POWER or l4-rx WINDMILL IN VARYING WINDS.

Velocity of Wind (miles per hour).

0--5 6-10 11-15 16-20 21-25 26-30 31-35


It will be apparent from the foregoing figures that practically
the whole of the pumping for a small sewerage works may be done
by means of a windmill, but it is undesirable to rely entirely
upon such a system, even if two mills are erected so that the
plant will be in duplicate, because there is always the
possibility, although it may be remote, of a lengthened period
of calm, when the sewage would accumulate; and, further, the
Local Government Board would not approve the scheme unless it
included an engine, driven by gas, oil, or other mechanical
power, for emergencies. In the case of water supply the
difficulty may be overcome by providing large storage capacity,
but this cannot be done for sewage without creating an
intolerable nuisance. In the latter case the storage should not
be less than twelve hours dry weather flow, nor more than
twenty-four. With a well-designed mill, as has already been
indicated, the wind will, for the greater part of the year, be
sufficient to lift the whole of the sewage and storm-water,
but, if it is allowed to do so, the standby engine will
deteriorate for want of use to such an extent that when
urgently needed it will not be effective. It is, therefore,
desirable that the attendant should run the engine at least
once in every three days to keep it in working order. If it can
be conveniently arranged, it is a good plan for the attendant