Professor Lesiie on Electrical Theories. 33 
When the powdered charcoal is moderately thick, we are con- 
scious only of a light and sound ; yet, if the thickness be in- 
creased, this sound, which at first is only a faint whistling, grows 
dull and blunt, and by degrees more intense, till at last it be- 
comes loud and sharp * The same observations may be made 
with a thin surface of water in the bottom of a basin, by 
adding small quantities continually. 
But in this mode of performing the experiments, there is 
some inaccuracy ; for the contiguous portions of air become 
electrified, and by their flow, they assist greatly the effect of 
such slow conductors. Let, therefore, the water or other li- 
quids, be inclosed in bent glass-tubes of different diameters and 
lengths, and equal metallic balls cemented to the ends. In this 
way, it will be found, that a cylinder of water, one-fourth inch 
diameter and five long, discharges half a foot of coating in about 
one-fourth of a second, with a blunt noise and deep orange light ; 
oil of olives, treated in the same way, is slower in its effects, and 
produces a fainter noise. But sulphuric acid gives a much sharper 
sound, and the time is indistinguishable ; when mercury is used, 
the sound is vastly louder, though greatly inferior to that which 
the other metals would occasion. If the discharge is made by 
a harpsichord wire, and by a common thick wire of the same 
length, the sound will be sensibly different. By extending the 
chain, the explosion will be gradually blunted, and even redu- 
ced to the dull noise of the water discharging rod ; and any fur- 
ther addition to the length will now be more perceptible than 
before. For, when the vibrations succeed with extreme rapi- 
dity, their impressions are confounded on the ear. And thus, 
as quick flashes, whatever be the difference of their intervals, 
affect the eye alike, so sudden pulses, though of various cele- 
rity, produce the same sensation on the organ of hearing. Hence 
the loudness of the explosion is not sensibly different, when the 
* We may also notice the quality of the light to vary. It begins with violet, 
and passes through the gradations of purplish, reddish, orange, yellow, and in the 
end assumes a bright white. The species of light emitted , seems to depend , however , 
more on the peculiar nature of the affected substance than on any other circumstance. 
Thus an electrical discharge through carbonic acid gas appears of a brilliant white , 
but through hydrogen gas of a dull red. A lump of sugar exposed to a shock , glows 
with a green light , while a ball of wood or ivory emits a crimson , and a body ofpow «. 
dered charcoal throws out a yellow gleam. 
VOL. XI. NO. 21. JULY 1824. 
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