458 Od. Belli—Hlectrical Discharges from circular Disks. 
Art. LIL.—Brief Contributions ‘as the Physical Laboratory of 
Harvard College. No. 17.—On the eer as Electrical 
Discharges from Circular Dike by C. J. BEL 
THE peculiar figures produced by the electrification of solid 
dielectrics have been studied by Lichtenberg; b: 
ezold (Untersuchungen iiber elektrische Staubfiguren, Pogg. 
Ann., exl, 145, 1870); by Prof. Kundt, Poge. Ann., exxxvi, 
612; by Theodore Karrass, Pogg. Ann., exl, 160, 1870; and 
ne H. Schneebeli, Archives des “Sciences Phys. et Naturelles, 
xlvi, 269 
If a small circular disk is connected with the i inner coating of 
a charged Leyden jar, and is suspended vertically over a glass 
plate coated with lycopodium, which rests upon a metallic 
e Q. , Plate connected with the outside coating of 
Sse the jar, a number of points of disturbance 
“will be seen on the glass beneath the rim of 
\ the oe disk, as in the accompanying 
td 
] The following investigation was under- 
\ : taken to discover the law which regulates 
Oe” the number of points hy greatest electrical 
om 5 * disturbance shown by the small circles in 
the figure. The apparatus used was arranged as follows: the 
telescope of a cathetometer was removed, and an insulated arm 
substituted for it. To this arm was clamped i in a vertical posi- 
tion a copper wire, at the lower end of which were attached the 
various circular disks used in the experiments. These disks 
Ruhmkorf coil. The dielectrics, consisting of glass plates, 
17 cm. square and 1 em. thick, rested u upon the plate of metal. 
Six circular disks of different diameters were used, whic 
were placed above the glass acd at a constant distance from 
it. Six experiments were made with each plate. The results 
are contained in the following table: 
i Calculated 
cen : | * | : . ° 8 | ‘number. 
41 mm.; 14 14; 13 | 14| 14] 14 sansa 
34 ii eis io et 11°6 
29 oe i. O+ 10) 40 9; 10 10° 
20°5 7 8 Y f 7 8 7 sh 
15°5 6 5 | 5 6 6 5 5° 
11°25 4 5| 4 5 3 4 4° 
