“Papa,” cried Tom, “I am quite impatient to learn how so extraordinary an effect can have been produced. You told me this morning that a phantasmagoria was nothing more than an improved magic lantern; but how is it possible for the slides to be so managed as to make the figures approach and retire from you, and above all, to make them move their bodies, and throw their arms into different attitudes?” “In the first place, the figures only _appear_ to approach you, for they are thrown upon a surface which never changes its place; the whole is therefore an optical illusion, arising from the fact that we estimate the distance of an object by its apparent magnitude; when, therefore, the figure began to diminish in size, the mind instantly assumed that it was receding from the eye; and the illusion was still farther heightened by the absence of all other objects[77] by which it might be compared.” At this moment Mr. Seymour was interrupted by the appearance of the performer who announced his intention of submitting another optical illusion, which, he trusted, would afford equal satisfaction. “Papa,” cried Tom, “how much do I regret my ignorance of optics. It is a great disappointment to me that I should witness so many curious exhibitions, without being able to understand the principles upon which they depend.” “I promise you, my dear boy,” replied Mr. Seymour, “that you shall be instructed in this branch of science during the Christmas vacation. Enjoy, therefore, the present amusements, and instead of repining at your ignorance, anticipate the pleasure which you will receive, when you shall be able to explain them.” A series of extraordinary effects were now exhibited by means of concave mirrors.[78] Aërial images were produced, so illusive in their appearance, that the spectators could not believe in their immateriality, until they attempted to grasp them. In this manner were presented flowers, fruit, a human skull, and a dagger; the latter of which terrified the spectator by the sudden and violent manner in which its point approached him. With this illusion the amusements concluded; the light of day was admitted; and the performer stepping forward, announced the termination of his exhibition in the words of Shakspeare:-- “Our revels now are ended: these our actors, As I foretold you, were all spirits, and Are melted into air, into thin air.” The villagers, as they poured out of the booth, and mingled with their companions in the fair, with their wonted propensity for the marvellous, related, in most exaggerated terms, the wonders they had encountered in the region of shadows. Nothing is swallowed with more avidity than tales of mystery, especially if spiced with a few grains of horror; we cannot, therefore, be surprised at the anxiety so generally by those who had not yet witnessed the optical performances to exchange their tickets for such as would secure their admission into the popular booth.