CHAP. IX.] 



THE LOCOMOTIVE. 



471 



cylinder in Stephenson's engine is to prevent an oscillating motion 

 which, the locomotive receives under the action of the two lateral 

 pistons, and which is shared in by all the carriages of the train. One 

 is reminded that it is partly for motives of equilibrium that M. 

 Dupuy de Lome has employed three cylinders in marine engines. 



We may take in the same way the Engerth type as the most 

 marked of the locomotive engines for slow service, used to drag 

 heavy loads. On looking only at its general physiognomy, and 

 comparing it with a Crampton engine, one sees in an instant that we 

 are dealing with a powerful engine, and if one may be compared to a 



FIG. 317.- Express engine: Crampton's type. 



race-horse, the other may no less fairly be compared to a cart- or 

 draught-horse. 



The mean velocity of an Engerth (for there are several varieties) 

 is 15 miles per hour; but they can drag a load of 450 tons. Their 

 weight is as much as 63 tons, which is borne partly, along with the 

 tender, on the wheels of the latter, but which is principally supported 

 by four pairs of wheels of equal diameter, coupled by connecting-rods. 

 Contrary to Crampton's type, the goods engines of this type have 

 several pairs of driving-wheels of small diameter and a long 

 stroke for the pistons of their cylinders. Great length is given to the 



