78 



TROPISMS 



TABLE I. 



Percentage difference in the 

 intensity of the two lights 



Average angular deflection of the 

 two paths of the larvse toward 

 the weaker light 



Per cent. 

 



25 



331/3 

 50 



66% 

 831/3 

 100 



Degrees 



- 0.09 



- 2.77 



- 5.75 



- 8.86 

 -11.92 

 -20.28 

 -30.90 

 -46.81 

 -77.56 



Patten also investigated the question whether the same 

 difference of percentage between two lights would give 

 the same deviation, regardless of the absolute intensities 

 of the lights used (Weber's law). The absolute intensity 

 was varied by using in turn from one to five glowers. The 

 relative intensity between the two lights varied in succes- 

 sion by 0, 8 1/3, 16 2/3, 25, 33 1/3, and 50 per cent. Yet 

 the angular deflections were within the limits of error 

 identical for each relative difference of intensity of the 

 two lights, no matter whether 1, 2, 3, 4, or 5 glowers were 

 used. Table II gives the results. 



TABLE II 



A TABLE BASED ON THE MEASUREMENTS OF 2,700 TRAILS SHOWING THE 

 ANGULAR DEFLECTIONS AT FIVE DIFFERENT ABSOLUTE INTENSITIES 



Number 



Difference of intensity between the two lights 



