5

πλ
5
is the form of a relation. Now this form of relation is the very
form of the relation between the two corrisponding parts of the
diagram. For example, let F, and F2 be the two distances of the
two foci of a lens from the lens. Then,

1 + 1 = 1
F F2 F0

This equation is a diagram of the form of the relation between the
focal distances and the principal focal distance;
two foci, and the conventions of algebra, [Dr?]
in [conjunction?] with the writing of the equation, establish
a relation between the very letters F1, F2, F3, regardless of their
significance, the form of which relation is the very same as
the form of the relation between the three focal distances that these
letters denote. This is a proposition quite beyond dispute. Thus, this