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ROYAL SOCIETY OF CANADA 



osi'ty of tlie specitrum, and, when plotted with the wave lengths of tiie 

 colours observed as abscissas gives a persistence of vision curve. 



I. It was observed - that when the eye is protected from light by 

 being blindfolded, or by remaining in a dark room^ the time of the per- 

 sistence of all colour impressions was increased. Experiments were 

 accordingly made to determine how this effect varied with the time of 

 darkness adaptation. Observations of the persistence of vision were made 

 on four colours, red, yellow, green and blue, after intervals of darkness 

 adaptation of one, three, five, ten and fifteen minutes. The wave lengths 

 of the colours observed and other measurements, are given in table 1, 

 and the results are shown graphically in figure 1. For convenience in 

 plotting, the ordinates are the differences between the normal readings 

 and those made after the différent intervals of adaptation. The curves 

 are of the ' saturation ' type, and show that, as far as the persistence 

 of vision is concerned, darkness adaptation produces its maximum effect 

 in about tive minutes, the measurements after the ten and the fifteen 

 mdnute intervals, showing no increase over those for five. There is, 

 indeed, .an indication in the curves of a partial return to the normal 

 condition of the retina between the five and the fifteen minute intervals 

 of adaptation. 



It will also be noticed that the maximum is least in the case of the 



brightest color used — X = .567 fx — , and greatest for the feeblest 



- A = .463 fi. 



TABLE I. 



II. A similar series of curves was obtained after fatiguing the 

 l-etina by exposure to light of certain definite hues. Readings off the 

 pensiatenoe of vision were made after intervals of fatigue of one, two, 



2 Ibid., p. 265. 



