For our Water Supply. 255 
This is a very important deduction from Mr. Hodgkinson’s 
premises, as it proves one of two things. If his evaporation 
is right, then the 3:26 inches must be supplied from a spring, 
or from some distant and higher level beyond the limits of the 
nine acres. If, on the other hand, the rainfall of the nine 
acres is the only source of supply, then the evaporation for 
our three hottest months cannot exceed 6:91 inches. Either 
alternative would be sufficiently embarassing. 
Dr. Davey has shown ‘that the temperature of our three 
summer months, during last season, exceeded the temperature 
of the corresponding months in London, according to the 
meteorological tables of the Royal Society, by 10° of Fahr., 
and also that our dryness exceeded that of London by two and 
one-fourth to one. From these data we are warranted, ac- 
cording to the tables of Dr. Dalton, to compute our evapora- 
tion at nearly three times the English evaporation ; but, if we 
are to trust Mr. Hodgkinson’s experiments in the pond, our 
evaporation will only exceed Dr. Dalton’s estimate for June 
by less than half an inch for each of the three months. And, 
if we further deduct one inch of dew, which Mr Hodgkinson 
has allowed for the three summer months, his estimate of the 
evaporation accurately deduced from his own premises, will 
almost exactly equal the English evaporation. ‘ 
The watershed of the nine acres for twelve months, cal- 
culated at fifteen per cent. of the rainfall, is equal to 27:76 
inches, which, added to the rainfall of 30-85 inches, gives four 
feet 10°61 inches, as the available supply for the pond, but 
Mr. Hodgkinson’s evaporation is five feet 6-6 inches. How is 
it then that the pond does not dry up? And how shall we 
account for a depth of ten feet of water in the summer 
months? It only receives four feet 10°61 inches, and it eva- 
porates five feet 6.6 inches, the difference amounting to 7-99 
inches. 
The conclusion is inevitable that the balance is made u 
from a spring, or some other source independent of the 
rainfall. : 
And, this being proved, who is to compute the amount of 
water thus supplied? or what confidence can be placed in an 
estimate of the evaporation based on such uncertain data? 
Thus, to determine the amount of this lateral supply is purely 
an impossibility, and to assume the amount is to beg the whole 
question. 
After the explanation given above respecting dew, it will 
be of no use to allege that the balance is made up in this way. 
If nine inches of dew are assumed to be condensed on the 
