( 361) 
From this we find: 
9A 12A 15 A 
—— = 0.95 —— = 0.78 —— = 0,74. 
6A a 9A 12A ad 
And from the 3 last measurements I got: 
9A 12A 15A 
— == 0.782 —=0.761 — =0.775. 
Oa 7 oA 76 eA 0.775 
9A 
For the value of EE the two results do not agree very nicely; 
12A d 15 A 
as for TE 
So now we know, that by increasing the number of primary 
turns of the induction-coil we soon reach a maximum for the inten- 
sity of the induced current and that by continuing to increase the 
number of turns we arrive at a decrease in the strength of the 
induced current. 
the correspondence is very good. 
It was obvious to think, while searching for an explanation of 
this phenomenon, of the possibility that the iron in the coils of 
higher order would be much nearer to its magnetic saturation point 
than in the coils of lower order. In that case the undulations of 
the microphone-current would bring about, in coil 15 A for instance, 
smaller variations in the magnetism of the iron than would be the 
case in coil 3 A. 
This current of thoughts led me to compare the coils with iron 
with those without iron as regards the intensity of the induced cur- 
rents furnished by them. The method I followed for this was just 
the same as the one I had followed for getting Table III. 
The result of this investigation is found below. If we call A the 
current induced by a coil with iron and B the current induced by 
a coil of the same order bat without iron, we then find: 
For coil: | 3 | 6 | 9 12 15 
The value for Le | 6.50.) : 8.9% | 9, B0r I oer Ie as 
or for the efficiency of the iron, if we | | 
take that for coil 3 A to be equal to 1: 
0.47 | 0.35 | 0.97 
