In order to appreciate the nature of Maxwell’s contributions, let us recall how matters stood in his day. If we confine-our attention to regions of space where no electric currents, no charged bodies or magnets are present, so that solely the electric and magnetic fields need be considered, the fundamental law of electromagnetism is Faraday’s law of induction. This law states that a variable magnetic field generates an electric field. Maxwell, however, considered that this law, standing alone, lacked symmetry; so he formulated the hypothesis that conversely a variable electric field should generate a magnetic one, and proceeded to construct his theory with this idea in view.[40] In the particular case of free space in which only fields but no charges or currents are present, Maxwell’s equations of electromagnetics, termed field-equations (since they describe the state of the electromagnetic field), can be written: [Pg 127] where represents electric field intensity, magnetic field intensity, denotes time, and a most important constant about which we shall have much to say later. As for “div” and “curl,” they represent mathematical operations of a peculiar sort. At any rate, the reader need not be alarmed at these equations, for it is not necessary that we understand them. Suffice it to say that (2) represents Faraday’s law of induction, while (4) constitutes the hypothetical law postulated by Maxwell in order to ensure symmetry. Prior to Maxwell’s investigations the fourth equation would have been written “”; hence it is the adjunction of the term which constitutes the originality of the theory. From his field equations, Maxwell by purely mathematical means was able to deduce the two additional ones: