A very careful and important determination of the electrochemical equivalent of silver has been made at the observatory of the Physical Institute of Wuerzbourg, and the results are that an ampere current flowing for a second, or a coulomb of electricity deposits 1.1183 milligrammes of silver or 0.3281 milligramme of copper, and decomposes 0.09328 milligramme of water, a result agreeing closely with that of Lord Rayleigh recently communicated to the Physical Society. An ampere therefore deposits 4.0259 grammes of silver per hour; Kohlrausch's value is 4.0824, a value hitherto accepted universally. This value is so useful in measuring electric currents with accuracy, and free from the disturbances of magnetism, etc., that it is eminently satisfactory to find the German value agree with that of Lord Rayleigh, which will probably be adopted by English electricians. * * * * * A NEW STANDARD LIGHT. Herr Hefner-Alteneck has suggested a new standard light for photometric purposes, which promises to be very simple and effective in operation. The light is produced by an open flame of amyl-acetate burning from a wick of cotton fiber which fills a tube of German silver 1 in. long and 316 mils. internal diameter; the external diameter being 324 mils. The flame is 1.58 in. high from top to bottom; and it should be lighted at least ten minutes before using the light for testing. A cylindrical glass chimney surrounds it to ward off air currents. About 2 per cent. of the light is absorbed by the glass. The power of the flame is that of a standard English candle; and experiments have shown that amyl acetate, which besides is not expensive, is the best fuel for steadiness and brilliance. Neither the substitution of commercial amyl-acetate for pure nor the use of a wick of cotton thread for loose cotton fiber alters the illuminating power; but the wick should be trimmed square across the mouth of the tube, for if it project and droop the illuminating power is increased. * * * * * [NATURE.] DR. FEUSSNER'S NEW POLARIZING PRISM.