knowledge thus far accumulated by physical cience as being of a lasting character, What then is the substance of these findings? First of all, it must be noted that all data of phys- ical knowledge are founded on measurements, and that every measurement takes place in space and time with the orders of magnitudes varying from the inconceivably vast to the infinitesimally small, We can get an approximate idea of the dis- tance of the cosmic regions from which a message can still reach us if we consider that light, which traverses the distance from the Moon to the Earth in a second or so, requires many millions of years to arrive from those regions to our planet, On the other side of the picture, physical science must calculate with spatial and temporal magnitudes, the infinite smallness of which can be realized by the comparison of a head of a pin with our entire planet, Measurements of the most varied kinds have been consistent in leading to the conclusions that all physical occurrences without exception can be reduced to mechanical or electrical processes, produced by the movements of certain elemen- tary particles, such as electrons, positrons, protons