to increase the weight on the engine's driving wheels. "^ As we 

 shall soon see, the use of the train's weight to increase the locomotive's 

 adhesion was one of the cardinal principles of the grade-climbing 

 engine. At the same time, 1 835-1 837, George proposed a scheme 

 to increase the locomotive's traction by use of a special rail with 

 rollers running under the driving wheels. The rollers would be 

 under pressure, pulling the driving wheels hard against the top 

 surface of the rail. The fallacy and impracticability of this idea 

 was quickly pointed out, and it was never tried. "^ Each of these 

 ventures shows that Sellers was concerned with locomotive adhesion 

 sometime before he began work on the drop hammer or the center- 

 rail engine. Too, there had been much local interest in grade- 

 climbing locomotives since the opening of the cog railway on the 

 incline of the Madison and Indianapolis Railroad in 1845. ^^ 

 about the same time that Harkness was building his first locomotives 

 (1846- 1 847), Sellers' idea for a grade-climbing locomotive began 

 to mature. 



His engine operated on the level as a conx'entional machine. 

 When on a grade, two smooth gripper wheels, mounted under the 

 locomotive and driven by an auxiliary set of cylinders, engaged a 

 center rail, thus adding their tractive effort to that produced by the 

 driving wheels. The weight of the train became a positive rather 

 than negative factor, since it pulled upon a drawbar connected to 

 the gripper wheels by means of toggle-levers; thus, the heavier the 

 train and the steeper the grade, the tighter the grip of the adhesion 

 wheels on the center rail. Although Sellers did not admit it, this 

 principle was not a net gain, for the friction on the journals sup- 

 porting the gripper wheels increased with the load of the train. 

 The toggles and the levers by which the adhesion wheels were 



'•* A patent was issued to Chai'les and G. E. Sellers on May 22, 1835 (no number); 

 the restored patent is now in the U.S. National Archives, Business and Economics 

 Records Section. The specifications are in vol. 23, pp. 429-30, of restored patents; 

 the drawing number is X 8839. In this scheme a lever fastened to the rear of the 

 boiler or frame of the locomotive (4-2-0's only), with the driving wheels' axle 

 as the fulcrum, would be attached to the train in such a way that the weight of 

 the train, when ascending a grade, would pull on the lever and cause the engine to 

 tip up, thus throwing the weight normally carried by the leading wheels upon the 

 drivers. 



'^ See Sellers, Improvements, p. 17, for a description. 



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