Part 10 (2/2)
Q. _Why is this JET sometimes of a GREENISH YELLOW colour?_
A. When a lump of coals lies _over the hot bars_, or the coals below it are not _red hot_, the gas which bursts from the lump _escapes unburnt_, and is of a greenish colour.
Q. _Why does the gas escape UNBURNT?_
A. Because neither the _bars_ nor _coals_ (over which it pa.s.ses) are _red-hot_.
Q. _Why does a BLUISH FLAME sometimes flicker on the surface of hot cinders?_
A. Gas from the hot coals _at the bottom of the grate_ mixing with the _carbon of the coals above_, produces an inflammable gas (called carbonic oxide), which burns with a blue flame.
Q. _Why is the FLAME of a good fire YELLOW?_
A. Because both the hydrogen and carbon of the fuel are in a state of _perfect combustion_. It is the _white heat of the carbon_, which gives the pale yellow tinge to the flaming hydrogen.
Q. _What is LIGHT?_
A. Rapid _undulations_ of a fluid called _ether_, striking on the eye.
Q. _How does COMBUSTION make these undulations of LIGHT?_
A. The atoms of matter (set in motion by heat) _striking against_ this ether, produce _undulations_ in it; as a _stone_ thrown into a stream, would produce undulations in the _water_.
Q. _How can UNDULATIONS of ether produce LIGHT?_
A. As _sound_ is produced by _undulations of air_ striking on the _ear_; so _light_ is produced by undulations of _ether_ striking on the _eye_.
Q. _What is ETHER?_
A. A very subtile fluid, which pervades and surrounds _every thing we see_.
Q. _Mention a simple experiment to prove that LIGHT is produced by rapid MOTION._
A. When a fiddle-string is _jerked_ suddenly, its rapid vibration produces a grey _light_; and when a carriage wheel revolves very quickly, it sends forth a similar light.
Q. _Does HEAT ALWAYS produce LIGHT?_
A. No: the heat of a stack of hay, or reeking dunghill, though very _great_, is not sufficient to produce _light_.
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