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(7.) Atoms—Molecules.—Impenetrability must not be confounded with inseparability. Every body which has been brought under human observation is separable into parts; and these parts, however small, are separable into others, still more minute. To this process of division no practical limit has ever been found. Nevertheless, many of the phenomena which the researches of those who have successfully examined the laws of nature have developed, render it highly probable that all bodies are composed of elementary parts which are indivisible and unalterable. The component parts, which may be called atoms, are so minute, as altogether to elude the senses, even when aided by the most powerful scientific instruments. The word molecule is often used to signify component parts of a body so small as to escape sensible observation, but not ultimate atoms, each molecule being supposed to be formed of several atoms, arranged according to some determinate figure. Particle is used also to express small component parts, but more generally is applied to those which are not too minute to be discoverable by observation.