RARE

, in Physics, is the quality of a body that is very porous, whose parts are at a great distance from one another, and which contains but little matter under a great magnitude. In which sense Rare stands opposed to dense.

The corpuscular philosophers, viz, the Epicureans, Gassendi<*>s, Newtonians, &c, assert that bodies are rarer, some than others, in virtue of a greater quantity of pores, or of vacuity lying between their parts or particles. The Cartesians hold, that a greater rarity only consists in a greater quantity of materia subtilis contained in the pores. And lastly, the Peripatetics contend, that rarity is a new quality superinduced upon a body, without any dependence on either vacuity or subtile matter.