( 370 ) 
of the iron. But currents of such intensity are not used in our 
microphones. 
So the fact that the influence of the iron diminishes if the num- 
ber of primary turns is increased, cannot be explained by slowness 
or saturation of the iron. 
It seemed of some importance to me to investigate experimentally 
whether the bundle of iron wires giving so much less effect in coil 
15A than in 3A, is also less subject to magnetic changes in 15A 
than in 3A. 
For that purpose two apparatus were made, one of which is 
shown in fig. 7. It is an induction-coil of exactly the same dimen- 
sions as the coils used until now; but one of the two wooden 
flanges is transformed into a vibrating-box for an iron diaphragm, 
covered with and held in position by a mouth piece provided 
with a circular aperture. So the whole forms a telephone, in which 
the bundle of iron wires plays the part of the permanent magnet 
with attached iron core or armature in the ordinary telephone. One 
of the two apparatus was wound with wire quite similar to coil 
15A, the other one like 3A. Care had been taken that the end of 
the bundle of iron wires was in both coils as accurately as possible 
at the same distance from the diaphragm. 
The experiment was now arranged as indicated in fig. 8. B is 
a storage-cell, M the microphone. The primary wire of 3A is con- 
nected with the contacts of rest of the two keys, that of 15A with 
the working contacts. The secondary wires are both shunted by 
a coil of wire (a) quite similar to that of our electro-dynamometer 
and in which also a bundle of iron wires under an angle of 45° to 
the winding-plane has been put. Before the microphone were the 
tuning-fork and the resonator as usual. If both keys were pressed 
down, telephone 15 spoke; if they were mot pressed down, it was 
the turn of 3. 
The experiment showed, that 15 gave a distinctly stronger sound 
than 3. 
Then I exchanged the storage-cell acting on the microphone for 
a Leclanché-cell and placed the tuning-fork a little farther from the 
resonator, which caused the undulations of the primary current to 
become feebler. Now again telephone 15 gave a stronger sound than 
telephone 3. 
So this experiment does not give us any light for the problem 
we wished to solve. We should be more inclined to conclude from 
it, that the iron in the coils of higher order ought to have more 
efficiency than in those of lower order! 
