( 402 ) 
different. methods represented respectively in Fig. 3 and Fig. 9: 
Coil | 3 | 6 | 9 12 | 15 
2 found according to fig. 9 | 6.52 | 5.9. | 6.51 As | 3.94 
A en | a 
= found according to fig. 3 | 5.56 3.95 2.59 1,05 1.48 
Weakening of the primary current 
Lay 1.49 2.13 2.45 2.66 
by the iron | 
we see that the figures of the 2"4 row and those of the 3'¢ row 
differ pretty much. 
In measuring according to Fig. 9 we have taken care that the 
primary strength of the current always had the same value, whether 
the induced current of coil A or that of coil B was measured. When 
measuring according to fig. 3 we have not heeded that. So if the 
two methods give different numbers, the reason can be looked for 
only in the change which the strength of the primary current suffers 
in consequence of the iron. 
Comparing the numbers of the 2"¢ with those of the 3" horizontal 
row of the table given above, we see that the latter are all smaller 
than those of the 2"¢ row. This must evidently be explained 
from the fact, that in measuring according to fig. 9, only the useful 
factor of the influence of the iron — the increasing of the coefficient 
of mutual induction — is prominent, whilst if we act according 
to fig. 3, the disadvantageous factor of the influence of the iron also 
has a part in it: the increasing of the self-induction of the primary 
and the weakening of the primary current caused by it. 
Besides the fact that the numbers in the 3rd row of the above 
table are smaller than those in the 2"¢ row, we also see that the 
3:4 row converges much more. This is due to the weakening 
of the primary current by the introduction of the iron core being 
greater for the coils of higher order than for those of lower order. 
So the disadvantageous factor of the iron is the greatest for coils of 
higher order. This weakening can be calculated by dividing the 
numbers of the 2nd row by those of the 3'¢; the numbers obtained 
in this way I placed in the 4 horizontal row of the table. 
Although it is sufficiently known that this weakening of the current 
by the iron increases with the number of primary turns, yet I have 
