490 Mr. Bowlker on the Lengthening of the Spark from 
its terminal was some distance from the main positive sparking 
terminal ; it was then found that a large sheet of mica inter- 
vening between it and the spark-gap caused the effect to 
cease entirely. When the mica, however, had slits cut in 
it parallel to the spark-gap, so as to necessitate any luminous 
radiation to the negative terminal or to the spark-gap passing 
through the mica, whilst the slits offered a good passage for 
the electrons discharged from the positive assister to the 
spark-gap—then the effect was almost as great as when the 
mica was withdrawn. Thus the effect was not due to luminous 
or ultra-luminous radiation, or tosome form of Hertzian oscil- 
lations, but was due to the ionization of the air by the positive 
discharge from the assister. The impulsive rush of the 
electricity into the positive assister apparently gives the 
. . * . dV . 
discharged ions power to ionize a longer spark-gap; - lem 
greatly increased. 
When experimenting with positive assisters, it was found 
co) ? 
that the longest spark was obtained by placing the assister 
Pp “ o 
in the line of the spark-gap, one end almost in contact with 
the positive terminal. A short assister in this position seems 
just as effective as a longer one. An assister 5 mm. in length 
gave about 3 per cent. longer spark than assisters of 90 mm., 
60 mm., and 140 mm., and 22 per cent. longer spark than one 
’ ? 5 
of 400 mm. coiled into a length of 100 mm. 
In order to experiment on the action of the negative 
assister, an arrangement was made as shown in fig, 2. 
Fig 2. 
In this, A is the positive terminal; K is the negative 
terminal; XX! is the negative assister ; L is the wire leading 
from the negative pole of the induction-coil. V is a valeanite 
screen interposed between the assister and the spark-gap. 
The term “‘assister attached’? means X’ in contact with h. 
