HYDROLOGY OF NEW YORK 



107 



the nations of the earth being fortunately agreed upon- their 

 measures of time, have settled upon one second of time as the 

 unit to use in measuring water. Nevertheless, thesjnillion United 

 States gallons in twenty-four hours has become a standard for 

 city water supply practice in the United States, and an acre in 

 area covered an inch or a foot deep in a month or in a year is 

 used in irrigation practice. But I would warn all engineers to 

 be very slow to add to the number of such standards of measure 

 for flowing water, and to abstain from and frown down such 

 absurd standards as cubic yards per day, or tons weight of water 

 per day, or even cubic feet per minute (instead of second), and 

 other incongruities. . . As exercises in the art of arithmetic 

 for children such computations may have value, but in the work 

 of civil engineers they become a stumbling block to an advance 

 of knowledge, and while unduly magnifying the unessentials, they 

 indicate a deplorable lack of appreciation of the essentials of the 

 art of the civil engineer. 



Cubic measures do well enough for the contents of vessels, or 

 as we may express it, for dealing with the science of hydrostatics. 

 But so soon as the water to be measured is in motion, or so soon 

 as the science of hydraulics has been entered upon, we must get 

 clearly in our minds the idea of rates of flow, or of a procession 

 of such cubic volumes passing a given point in a certain unit of 

 time, as of a flow of so many cubic feet per second. 



Very little can be added to what Mr Herschel has here said. 

 It is a clear exposition of the whole subject. Such units as cubic 

 feet per day and cubic miles have clearly no place in a modern 

 paper on hydrology. 



The unit of inches on the catchment area may, however, be 

 pointed out as an exception to the foregoing general rule. This 

 unit is exceedingly convenient because it admits of expressing 

 rainfall and runoff in the same unit and without reference to the 

 area. It brings out a number of relations not otherwise easily 

 shown, as will be exhibited in discussing the tables accompanying 

 this report. 



Characteristics of the minimum runoff. Since the rainfall varies 

 so widely, the runoff, which is a function of the rainfall, will also 

 vary widely. On the Hudson river the maximum runoff of 33.08 

 inches, with a rainfall of 53.87 inches, occurred in 1892. The 

 minimum, with a runoff of 17.46 inches and a rainfall of 36.37 

 inches, occurred in 1895. On the Genesee river the observed maxi- 



