taking notice, that the threads or laminæ of which we have been speaking, in their natural ftate unite; that their union is fomething more than the mere appofition of loose furfaces; that they are not parted afunder without fome degree of force; that neverthe efs there is no glutinous cohesion between them; that, therefore, by fome mechanical means or other, they catch or clafp among themselves, thereby giving to the beard or vane its clofeness and compactnefs of texture. Nor is this all: when two lamina, which have been separated by accident or force, are brought together again, they immediately reclafp: the connection, whatever it was, is perfectly recovered, and the beard of the feather becomes as fmooth and firm as if nothing had happened to it. Draw your finger down the feather, which is against the grain, and you break, probably, the junction of fome of the contiguous threads; draw your finger up the feather, and you restore all things to their former flate. This is no common contrivance; and now for the mechanifm by which it is effected. The threads or laminæ above mentioned are interlaced with one another; and the interlacing is performed

by

by means of an infinite number of fibres or teeth, which the laminæ fhoot forth on each fide, and which hook and grapple together. A friend of mine counted fifty of these fibres in one twentieth of an inch. Thefe fibres are crooked; but curved after a different manner; for thofe, which proceed from the thread on the fide towards the extremity of the feather, are longer, more flexible, and bent downward: whereas those which proceed from the fide towards the beginning or quill end of the feather are fhorter, firmer, and turn upwards. The process then which takes place is as follows. When two lamina are preffed together, fo that these long fibres are forced far enough over the short ones, their crooked parts fall into the cavity made by the crooked parts of the others just as the latch that is fastened to a door, enters into the cavity of the catch fixed to the door poft, and, there hooking itfelf, faftens the door; for it is properly in this manner, that one thread of a feather is faftened to the other.

This admirable ftructure of the feather, which it is easy to fee with the microfcope, fucceeds perfectly for the ufe to which nature has defigned it, which ufe was, not only that the laminæ might be united, but that when one thread

thread or lamina has been feparated from another by fome external violence, it might be reclasped with sufficient facility and expedition *.

In the oftrich, this apparatus of crotchets and fibres, of hooks and teeth, is wanting; and we see the confequence of the want. The filaments hang loose and separate from one another, forming only a kind of down; which conftitution of the feathers, however it may fit them for the flowing honours of a lady's head-drefs, may be reckoned an imperfection in the bird, inafmuch as wings, compofed of these feathers, although they may greatly affift it in running, do not serve for flight.

But under the present division of our subject, our business with feathers is, as they are the covering of the bird. And herein a fingular circumftance occurs. In the small order of birds which winter with us, from a snipe downwards, let the external colour of the feathers be what it will, their Creator has univerfally given them a bed of black down next their bodies. Black, we know, is the warmest colour: and the purpose here is, to keep in the

*The above account is taken from Memoirs for a Natural History of Animals by the Royal Academy of Paris, published 1701, p. 219,

heat,

heat, arifing from the heart and circulation of the blood. It is further likewise remarkable, that this is not found in larger birds; for which there is also a reason. Small birds are much more exposed to the cold than large ones; forafmuch as they prefent, in proportion to their bulk, a much larger furface to the air. If a turkey was divided into a number of wrens, fuppofing the shape of the turkey and the wren to be fimilar, the furface of all the wrens would exceed the surface of the turkey, in the proportion of the length, breadth, (or, of any homologous line) of a turkey to that of a wren; which would be, perhaps, a proportion of ten to one. It was necessary therefore that small birds fhould be warmer clad than large ones; and this seems to be the expedient, by which that exigency is provided for.

II. In comparing different animals, I know no part of their structure which exhibits greater variety, or, in that variety, a nicer accommodation to their refpective conveniency, than that which is feen in the different formations of their mouths. Whether the purpose be the reception of aliment merely, or the catching of prey, the picking up of feeds, the cropping of herbage, the extraction of juices, the fuc

tion of liquids, the breaking and grinding of food, the taste of that food, together with the respiration of air, and in conjunction with the utterance of found; these various offices are affigned to this one part, and, in different fpecies, provided for, as they are wanted, by its different conftitution. In the human fpecies, forafmuch as there are hands to convey the food to the mouth, the mouth is flat, and by reason of its flatnefs fitted only for reception : whereas the projecting jaws, the wide rictus, the pointed teeth, of the dog and his affinities, enable them to apply their mouths to fnatch and feize the objects of their pursuit. The full lips, the rough tongue, the corrugated cartilaginous palate, the broad cutting teeth, of the ox, the deer, the horse and the sheep, qualify this tribe for broufing upon their pafture; either gathering large mouthfulls at once, where the grass is long, which is the cafe with the ox in particular; or biting close, where it is fhort, which the horse and the sheep are able to do, in a degree that one could hardly expect. The retired under jaw of a swine works in the ground, after the protruding fnout, like a prong or ploughfhare, has made way to the roots upon which it feeds. A

its

3

conformation