138 WILLIAM L. DOLLEY, JR. 



ciently short, a continuous impression will result, which is the same as 

 that which would result if the total light received in each period were 

 uniformly distributed throughout the whole period. 



Nearly all of those who have tested this law have concluded 

 that it holds for the effect of intermittent light of high flash- 

 frequency. 



Plateau (1835, p. 457), Helmholtz (1896), Kleiner (1878, p. 

 542), Wiedemann and Messerschmitt (1888, p. 465), and Lum- 

 mer and Brodhun (1896, p. 299-307) verified the law to within 

 the range of their experimental error. 



Fick (1863, p. 739) concluded that with intense illumination 

 the action of intermittent light is stronger than it should be 

 according to Talbot's law and that with very weak illumination 

 the reverse is probably true. 



Aubert (1864), however, maintains that the deviation from 

 Talbot's law which Fick found is of the same order of magni- 

 tude as his experimental error and that therefore his results 

 verify the law to within the limit of accuracy of his experiments. 



Ferry (1893, p. 338) verified the law for white light but found 

 quite large errors when the light transmitted through the ro- 

 tating sectored disk was of a bluer quality than that incident on 

 the other side of the photometer screen. 



Hyde (1906, pp. 1-32), however, as the result of an extremely 

 thorough piece of work, came to the conclusion that Talbot's 

 law, in its application to a rotating sectored disk, holds for white 

 light for all total angular openings between 288 and 10 degrees 

 to within a possible error of 0.3 per cent, which he states proba- 

 bly expresses the limit of accuracy of his experiments. He also 

 concluded that Talbot's law is verified for red, green, and blue 

 light though not to such a high accuracy as for white light. 



Parker and Patten (1912, pp. 22-29) on the contrary con- 

 cluded that intermittent light is measureably less efficient as a 

 stimulus for the eye than continuous light. Pfund, however, 

 points out that Parker and Patten's methods were at fault and 

 says (1914, p. 117) : "It is therefore established by methods that 

 are entirely free from objections that Talbot's law holds to a 

 high degree of accuracy for the human eye." 



