186 



WILLIAM BRODBECK HERMS 



A series of incandescent lamps ranging from 4 to 100 cp. on 

 a 110-volt circuit were available and used as specified in the fol- 

 lowing experiments, as was also a Nernst double filament lamp 

 on the same voltage. A single filament Nernst lamp on a voltage 

 of 220 was used for the light grader mentioned farther on. A 

 200-cp. arc light and a low intensity apparatus described and fig- 

 ured by Adams ('03, p. 30) were utilized to secure the intensities 

 at the higher and lower extremes respectively. For reference and 

 to illustrate its use the low intensity apparatus is again figured 

 (fig. 1). Thus it was possible at any time to procure a light of 

 very high intensity or of very low intensity. The following list 

 of diaphragms were used with the low intensity box. 



TABLE 2 



List of diaphragms used with the low-intensity apparatus, together with the result- 

 ant intensities secured through reflected light from a 7.2 cp. incandescent light. 



The low intensity box B (fig. 1) was so constructed that when 

 closed, light from an outside source could not enter it. In order 

 to note the position of the larvae at the beginning and end of a 

 given period a system of squares (each 1 sq. cm.) was constructed 

 by means of fine white threads crossed from side to side on an 

 oblong frame (^,fig. 1.) The squares were lettered and numbered, 

 the lettering A to 7 being transverse to the light rays, and the num- 

 bering 1 to 11 being in the direction of the rays, with the highest 

 number nearest the light. The frame rested on small blocks, 

 one under each corner, to allow space for the creeping animals. 



