ASTR. The original impressions in all cases are, I presume, from without. How is the internally excited idea presented as a prominent image before the eye?

Ev. That form of disordered vision to which I allude, occurring so often in nervous persons, or resulting from close application to study, does not often appear to depend on a turgid condition of the vessels of the choroid coat or retina. It is usually relieved more by tonics than by depletion; and very strange illusions of sight will sometimes be produced merely by depressing medicines, especially the preparations of antimony. Yet these dark specks appear to be floating before, and often at some distance withoutside the eye: therefore we may believe that excited images or more perfect forms may also appear before the retina palpable. Between the first impression and its recurrence a long period may have passed (memory being unlimited), and it is sufficient that one sole idea be excited to produce a succession, as a spark of fire will ignite a train of gunpowder, or as an electric spark will discharge a whole battery.

In the curious case of photopsia, or suffusio scintillans, we have a series of illusive spectra in the forms of "lucid points," and "yellow flames," and "fiery veils," and "rings of light." In some cases of ophthalmia, and in acute inflammation of the brain, the candles and other bright objects in the chamber will look like blood. Beguelin, as we read in the "Berlin Memoirs," by straining his eyes on a book, always saw the letters red.

There is a story in Voltaire that the Duke of Florence threw the dice with a field-officer of his enemy. The spots on the dice seemed, to his excited brain, like drops of blood: he instantly ordered a retreat of his army. And this is not won

derful; it is but excited sensibility, of which many analogies indeed may be artificially produced, as the flash of light from the pricking of the retina with a fine needle, and the beautiful iris which is formed by pressure on the globe of the eye. In the very interesting history of the prisoner in the dungeon of the Chatelet at Paris, the phosphorescence of the eye was itself the source of light, in this instance so powerful as to enable the prisoner to liscern the mice that came around him to pick up the crumbs, although the cell was pitchy dark

to others.

There are many curious illusions resulting from overstraining or over-excitement of the eye.

Dr. Brewster, in the Edinburgh Journal of Science, vol. iii., says, "If in a fine dark night we unexpectedly obtain a glimpse of any object, either in motion or at rest, we are naturally anxious to ascertain what it is, and our curiosity calls forth all our powers of vision. Excited by a feeble illumination, the retina is not capable of affording a permanent vision of the object, and, while we are straining our eye to discover its nature, it will entirely disappear, and afterward reappear and vanish alternately.

A friend of Buffon had been watching the progress of an eclipse through a very minute aperture. For three weeks after this there was a perfect spectrum of the lucid spot marked on every object on which he fixed his eyes.

Dr. Brewster had been making protracted experiments on some brilliant object, and for several hours after this, a dark spectrum, associated with intense pain, floated constantly before his eye.

In the third volume of his Physiology, Dr. Bostock thus concludes the account of his own ocular spectra: "It appeared as if a number of objects,

principally human faces or figures, on a small scale, were placed before me, and gradually removed, like a succession of medallions. They were all of the same size, and appeared to be all situated at the same distance from the face. After one had been seen for a few minutes it became fainter, and then another, which was more vivid, seemed to be laid upon it, or substituted in its place, which in its turn was superseded by a new appearance."

Coloured vision may arise from permanent defect or from acute disorder; from some peculiar refraction of a ray of light on the lens of the eye, or by the optical laws of the accidental colours.

The ray of white light consists of the three prismatic or primitive colours. Now if the eye is fatigued by one of these colours, or it be lost, mechanically or physiologically, the impression of two only will remain, and this accidental or complementary colour is composed of the two remaining constituents of the white ray. Thus, if the eye has been strained on a red colour, it is insensible to this, but perceives the blue and the yellow, the combination of which is green. So, if we look long on a green spot, and then fix the eye on white paper, the spectrum will be of light red. A violet spot will become yellow; a blue spot orange-red; a black spot will entirely disappear on a white ground, for it has no complementary colour, but it appears white on a dark ground, as a white spot will change to black.

By this law I may explain the impression made by black letters on the red ground of a play-bill, which appeared blue. The accidental colour of orange-red is blue; that of black is white. By looking on this, the black letter first becomes white, and the accidental colour of the red-blue, is transferred to the white ground of the letters.

ASTR. Then, as D'Agessau recommended the Parliament of Paris to leave the demoniac of our times to the physician, and not the divine, you would delegate the management of all those to whom the mysterious world of shadows is unfolded to the sapient leech with his vials and his lancet.

Ev. Nay, I presume not to so potent a faculty. Many of the slight imperfections of vision are, as I have confessed, merely exaggerations of romantic ideas floating in the memory; and this is not a novel notion, for Plato and other philosophers held it long before our time.

Musca volitantes are usually, though not always, substantial; i. e., depending on points or fibres in the axis of vision, on congestions, or varicose states of the vessels of the choroid or retina, or of atoms floating in the humours. These specks, which do not appear alike in the eyes of all, and the brilliant beams in the suffusio scintillans, so varied and so whimsical, might be readily moulded into human form by the imagination of an enthusiast or the feelings of the ghost-seer, who is usually morose and melancholy, in a state of longing for a ghost or a mystery.

But when many of the more confirmed illusions are depending on structural disease in the membranes and humours of the eye, I am confident in the resources of our science to relieve, if not to remove. Coleridge, indeed, has expressed his belief that by some convulsion of the eye it may see projected before it part of its own body, easily magnified into the whole by slight imagination. If this be true, the whole mystery of the Deathfetch is unravelled.

The nerves and their ganglia are often diseased when we least suspect ; and calcareous and scrofulous tumours, pressing on the optic axis, in the brain,

or on the pneumogastric nerve above its recurrent branch, and disease in the bronchial glands around the cardiac plexus, may exist, with the very slightest sensations of pain. Even in extreme disorganization of the brain, there may be remissions of painless repose; and in other cases, where pain is synchronous with illusion, the illusion may subside, although the pain remains; an indication or proof, indeed, of structural cause for the fantasy. And this discrimination, Astrophel, of the line of distinction between sanity and derangement is often of a hair's breadth; and the law confesses here the high value of pathology, seeing that, in cases of suicide or of idiocy, and other states which involve the right of sepulture, the conveyance of entailed estates, or personal responsibility, the judgment of the physician is held to be oracular.

MYSTERIOUS FORMS AND SIGNS.

"Fierce fiery warriors fight upon the clouds
In ranks, and squadrons, and right form of war,
Which drizzled blood upon the capitol:

The noise of battle hurtled in the air."-Julius Cæsar.

ASTR. Methinks you claim too much homage from our courtesy to your philosophy, Evelyn. Can we believe that all these wondrous forms and shadows are but an illusion of the eye, or of the mind's eye? And, if I grant this truth in regard to the eye of one mind, can we so easily libel the evidence of a multitude, to whom the world of shadows is unlocked?

We are now wandering in the very land of omens; and will this cold philosophy of thine presume to draw aside the veil of mystery which hangs over the mountain and the cataract of yon wild principality?