What is wool? 'The covering of the sheep, of course,' replies somebody. Yes; but what _is_ it? Let us ask Professor Owen. 'Wool,' he says, 'is a peculiar modification of hair, characterised by fine transverse or oblique lines from two to four thousand in the extent of an inch, indicative of a minutely imbricated scaly surface, when viewed under the microscope, on which and on its curved or twisted form depends its remarkable felting property.' At first sight this definition seems bewildering, but it will bear examination, and is really more tangible than, for instance, Noah Webster's definition of wool: 'That soft curled or crisped species of hair which grows on sheep and some other animals, and which in fineness sometimes approaches to fur.' It is usually that which grows on sheep, however, that we know as wool, and the number of imbrications, serratures, or notches indicates the quality of the fibre. Thus, in the wool of the Leicester sheep there are 1850--in Spanish merino, 2400--in Saxon merino, 2700, to an inch, and the fewer there are the nearer does wool approach to hair. [Illustration: Wool-sorters at Work.] Here is a still more minute description by Youatt, a great authority on wool: 'It consists of a central stem or stalk, probably hollow, or at least porous, and possessing a semi-transparency, found in the fibre of the hair. From this central stalk there springs, at different distances in different breeds of sheep, a circlet of leaf-shaped projections. In the finer species of wool these circles seemed at first to be composed of one indicated or serrated ring; but when the eye was accustomed to them, this ring was resolvable into leaves or scales. In the larger kinds, the ring was at once resolvable into these scales or leaves, varying in number, shape, and size, and projecting at different angles from the stalk, and in the direction of the leaves of vegetables--that is, from the root to the point. They give to the wool the power of felting.' This is the estimate of the chemical composition of good wool: Carbon, 50.65; hydrogen, 7.03; nitrogen, 17.71; oxygen and sulphur, 24.61. Out of a hundred parts, ninety-eight would be organic, and two would be ash, consisting of oxide of iron, sulphate of lime, phosphate of lime, and magnesia. What is called the 'yolk' of wool is a compound of oil, lime, and potash. It makes the pile soft and pliable, and is less apparent on English sheep than on those of warmer countries, the merino sheep having the most 'yolk.'