The London, Edinburgh and Dublin philosophical magazine and journal of science . e logarithm of the brightness (log I)and the critical frequency of disappearance of flicker. Itshows the different slope of the straight lines for differentcolours, and the abrupt change of slope at low accordance with the first fact we have the reversedPurkinje phenomenon at high and medium consequence of the second we have a true Purkinje effectat very low illuminations. A reversed Purkinje effect had previously been found withthe flicker photometer. The question was therefore rai
The London, Edinburgh and Dublin philosophical magazine and journal of science . e logarithm of the brightness (log I)and the critical frequency of disappearance of flicker. Itshows the different slope of the straight lines for differentcolours, and the abrupt change of slope at low accordance with the first fact we have the reversedPurkinje phenomenon at high and medium consequence of the second we have a true Purkinje effectat very low illuminations. A reversed Purkinje effect had previously been found withthe flicker photometer. The question was therefore raisedas to whether the flicker photometer could be considered asa means of dovetailing two pure flickers. One assumption 710 Messrs. H. E. Ives and E. F. Kingsbury on the • was tested out experimentally, namely, that the two alter-nated colours in the flicker photometer give no flicker whenthe intensity of each is such as to call for the same individualflicker. This means taking the two colours in the relativeintensities at which they have the same critical frequency. Fig. Isochroinatics, showing variation in relative brightness of spectrumcolours due to variation of illumination, Flicker Photometer. (Kepro-duced from previous paper, and to be compared with theoretical curvesfig. 8.) If the assumption were correct it would follow that if one plotted log - against log Is (where Is is the intensity of the ?*-s standard illumination, and Ic that of any colour) straightlines should be obtained. An extremely careful experimentaltest gave not straight lines but instead the curves of fig. factors were studied which might more or lessinfluence the results, but the real nature of the connexionbetween the critical frequency phenomena, represented \bj Theory of the Flicker Photometer. 711 the straight line relation, and the apparently irregular flickerphotometer values was left unexplained. It is this connexionwhich is now developed. 2. General Outline of Theory. The line of
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