42 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



EXPERIMENTAL. 



The observers were all students of the Cornell Laboratory: Miss 

 A. R. Jenkins, A. B. (J.) ; Miss J. B. Peirson (P.), Mr. C. E. Gallo- 

 way, A. B. (G.), and Mr. H. C. Stevens, A. B. (S.) ; for their patient 

 co-operation in a trying series of experiments the writer is grateful. 

 The writer (B.) also gave a series of sittings, the apparatus being oper- 

 ated in this latter case by Miss Jenkins, or by a hired assistant. All of 

 the observers are emmetropes, and all possess normal color vision. 



The investigation followed two general lines of inquiry : 



(1) The first group of experiments aimed to determine what 

 changes of tone a color stimulus undergoes during the movement of 

 its image across the retina. Here our sole concern was to find an answer 

 to the question: What is the chromatic character of the sensation 

 aroused when a constant color stimulus is applied successively to differ- 

 ent regions of the retina ? 



(2) The second group aimed to determine the relative extension 

 of the different retinal zones. Here our problem was : What is the 

 relative extension of the retinal areas within which the tones of the 

 different color stimuli are correctly recognized ? 



I. CHANGES OF COLOR TONE IN INDIRECT VISION. 



A. APPARATUS. 



These experiments were conducted in the dark-room of the labora- 

 tory. This room was constructed for optical research, and was so ar- 

 ranged as to render possible any desired degree of illumination. Dur- 

 ing our experiments the room was in deepest darkness. The apparatus 

 employed was the Hellpach perimeter. This was built to our order by 

 Zimmermann, the Leipzig mechanician, and was in all its essentials an 

 exact duplicate of the apparatus employed by Hellpach in a similar in- 

 vestigation.* It consists of a strong wooden frame about 1.5 meters 

 long, from each end of which there rises a stout upright post. One of 

 these posts is adjustable in height, and supports at its upper end a 

 steel quadrant of i.i meter radius. The quadrant is attached to its 

 support by means of an axis fitted into a bearing. This device enables 

 the quadrant to turn freely, its complete revolution describing a hemi- 

 sphere about a horizontal axis. The quadrant carries two lanterns of 

 blackened brass, each containing an incandescent lamp of 16 candle 

 power. One of these, the fixation-lantern, is made fast to the axis of 

 the apparatus. The other, the stimulus-lantern, is attached to the 

 quadrant by means of a metal clamp ; it may be slid along the quadrant 



*For illustration and description see Philosophische Studien, XV, 1900, S. 525ff. 



