United Mines, Gwennap. Muriate of soda 1·10 Muriate of lime ·15 Sulphate of soda ·50 Sulphate of lime 1·5 Sulphate of iron ·75 Alumina ·5 Silica ·15 ---- Total 4·65 Great St. George. Muriate of soda 1·35 Sulphate of lime ·74 Carbonate of iron ·70 Alumina ·50 Carbonate of lime ·10 ---- Total 3·4 [165] The discovery of the electrotype has been disputed, as all valuable discoveries are. Without, however, at all disparaging the merits of what had been done by Mr. Jordan, I am satisfied, after the most careful search, that the first person who really employed electro-chemical action for the precipitation of metals in an ornamental form, was Mr. Spencer, of Liverpool. [166] See Spencer, _Instructions for the Multiplication of works of Art in Metal by Voltaic Electricity. Novelties in Experimental Science_: Griffin, Glasgow, _Elements of Electro-Metallurgy_: by Alfred Smee, Esq. [167] The magneto-electrical machine is employed in Birmingham for this purpose; but I am informed by Messrs. Elkington that they do not find it economical, or rather that the electro-precipitation is carried on too slowly. [168] This has been done by Mr. Robert Were Fox, at a mine near Falmouth. By connecting two copper wires with two lodes, and bringing them, at the surface, into a cell containing a solution of sulphate of copper, this gentleman obtained an electrotype copy of an engraved copper-plate. [169] This has been most effectually accomplished by Mr. Bain. Mr. Hobson has had an electric clock, thus excited, in action for several years. CHAPTER X. MAGNETISM. Magnetic Iron--Knowledge of, by the Ancients--Artificial Magnets--Electro-Magnets--Electro-Magnetism--Magneto- Electricity--Theories of Magnetism--The Magnetic Power of soft Iron and Steel--Influence of Heat on Magnetism--Terrestrial Magnetism--Declination of the Compass-needle--Variation of the Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora Borealis--Magnetic Storms--Magnetic conditions of Matter--Diamagnetism, &c.