Note 1 — III EINSTEIN

Three Possibilities Anticipated. According to Newton’s assumption, light consists of corpuscles, or minute particles, emitted from the source of light. If this be true these particles, having mass, should be affected by the gravitational pull of the sun. If we apply Newton’s theory of gravitation and make use of his formula, it can be shown that such a gravitational pull would displace the ray of light by an average amount equal to 0.75 (seconds of angular distance.)1 On the other hand, where light is regarded as waves set in motion in the “ether” of space (the wave theory of light), and where weight is denied light altogether, no deviation need be expected. Finally there is a third alternative: Einstein’s. Light, says Einstein, has mass, and therefore probably weight. Mass is the matter light contains; weight represents pull by gravity. Light rays will be attracted by the sun, but according to Einstein’s theory of gravitation the sun’s gravitational pull will displace the rays by an average amount equal to 1.75 (seconds of angular distance).