XXXVIII. J. I. HAYCROFT. 



exist in very large areas, when it is remembered that the slope, the 

 absorbent nature of the ground, and the intensity of the rainfall, 

 vary considerably, even in the radius of a few miles. Even in 

 small areas the maximum rainfall, which is here being considered, 

 is what may be termed " patchy," and, although the slope is ever 

 varying, still its value may be approximated to within reasonable 

 limits, by suitable observations, but certainly not by independent 

 aneroid observations, a method which the author has known to 

 be employed. On examination of the formulae, it will be seen that 

 nine of them are supposed to give a means of determining the 

 number of cubic feet per second discharged from a catchment 

 area, in terms of that area, its length in some cases, and length 

 and breadth in others, combined with various constants, but no 

 account is taken of amount of rainfall, nor of the varying slope of 

 different catchments, so that, according to these formulae, the 

 same volume of water would have to be provided for, whether 

 the ground was flat or hilly, or whether the rainfall was at the 

 rate of one inch per hour, or twelve inches per hour. It is 

 hardly necessary to state that such formulae cannot possibly be 

 reliable. On the other hand, it would not be just to say that 

 therefore these formulae are of no use ; on the contrary, it is 

 probable they are applicable to conditions identical with 

 those whence they were derived. As, however, none of them 

 have been designed for use in these colonies, they cannot be 

 considered applicable to local conditions. 



Six other formulae give the area of opening required in square 

 feet, in terms of a constant, and the area of the catchment. 

 These also may be considered as of a specific nature, and not 

 adapted to general use, with the exception of that of Professor 

 Kernot, which has been shown to be applicable in portions of 

 these colonies. 



Five other formulae give the discharge of the catchment in 

 cubic feet per second, in terms of a suitable constant, determined 

 by the nature of the surface of the catchment, the rainfall of the 

 district, and the slope and area of the catchment, thus embracing 

 all factors necessary to make them generally applicable. 



