240 Royal Institution :— 
loudness of the spark were augmented when a core of soft iron was 
placed within the coil. The disruption of the current took place 
between the poles of an electro-magnet; and when the latter 
was excited, an extraordinary augmentation of the loudness of the 
spark was noticed. This effect was first obtained by Page, and 
was for a time thought to denote a new property of the electric 
current. : 
But Rijke had shown, in a paper the interest of which is by no 
means lessened by the modesty with which it is written, that the 
effect observed by Page is due to the sudden extinction of the 
primary spark by the magnet; which suddenness concentrates the 
entire force of the extra current into a moment of time. Speaking 
figuratively, it was the concentration of what, under ordinary cir- 
cumstances, is a mere push, into a sudden kick of projectile 
energy. 
7. The contact-breaker of an induction coil was removed, and a 
current from five cells was sent through the primary wire. The 
terminals of the secondary wire being brought very close to each 
other, when the primary was broken by the hand, a minute spark 
passed between the terminals of the secondary. When the dis- 
ruption of the primary was effected between the poles of an excited 
electro-magnet, the small spark was greatly augmented in brilliancy. 
The terminals were next drawn nearly an inch apart. When the 
primary was_ broken between the excited magnetic poles, the spark 
from the secondary jumped across this interval, whereas it was in- 
competent to cross one-fourth of the space when the magnet was 
not excited. ‘This result was also obtained by Rijke, who rightly 
showed that in this case also the augmented energy of the secondary 
current was due to the augmented speed of extinction of the primary 
spark between the excited poles. ‘This experiment illustrated in a 
most forcible manner the important influence which the mode 
of breaking contact may have upon the efticacy of an induction 
coil. 
The splendid effects obtained from the discharge of Ruhmkorff’s 
coil through exhausted tubes were next referred to. The presence 
of the coil had complicated the theoretic views of philosophers with 
regard to the origin of those effects; the intermittent action of the 
contact-breaker, the primary and secondary currents, and their mu- 
tual reactions, producing tertiary and other currents of a higher 
order, had been more or less invoked by theorists to account for the 
effects observed. Mr. Gassiot was the first to urge, with a water 
battery of 3500 cells, a voltaic spark across a space of air, before 
bringing the electrodes into contact; with the self-same battery he 
had obtained discharges through exhausted tubes, which exhibited 
all the phenomena hitherto observed with the induction coil. He 
thus swept away a host of unnecessary complications which had 
entered into the speculations of theorists upon this subject. 
8. On the present occasion, through the kindness of Mr. Gassiot, 
the speaker was enabled to illustrate the subject by means of a 
battery of 400 of Grove’s cells. The tension at the ends of the 
