124 Whitehead — Magnetic Effect of Electric Displacement. 



field when on alone gave a deflection in the same direction. 

 Thus the magnetic field when on alone also had an effect on the 

 position of the beam. With the beam at rest, when this field 

 was made a slow drift away was generally seen, the beam com- 

 ing to rest in some other position. Repeated efforts failed to 

 locate single positions that it seemed to prefer, though in cer- 

 tain neighborhoods the direction of the deflection seemed the 

 same. In some positions there was no deflection, though these 

 were never the zero positions for the electric field alone ; the 

 problem then seemed to bring the two zero positions together. 

 Since the disturbance due to the magnetic field did not ap- 

 pear to be the influence of the splits in the ring as before, for 

 it seemed independent of the distance of the dielectrics from 

 them, and since the intensity of the magnetic field was uni- 

 form, it therefore seemed that direct electric influence of the 

 coil or leading-in wires must be the cause, though the tin-foil 

 screen seemed as perfect as possible. The attempt was then 

 made to bring one of the positions in which the beam seemed 

 unafi^ected by the magnetic field alone, into coincidence with a 

 zero position for the electric field alone, by turning the coil 

 into various positions about its center. This process was most 

 tedious, involving as it did long waits for the beam to come to 

 rest, and at its best it seemed only a hit-or-miss method. The 

 condition sought, however, seemed so desirable, that repeated 

 efforts were made to bring it about. One of them succeeded; 

 and while the result obtained must be discredited in view of 

 the failure of all attempts to repeat the proper conditions, and 

 of other negative attemj^ts, it is nevertheless thought that the 

 following quotation from a note taken at the time should be 

 inserted here : " this condition was obtained March 18th ; the 

 beam was allowed to come to rest under the electric field; this 

 was then cut off and 100 volts put on the magnetic coil, which 

 caused no deflection of the beam. On putting on both fields 

 there was a slow deflection to the right of between 1^°" and 2^% 

 about one minute being required. The magnetic field was 

 then taken off and the beam allowed to move under the electric 

 field alone ; it resumed the former zero after one or two min- 

 utes. The magnetic field was then put on reversed ; there 

 resulted a much stronger deflection to the left which was 

 allowed to continue several minutes, resulting in a deflection of 

 5^°". Repetition could not be obtained, due to the fact that 

 after the large deflection the beam did not return to the origi- 

 nal zero position. (The heating of the a{3paratus due to the 

 large current in the coil (10 amperes) when applied for any 

 length of time frequently upset the equilibrium positions.) 

 The conditions, however, of the above observations were so 

 favorable that my belief in the presence of the effect was 



