in return, as a coloured stone is displayed by a similarly coloured foil. In the opposite case each vitiates, disturbs, and destroys the other.
567.
These experiments may be repeated with coloured glasses, by causing the sun-light to shine through them on coloured surfaces. In every instance similar results will appear.
568.
The same effect takes place when we look on coloured objects through coloured glasses; the colours being thus according to the same conditions enhanced, subdued, or neutralized.
569.
If the prismatic colours are suffered to pass through coloured glasses, the appearances that take place are perfectly analogous; in these cases more or less force, more or less light and dark, the clearness and cleanness of the glass are all to be allowed for, as they produce