OF ARTS AND SCIENCES. 117 



confirmed that the magnetism of the iron is unable to follow such 

 rapid oscillations, and therefore exerts no appreciable efiect. The 

 velocity of propagation in a wire has a definite value independent of 

 its dimensions and material. Even iron wires offer no exception to 

 this, showing that the magnetic susceptibility of iron does not ])lay 

 any l^urt in the case of such rapid motions.* 



Altlioiigh the iin[)ulsive impedance is apparently not affected by the 

 magnetic character of the wire, experiments lead me to believe that 

 discharges of the quick period of a Leyden jar are affected very appre- 

 ciably by tlie magnetic nature of iron, steel, and nickel conductors. 

 This effect, is so great that it dampens the electrical oscillations, and 

 makes it difficult to determine whether the time of oscillation is also 

 affected by the permeability of the conductor. 



The apparatus em[)loyed was similar to that described in the in- 

 vestigation of electrical oscillations with an air condenser.! Certain 

 important modifications, however, were made. The plane mirror which 

 was used in the former research was replaced by a concave mirror of 

 ten feet focus and three and a half 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, insu- 

 lated, and mounted on the edge of the rotating disk bearing the mirror. 

 It was metMllically connected with a grooved ring of brass miounted 

 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 taught by a rubber band. The 

 electrical discharge was thrown on to the circuit by thrusting 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 that occurred, therefore, was the one the oscillations 



* " Ersetzen wir den bisherigen Kupferdraht durch einen dickeren oder 

 dunneren Kupferdraht oder durch einen Draht aus anderem Metall, so belialten 

 die Knotenpunkte ilu'e Lager bei. Die Fortplanzungsgeschwindigkeit in alien 

 solchen Driihten ist daher gleich, und wir sind berechtigt, von derselben als 

 einer bestimmten Geschwindigkeit zu redcn. Auoh Eisendrahte machcn keine 

 Ausnahme von der allgemeinen Kegel, die Magnetisirbarkeit des Eisens kommt 

 also bei so schmalen Bewcgungen nicht in Betracht." — Ann. der Physik und 

 Cheniie, No. 34, 1888, p. 558. 



t Tiiese Proceedings, Vol. XXV. p. 109. 



