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INFLUENCE OF MAGNETIC FORCE ON THE ELECTRIC DISCHARGE. 



Professor Ttndall has exhibited at the Royal Institution a 

 brilliant series of experiments illustrative of the constitution of the 

 Electric Discharge and of the action of Magnetism upon it. The 

 Report occupies nearly five pages of the printed proceedings of the 

 Institution ; the following summary is from the Mechanics' Magazine. 

 The substance of the discourse was derived from the researches of 

 various philosophers, its form being regulated to suit the require- 

 ments of the audience. 



The influence of the transport of particles was first shown. The 

 carbon terminals of a battery of 40 cells of Grove were brought 

 within one-eighth of an inch of each other, and the spark from a 

 Leyden jar was sent across this space. This spark bridged with 

 carbon particles the gap which had previously existed in the circuit, 

 and the brilliant electric light due to the passage of the battery 

 current was immediately displayed. 



The magnified image of the coal points of an electric lamp was 

 next projected upon a white screen, and the distance to which they 

 could be drawn apart, without interrupting the current, was noted. 

 A button of pure silver was then introduced in place of the positive 

 carbon, a luminous discharge four or five times the length of the 

 former being thus obtained. The action of a magnet upon the 

 splendid stream of green light obtained in the foregoing experi- 

 ment was then exhibited, the light being bent hither and thither, 

 according as the poles of the magnet changed their position : the 

 discharge in some cases formed a magnificent green bow, which on 

 the further approach of the magnet was torn asunder, and the 

 passage of the current thereby interrupted. 



A discharge from Ruhmkorff's coil was next sent through an 

 attenuated medium ; and the glow, which surrounded the negative 

 electrode, was referred to. An electric lamp was placed upon its 

 back ; a horseshoe magnet was placed horizontally over its lens, and 

 on the magnet a plate of glass ; a mirror inclined at an angle of 45° 

 received the beam from the lamp, and projected it upon the screen. 

 Iron filings were scattered on the glass, and the magnetic curves 

 thus illuminated were magnified, and brought to clear definition upon 

 the screen. The negative light above referred to arranges itself, 

 according to Pliicker, in a similar manner. 



The rotation of an electric current round the pole of a magnet, 

 discovered by Mr. Faraday in the Royal Institution, nearly forty 

 years ago, was next shown ; and the rotation of a luminous current 

 from an induction coil in an exhausted receiver by the same magnet 

 was also exhibited, and both shown to obey the same laws. 



Into a circuit of 20 cells a large coil of copper wire was introduced ; 

 and when the current was interrupted, a bright spark, due to the 



