brisk vibratory
motion of the glass, occasioned by the successive formation and
condensation of small drops of water on the sides of the glass tube, and
the air rushing in to replace the vacuum formed.*

[Footnote *: This ingenious explanation was first suggested by
Dr. Delarive. --See Journals of the Royal Institution, vol. i.
p. 259.]

CAROLINE.

How very much this flame resembles the burning of a candle.

MRS. B.

The burning of a candle is produced by much the same means. A great deal
of hydrogen is contained in candles, whether of tallow or wax. This
hydrogen being converted into gas by the heat of the candle, combines
with the oxygen of the atmosphere, and flame and water result from this
combination. So that, in fact, the flame of a candle is owing to the
combustion of hydrogen gas. An elevation of temperature, such as is
produced by a lighted match or taper, is required to give the first
impulse to the combustion; but afterwards it goes on of itself, because
the candle finds a supply of caloric in the successive quantities of
heat which results from the union of the two electricities given out by
the gases during their combustion. But there are other circumstances
connected with the combustion of candles and lamps, which I cannot
explain to you till you are acquainted with _carbon_, which is one of
their constituent parts. In general, however, whenever you see flame,
you may infer that it is owing to the formation and burning of hydrogen
gas*; for flame is the peculiar mode of burning hydrogen gas, which,
with only one or two apparent exceptions, does not belong to any other
combustible.

[Footnote *: Or rather, _hydro-carbonat_, a gas composed of
hydrogen and carbon, which will be noticed under the head
_Carbon_.]

EMILY.

You astonish me! I understood that flame was the caloric produced by the
union of the two electricities, in all combustions whatever?

MRS. B.

Your error proceeded from your vague and incorrect idea of flame; you
have confounded it with light and caloric in general. Flame always
implies caloric, since it is produced by the combustion of hydrogen gas;
but all caloric does not imply flame. Many bodies burn with intense heat
without producing flame. Coals, for instance, burn with flame until all
the hydrogen which they contain is evaporated; but when they afterwards
become red hot, much more caloric is disengaged than when they produce
flame.

CAROLINE.