244 



BULLETIN OF THE BTJREATJ OF FISHERIES 



1923. That these results are not valid, because of the varymg amounts of light 

 reflected, depending upon the position of the sun and brightness of the day, can be 

 seen easily by referring to Figure 37, which shows photographs of these glazed tUes, 

 taken in front of a south window in bright but diffused light (not direct sunlight). 



It will be noticed at once that, optically, there is little difference, under these 

 conditions, between the amount of light reflected from a white or a black surface, 

 as seen in Figure 37, A and B, and even red is optically almost as "Ught" as white 

 under these conditions. It is thus evident that any experiments based upon the 

 use of such tiles are of little value in judging the effect of relative light intensities. 

 Accordingly data from unglazed tiles only have been considered of value in these 

 experiments. 



REACTIONS OF THE CYPRID LARV^ OF BARNACLES TO SPECTRAL COLORS 



The reactions of the cyprid larvae of two types of barnacles that cause fouling 

 {Balanus ampMirite and B. improvisus) were tested by exposure to monochromatic 

 light of known intensity. Light filters were selected that possessed a narrow trans- 

 mission band and were of known composition and thickness. In Table 11 is given 

 a list of all the filters used, with the limits of fight transmissions and the dominant 

 wave length of each filter. A copper sulphate filter was used to cut out the infra- 

 red light waves. 



Table 11. — List of filters used in experiments on reactions of the cyprid larox of barnacles to spectral 

 colors, showing total spectral transmission and dominant wave lengths 



(The letter " C " after a alter denotes a Corning glass filter. The numbers after the Corning glasses refer to the transmission carves 

 shown in Bureau of Standards Technological Paper No. 148. The letter " W" denotes a Wratten filter, and the number refers 

 to the transmission curves found in the booklet " Wratten Filters," published by the Eastman Kodak Co.] 



In order to separate the effect of color from that of intensity it was necessary to 

 determiue the total amount of light energy transmitted by each filter. The calibra- 

 tion of these filters was very kindly done by the United States Bureau of Standards. 

 By use of this information the total light energy transmitted through one filter could 

 be balanced by that transmitted through any other filter by moving the source of 

 illumination. By using two beams of light at right angles to each other, and each 

 of equal intensity, the relative effects on large numbers of cyprids were determined 

 for all the filters. 



The results of these experiments are summarized in Figmre 38, which clearly 

 indicates a great difference in the stimulating efficiency of various spectral colors. 

 Jn the region of the spectrum between 500 and 600 mu-mu, or from light blue to 



