236 



The Data on which we have to depend 



In difficult scientific questions to whom are the public and 

 the Legislature to look, if not to the Philosophical Society ? 

 And shall it be said that they have looked to us in vain ? 



I am also induced on other grounds to bring this subject 

 before you. 



It will not be forgotten that Messrs. Acheson and Christy, 

 in their report on the Yan Yean Reservoir scheme, assumed 

 that 10-69 inches of the rainfall of the Plenty basin would 

 be available for the reservoir, while Mr. Hodgkinson clearly 

 showed, by a reference to Mr, Charnock and Mr. Howard, 

 who are the best recent authorities on the subject, that with 

 a rainfall varying from 24 to 36 inches, the available rainfall 

 for the average surface of England varies from 4*88 inches 

 to 5*33 inches, the mean of which is 5*20 inches, with a mean 

 rain of 30*6 inches. Thus these gentlemen have assumed 

 for the Plenty basin an available rainfall more than double 

 that of England. 



I had imagined, therefore, that Mr. Hodgkinson had 

 demonstrated the fallacy of " the excessively small rate of 

 evaporation assumed by those gentlemen," and that their 

 enormous estimate of the available rain was utterly at 

 variance with the recorded observations of all other meteor- 

 ologists." It appears, however, that they are by no means 

 convinced of their error, and that they congratulate them- 

 selves in the belief that they have arrived at the very same 

 result with Mr. Hodgkinson, only by a different method. 



When the pi^emises are so very opposite, it would be 

 singular indeed if the conclusions were the same. 



I cannot, therefore, understand how they have deceived 

 themselves into the belief that they have arrived at the same 

 results with Mr. Hodgkinson, unless after this singular 

 method. • 



They assume double the amount of available rainfall that 

 he does, and, at the same time, they rely on Dr. Davey's 

 estimate of the evaporation from the reservoir, which 

 is nine feet, while he rejects Dr. Davey's estimate of 

 the evaporation, and assumes five feet and a half fronj. 

 his own observations on a pond. But they altogether 

 forget that, while they generously leave 9,386 gallons per 

 minute for the use of the district, he only allows 500 gallons 

 per minute, or an equivalent to eight inches in the reservoir, 

 which is less than one-eighteenth part of what they allow ; 

 and they also forget that a mere coincidence in their results 

 proves nothing in their favour ; on the contrary, when similar 

 jresrults are obtained from data which are altogether dissimilar 



