r 121 ] 



XVII. On Alternating Discharges in vacuo. 

 By Dr. K. Domalip*. 



(T*\ ASSIOTf was the first to observe and describe reciproca- 

 vDT ting luminous electric currents. He observed that, 

 upon connecting the poles of a RuhmkorfTs coil with tinfoil 

 coatings on the outside of a vacuum-tube, instead of passing 

 the current directly through it, he obtained a finely stratified 

 luminous discharge between the two coatings, which under the 

 influence of a powerful magnet resolved itself into two similar 

 portions, in which the stratifications were curved with the 

 concavities in opposite directions. 



Similar double currents are also obtained by simply con- 

 necting one of the two coatings with one of the two wires of 

 the EuhmkorfF's coil. The current becomes stronger when 

 the second coating is connected with the earth. 



These double currents, as is well known, are easily explained. 

 When the current is excited, the positive electricity becomes 

 accumulated on the one coating, and the negative on the 

 other. The positive electricity acts inductively on the elec- 

 tricity of the tube, fixing the negative electricity and setting 

 the positive free. The opposite action takes place on the 

 other tinfoil coating, the positive electricity becoming fixed 

 and the negative free. The electricities set free in the tube 

 at the two coatings unite, and form the first current. The 

 opposite electricities accumulated on the exterior of the tube 

 next unite through the coil, and the electricities condensed on 

 the interior surfaces of the tube are set free and unite, form- 

 ing the second current, which is opposed in direction to the 

 first. The two currents are consequently not simultaneous, 

 but consecutive. 



Pliicker % also obtained reciprocating currents, by using a 

 long and highly exhausted tube into one end of which an elec- 

 trode was fused. When this electrode was connected with 

 one pole of a Euhmkorff 's coil, whilst the other end remained 

 free or was placed in communication with the earth, currents 

 were obtained which were double, as could be shown by means 

 of an electromagnet, under the action of which the course of 

 the one current can be distinguished from that of the other ; 

 the two currents are of equal intensity. 



Pliicker obtained also alternating currents, by connecting 

 with the earth any point of a tube through which the direct 

 current from the coil was passing ; even the inductive action 

 of the hand was sufficient to produce such double currents. 



* Translated from a separate impression communicated by the Author, 

 t Proc. Roy. Soc. March 4, 1858. % Pogg. Ann. vol. cvii, p. 77. 



