50 
On Water Supplies suited to 
For low falls, say 6 feet and under, and where the height to 
which the water has to be raised is more than fifteen times the 
fall, Poncelet Undershot Wheels are the simplest, cheapest, and 
most efficient. The wheels in question (Figs. 4 and 5) differ 
from ordinary wheels, in having the buckets or paddles rather 
deep in proportion to the diameter of the wheel, and curved in 
such a way that the thin stream of water entering at the bottom 
of the wheel runs up the blades a certain distance and then 
slides down again, in both operations imparting its energy to 
the wheel. In the form represented in the figures, the wheel is 
supported by a pair of cast-iron sides, united by a bottom piece, 
to which the proper form is given ; the thickness of the jet is 
regulated by a sliding-plate curved to the form of the wheel, 
and which can be adjusted so as to proportion the volume of 
water flowing into the wheel to the work to be done. One of 
the side plates carries a pair of pumps, which are actuated 
directly by a crank fixed on the axis of the wheel, the whole 
arrangement being thus self-contained. The wheels are usually 
placed in a vault, or sunk in a brick-lined pit by the side of the 
stream ; the water is led in and out by means of iron or earthen- 
ware pipes, and a regulating sluice is fixed and so arranged as 
to be opened by a turncock's key, without the necessity of 
entering the wheel-house. A valuable property of this kind of 
water-wheel is the comparatively high speed at which it runs ; 
that speed should be such that the periphery of the wheel moves 
half as fast as the jet of water which works it. Thus a wheel 
5 feet in diameter, worked by a fall of 1^ feet, would make 18 
revolutions per minute, and consequently moderate-sized pumps 
can be worked direct from the main shaft without the inter- 
vention of gearing. I have erected wheels of this kind success- 
fully, where the fall was as low as 3 inches — in fact, a mere 
rapid stream ; and in one interesting case, a chalk spring in the 
Essex marshes, having a fall of from 5 inches to 10 inches, 
works a Poncelet wheel 3 feet in diameter and 8^ inches wide, 
actuating a pair of pumps 1^-inch diameter and 5-inch stroke, 
raising ^ gallons of water per minute 80 feet high, to supply a 
large homestead and gentleman's residence. A large tank made 
of concrete stores the water pumped during the night for use in 
the daytime. 
The cost of these wheels and pumps ranges between 50/. and 
80Z. They require periodical oiling, and efficient strainers should 
be fitted to the intake so as to keep out weeds and rubbish. 
Water-wheels of all sizes, and more especially those made for 
low falls, are greatly hindered in their action by backwater, - 
that is, by the general rise in the level of a stream in consequence 
of floods, and as this l iso ficquently reaches an amount greater 
