LOCOMOTIVE ENGINE AND KAILWAY GRADIENTS. 155 



Now, if we take the last column of the table, comprising 

 the sum of the total resistance due to the different retarding 

 forces, it will not only be easy to compute the force in lbs., 

 or horses' power necessary to overcome the resistance, but 

 it will also be easy to determine the load which a well- 

 constructed locomotive engine, having 16 inch cylinders, 

 will drag up the differently elevated gradients at the rate 

 of 33 miles an hour. 



Before entering upon these calculations, it may however 

 be necessary to state the properties and conditions of the 

 engine on which they are founded ; and, in order to ensure 

 sufficient accuracy as regards the ppwer, I have taken the 

 pressure upon the piston at 40 lbs. on the square inch, the 

 cylinders 16 inches diameter, 18 inches stroke, 5 feet driv- 

 ing wheels, and travelling at the rate of 33 miles an hour. 

 Now, an engine of those dimensions, acting with an effective 

 pressure of 40 lbs. on the square inch, will exert a force (the 

 piston moving at a velocity of 555 feet per minute) of 

 8,924,400 lbs., or 270 horses* power. This taken as a mea- 

 sure of motive power, clearly exhibits the immense force given 

 out by the locomotive engine at high velocities. In the first 

 column of the table we have the inclination of the gradients; 

 in the second, the resistance per ton on a horizontal plane ; 

 in the third, the resistance due to gravity ; and in the fourth 

 the total resistance per ton, or the retarding force which 

 the engine has to overcome upon every ton raised on gradi- 

 ents varying from 1 in 20 to 1 in 200.* 



* On consulting the experiments, it will be found that a less powerful 

 engine (the Baltic), with only 14 inch cylinders, carried a greater load up 

 the Hunt's Bank gradients. This may, however, be accounted for by the 

 increased effective pressure upon the piston, which in this case was from 

 60 to 65 lbs. on the inch, considerably more than that given above. 



