472 



THE APPLICATIONS OF PHYSICAL FORCES. BOOK iv. 



boiler the cylindrical body and the tubes, and great dimensions to 

 the fire. 



In this, in the large heating surface, and the vaporizing power of 

 the boiler, lie the secret of the enormous force of traction with 

 which this remarkable type is endowed. 



FUJ. 818. Goods engine for slow trains : Kngerth's type. 



The first Engerths l were provided with a set of cog-wheels, with 

 the object of enabling them to ascend the inclines of the Soemmering. 

 The types of mixed engines, or locomotives of moderate speed, 

 partake of the characters of the two first types. Two pairs of coupled 



FIG. 310, Goods engine on the Northern Railway of France, with twelve coupled wheels and two 



cylinders. 



wheels of a diameter varying between 1*50 and 1'70 metres, a moderate 

 length of the stroke of the piston, a weight of about 25 to 30 tons, 

 the regulation velocity 29 miles per hour, a force of traction of 180 



1 So called from the name of the inventor, an Austrian engineer, who designed 

 them at first for use on lines with heavy inclines. 



