( 408 ) 
DET 2,73 shows us, that with coil 15 B in our microphone- 
cireuit, (i. e. with a coil without iron), we shall hear as much as 
with 6 A (the best of our coils, as far as intensity goes) if only 
we use 2,73, let us say 3 times, the number of cells as for 6 A. 
The resistance of the battery is neglected and moreover this calcu- 
lation holds good only for the tone Fa 3. 
The experiment with the telephone confirmed this entirely. Before 
the microphone the tuning-fork and resonator were placed as usual; 
by means of 4 Morse-keys we could bring into the circuit 
6 A with 1 Leclanché-cell as well as 15 B with 3 cells It was 
found that not the slightest difference in the intensity of the sound 
was to be heard whether 6 A or 15 B was used. In the same 
way I compared 15 A with 2 Leclanché-cells with 15 B with 3 
such cells. In both cases the intensity was exactly the same. 
Sharper tones are weakened in a greater degree by the self-induction 
of the primary coil than lower ones. If I had made these experi- 
ments with a tuning-fork of a sharper note, I would have obtained 
other numbers; the series I found on page 367 for 2 would have 
converged much more. 
We have till now occupied ourselves only with the intensity of the 
currents (or of the telephonic sound) induced by our various coils. 
We shall now try to investigate which coils are best adapted for a 
pure articulation. 
In general we can assume that for our purpose those coils in the 
first place come under consideration, which render a simple tone, 
produced before the microphone, also as a simple sound in the tele- 
phone; and which will reproduce a compound tone in such a way 
that the mutual relation of the intensities of the simple tones out 
of which the compound consists, is the same for the reproduced sound 
as it was for the original sound. ‘Theoretically the induction coils 
with iron core must necessarily be inferior to those without iron: 
1. because by the self-induction of the primary coil with iron the 
sharper tones weaken more than the lower ones, so the quality of the 
reproduced sound will not be the same as that of the original. This 
is in less degree the case in the coils without iron. 
2. because a simple sound does not induce one sinusoidical 
current in the secondary wire of a coil with iron core, but two such 
currents, which are somewhat shifted in respect to each other, One 
of the sine currents is induced by the primary current, the other 
