the Composite Nature of the Electric Discharge. 49 



turbed around their edges. The portion of the discharge which 

 makes these holes lasts -j-% second ; and the holes are separated 

 by intervals which gradually decrease in size toward the end of 

 the discharge, so that the last spark-holes are separated about 

 one half of the distance which separates the holes made at the 

 beginning of the discharge. The average interval between the 

 spark-holes is T lg second. After this portion of the discharge 

 has passed there is a period of quiescence lasting about ysW 

 second; then follows a shower of minute sparks, which forms 

 the short dotted line above spoken of. This spark -shower lasts 

 3-5-0 of a second, and is formed of 30 sparks; hence the ave- 

 rage interval separating these sparks is t^Vsf second. The inter- 

 vals separating these sparks, however, are not uniform, but are 

 smaller in the middle of the spark-shower than at the begin- 

 ning and at the end of this phenomenon. The spark-shower, 

 indeed, is a miniature of the phenomenon obtained when a 

 Ley den jar is placed in the circuit of the coil, and which is 

 described below. The above numbers were determined as the 

 average measures on six disks. It is here to be remarked that 

 all the discharges studied in this paper were made by sud- 

 denly depressing the platinum-faced " break " of the primary 

 circuit, and the break was held in this position until the disk 

 had been removed from between the points or balls. 



2. Discharge of large inductorium between platinum points one 

 millim. apart, with a Ley den jar of 242 sc[. centims. connected 

 with the terminals of the secondary coil. 



After this discharge through the disk a very remarkable 

 appearance is presented, the full description of which I reserve 

 for a more extended paper. The discharge in its path around 

 the disk dissipates little circles of carbon. There are 91 of 

 these circles, each perforated by 4, 3, 2, or 1 hole. I shall 

 here have to adopt a new nomenclature for the description of 

 this complex phenomenon. I call the whole act of discharge 

 of the coil the discharge. Those separate actions which form 

 the little circles by the dissipation of the carbon I denominate 

 flashes ; and the perforations in these circles I call sparks. The 

 discharge in the above experiment lasts g-y of a second. The 

 flashes at the beginning of the discharge are separated by inter- 

 vals averaging -gfa second up to about the tenth flash ; after 

 this the intervals of the flashes rapidly close up, so that during 

 the fourth fifth of the discharge they follow at each 3-^2 °f a 

 second. During the last fifth of the discharge the intervals 

 between the flashes gradually increase, and the last flash is 

 separated from its predecessor by y-oVo °f a second. 



3. Discharge of large inductorium between brass balls, one 

 centim. in diameter, separated one millim., with a Ley den jar of 



Phil. Mag. S. 4. Vol. 49. No. 322. Jan. 1875. E 



