Thus every quaternion may be written in the form q = Sq+Vq, where either Sq or Vq may separately vanish; so that ordinary algebraic quantities (or **scalars**, as we shall call them) and pure vectors may each be regarded as special cases of quaternions.

A n are **scalars**, and in particular applications may be restricted to real or complex numerical values.

This idea finds fuller expression in the algebra of matrices, as to which it must suffice to say that a matrix is a symbol consisting of a rectangular array of **scalars**, and that matrices may be combined by a rule of addition which obeys the usual laws, and a rule of multiplication which is distributive and associative, but not, in general, commutative.

Combebiac's tri-quaternions, which require the addition of quasi-**scalars**, independent of one another and of true **scalars**, and analogous to true **scalars**.

To fix a weighted point and a weighted plane in Euclidean space we require 8 **scalars**, and not the 12 **scalars** of a tri-quaternion.

Let n, w be two quasi-**scalars** such that r t e =n, con = w, nw =w 2 = o.

The axis of the member xQ+x'Q' of the second-order complex Q, Q' (where Q=nq+wr, Q'=nq'+wr' and x, x' are **scalars**) is parallel to a fixed plane and intersects a fixed transversal, viz.

Thus, in place of his general tri-quaternion we might deal with products of an odd number of point-plane-**scalars** (of form, uq+wr) which are themselves point-plane-**scalars**; and products of an even number which are octonions; the quotient of two point-plane-**scalars** would be an octonion, of two octonions an octonion, of an octonion by a point-plane-scalar or the inverse a point-plane-scalar.