257 







either the highest or the lowest position within the tube. When the 

 axis of the tube makes an angle of 45 both with the axial and 

 equatorial direction, the epibolic curve is found to be a fine spiral. 



If neither of the two conditions mentioned above can be fulfilled, 

 i. e. if the current cannot proceed either along a free magnetic or an 

 epibolic curve, no voltaic arch will be obtained ; the current will be 

 disturbed, and its light diffused. This, for instance, is the case when 

 the above-mentioned cylindrical tube is placed axially on the two 

 poles of the magnet : there will be seen above each of these poles a 

 luminous epibolic straight line, lying within the horizontal plane 

 which passes through the axis of the tube, one on each side of this 

 axis ; but there exists neither a line of magnetic force nor an epi- 

 bolic curve, joining the extremities of the two epibolic straight lines 

 between the poles ; hence diffusion of light. 



There are other classes of phenomena not at all indicated and ex- 

 plained by the laws of electro-magnetism. In many cases the magnet 

 extinguishes the light of the current, without altering its intensity. 

 I sent the discharge of Ruhmkorff s apparatus at once through two 

 exhausted tubes, communicating by a copper wire. The first tube, 

 about eight inches long and highly exhausted, was brought over the 

 iron pieces of the electro-magnet into an equatorial position, while 

 the second one was placed at some distance from the poles. Whilst 

 the magnet was not excited, both tubes became luminous by the 

 transmitted current ; when it was excited, the light of the first tube 

 entirely disappeared, while the appearance of the second did not 

 undergo the least change. Hence we conclude that the disappear- 

 ance of the light does not prove the extinction of the current. 



Similar results are obtained when a tube having the shape of the 

 annexed drawing is brought with its narrow middle part between the 



two iron pieces. In this case the light disappears where the magnetic 

 action is greatest, but not in the other parts of the apparatus. Some- 

 times before the light disappears, its colour is entirely changed, while 

 in other cases, the magnetic force being less strong, only the change 

 of colour takes place. The violet colour of sulphurous acid and of 

 vapour of bromine is thus transformed into a fine green, and the blue 

 of chloride of tin becomes a beautiful colour of pure gold. 



