When experiment had proved that every imaginable form of cheap metal could be coated with silver or gold, by the agency of electro-chemistry, an immediate demand was created for designers, modellers, and moulders. Vases of the most beautiful forms were to be produced in metal which should have the properties of solid silver without its costliness. The common metal vase is dipped into a tank containing a solution of silver. It is placed in connection with the wires of the galvanic battery. Atom after atom of the silver in solution clings to the vase, which soon comes out perfectly silvered. The burnisher completes its beauty. It is the same with a solution of gold. The pride of riches may boast the value of the solid plate, which tempts thieves to "break in and steal." The nobler gratification of taste may secure the beauty without the expense or risk of loss. But the great principle thus brought into practical use is carried farther in the realms of art. It becomes a copying process. It can multiply copies of the most minute engraving without in the slightest degree deteriorating the beauty of the engraver's work. The copy is as good as the original. The same principle of depositing one metal upon another in minute atoms has produced galvanized tinned-iron--iron which will not rust upon exposure to weather, and thus applicable to many purposes of building--and iron which can be applied to many objects of utility with greater advantage than tin-plate. There are few houses now without their daguerreotype portraits of some member of the family. This is a portrait copied from the human face by a sunbeam. The name daguerreotype is derived from the Frenchman Daguerre, who announced his discovery at the time when our countryman, Mr. Fox Talbot, was engaged in working out the same wonderful problem. We notice this branch of recent invention merely to point out how science and art call forth mechanical labour. When every house has its little portrait, there will naturally be a great demand for frames. The manufacture of daguerreotype-frames, both here, and in the United States, has furnished a new field of employment. Every scientific discovery, such as photography, is a step in advance of preceding discovery. If Newton had not discovered the fundamental properties of light, in the seventeenth century, we should, in all likelihood, have had no photography in the nineteenth. Abstract science is the parent of practical art. [Illustration: Newton.]