COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 43 



and securely clamped at any desired distance from the fixation-lantern ; 

 its distance from the eye of the observer therefore remains constant 

 and equal to that of the fixation-lantern. The quadrant is graduated, so 

 that the setting of the movable lantern may be read off conveniently. 

 The quadrant also carries at its axis a graduated metal disc which 

 rotates with the rotation of the quadrant under a stationary indi- 

 cator; this device enables the experimenter to determine exactly in 

 what plane the quadrant stands at any given setting. 



H 



PERIMETER EMPLOYED IN PRESENT INVESTIGATION. 



A, head-rest and eye-shield; BE, graduated steel quadrant with counter- weight; the quad- 

 rant revolves upon an axis at E. D, movable lantern carrying the stimulus-color; E, stationary 

 fixation-lantern; F, circular patch of stimulus-color; H, fixation point. The quadrant revolves 

 through 360. It may be clamped. and held securely upon any meridian which it crosses in the 

 course of its revolution. The stimulus-lantern may be clamped at any point upon the quad- 

 rant. This arrangement enables the experimenter to expose his stimulus-color at any point 

 upon the surface of the hemisphere described by the quadrant. 



The second upright carries an adjustable head-rest. This consists 

 of padded supports for the chin and the forehead; it is also provided 

 with a felt shield which screens the unused eye. At the beginning of 

 each sitting the observer seated himself before the apparatus and ad- 

 justed the head-rest to the most convenient position. Then the height 

 of the axis of the perimeter was so adjusted that the observer's eye was 

 at the center of the hemisphere described by the rotating quadrant. 



The two lanterns, although already encased in brass, were further 

 inclosed in boxes of black cardboard, and the whole wrapped in several 



