There is a phenomenon in colour which must be alluded to, and which possesses more than a passing interest to the art world, and that is colour contrast. Perhaps one of the best methods of showing this is by our colour patch apparatus. If we throw the reflected beam and the colour patch on a square as before, and place a rather thinner rod in front, so that the two shadows lie on a background of the combined white light and spectral colours, on passing a slit through the spectrum, the shadow which is illuminated by white light will appear anything but white. Thus if we allow yellow spectral light to illuminate one shadow, the other will appear decidedly of a blue hue; if a green ray it will be of a ruddy hue; if a blue ray of a yellow hue; that is, all the contrast hues will appear to the eye to tend towards a complementary tone to the spectral light. The kind of white light illuminating the shadow has a marked effect on the tone, as might be expected. The following table shows the contrast colour of the white illuminated shadow when the white light used was that of a candle. +---------------+-------------------+---------------+------------------+ | | Contrast | | Contrast | | Spectrum | Colours in | Spectrum | Colours in | | Colour. | Electric light. | Colour. | Gaslight. | +---------------+-------------------+---------------+------------------+ | Cherry red | Green gray | Cherry red | Green gray | | Scarlet | Bluish green gray | Scarlet | Sap green | | Terra-cotta | Blue gray | Light red | Green gray | | Raw sienna | Light blue gray | Olive green | Pink gray | | Olive green | Umber | Apple green | Mauve & black | | Emerald green | Pinkish lavender | Emerald green | Pink terra-cotta | | Grass green | Light pink | Emerald green | Pink terra-cotta | | Bluish green | Dark pink | Bluish green |Pinker terra-cotta| | Signal green | Salmon | Peacock blue | Salmon | | Cyanine blue | Yellow ochre | Prussian blue | Reddish yellow | | Ultramarine | Raw sienna | Ultramarine | Raw sienna | | Violet blue | Brownish yellow | Violet blue | Brownish Orange | | Blue violet | Green yellow brown| Blue violet | Brownish yellow | | Violet | Burnt sienna | Violet | Yellow ochre | +---------------+-------------------+---------------+------------------+