My object is to present a theory of operational invariants for the binary quantic of order
n
. Many of the results that are here given have been explicitly or implicitly given in the works of Cayley, Clebsch, Gordan, and other writers, but not from the present point of view or in the convenient notation that will be adopted. Some quite new results are reached, which will be found to throw much light upon the work of others. 1. In the algebraic theory we take the quantic to be
a
n
x
= (
a
1
x
1
+ a
2
x
2
)
n
, and
b, c, d
, . . . as alternative symbolic letters to
a
. We then have symbolic factors of two types, viz., the suffix type,
a
x
, and the bracketed or determinant type (
ab
).