the Discharge of a Leyden Jar. 253 
urements were from time to time transferred machanically to 
paper, without inspection. After the end of the experiment, 
the actual size of the image on the ground-glass was measured, 
furnishing thus the test of the degree of accuracy attained. 
Observations. 
33°5 millimeters. 35° millimeters. 
34°3 42° 
31:2 43°3 
34°6 42°3 
33°6 44°4 
32°8 45 
34°] 44°5 
33°5 41.5 
28° 42° 
34° 43°9 
32° — 
30° average 42°39 
34°4 actual size 43°50 
32° 
34°4 
31°5 
29° 
34: 
34°] 
average 32°6 
actual size 32- 
about 25 per cent. I may remark here that my friend Presi- 
dent Morton, who repeated for me some of these experiments, 
obtained without difheulty similar resul 
ts. 
icrometer dise.—It was considered desirable, figs are 
illuminated by a multiple electric spark, the disc w 
