We can conceive that climate may produce an alteration of the quality of wool in three ways, which ought to be discriminated before we can form precise notions on this subject.

First, It may operate directly on the filament it self while growing, so as to render the particular parts of that filament coarser or finer in proportion to the degree of heat that prevailed at the time every separate part of the filament was produced;

or,

Second, The heat or cold may be conceived capable of producing such a total change in the animal economy as to dispose those fheep which have ever been subjected for a sufficient length of time to its influence, to produce a greater or smaller quantity of wool, and also to alter its quality iu respect to finenefs, &c. not only at the present time, but even during the whole future period of its life, or

Third, This over-ruling influence of climate may be supposed to be so powerful as not only to produce a permanent change on the temperament of the animal itself, which fhall affect the quality of its fleece as long as the animal which has once been subjected to that heat, fhall live; but also to affect the progeny, so as to dispose them ever afterwards to produce wool of the factitious kind, if you please to admit that phrase, which was created by the influence of climate on the parent animal. On each of these heads I fhall beg leave to offer a few remarks after having made a few preliminary observations.

Parallel between wool, bair, &c. and vegetables. Wool and hair resemble vegetable productions in some respects very nearly, though in other respects they differ from them considerably. Like vegetables from the earth, these animal substances spring out from the skin, to which they firmly adhere, and from which they seemingly draw the nourishment that sustains them; like vegetables too they advance in length by gradual increment, which though not perceptible at the time, can be easily measured by comparing their length at different periods. The `variety of kinds of vegetable productions is very great, and they differ in their habitutes and peculiarities amazingly, some being perennial, some annual, some of large stature, others small, &c; and though among the annual productions referable to this class, the diversity is comparatively smaller, yet it is still very considerable. Some kinds are annual, as wool and the body hairs of most animals, others are peren nial, as the tails and manes of horses, the hair of the human head, &c. Some kinds continue to advance during the whole period of the animal's life, with nearly an equal degree of increment in equal times, as the human beard; while others soon attain their full stature, and remain ever afterwards entirely stati onary, as the hair of the human eyebrow, but still more particularly so, the eye lashes. In these, and other respects, the similarity between these animal and vegetable productions is very obvi

aus.

Their difsimilarities, though not so obvious at first sight, are also very considerable. Among vegeta bles it is a general rule that the augmentation in size is by an additional increment, not only in length, but in their other dimensions also: among these a nimal productions, it is a rule equally general, that the whole of the increase in size consists in their gradual elongation only. Human head hair grows every day longer and longer; but its thicknefs continues nearly the same. Among vegetables too their gradual elongation very generally takes place nearly at the points of the shoots, while the parts below remain stationary in that respect; but the case is quite reversed with regard to wool and hair: for in them the growth takes place entirely at the bottom of the stem, while the points never, that I have been" able to observe, make the smallest advances.

This progrefs of the growth of wool is beautifully illustrated by an experiment that has been made many millions of times in Scotland, though without any intention of illustrating this fact, viz. the laying of sheep with tar, commonly called smearing. About the month of November, annually, most of the farmers in the south of Scotland, cover the whole surface of the body of their heep, with a composition of tar and butter in certain proportions. This is done by separating the wool on the surface in long fhades, and prefsing the composition upon the fkin and along the roots of the wool by means of the finger. The tar thus laid on adheres to the wool at that place, and makes a black mark, which remains quite perceptible as long as the wool remains upon

Nov. 13 the fheep: but this mark gradually rises from the fkin as the wool grows, so that at fhearing time it is found to be nearly in the middle; the under part of the wool, which had grown during the winter and spring being of a pure white, below this black ring. The progrefs of the growth of the hairs of the human beard is equally observable in the operation of fhaving, where it is evident that the stumps only advance by a gradual protrusion, as it would seem, of the hairs through the fkin, very unlike to that which takes place when the stem of a vegetable is cut over, which remains for ever stationary, and new fhoots only push out from around it.

But the most remarkable difsimilarity that takes place between vegetables and these animal productions, is in regard to their propagation. Vegetables are reared from seeds; and may be transplanted from one soil to another, whereas these animal productions are appropriated by nature, each not only to the particular animal to which they belong, but also to the particular part of the animal from which they spring and if in some cases it be in the power of man to eradicate these, this is always a work of great violence and difficulty; but it is very doubtful if in any case he can be able to rear them where they would not naturally grow; and in no case can he transplant those of one clafs into the place of another.

Another pretty obvious difsimilarity between vegetables and these animal productions is, that though cold tends in general to retard the growth of

vegetables, and to stint their size in all their dimen sions, it seems in these respects to have no percep tible influence on animal hairs. The human beard advances nearly with the same rapidity in winter and in summer; and is equally soft or rigid in cold or in warm climates and from the experiment above related, it appears that wool advances equally fast during the winter as the summer months. Indeed it has been by many supposed that cold weather rather promoted than retarded the growth of wool, and animal hairs: but this opinion we fhall have occasion afterwards to examine.

Among the annual animal productions themselves, there are many striking difsimilarities; many of which, the limits I prescribe to myself in this essay, prevent me from pointing out; but it is necefsary f fhould remark some of them. The most useful to man of all these animal filamentous productions is the wool of fheep; and as our object here is chiefly to ascertain the most striking peculiarities of wool, some circumstances that tend to discriminate it from other animal filaments that nearly resemble it, may not be unacceptable to the reader.

The wool of sheep, like the body hair of horses, cattle, and most other animals, begins and completes its growth in one year; and like them also, after ha ving completed its growth it loosens of itself from the skin and falls off, being succeeded by another fresh crop which comes in its stead. But it differs from them in respect of the uniformity of its growth, and the regularity of its fhedding. Every filament of wool seems to keep exact pace with another in VOL. Xviii.

H