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different kinds of roads. As roads are at present constructed, narrow wheels are not so injurious as formerly; and, until certain data be obtained, it will perhaps be advisable to make the tires not less than If, or more than 2^ inches.*
The convenience of travellers has been very little attended to in arranging the size of the bodies, and the height and depth of the seats inside coaches.
The object should be to enable the traveller to sit in such a position as will admit of his performing a long journey with the least fatigue.
A slight degree of consideration will make it clear, that the seats should be so high as to give ample room for the legs, and thus allow the whole length of the thighs to press upon the seats, and be supported by them. If the legs have not room to be nearly upright, and are therefore thrown forward, the fore part of the thighs are elevated, and the weight of the body is made to rest on the upper part of them, so as to produce a partial strain on the muscles in supporting the body.
* In France, the law requires that every diligence, which, with its loading, weighs one ton and three quarters, shall have the tires of the breadth of inches; and that every diligence which weighs three tons shall have the tires of the breadth of 4£ inches. As the roads of France have of late been much improved, the very great inferiority of coach-travelling in that country to what it is in this may be mainly attributed to this very absurd law respecting the tires of wheels. If, as in this country, there was no law for regulating the wheels and weights of diligences, the roads of France would soon be covered with light fast travelling carriages.
In addition to this, the body is thrown backwards, and the weight of it is thereby supported with a considerable strain on the muscles of the back, which leads to fatiguing them. There can be no doubt that a person who sits on a high, deep, and broad seat, and in an erect posture, as he does naturally on a well-formed high chair, will suffer less fatigue than one who sits on a low seat, and in a reclining posture.i
For these reasons, the floor of the well should be 7 inches below the body of a coach; the seats should be 15 inches above the bottom of the well; the cushions of them should be 4 inches thick, the depth of them 18 inches, and the breadth of them
* This is too true of all sorts of stage-coaches on the English roads. Much requires to be done to improve the mail-coaches, so as to render them less fatiguing to travellers going long distances. At present, the whole weight of a traveller's body. is supported on the projecting bones at the root of the spinal column, which itself is unsupported throughout its whole length; as, from the perpendicular back given to the seats, the shoulderblades are the only parts of the trunk which can touch them. If in the new coaches the seats should be made of the breadth proposed, and if they be made 1 \ inches higher in front than at the back, then the whole of the thigh will find support, and by the action of its muscles considerable relief will be given to the other parts. Much may also be done to give relief to the traveller, by improving the hand straps; long pendulous straps, with their loops adjustible to different heights (as in some of the French diligences), would afford great relief, by affording a rest for the elbow of an arm passed through them.— Extract from a Letter of Sir John Robisson, Secretary to the Royal Society, Edinburgh.
44 inches. The height of the roof from the cushions should be 3 feet 6 inches, and the width of the door 21 inches.
By making the depth of the seats 18 inches, and allowing 2 inches for the breadth of the back panel and inside stuffing, the breadth of the side panels, outside, will be 20 inches. They should slope from the seats to the roof with a rake of 1^ inches.
According to the established law of mechanics, that the higher the wheel the easier a weight upon it is drawn, when a carriage has two sets of wheels, one of which is necessarily lower than the other, the body of such a carriage should be so constructed, and so placed over the wheels, that the greatest possible portion of the load should be over the hind wheels. When the carriage is loaded, the fore wheels should press but lightly on the ground, only in such a degree as is necessary to prevent the fore part of it from tilting up.
In order to place the weight as far behind as possible, the body should be set as far back as it can be set, with allowing for the opening of the door. By rounding the door at the bottom, it may be set 4 inches within the front part of the rim of the hind wheel.
The hind boot should extend to 4 inches outside of the hind wheel, and this will be found to make its length 36 inches.
The height of the hind boot should be 32 inches, and the breadth of it as great as it can be made, by setting the side springs as far as possible asunder. If the side springs were fastened under the hind axle, the hind boot might be made of the whole breadth of the body of the coach. *
The bottom of the fore boot should be on the same level as the bottom of the hind one.
The height of it should be 32 inches.
To give sufficient space for the passengers to move behind the coachman's seat, there should be 12 inches between the body and the seat, and the seat of the coach-box should be 15 inches wide. The fore boot, at the bottom, should be 25 inches in length, from a line drawn from the widest part of the body, 30 inches in breadth, and 34 inches in height.
With a view of explaining how necessary it is to make use of long and pliant springs, the following extracts have been taken from the treatises of Mr. Davies Gilbert and Mr. Edgeworth.
Extract from the Treatise on Wheels and Springs for Carriages, by Davies Gilbert, Esq., M.P., F. R. S.
"Springs were in all likelihood applied at first to carriages with no other view than to accommodate
* One horse carts are in common use at Paris capable of holding 30 ewt, which are supported on horizontal springs, 5 feet long, fastened under the axle. A moderate-sized horse draws one of these carts with great ease when fully laden. There are also in Paris a number of omnibusses supported on springs in this way.
travellers. They have since been found to answer several important ends.
"They convert all percussion into mere increase of pressure; that is, the collision of two hard bodies is changed, by the interposition of one that is elastic, into a mere accession of weight. Thus the carriage is preserved from injury, and the materials of the road are not broken; and, in surmounting obstacles, instead of the whole carriage with its load being lifted over them, the springs allow the wheels to rise, while the weights suspended upon them are scarcely moved from their horizontal level. So that if the whole of the weight could be supported on the springs, and all the other parts supposed to be devoid of inertia, while the springs themselves were very long, and extremely flexible, this consequence would clearly follow, however much it may wear the appearance of a paradox, that such a carriage may be drawn over a road abounding in small obstacles without agitation, and without any material addition being made to the moving power or draught." .
Extract from a Letter of Davies Gilbert, Esq.
"A carriage without springs, moving over a rough road, has to be lifted over obstacles, or out of depressions, and all the power expended in overcoming inertia is pure loss; but the force exerted in elevating the weight is in a great measure by the preceding or subsequent descent. Now, under the supposition in my paragraph,