54 RAILWAY CONSTRUCTION. 



round sharp curves is detrimental to all the parts brought into 

 contact. Not only is there the constant tendency to mount the 

 rails, and spread the gauge, but the tiny shreds of steel scattered 

 all along close to the rail particles ground off' the rails, or off 

 the wheel-tyres, or both testify to useless wear, unnecessary 

 friction, and great waste of motive-power. 



The gradual increase of accommodation and conveniences in 

 the carriage stock of European railways led to the gradual 

 increase in the length of the vehicles. The six- wheeled carriage 

 superseded the four-wheeled carriage, on account of its increased 

 steadiness when running, but the introduction of long sleeping- 

 cars, dining-cars, and corridor cars necessitated some better 

 wheel arrangement than the ordinary six-wheel type could 

 supply. The six wheels had been spread as far apart as was 

 admissible for carrying weight and passing round curves, and 

 something had to be done to meet the demand for still longer 

 carriages. Many of the six -wheeled carriages at present running 

 on our own home lines have a fixed wheel-base as long as 22 feet, 

 and with this length the horn-plates must undergo a very 

 considerable strain when adapting themselves for the passage 

 round curves of small radius. On a curve of 15 chains radius 

 (990 feet) a chord of 22 feet will have a versed sine or offset of 

 0*73 of an inch, and on a curve of 10 chains radius (660 feet) an 

 offset of I'lO of an inch. Fortunately, curves of the above small 

 radius are not very numerous on our main lines ; but wherever 

 they do occur, the conflict between the long fixed wheel-base 

 rolling-stock and the permanent way must be very severe to 

 both. Several descriptions of eight-wheeled carriages have been 

 tried on our home lines ; but the system which is now most in 

 favour is the ordinary bogie truck, which has been in use for so 

 many years on all American railways. A bogie truck is really a 

 short carriage frame complete in itself, with its wheels, springs, 

 and brake appliances, and is attached to the under side of the 

 carriage body by a central pivot, round which the truck can 

 swivel or rotate sufficiently to adapt itself to the curved portions 

 of the line. With a bogie truck at each end of a long carriage, 

 the vehicle will pass as easily round curves as on the straight 

 line, side pressure, or grinding against the rails, is obviated, and 

 friction is reduced to a minimum. The bogie truck may consist 

 of four wheels or six wheels, according to the length and weight 

 of the carriage to be supported. 



