In octonions the analogue of Hamilton's vector is localized to the extent of being confined to an indefinitely long axis parallel to itself, and is called a **rotor**; if p is a **rotor** then wp is parallel and equal to p, and, like Hamilton's vector, wp is not localized; wp is therefore called a vector, though it differs from Hamilton's vector in that the product of any two such vectors wp and coo- is zero because w 2 =o.

P is a **rotor** and coo- a vector), is called a motor, and has the geometrical significance of Ball's wrench upon, or twist about, a screw.