184 



nutting: precision colorimeter 



correction to the absolute color scale based on the average proper- 

 ties of a number of normal eyes. 



The new colorimeter is so arranged that light of a pure spectral 

 hue may be mixed with white light to match the unknown or, 

 in the case of purples, it is mixed with the unknown to match 

 white. The match is made with a Lummer-Brodhum photometer 

 cube. 



Fig. 1. Diagram of precision Colorimeter. 



The figure is a diagram of the optical parts of the instrument. 

 Collimator 1 is movable, all the remaining parts are fixed. Colli- 

 mators 1 and 4 with prism P form an ordinary spectroscope with 

 pin hole ocular. The white and unknown lights enter thru colli- 

 mators 2 and 3, in direct or inverse order according as the match is 

 to be made with the dominant hue or its complementary. In 

 analyzing reflected light the necessary collimator is raised or 

 rotated or even removed entirely if sunlight is used. 



Wave lengths are varied simply by rotation of collimator 1. 

 Intensities may be varied by (1) varying slit widths, (2) rotating 

 sectors, or (3) by rotating one of a pair of nicols placed just inside 

 each slit. The colorimeter now in use is provided with a bilat- 

 eral slit on the first collimator while collimators 2 and 3 are pro- 

 vided with pairs of nicols. 



