54 Herbert Eugene Walter 



fined the upward rays to reflections within the hood itself, at the 

 same time permitting the escape of heated air. On a table directly 

 under the suspended light lay a horizontal sheet of plate glass 

 (F,) affixed to the upper surface of which was a circular ring 

 (G) made of a mixture of paraffine and lampblack. There was 

 thus formed a circular water-tight aquarium twenty centimeters 

 in diameter and two centimeters deep, in which the worms could 

 be observed. On the top of this circular ring rested a black dia- 

 phragm (i/),the aperture of which was sufficiently small to exclude 

 any side reflections which might come from the black paraffine 

 wall. 



The aquarium, it must be explained, did not rest directly on the 

 table but was mounted as the cover of a box (/), the interior of 

 which had been rendered largely free from reflecting surfaces by 

 the use of black camera-paint. One side of the box was removed 

 and, facing the opening thus made, a mirror (K) was placed at an 

 inclination of 45 with the horizon. The end of a square tun- 

 nel (L), ten feet long and made of black cloth stretched upon a 

 framework of wood, fitted close up to this opening. Suspended 

 from the lower edge of the hood and surrounding the aquarium 

 were adjustable black draperies (M) designed to shut out possible 

 side light and at the same time to allow a hole for the eye of the 

 observer. It will be seen that all light reaching the aquarium 

 comes from the lamp above by passing through the heat screen. 



After illuminating the field of observation the light passes 

 through the glass floor of the aquarium and is reflected by the 

 mirror into the black tunnel. Most of the light is absorbed in the 

 tunnel, only an insignificant minimum being reflected back to the 

 aquarium floor. Otherwise complications in the character and 

 intensity of the light might arise. 



By moving the hood (B) up and down and by using lamps of 

 different candle powers a variety of intensities was obtained. The 

 lamps used were tested by means of a Lummer-Brodhun pho- 

 tometer, the loss by reflection from the surface of the water both at 

 the heat screen and at the aquarium being reckoned out in deter- 

 mining the different intensities employed. 



By simple observation, data for such criteria of behavior as 



