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Show I Lamp-Shades and the Eyes, Prof. II. Cohn, in his pamphlet "Ueberder , Belcuchtungswerth dcr Lainpcnlockcn" (Weisba i den, 1SS5), describes a lomj series of determination.' l -of the relative values of various forms of lamp I? jjBw - mr- -shades. The method pursued was to measure tlu Em brifirhtness of white paper lying on a table ove 'which the soiirre of artificial lijrht was suspender, at a given distance by means of a Weber photometer. As one would anticipate, thcgenerahjfl'ectofashade K is to increase very greatly the illumination immedi F ately under the light, and not modify it notably a I ( an. angular distance greater than forty-five degree.- from this region. The last section of the pamphlet which deals with the illumination requisite for eas ie'st use of the eyes, is of the most general interest - Taking as a measure of the value of the iiluminatioi in this sencethe number of lines which can be re art .from a newspaper in a minute, and as the unit o illumination that of a normal candle a perpcndicula ..'distance of a metre from the paper, he finds that th .best illumination is not .'ess than fifty such units "Since even a fifth of this illumination is very rarely , secured, except immediately under a Jatup providec with a good shade, the author emphasizes the con . elusion that few school-children work in a satisfac "" ,-T Science |