SCIENCE OF COMMON THINGS. 



Pores of a body. Compressibility. Density. 



31 What are the pores of a body ? 



No two particles of matter are supposed to be in 

 actual contact with each other; and the openings, or 

 interstitial spaces between these particles, are called 

 pores. 



33 What is the reason that a sponge, apiece of tcood or metal, can, by 

 pressure, be made to occupy a smaller space than it did originally f 



Because the particles of which the sponge, the piece 

 of wood or metal, are composed, are by pressure 

 brought more closely together, diminishing at the same 

 time the pores and the space the body occupies. 



33 What then is compressibility ? 



That quality of matter in virtue of which a body 

 allows its volume or size to be diminished, without 

 diminishing the number of atoms or material particles 

 of which it consists. 



34 What reason have we for supposing that no two particles of matter 

 are in absolute contact f 



Because all known bodies, whatever may be their 

 nature, are capable of having their dimensions reduced 

 without diminishing the amount of matter contained in 

 them ; hence the space by which the volume may be 

 diminished must, before diminution, consist of pores'. 



35 What is density f 



The proportion of the quantity of matter in a body to 

 its magnitude. Thus, if of two substances one contains 

 in a given space twice as much matter as the other, it 

 is said to be twice as dense. 



36 What connexion is there between the density of a body and its 

 porosity ? 



A body will be more or less dense according as its 

 particles are near to or remote from each other ; and 

 hence it is evident that the greater the density the less 

 the porosity, and the greater the porosity the less the 

 density. 



37 Why do we caU lead heavy, and feathers light ? 



Because the amount of matter contained in a quan- 

 tity of lead occupying a given space is much greater 

 than in a quantity of feathers capable of occupying the 



