110 Mr. J. E. Moore on a Continuous and 



magnetic moments of the sample, at the points in the alter- 

 nating-current waves at which the instantaneous direct current 

 passes in the magnetometer system. Since the centre of the 

 I-magnetometer helix lies in the prolongation of the axis of 

 the long rod, and the magnetic field due to the long rod is 

 symmetrical about its axis, the deflecting force exerted on the 

 I-magnetometer helix by the long rod is independent of the 

 angular position of the I-magnetometer helix about the ver- 

 tical axis of suspension of the magnetometer system. If, then, 

 we adjust a coil of wire so that its centre is in a horizontal 

 line (normal to its plane) passing through the centre of, and 

 perpendicular to that magnetometer helix capable of displace- 

 ment about a vertical axis only (called hereafter the H-mag- 

 netometer helix) ,and pass through this coil the same alter- 

 nating current that magnetizes the sample, the H-coil will 

 receive a horizontal angular displacement, and through the 

 mechanical connexions of the parts of the moveable system it 

 will carry with it through the same horizontal angle the 

 I-magnetometer helix. This horizontal displacement being 

 made against the restoring couple of the fine silver wire 

 bifilar suspension of the system, is equilibrated partly by the 

 restoring couple of the bifilar suspension proper (which varies 

 as the sine of the angle of displacement), and partly by the 

 torsion of the bifilar wires (which varies directly as the angle 

 of displacement). Hence for small horizontal angular de- 

 flexions the angular displacement may be taken proportional 

 to the product of the magnetic moments of the coil carrying 

 the magnetizing current and the H-magnetometer helix, at 

 the point in the alternating current waves at which the helix 

 becomes a magnet. But the magnetic moment of the H-mag- 

 netometer helix may be kept constant throughout an experi- 

 ment; hence, as will be seen from curve (/>), fig. 2, the 

 horizontal angular displacements may be taken proportional 

 to the magnetic action, or the magnetizing force of the cur- 

 rent, at the points in the alternating-current waves at which 

 the instantaneous direct current passes through the magneto- 

 meter helices. 



If it is desired to measure the losses of energy in iron 

 magnetized by continuous currents, or the " static " losses of 

 iron, plainly the only change of arrangement in the curve- 

 tracer is to substitute for the intermittent current through 

 the magnetometer system a direct current of the same mean 

 intensity, to replace the source of alternating current by a 

 continuous-current source, and provide a regulating resistance 

 for varying the continuous magnetizing current from zero to 

 the maximum value required. 



