474 Mr. J. M. Kuehne on the Electrostatic 



In the groups " electromagnetic deflexions " column A 

 gives the scale readings with both charging and magnetizing 

 circuits closed, and column B the readings taken alternately 

 with tbe A readings,' but with the magnetizing current re- 

 versed. A — B therefore gives twice the electromagnetic 

 deflexion. Each " reading " is the point of rest determined 

 from three successive turning-points. The differences A— B 

 are obtained by subtracting each B reading from the mean 

 of the preceding and following A readings. In the groups 

 "torsional deflexions'" the A readings are taken under the 

 same conditions as the A readings in the other groups, and 

 the B readings are obtained by turning the upper torsion- 

 head over 20 cm. of the scale, so as to produce a deflexion in 

 the same direction, and of neatly the same magnitude, as that 

 due to reversing the magnetic field. Both the electric and 

 magnetic fields were left unchanged while the torsion deflexions 

 were made. 



If now 2d is the mean A — B for the electromagnetic, and 

 2d' the mean for the torsional deflexions, D the scale distance, 

 and cf) the moment of torsion of the suspension wire, then the 

 observed moment due to the electromagnetic effect is 



T d 10 , 



Hence from the above set the observed moment is 



T , 1-13x5x58-2 co -, 

 L/= — r-rn — iwwr- ='63 dyne cm. 

 1-34x388 J 



while from theory 



828 x 9-9 X -49 c . , 



L = ~ jjro — ='64 dyne cm. 



27rxl(r J 



In the following table of results : 



Ei = the " effective" charging E.M.F. in volts. 



E 2 = the "effective" E.M.F. in volts induced in one 



turn of a conductor encircling the magnetic field. 

 2i = tbe (double) deflexion due to the electromagnetic 



effect, in cm. 

 2d' = the deflexion due to turning the torsion-head through 

 an angle 20/2D. 

 L = the moment in dyne cm. calculated from theory. 

 L/ = the measured moment in dyne cm. 



The last column gives the percentage deviation of the 

 observed from the theoretical value of the moment. The 



