Whitehead — Magnetic Effect of Electric Disj^lacemeiit. 125 



mncli strengthened after the many recent failures to detect any 

 evidence of it." 



FaiKng to repeat the condition as above described, a light 

 strip of wood was placed along a diameter on top of the inner 

 ring. This strip took up a sufficient charge to give the beam 

 the position of delicate eqnilibrium when the beam was paral- 

 lel to it, i. e., directly over it; it could be rotated to any posi- 

 tion on the ring without opening the case, by means of a device 

 not shown in the sketch ; the rod of the damping vane passed 

 through a hole at its center. A number of experiments were 

 made with the following order ; the beam was allowed to find 

 a stationary position under the influence of the magnetic field 

 alone. The interior being visible through the glass cover of the 

 casing, the wooden strip was turned so as to be parallel to and 

 directly under the beam, with the idea that the zero positions 

 for the two fields would be brought into coincidence. It was 

 found that in most cases any movement of the strip would 

 upset the position of equilibrium due to the magnetic field. 

 Frequently, however, the condition of coincidence was ap- 

 proached, and in all these instances when the effect was looked 

 for the results were either spurious or negative. That is, if 

 there was a deflection, as sometimes to the amount of 1"™ or 

 2™™, neither its direction or amount changed with a reversal of 

 field ; or often there was no deflection at all for either phase 

 of the field. 



Differences in deflection for the two phases of either fleld 

 were now looked for ; the wooden strip was discarded and the 

 beam allowed to find a stationary position under the action of 

 both fields. That is, the electric field was put on and a steady 

 state reached ; then the magnetic field, resulting in a deflection 

 of usually between one and two centimeters to a new position 

 of equilibrium. The magnetic field was then quickly reversed 

 and a change in the position of the beam looked for. In a 

 series of observations in which the conditions seemed perfect, 

 no change at all could be noted when the field was reversed, 

 there being either no deflection at all, or less than 1™'^ without 

 regularity. In these experiments the coil only carried 2'6 

 amperes, giving a calculated effect one-half of that estimated 

 above ; 5*3 amperes, i. e., 200 volts on the coil, during the time 

 required for the beam to come to rest, heated the interior to an 

 extent sufiicient, by reason of air currents or expansion of the 

 ring electrodes, to cause erratic oscillations of the beam about 

 its zero position. 



While it was thought that at the comparatively low frequency 



of the alternating circuit, 133 cycles per second, a possible lag 



of the displacement current, owing to molecular friction or other 



cause, could hardly make itself felt, it nevertheless seemed 



Am. Jour. Sci.— Fourth Series, Vol. XIV, No. 80.— August, 1902. 

 9 



