( 409 ) 
by the magnetism of the core. For the sake of brevity we shall call 
the former the galvanic, the latter the electro-magnetic induction 
current. Now as the strengthening and weakening of the magne- 
tism of the iron core, caused by the changes of the primary current, 
requires a certain time, the induced currents, produced by those 
changes of magnetism will appear and disappear‘ later than the 
currents induced directly by the primary current. The tables given 
on pages 402 and 406 enable us to calculate about how many times 
the electro-magnetic induction current is stronger for the diferent 
coils than the galvanic. So e.g. for coil 3 A: 
The currents induced by 3 A and 3 B are in the proportion 1 : 0.18 
(table page 406). The primary current of coil 3 B becomes 1.17 times 
weaker by the introduction of the iron (table page 402). So the 
galvanic induction current produced by coil 3 when iron is introduced 
into it (in other words the galvanic induced current given by 
coil 3A) has the intensity 2 = 0.15 if 1 is the whole current 
induced by 3 A. Now the latter current is the sum of the galvanic and 
of the electro-magnetic current; the galvanic being —0.15, the electro- 
magnetic will be equal to 0.85. It follows from this, that the 
abe ke . 85 oie 
electro-magnetic induced current for coil 3 A is a times 
stronger than the galvanic. 
In this manner we find for the coils 3A, 6A, 9 A, 12 A, 15 A 
the proportions 5:7, #97 5:25,°3.85°° 30 
With 3A the electro-magnetic induced current will be so much 
stronger than the galvanic, that the latter will not be able to give 
any change to the quality of a simple sound. If we suppose the ampli- 
tude of the diaphragm ot the telephone to be proportional to the 
strength of the induced currents, the intensity of the sound will be 
proportional to the square of the strength of the current. For 3 A 
the electro-magnetic tone will be 5.7? = 32 times stronger than the 
galvanic: so it is not probable that the latter will have any per- 
ceptible effect. 
In this respect 3 A will probably be the best coil as far as articu- 
lation goes. But also in respect to the 2rd condition, named on page 
9 for a good articulation, 3 A will be the best of our A-coils, the 
self-induction being less than in any of the 4 other A-coils. 
With 15 A the proportion of the electro-magnetic induced current 
to the galvanic = 3, so the proportion of the two tones = 9. In using 
this coil there will be the greatest chance that a simple tone made 
before the microphone will be reproduced with changed timbre by 
