The contrasts here shown are not so visible when the two shadows of the rod occupy the whole of the white square, but are decidedly increased by the shadows occupying only a part of the field, the margins being illuminated with a mixture of the two lights. Not only are there contrasts with coloured light and white, but the relative position of one colour to another may alter the hue of each to the eye. The following experiments indicate what change can be expected in contrasted colours. The double colour apparatus was used as described at page 122, and a slit was placed in four different positions in the spectrum, viz. in the red, orange, green, and violet, to form patches, and another slit was placed in the same four positions in the other spectrum, and the contrasts noted. +-----------------+----------------------------------------------+ |Original Colours.| Change due to Contrast. | +--------+--------+----------------------+-----------------------+ | Red | Orange | Red became yellower | Orange became green | | | | | grey | | " | Green | " unaltered, but | Green unaltered, but | | | | brighter | brighter | | " | Blue | " became more | Blue became greener | | | | orange | | | " | Violet | " became orange | Violet, no marked | | | | | change | | Green | Orange | Green became bluer | Orange became yellower| | " | Blue | " became olive | Blue became more | | | | | violet | | " | Violet | " became yellower| Violet became bluer | | Orange | Blue | Orange became redder | Blue became bluer | | " | Violet | " became greener | Violet became bluer | | Violet | Blue | Hardly altered | Hardly altered | +--------+--------+----------------------+-----------------------+ These contrasts were in most cases very marked, as would be seen by causing the same colours to fall on a different part of the screen, outside that on which the comparisons were made.