Book IV. 



CARTS. 



429 



axle {Jig. 381.) the cart, &c. becomes much less liable to such accidents, because the 



centre of gravity (g) and the centre of suspension 

 (the axle) are brought much nearer together ; the 

 former being placed nearly over the latter, at a small 

 distance only from it. A horse falling with a loaded 

 cart so constructed, will experience but little increase 

 of weight upon him while down : the cart will be 

 divided as before, by the line a b, into two parts ; but it 

 will be observed, these portions differ but little in 

 their respective magnitudes. The centre of gravity (g) will be thrown forward, but 

 in a very trifling degree. In carts, &c. it will almost always happen that the centre of 

 gravity will be above the point of suspension (the axle) ; but in gigs, &c. the body may be 

 placed so low that the centre of gravity may fall below that point, when the body will 

 ftlways maintain an erect (i.- e. a horizontal) position, and, should the horse fall down, 

 will operate to lift him up again. A gig so constructed would be almost beyond the 

 possibility of those serious, and frequently fatal, accidents, which occur from the falling 

 of the horse. {IV. Baddeley,jun. in Mech. Mag. vol. xii. p. 204.) 



2748. The power of wheels has no dependence on the height of the wheels, or the length of their spokes, 

 but depends wholly on the power of draught that is joined to their axles, and to the forward motion, or 

 the progress of the carriage. If the carriage were placed upon skates completely polished, and upon 

 smooth ice, it would be drawn by as little power as if it were placed upon wheels. The use of wheels 

 is to lessen the resistance to the carriage by friction, or rubbing upon the ground, or upon the floor upon 

 which the carriage is to be moved ; that resistance is least of all when the ground is hard and smooth, 

 such as a rail-road of iron ; it increases upon soft and upon rough ground ; and it increases still more 

 when the carriage must be drawn up an ascent, according to the steepness of the ascent, because the 

 power of draught must be able to lift the carriage, it may be said, step by step, up the ascent ; and when 

 the ascent is soft or rough, more power of draught is necessary. When the wheels are dished they plough 

 the soft ground, and grind the rough ground, and thereby they increase the power of resistance, and require 

 more power of draught to overcome the absurdity of their own form; and thus they cause the continual 

 shaking of the joints of the carriage, and the wearing of the iron and of the wood of which it has been 

 made. Narrow wheels are drawn rather more easily through small loose stones ; but, upon every other 

 kind of ground, broad wheels that are rollers are drawn more easily, or with less power, and the benefit of 

 them to the roads is greater according to their greater breadth. High broad wheels do not sink so deep 

 into soft ground as low wheels do ; but, if the low wheels be made broader, the benefit obtained will be in 

 proportion to the additional breadth. The axles of high wheels turn seldomer round, or the wheels turn 

 sekiomer round the axles, which is an advantage; but high wheels must be weightier than low wheels, 

 which is a disadvantage. High wheels are useful to carry great stones, or great trees, under the axles ; 

 and loads of every kind, alive as well as dead, ought to be hung as low as possible. And every load ought 

 to be hung, or to be placed, upon springs, which will allow the carriage to be lighter ; and the lower it is 

 hung, or placed, it will be so much safer from overturns, there will be less shaking, and less power of 

 draught will be required. {Sir Alex. Gordo7i, in Farm. Mag. vol. xx. p. 150.) 



2749. The construction of wheels has been much improved by the introduction of cast-iron naves or 



stocks These stocks are found particularly suitable for warm 

 climates, and scarcely any others are exported. Messrs. Mor- 

 ton, of Leith Walk, have renewed the spokes in them after 

 they have been in use twenty years, and found the stocks as 

 good as when new. {Gard. Mag. vol. vi.) In England wrought- 

 iron spokes have been employed, which are found to succeed 

 perfectly, and, from their durability, will, in the end, be found 

 cheaper than wood. 



2750. Jones's improved iron wheels (Jig' 382.) are 

 formed wholly of cast and wrought iron. The 

 felly, or periphery of the wheel (a), is made of 

 cast iron, with conical holes on the outside, con- 

 tracting towards the centre, through which the 

 spokes, made of iron rods, are to be passed, and 

 secured in the box, or nave (6), near the centre 

 of the wheel, by nuts screwed on to the reverse end 

 of the rods, by which means they are drawn tight. 

 {Newton s Journal, vol. i. 2d Series, p. 154.) 



2751. A great improvement in the construction of 

 axles for carriages, carts, and waggons, has been 



made by George Burges, Esq. M. A. of Cambridge. Instead of one circle moving 

 within another, as in all common axles ; or one circle moving within another, this other 



having grooves for retaining oil in the manner of the 

 patent axles ; Mr. Burges's axle is a circle {Jig. 383. 

 a) moving within six points, formed by six equal 

 convex segments, which hold oil in their angles {b) : 

 the friction is thus reduced to a minimum in theory ; 

 and with case-hardened iron, and abundance of oil, we 

 should think it could not be otherwise in practice. 

 Mr. Burges has had the axles of his own carriage 

 constructed in this way for some years. ( Gard. Mag. 

 vol. v.) 



2752. The Scotch one-horse coup cart is used either 

 without or with {Jig. 384.) a frame for the purpose of 



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