STUDIES ON SPECTRAL SENSITIVITY OF BIRDS. 101 



January 21. In order that we may readily reach the hraits with the arc, I changed wave- 

 length to X = 4050, with all other conditions as in the test on January 19, except that the slit 

 in the collimator was opened to 0.75 mm. 



25 sec. Light on left, response right. 



30 sec. Light on right, response right. Hesi- 

 tated 20 sec. before starting. 



27 sec. Light right, response wrong. Hesitated 

 15 sec. 



40 sec. Light right, response wrong. Hesitated 

 15 sec. 



40 sec. Light on left, response right. Evident 

 that left position habit is forming. 



30 sec. Light on right, response wrong. 



55 sec. Light on right, response right. 



35 860. Light on left, response right. Hesitated 



22 sec, then first went wrong and then 



turned to left. 

 30 sec. Light right, response wrong. Hesitated 



25 sec. 

 33 sec. Light right, response wrong. 

 30 sec. Light left, response right. 



On analysi.s it will be found that on all of the trials except two the bird went 

 to the left side. As before, the first column shows the number of second.s 

 required to bring the light clearly over my threshold. Since this was the 

 greatest intensity of light which I could obtain with any purity, and since, 

 further, the results seem reasonably clear, I decided not to make further tests 

 on the violet region for fear of setting up a troublesome position habit (which 

 would interfere with the work in the red region). The above tests show with- 

 out further discussion that X = 40-50 under the given conditions is beyond the 

 pigeon's limit of spectral sensitivity. Since the tests on January 19 show that 

 at highest intensity \ = 4350 is not beyond the limits, it follows that the limit 

 lies somewhere between X = 4350 and X = 4050. The pigeon is somewhat less 

 sensitive to violet rays than is either man or chick. To completely work 

 out this decrease in sensitivity in quantitative terms, while a fruitful problem, 

 is beyond the scope of the present work. 



LIMITS AT THE RED END. 



January 22. In the tests on the sensitivity in the red region the Nernst was again used 

 as the source. The sUt in the collimator was set at 0.5 mm. and in the objective at 1 mm.; 

 10 minutes adaptation before beginning the tests was allowed and 10 seconds adaptation 

 was allowed on each trial after the light was turned out before exposing stimulus light. 

 Reading: X =6.350. 



( 7) Color right, response right. 

 ( 8) Color right, response right. 

 ( 9) Color left, response right. 



(10) Color left, response right. 



(11) Color right, response right. 



(1) Color right, response right. 



(2) Color right, response wrong. 



(3) Color left, response right. 



(4) Color right, response right. 



(5) C^olor right, response right. 



(6) Color left, response right. 

 Has broken position habit carried over from violet. Animal hesitated at first and did not 



seem eager to work. 



We thus .see that changing directly from violet end, where left position habit 

 was formed, to red end, resulted in the breaking of position habit. This 

 confirms our results of the previous day in a striking way. The light now lying 

 within the bird's range again controls the response. 



January 2S. X = 6840; otherwise conditions same as above, except that slit in the colli- 

 mator was opened to 1 mm. 63 per cent correct. 



28* sec. Light right, response right. 

 18 sec. Light left, response wrong. 

 18 sec. Light left, response right. 

 20 sec. Light right, response wrong. 

 22 sec. Light right, response right. 

 18 sec. Light left, response right. 



16 sec. Light left, response right. 



20 sec. Light right, response wrong. 



22 sec. Light right, response right. 



20 sec. Light left, response right. 



25 sec. Light left, response wrong. 



♦First column shows time reiiuired for the observer to see light.. Stimulus light w:is then 

 exposed to animal. 



