88 



BULLETIN 119, U. S. NATIONAL MUSEUM. 



tributed over four pairs of wheels, two of them being in front. The clumsy 

 outside wooden beams that acted as frames are abandoned for iron bars tlaat 

 are not susceptible to changes of temperature and form a light frame which 

 carries the boiler securely and with small superfluous weight to which all op- 

 erating mechanism is strongly fastened. The engine meets the essential re- 

 quirements of lightness and strength sufficient to control the increasing power. 

 The elementary locomotive with a single pair of driving wheels is deficient in 

 adhesion and what seems a backward step is taken to make an important move 

 forward. The first engines built before the advent of the swiveling truck were 

 generally carried by two pairs of coupled wheels which gave sufficient adhesion. 

 In the United States one pair of these wheels was abandoned for the leading 

 truck, while in Europe the four-coupled arrangement was adhered to, but :i 

 single pair of carrying wheels was introduced in front or in the rear. 



When it became apparent in the United States that a single pair of driving 

 wheels made a very slippery engine, various forms of traction increases were re- 

 sorted to with very little satisfaction. Then an engineer proposed adding an- 



FIG. 43. COMPLETE WORKING MODEL OF "AMERICAN " TYPE LOCOMOTIVE, 1900 



other pair of driving wheels, the same pair that had been thrown out by the 

 Jervis truck, and won fame and fortune by the invention. The clan Campbell, 

 led by their chief, the Duke of Argj'U, have won many victories since, breekless, 

 they first emerged from the wilds of Lorn, but no victory was so abiding and 

 lucrative as that of Henry R. Campbell when he added a pair of driving wheels 

 to the slippery locomotive. 



Campbell gave the basis for the American locomotive, but it had to pass 

 through much torturing experiments, due mostly to following of fallacies and 

 fashions, before it emerged from the hands of its friends a highly perfected 

 engine. The Campbell was rudimentary to a degi-ee, but it provided a founda- 

 tion to succeeding builders. A heavy outside wooden frame carrying a boiler 

 and having pedestals to secure the four-wheel leading truck and the two pairs 

 of driving wheels set very close together formed the visible outlines of the en- 

 gine. The cylinders were inside under the smoke box and transmitted the 

 power through a cranked axle. It was patented in 1836 and was noted for un- 

 yielding, hard-riding characteristics. 



For about twenty years, the "American " locomotive was the Rome toward 

 which nearly all locomotive designers traveled. It was a pity that the public 

 demand for increased speed of passenger trains and decreased freight charges 

 should have moved railroad managers to command that more powerful loco- 



