C. HORIZONTAL INTENSITY. 



As already mentioned in the introduction, the magnetic apparatus 

 E. A. ZSCHATJ No. 289 was arranged for the taking of both deflection obser- 

 vations at two different distances, and observations of the deflectors' time 

 of vibration, whereby the absolute value of the horizontal intensity may be 

 determined when the constants of the instrument are known. 

 If the following signs are employed: 

 H = absolute horizontal intensity 

 <p = angle of deflection 

 e = distance of the deflector 

 k = a constant depending upon the distribution of magnetism in 



the deflecting and deflected magnets 

 k' = induction coefficient 

 K = moment of inertia of the magnet 

 T = time of vibration, corrected for rate 'of chronometer, arc of 



vibration and torsion force of the suspending thread, 

 a = temperature coefficient 

 ft = coefficient of dilatation for brass (O'OOOISO) 

 ft' = coefficient of dilatation for steel (0'000124) 

 t = temperature of magnet during the vibrations 

 f = temperature of magnet during the deflections, 

 we have 



H = = l + (rt-l(tf+a(t- f ) , (1) 



