4. The subjects of sculpture, with a few exceptions, are the same as those of painting; and the course of study essential to proficiency in either, is very similar. They both require much taste and practice, and a thorough knowledge of the human form and other objects frequently represented. The young artist begins with imitating the most perfect models of Grecian art; and, after having become well acquainted with their beauties, he proceeds to the imitation of nature. 5. When any considerable work in stone or marble is to be done, the sculptor forms a model of clay or wax, to guide him in the execution. The soft material is moulded to the proposed form with the hands and small instruments of ivory. The model is by far the most difficult part of the work, and it is here the genius of the artist is to be displayed. The process of copying the model in stone or in any other substance, is an operation merely mechanical, and can often be done by another person as well as by the scientific sculptor himself. 6. The model having been prepared, the block of marble or stone is marked at certain points corresponding to its chief elevation and concavities. The material is then wrought to the rough outline of the figure, by means of strong steel points, drills, and other perforating tools; and the asperities are afterwards removed with chisels, and with rasps and files of different shapes. When a high polish is required, it is produced by friction with pumice-stone, tripoli, and straw ashes. 7. Marble and stone are carved in a similar manner; but the latter, being softer, can be wrought with less difficulty. The defects which may be met with in the stone are repaired with a composition of plaster of Paris and the same stone, pulverized and mixed with water. 8. _Casts_ in plaster of Paris and bronze are taken from models, statues, busts, bas-reliefs, and living persons. To do this, it is necessary to form a mould from the subject to be copied. This is done by spreading over it some soft substance, which can be readily forced into all the cavities, and which will harden by drying or cooling. Plaster of Paris is the most usual material employed for this purpose. 9. When the subject is a bas-relief, or any other one-sided figure of a similar kind, the mould can be withdrawn without injury, in a single piece; but if it is a statue, or any other figure of like form, it is necessary to divide the mould into several pieces, in order to a safe removal. These pieces again united constitute a perfect mould. While the artist is forming the mould on the face of a living person, the latter breathes through tubes inserted into the nostrils.