170 Professor Tyndall, on the Influence of [Jan. 20, 



of the action of magnetism upon it. The substance of the discourse 

 was derived from the researches of various philosophers, its form being 

 regulated to suit the requirements of the audience. 



1. The influence of the transport of particles was first shown by an 

 experiment suggested, it was believed, by Sir John Herschel, and per- 

 formed by Professor Daniell. 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. 



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

 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 silver was first observed to glow, and afterwards 

 to pass into a state of violent ebullition. A narrow dark space was 

 observed to surround one of the poles, corresponding probably with 

 the dark space observed in the discharge of Ruhmkorff's coil through 

 rarefied media.* 



3. The action of a magnet upon the splendid stream of green light 

 obtained in the foregoing experiment was exhibited. A small horseshoe 

 magnet of Logemann was caused to approach the light, which was 

 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. It was Davy 

 who first showed the action of a magnet upon the voltaic arc. The 

 transport of matter by the current was further illustrated by a series 

 of deposits on glass obtained by Mr. Gassiot from the continued dis- 

 charge of an induction coil. 



4. A discharge from Ruhmkorff's coil was sent through an 

 attenuated medium ; and the glow, which surrounded the negative 

 electrode was referred to. One of the most remarkable effects hitherto 

 observed was that of a magnet upon this negative light. Pliicker had 

 shown that it arranges itself under the influence of the magnet exactly 

 in the direction of the magnetic curves. Iron filings strewn in space, 

 and withdrawn from the action of gravity, would arrange themselves 

 around a magnet exactly in the manner of the negative light. 



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, 



* Mr. Faraday noticed this dark stripe while the speaker was making his pre- 

 paratory experiments. 



