OBSERVATIONS ON THE FALL OF RAIN. 165 
water flowing from the ground bears to the rain 
which falls upon it. The extent of country from 
the surface of which the water would naturally 
drain to the reservoir may be easily ascertained, 
the depth of rain in a given time may be measured 
by gauges placed in different parts of the drain- 
age ground, and the quantity which is discharged 
from the reservoir, or which runs to waste in the 
same period, may, by proper observations, be 
correctly calculated. Here there is, in a given 
district, everything which is required, and by a 
sufficient number of observations, data will be 
obtained for forming a judgment upon the proba- 
ble result in a similar locality. 
Some of the more important observations, 
which, under such favourable circumstances, have 
of late years been made, we will now proceed to 
notice. 
During the construction of the Bann Reservoirs 
in the north of Ireland, attempts were made te 
Aa 
