RELATIVE STIMULATING EFFICIENCY OF LIGHT 145 



by means of black cloth which covered the walls of the room. 

 There was consequently very little light in the room aside from 

 that in the beams. One of the lamps was in an adjoining room, 

 and the beam from it passed through an aperture in the interven- 

 ing wall. The other lamp was placed upon a support so that its 

 position could be easily changed. In some of the experiments 

 the light in one of the beams was intermittent. The intermit- 

 tent light was produced by means of a rotating sectored disk 

 connected with a small motor which was run on Edison storage 

 batteries. The motor and sectored disk as well as the lamp were 

 all placed in an adjoining room, separated by a 30 cm. thick 

 brick wall from the room in which the experiments were performed, 

 so as to reduce vibration as much as possible. The flash-fre- 

 quency and the duration of the flashes and of the dark periods 

 between the flashes of the intermittent light was controlled by 

 using different disks with apertures of various sizes and by vary- 

 ing the number of revolutions per second. 



Not only was the behavior of the animals observed closely by 

 the investigator but the butterflies themselves were forced to 

 make permanent records of their own behavior. This was done 

 by allowing them to walk on sheets of paper (15 by 21 cm.) 

 which had been covered with soot from an oil lamp. The trac- 

 ings made by the insects were made permanent by means of a 

 coat of shellac. Tests showed that the behavior was not affected 

 by the soot. Upon the sheets bearing the tracings of the insects 

 were also marked the limits and direction of the beams of light. 

 Individuals were given a varying number of trials under the same 

 conditions. Sometimes 5 were given and at other times more. 

 An insect was never allowed to make more than 10 tracings on 

 one sheet. Where more trials were given other sheets were used. 

 Usually an animal was given 5 consecutive trials from a point 

 facing one source of light. It was then given 5 trials from a 

 point facing the other source. In analyzing the tracings made a 

 line was drawn bisecting the angle made by the rays of light in 

 the center of each beam. The angle that each tracing made 

 with this line was then measured. If, for example, the tracing 

 was at an angle of 10 degrees with the line bisecting the angle 



