INTRODUCTORY 7 



" as the ratio of the root-mean-square, or virtual 

 value, to the true mean or average value) was 10 per cent, 

 higher for the iron-clad machine than for the smooth-core 

 machine. Some firms at that time took advantage of the 

 re loss obtained on such nni-slot machines. The core 

 losses which they quoted for their transformers were such as 

 would he obtained when the " form factor" was at least 

 10 per cent, higher than that of a sine-wave alternator. The 

 ft. rm factor of a sine wave is 1,11, and the form factors of 

 uni-slot single-phase alternators were usually at least 

 i 1 .10 X 1,11 =) 1,22. It is highly important that the present- 

 day student should have these points w< -11 in mind, since they 

 are apt to be less appreciated when read from books than 

 in our case, they w.-re obtained at first hand by 

 experiences which at the time were actually distress in-.:. 

 \Yhih- th- nionYrn alternator is usually required to supply a 

 sine wave of pressure, nevertheless various conditions tempo- 

 rarily otvuiTinu' in electrical networks often occasion a very 

 able distortion of the wave lorm. It is certainly 

 to specify that core losses shall be 

 measured from a circuit supplying a sine wave of pressure. 

 his 10 per cent, discrepancy in the way 

 mtered at our works was largely due to 

 insight 



I'p t.. ' "iir trailer: : almost all 1 



designed for 125 cycles and for a lighting 1 . for 



..lying ii. ' ' tlM iion-indii 



: ..f this load, tln-rr had been no OOOftttOO i> devote 



attention to decreasing the inductance of the 

 windings. Th- pr-ddein OJ had r, 



:lv to rniiihining a nuninium mean length of magi 



nt with a minimum mean length of turn of tin winding. 



In th. development of the polyphase induction 



.Inch I. .-cairn- an important i ud 1898, 



as soon found quite impossible to employ these ligh 



