THE DISTURBAN'CE OF ISOMAGXETICS. 161 



Ohscrved lime of vibration. 



Deflection for complete) , , , , Deflection for comi)letel 



11. 1 ■... .. . , , 13'.8 



rotation of torsion head. ) rotation of torsion head. 



The temperature coefficient for the nionieiit of the mafj-net was 

 taken from calculation« made on the observation.s at Lsshiki. 



Temperature Coefficient of Magnetic Momoit : — In the former 

 survey, no correction for the difference of temperature in vibration 

 and deflection experiments was applied in the reduction of the obser- 

 vations of horizontal intensity. This gives the moment of the 

 magnet at mean temperature; l:)ut the vahie of the horizontal intensity 

 is affected inasmuch as the magnetic moment was different in the two 

 experiments; it will have been less if the temperature was higher in 

 the vibration than in the deflection experiment, and vice versa. 



The determination of the temperature coefficient of a magnet is a 

 matter of some difficult3\ It is desirable to determine the effect of 

 temperature on the magnetic moment Ijy placing the magnet in the 

 same state as in the determination of horizontal intensity. By taking 

 the number of observations of horizontal intensity at dift'erent hours of 

 the day, so that there is sufficient difference of temperature during the 

 experiments, we can obtain data for the calculation of the temperature 

 coefficient. With this object in view, many observations of the 

 horizontal intensity were made at Nagoya. 



