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Chemistry and Physics. 423 
ternate change in the direction of the currents were pretty plain. By 
the introduction of tubes of sulphuric acid, the number of these bands 
could be reduced to one, and then by continuing the process, the dis- 
s before. 
Feddersen found that the length of the spark, and the amount of the 
charge of electricity, had no sensible effect on the duration of a s gle 
oscillation ; with ten jars of the above mentioned electrical capacity, and 
a tolerably short metallic circuit, he obtained, 
or a 4mm. spark. For 8mm, 
Time of one oscl. 0°00000304 sec. 0°00000805 sec. 
With 16 jars and a very long circuit, he obtained, 
. For a 14mm. spark, 3 
Time of one oscl. 0°0000511 sec. 00000514 sec. 
The alteration of the area of the electric surface, (number of jars,) 
exercised an influence according to the la 
t—aa/s 
hous; not one-tenth of the w ; | 
them, and either smoke or rarified air would have drifted with the wind, 
which was blowing sensibly at the time, whilst the dark rays went up- 
ward straight as arrows. Again: the had 
nothing to do with it, was shown by a similar brush or ray appearing at 
the top of a certain little ventilator in the roof of one of the houses 
shown, and not out of the parts emitting air, but 
spike at the top. 
_ This circumstance convinced me at the time that the phenomenon was 
an electrical one, invisible to the eye, but abundantly visible or a 
to the photographic camera, and the occasion Was perfectly e 
rit ‘conclusion of a week of unusually hot, calm 
_ 1 On the action of very weak electric light on the iodized plate, by Prof. 0. N. 
Rood, this Journal, March, 1864, p. 207. 
