Coach-makers apply distinct names to a great many varieties of springs ; but those which are most generally used may be briefly enumerated. The straight spring, if single, is the single-elbow spring. The double-elbow spring is a straight spring, acting on both sides of the fixed point. It is a kind of spring very extensively used in stage coaches, omnibuses, and light two-wheeled vehicles. Elliptic springs are used single iu some carriages, between the axle and the frame work ; the spring resting on the axle, and being connected with the carriage by means of a curved bar of iron, called a dumb-iron, placed over it like another spring. The spring is then called an under-spring. Elliptic springs are often used in pairs, under the name of springs, the two springs being hinged together at each end, so as to form a long pointed ellipsis. In this way elliptical springs are much used in such four-wheeled carriages as have no perches. C-springs consist of two thirds of a circle, lengthened out into a tangent; the tangent being laid horizontally, and bolted down to the framework of the carriage. When these springs are used, the body is not, as in most other cases, connected immediately with the springs, but is suspended by leather straps, which pass round the back of the springs, and are fastened to the framework near to their base. Telegraph springs are combinations of straight springs in seta of four. Two are placed longitudinally, resting either immediately upon the axles, or upon the lower framework of the carriage ; and two others, placed transversely, are suspended from their ends by shackles. The body is supported upon the centres of these transverse springs. Tilburg springs are another combination of straight springs. Two single•elbow springs are attached to the hinder part of the body, and suspended by leather braces from a transverse spring elevated on an iron standard at the back of the framework. The front of the body is suspended from the shafts by two single-elbow springs with short leather braces ; and sometimes a pair of double-elbow springs are interposed between the shafts and the axle. Dennet-springs are a combination of three straight springs, two of them placed across the axle, and attached at their fore ends to the shafts or the framing of the body, and the third placed transversely, suspended by shackles from their hinder extremities, and fastened to the body at its centre. The bodies of private cabriolets are usually hung upon Csprinf,s, with small curved springs in front, and double-elbow springs frequently added between the shafts and the axle. The combination of springs used in under-spring carriages is the most effective which has yet been discovered for producing the minimum of concussion or motion to the passengers. The body of
such a vehicle is suspended by braces from C-springs; and the frame work of the carriage to which the C-springs are fastened, is supported upon under-springs, which intercept concussion from the unevenness of the road.
Of these various springs, none but the C-springs with leather braces allow universal motion to any important extent. In seme carriages loops of leather or caoutchouo have been used, instead of iron shackles, for connecting straight springs, by which means the motion is rendered pleasanter, and the rattling noise of the shackles is avoided. Another defect of ordinary springs is their want of adjustibility to the weight they have to carry. They must, of course, be made strong enough to sustain the maximum weight they are intended to bear ; but, by being so, they become too stiff to play easily under a light load. To meet the deficiencies of the springs in common use, Mr. Bridges Adams con trived one on the principle of the bow, which will yield in any direction, and may be made capable of adjustment, by means of screws, to a light or heavy load. This spring consists of a single plate of well-tempered steel, forced into a curved form by the tension of a chord of prepared hempen rope, or of a riband of iron or steel, and to which the axle is attached. There are two bow-springs, a b and c d, connected with each other and with the same axle. These aro jointed together at b c, and attached to the body, of which the lower framing is shown at f f, by movable joints at a and d, which allow the springs to leugtheu and shorten in playing. The chord of each bow is in two parts of unequal length, each of which is connected at one end with the bow, and at the other with the axle at c; so that the chord of the bow, a b; takes the direction a e b. and that of the bow, c d, the direction c c d. Among the advantages claimed for them are their lightness and extreme elasticity, arising from the superior quality of the steel, and the absence of the friction which attends the action of the common laminated springs.
All the springs that have been alluded to in this article are bearing springs, for supporting the weight of the body of the carriage, and of the load which it conveys. In ordinary carriages no other springs are used ; but in those employe() upon railways, springs are also used to impart elasticity in the direction of the line of draught, so as to reudor the starting and stopping of the carriages gradual and easy.