4 Prof. Pliicker on the Action uf the Magnet 



employed, just as the spectra of Davy's arc show the character 

 of the electrodes. 



Under the inducnce of a magnet, Davy's arc of light assumes 

 tJie form of a magnetic curve, if the end-points of the two electrodes 

 are so situated with respect to the magnet as to constitute two 

 points of the magnetic curve. If the end-points of the two elec- 

 trodes are brought into another position where the above con- 

 dition is no longer fulfilled, the arc can no longer exist ; it must 

 be broken, and, according to the density of the surrounding 

 gas, gives rise to the appearance of a springing, hissing, or 

 undulatory light. 



The previous experiments in this direction of so many eminent 

 physicists, are amply sufficient for consideration from this point 

 of view. I shall therefore at pi'esent only refer to my own 

 observations, which will be found in the next succeeding paper. 

 With the exception of some older ones, they have been performed 

 with the direct purpose of verifying Law I. 



81. (2) One of the two extreme points of the electric discharge 

 is fixed, and the second is subjected only to the condition of lying 

 on a given surface of arbitrary form. These conditions obtain 

 in the remarkable behaviour of that light which I have called 

 the magnetic light, on the very account of its adopting the path 

 of magnetic curves. This light is formed in exhausted tubes 

 at the negative electrode, and passes in all directions from every 

 point in it, to the walls of the glass tube surrounding this 

 electrode, which become more or less blackened by the trans- 

 ported platinum. What becomes of this electric light after it 

 has touched the walls, is a question which cannot be considered 

 in this place. If the electrode be isolated with the exception of 

 a single point, this point is the only one from which the electrical 

 discharge takes place, and whose different paths, corresponding 

 to elementary currents, are made visible by the single luminous 

 rays. (For our present purpose of consideration it is indifferent 

 whether all the rays proceed from the fixed point, or travel 

 towards it.) Every such elementary current, according to the 

 above Law I., can only be in equilibrium under the influence of 

 the magnet when it is bent in a magnetic curve; and here this 

 curve is the same for all elementary currents, and is perfectly 

 defined by passing through the given fixed point. The whole 

 light, therefore, proceeding from the unisolated point is concen- 

 trated, therefore, in the magnetic curve passing through it; and 

 the curve becomes in consequence brightly luminous. The 

 whole continuous series of light-radiating points of the M?dsolated 

 negative electrode, corresponds to a continuous luminous surface 

 formed from magnetic curves. 



Inasmuch as the magnetic curves remain the same if the 



