Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . ruction of the involute curve may be seen to expressthe relation sCT I le ^^ ^ units of length (47) 0 and I Ig dOj in units of length (48) 2 in the upper and lower hemispheres respectively. When the zones are taken of 20°, it is advantageous to selectas their midangular elevations +80°, +60°, +40°, +20°,+ 0°, -20°, -40°, -60°, -80°. This leaves no uncompletedarc at either terminus, and it avoids any discontinuity in the LIGHT-FLUX CALCULATIONS 155 involute curve at the horizontal line. The first
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . ruction of the involute curve may be seen to expressthe relation sCT I le ^^ ^ units of length (47) 0 and I Ig dOj in units of length (48) 2 in the upper and lower hemispheres respectively. When the zones are taken of 20°, it is advantageous to selectas their midangular elevations +80°, +60°, +40°, +20°,+ 0°, -20°, -40°, -60°, -80°. This leaves no uncompletedarc at either terminus, and it avoids any discontinuity in the LIGHT-FLUX CALCULATIONS 155 involute curve at the horizontal line. The first arc is drawnfrom -f 10° to — 10° with the radius equal to the mean horizontalintensity. The Fluxolite Paper.—The fluxolite diagram devised by-Mr. Wohlauer offers a convenient means of determining theluminous flux and spherical candle-power. The value of theflux is obtained by simply adding a number of linear dimensionsdrawn to scale and multiplying the same by some constant depends for its value upon the number of angularsubdivisions of the spherical area. 180 165. 0° 15° 30 Fig. 90.—Wohlauers fluxolite paper. It can be shown geometrically that the altitude and hence thearea of a zone is proportional to the sine of the angle, measuredfrom the vertical axis, which bisects the zone. Hence if theimaginary spherical area be divided into n numbers of equi-angular zones and assuming the midzone intensity to be theaverage for the zone, then the flux in any zone will be F = KI^ma, (49) where / is the average intensity of the zone, a the bisecting angle Ilium. Eng., N. Y., Vol. 3, p. 655, Feb., 1909; Vol. 4, p 491, Nov. 1909:Vol. 4, p. 148, April, 1909; Vol. 5, p. 132, May, 1910. 156 LIGHT, PHOTOMETRY AND ILLUMINATION measured from the vertical axis and K a constant the value ofwhich depends upon the number of zonal subdivisions. Referring to Fig. 90 and representing the flux in successivezones from the nadir by F^, F^, etc., and the average intensitie
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
