the name of a new art which we owe to Mr Macpherson of Rome. A photograph, impressed on the surface of a lithographic stone, is treated in the ordinary way, and copies afterwards taken of it. Two different processes have been patented in England, one by M. Poitevin, and the other by Mr Newton as the invention of Messrs Culling and Bradford of Boston.

In M. Poitevin's patent the stone is covered with one or more films of a mixture of albumen or gelatine, and a concentrated solution of bichromate of potash. This film is then dried if a negative plate is to be copied upon it; but it may be used in a moist state if it is to receive the picture in the camera. When the surface is dry it is moistened with a sponge, and while moist the lithographic ink is applied to the surface by a ball or dabber, or other means, when it will be found to adhere only to those parts which have been affected by light.

In Messrs Culling and Bradford's process, a film of prepared gum-arabic is used which has been deprived of its power of intimate union... with the stone, while at the same time it is rendered capable of becoming fixed or insoluble by the action of light. When this film is subjected to the action of a solution of soap, the parts acted upon by light are not injuriously affected by it, and an insoluble soap is formed on the stone to produce the printing surface. The exciting solution is

Water ........................................ 1 qt. Sugar or molasses .................. 100 gr. Gum-arabic .............................. 1 oz. Bichromate of potash ............ 100 gr.

The sugar retards the immediate fixing of the gum upon the stone, and the chromic salt causes it to be more firmly fixed, or to be less soluble when exposed to light. When the film is dried, it may be exposed in the camera, or placed under a negative.

In the first of these processes the blacks are produced by the parts on which the light has acted; and on the second by those upon which it has not acted.