100 



HOMING AND RELATED ACTIVITIES OF BIRDS. 



The responses were exceedingly rapid. The one error was probably caused 

 by giving 4 tests on left side, and then changing. 



January 18. By referring to the work on the chick it will be seen that the standard 

 condition was 10 minutes dark adaptation and 5 seconds adaptation before exposing light. 

 In the test below the slit in the collimator (Si) was narrowed to 0.5 mm. and the slit in the 

 objective (8^) to 1 mm. Wave-length was changed to X =4350. Under these more difficult 

 conditions the results were 28+ per cent correct. 



(1) Light on left, response wrong. 



(2) Light on left, response right. 



(3) Light on right, response wrong. 



(4) Light on right, response wrong. 



(5) Light on left, response right. 



(6) Light on right, response wrong. 



(7) Light on right, response wrong. 



Under such conditions the stimulating effect is not sufficient to control 

 reactions. In this case the light was not visible to me, but it became visible 

 when 17 seconds adaptation was allowed between turning out of light and 

 exposure of stimulus. 



January 19. Animal was again tested under same conditions, except that I waited before 

 admitting animal until light became clearly visible to me. The seconds noted in first column 

 give periods of adaptation before admitting animal. Results: 



50 sec. Light on right, response right. 



35 sec. Light on left, response right. 



45 sec. Light on right, response right. 



40 sec. Light on right, response wrong. 



30 sec. Light on right, response right. 



35 sec. Light on left, response right. 



30 sec. Light on right, response wrong. 



40 sec. Light on right, response wrong. 



40 sec. Light on right, response wrong. 



Since left position habit was setting in, I next widened slit in collimator to 

 1 mm. and allowed 60 seconds for adaptation. Light was visible to me at 

 end of 10 seconds. 



Light on right, response wrong. 



I next opened slit in objective to 2 mm. (light visible to me at end of 4 

 seconds) and allowed 60 seconds adaptation. 



Light on right, response right. 

 Light on right, response wrong. 



It is evident that we are working here on threshold at the present intensity. 

 Again the tests show clearly that there is no very great sensitivity to the 

 violet that the pigeon's retina is even less sensitive than the human retina 

 to those rays. 



January 20. I next tried the effect of greatly increasing the intensity of the light. 

 The automatic B. & L. arc was used as a source instead of the Nernst: slit in collimator 

 changed to 0.5 mm., slit in objective to 1 mm. The light so obtained was clearly over my 

 threshold the moment it was exposed. Results: 



(1) Light on right, response right. 



(2) Light on right, response right. 



(3) Light on left, response right. 



(4) Light on left, response right. 



(5) Light on right, response wrong. 

 ((i) Light on right, response wrong. 



Up to this point a 30 seconds adaptation period was given. Since the last 

 two tests gave wrong responses, I increased adaptation to 60 seconds. 



(7) Light on right, response right. 



(8) Light on left, response right. 



( 9) Light on right, response right. 

 (10) Light on left, response right. 



In this series it is clear that the limit of spectral sensibility has not yet been 

 reached. 



