Windmill

(wind'mil.) (Mach.) A machine erected in elevated positions, and provided with vanes or sails, which are so placed as to be turned by the wind. In order that the wind may regulate the position of the mill, a vane is placed on the side which is opposite the sails, and by a simple mechanism turns them always to the wind. When the mill is not too large, it is either turned round on a vertical axis, with a lever, or the roof alone with the axle and wings is moved. In the former case it is called a German mill, in the latter a Dutch mill. On account of the inconstant nature of the wind, it is nece ary to have some provision for accommodating the resistance of the sails to the degree of violence with which the wind blows. This is generally done by clothing and un clothing them; that is, by covering with canvas or thin boards, a greater or smaller portion of the frame of the sails, according to the force of the wind at different times. A method has been devised for producing the same effect, by altering the obliquity of the sails; and windmills have been so made as to regulate their own adjustment. An horizontal arrangement of the sails has been frequently tried, but it has never been found to answer. The moving force being very irregular and entirely interrupted in calm weather, windmills are applicable only in particular cases; they are used in Holland very advantageously for drainage. The angle which the sails should make with the plane of the arms has been the subject of much investigation. [s. 963]