Farms and Villages. 
49 
But small streams are very often subject to great variations 
in the volume of water they discharge ; it is necessary, there- 
fore, to ascertain the past history of the brook, and determine 
how many days in the year the water will fail altogether, or be 
very deficient. Frequently the features of the county allow 
half the scanty flow to be dammed back by means of a weir 
Figs. 4 and 5. — Section and Plan of a Poncdet Undershot Wheel. 
placed across the stream, and the water so impounded at night 
at a higher level may be used for pumping in the day ; but even 
that resource fails at times, and then the only alternative is to 
make the pumping machinery sufficiently powerful, and to pro- 
vide storage room sufficient to take advantage of the abundant 
flow of water during wet weather. 
VOL. XXIII. — S. S. E 
