. Contrast sensibility of the eye . n was illuminated bymeans of the locomotive headlightlamp L3, Fig. 1, operated at 29volts. By means of sectored diskson the motor M2 the intensity ofthe general illumination on thescreen was regulated. The lamp,L3, was inclosed by a metal cylinderwith a suitable aperture. An ad-ditional black screen, d, was placedjust beyond the disk. These pre-cautions assured us that the screenreceived a negligible amount of il-lumination from the light-coloredwalls of the room. The screen was,furthermore, surrounded by a black-cloth border. The projection lan-tern by mean
. Contrast sensibility of the eye . n was illuminated bymeans of the locomotive headlightlamp L3, Fig. 1, operated at 29volts. By means of sectored diskson the motor M2 the intensity ofthe general illumination on thescreen was regulated. The lamp,L3, was inclosed by a metal cylinderwith a suitable aperture. An ad-ditional black screen, d, was placedjust beyond the disk. These pre-cautions assured us that the screenreceived a negligible amount of il-lumination from the light-coloredwalls of the room. The screen was,furthermore, surrounded by a black-cloth border. The projection lan-tern by means of which the vari-able strip of light was projectedupon the screen was equipped witha miniature signal lamp, L2, oper-ated at 6 volts. The two lamps, L2 and L3, Fig. 1, were operated onstorage batteries, and voltage was kept constant to volt. 682 Scientific Papers of the Bureau of Standards [Vol. 15 The lantern was provided with a bilateral slit, whose construc-tion is shown in detail in Fig. 3. Its chief parts were two jaws,. /, smoothly displaceable horizontally in guides, g, under tensionof two springs, s. The displacement of the jaws—that is, the rZZiaiil Contrast Sensibility of the Eye 683 opening of the slit—was varied by means of a cord, cy attached tothe jaws and passing over pulleys, p, to the winch, wt operatedby the key, k. To limit the aperture vertically to a requiredheight, a diaphragm, D, of any desired width could be insertedinto guides, g. This simple slit mechanism when in good con-dition gave entire satisfaction for the purpose in hand. A secondsectored disk, Mu Fig. 1, was placed before the projection lan-tern to control the brightness of the variable strip. To determinethe length of a strip projected upon the screen a scale, T, Fig. 1,was projected alongside of the strip by means of the lens, /.When measurements of the length of the strip were made, thelight from lamp, L3, was eclipsed by means of a screen operatedby a lever which simultaneously c
Size: 1170px × 2137px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishernatio, bookyear1919
