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268 NOTES. [BK. II.
motion to the molecules adjacent, act upon others, and thus motion is propagated further and further in all directions. The theory of Aristotle is much the same— there is a diaphanous medium which may well represent the subtle ether, and which, when potential, that is quiescent, is darkness, and when set in motion by colour, (the property of which is to render it motive), is light, renders objects visible, that is. Thus, the same diaphaneity when passive, that is, potential, is darkness, when active, that is, in reality, is light, and the cause of objects being visible. The value of the hypothesis is diminished by the identification of the "diaphaneity" with air and water and solid bodies, because of their affinity with the supernal region or firmament above, which, together with all the heavenly bodies, was supposed to be of igneous nature; and to be corporeal, circular, and in constant motion.
Note 3, p. 94. Light is the active state, &c.] The diaphaneity which, when passive, is darkness, when set in motion and made active, is light, is made visible, that is; and thus light, being a mere condition of the diaphaneity, "is not a body, for, were it so, there would be two bodies in one, which is an impossibility." It may now seem strange that Aristotle should have paid so little attention to the opinion of Empedocles, "that light arrives midway from the sun, before it reaches the sight, or the earth;" for although it differed from his own, in regarding the sun
- Meteorologica, 3. 2.
- De Cœlo, 2. 3.