THE DISTURBANCE OF ISOMAGXETICS. 167 



or its effect is to incrense the temperature coefficient by about 3 per cent. 

 Correction for the induced Magnetism : — Tlie magnetic moment 

 arising' from the mao-netization indiicel in the vibration mao-net l)v a 

 given magnetic field, comparable with that of the earth, was determined 

 by the magnetometric method. The magnet was placed on the 

 deflection bar, as in the actual deflection experiment, and was subjected 

 to various weak fields obtained by means of a solenoid enclosing the 

 magnet and the bar together. The deflection due to the permanent 

 magnetism of the magnet was compensated by means of anotlier bar 

 magnet placed on the other side of the magnetometer on the deflec- 

 tion bar. A solenoid, 23 cm. in length and 2.() cm. in diameter, 

 was wound in four layers with fine insulated copper wire, the total 

 number of turns being 71 per cm. The effect of tlie solenoid alone 

 was calculated by observing the deflections Avhen the known current 

 was passed through tlie solenoid, the magnet being ttdcen away. 

 This deducted from tlie deflection when the magnet was put in, gave 

 the deflection proportional to the moment induced by the field. For 

 observing the deflection, a scale cut in mm., was placed at a distance 

 of 4.2 metres from the magnetometer. By means of a. telescope, the 

 deflection could be read to the tenth of a scale division. At eacli ob- 

 servation of deflection, the magnetometer zero was noticed, to guard 

 against any changes of declination. The fallowing are the results 

 obtained by Messrs. Ota and Xak:inuu'a : — 



