506 Mr. J. Trowbridge on Damping of 



Although the impulsive impedance is apparently not affected 

 by the magnetic character of the wire, our experiments lead 

 us to believe that discharges of the quick period of a Leyden 

 jar are affected very appreciably by the magnetic nature of 

 iron, steel, and nickel conductors. This effect is so great 

 that it damps the electrical oscillations, and makes it diffi- 

 cult to determine whether the time of oscillation is also 

 affected by the permeability of the conductor. 



The apparatus employed was similar to that described 

 in my investigations of electrical oscillations with an air- 

 condenser (Proc. American Academy of Arts and Sciences, 

 May 28, 1890). Certain important modifications, however, 

 were made. The plane mirror which I used in the former 

 research was replaced by a concave mirror of 10-feet focus and 

 Ott inches in radius. This mirror was mounted upon the end 

 of the armature -shaft of a one-half horse-power electric motor. 



The discharging apparatus consisted of a sharp cutting-tool, 

 insulated, and mounted on the edge of the rotating disk bear- 

 ing the mirror. It was metallically connected with a grooved 

 ring of brass mounted upon the shaft and insulated from it 

 by hard rubber. Around this was wound a copper wire, one 

 end of which was connected with the discharging wire and 

 the other drawn taut by a rubber band. The electrical 

 discharge was thrown upon the circuit by pushing forward a 

 lever, which brought a solid hinged frame containing a strip 

 of soft type-metal into contact with the rapidly revolving 

 steel cutting-tool. An electrical contact was thus insured by 

 the tool cutting a groove in the strip of type-metal. In order 

 to avoid a spark at the contact, the type-metal was thickly 

 covered with a wax of peculiar composition. The only spark 

 therefore that occurred was the one the oscillations of which 

 I desired to study. At each trial the type-metal was moved 

 so as to expose a new cutting surface. The type-metal was 

 insulated from the rest of the apparatus but connected with 

 the outer coating of the Leyden jar. First, both terminals 

 of the Holtz machine were throwu off, and immediately after, 

 the cutting-tool, ploughing its way through the type-metal, 

 placed the outer coating of the Leyden jar in circuit with one 

 of the two parallel wires leading to the terminals of the spark. 

 The other wire w T as permanently in connexion with the inner 

 coating of the jar. 



reden. Auch Eisendrahte machen keine Ausnahme von der allgemeinen 

 Regel, die Magnetisirbarkeit des Eisens kommt also bei so schnellen 

 Bewegungen nicht in Betracht." — Ann. der Phi/sik imd Chemie, vol. xxxiv. 



1888., p. 558. 



