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CH. XII.]
VITAL PRINCIPLE
189
it should be saturated; nothing like this, however, can happen to a stone, but it can to water, and that to a distance. The air is mobile in the highest degree, and, provided it be still and in one mass, it both acts and is acted upon. It is better, therefore, in the case of refraction, to assume that the air, in so far as it is one mass, (and it is so over every smooth surface,) is impressed by form and colour, rather than that visual rays issuing from the eye are refracted. Thus, the air, in the case of vision, gives motion to the sense, as if the impress upon wax had been transmitted to its extremity.
