PSYCHOPHYSICAL EXPERIMENTS. 665 



ployed, even moderately bright or faint light giving bad results, 

 while lights of about 1-2 candlepower could be compared with the 

 smallest margin of error. Shieldinj; the eyes from extraneous 

 light was found to be necessary, as it is difficult to ensure a suffi- 

 cient fixity of attention. 



The bearing of these results on Weber's law is obvious. 

 According to them, the proportionality between the increment of 

 sensation and the percentage increase of stimulus only holds a 

 very limited range, the constant of proportionality being quite 

 different for bright lights and those of moderate intensity, while 

 for lights of extreme brightness it seems likely that all difference 

 of sensation is lost. 



2nd. The rate at which visual impressions must succeed each 

 other in order to be fused. 



This experiment was tried in conjunction with Professor Hay- 

 craft, of Mason College, Birmingham, who devised the method 

 and constructed the apparatus. A large pendulum in the form of 

 a segment of a circle was employed, and adjustable slits could be 

 placed, at any desired position along the arc. The observer was 

 stationed in a darkened enclosure behind the pendulum, which 

 could be viewed through an aperture in the side of the enclosure ; 

 hence no light could enter the enclosure save when a slit was 

 passing the aperture. The slits were adjusted by a second experi- 

 menter. The largest time interval which allowed of the fusion of 

 the impressions was found in this May for a single observer to be 

 about l/22nd of a second for white light and 1/I8th for red. The 

 difference between tlie two was well marked, for the same placing 

 of the slits which allowed the impressions from the red light to 

 be fused left those from the white light distinct, though the slits 

 had only to be displaced through a very small distance in order to 

 fuse the impressions from the white light. 



In both sets of observations recorded in this paper blank experi- 

 ments were intercalated, in order to guard against possible bias on 

 the part of the observer, who of course was kept in ignorance of 

 the actual condition of the apparatus, except in so far as the 

 observations themselves disclosed it. 



-o-».J(-o- 



13.— SIMPLIFICATION OF DIFFICULTIES IN CON- 

 NECTING THE TONIC SOL-FA AND THE 

 OLD NOTATION. 



i?y TF. A. JONES. 



