ters of wood, like
miniature tooth-picks, thinner and shorter than lucifer-matches, whose
points he has had dipped in melted sulphur; also a small spare lump of
sulphur of the size of a pea or bean, in reserve. The cook should have a
regular tinder-box, such as he happens to have been used to, and an
abundance of wax lucifers. Paper fusees are not worth taking in travel,
as wet entirely spoils them.

There are usually three separate agents in making a fire, each of which
may be varied in many ways and requires separate description. 1. The
Spark or other light to start with. 2. The Tinder; that is, some easily
ignited and smouldering substance. 3. Fuel, judiciously applied to the
burning tinder, or other feeble light, so as to develop it into a
serviceable fire.

To obtain Fire from the Sun.--Burning-glasses.--The object-glass, and
every other convex glass of a telescope is a burning-glass, and has only
to be unscrewed to be fit for use. The object lenses of an opera-glass
are very efficient. The larger the glass and the shorter its focus, the
greater is its heating power. Convex spectacle glasses and eye glasses
are too small and of too long a focus to be used with effect, except when
the sun is very hot. An old-fashioned watch-glass, filled with water, and
having the rays of a powerful sun glittered down upon it vertically by
help of a mirror, will give a light. Dr. Kane and other arctic travellers
have made burning-glasses of ice.

Reflectors.--The inside of the polished metal cover of a hunting-watch
will sometimes converge a sufficiency of rays, to burn. The vestal fire
of Rome and the sacred fire of the Mexicans were obtained by means of
reflectors. If I understand aright, they consisted of a stone with a
conical hollow, carefully polished, the apex of the hollow cone was a
right angle: the tinder was held in the axis of the cone. See Tylor's
'Early History of Mankind.'

Black Tinder.--Tinder that is black by previous charring, or from any
other cause, ignites in the sun far sooner than light-coloured tinder.

Fire by conversion of motion into heat.--General Remarks.--When a moving
body is arrested, heat is given out; the quantity of heat being in exact
proportion to the mass, multiplied into the square of its velocity. Thus
if a cannon ball be fired at an iron target, both it and the ball become
exceedingly hot. There is even a flash of light when the velocity of the
ball is very high. When bullets are fired