STRIDE IN THE ELECTRIC DISCHARGE. 383 



more numerous and narrower in proportion as the intermis- 

 sions of the contact-breaker are more rapid, which I have 

 observed to be very notably the case, the evidence seems 

 strong, if not conclusive, that the striae or bands are due to 

 the mechanical interference or reciprocal impulsions of two 

 or more discharges, or rather of the impulsions on the medium 

 affected.* 



I will take this opportunity of mentioning one experiment 

 which I believe to be new and not devoid of interest. M. 

 Plucker and Mr. Gassiot have published several interesting 

 experiments on the effects produced by magnets on the striae 

 or on the electric discharge in highly attenuated media, com- 

 monly called vacuua. 



In repeating some of these experiments with a vacuum- 

 tube kindly given me by Mr. Gassiot, two feet nine inches long 

 between the platinum wires, and one inch internal diameter, 

 I found that when the pole of a powerful bar magnet was 

 brought close to the positive platinum in a certain direction, 

 the visible discharges only passed occasionally and at intervals 

 through the tube, notwithstanding the apparatus went on 

 working, and the contact-breaker vibrating as usual. After 

 many experiments, I found that I could stop the discharge 

 entirely, by placing the poles of two magnets opposite each 

 other and in a particular direction with reference to the line of 

 discharge. The two platinum wires in this tube are inserted 

 perpendicularly to the axis, and penetrate half an inch into 

 the tube. If, now, the tube be placed horizontally, the plati- 

 num wires uppermost, and the observer looking along the tube 

 from the positive to the negative wire, the north pole of the 

 magnet should be placed on the right-hand side, and as nearly 

 as can be to the positive platinum, i.e. touching, or nearly so, 

 the glass tube, while the south pole of another magnet is 

 similarly placed on the opposite or left-handed side. The dis- 

 charges cease entirely, and there is no conduction through 

 the tube, showing that it is not a case of dark discharge, 

 but an arresting of the passage of the discharge through the 



* This conclusion is too limited. Mr. Gassiot subsequently to the publication 

 of this paper obtained the strise with the voltaic arc. This is, however, regarded by 

 some as intermittent, and is at all events not a single discharge. W.R.G., 1874. 



