8 



ELEMENTS OF SCIENCE 



that this naturally suggested method has been actually 

 employed by them. Thus, the number " five " is some- 

 times called a " hand," and " six" is spoken of as " take 

 the thumb " that is, " begin to make use of the other 

 hand." "Twenty," the number of all the digits com- 

 bined, is sometimes denoted by the term " a man," and 

 "ten "by "half a man." 



The same thing is shown by Roman numerals, where 

 I, II, III, and IIII indicate one to four fingers, while 

 " five " is expressed by a sign representing the thumb 

 upstanding by itself, and the four fingers in a group 



FIG. i. 



V 



opposite it V. To express ten, there were the two 

 hands crossed obliquely X. 



Thus an arrangement of numbers in groups of ten 

 naturally suggested itself ; and thus ten is the " root " 

 number, or " radix," of the system of counting actually 

 adopted. As written down they form a system of 

 notation, and there being ten symbols (0123456 

 7 8 9) to that system, it is called a decimal system of 

 notation. But other " root numbers " might have been 

 selected, as we shall shortly see, each giving rise to its 

 own " system of notation." 



The . Roman numerals, though plainly expressing 



