20 



IOWA STUDIES IN NATURAL HISTORY 



of a column whose base is one square centimeter. Dm is 

 the distance in centimeters from the surface to the middle 

 of the stratum, and (1.000,000-D) is the loss of weight as 

 a decimal fraction of unity. 



In Okoboji lake the values are in the example taken 

 RT of 35 m.-40m.=1.6 cm. (table 5) 

 Dm=3750 cm. 

 (1-D) =0.000,348 



The result is 2.088 ; that is, the transport of the warmed 

 water from the surface to the 35m.-40 m. stratum calls for 

 2.088 gram-centimeters of work per square centimeter of 

 the lake. In this computation no account is taken of the 

 viscosity of the water as a hindrance to mixture. 



In this way the work needed by each stratum may be 

 computed. The value of RT-Dm would be computed once 

 for all for each stratum of the lake likely to be needed; it 

 is called in later tables the factor for that stratum. In gen- 

 eral we compute it by single meters to 20 m. and by 5 m. 

 intervals below that depth. The value of (1-D) is taken 

 from a table. (See Birge '16, p. 391). 



In this way is computed the value of the direct work as 

 shown by the following table : 



TABLE 13— OKOBOJI LAKE. DIRECT 

 WORK, JULY 30, 1919 



AND DISTRIBUTED 



Notes: 1. In Col. C, two ciphers 00 are omitted at the right of 



