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ROYAL SOCIETY OF CANADA 



permit of the latter readings being uninfluenced by those going before. 

 The results are tabulated below: — 



38. It will be noticed in the above experiments with coloured 

 glasses that the periodicity for Gr is slower when G follows I B than 

 when it follows E ; and that when I B comes last, the periodicity for 

 it is only a trifle, whereas when, E comes last it is considerably smaller 

 than the periodicity for E. Thus it is seen that exposure to one kind 

 of light, and " fixing " the eyes, mlaJvCs the oscillations not only slower 

 for that light but for other light also, to which the eyes are exposed 

 immediately afterwards (although there are relative changes after 

 exposure) , 



39. An attempt was made at this time with Norremberg's appa- 

 ratus to asceriiain the effect of polarised light upon the periodicity or 

 plane of the oscillations; but the lustre of the reflecting mirror made 

 it impossible to see the image. 



40. Several sets of readings with coloured glasses were taken at 

 this time with lights of two intensities (approximately reproducible), 

 but, as a black object was always " fixed " in order to make the imiage 

 more distinct, all the results exhibit periodicities for very low intens- 

 ities; in each case, however, where the question of fatigue does not 

 enter, the periodicities for I B were somcAvhat smaller than the period- 

 icities for E, although with very low intensities the differences in 

 periodicity are not so marked as with moderate intensities. 



41. A summary of these results is given in the following table; 

 (1) represents a light of very low intensity, the flame used was about 



^ In the figures and text the following contractions are used: R, red; O, 

 orange; T, yellow; GY, greenish yellow; G, green; GB, greenish blue; CB, 

 cyanic blue; IB, indigo blue; W, white: BTk, black; and "none " means 

 that no glass was held before the eyes. 



