INTRODUCTION. XXXVll 



an elementary body (element) is the smallest amount of the element which can enter 

 into a chemical combination. Just as ponderable matter consists in its ultimate 

 parts of ponderable atoms, so does the ether consist of analogous small ether-atoms. 



Ponderable and Imponderable Atoms. The . ponderable atoms within 

 ponderable matter are arranged in a definite relation to the ether-atoms. The 

 ponderable atoms mutually attract each other, and similarly they attract the 

 imponderable ether-atoms; but the ether-atoms repel each other. Hence, in 

 ponderable masses, ether-atoms surround every ponderable atom. These masses, 

 in virtue of the attraction of the ponderable atoms, tend to come together, but only 

 to the extent permitted by the surrounding ether-atoms. Thus the ponderable 

 atoms can never come so close as not to leave interspaces. All matter must, 

 therefore, be regarded as more or less loose and open in texture, a condition due to the 

 interpenetrating ether-atoms, which resist the direct contact of the ponderable atoms. 



Aggregate Condition of Atoms.- The relative arrangement of the molecules, 

 i.e., the smallest particles of matter which can be isolated in a free condition, 

 determines the aggregate condition of the body. 



Within a solid body, characterised by the permanence of its volume as well as 

 by the independence of its form, the molecules are so arranged that they cannot 

 readily be displaced from their relative positions. 



Fluid bodies, although their volume is permanent, readily change their shape, 

 and their molecules are in a condition of continual movement. 



When this movement of the molecules takes so wide a range that the individual 

 molecules fly apart, the body becomes gaseous, and as such is characterised by 

 the instability of its form as well as by the changeableness of its volume. 



Physics is the study of these molecules and their motions. 



Forces. 



1. Gravitation Work done. All phenomena appertain to matter. These 

 phenomena are the appreciable expression of the forces inherent in matter. 

 The forces themselves are not appreciable, they are the causes of the phenomena. 



Gravitation. The law of gravitation postulates that every particle of 

 ponderable matter in the universe attracts every other particle with a certain 

 force. This force is inversely as the square of the distance. Further, the 

 attractive force is directly proportional to the amount of the attracting matter, 

 without any reference to the quality of the body. We may estimate the intensity 

 of gravitation by the extent of the movement which it communicates to a body 

 allowed to fall, for one second, through a given distance, in a space free from air. 

 Such a body will fall in vacuo 9 -809 metres per second. This fact has been arrived 

 at experimentally. 



Let us represent # = 9 -809 metres, the final velocity of the freely falling body at the end of 

 one second. The velocity, V, of the freely falling body is proportional to the time, t, so that 



* V = ^ (1); 



i.e., at the end of the 1st sec, and V = <7, 1 =# = 9*809 M the distance traversed 



s=l* 2 . (2); 



'A 



