170 THE DIKECT-CntHKXT MOTOR CH. VIII 



Since M is equal to c^ the induced volt?, divided by 

 //. the number of revolutions per second, it follows that 



(*p 



Mc= . but ce is the work done per second, hence M>- is the 

 n 



work done per revolution. If then we are given Me and 

 37", we can find the work done per second, that is the rate 

 of working, or the power, by simply multiplying the 

 product 3/c by the number of revolutions per second. 



The ratio of the watts to the revolutions per second, 

 sometimes called the ' mass factor,' has been used as a 

 basis for the comparison of dynamos, its true significance 

 not, however, being perceived. The fact seems to have 

 been overlooked that the ratio of the induced volts to the 

 revolutions per second is a constant, so long as the number 

 of useful lines per pole remains unaltered, being, in fact, 

 what we have termed the induction factor. 



While the force factor and the so-called '.mass factor' 

 are one and the same thing, the latter is expressed in a 

 way involving the idea of speed, and consequently of 

 power, while the former indicates the real nature of this 

 ratio, showing that it is independent of speed, and there- 

 fore not a power unit, much less a mass unit, but a force 

 unit. 



Example 42. A four-pole dynamo with armature 

 parallel connected, giving p=l, has 440 surface con- 

 ductors, with 16 - 1 x 10 6 lines per pole. The induction 

 factor is 77 and the force factor for 600 amperes is 

 77x600 = 46-2 kilodynes; the power at 450 r.p.m. is 

 46-2 x7'5 = 346 kilowatts. The dynamo is a General 

 Electric four-pole railway generator. 



Example 43. A ten-pole dynamo with armature 

 parallel connected has 1,440 surface conductors and 



