480 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



for an engine with smooth iron bands, for in the latter case the wheel 

 crushes the ballast and causes a considerable loss of force. 



A locomotive of this kind might be driven in a prairie without 

 leaving any great marks of its passage. On a horizontal road, it can 

 draw 30 tons with a velocity bearing from 2J to 6 miles an hour. Its 

 effective force is from 16 to 18 horse power. Many are employed in 

 different parts of England to carry coal from the pit to neighbouring 

 factories, and in Edinburgh. Thomson has applied his locomotive to 

 the traction of omnibuses. Lastly, attempts have been made in India 



FIG. 323. Thomson's road-engine. 



with these engines, in the postal service, for carrying its bags, in the 

 province of Punjaub between the towns of Loodlana, Ferozepore, and 

 Lahore. 



The design we give here of Thomson's road-engine will suffice to 

 render the general arrangement of the parts comprehensible. We see 

 that the steam-engine has a horizontal cylinder, c, communicating the 

 motion by a connecting-rod to a doubly-bent driving-shaft provided 

 with a pinion, working in a cog-wheel, fixed on the driving-wheel. On 

 account of this arrangement the velocity given to the axle R of the 



