24 THE LIFE OF DEVILS LAKE 



In each experiment the time and weather conditions were noted 

 and one exposure made in aii- for comparison with those under 

 water. 



The results obtained with this apparatus, some of which are 

 illustrated in plate 6, show marked differences on different dates 

 dependent on the altitude of the sun and the turbidity of the water. 

 Many other factors enter in, such as condition of the air and of the 

 surface, but the first two are most important. 



Regarding the influence of the condition of the surface on the 

 readings, both Shelf ord and Gail (1. c.) and Anderson and Walker 

 (I.e.) agree that a large proportion of the light is cut off by a 

 rough surface and that this proportion may change very greatly 

 from time to time. I have not made a careful study of this point, 

 as most of my readings have been made in comparatively quiet 

 water. Two series of exposures to test it were, however, made on 

 October 10, 1923, between 2 :13 and 2 :24 p. m., one where the water 

 was almost calm, the other where the surface was rippled. They 

 show only a slight difference in surface penetration in nearly calm 

 and rippled water. 



The results show^ a much greater diminution of light in Devils 

 Lake than in Puget Sound (fide Shelf ord and Gail), about the 

 same as that in Seneca, Cayuga, and Canandaigua Lakes, N. Y. 

 (fide Birge and Juday 1921), but considerably less than that found 

 by Anderson and Walker in some of the Sandhill lakes in Nebraska. 

 Neither the first nor the last of these, however, have recorded the 

 turbidities at the time of observation, which makes impossible any 

 direct comparison of our results. Birge and Juday have recorded 

 the transparency in terms of the Secchi disk, their results showing 

 very clearly the influence of turbidity on transmission of solar ener- 

 gy- 



My own observation show fnrtlier a marked difference in per- 

 cent of transmission between July, August and November. This 

 agrees with the results of Anderson and Walker and is to be ex- 

 pected from the difference in altitude of the sun on those dates. 



A brief examination has also been made of the penetration 

 of red and blue, as compared with white light; using for this pur- 

 pose filters of red and blue glass, whose transmission has not been 

 tested speetroscopically, together with Cramer's "spectrum process" 

 and "iso" plates. The results indicate a lower penetration of blue, 

 and red, than of white light. 



Temperature records have been taken with all of the plancton 

 collections. In some eases the Negretti-Zambra thermometer ha.s 

 been used, but generally they have been taken on a chemical ther- 

 mometer. These have not been standardized and varied somewhat. 



