226 



BULI^ETIN OP THE BUREAU OF FISHERIES. 



sorption due to turbidity and the selective absorption due to stain obscure the selective 

 absotption of the water, as water, after the first meter has been passed. In that meter 

 of water is absorbed practically all of the energy contained in that part of the spectrum 



Per cent e 



Fio. 2. — Curves of transmission of sun's radiation, Seneca I^ake, Aug. i, 1918. The vertical ajtis gives depth and the horizontal 

 asisgivespercent of the total radiation of the sun. ^-^4, direct observations; B-B, vertical sun; C-C,ineansun. Thesun's 

 rays passed thixjugh a thickness of 100 cm. water of the lake at the depth of 94 cm. Dots are placed corresponding to this depth 

 on the ctuve A-A , and from these is plotted the curve B-B, for the sun in the zenith when depth and stratum traversed by 

 rays are equal. 'The rays pass through a mean distance of 115 cm. during the warming season in reaching a depth of 100 cm. 

 These points are marked on the curve B~B, and from them is plotted the curve C-C or the curve of mean sun. (See Table 

 12, p. 228.) 



lying below the A line which is commonly taken as the lower limit of the visible spec- 

 trum. 



The general result of these observations is, therefore, plain. Under the conditions 

 of the time and place 21 to 22 per cent of the sun's energy delivered to the surface was 



