t the vibrations are too slow show clearly that it is the dark and not the light rays that was repeated with the spectrum thus obtained. A sheet of to awaken sensation on the retina. The atmosphere, which is produce these effects, Professor Tyndall placed the thermo- paper properly prepared, on… … alum cell, A, cuts off the light, but the needle is found deflec- platinum coated with platinum black in the same position. ted though no lightappears at the focus. Platinum, he explained, with its surface thus prepared acts in regard to the invisible heat rays just as the sulphate of POLARIZATION…
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