. The Philosophical magazine; a journal of theoretical, experimental and applied physics . e joint were strictly constant. Table II. gives values ofthe width of air-gap equivalent in magnetic resistance to thejoint, as determined from this experiment. Table II. s. Width of air-gap equivalent to the joint, in centimetres. 4000 00026 6000 00030 8000 00031 10000 00031 12000 0-0035 14000 00037 Data relating to a second experiment in which a cut withtrue-plane surfaces was introduced in another iron bar willbe found in the former ])aper. Fig. 2 shows the graphictreatment of this example, and it wil
. The Philosophical magazine; a journal of theoretical, experimental and applied physics . e joint were strictly constant. Table II. gives values ofthe width of air-gap equivalent in magnetic resistance to thejoint, as determined from this experiment. Table II. s. Width of air-gap equivalent to the joint, in centimetres. 4000 00026 6000 00030 8000 00031 10000 00031 12000 0-0035 14000 00037 Data relating to a second experiment in which a cut withtrue-plane surfaces was introduced in another iron bar willbe found in the former ])aper. Fig. 2 shows the graphictreatment of this example, and it will be seen that the dottedcurve which exhibits <i^ —<^ is in this case slightly concavetowards the axis of 33, whereas in the former example it was 324 Professor Ewinsf o?? Joints slightly convex. The deviations from straightness are inneither case more than may well be set down to uncer-tainty in the experimental data ; and taking the two examplestogether it seems very probable that the joint is equivalentto an air-gap of sensibly constant magnetic resistance. In Fier. 2. 14000. * 4000 2 4 6 8 10 12 14 16 Magnetizing Force due to Solenoid. the first example the width of the equivalent gap was about00033 cm.: in this case its mean value is about 00036 cm. Small as these gaps are, it is difficult to believe that themetallic surfaces were actually separated so far, and it seemsmore probable that the magnetic resistance of a joint is duein part to a reduction of permeability in the metal itself atand close to each surface, as a result of the influence ofsurface conditions in affecting the grouping of the molecularmagnets. Since the joint is equivalent to an air-gap of sensibly con-stant width it is easy to apply a graphic construction, likethat used by Lord Rayleigh in the case of ellipsoids*, to de-termine the influence which the joint must exert in any cyclicor other magnetizing process ; or, conversely, to determinefrom experiments made on a circuit in which there is a j
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