2 ROBERT M. YERKES AND JOHN B. WATSON 



University, and Mr. William Gaertner of Chicago. Mr. B. 

 Spencer Greenlielcl, formerly mechanician in the Harvard Psy- 

 chological Laboratory, has aided us in many ways, but espec- 

 ially by making drawings of the various parts of our apparatus. 



For information and advice on varied topics we thank Pro- 

 fessors G. H. Parker, H. W. Morse and G. W. Pierce of Harvard 

 University; Doctor Louis Bell, consulting electrical engineer, 

 Boston; Professor J. W. Baird of Clark University; Pro- 

 fessors Edward L. Nichols and E. B. Titchener of Cornell Univer- 

 sity; Mr. A. J. Marshall and Mr. G. A. Anderegg of New York; 

 Mr. Willard Greene; Doctors P. G. Nutting and W. W. Coblentz 

 of the United States Bureau of Standards ; Mr. James Wallace 

 of the Cramer Dry Plate Company; Eimer and Amend; Metz 

 and Company; the National Electric Lamp Association; Mr. J. 

 G. Biddle, and the Arthur H. Thomas Company. 



The late Professor W. A. Nagel of the University of Rostock, 

 master of the technique of physiological optics and throughout 

 his life a specialist in the problems of vision, was especially 

 painstaking in his efforts to further our investigation. His 

 death in the prime of life leaves with us a keen sense of personal 

 loss. We desire to express our appreciation of the man and 

 the scientist.' 



During the early portion of our investigation, we profited 

 by the valuable assistance of Doctor E. G. Congdon. He worked 

 especially on the problems of ray filters. The authors wish to 

 emphasize the importance of Doctor Congdon's share in the 

 investigation. Except for the fact that he is not in any way 

 responsible for the methods and apparatus which we have 

 during the past two years decided to perfect and recommend 

 as standard procedures, his name should appear as a joint 

 author of this monograph. 



Professor Yerkes, who was charged by the Committee with the 

 general direction of the work, is chiefly responsible for the pre- 

 liminary portion of the report and for the method and apparatus 



^ After this manuscript had been written, with the exception of the final descrip- 

 tions of the light and color apparatus, there appeared in Tigerstedt's Handbuch 

 der physiologischen Methoilik an admirable review and discussion of " Methoden 

 zur Erforschung des Licht- und Farhensinns " by Professor Nagel. Since Professor 

 Nagel in his paper presented some of the material which we had intended to pub- 

 lish, it has seemed to us desirable to omit certain portions of our report, as origi- 

 nally planned. We especially commend Professor Nagel's discussion to those 

 who are interested in human vision. 



