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Throughout all this the gorgeous colouring that a summer's mid-morning throws over imperial Rome. Above, that canopy of translucent blue, iridescent and scintillating with a thousand colours, flicks of emerald and crimson, of rose and of mauve that merge and dance together, divide and reunite before the retina, until the gaze loses consciousness of all colour save one all-pervading sense of gold.
On a circular white disk, about halfway between the center and circumference, fix a small, black, oblong disk, and rapidly rotate it by means of a rotating wheel. There appears a ring of gray on the black, showing that the impression on the retina lasts a certain time. Optic Disks. Experiment 181. Attach it so as to rotate it rapidly, as on a sewing machine.
In an instant she had passed; and it took a little while for the blur of black and white that she had flashed upon his retina to clear into an image which even then, from under-exposure, was obscure and piecemeal: a black riding-habit, of some flexile stuff, that fluttered in a multitude of pretty curves and folds; a small black hat, a toque, set upon a loosely-fastened mass of black hair; a face intensely white a softly-rounded face, but intensely white; soft full lips, singularly scarlet; and large eyes, very dark.
From all these experiments it appears, that the spectra in the eye are not owing to the mechanical impulse of light impressed on the retina, nor to its chemical combination with that organ, nor to the absorption and emission of light, as is observed in many bodies; for in all these cases the spectra must either remain uniformly, or gradually diminish; and neither their alternate pretence and evanescence as in the first experiment, nor the perpetual changes of their colours as in the second, nor the flash of light or colours in the pressed eye as in the third, nor the rotation or libration of the spectra as in the fourth, could exist.
The senses, too, are invaded and dulled. Double vision is produced, the eyes not being so controlled as to bring the image upon corresponding points of the retina. Diseases Produced by Alcohol. The diseases that follow in the train of the alcoholic habit are numerous and fatal. It lays its paralyzing hand upon the brain itself, and soon permanently destroys the integrity of its functions.
The scene was engraved for years on the retina of Knight's eye: the dead and brown stubble, the weeds among it, the distant belt of beeches shutting out the view of the house, the leaves of which were now red and sick to death. 'You must forget me, he said. 'We shall not marry, Elfride.
They all have a brain and nerves, and some of these nerves may be sensitive to light; but have no combination of retina, membranes, humors, etc., by which the distinct image of an object may be formed and conveyed by the optic nerve to the cognizance of the internal perception, or the mind. The animal in this case would be merely sensible of the difference between light and darkness.
I must allude to one or two points in the histology and physiology of the organs of sense. The anterior continuation of the retina beyond the ora serrata has been a subject of much discussion.
In this experiment the retina, after being some time kept in the dark, becomes so sensible to a small quantity of light, as to perceive distinctly the greater quantity of red rays than of others which pass through the eyelids. A similar coloured light is seen to pass through the edges of the fingers, when the open hand is opposed to the flame of a candle.
We have just seen how the eye deals with rays of light coming from a distance, which are practically parallel. When, however, books or other objects are brought near the eye, the rays of light coming from them do not remain parallel, but begin to spread apart, or diverge; and a stronger lens is required to bring them to a focus upon the retina.
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