AMERrCAN INSTITUTE. 579 



The friction of a locomotive engine is the resistance which it op- 

 poses to motion. It is the force that must be applied to it to over- 

 come all the frictions that oppose its progress at the moment it exe- 

 cutes the traction of a train. At that instant it must possess, 

 lat. A power sufficient to make the train overcome the resistance 

 of all the loaded cars. 2d. And also a power sufficient to pro- 

 pel the engine itself along, and overcome its own friction. The 

 2d power that propels the engine, is the friction of the engine; 

 while the first is the resistance of the load, and both together 

 constitute the total power applied. If an engine is compelled to 

 draw after it a load, the resistance of which, creating an increase 

 of pressure on all parts of the mechanism, must augment the 

 friction on every one of its points, and necessarily, the total 

 resistance of the engine. At every turn of the wheel there is a 

 complete revolution, and consequently, a complete friction of the 

 whole mechanism, and proportional frictions on all the com- 

 pressed points, upon the crank of the axletree and all the points 

 in general. Friction increases in proportion to the load an en- 

 gine draws. In the wheel and axle the friction on the axis is 

 nearly as the weight; in the diameter of the axis and the angu- 

 lar velocity, it is very small. In most screws made use of on 

 locomotives, the friction of the screw is equal to the pressure. 

 The friction of smooth woods and highly polished metals, without 

 oil, on each other, is nearly equal to one-fourth of the pressure. 

 The gudgeons of locomotive and car wheels should be made of 

 highly polished steel, and collars of solid brass, which will 

 conquer friction. 



The aim of our researches must be to discover the amount of 

 friction for different loads, in order to deduce from it the surplus 

 resistance created on the engine by each ton of the load. When 

 an engine executes the traction of a train, we know the pressure 

 in the boiler by inspecting the guage; but we do not know pre- 

 cisely the pressure of the steam in the cylinder, because, in pass- 

 ing from the boiler to the cylinder, the elastic force of the steam 

 changes. If we could know the pressure in the cylinder, or on 

 the piston, by calculating the total effect of that pressure on the 

 area of the piston, we might find the exact valuation of the power 

 applied by the engine. We know the resistance opposed to the 

 motion ; it being composed of the resistance of the train and 

 engine. 



If an engine when drawing a load, increased in velocity con- 

 stantly, it is certain that there would be an excess of power over 



