balance be preserved, by a slight exertion of the tail and the point of a wing, easily moved, or restored to its place by a very slight impulse, and opposing no surface to the wind which the bird cannot easily counteract. In the fluttering repose, the wings are caused to act vertically alone; and thus, a fixed position is easily maintained. In the humming-bird, there is the same power, for a wellknown purpose."*

EIGHTH WEEK-THURSDAY.

BIRDS. THEIR POWER OF VISION.

THE vision of birds is not less remarkably adapted to their situation and necessities, than their faculty of moving through the air. In this order, the formation of the eye has several peculiarities, with regard to the nature of which, in some particulars, physiologists are not altogether agreed; but it is well known, that this organ is in birds proportionally larger and more prominent than in other animals, which enables them to command a more extensive range of vision; that the substance of the eye is more hard and horny, which compensates for the danger to which its prominence subjects it; that its nictitating membrane is admirably contrived, as an additional security against peril from branches of trees, or other objects, with which its habits render it liable to come in contact; that its power of altering the focus of vision, in certain tribes, is peculiar and great; and that there is yet another part of the organ, whose use has not been very clearly ascertained, but which is supposed powerfully to assist the sight, called, by the French Academicians, the purse or comb.

Without dwelling further on the general structure of the

* Attributes of God, vol. ii. pp. 100–105. [Dr. Macculloch may be a very ingenious, but he certainly is not, if we may judge from this specimen, a very clear writer. The passages quoted require some study. AM. ED.]

eye, in this class of animals, I shall notice some circumstances, which practically show a very striking adaptation of the faculty of vision, in various species, to their habits and wants. And I begin, by observing, that night-birds have their eye peculiarly formed, for seeing in the twilight. M. de Blainville remarks, that, besides being comparatively very large, this organ is, in the class alluded to, flat, both before and behind, while the transparent cornea is placed at the end of a sort of tube. The retina is consequently large and extended, as well as the iris, while the membranes, being probably more soft and delicate, are more susceptible of impressions from a small quantity of light. The owl and the woodcock are of this description. These species, the former in particular, though by no means of acute vision by day, are remarkably quicksighted in the evening, when they stir abroad in search of their slumbering prey.

But it is to instances of day vision, that I intend particularly to devote this paper; and the first example I shall adduce, is that of the carrier-pigeon. It is believed that the remarkable faculty by which this bird finds its way to its distant home, is almost exclusively its power of sight. This opinion is supported by the manner in which it executes its journeys, so far as this has been ascertained. When let off from a low station, in an unknown locality, it rises by irregular excursions to a certain height, and then commences its route by a rapid flight in gyrations, taking in a larger and larger space at every turn, and thus obtaining a complete survey of the whole district in every direction; and it is supposed to continue this circular motion till some known object arrests its vision, and makes it aware of its position, when it darts forward with incredible velocity in the right direction. If liberated from a balloon, when high in the air, the bird drops perpendicularly downwards, till it comes within such a distance of the earth, that it can distinguish landmarks, and then commences its wheeling flight, as already described.

If this account be correct, the velocity of the carrierpigeon is indeed incredible. M. Antoine relates, that a

III.

21

IX.

gentleman of Cologne, having business to transact at Paris, took with him two carrier-pigeons; and, having arrived at the metropolis, he tied a letter to each of his pigeons, and despatched them at eleven o'clock precisely. One of them arrived at Cologne at five minutes past one o'clock, and the other nine minutes later, having thus completed a journey of three hundred miles in little more than two hours! This was at the rate of nearly one hundred and fifty miles an hour, supposing their flight had been in a direct line. If it was circular, as observation would lead one to suppose, the extent traversed must have been immensely greater.

Audubon gives a similar, though considerably less marvellous, account, of the velocity of the American pigeon. He says, that pigeons have been killed, in the neighborhood of New York, with their crops full of rice, which they must have collected in the fields of Georgia or Carolina, these districts being the nearest in which they could have procured a supply of this kind of food. "As their power of digestion is so great, that they will decompose food entirely in twelve hours, they must in that case have travelled between three hundred and four hundred miles in six hours, which shows their speed to be, at an average, about one mile in a minute. A velocity such as this would enable one of these birds, were it so inclined, to visit the European continent in less than three days." This naturalist goes on to observe, that the great power of vision possessed by the pigeon, enables it, as it travels at that swift rate, to inspect the country below, and discover its food with facility; which he has ascertained by observing, that when traversing barren tracts, they keep high in the air, to descry distant lands; whereas, when the country is fertile, they fly lower, to fix on the part most plentifully supplied with food. "As soon," he graphically adds, "as the pigeons discover a sufficiency of food to entice them to alight, they fly round in circles, reviewing the country below. During their evolutions on such occasions, the dense mass which they form exhibits a beautiful appearance, as it changes its direction, now displaying a glittering sheet of azure, when the backs

of the birds come simultaneously into view; and anon suddenly presenting a mass of rich deep purple. They then pass lower over the woods, and are for a moment lost among the foliage; but again emerge, and are seen gliding aloft."*

It would appear, from an observation of Professor Lichtenstein, that birds which feed on carrion may probably resort to circular flights, similar to the pigeon, in order to discover a carcass. He remarked, when travelling in Southern Africa, that if an animal chanced to die, in the very midst of the most desert wilderness, in less than half an hour there was seen, high in the zenith, a number of minute objects descending in spiral circles, and increasing in visible magnitude at every revolution. These were soon discovered to be a flight of vultures, which must have observed, from a height viewless to the human eye, the dropping of the animal immediately marked out for prey.†

Dr. James Johnstone mentions a fact illustrative of the same view. During the northeast monsoon, when the wind blew steadily in one point for months in succession, he observed a concourse of birds of prey from every quarter of the horizon, hastening to a corpse that was floating down the river Ganges. Their sudden appearance he accounts for, in the same manner as Professor Lichtenstein, by their soaring high in the air in search of food. It could not be owing to the acuteness of scent, as they crowded in from the points from which the wind blew, as well as in the opposite direction. It has indeed been ascertained, by positive experiment, that vultures, and other birds of prey, are guided to their food by the sight and not by the smell. Audubon, being desirous of satisfying himself on this point, caused a large dead hog to be concealed in a narrow and winding ravine, which was filled with briers and high cane. This was done in the month of July, in a tropical climate, where putrefaction takes place with great rapidity. Yet, though many vultures were seen, from time to time, sailing in all direc

* Ornithological Biography, p. 323.

Travels in Africa.

tions over the spot, they seemed perfectly unconscious of its presence, while the dogs found their way to it, and devoured the flesh. On the other hand, when Audubon stuffed a deer-skin full of hay, and laid it down on its back, in the attitude of a dead animal, it was, in the course of a few minutes, visited by a vulture, which tore open the dried skin, and did not retreat till it had torn out large quantities of the hay, and perceived that there was no flesh within. These experiments seem to be

conclusive.

EIGHTH WEEK-FRIDAY.

BIRDS. THEIR VOICE.

WHEN a little quaker girl of my acquaintance was once humming a tune in the presence of a stiff maiden aunt of the same profession, the old lady, scandalized at what she considered an unbecoming levity, said to her, reproachfully, "Rachel, who taught thee to sing?" On which the child archly replied, "It was the little birds, aunt, that taught me to sing." There was much truth, as well as sweetness, in this reply. It is the hand of the Creator which has given the power of song to the birds; and it is the same hand which has bountifully gifted man with a musical ear, and a musical voice. The inference is irresistible, that music is intended to add to the enjoyments of the human race; and that to refuse the gift, is to show equal ingratitude to the Giver, as when we abuse it.

There is something at once peculiar and delightful in the musical intonations of the feathered tribes, which affords a clear indication of beneficent design. The music of the groves has always been a favorite theme with the poet; and civilized man is probably more alive to the pleasure derived from this source than the savage; but there is no class of rational beings to whom the song of the little warbler is not a source of enjoyment. Let any