368 PROCEEDINGS OF SECTION H. 
The tractive force and steam consumption of an engine are 
directly proportional to cylinder volume, and inversely pro- 
portional to wheel diameter, and there is no need, from a 
theoretical point of view, of large wheels, even in the fastest 
engines. Small cylinders coupled to small wheels should give 
the same result as large cylinders coupled to large wheels. 
In early days huge driving wheels of & ft. to 10 ft. diameter 
were used in the hope of obtaining high speed, but of late years 
the tendency has been to abandon these large diameters. By 
reducing size of cylinders, pistons, and wheels, and driving them 
at a faster rate, many advantages are obtained; the size and 
cost of these parts are reduced, they are more easily handled, 
and weight is saved, which enables additional size to be given 
to boiler and furnace, and thus steam supply and speed in- 
creased. Further, with reduced diameter of wheels, the rigid 
wheel base can be shortened, and so curves passed more easily, 
and the smaller weight of that part of the machine that acts 
on the road without the intervention of springs must be a relief 
to rails and sleepers. However, the increased speed of rotation 
with small wheels necessitates better balancing, for the in- 
jurious actions due to imperfect balance vary as the square of 
the number of revolutions made in a given time. The locomo- 
tive of the future, in the writer’s opinion, will be one with a 
very ample boiler and furnace, and cylinders, wheels, and 
mechanism of very moderate size, scientifically designed to save 
every ounce of unnecessary weight, of the strongest : possible 
material, with large bearing surfaces, and balanced in the best 
possible manner. 
200 
400 
496 
Normal balancing of crank shaft and pair of wheels at unit 
radius. Revolving weight at each crank pin, 600 lbs. The 
