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VIII. Experiments in Electric and Magnetic Fields, Constant 

 and Varying. By Messrs. Kimington and Wythe Smith.* 

 [Plate IV.] 



THE object the authors have in bringing these phenomena 

 before the Society is not to establish any new theory, 

 nor to show imperfections in present theories, but to exhibit 

 experiments which help the actions taking place in a dielec- 

 tric under stress to be more easily grasped. 

 The experiments are divided into two sets : — 



(1) Performed in electric fields. 



(2) Performed in varying magnetic fields. 

 Although these two fields cannot exist separately, their 



effects are isolated. 



Set 1. Constant Electric Field. 



A constant electric field was produced by two charged 

 metal disks + and — , each of which was stuck on the out- 

 side of a glass plate (Plate IV. fig. 1). The object of the glass 

 plates was to prevent brush discharges between objects placed 

 in the field and the plates. 



Fig. 1, a, b represents a partially exhausted electrodeless 

 tube, placed in the uniform electric field. In the position 

 shown, the tube is at a uniform potential. Now let it rotate 

 in the direction of the arrow ; the potential of a will fall and 

 that of b rise until the P.D. between the ends is sufficient to 

 break down the tube. There will then be a convection - 

 current equalizing the potential, during the continuance of 

 which the tube will glow. On rotating still further a similar 

 action will take place. 



The effect of these actions is to produce a double fan-shaped 

 set of images, as shown in fig. 2. The number of images in 

 the fan depends on the intensity of the field. 



This phenomenon is intensified by constricting the middle 

 part of the tube. 



In designing the tubes for these experiments, care was 

 taken to have the point where they were connected to the 

 pump in such a position that there was no tendency for dis- 

 charge to take place at these points when in use. The tubes 

 used in this experiment are shown in fig. 3 (a, 5, c, and d) . 

 The stem was used to connect them to the whirling motor. 



The surfaces of these tubes should be fairly clean and dry, 

 and it is advisable with a new tube, or one left unused for some 

 time, to excite it between the knobs of an influence-machine. 



In the double fan-shaped set of images (see fig. 4, a) one 



* Communicated by the Physical Society : read November 25, 1892. 



