[XXIII.]
CONDITIONS OF THE INCREASE OF COLOUR.
Here too an increased displacement of the object produces a greater appearance of colour.
This increased displacement occurs,
1. By a more oblique direction of the impinging luminous object through mediums with parallel surfaces.
2. By changing the parallel form for one more or less acute angled.
3. By increased proportion of the medium, whether parallel or acute angled; partly because the object is by this means more powerfully displaced, partly because an effect depending on the mere mass co-operates.