PINGER L.AKES OP NEW YORK. 



221 



DISTRIBUTED WORK. 



Table 4 deals' with the direct curve of work. It gives for each stratum the amount 

 of work necessary to convey the warmer and lighter water from the surface to the 

 depth in question, assuming that the lower water has a temperature of 4.0°- In warm- 

 ing all strata below that at the surface most of the work is performed in the strata 

 above that for the benefit of which the work is done. If the work for each stratum is thus 

 distributed to the several strata above it, we derive the curve of distributed work. (See 

 Birge, 1916, p. 355). This is shown for the mean of each lake in Table 6 and for Seneca 

 Lake in figure 3. The numbers for each stratum show how many gram centimeters 

 are necessary to distribute through the stratum the heat retained in it and to convey 

 through it the heat which goes on to lower strata. The table shows how shallow is 

 the stratum which receives most of the work of the wind. More than 94 per cent of 

 this work is expended in conveying the heat through the upper 20 m. of the lake. While 

 the effect of the wind extends to the bottom, even in Seneca Lake, the work done in 

 the deeper water is very small, as measured by the fall in density due to increased tem- 

 perature. In the upper 5 m. are found from 43 to 50 per cent of the work and in this 

 stratum the largest deductions from the apparent work are to be made for the influence 



of direct insolation. 



Table 6. — Distributed Work, Mean. 



■ (Note. — This shows work done in each stratum in distributing: the heat brought to it, and in carrying on to the next stratum the 

 heat which passes through it. This is computed only for the means of the lakes.] 



SUBTRACTION CURVES. 



Table 7 shows the data for the mean subtraction curves of the three lakes. (See 

 Birge, 1916, p. 384.) It shows the number of calories which pass through the several 

 levels of the lakes and the amount of work needed to distribute them through the water 

 below these levels. Comparison of the data at the surface shows that 12 to 14 cal. of 

 heat are distributed through the subjacent water by i g. cm. of work. At lower levels 

 the temperature declines and the decrease in density falls off even more rapidly with 

 the result that an increasingly large number of calories is distributed by i g. cm. of 

 work. At the depth of 10 m. the ratio is 25 to 30 cal. to i g. cm. ; at 20 m. the ratio 

 rises to 40:1 or 50:1; at 30 m. in Seneca Lake and at 40 m. in the others it has risen 

 nearly or quite to 100:1. This relation explains how in lakes of great depth a large 

 quantity of heat is carried in spring to the lower water. The great quantity of work 



