CHAPTER II. 



PHYSICS MATTER AND THE ATTRACTIVE FORCES. 



PHYSICS deals with matter and energy. It treats of the prop- 

 erties and phenomena of matter due to the action of the dif- 

 ferent forms of energy. We know many things about how 

 matter appears, and many things about how energy acts, but 

 we know very little about what matter really is and very little 

 about the true nature of energy. 



A rod of iron may be heated, may be melted, may be molded 

 or worked into any form, it may be made a magnet, all without 

 change of substance. But if the rod of iron is exposed to- moist 

 air it soon begins to change into a reddish substance called rust, 

 or if we expose it to the action of strong acids other changes 

 occur and other products are formed. Experiments with other 

 substances show that matter is subject to two groups of changes 

 or phenomena, one resulting in change of substance, the other 

 resulting merely in change of form or structure without change 

 of substance. 



Chemistry treats of those phenomena which result in change 

 of substance or composition, while physics treats of those phe- 

 nomena which do not result in change of substance. While this 

 is the distinction usually made between physics and chemistry it 

 scarcely exists in nature. There is a wide field of common ground 

 between these branches of science called chemical physics, which 

 considers heat, light and electricity in some of their phases, and 

 discusses some of the phenomena of gases and other subjects 

 which seem to involve both groups of changes. 



The earth, air and water, plants and animals, are composed of 

 matter. Matter occupies space, it extends in three directions 

 that is, it has length, breadth and thickness, and as far as known 

 matter is indestructible. 



(15) 



