It his been a favorite' idea for many years with amateur and professional mechani cians (especially the former) to make a light carriage which could be used upon ordi nary roads, and which should contain a steam-engine and boiler to propel itself. In spite of innumerable attempts no permanent success has yet been obtained in this direction, notwithstanding that great progress has been made in constructing steam traction engines for common -roads. The fact seems to be th it, whilo a self-pro pelling steam-carriage to carry only the weight of a passenger or two can be matte without much difficulty. its cost will be proportionately so heavy, and the trouble of it order as well as of working it, so great, that it will not succeed commer The true application of steam upon common roads is in the drawing of heavyloadi which would otherwise require an inconveniently large number of horses. Engines for this purpose are called traction-engines, and their use, notwithstanding determined. and too often ignorant opposition, seems to be yearly on the increase. Traction-engines may be divided into two classes—those with rigid tires on their wheels. and those with flexible tires. The former class is the older, and includes many ingenious but mistaken contrivances for laying down what wits equivalent to an endless railway for the engine to run upon, which was at one time thought by ninny essential to its success. The host
engines at present made with rigid tires are those of Messrs. Aveling and Porter of Rochester, which are simple and substantial in construction, and are used largely both in this country abroad. Of the second class of traction engines those fitted with Thomson's patent india-rubber tires, and by the inventor called road.-steamers, are the only ones that have conic into anything like extended use. These tires are simply rings of india-ruber, 4 or 5 in, thick, stretched over the rim of the wheel, and protected by a flexible Miele of steel shoes from being damaged by stones, etc. The advantage of flexi ble tires is the greater adhesion (in proportion to weight) which they give to the engine, and the saving the machinery from shocks and jars. They will doubtless he still more largely used when more lengthened experience has perfected their construction, hut the great cost of the india-rubber has hitherto much hindered their extended adoption.