10 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIX.) 
ends, and then introduced as cores into the helices. For the purpose of submitting 
liquid bodies to the same action, tubes of glass were provided, furnished at the ends 
with caps ; the cylindrical part of the cap was brass, and had a tubular aperture for 
the introduction of the liquids, but the end was a flat glass plate. When the tube 
was intended to contain aqueous fluids, the plates were attached to the caps, and the 
caps to the tube by Canada balsam ; when the tube had to contain alcohol, ether or 
essential oils, a thick mixture of powdered gum with a little water was employed as 
the cement. 
2195. The general effect produced by this form of apparatus may be stated as fol- 
lows : — The tube within the long helix (2190.) was filled with distilled water and placed 
in the line of the polarized ray, so that by examination through the eye-piece (2150.), 
the image of the lamp-flame produced by the ray could be seen through it. Then the 
eye-piece was turned until the image of the flame disappeared, and, afterwards, the 
current of ten pairs of plates sent through the helix; instantly the image of the flame 
reappeared, and continued as long as the electric current was passing through the 
helix ; on stopping the current the image disappeared. The light did not rise up 
gradually, as in the case of electro-magnets (2170.), but instantly. These results 
could be produced at pleasure. In this experiment v/e may, I think, justly say that 
a ray of light is electrified and the electric forces illuminated. 
2196. The phenomena may be made more striking, by the adjustment of a lens 
of long focus between the tube and the polarizing mirror, or one of short focus be- 
tween the tube and the eye ; and where the helix, or the battery, or the substance 
experimented with, is feeble in power, such means offer assistance in working out the 
effects ; but, after a little experience, they are easily dispensed with, and are only use- 
ful as accessories in doubtful cases. 
2197- In cases where the effect is feeble, it is more easily perceived if the Nichol 
eye-piece be adjusted, not to the perfect extinction of the ray, but a little short of or 
beyond that position ; so that the image of the flame maybe but just visible. Then, 
on the exertion of the power of the electric current, the light is either increased in 
intensity, or else diminished, or extinguished, or even re-illuminated on the other side 
of the dark condition ; and this change is more easily perceived than if the eye began 
to observe from a state of utter darkness. Such a mode of observing also assists in 
demonstrating the rotatory character of the action on light ; for, if the light be made 
visible beforehand by the motion of the eye-piece in one direction, and the power of 
the current be to increase that light, an instant only suffices, after stopping the current, 
to move the eye-piece in the other direction until the light is apparent as at first, 
and then the power of the current will be to diminish it ; the tints of the lights being 
affected 'also at the same time. 
2198. When the current was sent round the helix in one direction, the rotation 
induced upon the ray of light was one way ; and when the current was changed to 
the contrary direction, the rotation was the other way. In order to express the direc- 
