Facts in Reference to the Spark, &c. 327 
To show the radiating powers of the different surfaces, the sheath 
is turned so that the open side is exposed to the air; the absorption 
of heat now becomes sensibly constant, and the greater or less height 
of the liquid in the tube, is determined by the less or greater radiat- 
ing power of the exposed surface. 
The order in which the surfaces are exposed may, of course, be 
so arranged as not to require the temperature of the source of heat 
to be kept constant. 
Such an apparatus, placed before a stove, would make an admira- 
ble illustration in a school, or a vessel of water, colder or warmer than 
the room, may be used as the radiating or absorbing body. For the 
tin vessel here described, a common square glass bottle may be sub- 
stituted, without disadvantage. Even a common glass phial, made 
into an air thermometer by inserting a tube through a tight cork, in- 
to some liquid occupying the lower part of the phial, and provided 
with a movable coating of tin foil, gilt paper, writing paper, and pa- 
per covered with lamp black, when placed before a fire, or in a room 
of which the air is warm, when the external air is cold, brought near 
a window, will afford an interesting and instructive illustration. 
Philadelphia, February, 1835. 
Art. XXIV.—Facts in reference to the Spark, &c. from a long 
conductor uniting the poles of a Galvanic Battery; by Josrrn 
Henry, Professor of Natural Philosophy in the College of New 
Jersey, Princeton. 
TO THE COMMITTEE ON PUBLICATIONS. 
GrentLemen,—The American Philosophical Society, at their last 
stated meeting, authorized the publication of the following abstract 
of a verbal communication made to the Society, by Professor Hen- 
ry, on the sixteenth of January last. A memoir on this subject has 
been since submitted to the Society, containing an extension of the 
subject, the primary fact in relation to which was observed by Pro- 
fessor Henry as early as 1832, and announced by him in the Amer- 
ican Journal of Science.* Mr. Faraday having recently entered up- 
on a similar train of observations, the immediate publication of the 
* Vol. XXII, p. 408. 
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