But what is the nature of it? There are
three factors in the phenomenon. In the first place, the mechanical
peculiarity of flame, or gas in the moment of combustion, as compared
with a gas like air merely heated, is _an almost explosive velocity of
ascent._ The physical peculiarity from which this results is the
intensity of its heat--commonly stated at 2,000 degrees, as to our
common illuminating gas--acting instantaneously throughout its mass,
just as in gunpowder. The gas goes up the flue in its own flash, like
the ignited charge in the barrel of a gun: the burning coals can only
_send_, and by a leisurely messenger, namely, the moderately heated
gases, and contiguous air, that rise only by the gravitation or
pressure of the surrounding atmosphere.
And yet it is not the small flame itself that roars in the chimney but
the rush of air induced by it. The semi-explosion of flame is but for
an instant, though constantly renewed, and its explosive impulse
cannot carry its light products of combustion very far through
stationary and resistant air. It is _the induction of air_ carried
with it by such semi-explosive impulse (under proper mechanical
conditions) that is strange to our observation and understanding, and
is the second factor in the phenomenon we are accounting for and
preparing to utilize.
The process, as it actually is, may be clearly exhibited by a very
simple means. Let anyone take a tube, say an inch in diameter--a roll
of paper will do as well as anything--and, applying it closely to his
mouth, try the whole force of his lungs through it upon any light
object.
Pages:
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131