TRACTION

This term, which formerly applied only to the transport of goods in wheeled vehicles, has of years been extended to the haulage driving of ploughs, diggers, and agricultural implements. The methods of traction may be according to the source of power ployed, as animal traction, mechanical traction, and electric traction. Animal Traction.—The animals for this purpose in this country r chiefly horses, mules, and a es. many lands oxen are freely employed, and in certain African and countries use is made of the and the camel. In Holland and where on the Continent dogs are ed to draw-carts, but the Cruelty Animals Act of 1854 prohibited use in Britain. In consequence of rapid development of motor the use of animals is rapidly declining, especially in large modern cities, Mechanical Traction.— The mover generally utilized for mechanical traction is either the steam engine or some form of the gasoline tor engine. Suitable types of these be used on railways or tram'ways, is principally for haulage on roads eo ine sae ees driving wheels of large Game prevent sinking in mud, the width rim ranges from 15 in. upwards and bearing surface of the rim is fitted with raised strips of to prevent skidding. The must be able to take gradients as as 1 in 10, and should have an speed, when loaded and with heeds 8 m. per hour. On roads ordinary character horse power cheaper than steam haulage for loads up mica, to 214 tons; for much heavier loads a saving of from 40 to 50 per cent. may be effected by employing steam traction. Much higher speeds are obtained by the tract are, as a means use of the petrol motor, which treaadvantages of transport po e es Many and superseding, the over, and is rapidly tract handied, steam engine, being more easily been and more eco nom more quickly started, of been ical in use. Attempts have also move on tracmade to utilize compre ed air Keble, tion engines, but so far these have not met with much succe . for Where very long and steep gradients or cable traction has have to be overcome, leading advantages over been found to po e the steam engine and the - petrol motor, religious | I these cases a moving steel cable is political placed in a conduit below the level of more BS ear ey and is Cala ad paaied Dede re through a slot in the road. The method was] is in use on some mountain railways and in a few cities. For urban tramway late | traffic the cable system po e es some and | Serious disadvantages, of which perhaps other | the two chief are, first, its want of different elasticity—the system cannot be extend cla ified| ed without heavy capital expenditure; em-| and, second, the fact that a breakdown | #t any point puts the whole system out of action. used Electric Traction.—Ther cit on ere are to-day are many systems of electric traction in In] operation. While differing widely in | details, these are all merely applications. Asiatic| of one common fundamental principle. elephant] Electric current is supplied to an electric else-}| motor, which is connected either directly harne -| or by gearing with the wheels of a veto|hicle and as the motor revolves the their | wheels are driven round and the vehicle the|is propelled. The current employed traction,| to drive the motor may be supplied | either from wires, overhead or underground, as the case may be, or from prime} accumulators or secondary batteries; | carried in the vehicle. In the former’ traction | case the current is generated at a central mo-| station, distributed along the wires, and may | transferred from them to the motor by but it|a traveling contact; where secondary ” or| batteries are employed, these must be cee eat a Ak atc) by a dynamo. The) has rst of t i f To suitable for or railways allWare and ant ome tramways;; the ectric! the motor rears cars and Wad motor iudtet launches. anne aa | usually Owing to the weight of the batteries,, metal, | the utility of accumulator cells for pur-: engine] poses of propulsion is strictly limited., steep | On the other hand, those systems which | average| depend upon current generated at a; trailer,| central station and distributed along: of} conductors are capable of serving wide: is| areas, and are now generally employed | 4 means of traction in all large commumidway ies throughout the civilized world. conductor ese systems may be broadly cla ified and is cording to the method of fixing the simple ducting cable as follows: ‘1) Three-rail Systems.—In these the switch 1duct or is laid on the railway track car is sween the rails, or is fixed a short the tanee above the ground at one side stud the track. It is made of steel, the at the gths being firmly bolted together to of m a continuous conductor, and the viated. ole mounted on porcelain or gla metal yports to secure efficient insulation. studs e current is collected from this third current. 1 by a sliding shoe of iron, and after the ing through the motor is returned this the dynamo along the outer rails. of is system being reliable, inexpensive, underground d capable of dealing with very heavy objection ds, is very generally used for electric consumption Iways. with (2) Overhead Wire Systems.—In sys to as ns of this cla , the current is conveyed mg a copper wire or cable suspended means m standards at a considerable height this ove the top of the car. Contact is ide by 2 trolley, and, as in the pre-