Nipher — Nature of the Electric Discharge. 9 



In Plate IV loud disruptive discharges are similarly 

 treated, the Leyden jars being connected with the ter- 

 minals. In Figs. A and B the hole in the copi^er plate 

 is opposite the positive terminal, but in B the hole was 

 covered with a thin sheet of paper which was hung 

 over the upper edge of the plate. Its effect was to ob- 

 struct the drainage flow exactly as would have been done 

 if the hole had been filled with copper. Disruptive dis- 

 charges along this obstructed path are then also pre- 

 vented. In Fig. C, the hole in the copper plate was oppo- 

 site the negative knob. The discharge knobs and rods 

 were put more nearly in line than in the former case, in 

 order to give the negative terminal a better opportunity 

 to behave as the positive had done in Fig. A. The dis- 

 charge was apparently exactly the same as if no hole 

 existed in the plate. 



If the knobs are separated somewhat more widely, 

 than in the experiments just described, and the copper 

 plate is placed midway, no sparks will pass to the plate 

 if the drainage column is obstructed by the plate. They 

 pass when it is removed. A continuous plate of sufficient 

 size, or a plate having an opening in it, which is covered 

 with a sheet of paper, will obstruct the drainage column. 

 It reaches the plate, and reappears at its edges and 

 corners. It may curve towards the cathode knob from 

 the edges of the plate. If they are so far from the 

 cathode that this conducting channel does not reach the 

 negative glow, no spark will pass. The effect of displac- 

 ing the plate in its own plane so as to diminish the dis- 

 tance from one edge of the plate to the negative knob, 

 is shown in Plate V, Fig. A, and in Plate VI, which is 

 an enlarged copy of a similar photograph. The luminous 

 conducting column along which the discharge passed could 

 be distinctly seen just before the spark passed. This 

 glow does not show in the photograph, partly because 

 the development was not continued long enough to bring 

 it out, and partly because the light of the discharge ob- 

 scures it when this is attempted. It is evident that mole- 



