Magnetization of Iron in Bulk. 623 
; 
The upper areas represent the changes of magnetic flux 
with increasing currents, the lower with decreasing. The 
area A of each curve was measured with a planimeter. 
Fie. 1.—Typical Record for Half a Hysteresis Loop. 
(Hach area denotes the change of B for an observed change of 1.) 
ne 
A 4 | | | 
| | | | | 
“ee id 
PELL we 
7 earali 
a ace ite 
Knowing, then, the voltage e for one centimetre deflexion 
and the seconds s the periphery of the drum took to move 
one centimetre, the area multiplied by the product es gave 
the total lines threading the exploring coil. The corresponding 
change in flux density 
8 
pa Aes x 10 Lee 
Na 
A having in succession the values recorded. The flux density 
at any current is then & times the sum of the areas up to 
that point. The value of the magnetizing current at each 
pause was noted by the observer. The areas can be readily 
checked by allowing the current to change from zero 
to the maximum and back to zero without pause, when it is 
found that the agreement between the areas so found and the 
separate steps is within 1 per cent. 
The difference between the areas above and below the zero 
line represents the residual magnetism. 
The results of the tests on the two rings are given in 
Tables I. and IL. and in fig. 2. 
The observations are reduced ina manner similar to the 
“step by step” method of ballistic testing. The labour could 
be greatly reduced by the use of a quantometer *, if that most 
useful instrument were generally available. Dr. Beattie 
having kindly lent his, the tests were repeated, obtaining 
* Vide The Electrician, vol. 1. p. 383. 
2X2 
