ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
93 
bent the oscillation is conical or elliptical, and the figure produced by the discharge is then 
much more continuous and beautiful, because the distance from the point to the plate 
remains nearly constant. The difference of the amount of excursion of the wire when 
positive or negative is one of the many instances of the difference of the positive and 
negative electric force. 
In the foregoing aocount of the length of the spark no mention has been made of 
the atmospheric conditions in relation to pressure, temperature, or hygrometric 
state, because it was found that it was not affected thereby to any appreciable 
amount, the laboratory being warmed during the cold period ; but it is nevertheless 
certain that some effect must be produced by variations in temperature, as it was 
found that a very high temperature, such for example as that produced by the 
flame of an insulated spirit lamp, caused a much greater jump between the terminals, 
for instance, with 8040 cells, the length of spark between a point and a ball 1 inch 
in diameter was 1 inch, and between two points 1 *37 5 inch; the length of the spark 
is somewhat influenced by the position of the flame, and is greatest towards the point 
or oxidising part of it. 
When the terminals are placed opposite to two gas jets emanating from the same 
gas pipe in metallic communication with the gas main, and consequently to Earth, the 
flame opposed to the negative terminal is attracted, and that opposed to the positive 
repelled, as was observed to be the case with static electricity by M. Neyreneuf,* 
at whose request we have made the experiment. Fig. 20 shows the arrangement and 
effects observed. 
Fig. 20. 
We have already stated that in most cases the nature of the metal makes no 
difference in the length of the spark, and this applies to brass, copper, silver, steel, 
platinum, magnesium, and zinc ; but there is a striking exception, namely, aluminium, 
which gives a considerably longer spark when used for a terminal in the shape of a 
point ; thus, when the point was positive, with — 
* Annales de Chemie efc de Physique, 5e serie, t. ii. 1874. 
