In larger masses, or in masses of aggre gated atoms, so classed that their peculiar properties are mutually neutralized, phe nomena are exhibited which bear a great resemblance to one another through con siderable classes of such compounds, whose elements we have reason to be lieve differ very considerably ; and other properties are found to exist in all, and differing only in degree or intensity. These last are the subjects of physical in vestigation: they are called emphatically the properties of matter ; and the laws of their mutual influences are the founda tion of mechanical These properties may be regarded as either es sential or contingent. The essential properties of matter are usually reckoned the following : 1. Divisilnlity, or the property which every known substance possesses of being separable into parts, and these again into smaller parts, and so on until the parts become inappreciable to our senses ; nor can any limit be placed on the subdi vision.
2. Impenelrability, or a resistance ex erted by every body to the occupation of its place by another. This resistance is of various degrees of intensity, depend ent on the state and atomic composition of the bodies ; but no two bodies can simultaneously ()occupy the same place.
8. Porosity, or the separation of the particles or atoms from each other by in tervals or pores. Every substance with which we are acquainted is more or less porous.
4. Compressibility, or the property in virtue of which the volume of every body may be contracted into smaller di mensions.
Among the essential properties of mat ter may also be included extension and figure ; but these belong also to space, and form the subject of geometry.
The contingent properties of matter are mobility and weight. Matter in every form is capable of being moved from one place to another ; and every substance gravitates towards the centre of the earth. But motion has reference to space, and weight to the attraction of other matter.
The above are the general properties of matter, upon which physical investi gations depend. There are, however, various other qualities belonging to par ticular substances, or to matter in par ticular states, the consideration of which is important in mechanical philosophy. Among these the principal are elasticity, fluidity, hardness, rigidity, solidity—for which see the respective terms.