MANCHESTER, FROM 1786 To 1857 1ncLusIve. 165 
there will doubtless be some years among the series in 
which it will be above the average. A reference to the 
chart will show the variation of the series very clearly, 
and by reference to the tables the following remarkable 
differences will be found. From 1795 to 1814 inclusive 
the mean of 20 years is 33°044 inches; from 1815 to 
1836 inclusive the mean of 22 years is 38161; from 
1837 to 1852 inclusive the mean of 16 years is 36°328 ; 
while from 1853 to 1857 inclusive the mean of 5 years 
is only 31-371; showing the correctness of Dr. Dalton’s 
remarks as to the importance of a long continued series of 
observations to obtain a satisfactory table of the mean 
quantity either for each month or the whole year. 
