2 20 THE POPULAR SCIENCE MONTHLY. 



ropean mills, and the other by the direct pressure of the wind against 

 a side-vane. In centrifugal mills the wind-wheel consists of a number 

 of radial arras firmly secured in a metal hub, with sections between 

 them pivoted so that they can swing into a position in which the ends 

 of the slats only are exposed to the wind. They are held in the 

 plane of the wheel by a counterweight, and thrown out of this posi- 

 tion by the action of a ball-governor. This governor may be placed 

 in various jjositions on the wheel, and act upon the movable section 

 directly or through the medium of connecting rods. In one form of 

 wheel the balls are placed upon the framing so that when the wheel is 

 at rest they hang down upon its face, but as it revolves fly out, and in 

 doing so turn the sectors. The angle at which the wheel-surface is 

 exposed to the wind is thus altered with every variation in its velocity, 

 and the motion of the wheel consequently kept nearly uniform, in a 

 manner similar to that of a steam-engine. When the wind attains a 

 velocity greater than a certain number of miles an hour, the action of 

 the governor keeps the slats in the position in which their ends are 

 alone exposed to the wind. The velocity at which the wheel will com- 

 pletely close can be regulated by the counterweight, which is movable 

 on its arm by means of appropriate connecting rods, from the base of 

 the tower. 



This method of regulation has been found to answer very well in 

 practice, but it has several grave objections. The construction is 

 necessarily such that there are a large number of joints on which the 

 wear is very considerable ; and with so many movable parts the lia- 

 bility to derangement is greatly increased. The failure of any of the 

 parts during a high wind would endanger the safety of the wheel, and 

 perhaps cause its destruction. The second form of mill, that using 

 the vane-governor, is much simpler in construction, has fewer parts, 

 and is consequently more durable. It is, therefore, to a considerable 

 extent supplanting the older form. The wheel in it is solid that is, 

 without movable sections and is turned about a vertical axis in such 

 a way that its angle with the direction of the wind varies with the 

 pressm-e of the latter. The devices by which this is accomplished vary 

 somewhat in different mills, but the method is essentially the same in 

 all. In one, a small vane, placed back of the wheel, is hinged upon 

 the frame of the large rudder- vane, and when the wheel is at rest hangs 

 vertically downward. It is connected by means of rods with the wheel 

 in such a way that, when the pressure on this exceeds a certain amount, 

 the vane will be raised toward an horizontal position. In so moving it 

 turns the wheel by suitable mechanism toward the rudder-vane, AYhen 

 the pressure of the wind is sufliciently great the small vane is raised 

 to an horizontal position and the wheel swings parallel with the rudder. 

 The whole apparatus, wheel and rudder, then becomes simply a weather- 

 vane, is exposed as little as possible to the wind, and is in the best 

 position to escape injury when this is very high. 



