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 particles being the stars of which it is composed; the earth, one of these particles, may be considered as a body, when its particles will be the air, the water, the stony crust and the central nucleus; then the air may be considered as a body composed of many particles, the water may be considered as a body composed of particles, the stony crust as a body composed of particles, and finally the nucleus as a body composed of particles. In this sense it will be understood we sometimes speak of something as a body and again of the same thing as a particle. A body and its particles are reciprocal. When we consider a body as composed of particles we consider internal relations, but when we consider the particles severally their relations to one another are external. Thus a body has internal relations and external relations, and every particle of the body also has internal relations and external relations, if it is composed of parts.

A substance is an aggregation of like particles in one body or a number of bodies. Bodies are composed of substances. For example, the air is a substance which is again composed of substances; the water is a substance, and this water is oxygen and hydrogen and contains in solution many other substances. In the envelope of rock a great variety of substances are discovered; then there are vegetal and animal substances. Thus in the hierarchy of bodies there is discovered to be a hierarchy of substances, extending from elements to protoplasm. The vast multitude of substances have so far been resolved into about seventy seemingly simple substances, but there is reason to believe that they are to be still further resolved into one primordial