These two quantities, the electric force and the magnetic force, are called the wave vectors, and they both lie in a plane perpendicular to the direction in which the wave is travelling and at right angles to one another, the electric force being perpendicular to the surface of the earth.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
I shall only mention the name of that important class of magnitudes having direction in space which Hamilton has called vectors, and which form the subject-matter of the Calculus of Quaternions, a branch of mathematics which, when it shall have been thoroughly understood by men of the illustrative type, and clothed by them with physical imagery, will become, perhaps under some new name, a most powerful method of communicating truly scientific knowledge to persons apparently devoid of the calculating spirit.
"Five of Maxwell's Papers"
James Clerk Maxwell
On the other hand, if the basic directions are too widely spread or if the major sector vectors are widely separated with little or no representation between, the net trend density may become an abstraction, expressing the idea of a mean direction but pointing down an avenue along which no migrants are traveling.
"A Quantitative Study of the Nocturnal Migration of Birds. Vol.3 No.2"
George H. Lowery.