16 THE PROPERTIES OF MATTER. 



(a.) A body is any separate portion of matter, be it large or small, 

 as a book, a table, or a star. The term is nearly synonymous with 

 mass, but has not so distinct a reference to the absolute quantity of 

 matter. Bodies or masses are composed of molecules ; molecules 

 are composed of atoms. 



(&.) On account of inertia, the body cannot change its own posi- 

 tion ; on account of mobility any mass of matter may be moved if 

 sufficient force be applied. This changing of position is called 

 motion ; motion presupposes force. (See 64.) 



41. What is Divisibility I Divisibility is that 

 property of matter by virtue of which a body may 

 be separated into parts. ifil . 



(a.) Theoretically, the atom is the limit of divisibility of matter. 

 Practically the divisibility of matter is limited before the molecule 

 is reached ; our best instruments are not sufficiently delicate, our 

 best trained senses are not acute enough for the isolation or percep- 

 tion of a molecule. Nevertheless, this divisibility may be carried 

 to such an extent, by natural, mechanical (physical) or chemical 

 means, as to excite our wonder and test the powers of imagination 

 itself. It is said that the spider's web is made of threads so fine 

 that enough of this thread to go around the earth would weigh but 

 half a pound, and that each thread is composed of six thousand fila- 

 ments. A single inch of this thread with all its filaments may be 

 cut into thousands of distinct pieces, and each piece of each fila- 

 ment be yet a mass of matter composed of molecules and atoms. 

 The microscope reveals to us the existence of living creatures so 

 small that it would require thousands of millions of them to aggre- 

 gate the size of a hemp-seed. Yet each animalcule has organs of 

 absorption, etc. ; in some of these organs fluids circulate or exist. 

 How small must be the molecules of which these fluid masses are 

 composed ! What about the size of the atoms which constitute the 

 molecules ? A coin in current use loses, in the course of a score of 

 years, a perceptible quantity of metal by abrasion. What finite 

 mind can form a clear idea of the amount of metal rubbed off at 

 each transfer ? 



4:2. What is Porosity? Porosity is that prop- 

 erty of matter by virtue of which spaces exist 

 between the molecules. 



