* Diffuse phosphoric light. l. 177. I have often been induced to believe from observation, that the twilight of the evenings is lighter than that of the mornings at the same distance from noon. Some may ascribe this to the greater height of the atmosphere in the even∣ings having been rarefied by the sun during the day; but as its density must at the same time be diminished, its power of refraction would continue the same. I should rather suppose that it may be owing to the phosphorescent quality (as it is called) of almost all bodies; that is, when they have been exposed to the sun they continue to emit light for a considerable time afterwards. This is generally believed to arise either from such bodies giving out the light which they had previously absorbed; or to the continuance of a slow combustion which the light they had been previously exposed to had excited. See the next note.
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