Influence of Magnetic Force on the Electric Discharge. 289 
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 horse- 
shoe 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 mag- 
nificent 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 discharge of an induction coil. 
4. A discharge from Ruhmkorff’s coil was sent through an at- 
tenuated 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strewn in space, and withdrawn from the action of gravity, would 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, and brought to clear definition upon the screen. The 
negative light above referred to arranges itself, according to Plucker, 
in a similar manner. 
5. 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. This 
beautiful experiment was devised by Dela Rive. 
6. Into a circuit of 20 cells a large coil of copper wire was intro- 
duced ; and when the current was interrupted, a bright spark, due to 
the passage of the extra current, was obtained. The brightness and 
_* Mr. Faraday noticed this dark stripe while the speaker was making 
his preparatory experiments. 
