Electrical Oscillations on Iron Wires. 507 



Besides the short lead wires above described, the discharging 

 circuit consisted of two parallel wires 30 centim. apart and 

 510 centim. long. These were the only portions of the appa- 

 ratus changed during the experiment, and they were replaced 

 by wires of different material and of different size. The other 

 conditions — length of spark, lead wires, and the copper cross- 

 wire connecting the outer ends of the long parallel wires — 

 remained undisturbed throughout the experiment. 



The Leyden jar was charged each time as nearly as pos- 

 sible to the same potential, judging by the number of turns 

 given the Holtz machine. It is unfortunate that no more 

 accurate means of measuring it were at hand, although the 

 different negatives showed but slight variation. The capacity 

 of the jar with alternations of this period was 5060 elec- 

 trostatic units. 



I describe the discharging portion of the apparatus 

 minutely, for the success of an investigation of this nature 

 depends upon the suppression of all sparks save that which 

 one wishes to observe, and my method surely and completely 

 accomplished this. The photograph of the spark could thus 

 be made to fall very accurately on the sensitive plate. When 

 one considers that the image of the spark was flying through 

 the air on a circle of ten feet radius with a velocity of a 

 mile a second, it will be seen that an extremely small 

 deviation in the point of contact between the cutting-tool 

 and the type-metal would have thrown the image entirely 

 oft' the sensitive plate. A singular phenomenon was noticed 

 in this connexion. When a comparatively low potential 

 was used, such as that afforded by the air-condenser used in 

 our previous investigation, the cutting-tool ploughed two or 

 three millimetres along the surface of the type-metal before 

 a spark passed at the point in the circuit where it was desired. 

 With higher potentials this phenomenon was also observed 

 but the extent of cutting was diminished. It is possible that 

 the insulating wax may have melted under the sudden blow 

 of the cutting-tool, and, flowing around it, prevented instant 

 contact. This seems to me improbable, for a deep and clear- 

 cut groove was made in the soft type-metal. Great attention 

 was paid to the solid structure of this contact apparatus. 

 It was entirely separ. 3 from the support of the revolving 

 parts and was perfectly steady. 



The other end of the armature-shaft was lengthened into a 

 cylindrical chronograph, similar to that described in the 

 article already cited, and its performance left nothing to be 

 desired. A small Ruhmkorf coil excited by two storage 

 cells, and interrupted by a seconds pendulum, gave a record 



