American cinematographer (Jan-Dec 1926)

Twenty-four AMERICAN CINEMATOGRAPHER December, 1926 The reflected ray will also be found to lie on the same plane as the incident ray, in the figure, this plane being, as we said, the plane of the paper. If A B is the surface of a mirror, and we place our eye at the point R. we will see an image of the point L, situated at L', behind the mirror, on the prolongation of the ray O R, and at a distance from O, equal to the distance L O. Huyghens Construction of Reflected Rays According to His "Undulatory Theory" ^ u '' / y ^l v^A^^yV ' >' y\ Ayr ' isy *'* ,---'"'" \ ' FIGURE 3 A B Equals Reflecting Surface. L Equals Luminous Body. L' Equals Image of Luminous Body. L O; L O'; L O3; L O3 ; L O4 Equals Incident Rays. P2 P4 Equals Incident Wave Front. 0 0';0'0"; O2 O2' ; O3 O3' ; O4 O4' Equal Re flected Ravs. P'2 P'4 Equals Reflected Wave Front. ON;ON';0 N2 ; O N3 ; O N4 Equals Normals to Reflecting Surface.. LET A B be the reflecting surface and L the luminous body, emanating rays in all directions, among which we select the rays L O ; L O1 ; L 0: ; L O3 ; L 0\ falling on the reflecting surface. As all these rays travel with the same velocity, at the time the ray L O will have reached the point P of the reflecting surface, the ray L O2 will have reached the point P: and the rays L O1 ; L ()'; L O4 will have reached the respective points P1 ; P3 P4, forming a wave front P2 P4. At the same instant the ray L O strikes the reflecting surface, the point P becomes the center of a disturbance, creating a wave which bounces away from the surface. The incident ray is thus reflected back upon its own path, in the direction O L, while the ray L P2, for instance, will have to continue to O2, from whence it is reflected in the direction O2 O'2, forming with the normal N2 O2 an angle equal to the angle of incidence L O2 N2. At the same instant in which the reflected ray O L reaches the point P', the reflected ray O2 O'2 will reach the point P'2, because light travels with the same velocity, and the distances L O plus O P' and L O2 plus O P'2 are equal. Following the same construction for all the other rays we find the reflected light to form a wave front P'1 P'4> whose center of curvature is at L', behind the reflecting surface, at the intersection of the prolongation of the reflected rays and at a distance U P from the reflecting surface, equal to the distance L P, which is the distance of the luminous point to the reflecting surface. IT is obvious that a luminous object, such as any incandescent portion of matter emits its own luminous rays. A non-luminous body is rendered visible by the rays it reflects. Each and every point of a non-luminous body becomes the center of disturbance in the luminous ether at the particular point, and the reflected ray behaves as if it was originated at that very point of the body. In other words, the non-luminous body acts as a luminous one as long as it is stricken by incident light, and the intensity of its acquired luminous power is controlled by the intensity of the incident light from the luminous body, and by its own composition. Now, let us suppose that we place a well defined object in front of, and at a certain distance from a plane mirror M, as illustrated in (Continued on Page 25) FIGURE 4 O Equals Object. W Equals Reflecting Surface. O' Equals Virtual Image of Object O.