The Real Apparition.
Behind a partition place, in a position somewhat oblique, a concave mirror, which must be at least ten inches in diameter, and its distance from the partition equal to three fourths of the distance of its centre.
In the partition, make an opening of seven or eight inches, either square or circular: it must face the mirror, and be of the same height with it. Behind this partition place a strong light, so disposed, that it may not be seen at the opening, and may illumine an object placed near it, without throwing any light on the mirror.
Beneath the aperture in the partition, place an object that you intend shall appear on the outside of the partition, in an inverted position, and which we will suppose to be a flower. Before the partition, and beneath the aperture, place a little flower-pot, the top of which should be even with the bottom of the aperture, that the eye may see the flower in the same position as if its stalks came out of the pot.
Take care to paint the space between the back part of the partition and the mirror black, to prevent any reflections of light from being thrown on the mirror; in a word, so dispose the whole that it may be as little enlightened as possible.
When a person is placed at the point of vision, he will perceive the flower that is behind the partition, at the top of the pot; but, on putting out his hand to pluck it, he will find that he attempts to grasp a shadow.
Observations.
The phenomena that may be produced by means of concave mirrors are highly curious and astonishing. By their aid spectres of various kinds may be exhibited. Suppose, for example, you were to tell any one, that at such an hour, and in such a place, he should see the apparition of an absent or deceased friend (of whose portrait you are in possession); in order to produce this phantom, instead of the hole in the partition, 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 properly reflected by the mirror, which must be large and well polished. Then, having introduced the spectator at another door, and placed him in the proper point of view, you suddenly throw open the first door, when, to his great astonishment, he will immediately see the apparition of his friend.
It will be objected, perhaps, that this is not a perfect apparition, because it is only visible at one point of view, and by one person. But it should be remembered, that it was an established maxim in the last century, that a spectre might be visible to one person, and not to others. So Shakespeare makes both Hamlet and Macbeth see apparitions that were not visible to others, present at the same time. It is not unlikely, moreover, that this maxim took its rise from certain apparitions of the kind, that were raised by the monks, to serve some purposes they called religious; as they alone were in possession of what little learning there then was in the world.