CARRIAGES. This subject, in detail, would form many an ample volume. The great variety of opinions, the imperious demands of locality, and the appropriation to particular purposes, must inevitably create a curious diversity in the practices of a nation. Confining ourselves to gene ral principles, we shall discuss only those points which serve as a general guide, and may prove useful in giving the reader some idea as to the several properties of the vehicles now in use.
1. We consider ease of draught as in dispensible. For this purpose the fore wheels of a carriage should always be sufficiently large to bring the centre of the axle to an angle, of about fifteen de grees, with that part of the haime, or collar-frame, on which the trace fixes ; that being ascertained to be the best rela tive position between the animal and what he has to draw at.
2. We look to proximity of rotation, thatis, the place where the wheel touches the ground, and its relation to a perpen dicular draft from the croup of the horse, as being an essential matter : for the draft will assuredly be more oppressive in pro portion as the point of rotation is removed. Hence long shafts, great space between the fore and hind wheels, and all the re presentatives of those primary errors, should be, in tote, abolished.
3. We judge the size of wheels, that is the length of lever, by which they are moved around their axis, to be of the greatest moment.
4. Where a road is firm, we hold it ex pedient to reduce the bearing point, name ly, the edge of the wheel, into as small a diameter as may be found capable of sus taining the incumbent pressure.
5. Where roads are soft and quaggy, we deem the broad tire to be preferable; both because it bears up the load, and allows of less sinking, whereby consider able opposition would be created; and that such a construction is more favour able to the track in which the carriage may have often to travel.
6. The axis of every wheel ought to move with as little friction as possible : this may be effected by making the spin dle as small and as short as circumstances may allow; taking care to lubricate the connecting parts well, so as not to allow of the smallest tendency to adhesion.
Wheels intended for travelling over un equal surfaces should be dished, so that the spokes may successively be upright whenever they come under the axle. The bend of each end of the axle downwards is a convenience, and contributes to the foregoing effect, while it causesIthe up.. per parts of the wheels to diverge, and gives more scope for the body of the ma chine : in some instances, where light but bulky burthens are in question, this is a desideratum; though it contracts the space between the points of rotation, and renders the machine more liable to over. turn. The load should generally be car ried more in the centre of four.wheeled carriages than is usually done. Carmen have a great partiality for burthening the fore.wheels : this is a most absurd prac tice, because they, being less in diame ter, are more subject to be impeded by low ob stacles th an the hind wheels, which, being larger, travel over ruts and clods with much more facility. In regard to the height of loads, it is proper to state, that whenever a line drawn perpendicular to the horizon, and touching the corner of a square load, touches the ground on the outside of the tire of the opposite wheel, the carriage must overset, the line of gravity then becoming exterior to the support ; and vice versa. From this we see, that loads carried low are in general very safe ; while such as are injudiciously ele vated, which too many of our stage coaches are, teem with danger. In two wheel carriages, the load in going down hill bears extremely heavy on the shaft horse : this should be obviated by cock ing the cart backwards, according to the practice in the west of England.