[ 122 ] 



made curved with their concavity backwards, increased 

 efficiency will be obtained to that which is obtained from fldt 

 vanes. The race or channel should be short in the case of 

 all the wheels, though the tank or reservoir of water should 

 be as large as possible, that the current may be even and 

 uninterrupted. If the stream is constant a reservoir is not 

 required but a burnt clay-pipe on a masonry channel or 

 race, increases the efficiency of a wheel. When a water- 

 wheel is drowned i.e., when the tail is not sufficiently low to 

 allow the water to run off freely, its efficiency is reduced by 

 about one-fourth. The breast wheel should have buckets 

 instead of floats, that by means of the weight of the water 

 in the buckets the wheel may go down more readily, the 

 buckets discharging their contents while going down. Thus 

 constructed the breast-wheel may be of the same efficiency 

 as the overshot wheel which receives the impulse earlier. 

 But the bucket arrangement still further improves the 

 efficiency of the overshot wheel. Fig. 8 represents in section 

 an overshot wheel with the bucket arrangement. Fig. 9 repre- 



FIG. 8. THE OVERSHOT WATER-WHEEL. 



sents a breast-wheel with the ordinary kind of float, while 

 Fig. 10 represents an undershot wheel with curved floats. The 

 lower portion of the wheels should be encased in brickwork 



