8 THE PROPERTIES OF MATTER. 



other. Glass is brittle, and by this single property may 

 be distinguished from india-rubber. 



20. List of Universal Properties. The prin- 

 cipal universal properties of matter are extension, im- 

 penetrability, weight, indestructibility, inertia, 

 mobility, divisibility, porosity, compressibility, ex- 

 pansibility, and elasticity. 



21. List of Characteristic Properties. The 



characteristic properties of matter (often called specific or 

 accessory properties) are numerous. They depend, for the 

 most part, upon cohesion and adhesion. The most im- 

 portant characteristic properties are hardness, tenacity, 

 brittleness, malleability, ductility. 



22. What is Extension? Extension is that 

 property of matter by virtue of which it occupies 

 space. 



It has reference to the qualities of length, breadth, and 

 thickness. It is an essential property of matter, involved 

 in the very definition of matter. 



(a.) All matter must have these three dimensions. We say that 

 a line has length, a surface has length and breadth ; but lines and 

 surfaces are mere conceptions of the mind, and can have no material 

 existence. The third dimension, which affords the idea of solidity 

 or volume, is necessary to every form of every kind of matter. No 

 one can imagine a body that h^.s not these three dimensions, that 

 does not occupy space, or " take up room." Figure or shape neces- 

 sarily follows from extension. 



23. English Measures. For the purpose of com- 

 paring volumes, as well as surfaces and lengths, measures 

 are necessary. In the United States and England the 

 yard has been adopted as the unit, and its divisions, as 



