RESEARCHES IN MAGNETISM. 
531 
Diameter of wire. 
Mean circumference of ring. 
Number of turns in magnetising coil . 
Number of turns in induction coil. 
Deflection of battery galvanometer with 3 cells 
and 6'85 ohms total resistance. 
Earth-coil reading. 
Area of earth-coil. 
Number of turns in earth-coil. 
Earth’s vertical force. 
0"248 centim. 
3D 4 centims. 
474 
167 
362 
42-9 
1216 sq. centims. 
10 
0-34 
Hence magnetising force for one scale division of the battery galvanometer 
47r x 3 x 11 x 10 8 x 474 
— -—( 00969 ^ 
6-85 xl0 9 x 362 x 31-4 
And value of © for one scale division of the ballistic galvanometer 
1216x10x2x0-34 
167 x 42-9 x 
tt(0-248) 2 
= 23-89. 
In the following table the actual readings are given, and also the values of «§, 23, 3 
and k calculated from them. The ballistic readings at the beginning of the magnetis¬ 
ation are too small to allow k to be determined for the early points with any 
approach to accuracy, and its early values are therefore omitted. It has been 
assumed that the ring was initially free from magnetism, which can have been no 
more than approximately true, for it had been moved about in the terrestrial field 
before the readings were taken. 
The same experiment is shown graphically in Plate 57, fig. 1. It will be observed 
that although the changes of magnetism which occur during the removal and re¬ 
application of Jp are small compared with the whole magnetisation, they exhibit 
hysteresis very decidedly with respect to their argument <§. 
