Figure 30. — Another pre-1 900 view of John Bull, which was built in England by 



Stephenson in 1831. 



Early Locomotive History," and by J. G. H. Warren in his 

 "A Century of Locomotive Building," both excellent pub- 

 lications. In fact, however, the cylinder bore of the John Bull 

 was recently measured and found to be 11 inches. The stroke 

 of 20 inches as cited by all is correct. 



Many changes, some minor and some major, were incor- 

 porated in the John Bull during the next few years. The most 

 noticeable was the addition of a 2-wheeled pilot, suggested in 

 1832 by Robert L. Stevens to guide the locomotive around 

 the sharp curves common in the tracks of that era. In order 

 to attach the pilot to the front axle, the outside rods and 

 cranks connecting the front and back axles had to be perma- 

 nently removed, thus reducing the number of drivers from 

 four to two. The John Bull has ever since been driven by only 

 the two rear wheels (figure 30). The wheels of the pilot are 

 29 inches in diameter. 



Another early permanent change was the replacement of 

 the wooden-spoked wheels with those of cast iron. The old 

 wooden carriage-type wheels could not stand up under serv- 

 ice in America, where sharp curves in the tracks prevailed. 



41 



