confidered as an operation of Addition in 
all the books of Algebra. 
In the fourth example the figns are again 
diflimilar; but here the negative fum exceeds 
the pofitive. No matter: I fubtraft the lefs 
from the greater, as in the former example, 
and to the remainder 2, I prefix the fign of 
minus-, for, if I owe you 9 (hillings and can 
pay you only 7, there is a deficiency of 2, 
properly expreffed by 2y. 
In contemplating the fifth example, I im- 
mediately perceive, that there are no two 
quantities alike 5 and, as I am ignorant what 
thefe feveral letters, or quantities, may fig- 
nify, it is impoflible to add them by any 
other means, than by writing them down 
in fucceflion with their refpeftive figns, as 
in the under-written fum. 
If you take the trouble to read this letter 
a fecond time, with any degree of attention, 
you will not only comprehend the nature 
of Addition of whole numbers, vulgar and 
decimal fractions and of Algebraic quanti- 
ties; but you will have acquired a general 
idea of thefe feveral modes of computation. 
This general idea will confiderably facilitate 
your progrefs in mathematical learning. 
F 4 LET- 
