IOWA ACADEMY OF SCIENCE 
165 
THE HYSTERESIS LOOP. 
BY D. W. MOEEHOUSE AND HAEEY EAY WOODEOW. 
It is not proposed to introduce a new method for the determination of the 
hysteresis loop, but to introduce some advantageous modifications. 
The method is similar to the ring ballistic method outlined by Dr. R. A. 
Millikan. This method has the advantage over the old magnetometer method 
in that the lines of force are continuous through the iron. It cannot be used 
hov/ever if the iron is hard and causes any creeping. 
The revolving commutator is a plain application of the mercury cup com- 
mutator with which we are all familiar. The variable resistance is an applica- 
tion of the common resistance box, using knife edge sv/itches in place of the 
plugs. This gives a continuous current which can be increased or diminished 
by the throw of the switches. 
The current was increased by small steps and the value of the current taken 
by a potentiometer as the most accurate ammeter will not detect the small 
changes. The Induced current was measured by the throw of a ballistic galva- 
nometer and the throw evaluated by means of the earth inductor. 
The value of the magnetizing field increased more rapidly than the induct- 
ance until (H) reached the value of about two gauses, then the inductance 
increased much faster than (H), until (H) reacfhed the value 5.068 gauses and 
from this point the ratio of (B) to (H) became smaller and smaller and ap- 
proached zero as a limit making the curve approach a straight line parallel to 
the X axis. As the current decreased the curve crossed the Y axis at (B) = 
10,486 lines, giving 73.3 per cent for the retentivity. When the current was 
reversed the curve crossed the X axis at — 3.03 gauses which is the coercive 
force. ; 
