sket-bullets in their centre,
surrounded with a species of osseous pulp differing from the ordinary
character and constitution of ivory. There was frequently no
corresponding orifice on the surface of the tusk; and hence
Blumenbach, and other naturalists, were led to form some very
inaccurate notions regarding this circumstance. Mr Rodgers of
Sheffield some years ago forwarded a variety of such specimens to the
Edinburgh College Museum, and these were very closely examined by
Professor Goodsir, who, in a communication to the Royal Society of
Edinburgh, demonstrated that this arose simply from a property of
isolating foreign substances common to all osseous organised bodies:
the ball having been enclosed by the tusk in its pulpy secretion, and
corrosive action thereby prevented, the process of growth continued
without interruption.

Ivory is a solid, white, translucent substance, distinguishable from
bone by its beautiful texture of semi-transparent rhomboidal network.
The finest ivory is much more transparent than paper of the same
thickness. A thin transverse section placed under the microscope
exhibits a series of curvilinear lines diverging from the centre and
interlacing each other with great regularity and beauty, closely
resembling in appearance the engine-turning of a watch. It possesses a
specific gravity varying from 1.888 in the tooth of the walrus, to
2.843 in that of the elephant. Its mean gravity is therefore about two
and a half times greater than water. The best, finest, and most
valuable ivory is that obtained from the African elephant. When
recently cut, it exhibits something of a yellowish transparent tint,
which is due to the oil it contains, but this gradually changes to a
beautiful and permanent white. It is not easily stained or destroyed
by exposure to the atmosphere, and on that account is used in the arts
for all the higher purposes, and especially for carved ornaments--such
as chess-pieces, crucifixes, and articles of _virtu_. Indian ivory, on
the contrary, when first cut, is perfectly white, but it becomes
yellow and discoloured with age and exposure. A good illustration of
this circumstance is presented by the dingy-coloured keys of an old
pianoforte.

This popular definition of good and inferior ivory is however, in
point of fact, somewhat incorrect, since ivory obtained from the coast
of Africa is often much inferior to that obtained from the Indian
Archipelago. The best rule for determi