52 



Herbert Eugene Walter 



turn more in the dark than in the hght, going clockwise or contra- 

 clockwise with equal readiness. Finally, they make more indefi- 

 nite changes in their paths in the dark, but fewer definite changes 

 than in the light. 



TABLE II 



Percentage of definite and indefinite changes in the character of the course in dark and in light of di^erent 



intensities 



Details of the several intensities employed 



Light in candle meters 



Definite changes (angular or tangential 

 changes), per cent 



Indefinite changes (S-shaped paths), per 

 cent 



No change in character of course, percent 



Number of observations 



(dark) 



Average 

 for all in- 

 'tensities 



■94 



37 



78 



126 



'55 



217 



431 



47 

 35 

 34 



28.5 

 23 



'•5 



316 



30 



27 



37 



32 



35 



B Non-Directive LicrJit 



O 



a Apparatus 



To test the eff'ect of purely non-directive light, it is of course 

 necessary to eliminate the possible influence of directive light. 

 This may be done by projecting the light upon the moving worms 

 in such a way that they are unable to go either toward or away 

 from the source of the light. Whatever effect is obtained under 

 such circumstances must be ascribed to the non-directive power 

 of hght. 



The elimination of the directive influence of light can be accom- 

 plished by means of various devices, (i) The light may be made 

 to fall vertically from above upon a horizontal field; (2) it may be 

 reflected vertically from below so as to pass through a transparent 

 field at right angles to the plane of the field; (3) methods i and 

 2 may be combined. The a'pparatus finally used in the majority 

 of experiments with non-directive light, was based upon the method 

 first mentioned. 



