The substance usually employed for these engravings is wood of a close grain; on this account box-wood is generally selected. The impressions are obtained from wood-engravings upon exactly the same principle as are the impressions from typography; and they can also be worked off at the same time with the descriptive text. This is a superiority which wood possesses over other engravings, and recommends itself to publishers on account of the immense saving in the expense of a double process in procuring copper-plate illustrations for typographical works, and enables them to keep pace with the ruling passion of this literary era--cheap publications. ON COPPER. The art of engraving on copper plates, for impressions, is alleged to have been invented by Peter Schoeffer, one of the early printers, and son in-law of John Faust, about the year 1450. The honour of this invention is also claimed by a Florentine goldsmith of the name of Finguires, who dates his invention in 1540. This artist having used liquid sulphur to take an impression of some chasing and engraving he had made, observed a blackness produced by the sulphur left in the deepest parts of his work, whence he obtained an impression on paper. But we have no hesitation in giving the preference to Schoeffer, who, we have previously remarked, was of an ingenious turn, and assisted Guttenburg in producing moulds for casting his types; in addition to which, some of the books printed by him are ornamented with head and tail-pieces, with other rude attempts at engraving; and likewise because Schoeffer’s claim to the honour was acknowledged before Finguires was born. Of engraving there are various kinds; that called by connoisseurs, the legitimate mode of engraving, is what is termed the _line_ or _stroke_ mode. Numerous have been the British artists who have excelled in this style, in affording the means of multiplying our graphical productions. The next species of engraving we will notice is called the _stipple_, or chalk style,--imitations of chalk drawings. Portraits and historical pieces are executed in this style, which the celebrated Bartolozzi brought to perfection. The third species we will mention, cannot properly be called engraving; the effect is produced by scraping and rubbing; this kind is called _chiaro obscuro_, or mezzotinto; producing prints which have the effect of Indian ink drawings. A fourth species of engraving is what is commonly used for landscapes, which produces an effect like a pencil water-colour drawing; which is called _aquatinta_. In all of these kinds of engravings upon copper the artists find the sulphuric acid, or aquafortis, a most powerful agent. Sometimes, indeed, it is suffered to execute the whole of the process of the graver, especially when it is called an etching. For the same reasons as those mentioned with regard to wood engravers, we shall abstain from naming any of the very eminent artists now living.