( 368 ) 
We see from these numbers that the influence of the iron on the 
intensity of the induced current is much less in the coils of 
higher order than in those of lower order. And comparing these 
numbers with those we gave on page 11 for the value of A we 
see that the decrease of the effect of the iron between 3 A and 6 A is 
still compensated by the increase of the number of primary turns, 
but that higher than 6A the decrease of the effect of the iron 
predominates and that the increase of the number of turns is then 
no longer sufficient to make good that decrease. 
To investigate whether in reality an approach to saturation of 
the iron may be regarded as the cause of this phenomenon, the 
magnetism of the iron core of coil 15 A was investigated as follows for 
different currents: In fig. 4, M is a bell-magnet hanging on a fibre 
in a copper damper. In the line ab perpendicular to the magnetic 
axis the coils 15 A and 15 B were placed. First the iron core was 
taken out of coil 15 A, then the two coils, 15 A (without iron) and 
15 B, were placed at such distances from the magnet, that a current 
of 1 Ampère, traversing both in opposite directions, did not give a 
deviation to the magnet. Now the iron core was again put into 
coil 15 A and the latter laid in exactly the same place as before. 
The distance from the centre of the bell-magnet to the middle of 
the iron core was 307 mm. 
Now the Morse-key was pressed down; as soon as the index 
attached to the magnet stopped, the position was read, and at the 
same time the Ampère-meter was read by a second observer. This 
was a necessary precaution, because, at least when using strong 
currents, the index of the magnet as wel] as that of the Ampere- 
meter slowly went back to zero in consequence of the increase of 
resistance of the coils caused by the heating of the wires. To be 
quite sure that the coils had not been damaged by the strong 
currents, the iron was removed out of 15 A after the measurements 
were made and a current of 1.5 Ampère led through the two coils 
in opposite direction: the magnet remained in its position of equi- 
librium just as at the beginning of the experiment before the iron 
was put into 15 A. 
Fig. 5 represents the results of these measurements in the form 
of a curve; the ordinates are proportional to the magnetic intensity, 
the abscissae to the strength of the current. The figure shows, by 
the small circles, that 1 have taken fifteen readings witha strength 
of current, increasing from 0.11 to 1.53 Ampère. « is the angle 
between the magnetic axis of the magnet and the magnetic meridian. 
Now the current in the primary wire of 15 A, connected with 
