an Induction-Coil by the Aid of Ausxilary Wires. 497 
sheet of vuleanite is brought up close to its point, the 
negative discharge is either entirely prevented or is quickly 
reabsorbed. 
A somewhat similar explanation probably accounts for 
the fact that when an imperfect conductor is brought near 
the positive terminal of an induction-coil, the spark is 
lengthened ; the induced negative charge and the discharge 
of negative electrons from this conductor giving increased 
energy, by their attraction, to the discharged positive 
electrons. | 
It will be found that the frayed end of a strip of asbestos 
cloth acts as an excellent assister when brought close to 
the positive terminal, being most effective when put to 
earth. 
A striking experiment illustrating this subject which 
‘brings out the effect of the positive electrons in causing a 
spark-discharge, as compared with the negative electrons, is 
made by placing the two similar terminals of wires from an 
induction-coil in a glass tube; arranging that the spark 
remains of the same length when the commutator is reversed. 
Now when a few turns of thin wire are wound round the 
glass tube, almost touching it and not too near to the positive 
terminal, the length of the spark 1s greatly increased when 
one end of this wire almost touches the negative end of the 
induction-coil, but the length is hardly altered when the 
commutator is reversed. In one experiment it was found : 
Unassisted, sparking distance.........5........ me (if) invite 
With wire coil to negative end, sparking distance. =125 
With commutator reversed, sparking distance .. = 74 
In order to ascertain whether the effect of the negative 
assister was cumulative, it was endeavoured to find evidence 
of reflexion of the impulse action of the assister, but the 
experiments failed to give any results. 
It would be interesting to find what increase of spark-length 
could be obtained from two points, maintained at a steady 
difference of potential, by the rapid rotation of assisters in 
very close proximity to the terminals ; various rates of rotation 
being employed giving various values of A . The author 
had not a sufficiently steady supply of high-tension electricity 
to try this experiment. . 
Phil. Mag. 8. 6. Vol. 8. No. 46. Oct. 1904. 2M 
