150 Failure of the Van Yean Reservoir. 



stream of the Plenty is not confined within its ordinary banks, 

 but for eight months of the year is widely extended over 

 their level sm'facc; a condition of things which was never 

 witnessed by any of the settlers or residents on the river with 

 whom I have conversed. 



How much better would it have been for the Committee of 

 a Philosophical Society to have disregarded theory altogether, 

 and to have rigidly adhered to their own measurements, as 

 well as those of Mr. Blackburn and Mr. Hodgkinson, and to 

 have made these the basis of their calculations. 



Theory, based upon experiments conducted in this colony, 

 would possess a scientific interest and value, but otherwise it 

 is practically valueless. 



Speculative philosophers, who embark in abstruse scientific 

 investigations with incorrect or inapplicable data for their 

 guide, will soon find themselves lost in a pathless ocean, Avith- 

 out a compass and without a chart. 



Dr. Prout, one of the ablest writers on Meteorology, thus 

 expresses himself with reference to the different estimates 

 that have been made of the watershed of England: — 



These statements of the water that is condensed and evaporated in 

 Great J^ritain, can only be viewed as rude approximations; and even 

 admitting them to be correct, they could scarcely be applied with any 

 advantage to an inquiry into the actual condensation and evaporation in 

 other countries or climates, which in all instances must be determined 

 by observation and experiment. 



Before taking leave of Mr. Dempsey, I wish to state my 

 entire concurrence in the liberal views he expresses with 

 reference to the amount of water required for a city of 

 100,000 inhabitants. 



Although, he says, twenty gallons per head might be suffi- 

 cient for domestic and manufacturing purposes, and for the 

 extinction of fires, yet he advocates a constant service of 

 thirty gallons per head, and is of opinion that extravagance 

 in water should always be permitted; and for the purpose of 

 cleansing and watering the streets and thoroughfares, for the 

 supply of fountains, public gardens, and pleasure grounds, 

 and other miscellaneous and occasional purposes, he considers 

 that one-tenth of an inch per day, should be allowed for the 

 whole area. Part of this is supplied from rain, so that for a 

 city covering one thousand acres, he allows fifteen gallons per 

 head additional, making in all forty-five gallons, and if he 

 were consulted about the proper supply for Melbourne, he 



