Rd 
( 405 ) 
were pressed down, 3 B was connected with the measuring-instrument ; 
if the keys were in rest, 3 A was connected with it. 
ne 
The values for E found according to this method are placed in 
the 3 horizontal row of the following table. The measurements 
were taken in quite the same way as indicated in tables II and III. 
A found according to fig. 12, 13 and 14 
b 
Coil | 3 | 6 | 9 | 12 15 
mmm [ 
= found according to fig. 9 | 6.52 | 5.9 | 5.51 | 4.78 | 3.94 
i : 3 
{| 4,94 5.03 4.91 4.25 3.92 
| 
. MA } : 
As will be seen, — is smaller in the 3rd row than in the 224 row 
) bl 
B 
for all coils. This is made clear by the following consideration : 
In fig. 13 the current of B is measured whilst the secondary wire 
of A is open. On the other hand, in fig. 9 the secondary of A was 
closed when the current of B was measured. This closing of the 
secondary wire of A weakens the variations of the magnetism of the iron 
core, and by this weakening the current in the primary is strengthened ; 
so the deviation given by coil B to the electro-dynamometer will be 
greater in the case of fig. 9 than in that of fig. 13. 
In fig. 12 the current of A is measured whilst the secondary wire of 
B is open. In fig. 9 the secondary of B was closed whilst A was 
being measured. The opening or closing of the secondary of B will 
however give rise to only a trifling difference in the strength of the 
primary current, and the deviations given by A to the electro- 
dynamometer will have about the same value whether the meas- 
urements are made according to fig. 12 or to fig. 9. 
A , 
The result is that PB determined according to fig. 9, must be 
greater than = measured according to fig. 14 
We see that the difference between the numbers of the 2™4 row 
and those of the 3 row is smaller for the coils of higher order ; 
for coil 3 the difference is rather great, whereas for coil 15 it has 
almost disappeared. This is owing to the fact, that the closing of 
the secondary in a coil of higher order causes a smaller decrease in 
the magnetic changes of the iron core than in coils of lower order. 
27 
Proceedings Royal Acad. Amsterdam, Vol, LV. ~ 
