230 T1IK DIRECT-CUR HK NT .MT<)|; (II. XI 



in one-third of the given time. The final speed is there- 

 fore given by the equation 



,= 1-5 l} KM;. 



v 



Now is the mean speed ; hence for the best 



arrangement the final speed is 50 per cent, greater than 

 the mean speed. We have here the practical limit of the 

 application of this principle namely, the limit of speed, 

 since the use of the best diameter involves high speeds for 

 long distances. If, in Example 54 for instance, the time 

 was kept fixed at eighty seconds, and the distance to be 

 travelled increased to 800 yards, the final speed would 

 increase to 30'6 miles an hour. This is shown in the 

 following table : 



Time. Distance. Menu speed. Final speed. 



Seconds Yards Miles an hour Miles an hour 



80 

 80 

 80 

 80 

 80 



In working out this problem we assume that when 

 more than one motor is used the motors are connected 

 in parallel. We have now to see how these equations 

 apply when two motors are connected in series at the 

 start. 



When connected in parallel throughout, the acceleration 

 is uniform up to full speed. If the motors are 

 connected in series at starting, we get the same 

 acceleration as before with less current from the line. 



