In 1842, a general issue of these Works, in weekly sheets or numbers, at twopence each, was commenced by the late Mr. Robert Cadell, of Edinburgh, and completed in 1847. Of this edition, up to the present period (1858), the astonishing number of TWELVE MILLIONS OF SHEETS have been issued, the weight of which amounts to upwards of 335 tons! Another edition was published simultaneously by Mr. Cadell in monthly volumes at 4s., each containing about 360 pages; this series has reached a sale of more than 500,000 volumes. A third cheap issue, at eighteenpence a novel, is now being published by the present proprietors, Messrs. Adam and Charles Black, of Edinburgh. Nearly 300,000 volumes have already been printed of this edition. It may be mentioned here, although hardly coming within the scope of the present article, but as affording a striking example of what literature has contributed to the revenue of the country in the person of a single author, that upwards of 3,500 tons' weight of paper[16] have been consumed in producing the various editions of Sir Walter Scott's Writings and Life; and the duty paid to Government on the paper, even at the present reduced rate, amounts to no less a sum than £51,450! Since the Juries made their Reports, the development of cheap literature has been greatly extended. Newspapers, some of which contain eight full-sized pages, of six columns each, printed in small type, are sold for the marvellously low price of a penny, and are stated to issue as many as 50,000 copies daily; and some of the newspapers and other periodicals, printed on good paper, are issued for a halfpenny. Among the works of a standard character, published at prices which nothing but a very extensive scale could make remunerative, may be mentioned the popular series which includes "The Reason Why," and "Enquire Within upon Everything." Of the eight volumes already issued, each containing about 350 closely printed pages for half-a-crown, nearly 170,000 copies have been sold within a period of less than three years. LITHOGRAPHY. The art of printing from stone was invented at the end of the last century by M. Aloys Senefelder, of Munich; but it was not brought to such a state of perfection as to be practically useful until many years afterwards. The principle on which Lithography depends is the different chemical affinities of water for oily and for earthy substances, which cause it to run off from the one and adhere to the other. The drawing or writing is made in oily ink upon a smooth calcareous stone that will absorb water, so that, when the stone is moistened, the water adheres to it and leaves the lines of the drawing traced upon it dry. An inking roller, charged with an oily ink, is then passed over the stone and inks the drawing, but leaves all the other parts of the stone quite clean. A damped paper is next laid on, and when subjected to great pressure, an exact copy of the drawing or writing is produced.