24 Book of Locomotives 



By 1900 the trains had so increased in 

 weight that the " single driver " was 

 doomed and soon after, in 1901 in fact, the 

 last batch was built these on the Great 

 Northern. 



A word here on locomotive wheel for- 

 mula. The first engines were all of the 

 four-wheeled variety. We may conven- 

 iently take a small o for the leading or 

 trailing wheels, and a large O for the 

 driving wheels. Thus the " Rocket's " for- 

 mula was O o, then we find designers 

 deciding that if they coupled the four wheels 

 of the engines intended for coal or goods 

 traffic, greater loads could be taken. These 

 were expressed as O O. The next step was 

 found when we get to the Great Western's 

 opening in 1838. Here the boiler of the 

 engine had grown in length, as well as 

 diameter, so another pair of wheels, to take 

 some of the weight, was added. Thus the 

 " North Stars " wheel formula was expressed 

 as o O o. 



By the time the " eight-footer " came 

 along the leading bogie had been added for 



