Sensations caused by a Magnetic Field. 193 



slotted armature produced harmonics in the current and 

 voltage waves. In order to determine the nature of the 

 wave-forms a series of oscillograms were taken, both of the 

 current passing through the coil and the voltage impressed 

 upon its terminals. Although the relative magnitude of the 

 fundamental and the harmonics, as well as their phase 

 relation, varied for the several speeds and loads, the wave- 

 forms were fairly uniform. In fig. 6 is shown a typical 

 current wave : — Oscillogram L 31 : /= 30 cycles, E = 96 volts, 

 1 = 5 amperes. The wave was analysed, and its equation 

 found to be 



Y= 3\L7 sin (# + 3° 15') +0-31 sin (3a; -26° 20') 



+ 0-06sin(5.r-48° 17'). 



Hence the 3rd harmonic is 9*8 per cent, and the 5th 

 harmonic 1*9 per cent, of the fundamental. 



In fig. 7 is shown a typical voltage wave as impressed 

 upon the terminals of the coil : — Oscillogram L 27 : 

 /=58'5 cycles, E = 895 volts, 1 = 24*4 amperes. Its equa- 

 tion was found to be 



Y=2-24sin(#-0°56')+0-63 sin (3^ + 175° 530 

 + 0-12 sin (5tf-ll° 03'). 



Hence the 3rd harmonic is 28*1 per cent, and the 5th 

 harmonic 5'4 per cent, of the fundamental. 



For frequencies above 67 cycles the current was obtained 

 from mi alternator having a smooth-core armature and a 

 normal full-load rating of 35 K.W., 137 cycles, 1100 volts. 

 Several oscillograms were taken of the current and voltage 

 waves, all showing approximately simple sine waves. In 

 fig. 8 is shown a typical oscillogram (L 55) for this machine : 

 /=102 cycles, V = 250 volts (upper curve), 1 = 4 amperes 

 (lower curve). 



We have not determined what effect, if any, these dis- 

 tortions of the impressed stimuli from the simple sine form 

 may have upon the threshold values. For current waves 

 similar to fig. 6 the maximum is somewhat less than 

 y/2 times the effective value. Hence the actual value of 

 H and H' would be correspondingly less than the values 

 #iven in the tables. For the voltage wave as in fig. 7 the 

 maximum is greater than for the equivalent simple sine wave. 

 The wave is also more peaked, and hence the duration of the 

 voltage above the average value is reduced. It seems likely 

 that the shortening of the time in which the induced voltage 

 is above a given value may, within limits, neutralize the 



Phil. Mag. S. 6. Vol. 2S. No. 164. Aua. 1914. O 



