“My dear young lady,” observed Mr. Seymour, “I never heard a better story for illustrating the illusions to which the senses are exposed; and if you will read the second letter on ‘Natural Magic,’ by Sir David Brewster, you will obtain a ready explanation of your vision--but let us examine it philosophically. In the first place you acknowledge that your imagination had been previously excited during your ramble through the wood, and more especially by your reverie at the statue of Time; now it is well known that such a condition of the mind prepares and adapts the organs of vision for those illusions which I am about to explain. You have told us that, on your descent into the valley, the moon had withdrawn its light, and several minutes had elapsed before an object became visible, and that was the _white_ foam of the waterfall.” “If I rightly remember, Brewster has stated that the spectres that are conjured up by the imagination are always _white_, because no other colour can be seen at night,” observed Mrs. Seymour. “Undoubtedly,” replied her husband; “and as these spectres are formed out of objects whose different parts reflect different degrees of light, their fainter parts will appear and disappear with the ever varying degree of illumination which is occasioned by the moon shining through a veil of clouds, and a change even of shape will be thus produced which will impart to the object in question the semblance of a living form. The actual state of the eye itself will also greatly assist in completing such an illusion; for, in consequence of the small degree of light, the pupil expands to nearly the whole width of the iris, in order to collect every ray, and in such a condition it cannot accommodate itself to see near objects distinctly, so that the form of a body actually becomes more shadowy and confused when it comes within the very distance at which we count upon obtaining the best view of it.” “You have certainly explained the reason why bodies seen under a faint illumination may appear distorted and caricatured; indeed, I now remember that Sir Walter Scott, in his “Pirate,” has given us a very good illustration; for Cleveland when abandoned on Coffin bay is said to have seen many a dim and undefined spectre in the misty dawn. But I am still at a loss to understand how the vision I witnessed in the valley could have been conjured up,” said Miss Villers. “It was the doubtful and flickering light of the clouded moon upon the mass of white sandstone,” said Mr. Seymour. “It is a great law of the imagination, that a likeness in part tends to become a likeness of the whole. The sandstone presented, in the first instance, a form somewhat resembling the human figure, or some part of it, when your active imagination immediately completed the outline; just in the same way as we trace images in the fire, or castles in the clouds, or grotesque figures of men and animals on damp walls.”(46)