58 RAILWAY CONSTRUCTION. 



towards the centre ; but upon entering a curve they come into 

 play, and allow the truck to move out sideways to the right 

 or left, according to the direction of the curve, the one pair of 

 links assuming a flatter angle, while the other pair approach 

 nearer to the vertical, the extent of side movement depending 

 on the amount of the curvature. When the engine enters the 

 straight line again, the bogie truck resumes its central position. 



The Bissell truck consists of one pair of wheels connected 

 to a triangular framework, as shown in Fig. 46. The axle-boxes 

 are attached to the side of the triangle which lies parallel to the 

 axle, the other two sides terminate in a circular ring which 

 works round a centre pin fixed to the engine. These two sides 

 are practically the radii of a given circle, and permit a large 

 amount of lateral movement, which can be controlled by placing 

 suitable stop-pieces to limit the side play to the extent desired. 



Radial axle-boxes have been tried on the engines of some 

 railways. In the best types the opposite boxes are braced 

 together by a diaphragm, or plate-iron framework, to ensure 

 that both boxes work together. The curved faces of the horn- 

 blocks, in which the radial axle-boxes slide, are struck from 

 a centre taken at some point to the rear of the normal centre 

 line of the axle, and stops are placed at proper distances to 

 control the extent of lateral movement. Although the advocates 

 of radial axle-boxes may urge some points in their favour, there 

 are few engineers, if any, amongst those who have had practical 

 experience of both systems, who would for a moment claim for 

 the radial axle-box anything but a modicum of the many 

 advantages obtained by the four-wheeled bogie truck. 



As one of the principal functions of a four-wheeled bogie 

 truck for an engine is to act as a path-finder, or guide, to the 

 ether wheels which constitute the fixed or rigid wheel-base 

 portion of the machine, it follows, therefore, that the full benefit 

 of the bogie truck can only be obtained when it is placed at the 

 leading, or front, end of the engine. In this position the bogie, 

 with its swivelling arrangement and smaller weights, is the 

 first to pass over the rails, and in doing so shapes the course 

 and prepares the way for the easy running of the heavier wheel 

 weights which have to follow. When the bogie truck is placed 

 at the rear end of the engine, its action is restricted to affording 

 lateral movement only, and the driving and coupled wheels have 

 to force or pound themselves round the curves in a jerky, 



