( 407) 
From this we see, that the decrease of the intensity of the induced 
current by the increase of the number of primary turns is much smaller 
for the B coils than for the A coils. The intensity increases as we see, from 
3B to 12B, but that increase becomes less and less and is at 
last negative from 12 B to 15 B, The reason for 15 B giving a weaker 
induced current than 12 B can be found in the inerease of resistance 
of the primary cireuit, without reckoning with the self-induction: 
The resistance of the microphone is 3.5 Ohm, that of the coil 12 B 
is 4.9 Ohm and that of 15 B 6.4 Ohm; the resistance of the miero- 
phone can be neglected. Then in the first case the whole resistance 
of the primary circuit is 8,4 and in the second case 9.9 Ohm. The 
proportion of those resistances is 1.18; the proportion of the number 
of turns in both cases is Tian 1,25. 
If we introduce into a circuit, in which a microphone and a 
battery have been placed, a dead resistance causing the entire 
resistance (when the microphone is at rest) to become n times 
15 
2 
: 1 
greater, the strength of the current will be reduced to — of its 
n 
former value and the change of resistance in the microphone will also 
| 
retain but — of its former value. The undulations of the primary 
n 
current will be reduced in this case to of their former value, 
1” 
So in the above-mentioned case, by substituting coil 15 for coil 
12, the undulations of the primary current become 1,18? = 1,39 
tines smaller. On the other hand the number of primary turns 
becomes 1,25 times greater. So according to this calculation, the 
OC 
. ‘ as P 
induced current given by 12 B would have to be yt ten 1,11 times 
stronger than those given by 15 B. The numbers in the table on 
qr 
~] 
page 406 give for that proportion — — 1,04. If we take into con- 
cr 
ort 
sideration that the measurement of the resistance of a microphone 
at rest often gives very different values, then we may consider the 
correspondence between these two proportions to be quite sufficient. 
In the table on page 406 we see, that when 6 A connected with 
microphone and battery gives an induced current 1,507, 15 B will 
induce in the same circumstances a current 0,55. ‘That proportion 
21* 
