The author's object was to obtain an instrument which might register the changes of the wind in the absence of the observer. For this purpose he connected a vane with a vertical axis, at the lower end of which the horizontal revolution was changed to a vertical revolution by bevelled wheels; and the axis of the vertical wheel carried an index and pencil; which described on a vertical dial of slate, or of polished porcelain, all the changes experienced by the vane above. In this manner, however, the instrument registered the changes occurring during only one revolution of the vane. In order to obtain the registration of a greater variety of changes,—when the wind has blown all round the compass more than once, the following addition was made. “Each bevelled wheel containing 42 teeth, a pinion of 21 leaves was fitted to the axis of the vertical wheel, which pinion plays in the teeth of a smaller wheel with 42 teeth also provided with a pinion of 21 leaves. This last moves a second small wheel of 42 teeth, which again turns round the axis of the primary vertical wheel.