Whitehead — Magnetic Effect of Electric Displacement. Ill 



metal coatings which were connected to an induction coil. 

 The winding on the ring being connected to a telephone 

 receiver, sounds were obtained on charge and discharge of the 

 coil. Very slight conductivity in the paraffin would have 

 caused this. 



Nicolaieff. — Nicolaieff in 1895"^ suspended a ring of paraffin 

 between the two poles of an electromagnet, the plane of the 

 ring being vertical and making an angle of 45° with the axis of 

 the poles. The E.M.F. induced in the ring when the magnet 

 is excited by an alternating current, sets up a displacement 

 current which, by its magnetic reaction on the exciting field, 

 creates a couple tending to make the ring turn and set itself 

 perpendicular to the field. He excited the magnet first with 

 direct current, getting a deflection due to the magnetic qualities 

 of the ring, then with alternating current of the same intensity, 

 causing a different deflection, the difference being due to the 

 displacement current. The record of observations is not given 

 in the paper, the author simply stating that the deflection was 

 greater when the magnetic field was alternating than when 

 direct ; and was greater the greater the frequency. For 12 

 cycles per sec. the increase was 9^^' over the constant magnetic 

 field, for 15 cycles 12^' ; in this case also conduction would 

 cause the observed effect. 



Blondlot. — Recently M. R. Blondlotf looked for an electric 

 displacement in a mass of air moving in a magnetic field. He 

 forced a blast of air through a rectangular passage, two sides 

 of which were pole faces of a magnet, the other two a pair of 

 condenser plates. The plates were connected by a wire which 

 was broken at the instant the blast was at its maximum, so that 

 the plates should be left charged if there was any electric dis- 

 placement in the mass of air. He calculated the expected 

 effect and calibrated his electrometer to read it ; the results of 

 a number of experiments were invariably negative. Making 

 use of this experimental fact, he then proves theoretically the 

 absence of any electromagnetic action of a magnetic field on a 

 displacement current. 



Present Research. 

 General Theory. 



The series of experiments hei-ein described were undertaken 

 in view of the continued uncertainty of the results of all effort 

 to observe the magnetic effect of electric displacement, and in 

 view of the fact that the method employed had certain advan- 

 tages over those used heretofore. 



* Jour. Phys., vol. iv, 1895, pp. 245-254. 

 t Jour. Phys., Jan. 1902, p. 8. 



