2 THE DOMAIN OF PHYSICS. 



know that this one grows only in wet ground, that another 

 is valuable for such and such an end, and that a third 

 has certain form, size, and color. This general informa- 

 tion may be valuable, but it is only when the facts are 

 classified, and the plants grouped into their respective 

 orders, genera and species, that the knowledge becomes 

 entitled to the name of botany, a science. 



2. What is Matter? Matter is anything that 

 occupies space or " takes up room." 



There are many realities that are not forms of matter. 

 Mind, truth, and hope do not occupy space ; the earth and 

 the rain-drop do. 



3. Divisions of Matter. Matter may be con- 

 sidered as existing in masses, molecules, and atoms. 



A clear apprehension of the meaning of these terms 

 is essential to a full understanding of the definition of 

 Physics as well as of much else that follows. 



4. What is a Mass? A mass is any quantity 

 of matter that is composed of molecules. 



The word molar is used to describe such a collection of 

 molecules. 



(a.) The term mass also has reference to real quantity as distin- 

 guished from apparent quantity or size. A sponge may be com- 

 pressed so as to seem much smaller than at first, Imt all of the 

 sponge is still there. Its density is changed ; its quantity or mass 

 remains the same. This double use of the word is unfortunate, 

 but the meaning in any given case may be easily inferred from the 

 connection. 



(&.) The quantity of matter constituting a mass is not necessarily 

 great. A drop of water may contain a million animalcules ; each 

 animalcule is a mass as truly as the greatest monster of the land or 

 Sea. The dewdrop and the ocean, clusters of grapes and clusters 

 Of stars, are equally masses of matter. 



