A properly comnion to all forms of matter is that of if two portions of different kinds of matter are brought closely is believed that there i, always a passage across the hounding surface of molecules of the two kinds of matter. Sometimes this pas sage t•an be actually observed, e.g. in the ease of any two gases. two such liquids as water and .1 alcohol. two such solids as lead and gold.
Since matter as such has so many properties: ,1 inertia. weight, size, elasticity, etc.. two portions Ut matter may Inive some properties common I and not others. Therefore if two portion, of matter are to lie defined as equal, or to have equal quantities, iL is necessary to select sonic basis of comparison. Ity definition, two portions of matter are said to have equal equal they have the same inertia; the experimental test being imagined somewhat as follows: Subject one body to the propulsive action of a compressed spring, measure its ity along a smooth horizontal table; compress the sa MP spring to the same amount as before, allow it by its expansion to set in motion a second body. and measure its velocity: if these two a re the same, the two bodies have the same inertia.
and later Besse'. proved that the celeration of a falling body toward the earth at any one place on the surface is a constant for all kinds and amounts of matter. (See
(unAvir.vrio.s.) it g. The weight of a body of mass nt is tan: and so if two bodies have the same mass, as defined above, they also have the same weight. and eonversely. Consequently the mass of a body is always in practice measured by comparing its weight with that of a tion of standards. A standard hotly is chosen, a grain; other bodies of the same mass are made; (idlers whose masses are fractions or tiples of that of the standard; etc. Such a set cif bialies is called a of It is believed that matter as such is structible; that is, however it changes its form or whatever reactions it Undergoes, a portion of matter preserves its mass unaltered. This idea, which is entirely in accord with all experiments and is vaned the principle of the conservation of !natter. It is perfectly possible that the in ight of a body changes as its ture, or one of its other properties. is altered, lint there is no experimental ovidenee in favor of an idea. For full diseussion of properties of matter, the reader may consult Tait, Proper ties of Nutter (Edinburgh. I'M).