“Sir David Brewster, in his late work on Natural Magic, has given us a beautiful illustration of the same principle; it is as follows,” said Mr. Seymour. “A figure dressed in black and mounted upon a white horse, was riding along exposed to the bright rays of the sun, which through a small opening in the clouds was throwing its light only upon that part of the landscape. The black figure was projected against a white cloud, and the white horse shone with particular brilliancy by its contrast with the dark soil against which it was seen. A person interested in the arrival of such a stranger, had been for some time following his movements with intense anxiety; but upon his disappearance behind a wood, was surprised to observe the spectre of the mounted stranger in the form of a white rider upon a black steed, and this spectre was seen for some time in the sky, or upon any pale ground to which the eye was directed.”
“I cannot understand why the spectre should be opposite in colour to the real image,” observed Tom.
“It is a law of vision which you must for the present take for granted,” answered his father; “that such is the fact, however,” continued he, “I will satisfy you by a very simple experiment.”
Mr. Seymour here placed three different coloured wafers in a triangular form on a piece of white paper, and instructed his son to fix his eyes steadily upon them for a minute; this having been performed, he next directed him to turn them from the wafers to a blank part of the paper, and to tell him what he saw.
“I see,” exclaimed Tom, “three spectral wafers, but the colours are different; the red wafer is represented by a green, the violet by a yellow, and the orange by a blue.”
“You now then understand what is meant by the spectral or accidental colour of a body:--But let us return to the subject of the Thaumatrope,” said Mr. Seymour.
“Behold!” continued he, “the Trojan ships!”
“Ay, ay, sure enough,” said the vicar; “but let me see, are their forms according to ancient authority? Very well indeed, Mr. Seymour. Very well; the poops have the bend so accurately described by Ovid and Virgil--‘puppesque recurvæ,’ as the poet has it. And there is the triton; but is its size in proportion to the vessel? Yes, sir, you are doubtless correct, the figure is generally represented of considerable magnitude on ancient medals; and Silius Italicus, if my memory serves me, alludes to the weight of the image having on some occasions contributed to the wreck of the vessel.”
“Spin them round,” said Mr. Seymour.
The vicar complied; exclaiming at the same moment, “‘Vos ite solutæ. Ite deæ pelagi.’ They are positively converted into sea-nymphs. ‘Mirabile monstrum!’” cried Mr. Twaddleton.