488 Mr. Bowlker on the Lengthening of the Spark from 
A wire similarly placed with regard to the negative 
terminal has no effect, if the condenser is properly adjusted. 
The ratio of the increase depends upon the shape of the 
terminals, but the actual length of the spark tends towards 
« maximum almost independent of the shape of the ends. 
Also, if an insulated wire be placed at right angles to the 
negative wire, near its terminal, the length of the spark is 
similarly increased, to some extent if touching the negative 
wire, to a greater extent if almost touching; whereas when such 
a wire, if thick (in the experiments one of 3°4 mm. diameter 
was used), and with well-rounded ends, is similarly placed 
with regard to the positive wire, it has no effect on the length 
of the spark. 
Hither of these phenomena give us a ready means of 
determining the nature of the poles of an induction-coil. 
The second effect, with the negative terminal, takes place, 
to a gradually diminishing extent, when the detached wire is 
at a distance from the terminal, vanishing when the point of 
application is about three times the length of the spark-gap. 
The results of one experiment to show these effects are 
given below. 
Positive terminal of wire ‘45 mm. diameter. 
Negative terminal of wire 1°60 mm. diameter. 
Length of 
Spark-gap. 
Petiameteteu. 5's’. ss cee ee 40 mm. 
Positive assisted... 5).u5 <0) % 2h, Gar 
Negative assisted ...... sia ye GB. «5; 
Current reversed. 
Himessiahem te Lyi «Gai SERS SGT" 
Posriive assmted .. ok. ences es Gf. 45 
Negative assisted «........... G5). 55 
The ratio of increase of length of spark varies for different 
original spark-lengths. This is seen from the following 
series of experiments between the same terminals :— 
Ratio. 
Unassisted spark-length.. 16mm. Positive assisted... 25mm. 1°56 
Negative assisted.. 23 1-44 
Unassisted 8 2 20 Positive assisted .. 39 1:70 
Negative assisted.. 36 1:57 
Unassisted 3 oe O4 Positive assisted .. 60 76 
Negative assisted... 59 1-73 
Unassisted 5 .. 40 Positive assisted .. 66 1°65 
Negative assisted... 65 1:62 
Unassisted 7 1.62 Positive assisted .. 89 1:45 
i Negative assisted.. 86 1:39" 
Unassisted * Seis Positive assisted .. 133 1:36 
Negative assisted. . 130 1°32 
Unassisted A og LS Positive assisted .. 135: - 119 
Negative assisted. . 135 1-19 
