OBSERVATIONS ON THE FALL OF RAIN. 163 
Perhaps the most serious difficulties which have 
hitherto existed, consist in the extensive scale on 
which the observations should be made to be of 
any real value, and the accuracy required in as- 
certaining the quantity of water actually dis- 
charged from a certain extent of country. The 
measurement of a single flood may be omitted, 
and yet that flood may send down as much water 
in one day as would pass off in two months of 
ordinary weather. 
Of late years works have been constructed in 
some parts of the country, by using which as a 
means of observation, these difficulties have been 
to a great extent removed. 
The demand for moving power consequent on 
the great extension of our manufactures, very 
early led to the application for that purpose of 
every important stream in the manufacturing dis- 
tricts. As improvements in the face of the 
country and in agriculture kept pace with com- 
mercial prosperity, the former general regularity 
of the rivers was found to be considerably dis- 
turbed by the effects produced by the making of 
roads and the better draining and cultivation of 
the land. The drains and roads form so many 
