an Induction-Coil by the Aid of Auxiliary Wires. 495 
Assister-length. Spark-length. 
2 cm. 105 mm. 
4 em. 105 
16 cm. 107 
26 ecm. 106 
32 em. 106 
Showing that the length of the assister makes no appreci- 
able difference in the length of spark. 
In the course of the experiments it was found that if the 
end of the assister towards the positive terminal was pointed 
the effect was somewhat greater than if blunt; also that an 
assister whose end was made up of a brush of widely separated 
wires was more effective than a single wire. 
The most effective negative assister was a semicircle of wire 
almost touching the negative wire close to its terminal and 
having the positive terminal as centre. 
In the experiments with the negative assister arranged as in 
fig. 2, the increase of sparking distance depends upon the length 
of the spark passing between the assister and the negative wire; 
when this spark is extremely small there is very little increase 
in the main spark-length, but as the assister gap is increased 
there are two values of it which give maxima values for the 
main spark-gap. This is shown in the following experiments 
with an assister 100 mm. long. 
Negative assister gap. Spark-length. 
SP UCU TEIN 0 res vas is bial « 107 mm. 
cri) |) eee ear 96 
Eben ote rene OE 3 ie! ly 108 
ar eo8 Oe ae 102 
rp ca 435, dochece. ak a 3 84 
Whee 20" 79 
A similar lengthening of the spark is obtained when the 
assister, instead of being separated by a short gap from the 
negative wire, is separated by a short gap from a wire put to 
earth. Thus in one case :— 
Spark-length. 
LU THPS STS ett BL 2) 2) a 77 mm. 
Wy til assisser fovGanin. ..... ec be ce cel 82 
Assister gap to earthed wire =] mm..... 102 
That the increased length of spark produced by a negative 
assister is due to the electrons discharged from the positive 
terminal is shown by an experiment in which the positive 
wire bifurcates giving two terminals ; then a negative assister 
acting on one of these causes sparking between the other 
positive terminal and the negative terminal, but if a sheet of 
