. Practical physics. The Zeiss binocular 400 IMAGE FORMATIOX A further advantage which is gained by the Zeiss binocular is due tothe fact tliat the two objectives are separated by a distance which isgreater than the distance between the eyes, so that the stereoscopiceffect is more prominent than with the unaided eye or with the ordinaryopera glass.* 462. The periscope. A periscope is a sort of double-jointed telescopewhich makes use of total reflection twice, — at the top and at the system of lenses gives a magnification of about 11 diameters, as. Fit;. 438. A parabolic reflector th
. Practical physics. The Zeiss binocular 400 IMAGE FORMATIOX A further advantage which is gained by the Zeiss binocular is due tothe fact tliat the two objectives are separated by a distance which isgreater than the distance between the eyes, so that the stereoscopiceffect is more prominent than with the unaided eye or with the ordinaryopera glass.* 462. The periscope. A periscope is a sort of double-jointed telescopewhich makes use of total reflection twice, — at the top and at the system of lenses gives a magnification of about 11 diameters, as. Fit;. 438. A parabolic reflector this has been found best to make ships appear at their true distancesfrom the submarine. There is no stereoscopic effect, since the periscopeis not double like a binocular. 463. Parabolic reflectors. For the projection of a more nearly cylin-drical beam than is possible with spherical mirrors, it is customary touse parabolic reflectors, as in automobile headlights (Fig. 438, (1) and(2)). The light is placed a little closer to the reflector than the i)rinci-pal focus, so that the reflected light may spread somewhat. The sameprinciple is employed in searchlights, except that the source of light(usually a powerful arc) is kept more nearly at the principal focus ofthe reflector. The Sperry 60-inch searchlight, the most powerful in theworld, has a beam candle power of approximately two thirds that of thesun, and its light is plainly visible at a distance of one hundred miles. * Laboratory experiments on the magnifying powers of lenses and on theconstruction
Size: 2267px × 1102px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
