1 "The swan uplifts his chest, and backward flings His neck, a varying arch, between his towering wings.-WORDSWORTH. and the motion is so rapid that the stroke is much more weighty than would at first be supposed from the mere volume of the striking instrument. 930. When we consider that the effect of a stroke is made up of two elements, the quantity of matter and the velocity, and that the effect increases only as the quantity of matter, while it does so as to the square of the velocity, we can easily understand how soon rapidity of motion will make up for any inferior weight in the moving instrument. One-fourth the quantity of matter moving with four times the velocity, has an effect in the proportion of sixteen to four, that is, it has an effect four times as great. 931. Why do swans in their migrations fly very high? They take a very high flight in order to avoid the attacks of the eagles and falcons, against whom their powers of resistance would ill defend them if the latter got "the sky" of them. 932. To everything above it in the air, the falcon is comparatively harmless; by taking "the sky" of the falcon, the swan is enabled to perform its migratory trip in safety. 933. Why are swans in making their migratory flights governed by the state of the wind? Because, on account of their bulk and the weight of their closely set feathers, they cannot make way against the wind. Hence they almost invariably go with the wind; and wait, or even halt on their journey, if the wind is adverse. 934. Why has the plumage and character of the swan remained for many centuries unchanged? Because of its wild nature; it is less subject to domestication than almost any kind of bird, pining in captivity, and never breeding, unless allowed to do so within its own haunts. 935. Why should the alleged "dying song" of the swan be rejected as fabulous? That the swan, usually mute, should utter a pleasing musical note at its death is contrary to all experience and philosophy. L "A cormorant flew several times round the ship. As these birds are seldom, if ever, known to fly far out of sight of land, I judged that some was not far distant."-CAPT. COOK. That it should be true, indeed, would be in contradiction to the whole analogy of nature, the voices of pain in animals, and especially at the hour of death, being without a single exception unpleasant to the ear. 936. What peculiarity is there in the structure of the foot of the cormorant ? The tarsi are stronge rand more tendinous than in swimming birds; they are straighter set; the toes collapse more, and thus the birds can walk better, and also stand firm on the slippery points of rocks. The peculiarity in form is the web continued to the hind toe, and the general position of the web being inwards rather than forwards, as may be seen in the annexed figure of the right foot of the cormorant, with the side outwards, which is turned towards the centre of the bird. 937. If the prey is on the surface, and small, these birds can capture it by a snap of the bill, and ascend again without losing the wing, in the same manner that the skimming birds take the greater part of their food; but if the prey is under the surface, and large, the wing must not only suspend its action, but be partially closed, and the bird must thus enter the water, using it wings as agents in again ascending. 938. Why are stormy petrels enabled to run upon the surface of the water? Because the lightness of their bodies, and the action of the wind upon their wings, enable them with ease to assume this position during a storm. In calm weather they perform the same manœuvre, by keeping their wings just so much in action as to prevent their feet from sinking below the surface. "Such murmur fill'd Th' assembly, as when hollow rocks retain The sound of blustering winds, which all night long 939. There are few persons who have crossed the Atlantic that have not observed these wanderers of the deep skimming along the surface of the wild and and dangers to the hapless mariner, but as wicked agents, connected somehow or other in creating them. "Nobody," they say, "can tell anything of where they come from, or how they breed, though (as sailors sometimes say) it is supposed that they hatch their eggs under their wings as they sit on the water." This mysterious uncertainty of their origin, and the circumstances above recited, have doubtless given rise to the opinion so prevalent among seafaring men, that they are in some way or other connected with supernatural powers in the air. In every country where they are known, their names have borne some affinity to this belief, They have been called witches, stormy petrels, the devil's birds, and Mother Cary's chickens, probably from some celebrated hag of that name; and their unexpected and numerous appearance has frequently thrown a momentary damp on the mind of the hardiest seaman. 940. Why are sea-birds enabled to breast the waves in tempestuous weather? Because the waves, instead of rolling with the velocity of the wind (as is commonly imagined), roll very little. When we look at them from the shore and with a side wind, they seem to roll on, and they always appear to move slower in a fresh breeze. They heave and sink, the times being as the square roots of their lengths, so that, if a wave four feet broad changes from ridge to trough in four seconds, one of sixteen feet will change in eight seconds. Now, as the apparent forward motion is half the width, the four-feet wave will appear to move at the rate of rather less than a mile and a half in the hour, the sixteen-feet wave at rather less three-quarters of a mile in the hour, which is very slow motion, m "By them there sat the loving pelican, Whose young ones, poisoned by the serpent's sting, 941. Thus in the case of single waves, the middle of the slope is a point of rest, 1 on which the sea-bird can sit with little more difficulty than on the calm surface. This will, perhaps, be made bplainer by the accompanying diagram, in which two birds are represented as being at rest on the wave: a b is the mean level or calm line of the sea, cutting both the black and dotted curve on the points o o. The figure 1 represents the ridge, and 3 the hollow, at one end of the vibration; 4 the ridge, and 2 the hollow, as shown by the dotted line at the other. The bird at b on the turning-point is not moved either up or down; and as that point is alternately on the windward and the leeward of the wave, the wave keeps the bird from drifting in the first case, and shelters it in the second. 942. Why has the pelican a large pouch attached to its lower mandible? The pouch answers nearly the same purposes that the crop does in birds which possess such an organ. The food is taken into it in much larger quantities than the digestive stomach can receive at once; and is gradually received into the stomach as the process of digestion goes on. But the pouch serves another and a remarkable purpose. The pelican, though seeking its food in the sea, builds its nest at a distance from it, generally in ruins which have become dry and waste; and this is the reason why the name of the pelican is so frequently associated in writings with that of the wilderness. The pouch, therefore, serves as a receptacle, in which the pelican conveys food to its young, in nests which lie remote from the shore. The food designed for the young becomes macerated or softened by the action of the pouch; and when the nest is situated in a very arid district, the old bird uses the pouch to carry water to its young. MISCELLANEOUS. 943. Why when birds migrate, do the old ones generally precede the young ones? Because the moulting of young birds takes place at a later period than that of old ones; so that they are not sufficiently recovered from the weakness which attends this process, to endure the fatigues of a journey at a time when the old birds are ready to undertake it. 944. By what circumstances is the migration of birds governed? The time at which birds of passage arrive in Britain, or quit it, varies according to the species. Natives of the northern countries of Europe come to us at the end of autumn or the beginning of winter; and in the first fine weather avoid our heat, as they had done excess of cold; they return to lay their eggs in the north. Other birds, which are born in our own country, and which may be considered as properly belonging to it, quit us in autumn; and after passing the winter in warm climates, they revisit us in the spring, or perhaps, avoiding the moderate warmth of our summer, they emigrate to Arctic regions. Others again, natives of southern climates, come to the north to escape from the ardour |