The Measurement of Magnetic Hysteresis . the centre of the wire, while the ordinates represent the correspondingvalues of Hq, />([= Bq/Hq] and h^ respectively. The nearly straight line passingthrough the origin indicates the value Aq would have if the flow of induction from thewire occurred entirely at its ends, in which case the poles would be concentratedat the ends of the wire. This line represents h^ = 2IqA/P, where Iq \= (Bq—HQ)/47r]is the mean maximum of intensity of magnetisation at the centre of the wire, and 21is the length of the wire. Initially h^ is nearly proportional to Bq. Si
The Measurement of Magnetic Hysteresis . the centre of the wire, while the ordinates represent the correspondingvalues of Hq, />([= Bq/Hq] and h^ respectively. The nearly straight line passingthrough the origin indicates the value Aq would have if the flow of induction from thewire occurred entirely at its ends, in which case the poles would be concentratedat the ends of the wire. This line represents h^ = 2IqA/P, where Iq \= (Bq—HQ)/47r]is the mean maximum of intensity of magnetisation at the centre of the wire, and 21is the length of the wire. Initially h^ is nearly proportional to Bq. Since, however, much of the induction 0 2 100 MESSRS. G. F. C. SEAELE AND T. G. BEDFOED leaks out from the wire by the cylindrical surface, thus developing a distribution ofmagnetism along the wire, Aq is considerably greater than it would be were the ^ poles *at the ends of the wire. As Bq increases, h^ increases less rapidly, reaches a maximumfor a value of B^ [10300] somewhat greater than Bq [8400], the value corresponding 100 ?030. ?025 •020 Scale for h •015 •006 0 2000 4000 6000 8000 10000 12000 Magnetic Induction Ba 14000 18000 18000 20000 Fig. 18. to fji the maximum value of ^, and then diminishes. As B^ increases still further,Aq diminishes rapidly till B^ reaches the stage where /x begins to diminish compara-tively slowly. After passing a minimum \ again increases, and in this last stageis less than 2IqA/^^. § 76, The experiments of Mr. C. G. Lamb, On the Distribution of MagneticInduction in a Long &on Bar,^ serve to explain the rise of h^ to a maximum, and itssubsequent fall. For he found that as B(3 increases from zero, the percentage of theinduction at the centre of the rod which leaks out between the centre and the end of ?X- i Proc. Phys. Soc., vol. 16, p. 509; or Phil Mag., Sept., 1899. ON THE MEASUEEMENT OF MAGNETIC HYSTEEESIS. 101 the rod, increases until Bq reaches Bq approximately. Thus as Bq increases we may-regard the poles ^ as moving inwards toward
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