of the object, the appearance of colour exhibits itself in a greater degree. This takes place in subjective experiments, to which, for the present, we confine ourselves, under the following conditions.
210.
First, if, in looking through parallel mediums, the eye is directed more obliquely.
Secondly, if the surfaces of the medium are no longer parallel, but form a more or less acute angle.
Thirdly, owing to the increased proportion of the medium, whether parallel mediums be increased in size, or whether the angle be increased, provided it does not attain a right angle.
Fourthly, owing to the distance of the eye armed with a refracting medium from the object to be displaced.
Fifthly, owing to a chemical property that may be communicated to the glass, and which