Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . Martens photometer (vertical section). PORTABLE PHOTOMETERS 127 the light transmitted by this plate is reflected by the prism Fand is received at the eye-piece through the prisms B. Thisphotometer may be calibrated similar to the Weber and its rangecan be extended by increasing the density of the plate at A. The Marten Portable Photomeier.—A horizontal sectionalview of the Marten portable photometer is shown in Fig. 61and a vertical section in Fig. 62. The light to be measured falls M nil iiiiii
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . Martens photometer (vertical section). PORTABLE PHOTOMETERS 127 the light transmitted by this plate is reflected by the prism Fand is received at the eye-piece through the prisms B. Thisphotometer may be calibrated similar to the Weber and its rangecan be extended by increasing the density of the plate at A. The Marten Portable Photomeier.—A horizontal sectionalview of the Marten portable photometer is shown in Fig. 61and a vertical section in Fig. 62. The light to be measured falls M nil iiiiii iiiiii III 11 Ml nil I III II nil Il i1 Fig. 63.—Ryans photometer. on the test plate F which is observed through the sight tube Vthrough which may also be seen the surface of the plate p, illumi-nated by the comparison lamp B, through a pair of mirrorsSy and S^. These mirrors may be moved nearer or away fromthe lamp by means of a rack and pinion device T thus varyingthe intensity on the plane p. The photometrical setting isindicated by a pointer attached to the mirrors and is read directly. Fig. 64.—The Burnett photometer. from a scale graduated proportionally to the square of the dis-tance through which the light from B passes in reaching p. In Ryans photometer, Fig. 63, the light to be compared fallsat A upon one surface of the photometric device, 5, whichconsists of a translucent block, diagonally divided by a thin,opaque film. The comparison lamp, C, illuminates the otherhalf of the block. The distance between this lamp and the 128 LIGHT, PHOTOMETRY AND ILLUMINATION block is varied by means of the rod, D, upon which is calibrated ascale which indicates the results of the photometric photometric device, B, is viewed through the side, equalportions of the two halves of the block being present in the fieldof vision. A vertical section of the Burnett photometer^ is shown in The light to be studied falls upon a test-plate. A, whichis one surface of a
Size: 1869px × 1337px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
