The right-hand expression in equation 14 is usually denoted by the 

 title "degree-days of frost;" A degree-day of frost la defined as a 

 day with a mean temperature 1-degree Centigrade below the freezing point 

 of sea water. While the freezing temperature of sea water varies with 

 salinity, it is here assumed to be -1.8°C. A degree-day of frost is 

 then 1 day with a mean temperature of -2.8°C. Degree-days of frost 

 usually are accumulated for forecasting over periods of 15 or 30 days* 

 By giving the following values to some of the terms in equation 14* 



* i - 0.9 



K = .080 



gm 



ki , .389 JfcCfii 

 1 cm °C day 



k - 062 K £ Cal > 

 k s ~ • ot " d cm °C day* 



the formula can be used directly to forecast the ice in terms of degree- 

 days of frost , 



f < V T)dt, 



T 



Thus, for a given value of l s all terms in the equation are known except 

 1^ and Qip. A given 1^ and likewise the corresponding Q T , can be selected 

 from the potential curve. By substituting 1^ and Q^ into equation (14) 

 and by evaluating the area under the potential curve between the proper 

 limits for the expression 



>Q (h) 



l[(Z)dQ T (Z) 







the number of degree-days of frost required to form 1. centimeters of ice 

 can be computed. 



To eliminate the necessity of computation, the end results of the 

 derivation have been presented in the form of tables (Tables 3-12). In 

 addition the integral 



-Q T (h) 

 f l[(Z)dQ T (Z) 



had to be evaluated by approximation methods. It was found from the majority 

 of potential curves that the integral could be approximated as 



H 



~2~ QT(n). 





