CRANKED AXLE. 



by connecting the rods with spokes at right angles to each other. 

 By such an arrangement, the combined effects of the two cranks 

 will be invariable, or nearly so, the effect of either increasing 

 exactly as that of the other decreases. 



10. The cylinders are sometimes placed between and sometimes 

 outside the wheels. 



If they are placed between one pair of wheels the axle of another 

 pair is formed with two cranks, placed at right p5<r 



angles to each, which are worked by the con- 

 necting-rods of the pistons. 



Such a double-cranked axle is shown in 

 tig. 2, the cranks being seen in a position 

 oblique to the plane of the diagram. The 

 connecting-rods are understood to be attached 

 to the cranks at B, and the wheels, which are 

 to be driven, are keyed upon the extremity of 

 the axle at G. 



When the cylinders are placed outside the 

 wheels, the connecting-rods are attached to 

 two spokes, one upon each of the wheels which 

 they are intended to drive, these two spokes 

 being in positions at right angles to each 

 other, and the wheels being keyed upon the 

 axles, so that b the wheels and axles turn 

 together. 



11. It may be stated generally that the 

 wheels of railway vehicles and engines do not 

 turn upon their axles like those of common 

 road carriages, but are always fixed upon the 

 axles, so that the wheel and axle turn toge- 

 ther, and, consequently, whether the force 

 of the connecting-rods act upon the spokes of 

 the wheels, or upon cranks formed upon the 

 axle, they will be equally efficient in impart- 

 ing rotation to the wheels and consequently 

 impelling the engine. 



12. The locomotive engine is commonly sup- 

 ported on three pairs of wheels. In some cases 

 of small and light engines there are only two 

 pairs, and in others there are four pairs. 



The general form and disposition of the parts of a locomotive 

 upon three pairs of wheels is shown in fig. 3. In this case the 

 two cylinders are placed immediately in front of the fore wheels 

 and under the chimney. The intermediate pair of wheels are 

 driven by the connecting-rods. 



117 



