XX11 INTRODUCTION. 



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. 



1 . 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 g = 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 = 9t (1); 



