1893-1902. No. 6.1 



TERRESTRIAL MAGNETISM. 



29 



observations. 1 have therefore deemed it best simply to employ the values 

 deduced from the observations that Amundsen made with great accuracy 

 under most favorable conditions. These include a long series of deflec- 

 tions with both deflectors placed at both distances in various temperatures 

 from — 1.3° C to + 20.7°. The temperature coefficient adopted is therefore, 



for magnet V, a7= 0.000243 



for magnet F7, av7= 0.000625. 

 If we call the angle of deflection at 0°, cfo, and the time of vibra- 

 tion at 0°, To, we obtain from equations (1) and (2), 



sm cfo ■ 



rp2 



■'■0 



Sin f/i 



^2 



l + (2/i' + «)L 



or, substituting the values of /?, ^' and a, we obtain the following for- 

 mulae for the reduction of the angle of deflection and the time of 

 vibration to 0°: 



For magnet V, log sin cpo = log sin rp -)- 12.93 t^ . 10" 



log To =logr - 5.1 



t^ . 10' 



For magnet VI, log sin epo = log sin rp -\- 29.60 ttf . 10 

 log To = log T 



- 14.09 iy. 10" 



(4) 



DETERMINATION OF THE CONSTANTS G AND /.l. 



The following table gives the values of C and fi that have been 

 found at various times for the two deflectors, V and VI, placed at the 

 distance e = 29.840 cm., and E = 39.638 cm. It should be remarked 

 that in all these cases, the small declination needle, L, has been em- 

 ployed as deflected magnet. 



