[2] Neither the description of the apparatus nor the recapitulation of the whole theory, so often alluded to by the author, were ever given.—T.

[3] [Plate 3]. fig. 1.

[4] The grey square is introduced in the same [plate], fig. 1, above the coloured squares.

[XIX.]
ACHROMATISM AND HYPERCHROMATISM.

[285.]

Formerly when much that is regular and constant in nature was considered as mere aberration and accident, the colours arising from refraction were but little attended to, and were looked upon as an appearance attributable to particular local circumstances.

[286.]

But after it had been assumed that this appearance of colour accompanies refraction at all times, it was natural that it should be considered as intimately and exclusively connected with that phenomenon; the belief obtaining that the measure of the coloured appearance was in proportion to the measure of the refraction, and that they must advance pari passu with each other.