On railways, a steam engine will rea dily draw 200 tons 12 miles in an hour, which, compared with a horse at 12 cwt., 8 miles, with 12 traction, is 4000 x 12= 48,000 to 1152, or nearly 42 to 1. Hence, the engine operates with the power of 42 horses, and if of greater estirnatosd power, the difference is lost in imperfect contact of wheels, in friction, dec. If the horses' speed were taken at 9 or 10 miles, it would accord with cruel practi ces which ought not to be data, that this would reduce the engine's power only to 35 or 36 horses.
But an engine can work 24 hours per day, and a horse but 11 hour at this rue; hence, the working power of the engine would be 16 x 42, or 672 horses.
The cost is another consideration ; a railway of 12 miles in Britain costs 80 or 40,000/. but it will last 20 years ; 672 horses and harness would cost 20,000/. renewable every four years. The coke for 200 tons for 24 hours, would be 61 tons, and assistance about Si, but the horses would cost 75/. for keep.
On a level railroad, the force of draught, or traction, is about the 240th, e. 1 cwt. of force is requisite to draw 12 tons. In an ascending road, this force must be increased by the ratio of the rise to the length. Thus, a rise 1 foot in 60 would demand a 60th of the weight, or 12 tons would demand 4 cwt. of fOree more, or 5 cwt. One foot in 100 would require 2.4 more, or 8.4 cwt. to draw it, and so on. This difficulty is obviated by a horse-wheel at the top of each plane, or by dividing the load at bottom, and re-uniting at top. A station engine, or
an extra engine, requires to be made ready. But, in general, an engine does not travel with all its power, so that in clinations of 1 in 240 feet may be sur mounted by enlarging the throttle valves, so as to double its own power. A heavy mass, rolling the contrary way, would obviously give the requisite force ; while the pulling it up again would be conveni ent in descents. Lardner suggests lifting stages, on the principle of canal locks. Perkins showed, that, by increasing the strength of the apparatus, we might use steam, so excited by increased mo tion as to press with a force of 2000 lbs. to the square inch.
The fire-tubes are now increased from 100 to 150 of 1, 1.5, and 2 inches diame ter, so that no heat is lost, and the water is everywhere in contact with the pipes filled with excited air, which, in all eases, is the means of transmitting the motion of fixed oxygen to bodies within its ascending current.
For security, also, the steam is confin ed within plates, so that their reduced strength is a constant safety-valve.
The crank, connected with the wheels, makes a revolution at each stroke of the piston ; hence, the velocity is governed by the rapid generation of steam, and this is as the heat. If the wheels are 5 feet or 16 round, 16 into the strokesper minute expresses the velocity on level ground.