LX. DISCUSSION. 



character to assuming that the 6 inches might have fallen in 12 

 hours instead of six, and that the rate of fall was one-half an 

 inch per hour ; but having decided the proportion of the total 

 rainfall which reaches the outlet, this should then be multiplied 

 by the half-inch rainfall, to obtain the actual maximum flow of 

 water in cubic feet per second per acre. The difficulty in this 

 method was the determination of the time the rainfall took to 

 run to the outlet from the extreme portions of the catchment ; but 

 having decided this, no reduction factor was necessary, excepting 

 the C in Mr. Chamier's formulae, which must include evaporation' 

 percolation, and all retentions of flow. It was obviously absurd 

 to divide the total rainfall by the time of flow from the remote 

 portions of the catchment, and use the value so obtained for R 

 in a formula of the Biirkli-Ziegler type. 



Mr. Merfield said he wished to add to the already long list 

 of formulae another, that might be of interest* : — 



= 440 RM/V. 

 The author of the formula says : " The full amount of the 

 rainfall per hour should be used in the formula, for areas of one 

 square mile and less." This he assumes to be one inch per hour, 

 but for larger areas he gives a table for the rainfall. He thought 

 that the formula of Mr. Chamier might well have been eliminated 

 from the author's list. Although it might to the uninitiated 

 appear to be new, it could be shown by a simple reduction 

 to be essentially identical in form with that of Prof. Kernot. 



The Author, in reply, said he could not agree with Mr. 

 Burge iu a general condemnation of all formulae, except when 

 they were of the type referred to, where the constant had so 

 much to represent ; it was, indeed, for this very reason that 

 formulae of the Biirkli-Ziegler type, when used intelligently, 

 became useful. Mr. Simpson was in error in calling the various 

 formulae referred to empirical ; as a matter of fact, these formulae 

 were rational, as they could be derived by the application of 

 known laws, and there was a total absence of experiment, which 



* 1. Jour. N.Z Inst. Surveyors, vol. III., pt. 8. The notation is altered to agree with 

 that used by Mr. Haycrofi. Y=vel. in miles per hour. 



