waves through this medium. A correct solution of these (and analogous) problems requires the use of re­ lativistic principles. This remark remains valid even at low velocities, since first-order terms in (v/c) often playa fundamental role in the equations. The "applicational" approach used in the text should be acceptable to space engineers, nuclear engineers, electrical engineers, and more generally, ap­ plied physicists. Electrical engineers, in particular, are concerned with re­ lativity by way of the electrodynamics of moving bodies. This discipline is of decisive importance for power engineers, who are confronted with problems such as - the justification of a forcing function (-D~/Dt) in the circuit equation of a moving loop - a correct formulation of Maxwell's equations in rotating coordinate systems - the resolution of "sliding contact" paradoxes - a theoretically satisfying analysis of magnetic levitation systems.