32 Prof. H. F. Weber on Electromagnetic and 



experiment, I was unable to effect any material change in my 

 final result, I am compelled to see, in the divergent results of 

 MM. Wilh. Weber, F. Kohlrausch, and L. Lorenz (who more- 

 over conducted the investigation each according to one method 

 only), values affected with errors of observation. 



I. Determination of the Absolute Value of the Siemens Resist- 

 ance-Unit on the basis of the Laivs of Magneto-Induction. 

 As ray first method of experiment for the determination of 

 the value of the unit in question I chose a procedure which 

 had already been employed by Wilhelm Weber on the intro- 

 duction of absolute measurements of resistance * ; and I 

 managed it so that it could be carried out under two different 

 conditions. • - 



Two exactly equal, extremely regularly wound cylindrical 

 spirals were connected with a multiplier so that their axes fell 

 into one and the same horizontal straight line, which was per- 

 pendicular to the magnetic meridian. The inner radius of 

 the spirals was 144*43 millims. ; the outer radius amounted to 

 184*46 ; the depth of the space occupied by the turns amounted 

 consequently to 40*03 millims. ; its breadth was 53*64 millims. ; 

 and each spiral numbered 691 turns. A most powerful paral- 

 lelepipedal magnet (its length, breadth, and height were 80, 

 20*1, and 21*1 millims. respectively) was placed withits centre 

 exactly in the axis of the two spirals, and as nearly as possible 

 in the middle between the central planes of the latter ; it was 

 supported by a thin brass wire of about 3 metres length. The 

 stated dimensions of the multiplier and the magnet are of such 

 a magnitude that, in the calculation of the mutual action 

 between multiplier and magnet, in the place of the latter a 

 system of two magnetic poles of equal magnetic moment could 

 be put. 



If a magnet within a multiplier be rotated a small angle 

 from its position of equilibrium and left to the forces acting 

 upon it, it will describe isochronous oscillations, the amplitudes 

 of which diminish in a geometrical progression. With the 

 multiplier " open " 

 the oscillation-period 



Ti 



A /MH , B / A V ' 



and the logarithmic decrement of the amplitudes | 

 * - A T 

 * Electrodynami&che Maassbestimmungen, p. 232. 



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