ON RAILWAY CONSTANTS. 245 



Hence the pressure per square inch was 46 lbs. If 14*5 lbs. be deducted for 

 the atmosphere, there will remain 31*5 lbs. per square inch to overcome all 

 the resistances, including those of the engine itself. 



The sura of the areas of the pistons being 246 square inches, the total 

 pressure upon them, after deducting the resistance of the atmosphere, was 

 246 X 31*5 = 7749. If we allow 2 lbs. per square inch to represent the re- 

 action of the blast pipe, the effective pressure will be 7257 lbs. This reduced 



o 



to the contact of the driving-wheels with the rails by multiplying it by » 



15*7 

 will give 1386 lbs. as the whole tractive force expended on the gross load. 



If 1 50 lbs. be deducted from this as representing the force expended on the 

 engine itself, there will remain 1236 lbs. to represent the actual force ex- 

 pended in drawing the train, including the tender. 



The weight of the train, including the tender, being in this case 70 tons, 

 the ratio of the weight to the gross resistance will be 126 to 1, and conse- 

 quently that will represent the mean angle of repose for a train of this mag- 

 nitude moved at 31 miles an hour. 



It may be useful to form an approximate estimate of the proportion in 

 which the total tractive force of 1236 is distributed between the different 

 sources of resistance. If we take the friction according to the results of the 

 experiments detailed in the first part of this Report to be at the rate of 5'5 lbs. 

 per ton of the gross weight of the load, the total amount of the friction of 

 the train of twelve coaches and tender, weighing 70 tons, will be 385 lbs. 

 Thus we shall have — 



Friction proper of the load ..... 385 lbs. 

 Atmospheric resistance 851 do- 

 Total resistance 1236 do. 



It follows, therefore, that this train of twelve coaches, engine, and tender, 

 moving down an inclined plane falling at the rate of 1 in 120, with a velocity 

 of 30*90 miles an hour, would not be accelerated, and that to move it down 

 planes of less inclination at the same speed would require an amount of trac- 

 tive power to be exerted by the engine, which would depend on the inclina- 

 tion of the plane. 



It was found in this experiment, that the mean evaporating power of the 

 coke was at the rate of 1 cwfr. of coke to 10 cubic feet of water, or ll"21bs. 

 of coke per cubic foot of water. This consumption of fuel does not greatly 

 exceed the common estimate for the consumption of coal in ordinary low- 

 pressure boilers. 



The results of this experiment are quite in accordance with those of all 

 the other experiments which have been stated in this Report. Lighter and 

 smaller trains, moving with the same speed, suffered greater resistance in 

 proportion to their weight, or what amounts to the same, they acquired less 

 speed with the same resistance. 



Taking the same estimate of the friction proper, the following table ex- 

 hibits the total resistances to which trains of different magnitudes were found 

 in these experiments to be subject when moving at the speeds given in the 

 fourth column, and the proportion in which these resistances are due to the 

 different resisting influences respectively : — 



