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Rh of light. Finally, this comet-meaning is itself not isolated; it is a related portion of the whole system of astronomic knowledge. Suns, planets, satellites, nebulæ, comets, meteors, star dust—all these conceptions have a certain mutuality of reference and interaction, and when the speck of light is identified as meaning a comet, it is at once adopted as a full member in this vast kingdom of beliefs.

Darwin, in an autobiographical sketch, says that when a youth he told the geologist, Sidgwick, of finding a tropical shell in a certain gravel pit. Thereupon Sidgwick said it must have been thrown there by some person, adding: "But if it were really embedded there, it would be the greatest misfortune to geology, because it would overthrow all that we know about the superficial deposits of the Midland Counties"—since they were glacial. And then Darwin adds: "I was then utterly astonished at Sidgwick not being delighted at so wonderful a fact as a tropical shell being found near the surface in the middle of England. Nothing before had made me thoroughly realize that science consists in grouping facts so that general laws or conclusions may be drawn from them." This instance (which might, of course, be duplicated from any branch of science) indicates how scientific notions make explicit the systematizing tendency involved in all use of concepts.

§ 4. What Conceptions are Not

The idea that a conception is a meaning that supplies a standard rule for the identification and placing of particulars may be contrasted with some current misapprehensions of its nature.

1. Conceptions are not derived from a multitude of