PHYSICS. 019 



netic substances but all bodies, as well as empty space, are fllled with cir- 

 cular currents of very small dimensions and that maf?netic substances 

 difler from non-magnetic substances only inasmuch as the number of cir- 

 cular currents present in the unit volume is much greater in the first 

 case than in the second. All magnetic phenomena may then be referred 

 to the property of the electric current of exerting a directive force upon 

 the molecular solenoids which fill all space, but which are present iu 

 greater numbers in the so called magnetic bodies, which place their axes 

 at right angles to its direction and tend to bring them into closer con- 

 centric attraction circles. The magnitude of this rotation of the axes, 

 depends, on the one hand, on the magnitude of the directive or mag- 

 netizing force, and, on the other hand, on the number of the molecular 

 circuits pre-existing in the unit volume, for which condition the term 

 "magnetic conductivity" may be employed, or that of "magnetic resist- 

 ance" for its reciprocal value. Since a magnetizing force, acting upon 

 the molecular magnets only, exerts a perceptible influence on the rota- 

 tion apart from each other of the paired elementary magnets when all 

 the neighbors in the magnetic circuit follow the motion and so are able 

 to produce a closed system of equilibrium capable of mutual attraction, 

 it follows that the rotation directly i)roduced by the magnetizing force 

 must be very small in comparison with the mutual strengthening of the 

 rotation in the closed magnetic circuit. The magnetic moment pro 

 duced must thus be essentially the product of the mutual strengthening 

 of rotation of which the magnetizing force is the cause. ( Wied. Ann., 

 XXIV, 93; Fhil. Mag., April, 1885, V, xix, 237; J. Phys., September, 1885, 

 II, IV, 426.) 



Bosanquet has i^ublished a series of magnetic measurements made to 

 test his theory of magnetism. His formulas suppose that each molecule 

 has one and only one axis of transmission (like a bead with a hole in it). 

 The axis is capable of transmitting a certain number of lines of force 

 and no more, and the molecular permeability is proportional to the 

 defect of saturation. (If the hole in the bead be packed with thin 

 wires the aperture remaining is represented by the number of wires 

 that remain to be got in.) Eegarding magnetism as a motion or dis- 

 placement, whether dynamic or static, we may thus speak of the molec- 

 ular i)ermeability as a coefficient of freedom within the molecule. The 

 reciprocal of the coefficient of the forces which tend to prevent the ro- 

 tation of the molecule as a whole may be spoken of as a coefficient of 

 freedom without the molecule. The product of these two coefficients 

 by a constant is a characteristic of a given approximate state of a given 

 piece of metal. As between the hard steel and the iron the product of 

 the coefficients of freedom is proportional to the maximum permeability. 

 In soft steel the molecular forces are chiefly extra-molecular, the free- 

 dom intramolecular ; iu hard steel the reverse is true. In soft iron 

 the average intra-molecular freedom is much greater than in hard steel, 

 the extra-molecuhir tre(Hlom about the same. In soft steel the extra- 



