ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
87 
With a Muirhead condenser of 13 microfarads’ capacity, the 8040 cells gave a spark 
of 0'265 inch between a blunt point, positive (it is impossible to retain a good point 
with such heavy discharges, as metal is carried off at each explosion), and a flat 
surface 0'125 inch diameter, negative. 
The actual jump of the spark when a point and disc or two points are employed 
as terminals is preceded by a luminous discharge (streamers), presenting phenomena 
of an interesting character, an extremely minute quantity of electricity passing as 
compared to that when the spark jumps and forms the arc, but still it is sufficient 
when caused to pass through a vacuum tube to illuminate it strongly.* 
In illustration of this we quote the following numbers based on the statement before 
made, namely, that the electro-motive force of the battery per cell is taken at 1 '03 
volt, and the internal resistance at 4800 X 5 + 3240 X 15 = 72,600 ohms. 
Weber. 
8040 cells in short circuit would give a current of 0'1140 
8040 cells, after the jump at 0'34 inch and the formation of the arc, the 
external resistance having been found to be 58,000 ohms 0'0634 
8040 cells, at 0'36 inch between the terminals, the measured resistance being 
327 megohms, with the point -positive 0'0000247 
8040 cells, at 0'36 inch between the terminals, the resistance being 274 
megohms, with the point negative 0'0000302 
8040 cells, at 0'30 inch between the terminals, the resistance 181 megohms, 
with the point negative . O’ 000045 8 
8040 cells, distance 1'16 inch, resistance 5800 megohms, the point positive or 
negative O' 00000 14 
Taking for unit the current which passes with no external resistance, that when the 
spark has jumped and the arc is formed is 51 per cent. ; at 0'36 inch distance, 
0'0217 per cent. = 4 ^ 7 - 0 -th ; at l'l 6 inch, 0'00123 per cent. = -grrboth. Taking for 
unit the current which passes when the arc is formed, the streamers at 0‘36 inch give 
a current of 0 ‘039 per cent., or -^g-jth part of it. 
Many determinations were made of the current passing between a paraboloidal point 
and a disc at various other distances beyond the striking distance. In order to make 
these measurements, the point was connected with one terminal of the battery, the 
other terminal being to earth ; the opposed disc was connected to one terminal of a 
Thomson galvanometer, whose constant had been accurately determined ; the other 
terminal of the galvanometer was to earth. Every care was taken to prevent leakage, 
and the shunts were adjusted to suit the current. A danger to be guarded against 
was the jump of the spark, as the current which would then pass would injure the 
galvanometer. 
From the above figures it will be seen that the streamer- discharge from a paraboloidal 
Proc. Roy. Soc., vol. xxiv. p. 169, 1876. 
