+ 
Composite Nature of the Electric Discharge. 437 
When one of these discs is revolved about 20 times per second, 
it is rendered very flat by centrifugal action. It can then be 
brought between points or balls, even when the latter are i 
rated by no more than mm. When in this position, the dis- 
charge between the points or balls perforates the disc and leaves 
a permanent record of its character, of the duration of the 
whole discharge, and of the intervals separating its constituent 
flashes and sparks. To obtain the time of rotation of the dise 
I use the method invented by Young in 1807 (see his Natural 
Philosophy, vol. i, p. 191). That is, I present momentarily to 
the rotating dise a delicate point which is attached to a vibrat- 
ing tuning-fork. The number of vibrations per second of this 
fork has been determined to the last degree of precision by 
means of a break-circuit clock, which sends at each second a 
spark from an inductorium through the fork’s sinuous trace on 
blackened paper, covering a revolving cylinder. The axis of 
the sinuous line on the disc is traced with a needle point, and 
reading-microscope, and the deviation of the whole discharge 
and the intervals separating its components can be determined 
‘to the -51,, of a second. 
Many results have been obtained with this apparatus. I de- 
fer their publication until I have geaterd examined them, and 
have extended this research with the study, not only of the dis- 
charge of the inductorium, but also of the frictional machine, of 
he Leyden jar and of the Holtz machine, under every con- 
dition of charged surface and of striking distance, and when the 
current is flowing freely over a conductor and when it is doing 
work. I here present, merely as examples of the value of the 
method, the results I have obtained in three conditions of ex- 
riment. 
* Onderzoekingen gedaan in het Physiologisch Laboratorium der Utrechtsche 
Hoogeschool, 1868-69. 
+ Archives Néerlandaises des Sci tes et naturelles, t. v, p. 292. 
Am. Jour. Sct.—Tarrp — Vou. VIII, No. 48.—Dec., 1874. 
