A LIMNOLOGICAL RECONNAISSANCE 17 



further use of so rough an estimate, but that the table may 

 not seem to imply that no heat whatever passes the 40.2 m. 

 level. 



For certain purposes it is necessary to state the amount 

 of heat at each level in terms of the area at the depth in 

 question rather than in those of the surface. The number 

 of calories, for instance, passing through each square centi- 

 meter of the lake at the depth of 10 m. is equal to the num- 

 ber of calories given in table 11 divided by the per cent of 

 the surface area which is found at 10 m., as is shown in 

 table 3. The following table gives the result: 



TABLE 12— CALORIES PER SQUARE CENTIMETER AT CER- 

 TAIN DEPTHS STATED IN TERMS 

 A-of the surface of the lake 

 B-of the area at the depth in question 



From tables 11 and 12 it appears that nearly one-half of 

 the heat-income remains in the upper five meters of the 

 lake; that more than half of the remainder is left between 

 5 m. and 10 m. ; that more than 90% is found above 15 m. ; 

 and that little more than 1% of the income is delivered into 

 the water which lies below 25 m. 



On the other hand, table 12, B shows that there is a very 

 considerable amount of heat delivered to each square centi- 

 meter of the several 5 m. planes of the lake. At the depth 

 of 30 m., for instance, there are found only 80 cal. per sq. 

 om., out of the 21,000 cal. which passed each sq. cm. of the 

 surface. Biit through each sq. cm. of the 30 m. plane there 

 passed 2460 cal. 



If that part of the lake below 30 m. be considered as a 

 lake by itself, its area (table 3) is 49.6 ha.; its volume 



