. * 
the Discharge of a Leyden Jar. 163 
Although with the improved micrometric method above de- 
scribed an interval of time as small as one millionth, or half a 
millionth, of a second could, as has been seen, be directly meas- 
still with its aid I never detected any sign that the dura- 
tion of the great body of the spark was other than absolutely instan- 
taneous ; as, however, all the light of the spark is due to incan- 
descent material particles, we must suppose that an infinitesimal 
portion of time is required for attaining its maximum bright- 
Rees, owing to the same reason its disappearance demands 
another distinct period however excessively minute. Hence, 
We may represent the luminous effects of the discharge by a 
A 7 2 
curve conforming more or less to that here figured, in which 
intensity of light is measured in a vertical, time im a horizontal, 
tion. This curve then, (the unbroken line), serves to give 
“harge practically separates it from what follows, practically 
*onstitutes it a first distinct act, and renders its measurement 
aK os : 'e cr, 3 > 
- Show that the curve really has a form substantially like that 
dott May instead of some such one as is indicated by the 
: ine, a 
_ For the ose of measuring, or at least setting, a limit at 
— side o de ininitctnal ae of time involved, I employed 
