ACTION OF PISTON ON WHEELS. 



Fig. 1. 



same manner as the arm of a man acts upon a windlass, thus 



imparting a continuous motion of revolution to the wheels. 



6. To render this action of the piston on the wheels more appa- 

 rent, the piston-rod, the connecting-rod, and the spoke or crank, 



are shown in fig. 1, in eight successive 



positions assumed by them during 



each revolution of the crank. The 



direction in which the connecting- 

 rod acts upon the crank is indicated 



by the arrow. 



The joint p unites the connecting- 

 rod with the end of the piston-rod, 



and the joint r unites it with the 



end of the crank or spoke, the fixed 



centre round which the crank or 



spoke revolves being c. 



While the piston makes a double 



stroke from one end of the cylinder 



to the other and back, the joint r 



makes one complete revolution round 



the centre c. 



In the position shown in A, the 



piston is at the end of the cylinder 



most remote from the crank, and the 



joint r is directly between the centre 



c and the joint p. 



In the position B, the joint r has 

 moved from that position, the piston 

 moving towards c, and the connect- 

 ing-rod and crank forming an obtuse 

 angle. The force of the steam im- 

 pelling the connecting-rod in the 

 direction shown by the arrow, acts at 

 an obtuse angle with the crank. 



As the piston continues to move, 

 the angle formed by the connecting- 

 rod and crank becomes less and less, 

 until in the position shown in c the 

 angle becomes a right angle, and 

 then the whole force given to the 

 connecting-rod becomes effective. 



In the position D, the angle formed 

 by the connecting rod and crank 



becomes acute, and in the position E, the joint r assumes a posi- 

 tion in a direct line with c and p, and the piston has reached 



i 2 115 



