under fide of the flank touches nothing; the only friction of this joint then is that of polifhed brass, moving under oiled leather, which, from the fmoothness of the furfaces, and their proximity to the centre, muft neceffarily be very fmall. That the air cannot enter the machine by this joint, is evident, becaufe the fuction being inwards, and water or oil in the cup above the leather, the air, preffing to get in, excludes itfelf, the joint being in fact a circular valve. This machine has many advantages over other pumps, befides its throwing out a greater quantity of water than any hitherto invented; particularly its not being liable to accident, there being no part of it which by working can be fuppofed to give way; the axis being of iron, about two inches fquare, and only two feet and a half long. It cannot choke with fand, ballaft, or any thing which prevents the operation of other pumps; and an accident from a cannon ball can as easily be repaired in this as any pump whatever, by replacing the part fhot away; for the whole machine takes to pieces at different joints fcrew ed together; and an entire machine may be fitted up in a quarter of an hour. The inventor has a patent for Great Britain and the plantations, notwith landing which he propofes to oblige those who have occafion for fuch machines on the most mo. derate terms; one of them will last 40 years, and for a common merchant-fhip will not coft 301. Introductory Definition. HAT we may be under. flood, in what we write on the fubject, we hope the candid will allow us the following leading principles, or maxims, without fearching for, or even expecting, a perfect ftyle or elegance of expreffion. I. That all carriages go eafier down hill than on level ground, eafier cn level ground than up hill, and barder up hill, as the fine of the angle of afcent (or nearly fo), till the angle becomes about 20°; or till the perpendicular afcent may be about one-third of the bafe line, at which time no power can be faid to draw a load up the fame fmooth hard plane that itself ftand upon *. . may II. That fandy roads (and fuch fort of fine gravel as may be confi dered as next akin to fand) are, generally speaking, the most pleajant and beft roads we have. But, though in general they may be fo, yet that meaning is far from being univerfal; for it feldom happens that the roads under the general idea of fandy roads, will bear much work in long, continued, gentle rains; therefore fuch roads must have breadth, in proportion to the work they are expected to bear, which muft ever be at the difcre By fmooth and hard is meant, fuch a condition as a mafon may be fuppofed to leave the face of a ftone in from his axe or chiffel, or when the common roads are in their hardeft or fmootheft condition. tion tion of him or them who have the directing power. III. That pavements can never be confidered as commodious roads, tho' often to be preferred in particular places and cafes. IV. That wash roads (however applauded by fome) are rarely with out notorious exceptions; though in particular places they too may be ufeful and neceffary. V. That roads whofe furfaces are chiefly composed of hard, rough gravel, replete with loofe pebbles, (or other irregular large ftones), though they may be comparatively good in dirty feafons, cannot be efteemed the moft eligible roads, whether confidered under faddles, traces, or wheels, VI. That broad wheels wear out roads, and themselves, much less than narrow ones; and (cæteris paribus) in drying feafons, even confolidate the furface of roads. This is not only demonftrable by the eftablished laws of mechanics, but, we prefume, fufficiently proved by the last ten years experience on the great roads round the metropolis for about an hundred miles diftance; but we apprehend, as there are many intervening roads, that it doth not yet amount to half the carriage of the kingdom. VII. That great inconveniences arife from the prefent manner of ufing broad wheels, viz. by their making the ruts or tracts too narrow and irregular at the bottoms for horfes to travel in: for though yet much this inconveniency may, in fome VIII. That to remedy the impedi * Where new roads are to be made through fuch a foil, might it not be of great fervice to fow it first with Timothy grafs, or fome vegetable of the fame nature? The roots of this grafs, according to Mr. Rocque, are fo ftrong, and fo interwoven with each other, that they render the wettest, softest land, on which a horse could not find footing, firm enough to bear the heaviest cart. [See p. 144.] ment ment arifing from the prefent way of ufing broad wheels, is a province for a fuperior wisdom and authority*. gons, it would generally help to preferve and commode the roads, and the horfes path, and would have its ufe to different and particular people and neighbourhoods. carts with broad wheels go only in the middle of the waggon-track, or other difference in the tolls or number of cattle drawing? perhaps no more than two, if under an augmented breadth. Nor can we help wifhing to be indulged with a fight of our humble opinion in print (conceived fo long-Query, if not better to have fince as the year 1755, and propagated among our affociatest) which, in plain truth, amounts to little more than the finding 2 means to have one axle, of all four-wheeled carriages, longer than the other; fo that the inner distance of the head of one pair of wheels be less than the outward diftance of the other; at least two feet, or perhaps two feet two, four, or fix inches; and then it would be lefs material what breadth the wheels themselves were of, fo that their tread be flat; or if one pair were two or three times the breadth of the other, provided the whole breadth of the four wheels be at least two feet, or other legal breadth, and the track made by fuch waggon twelve, thirteen, fourteen, or fifteen inches broad (and words can explain fuch liberty without danger of litigious confufion). If carts were to have the diftance of theirs either equal to the greatest or leaft tread of the wag IX. That the attrition, or friction, between the common wood axles. and the boxes of the wheels, is not more than one fixteenth of the whole draught . The projector of a late project, under the affected and pompous epithet of Friction annihilated, having allowed, and rationally proved, that his project could never amount to more than about half a horfe in a team of eight; and though that projector had flattered himself that his project came as near the total preclufion of that friction as the nature of things would admit; yet was he forced to acknowledge too, that his invention, when applied to carriages, muft have fome allowance farther for its own weight, which might be confidered as goods to be carried for nought ||. * Yet a certain method is humbly hoped from the well-collected opinion of the whole kingdom in parliament affembled. And hinted in a ludicrous petition to the editors of the Gentleman's Magazine, but was never touched by the prefs that we know of. By a general act relating to waggons, paffed latt feffions, waggons, &c. with nine inch wheels, fo conftructed as to roll fixteen inches furiace, are to pay but half toll; nine inch wheels not so constructed to pay twice, and narrow wheels three times as much. But the attrition, or rubbing of the fides of the wheels, in deep ruts and rough ftony roads, is indefinitely more. 1758. See the Chronicle, and other papers, about Auguft or September, Though Though this impediment of weight is a very material one in the iron arms now in ufe, it is amply compenfated by oil inftead of greafing, and the poffibility of drawing greater loads than wood could bear without firing, or retarding the speed of business. X. But there is another fort of friction, or rubbing, relating to wheel-carriages, of much higher import than that of the axis, especially in the narrow wheels, which is, their rubbing against the fides of the ruts when they get of any confiderable depth; which muft happen from various caufes; as, firft, whenever a wheel follows another thinner than itself, if both happen to tread fo as to go exactly in the fame track, this friction will be on both fides of the following wheel, before it can touch the bottom of the rut made by its forerunner: hence the edges of new wheels wear off much faster than the edges of old ones; and if they tread a fmall matter wider, or narrower, the impediment is greatly increafed, which impediment frequently happens from the imperfection of workmen; a circumftance not to be avoided. Whenever the bottoms of the ruts are compofed of large rough ftones, fome wheels, narrow ones efpecially, will get more on one fide, and fome on the other, as happens on rough pavements, but generally much worfe in common roads, though lefs confpicuous: the wheels are perpetually rifing and falling from one ftone to another, not only from the fummit to the pit-hole immediately before it, but when the edge of the wheel happens a little befide the crown of the ftone, probably flides fide ways off fuch ftone, with a forcible fhock, into the collateral depreffion; whilft every fuch flip wears off fomething from the wheel, fomething from the ftony road, and fome labour from the cattle drawing fuch load; and at every fuch flip the very ftone from which the wheel hath flipped rifes more or less in proportion to the fhock, till at length that very ftone is worn out, and forced above ground, from whence probably it falls again under the purfuing wheels, as if on purpofe to be ground to an impalpable powder, by the most facile means that art can contrive, and from whence wind or water conveys it into one. of their own fluid elements. XI. That this fort of friction, rubbing, or grinding, from the edges or fides of thin wheels, is much greater than in the broad ones. Hence, it is prefumed, the broad ones must last longer in proportion to the expence, and require less power to draw them with the fame load. XII. That high wheels will always travel eafier than low ones, till their own weight becomes an incumbrance, equal to the difficulty of furmounting obftacles by their fhorter radii. Now, we apprehend this incumbrance of the weight of wheels only will increafe nearly as the fquares of their diameters: hence, a wheel of double the height would have quadruple the weight; one of three times the height, nine times the weight, &c. but it may likewife be observed, that though the fmall wheels are capable of bearing the fame trial of ftrength as the large ones at first, yet certainly the large ones must be pre fumed fumed to wear longer, as the points that must come in contact with the road, to wear them out, are lefs frequent in proportion as the lineal dimenfions only (being of the fame breadth) where they tread the earth. We apprehend too, that mechanics and experience will nearly coincide in the proof, that wheels for carriages, to be drawn by horfes, and made of fuch timber as England moft aptly produces for the purposes of heavy loads, will be found to be fomewhere between four and fix feet diame ter. XIII. That the expence of fimilar wheels may be confidered nearly in proportion as their weights. Lower wheels, however, might be more ufeful if the roads were more even in their general furface; but the difficulty of furmounting the common obftacles of roads must prevail, for fome time at least, against very low wheels. N. B. The weight of wheels is not quite fo pernicious as if the fame lay in any other part of the carriage, or in the goods to be carried; but the difference is no more than that they add no friction in their boxes, which (by No. IX.) is only one fixteenth part; and that they, in fome meafore, prevent the overturning of high loads, by keeping the centre of gravity of the whole fomething lower than it would be, if the wheels were lighter. It is obferved that gentlemen of fpeculative faculties, and thofe who practife the carrying business, generally disagree in pofiting the goods in the waggon. The former prove by their art, (experimentally) that the load draws the eafieft when the heaviest part lies upon the hinder (as the larger) wheels. But, as thefe accurate experiments, and their conclufions, are generally drawn from regular plains, it is prefumed, that they frequently overlook that great advantage arifing from the ftrength of the thill-horfes when exerted in lifting the low wheels out of their hole, which may be more than equivalent to the height of the hinder wheels; but this being an undeterminable point, may be fruitlessly contested for ever. Though a late author (Mr. Bourne), notwithstanding the ill fuccefs of his public experiment near London *, has certainly merited greatly of mankind by his new-invented waggon, and his treatise wrote on the fubject of roads in general; yet it is much to be feared that feveral objections mult arife in practice, which he was not at that time aware of. As firft, it is prefumed that the lowness of his wheels are too far in the extreme, if he is not really mittaken in his reafoning upon their furmounting of obftacles, which may often be struck or driven before the wheels with a fliding motion, before they can mount the fummit of fuch obftacles; in which cafe the wheels of two or three times the height would have greatly the advan. tage. This great cylindric length would likewife have the fame kind of impediment, in every turning, as the conic wheels would in going ftrait forward, as he has rightly obferved. |