MATHEMATICAL FORMULAE 85 



adds that the improvement over the Burkli-Zeigler formula 

 lies in the fact that the latter, based as it is on observations 

 of small areas, is inapplicable to districts containing 1000 acres 

 or more, while the St. Louis coefficients make the formula good 

 to 10,000 acres. 



In a report to the city of Baltimore by the Sewerage Com- 

 mission (1897) is a report by Rudolph Hering and Samuel M. 

 Gray, Consulting Engineers. The four formulae given above are 

 discussed therein, together with a fifth deduced from diagrams 

 prepared for the Department of Public Works of New York 

 in 1889. This discussion is as follows (the formulae are here 

 repeated for convenience) : 



Hawksley: Q = c-A*r*s*\ for r = i, ^ = 3.95. 



Adams: Q = c-A*r*s^\ for r = i, cr = 1.03. 



Burkli-Zeigler : Q = c - rA M . 



for r = 2.75, cr = n.6i for built-up areas; 



cr= 9.59 for average city areas; 



^ = 4.79 for rural areas. 

 McMath: Q = cr-sAt; 



for r = 2.75, cr = 8.2i for built-up areas; 



cr = 3-39 f r suburban areas. 

 N. Y. diagrams : Q = cr A - 8 V 27 ; 



cr = 10.59 f r completely built-up areas; 



cr = 8.97 for well-built-up areas; 



cr = 6.59 for suburban areas. 



Rainfall. Assuming all the factors except the run-off and 

 the rainfall to remain constant, the formulae become: 



Hawskley: Q = const. X r 75 . 



Adams: Q = const. X r 83 . 



Biirkli-Ziegler: Q = const. X r. 

 McMath: Q = const. X r 



< = const. X r. 



Hering and Gray say: " There is hardly a question that, 



