434 
induction machine, depends obviously on the inferiority of 
quantity; and the difference (15) when the distances of the 
electrodes are 17: and 5'-5 must be referred to the same 
cause. In (5) the hand acts by facilitating the passage of the 
electricity, and in (6) and (7) the stratification increases in dis- 
tinctness with the increase of the battery current passed through 
the primary coil. In (8) and (11) the battery power is the same, 
but the latter has a more powerful induction coil, and its effects 
far surpass the other. Still more striking is the effect of combin- 
ing two machines, (4) and (5), where the power of quantity 
over this phenomenon is manifest; and that of connecting a 
Leyden jar with the terminals of the induction coil, which de- 
cidedly weakens the spark at the contact breaker, is also con- 
siderable. And it appears from (2), not only that it increases 
with the current, but that a certain amount is necessary to its 
production, less, as might be expected, for hydrogen than air. 
That the electrodes of the induction discharge exercise a de- 
cided influence on this phenomenon is shown by(7) and (8). In 
the latter the quantity of electricity which passed was probably 
less, but in the other the appearance of the hemispheric shells 
covering the whole disc is very striking, and suggests the idea 
of two systems of waves emanating from the positive point. 
It seems desirable to study the effect of points of different sub- 
stances; of the various velocities of the contact breaker; and 
of very intense induction,* and I hope soon to be able to 
do it. 
‘¢ In my former paper I expressed an opinion that oxygen 
and nitrogen are the only gases in which the electric discharge 
produces those rays which cause fluorescence, and promised 
to examine others besides those mentioned there, by means of 
* A very great increase of this machine’s power has recently been made 
by Ruhmkorff himself, by Stéhrer of Leipzig, and still more by Heerder ot 
Plymouth. We are, probably, far from the limit, though it has given sparks 
exceeding three inches. 
