ly chosen and well executed, the appearance will be
both wonderful and pleasing.

[Illustration: Fig. 24.]

_Gunpowder Exploded by Reflection._

Place two concave mirrors at about 12 or 15 feet distance from each
other, and let the axis of each be in the same line. In the focus of
one of them place a live coal, and in the focus of the other place
some gunpowder. With a pair of double bellows, which make a continual
blast, keep constantly blowing the coal, and notwithstanding the
distance between them, the powder will presently take fire.

_The Igniting Mirrors._

The rays of a luminous body placed in the focus of concave mirror,
being reflected in parallel lines, and a second mirror being placed
diametrically opposite to the first, will set fire to a combustible
body, by collecting those rays in the focus.

_The Armed Apparition._

If a person with a drawn sword place himself before a large concave
mirror, but further from it than its focus, he will see an inverted
image of himself in the air, between him and the mirror, of a less
size than himself. If he steadily present the sword towards the centre
of the mirror, an image of the sword will come out from it, point to
point, as if to fence with him; and by his pushing the sword nearer,
the image will appear to come nearer to him, and almost to touch his
breast. If the mirror be turned 45 degrees, or one-eighth round, the
reflected image will go out perpendicularly to the direction of the
sword presented, and apparently come to another person placed in the
direction of the motion of the image, who, if he be unacquainted with
the experiment, and does not see the original sword, will be much
surprised and alarmed.

_The Phantom._

You inform a person that at a certain hour, and in a certain place, he
shall see the apparition of a deceased friend, (whose portrait you
possess.) In order to produce this phantom, there must be a door which
opens into an apartment to which there is a considerable descent.
Under that door you are to place the portrait, which must be inverted
and strongly illuminated, that it may be brightly reflected by the
mirror, which must be large and well polished. Then having introduced
the incredulous spectator at another door, and placed him in the
proper point of view, you suddenly throw open the door, when to his
great surprise he will view the apparition of his friend.

_The Distorting Mirror._

Opticians sometimes grind a gla