334 The Data on which we have to depend 



and decomposition previously alluded to, of the sea water in 

 the interior of the crater. 



I have received from Dr. Davey, to whom I had previously 

 expressed my opinions on the foregoing subjects, a communi- 

 cation coroborative of the chemical theory which I have 

 advanced in the preceding pages. 



Akt. XX. — On What Data does the City of Melbourne 

 depend for an Adequate Supply of JVater from the Yan 

 Yean Reservoir, By Dayid E. Wilkie, Esq., M.D. 



Seyekal papers having been recently read before the Society 

 on the subject of the probable supply of water derivable 

 from Yan Yean, I think it of great importance now to inquire 

 upon what data we depend for obtaining this supply. 



I entertained the hope that the interesting questions treated 

 of in the papers above referred to would have induced some 

 of our scientific men to devote their attention to their eluci- 

 dation; and I confess that I am rather surprised that no one 

 seems disposed to Investigate those questions further, although 

 on a correct solution of them must depend all our hopes of 

 securing a sufficient supply of pure and wholesome water, 

 which would contribute so largely to our health and comfort, 

 and the failure of which would be so disastrous to the city. 



The question of evaporation, from its great importance in 

 relation to the subject of this paper, claims our first con- 

 sideration. 



Our meteorological expei'Ience in this colony is very limited, 

 and little is known with respect to the annual rainfall 

 in different localities. Judo-ino* from the tables that have 

 been kept in Melbourne for some years, there is reason to 

 believe that there is considerably less rainfall in Victoria than 

 in England. The geological features of the country are 

 unfavourable for the production of rivers, much of the rain 

 Avater being held on the surface, and lost by evaporation. 

 Our high temperature also conduces greatly to diminish the 

 proportion of the rain that would otherwise reach the rivers. 



Thus the physical conditions of the country are very un- 

 favourable for the preservation of water, and a great scarcity 

 prevails in many districts. Hence the importance of arriving 

 at a correct knowledge of the subject of evaporation, in order 

 that, in our endeavours to preserve water in parts of the 

 country that are ill-supplied, and to store it for the supply of 



