Evaporation Results in Neio South Wales and South Africa. 13 



convinced that but little practical obstruction was opposed to the 

 escape of water after an eight years' deposit had accumulated. There 

 is, I should state, one exceptional point in respect to silt. The canal 

 which leads water from the Carnarvon Eiver into the dam has 

 practically refilled the excavations, made by the contractor, with the 

 heavy silt resulting from the first cutting of the gully now so notice- 

 able where the stream enters the reservoir. The water, having 

 reached hard rock, will not continue this action at so rapid a rate 

 in future. 



In further confirmation of the general correctness of the results of 

 my investigations I can only state that having given — (1) The depth 

 of water stored, (2) Assumed the nearly invariable rate of percolation, 

 (3) Deduced the variable but seasonable rate of evaporation for 

 different depths, I was able to determine how much land could be 

 cultivated during each season without, in any single instance, dis- 

 appointing the tenants under my charge as to their supply of water 

 for irrigation. 



I trust I have shown that I have established a reasonable dis- 

 tinction between losses from evaporation and percolation in this 

 one particular instance. I have now the humiliating suggestion to 

 make that my determinations are utterly worthless, except on the 

 spot where they were made, for the simple reason that no observa- 

 tions of a like nature have hitherto been publicly recorded within 

 this Colony. 



The Government Astronomer of New South Wales gives to his 

 Colony, not only the rates of evaporation from open tanks judiciously 

 placed, but he collates these rates with others deduced from obser- 

 vations taken on a natural lake untrammelled by artificial bounds, 

 and he raises his gift to almost royal proportions by giving the 

 records, in his fourth map, of the rise, fall, and duration of floods in 

 all the watercourses draining the drier districts of the country which 

 employs him. From these last records, and knowing the local rates 

 of evaporation, engineers can determine, within reasonable limits, 

 losses by percolation proper to any soil crossed by those particular 

 rivers. 



Evaporation, which is primarily a friend to man, becomes a foe, 

 but one that may be honestly met, in storage matters. Percolation, 

 in some soils, is a very fiend to encounter in like works, albeit a true 

 friend, left to itself, in the natural disposal of rainfall. 



I have touched to-night but very imperfectly upon one theme 

 only ; but there are other subjects demanding even closer attention. 

 What posterity may do for themselves does not intimately concern 

 us ; what they will say of us will be much the same as we may justly 



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