The Electromagnetic Vectors

An electromagnetic fiels in the ether is usually specified by the values at each point and at each instant of two vectors E and H, but a more general specification is obtained by using the two vectors F=E + 1/c x (v x H), Q=H - 1/c x (v x E), where v is an arbitrary velocity representing at each point and at each instant the velocity of an imaginary recording instrument and c is the velocity of light. These vectors are of fundamental importance in electromagnetic theory for F is usually supposed to represent the force which the field would exert on a minute unit electric charge moving with velocity v and Q may be supposed to represent the force which the field would exert on a minute unit magnetic charge if such a thing could exist and move with velocity v. On account of the importance of these vectors F and Q it will be worth while to get a clear conception of the way in which they vary when the field remains constant and v varies.