we think it right to apprise them that they are all-the very worst of them very carefully preserved in this new edition. To use a celebrated phrase, this is too bad. Communications received from Mr. RusselR-a Fl-ms-Novice - Mr. Dowling-Clyde -E. S. L.-A Practical Engineer-T.-Mr. Gilbert P. S. W.-A Youthful Treader on the World's wide Stage-G. R. - An Amateur Turner W.-Mr. Jopling. Errata.-P. 293, col. 2, 1. 10 from the bottom, for Lecroir read Lacroix. P. 294, col. 1, 1. 19. for p. 6, read p. 5 Ib. col. 2, 1, 14, for houts," read "three hours." P. 295, col. 2, 1. 7, for" at Weymouth 5. 30m." read" at Weymouth 6h. 30m." P-299, col. 1. 1. 14, for 49 x2+6x -1590," read "x4— 9×3+6x2 — x=1590 ̧* LONDON: Published for the Proprietor, by M. SALMON, at the Mechanics' Magazine Office, No. 115, Fleet Street; where Communications for the Editor (post paid) are requested to be addressed. M. SALMON. Printer. Fleet Street. Mechanics' Magazine, MUSEUM, REGISTER, JOURNAL, AND GAZETTE. MECHANICAL KNIFE AND FORKCLEANER. Sir,-Your correspondent, "L. A. an Innkeeper," wishes to be informed of some cheap and expeditious plan of cleaning knives and forks. Herewith I send you two drawings of a plan for the purpose that occurred to my mind on reading his inquiry; and as he is an innkeeper, I think he will find it also very useful in cleaning boots and shoes. Fig. 1, shows the end view, and VOL. XII. fig. 2, the front of the machine; the letters A, B, C, &c., refer to the same things in both figures. A is a light iron pulley, fixed on the mandrill C, fig. 2. The rim of the pulley A is faced round with inch timber, round which a strap of thick, spongy, tanned leather, is well glued, which is again covered with a paste made of emery, or brick-dust, boiled in a little mutton-fat and bees'-wax, so that when cold it forms a solid body. This composition may be kept Y in cakes, and rubbed on when the pulley is running; but the best mode to be pursued in these respects will be found out after a little practice. This done, motion is given to the pulley by the foot on the treddle M, which moves the crank-shaft L and pulley K, round which is the card or strap I, driving the pulleys D, A, B, on the mandrill C. The knife being then gently applied to the surface of the pulley A, the knife will instantly become bright, if sufficient velocity is given to the pulley. bock's computations; and others in which we are charged with throwing an undue severity into our strictures. One very esteemed correspondent, in particular, hints that to make matters worse than they really are, we have affected to keep back some blunders committed by Mr. Lubbock; while, in fact, we have made the most of all we could find. Now so little ground is there for this unkind suspicion; so little disposed have we been to make the most of the case, as it stands, against Mr. Lubbock; so much has that severity with which a sense of duty to the public has compelled us to speak of Mr. Lubbock's speculations, been tempered by a feeling of indulgence towards Mr. Lubbock The forks and hilts of the knives may either be cleaned by a stiff circular brush, as shown at e, pulley A, personally-that we have, in truth, kept or by a pulley B, made of board, well glued and jointed together, and grooves turned in to fit the grains and swells of the forks, this must also be covered with the paste above-mentioned. For boots and shoes another mandrill C must be used, on which, instead of the two pulleys A and B, two circular brushes must be put; the one for cleaning off the dirt, and the other for polishing with, after blacking. E, E, are two she-centres, in which the mandrill C runs, screwed through the boss F of the iron frame G, G. The frame-ends G are bound together by an iron pillar or stay H, and fixed to the floor by the two bolts X, X. The pulley K is 24 inches diameter, D4 inches diameter, A and B 18 inches diameter and 4 inches broad. treddle M works on two studs or pins at Y, Y. The Should you think the above worthy a place in your Magazine, you will much oblige me by inserting it, for the use of "L. A." or any other of your readers. I am, Sir, yours, &c. Manchester, Dec. 2, 1829. F. THE SOCIETY FOR THE DIFFUSION OF We have received various communications from friends and correspondents on the subject of our review of Mr. Lubbock's dealings with the tides; some in which we are warmly thanked for so thoroughly exposing the gross fallacy and incorrectness of Mr. Lub back more blunders than we have set forth, and some quite as gross as any which we have made public. One example may suffice to satisfy our friend on this point; as well as any others who may have felt, like him, inclined to doubt the predominance of a compassionating principle in our critical nature. At p. 57, of the "Companion," there is a table of "Times of High Water," taken "from the Tide-Book;" and at p. 58, a table of "Moon's Time of Southing," taken "from the Nautical Almanac." From these two tables, and similar ones, Mr. Lubbock deduces means by methods which we have characterised (p. 310, of our last Number) as being "from the begin ning to the end objectionable." A good many reasons for thus characterising it we have laid before our readers— more than enough, we apprehend, to satisfy any competent judge-but the still stronger reason than any which we have now to notice we kept back, simply because we would not bear harder on Mr. Lubbock than was absolutely necessary. The hours and minutes taken from the Tide-Book" are in mean or clock time, as Rotherhithe Church clock (!!!) can testify; while the moon's southings in the "Nautical Almanac," are given in apparent or solar time; and Mr. Lubbock has in making his comparison and deducing his means, gone on the supposition that the time in both instances was the same! He has never thought of reducing the ap parent or solar to mean or clock time!! Now every one knows that in February and in part of January and March, the clock is nearly a quarter of an hour be fore the sun, while in greater part of October and November the clock is a quarter of an hour later than the sun 4 and that only four times a year do the GILMAN'S IMPROVEMENTS IN STEAM-ENGINES. mean and solar times agree. How irrational must that devotion to theory be, which leads a computer to neglect such a source of error as this; of error, so great, that Mr. Lubbock's computations may from this single cause alone be wrong to the extent of not less than half an hour at a time (a quarter of an hour each way)! Surely no person whose mind is open to conviction can stand up for the credit of computations thus carelessly made; or ask of us farther proof of the justice of that sentence of condemnation which we have felt compelled to pass on Mr. Lubbock and his lucubrations. CYLINDRICAL RAILWAY-CARRIAGE. The following account of a very novel and ingenious description of Railway-carriage, invented by a Mr. P. Fleming, engineer, at New York, is given by Dr. Jones, the superintendent of the Patent-office at Washington, in a recent number of the Journal of the Franklin Institute: "The carriage is a cylindrical body, which may have an axis passing through it, or gudgeons affixed to and projecting from its ends, for the purpose of drawing it. The wheels are iron rims placed around the cylinder so as to encompass it like hoops; these stand at a proper distance from each other, to run upon the rail; they are provided with flanches, or have their faces finished in any form suitable to the rail upon which they are to run. In the inside of the cylinder may be stowed boxes, barrels, bales, or other goods to be transported. When bars of iron, lumber, or other articles of considerable length have to be carried, the traction is performed in a different way; the carriage is then a hollow cylinder, not furnished with ends; the iron bars, boards, or plank, are passed entirely through it, and, of course, do not admit the employment of an axle, or gudgeons. In this case an endless rope is passed round the middle of the cylinder, which is furnished with double rows of pegs to form a groove, or checks, to retain the rope, or band, in its proper place. This rope also passes over a pulley, which is attached to the horse, or other drawing power, so as to work like the large and small wheels of a 323 lathe with their bands. Two, three, or more cylindrical carriages may be made to follow each other, when connected by bands in the same way. "Under this arrangement it is eviIdent that whatever is carried must roll with the carriage; but in transporting some kinds of goods, and particularly in carrying persons, this would, to say the least of it, be very inconvenient. To obviate this objection, a second cylindrical body is placed inside of the first, and is made sufficiently small to revolve within it. This is suspended upon the axis, or gudgeons, and is weighted on one side; so that whilst the outer cylinder rolls upon the road, the inner one will not revolve with it. It is proposed sometimes to make this suspension by the agency of friction-wheels, so as to leave but little more friction than that which results from the rolling of the carriage. The patentee says "What I claim is the use of a cylinder, or other volume of revolution, on a railway, as a carriage, or vehicle for transportation. "I also claim as my invention the use of the endless rope in the manner above described for progres sive motion. By means of this use of the cylinder and traction-rope friction is saved or avoided to a greater degree than by any machine now known. The traction-rope may be employed separately from the cylindrical railway-carriage in any other machine where similar progressive motion is required.'" |