A
B[(d + c)2n],
and the diameter of that area,
D = √([(d + c)2n]A/B
.7854)
which is the boiler diameter in inches, to which add D/16 on each side, or in all D/8 as the room to be left between the sides of the boiler and first tube.
The diameter finds its maximum limit in the gauge less the two half breadths of tire, and two or three inches allowance for attachment to the frame and other mechanical incidentals. The length must be enough to carry the leading wheels a sufficient distance from the centre of gravity of the engine.
ADAPTATION OF THE LOCOMOTIVE ENGINE TO THE MOVEMENT OF RAILWAY TRAINS.
358. First, as regards the nature of the traffic.
There are certain necessary causes of a bad application of power upon railroads; for example, when the trains are very much heavier in one direction than in the other, as we are obliged to use the same engine both ways, because when it arrives at one end of the road it must go back to start again. Where the traffic requires to be worked chiefly up hill, we use an engine much heavier to ascend with the load than is necessary to descend without a load. Different objects of transport require different speeds. Perishable freight, such as ice, beef, pork, cattle, &c., requires to be moved in much less time than grain, lumber, flour, coal, and manufactured articles. As a general thing, the difference between the characters of freight engines, as regards the nature of the traffic, can be adapted only with a view to amount, disregarding the nature.
With passenger traffic, however, there is a great variety of speeds made use of, and consequently may be a greater difference in the proportions of engines depending entirely upon the nature of the traffic.