234 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. 
. 
Art. XX.—On What Data does the City of Melbourne 
depend for an Adequate Supply of Water from the Yan 
Yean Reservoir. By Davip KE. Wixi, Esq., M.D. 
SEVERAL 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 experience in this colony is very limited, 
and little is known with respect to the annual rainfall 
in different localities. Judging 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 
water 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 
