162  O.N. Rood onthe discharge of a Leyden jar. 
tation was then by degrees carried up to 223 per second, when 
the lines were still distinctly visible, though of course with less 
contrast between the white and black, than was the case with 
low velocities or a stationary mirror. 
This experiment proves then, that the duration of the light 
accompanying the first discharge is considerably less than 
00 A of a second, probably less than half this period, or 
less than one ten millionth of a second of time. To make 
the attention was directed. To obviate this difficulty, I af- 
terward covered a piece of cardboard half an inch broad with 
alternate white and black lines of this character, their real di- 
ameter was ‘0075 in., that on the plate of glass being ‘0125 in. 
With these I repeated the above mentioned set of experiments 
with rapidity, obtaining with ease the same result, as some 0 
the lines were almost certain to be in the right part of the field 
of view. It is thus shown, that the first act of the electric ex- 
plosion lasted through an interval of time so short as to be. 
immeasurable with the means then at my disposal ; it is not 
impossible that it may still be reached by the use of finer lines, 
and a lens of greater focal length. 
ing but not without difficulty. These observations farther 
demonstrated the fact, that two ten millionths of a second 1s 
an interval of time quite sufficient for the production of dis- 
tinct vision, : 
