_Device_, that which is formed by design. _Design_, a representation of a thing by an outline; a sketch. Describe Wood Engraving. The subject is drawn on a block of box or pear-tree wood with a black-lead pencil, or with a pen and Indian ink; the wood is then cut away, so as to leave the lines which have been drawn, as raised parts. The ink is next applied, and by pressing damp paper upon the block, the impressions are obtained. Albert Durer, a celebrated painter of Germany, brought the art of engraving on wood and metal, and taking off impressions on paper, &c., to great perfection. How is engraving on copper, steel, &c., performed? This sort of engraving is performed with a sharp-pointed instrument called a _graver_, by means of which figures, landscapes, &c., are traced upon a flat surface of the metal: the lines are then filled with ink or a similar composition, and the paper pressed on the plate. When taken off, an exact copy of the plate is impressed upon its surface. [Illustration: COCHINEAL INSECTS AND PLANTS.] What is Lithography? A species of engraving on stone, from which impressions can be taken much more expeditiously and economically than from metal. The process depends upon the following principles:--First, the facility with which calcareous stones imbibe water; second, the power of oily substances to repel water. When drawings are executed upon the stone with crayons composed of oily materials, and the surface of the stone is washed over with water, the moisture is imbibed by the stone, but repelled from the engraving; and when the ink, which also contains oily substances, is applied, it adheres only to the drawing, and not to the other portions of the stone. The block is then passed through a press, and the impressions are taken off; as many as 70,000 perfect copies have been obtained from a single stone. _Expeditiously_, with celerity or dispatch. _Economically_, with economy; with frugality. You describe Pearls as being ranked among the number of Gems, although they are not Stones; what kind of substance are they? Pearls are excrescences found in the shells of a large species of oyster, which are supposed to be produced by a disease of the fish. The best pearls are generally taken from the most fleshy part of the oyster, near the hinge of the shell, but inferior kinds are found in all parts of the fish, and adhering to the shells. Pearls, from many allusions made to them in the Old Testament, were not only known to the ancients, but were regarded by them as costly and precious gems. How do they get the Oysters which contain them?