because the secretion of the murex or " purpura " is to be carried to the highest point of culmination by the action of the sun-light on fine linen saturated with the juice.
L.
MINERALS.
613.
The colours of minerals are all of a chemical nature, and thus the modes in which they are produced may be explained in a general way by what has been said on the subject of chemical colours.
614.
Among the external characteristics of minerals, the description of their colours occupies the first place; and great pains have been taken, in the spirit of modern times, to define and arrest every such appearance exactly: by this means, however, new difficulties, it appears to us, have been created, which occasion no little inconvenience in