We shall conclude our observations on the nature of ivory with an account of the tooth or horn of the narwhal, one of the cetaccous tribe. The hugest are ten feet long, and some inches thick at the lower extremity, forming a slender cone of a spiral figure. This tooth consists of ivory of the finest description, equally hard as elephants' ivory, and susceptible of a higher polish. But we do not know that all of it is of the same character ; and a preju dice against its ordinary use subsists among workers in ivory. Its texture is singular, dialing in most respects from all other ivory. On giving the highest polish to a transverse section of about an inch and a half in diameter, the cortical part proved or a very dull white, somewhat of a greenish cast, of a hard horny consistency, and about an eighth of an inch broad. Interposed between it and the substance of the tooth there appeared a bright white cir cumferential line, narrower and much harder than the bark. The surface was beautiful, quite homogeneous to the naked eye, with a few of the faintest concentric circles more transparent than the rest. Nothing more is percepti ble, without reducing the thickness of the ivory, and resort ing to the microscope. This being done, the faint circles of a section, about a 60th part of an inch in thickness, prove to consist of three lines, that in the middle darker than the others. Innumerable radiations of a fine feathery appear ance proceed from around the central cavity, and terminate somewhat within the circumferential line, but again be coming more conspicuous in what we have denominated the cortical part. These are not unlike the spiculm shoot ing out during the crystallization of certain salts. But all are tubular, and the fact is demonstrated, on subjecting a very thin longitudinal section to a magnifier of considerable power. We have not witnessed this peculiar conforma tion in any other ivory, though it is not improbable that the stria or radiations above alluded to in that of the elephant and whale's tooth may be analogous to it. No porosity was discovered in a longitudinal portion of the former, re duced so thin as to be bent double with ease. On throwing a particular light on the surface of the narwhal's ivory, an irregularity is visible from the tubular formation, consist ing of innumerable minute horizontal cavities. This pecu lia• structure merits farther examination, in which suitable attention should be paid to portions from various teeth. It is obvious, from what has been said, that the bony process of the narwhal is more probably a tooth than a horn.
Considerable anomalies are seen in the structure of the different kinds of ivory, and every tooth seems to have some thing peculiar to itself, especially in the arrangement of the concentric circles. In so far as our observations go, the most transparent is the hardest, which is particularly ex emplified in the pellucid rings above alluded to. Thus, on reducing a plane surface of ivory by any ordinary mechani cal operation, they will remain prominent, though the rest yield under it. The line interposed between the bark and the substance is also the hardest of the whole. We have seen the tusks of phocx free of enamel, and having a thick bark, with fine ivory, which we were unable to trace to any of the ordinary species. Circumstances may render it difficult to ascertain the fact, especially if the ivory be not recent. Ou examibing a small portion of an elephant's tusk lately discovered in Ayrshire, it proved somewhat harder th m recent ivory. The exterior consisted of au extremely thin Lout of a deep brown colour, surrounding a portion of a broad circular ring, wherein very numerous concentric lilies were visible. Within this appeared what seemed common ivory. But the fragment was small, which rendered its peculiarities less obvious ; and these consisted chiefly in the concentric lines.
Ivory' is found, by analysis, to consist of the phosphate of lime, and a gelatinous substance. The yellow colour ac quired by exposure to tire air, is supposed to arise from the combination of the gelatinous matter with the oxygen of the atmosphere. It is said that oxygenated muriatic acid
will restore the original whiteness. Some ivory is exceed ingly white from the beginning, and some whitens in dry ing, It is discoloured by being frequently handled, though the keys of an organ or piano most commonly used are said to retain their whiteness longer than the others. The co lour may be renewed by rt moving the external surface, provided the discoloration be only supeifi •ial. Artists dis tinguish ivory into white and green, the fin mer being cha racterized by a whitish or lemon coloured bark. When cut up, it is of a faint olive or greenish hue, but soon be comes of a beautiful white.
Ivory is applied to a vast variety of purposes in the arts. Its hardness and texture adapt it for many works where wood would be speedily destroyed, and to which metal is unsuitable. The most elegant sculptures are executed in ivory, not only of images, but even of landscapes after na ture; whereof the finest parts can only he compared to lace. It is universally employed for every kind of turnery, of which admirable specimens are brought from foreign coun tries; such as several hollow spheres, included within each other, successively, even to the number of 14, 15, or more; while the outside is carved in a variety of figures in open work. From its elasticity, it is used exclusively for making the balls employed in games of skill ; as billiards ; and also in those for demonstrating the doctrines of collision. It is sometimes formed into baskets of considerable size, elaborately wrought ; and we have heard of furniture com posed exclusively of ivory, inlaid with gold. The scales of almost all mathematical instruments arc made of it ; for which, if properly and sufficiently seasoned, it is in many respects superior to brass, and fine ivory is almost always used for miniature paintings. One of the purposes to which it is most extensively and usefully applied, is corob-making ; in which seventy teeth may he cut to the length of an inch, all executed by a saw ; and the ivory of the sea horse has superseded every ether kind in the fabrication of artificial teeth. Artists, attracted by the beauty of this substance, have endeavoured to apply it to purposes for which it does not seem adapted ; as in the construction of wind instru ments. Ivory flutes, for example, are inferior to those made of wood ; but whether this arises from the proper proportions of the materials not being yet ascertained, or whether the suitable vibration of the instrument or the in cluded column of air be trot produced, is probably not de termined. The ancients employed ivory more extensively in some respects than the moderns. It was formed into large statues by them, and we read in Scripture of the ivo ry throne of Solomon, ornamented with gold. Tne modern kings of Denmark, indeed, are said to have a magnificent throne, constructed of the teeth of the narwahl. Heyne expresses his surprise, that ivory should be known so much earlier among the Greeks than the Jews ; but it must be admitted, that nations are familiarly acquainted with num berless substances w hich never become the subject of writ ten descriptions. Medicinal virtues are ascribed by the Japanese, to the tooth of the narwahl ; they believe that it contributes to elevate the spirits ; to strengthen the memo ry ; nay, that it will contribute to the prolongation of life. Hence it bears a high price among them, and the sale of a single tooth has been known to realize a fortune to the owner. No such properties are ascribed to ivory in Eu• rope ; where, besides its use in the arts, we believe the only purpose to which it is applied, is making a weak glue from the shavings. The Dutch were wont to procure whole cargoes of the teeth of the narwahl in Europe, for export to Japan, while their commercial relations subsisted with that island.