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to note these. Those who see are less careful to do this, trusting to the ease with which they can be recalled.

It is well known that the pupils of the eyes of cats expand to a wide circle, to enable them to see their prey in the night, and are contracted to a mere chink by the glare of day. A beautiful contrivance for adapting the eyes of hawks, owls, cocks, and waterfowl to different degrees of light was discovered about fifty years ago by my friend, Mr. Smith, and published in the transactions of the Royal Society. Sir Philip Crampton also, without a knowledge of what Mr. Smith had done, made a like discovery in the eyes of water-fowl. It consists of a ring of bony scales, movable over each other by intervening muscles, and thus enabled to give more or less convexity to the cornea, which it surrounds. The neck of the swan, the goose, &c., is thus rendered as subservient to the will of the bird as is the trunk to the elephant. His structure and the acquisition of his food do not require that more senses than those of touch and smell should be placed at the ex

tremity of his flexible trunk; but aquatic birds, who have to search for their food under water and in mud, require the aid of all their senses, whether for search or notice of danger; and by that benevolent intelligence which with such surpassing skill adapts means to ends, we accordingly find that all the organs of sense are placed at the extremity of the bird's trunk. Analogous to this, faint sounds from distant explosions suggest the distance by suggesting what the sound would be if near. The pull of a kite-string suggests the height to which it has flown the faint sensation of touch, from the line to which the lead is appended, the depth to which it had been lowered-the fainter smell what it would be if near. But all this is but the play of the muscular sense.

It is generally supposed that we always infer the tangible reality from the visible sign by a law of reciprocal influence between the eye and the hand, so acutely demonstrated by Mr. Wedgwood; but if attention be given to what passes in our minds while looking through a tunnel or the aisle of a cathedral, when, notwithstanding the diminished appear

ance of the arches approaching the visual vanishing point, which, nevertheless, suggest equality with those nearest to us, we shall find that it is the nearest visual sign of the arches which is suggested by the distant, and not the tangible, since we may never have touched any part of the building.

This may, perhaps, be more readily apprehended by drawing a church, tree, or any large object, as it appears to the eye at different distances. I think it will then be clear, that the visual distant suggests the visual near, and not the tangible, since the effect on our thought is the same whether we have touched the object or not.

It is difficult to satisfy persons who have not made vision a subject of minute investigation that the eye does not measure lineal as well as angular distance; but that it actually does not take direct cognizance of a third dimension, but merely infers it from the luminous sign of the third dimension is well proved by a diorama, Sir J. M. Brunell's toy illusion of his tunnel, and by the following experiment, easily made, by any one with a knife and

a square foot of pasteboard:-Outlines of statues, vases, trees, &c., cut in pasteboard, and left adhering to the sheet; but so that when held between the eyes and the sun, or a lamp, the light may shine through the cut outline, and be deflected over the surface of the figure, it then presents the most perfect illusion of a solid-so that, if placed in a situation where it could not be touched, and looked at by the most scrutinising eyes of a person totally unacquainted with the real construction of what he saw, he must be disposed to believe that he saw a tangible third dimension, a substantial solid. Yet here there is nothing for the impression it makes but shade fringed with light, deflected on a flat surface.

By experiments made in the Lake of Geneva it was found, that a light refracted from under the water into the air was not visible at a greater distance than three hundred yards; but that, through the medium of a tube, held from the eye to some feet under the surface of the water, the same light was clearly distinguishable at the distance of

some miles. A bell rung under the surface was heard in air at about the same distance at which the light was seen; but when the ear was applied to one end of a tube, while the other was under the surface of the water, the sound was heard at the distance of some miles.

That odoriferous effluvia do affect the sense of smell more when inhaled through a tube, as by the elephant, any one may satisfy himself, by inhaling the fragrance of flowers through a tube.

In stating the influence of associates to produce excitement (get up the steam to work the human engine) Professor D. Stewart adduced in his Lectures the instance of a boy employed in a manufactory to attend to the opening and closing the valves of a steamengine. The momentary attention required for this was an intolerable restraint on his propensity to play with the idle boys near him. This strong and incessantly-urging motive to free himself from this restraint (always thinking about it) led him at last to think of the happy expedient of tying the

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