EXCESSIVE RAINS 41 



both cases rectangular hyperbolas. After drawing the two 

 curves their equations were determined to be 



y= 



for the curve of rare occurrence, and 



105 



y= 



for the rains of frequent occurrence, where y is the rate of rain- 

 fall in inches per hour, and x is the duration of the storm in 

 minutes. The two curves give the following comparisons, 

 which Prof. Talbot says are found to hold pretty generally 

 throughout the country in spite of great differences in the total 

 annual rainfall. 



10 minutes' duration, 9.0 or 4.2 inches rate 

 20 " " 7.2 or 3.0 



30 " " 6.0 or 2.3 



45 " " 4.8 or 1.7 



60 " " 4.0 or i. 4 



In checking his two curves it was noted that they were 

 drawn so that the rainfall shown by the upper curve of max- 

 imum rain would be exceeded once in 83, 107, 100, and 91 years 

 for the North Atlantic, South Atlantic, Gulf, and North Central 

 States, respectively; and that the other curve would be exceeded 

 once in 3.6, 3.1, 3.8, and 3.7 years for the same group of States, 

 respectively. 



In commenting on the individual city records, Prof. Talbot 

 says: " In summarizing the data of seventy-one years of rain- 

 fall of self-recording gages shown on these diagrams, it may be 

 noted that the curve of rare rainfall has not been reached in a 

 single instance, and that the curve of ordinary maximum rate 

 of rainfall for periods of less than forty minutes has not, with 



