D O C . 3 2 9 F U N D A M E N T A L C O N C E P T S OF P H Y S I C S 497 place: the concept of the "field." One electrically charged body might not now act directly upon another. It was surrounded hy a field which had Its own particular apace and time lawa A lbert Einstein. and could even detach ltself from the bodies. By the field was understood an energy condition of space which was described by mathematically con- tinuous functions, and which, as a physical reality, was as original as the elementary particles of matter. It soon appeared that this fundamental concept had to become a superstruc- ture In the sense that electrons and protrons were to be considered as only specially distinguished points of the field. This gave rise to electro-mag- netic mechanics as an attempt to de- duce mechanics from the laws of the field of electro-magnetism. Thus a foundation was laid to physics which. In principle, departed widely from Newton's and at the same time markedly surpassed New- ton's In logical consistency. Following upon this, the theory of relativity was nothing more than a further conse- quential development of the field the- ory. It showed that simultaneity In time had no absolute character and that Euclid's geometry did not hold with exactness. The laws of the rela- tive position of bodies proved to be a property of the gravitational field whose law was disclosed. Thus the field theory shook the fundamental concepts of time, space and matter. But upon one column of the edifice It made no assault: on the hypothesis of causality. From some single condition of the world at a giv- en time, all other previous and subse- quent conditions uniquely follow, based upon the laws of nature. Today, however, serious doubts have emerged about the law of caus- ality thus understood. This Is not to be charged to the craving for new sensations on the part of the learned, but to the momentum of facts which seem Irreconcilable with a theory of strict causality. It seems at this time as If the field, considered as a final reality, does not make proper allow- ance for the facts of radiation and atomic structure. We reach here a complication of questions with which the modern generation of physicists Is struggling In a gigantic display of in- tellectual power. Everyone knows that by means of ultra-violet light, and still more of Roentgen rays, elementary chemical processes can be produced of much greater energy than with the aid of red or yellow light. The Intensity of the radiation Is of no consequence whatever, only the color or frequency Is or Importance. As experimentally determined, the energy conveyed to the absorbing body In the elementary process of absorption depends on the frequency alone of the Incident radia- tion. For this fact the field theory could give no explanation. According to It. the local concentration of energy should depend on the Intensity alone of the radiation and not at all on Its frequency. On the basis of the field theory we do not understand why ra- diation of a given color should always give out—or absorb— energy In en- tirely definite portions only. Something similar appears In the revolution of electrons about atomic nuclei, which are natural Instances of high frequency. These conditions of motion are tied to wholly definite en- ergy values, which In the light of hitherto accepted mechanical theory appears totally unintelligible It Is pat- ent that these discontinuous energy conditions control the structure of m atter. Theories have already been [7] [8] [6]