( 84 ) 
fying any fum at pleafure, may render cal- 
culation lefs laborious. 
Suppofe, for example, the letter b repre- 
fents 750!. If I have two creditors, each of 
which owe me exactly this fum, and I want 
to know the whole amount, according to 
the rules of addition in common Arithme- 
tic, I proceed in this manner 750 
75 
1500. Butfup- 
pofing the letter b to reprefent 750!. I then 
place the two fymbols under each other, 
thus 
To b 
Add b 
The fum is a, equal to 1500!. 
This Science, in which letters are ufed in- 
ftead of figures, is called 4lgebra> a word 
derived from the Arabic al-giabr wolmokabala, 
fignifying, the art of refolution and equatiojz. 
It is fuppofed to have been invented in In- 
dia, and that the Arabs received it from the 
Perfians. It is certain however that it was 
brought into Europe by the Moors,' who 
conquered Spain in the 8th century. The 
firft printed book in Algebra was written 
by 
