86 Mr. R. H. M. Bosanquet on the Magnetic 
Lines of force. 
Axis of 
magnetizatior 
Lines of force. 
above figure, though they will only be parallel on the average 
to the mean axis of magnetization, where they issue from the 
molecule. 
Now it is known that many magnetic phenomena may be 
expressed by the hypothesis of a tension along the lines of 
force. If we suppose such a tension to exist here, we have 
a couple whose force is equal to the tension, and arm equal to 
the diameter of the molecule x sin @, tending to turn the axis 
of the molecule towards the axis of magnetization. If we 
suppose the molecules to give way to this force, the ends of 
the axes of the successive molecules approach each other, and 
the intermediate space, as well as the number of molecules, 
required to be traversed is diminished. This accounts for 
the increase of the permeability in the first part of the range 
of the induction. 
Without attempting to frame exact hypotheses we can see 
generally that the whole magnetic resistance may be ex- 
pressed by supposing the lines of force to form a zigzag, the 
obliquity of which diminishes as the tension of the lines of 
force increases. From this representation, assuming a law 
similar to Ohm’s law for electric circuits, we get the expression 
ae as representing the reduced resistance of a length / of 
COs 
the magnetic substance, 6 being an auxiliary angle represent- 
ing the mean obliquity of the zigzag. We have further to 
take into account the fact that all forms of iron and steel are 
capable of transmitting only a limited amount of magnetic 
induction through a given area. In the absence of any 
accurate knowledge as to the law which governs this part of 
the resistance of the molecules to the lines of force, I shall 
