PUMPING WATERS. 97 



80. Erected directly over the well in which is placed 

 the pump, the fan is supported on a light steel angle- 

 iron frame, and to which access is gained by a light 

 ladder. The pump is driven direct without gearing, 

 and generally works at about 60 r.p.m., but the driving 

 rod is not driven off the main shaft but usually from 

 a counter shaft, which is driven by gear wheels from 

 the main of a ratio of about 2-J- to i. The up-and- 

 down motion of the rod is then produced by an ordin^ 

 ary crank. The main shaft is not in the centre line 

 but some few inches away from it. The tail vane, 

 however, w r hich serves to keep the fan " head on " to 

 the wind, is exactly in the centre. This arrangement 

 controls the working of the mill in very high winds, 

 because the fan, by reason of its being not in the same 

 straight line as the tail vane, will tend to turn away 

 from the wind. In ordinary weather the tail vane 

 will counteract this through the medium of levers and 

 springs which are connected with the head of the 

 machine ; high winds, however, overcome the resist- 

 ance of these springs in proportion to their intensity, 

 and by turning the wheel to one side the speed is 

 reduced. Another means by which windmills are 

 governed is a side vane, which projects on the plane 

 of rotation of the wheel. The wind pressure on this 

 always has a tendency to turn the wheel edgeways to 

 the wind, this force being counteracted by a weight 

 which, however, is overcome by any abnormally 

 strong wind. 



Some mills have centrifugal governors. The 

 blades of the mill are connected in sets of about six 

 and fixed to a bar at the middle of their lengths. 

 A rotating action to this bar closes up the blades, 



7 



