246 



Tlie Data on which we have to depend 



river is correct^ he only allows one-seventeenth part to remain^ 

 and abstracts all the rest for the reservoir. 



In this I feel persuaded that Mr. Hodgkinson has also 

 erred, and there can be no doubt that if the Commissioners 

 should ever attempt to carry out his recommendation they 

 would find themselves overwhelmed with legal actions, and 

 would be compelled to make very heavy compensation to all 

 those whose interests might be affected by the loss of the 

 river. 



In my estimate I allowed 900 gallons per minute, or one- 

 third of Mr. Blackburn's December measurement of the river 

 at Yan Yean, and an idea of the smallness of even this 

 amount may be got by reflecting on the circumstance, that, 

 during the drought of 1851, when the Plenty had very nearly 

 ceased to flow, Mr. Blackburn's measurement in February 

 gave 865 gallons per minute. 



I think, therefore, that it will be readily admitted that 

 at least six inches must be deducted from Mr. Hodgkinson*s 

 estimate on this account, and six inches will supply 

 13,656. 



3. I have stated that I have no confidence in theoretical 

 estimates, and this is the reason that I preferred my estimate, 

 that was based on measurement to that which I computed at 

 four and half inches of the rainfall, merely as an approxi- 

 mation from English data, hence I allowed the difference 

 amounting to one foot five and half a inches in the reservoir, 

 as a margin for casualties. 



In my preceding remarks it is, I think, clearly shown that 

 I was wrong in assuming four and a half inches, and that I 

 ought to have assumed four inches of available rain as the 

 best approximation that can be arrived at from the most 

 trustworthy English data. There is thus a difference of only 

 6*43 inches between the two estimates, and there can be no 

 objection to leave this small amount for casualties, and, there- 

 fore, it may be deducted from Mr. Hodgkihson's estimate; 

 but as he has allowed six inches for loss of flood water and 

 from adsorption, I shall regard the 6*43 inches as an equivalent 

 for his six inches. 



4. I come now to consider the subject of dew. I explained 

 in my former paper that very little dew could be condensed 

 on the surface of water, and I allowed two inches only because 

 it was my firm conviction that, even without drawing off any 

 water from the reservoir, there would often be very little in 

 it ; and when the Avater is very shallow, a small quantity of 

 dew may possibly be condensed on the surface in very cold 



