THE DIRECT-CURRENT MOTOR CH. IX 



will be 430 pounds. This leaves us with only 210 pounds 

 per motor for accelerating, as compared with 1 ,030 in the 

 Liverpool motors. This difference is due to the fact that 

 the friction absorbs so large a proportion of the total 

 tractive effort. Speaking roughly, we may say that two 

 of the Liverpool motors in series will give for the same 

 current twice the pull of two of the South London motors 

 in series, and that the accelerations will show a still greater 

 difference in proportion as the friction is increased. If 

 the friction, instead of being 20 pounds per ton on 33-inch 

 wheels, is 10 pounds per ton, the acceleration of the South 

 London motors is increased from one-fifth to one-third that 

 of the Liverpool motors. 



Figs. 51 and 52 contain the records of tests made 

 on the Buffalo and Niagara Falls Electric Railway by 

 Messrs. H. P. Curtiss and H. 0. Pond. A full account 

 of these experiments may be found in the ' Street Railway 

 Review ' for July 1896. We may here note the following 

 data : 



The cars on which the tests were made were 36 feet 

 in length and weighed 13'6 tons. Each car is equipped 

 with four G. E. 800 motors, one on each axle. The velo- 

 city ratio is 4*78 and the wheel diameter 33 inches. The 

 motors are controlled on the series-parallel method in 

 pairs, thus : Step I., two in series, two in parallel. Step II. 

 four in parallel. The average tension of the line at the 

 car was 550 volts. The track where the tests were made 

 was straight and level. 



The vertical ordinates of the current curves give the 

 total current for the car, so that when in series the current 

 per motor may be taken as half, and when in parallel, as 

 one-fourth of the ordinate of the current curves. 



