Q. _Why does a JET of FLAME sometimes burst into the room THROUGH THE BARS OF A STOVE?_ A. The iron bars conduct heat to the _interior of some lump of coal:_ and its volatile gas (bursting through the weakest part) is kindled by the glowing coals over which it passes. 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 passes) 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_. Q. _Why is a YELLOW FLAME brighter than a RED HOT COAL?_ A. Because _yellow rays_ always produce the greatest amount of _light_; though _red rays_ produce the greatest amount of _heat_. Q. _Why is the LIGHT of a fire MORE INTENSE sometimes than at others?_ A. The _intensity_ of fire-light depends upon the _whiteness_ to which the carbon is reduced, by combustion. If the carbon be _white hot_, its _combustion is perfect_, and the light intense; if not, the light is obscured by _smoke_. Q. _Why will not CINDERS BLAZE, as well as FRESH coals?_ A. The _flame_ of coals is made chiefly by _hydrogen gas_. As soon as this gas is consumed, the hot cinders produce only an _invisible_ gas, called carbonic acid. Q. _Where does the hydrogen gas of a fire come from?_