120 THE AMERICAN MONTHLY [April 



feet will therefore be 9-16, and so on. At this rate of 

 decrease the intensity of light at a depth of ten feet will 

 be only about 5 per cent of that at the surface. 



The following experiments selected from the series 

 may be cited as a typical example of the results obtained: 



Cochituate water located in the Chestnut Hill Reser- 

 voir, April 29 to May 13, 1895. Temperature, 53°-62°. 

 Color, 0.58. 



Date. Depth. 



03 J:: 



On April 29, the bottles were filled with water from 

 the same source and suspended in the reservoir at the 

 depths indicated in the table. On that date the water 

 contained 319 diatoms per cc. After an exposure of two 

 weeks the bottles were drawn to the surface and the 

 water examined, with the result that the samples near 

 the surface showed an abundant growth, while those 

 which had been kept at a greater depth showed but a 

 slight increase. 



The temperature of all the samples was the same and 

 the only facts that varied were the intensity and quality 

 of the light. 



In order to better appreciate the relation between the 

 intensity of the light and the diatom growth we may 

 consider fig. 1. 



This diagram shows the relative diatom growths at 

 various depths and the corresponding intensity of light 



