350 DWIGHT E. MINNICH 



III. APPARATUS AND METHODS 

 1. Directive Light 



In the experiments of the present paper, both directive and 

 non-directive hght were . employed. Those involving directive 

 illumination were carried on in a circular area (fig. 1) 2.44 m. in 

 diameter, which was laid out in black lines on the concrete floor 

 of a dark room. Sixteen centimeters' above the center of this 

 area, ka incandescent lamp was suspended. The lamp employed 

 was a 100-watt, 115-volt, stereopticon, Edison mazda lamp. Of 

 several bulbs used in the course of experimentation, only the last 

 was determined photometrically, its candle-power being approxi- 

 mately 80. These lamps when new are calculated to furnish 

 100 c.p., but their efficiency decreases considerably with usage. 



In making tests in the directive light area, bees were started 

 creeping at the outer circumference. The course of the animal 

 as it traveled toward the light was then traced as accurately as 

 possible on a record bearing a plan similar to that of the light 

 area and drawn to scale. Such a record is shown in figure 1. 



£. Non-directive light 



a. Construction. The apparatus employed to furnish non- 

 directive light consisted essentially of a white-walled, cylindrical 

 chamber. This chamber was illuminated by an incandescent ~ 

 lamp, the light of which was diffused through a thin, white screen, 

 suspended a short distance below the lamp. Bees were admitted 

 to the apparatus through a small, circular opening in the center 

 of the floor, and the course of their creeping was then traced as 

 accurately as possible on a record. The apparatus was espe- 

 cially designed to afford a creeping animal a continuous photic 

 stimulation of uniform intensity over the entire surface of the 

 eye. A more detailed description is presented in the following,, 

 paragraphs (see, figure 2). 



' Distances from lamps to creeping surfaces were measured from the center of 

 the filament in all cases. 



