( 86 ) 
(5) 
To 2C+3/& 7* 
Add 42 6^4" ^ 
Sum 2c-\-i > b 7-K+4* 
The truth of the firft example is very 
obvious. Suppofe a to reprefent any pofitive 
quantity, once a added to three times a muft 
make four times a. 
In the fecond example, the quantities are 
both negative : they reprefent a want or de- 
ficiency. Now a want of one fhilling added 
to a want of 2 (hillings, amounts to a want 
of 3 /hillings, or 3^. 
But in example the third, the figns are 
different. How is it poflible to add a pofi- 
tive to a negative quantity ? It is impoflible; 
but it is very evident, that by taking one 
out of the other j that is, by fubtracYmg the 
lefs from the greater, I (hall difcover the 
amount: for, if I have 12 fhillings in my 
pocket, and owe you 9, which 9 is, to me, 
a negative quantity, I have yet a pofitive 3 
fhillings remaining} therefore the amount 
of my flock and debt taken together, may 
be properly exprefTed by +3*. This, I 
confefs, is a fpecies of Irifh Addition, per- 
formed by Subtraction: it is, neverthelefs, 
con-* 
