O. N. Rood on the Electric Spark. 223 
seems to indicate that each simple spark consists of two or more 
successive discharges of different intensity. The wood cuts show- 
ing the forms of the spark were executed from photographs en- 
larged 9 diameters; in them the bright portions of the spark 
are of course represented by dark shading, &c. 
/ HP 
| 
Distance of the brass ball from the sensitive plate yy inch. The most 
general form is that seen in diagram 2, at.1: the starlike figure is 
very distinct, one of the rings is included within its area and faintly 
Indicated by a deeper shade: the other ring 1s sometimes seen cir- 
siieeeribing it. . . Ld ee 
Yo .2. The rays are larger and the external ring 1s plainly visible. 
wand 45. .4 The rays increase in size and the ring is well developed. 
tu: Like the above except that the rays begin to grow irregular. 
» Kays quite irregular, both rings distinetly visible. 
Yo Yo: 5 1, 1yy, 144 The star loses its regularity and the rings are 
no longer symmetrically dis : : 
ly. N . sia passes Slt it is replaced by the electrical brush, or 
rather by discharges intermediate between the brush and the true 
spark, fig. 2; i 
These produce a strong impression on the plate and yield intense 
figures consisting of three parts: an external sharply de- 
fi circle, within aseries of dots arranged in a circle, and finally 
Mhermost of all a broad ring which may pass by delicate gra- 
pei into a star. This would indicate a the ported apak 
eg : i ces of at success! 
Pe ngsthaae gl these circumstances of at least Tore Sie the 
ye 
e 
ly su by the following experment: 
i the i obi i ks generally pass 
le plate is held obliquely the partial ge y Pp 
near its surfaces aa little distance before actually coming 
