Psychological Monographs Volume N . 24; General and Applied (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 Excerpt: ...use a result obtained with a given limited group of observers for only one intensity of light, to convert the photometric results of individual observers in other laboratories and for other intensities of light into anything at all closely approximating the correct energy values. It is obvious that in order to make the conversion in any given case with the same order of accuracy with which the direct energy measurements may be made, the same observers would have to be used, the same state of adaptation and sensitivity of the eye, the same intensity of light or approximately so (at least so far as adequate proof to the contrary for a large part of the intensity scale is concerned), the exact same range of wave-lengths and distribution of energy within the group of wave-lengths, and the same degree of purity of light as were used in making the original determination of the visibility curve which is meant to serve as the basis for making the conversion. Considering the first of these points alone, it will be remembered that Ives, working through the spectrum with the flicker photometer, found in a group of eighteen observers disagreements as great as I59 per cent for.487"; 114 per cent for.498"; 26 per cent for.518/1; 18 per cent for.537; 13 per cent for.556; 10 per cent for.576"; 28 per cent for.595;; 65 per cent for.615, _cents; 86 per cent for.635,1; and 122 per cent for.6551'. (Philos. Mag., 1912, 24, Ser. 6, pp. 856-863.) From this showing of low agreement from observer to observer with the flicker photometer, it is clear that the results for individual observers could not be used for the purpose of making the conversions recommended unless some means were had of correcting these results to those of the group for which the