FINGER LAKES OP NEW YORK. 

 Tabi,b II.— Transmission op Sun's Energy per Meter op Depth. 



225 



[NOTB. — Per cent of the energy found at the upper surface of each i m. stratum which is present at the lower. surface' of such 



stratum.] 



Stratum in meters. 



o-i 

 1-2 

 2-3 

 3-4 



Trans- 

 mission, 

 percent. 



SI. 4 



70. 2 

 72.6 

 71. o 



Strattun in meters. 



4-S 

 5-6 

 6-7 

 7-8 



Trans- 

 mission, 

 percent. 



69.6 

 69. S 

 71. 1 

 67.8 



Stratum in meters. 



8-9.. 



^10. 



Trans- 

 mission, 

 percent, 



73. 2 

 7S-9 



Table n is given as it stands in order to bring out the various small variations in 

 percentage which are inherent in the observations. In all cases the fraction of a 

 division of the galvanometer scale must be estimated and is, therefore, subject to error. 

 The value taken as zero is not a fixed one and in any observation may be recorded 

 slightly too low, or more probably a little too high. The motion of the boat, due to 

 the swell, as stated above, might introduce some errors in this case, especially in the 

 readings from the upper water. In figure 2 the results are plotted and a smooth curve 

 a-a is drawn through them. All of the observations are very close to the ciu-ve. It 

 is plain that there was transmitted through each i m. stratum of water below the surface 

 meter about 71 per cent of the energy received at its upper surface. It is not probable 

 that the higher transmission indicated in the 9 to 10 m. stratum has any significance. 

 A reading of 2.1 divisions of the scale at 10 m. instead of 2.2 divisions would bring this 

 interval into Une imith the others. 



Lake water differs widely from pure water in the quantity of energy transmitted. 

 If we assume a solar energy curve corresponding to a path of the rays in the air of 1.5 

 atmosphere, with about 0.5 cm. condensable water in the atmosphere, about 47 per 

 cent of the solar energy wUl be left after passing through i m. of pure water. The water 

 of Seneca Lake, therefore, cuts ofif about 25 per cent more than does piu-e water and adds 

 one-half to the loss due to pure water. Pure water transmits through the i to 2 m. 

 stratum nearly 80 per cent of the energy reaching its upper level and over 90 per cent 

 passes through all deeper i m. strata, the loss per meter rapidly declining to a minimum 

 of about 2 per cent of the energy incident on the upper stuface of the stratum. At 

 5 m., therefore, there would remain about 29 per cent of the original energy of the sun 

 and about 23.4 per cent at 10 m. instead of 5.4 per cent and i per cent found in Seneca 

 Lake. This wide difference between pure water and the lake water is probably due 

 chiefly to matter suspended in the water of Seneca Lake, since there is very little stain 

 present in the water. The suspended matter is partly organic but chiefly fine silt 

 derived from the soft shales that constitute much of the shores. 



In pure water the transmission through the i to 2 m. stratum is much smaller than 

 in those below. This is due to the rapid absorption of the rays of the red end of the 

 spectrum as compared with the slow absorption of the shorter waves. No such effect 

 seems to be present in the lake, nor is it ordinarily demonstrable in lakes. Sometimes, 

 but not commonly, the deeper strata of a lake show a transmission i or 2 per cent higher 

 than the i to 2 m. stratum, but in general the transmission in that stratum is nearly 

 the same as in those immediately below. This means that the large nonselective ab- 

 46104°— 21 3 



