MARXISM AND THE SPECIAL THEORY OF RELATIVITY 35 of relativity lead to some of the perversities to which references are made by people like Koestlcr who aim at peddling fancies and religion. We shall also examine the alleged connection between Einstein's theories and the philosophy of Mach, so that the comments on the reception to relativity in the Soviet Union arc understood in the proper light. CONTRADICTIONS IN NINETEENTH CENTURY PHYSICS Relativity arose out of the contradictions in the nineteenth century theories of electricity and magnetism and their inability to account for the empirical data which the highly developed techniques in expci indentation threw up. Several ad hoe attempts were made to patch up the discrepancies but what was called for was the re^examina-tion of the very foundations of physics and of our baUc conceptions in science. Such a re-examination was started by Einstein through his first paper on relativity in 1905. Two like electric charges repel each other with a force depending on the charges and the distance between them. Similarly two magnetic poles also exert forces on each other. Electric charges flowing in a wire constitute a current. A current has an effect on magnets and exerts forces on magnets;so also a magnet in motion produces a current in a conductor. Faraday and others studied the relationship between currents and magnets and summarised their studies in a set of laws. These laws describe the relation between electric fields and magnetic fields. Basing himself on these laws. Maxwell derived a set of equations showing how the electric and magnetic fields, connected with moving charges and magnetic poles, change with time and how these fields vary from point to point in space. These equations, called Maxwells equations, are a special type of relations known technically as linear partial differential equations. Maxwell's equations predicted that electric and magnetic fields would vary and spread like waves, and that these waves would have a certain fixed speed. The speed of the waves was obtained in Maxwell^s theory by taking the two natural units of electric charge. This value turned out to be 300,000 km per second, which also happens to be the velocity of light. This equality suggested that light was a form of wave motion of electric and magnetic fields. Later, Hertz demonstrated through electrical experiments that electromagnetic waves could indeed be produced as predicted by Maxwells equations. Light is only one of the forms of electro-magnetic wave motion. Radio waves, ultra violet rays and X-rays all belong to this class of wave motion. All these waves move with the same speed 300,000 km per second, which speed we may denote by the letter c. If light is a wave motion, in what medium were the waves moving? Water waves are carried through water, sound is carried through air or other matter. What is light carried through? It was postulated that the whole of space was filled with a medium called the