I9l(i] McEir< n: H i/driifp-aphic Obgcrvatioiis of Scripps liistitiil ion "279 



the surface, and e is the Naperian base, 2. TIM. The values computed 

 from this formula agree well with the results of photographic obser- 

 vations made in the Atlantic Ocean (Grien, 1913). Since dii-ect ob- 

 servations of the intensity of light have not been made in the water 

 of the San Diego region, the diagram (pi. 38, fig. 100) has been in- 

 cluded in this paper in order to give the best approximation possible 

 without direct measurement. It gives the average distribution of 

 relative light intensities with resi)eet to depth and the time of day, 

 and is based on the above formula and an empirical one representing 

 approximately the results of observations on the diurnal variation in 

 the intensity of solar radiation on a horizontal surface at sea-level, 

 between 20° N and 40° N. This formula is 



wt wt 



(2) / = 455 + 3S0 cos (- 105 cos — 



1 2 (i 



where / is the intensity at the depth of one meter, in arbitrary units, 

 and t is the time in hours measured from noon. Corresijonding to 

 these units formula (1) becomes 



(3) / = 1067e-""'-^:. 



In a later paper a detailed account of the unpublished investi- 

 gations referred to above will be presented. 



I wish to express my thanks to Mr. E. L. ilichael for his valuable 

 suggestions relative to the preparation of tlie manuscript. 



Transmitted February IS, 1916. 



SORIPPS IXSTITUTION FOR BIOLOGICAL RESE.\RCH OF THE UNIVERSITY OF CaLIFORXIA, 



La Jolla, Califorxia. 



