126 Whitehead — Magnetic Effect of Electric Displacement. 



worth while to shift the phase of either the electric or the 

 magnetic held bj a quarter of a period. For this purpose a 

 two-phase machine was used, one phase being put on the pri- 

 mary of the high tension transformer, the other directly on the 

 magnetizing coil. This separates the displacement current and 

 magnetic held by one-quarter of a period, if there is a lag of 

 one-quarter of a period in the coil due to its self-induction, 

 as was approximately the case in the experiments already 

 described. The machine operated at 38 cycles, and 85 volts 

 per phase ; the resulting displacement current is thus 



38 85 _ 



of the value calculated for the first arrangement ; at the lower 



frequency and voltage, however, the coil took 6*2 amperes, so 



6 • 2 

 that the magnetic field is - — ^ = 1-17 times that in the first 



5*3 



arrangement, so that the calculated magnitude of deflection is 



still appreciable ; the angle of lag is given by 



, 27r]S[L 237X • 05 . . o 



tan e = — .^- = — jf^ — = 3-05, .-. e = 72°. 

 IX 3*9 



The circuits were also arranged so that both electric and mag- 

 netic fields might be put on the same phase or one on each ; 

 this permitted, with the use of the reversing switches, a rapid 

 change of phase of either approximately 90° or 180° between 

 the displacement current and the magnetic field. In a series 

 of observations with this arrangement there appeared to be no 

 difference among the results of the several combinations of 

 phase. The beam was allowed to come to rest under the 

 electric field alone ; on putting on the magnetic field there 

 was the usual deflection, but there was no evidence of any 

 change either in direction or amount of this deflection when 

 the phase relations were altered at random. 



Summary and Conclusions. 



The mass of the evidence of this research is against the pres- 

 ence of the magnetic effect of electric displacement in an amount 

 given by Maxwell's expression. The single positive result 

 obtained with the final form of the apparatus must be ques- 

 tioned, for although the favorable conditions under which that 

 result was observed could not be obtained a second time, it is 

 thought that at times they were approached sufficiently to give 

 traces of any effect as great as that noticed. The final form of 

 the apparatus was undoubtedly that most likely to give results ; 

 in it there appear to be only two infiuences which might pre- 



