MEANS OF TRANSPORT. 



inches beneath the rail-top Q R is moving back- 

 wards at one-sixth of the speed of the axle L, and 

 therefore at one-sixth of the speed of the train. 

 Thus, when an express train is travelling 

 northwards towards Doncaster at the rate of 

 sixty miles an hour, every wheel of every carriage 

 has at every moment a part of its flange-rim 

 which is travelling backwards towards King's 

 Cross at the rate of ten miles an hour. 



3. A Sailing Boat which moves more swiftly 

 than the Wind which is driving it. 



The wind can drive ships by blowing upon 

 the sails in two different ways. When the 



E 



l I i i i i l i i i i i 



FlG. 4.-HOW SPEED DEPENDS ON THE SET OF THE SAILS. 



ship is to go in the same direction as the wind 

 is blowing, the sails can be set square across, 

 and the wind blowing from straight behind 

 blows straight on to the face of the sails, and 

 pushes them and the ship straight onward. 



This is shown in the first arrangement in 

 Fig. 4, in which the boat A B, driven by the 



