D O C . 3 8 7 T H E N E W F I E L D T H E O R Y 5 7 1 I.-MATTER AND SPACE. THE CHAIN OF DISCOVERY. The following, the first of two articles by Professor Einstein, is written as an explanation of his thesis for readers who do not possess an expert knowledge of mathematics. The first article is a historical sketch leading up to the introduction of the relativity theory. The second is an account of the new work. The translation is by Mr. L. L. Whyte. While physics wandered exclusively on the paths prepared by Newton the following conception of physical reality prevailed. Matter is real, and matter undergoes only those changes which we conceive as movements in space. Motion, space, and also time are [illegible] real, then that space must also be real within which bodies are conceived as accelerated. Newton saw this with perfect clarity and consequently he called space “absolute.” In his theoretical system there was a third constituent of independent reality: the motive forces acting between material particles, such forces being considered to depend only on the position of the particles. These forces be- tween particles were regarded as unconditionally associated with the particles themselves and as distributed spatially according to an unchanging law. The physicists of the l9th century considered that there existed two kinds of such matter — namely, ponderable matter and electricity. The particles of ponderable matter were supposed to act on each other by gravitational forces under Newton’s law, the particles of electrical matter by Coulomb forces also inversely proportional to the square of the distance. No definite views prevailed regarding the nature of the forces acting between ponderable and electrical particles. Mere empty space was not admitted as a carrier of physical changes and processes. It was only, one might say, the stage on which the drama of material happenings was played. Consequently Newton dealt with the fact that light is propagated in empty space by making the hypothesis that light also consists of material particles, interacting with ponderable matter through special forc- es. To this extent Newton’s view of Nature involved a third type of material particle, although this certainly had to have properties very different from those of the particles of the other forms of matter. Light particles had in fact to be capable of being formed and of disappearing. More- over, even in the 18th century it was already clear from experience that light travelled in empty space with a definite velocity, a fact which obviously fitted badly into Newton’s theoretical sys- tem. For why on earth should the light particles not be able to move through space with any ar- bitrary velocity? NEWTON’S SUCCESSORS. It need not, therefore, surprise us that this theoretical system built up by Newton with his [illeg- ible] should have been overthrown precisely by a theory of light. This was brought about by the Huygens-Young-Fresnel wave theory of light, which the facts of interference and diffraction forced on stubbornly resisting physicists. The great range of phenomena which could be calcu- lated and predicted to the finest detail by the use of this theory delighted physicists and filled many fat and learned books. No wonder then that the learned men failed to notice the crack which this theory made in the statue of their eternal goddess. For, in fact, this theory upset the view that everything real can be conceived as the motion of particles in space. For in fact this theory upset the view that everything real can be conceived as the motion of particles in space. Light waves were, after all, nothing more than undulated states of empty space, and space thus gave up its passive role as a mere stage for physical events. The aether hypothesis patched up the crack and made it invisible. The aether was invented, penetrating everything, filling the whole of space, and was admitted as a new kind of matter. Thus it was overlooked that by this procedure space itself had been brought to life. It is clear that this had really happened, since the aether was considered to be a sort of matter which could nowhere be removed. It was thus to some degree identical with space itself that is, something necessarily given with space. Light was thus viewed as a dynamic process undergone, as it were, by space itself. In this way the field theory was born as an