FUNDAMENTAL PROPERTIES OF MATTER. 19 



matter which a body possesses. A body is a definite portion of 

 matter, such as a knife, a piece of chalk, or a lump of coal. The 

 term substance is used to designate some particular kind of matter, 

 possessed of definite qualities, such as gold, water, glass, etc. We 

 distinguish three different conditions of matter, namely : Solids, 

 Liquids, and Gases. 1 These conditions of matter are known as the 

 three states of aggregation, and we will now consider the peculiarities 

 of matter when existing in either of these states. 



Solid state. Solids are distinguished by a self-subsistent figure 

 i. e., they have a definite size and shape. A solid substance forms 

 for itself, as it were, a casing in which its smallest particles 1 are en- 

 closed. The questions arise, By what means are these particles con- 

 nected? How are they kept together? No answer can be given 

 other than that the particles themselves attract each other to such an 

 extent that force is necessary to make them alter their relative posi- 

 tions. We see, consequently, that some form of attraction or at- 

 tractive power is acting between the particles of a solid mass, and 

 we call this kind of attraction cohesion, to distinguish it from other 

 forms of attraction. 



Force may be defined as the action of one body upon another 

 body, or as the action of particles of matter upon other particles 

 either of the same or of another body. Strictly speaking, we may 

 say that force is the cause tending to produce, change, or arrest 

 motion ; or it is any action upon matter changing or tending to change 

 its form or position. Force is a manifestation of energy, and may 

 be originated in a variety of ways. 



Energy is a universal property of matter ; it is its capacity for 

 doing work, and is measured by the work it can do. Doing work con- 

 sists in a transfer of motion, or energy, from the body doing work to 

 the body on which work is done. Wherever we find matter in motion 

 we have a certain quantity of energy which may be made to do work. 



As examples of different forms of energy we have motion of masses, heat, 

 light, electricity, chemical changes, etc. Under the influence of the different 

 forms of energy matter is constantly undergoing change. There are changes 

 in position, in temperature, in appearance, in the composition of substances, 

 and in many other directions. 



1 It has been shown lately that matter may exist in a fourth state as radiant matter. This 

 condition will be considered later. 



2 It will be shown later that all matter is supposed to consist of smallest particles, which we 

 call molecules. 



