LOCOMOTIVE ENGINE. 459 



about a ton and a quarter, when the engine is empty ; and when filled for working, 

 the weight is about two tons, making the total weight of the engine twelve tons 

 when full. The weight of the engine when empty is ten tons ; and that of the 

 driving wheels and axle is about a ton and three quarters, of which the cranked 

 axle has nearly a quarter of a ton. 



When an engine is required for heavy work, as for carrying goods, and the 

 adhesion of four wheels must be made use of for propelling it, the front wheels, L', 

 are made of the same size as the driving wheels, and coupled with them. The 

 cylinders have then to be placed lower, and inclined upwards towards the cranked 

 axle, in order that the piston rods and guides may clear the front axle, L", as that 

 is raised up to a level with the cranked axle C' and the former position of the 

 piston rod, by the wheels D' and L' being of equal size. The driving wheels are 

 in this case sometimes made less than five feet, in order to increase the power of the 

 engine, as the diminishing of the diameter of the wheels diminishes the leverage of 

 the load upon the engine, or increases the leverage of the engine in moving the 

 load. But the speed of the engine is diminished in the same proportion, as 

 the smaller wheels will advance a less distance than the larger ones in the same 

 number of revolutions ; but this is not material in the carrying of heavy goods, as so 

 great a speed is not required for them. In order to enable the engines to run faster 

 without having to make more strokes in the same time, the size of the wheels has 

 been increased, and a great many are now making with six feet driving wheels ; the 

 size of the cylinders has also to be increased to supply the increased power that is 

 required, and they are made 13 inches diameter with the same stroke, 18 inches. 

 Wheels have been tried lately of double the size, or ten feet diameter, and even 

 larger in some instances, for the purpose of still more reducing the velocity of the 

 piston, and diminishing the loss of power from the resistance of the waste steam, 

 which is the great difficulty in locomotive engines. But it appears very question- 

 able, whether the disadvantages arising from the use of such large wheels do not 

 more than compensate for their advantages in diminishing the velocity of the piston; 

 as there is a serious objection to them in their great weight, which, together with 

 that of the cranked axle, also proportionally increased, is necessarily unsupported by 

 the springs, and therefore the violent shocks produced by the rapid motion cannot 

 be eased by them. A certain velocity of the piston is also required for the effective 

 operation of the blast, and the velocity should for this reason be, probably, not less 

 than 300 feet per minute. Cog wheels, worked by the connecting rods, have also 

 been tried, doubling or trebling the velocity of the driving wheels ; but they are 

 objectionable, from their jarring action with so rapid a motion. 



OUTSIDE FRAMING, &c. The principal or outside frame, N'O'P', (Plates LXXXIX., 

 XC., XCI.,and XCII.,) is placed along the sides of the engine outside the wheels, and 



