442 Prof. E. Wilson. The Distribution of Magnetism 



With alternating magnetic force the phase-displacement is more 

 severe than in the corresponding condition with a rotating magnetic 

 field. At frequency 600 with alternating magnetic force the maximum 

 phase-displacement with a cylinder - 1 cm. diameter is of the order 

 160. With rotating magnetic force of frequency 1434, for a cylinder 

 of diameter and length each O'l cm., the maximum phase-displacement 

 is 122 and at 717 periods per second it is only 104. 



Table II shows that maximum phase-displacement occurs at lower 

 surface induction density the lower the frequency. This is also the 

 case in Table III with alternating magnetic force. 



It is unnecessary to publish all the curves of electromotive force 

 obtained. Figs. 8, 9, and 10 refer to a periodic time of 45 seconds, 

 and the corresponding values of induction density can be seen in 

 Table II. Fig. 8 gives the initial stages with small external magnetic 

 force in which the phase-displacements are relatively small, and the 

 No. 1 and 2 electromotive forces are important. In fig. 9, the electro- 

 motive forces of Nos. 1 and 2 coils are relatively smaller, and the 

 phase-displacements are large. In fig. 10, with high external magneti- 

 sing force, the electromotive forces are in phase and of equal relative 

 importance. 



It is interesting to note the relation between the average permeability 

 of the iron cylinder, and the rate at which the magnetism is propagated 

 to the centre. When the permeability is small the effects penetrate 

 rapidly. With large permeability in the iron the centre is reached 

 with greater difficulty, hence the diminished value of the induction 

 density at the centre and the increased phase-displacement. With the 

 high limits of induction density the average permeability is small and 

 the effects can penetrate more rapidly. 



With intermediate magnetic force at 22'5 seconds periodic time, the 

 electromotive force of No. 1 coil is diametrically opposed to that of 

 No. 3 coil. That is to say, the intensity of induction at the centre of 

 the cylinder is in the same direction as near the surface but of reversed 

 sign. 



IV. Longitudinal Variation of Intensity of Magnetic Induction. The 

 preceding remarks refer to the variation of intensity of induction 

 over a section of the cylinder at its centre 2 inches (5 '08 cms.) thick. 

 We have seen how the magnetism is propagated over this section 

 radially towards the centre. It is necessary to deal with the variation 

 of induction density as one proceeds from either end of the cylinder 

 to its centre. 



The electromotive forces of each of the coils I, II, III (fig. 1) were 

 observed simultaneously as in the case of coils 1, 2, 3, and by integra- 

 tion the maximum average intensity of magnetic induction over each 

 area has been found. An examination of these curves shows that the 

 effects of induced currents penetrate from each end of the cylinder 



