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with which all natural substances are clothed, ought not to be looked upon as belonging to them absolutely, but only as a property dependent on the reflection and absorption of light from their surfaces. The leaves of
Fig. 11.—Newton's Disc. plants, for instance, must not be regarded as being really green in themselves, but as being capable of absorbing certain portions of light, and reflecting others. Grown in the dark, the green substance contained in the plant and its leaves becomes white, and no longer possesses the property of absorbing red light, and reflecting green. A green leaf placed in red light becomes almost black, from its power of absorbing light of that colour; in the blue it reflects a much greater proportion of the coloured ray. A very striking experiment may be performed with a substance known to chemists as the