In laying the results of these observations before the Society, it was thought necessary to make a few remarks in explanation of the manner in which they were made.

The instrument consists of a fixed japanned cylinder, on which the points of the compass are marked, and a moveable portion, which revolves freely round the cylinder as the wind changes; the circular disk of a fly kept opposite to the wind by a weathercock vane, is made to revolve with a velocity proportional to that of the wind. The motion thus produced is diminished by means of endless screws, working in a pair of toothed-wheels, and carried down to a pencil, which, in its descent, rubs on the surface of the cylinder, and traces a broad line, whose length is proportional to the velocity of the wind, and the time during which it blows from any one direction taken jointly. The compartment of the cylinder on which the marks are made indicates the direction of the wind.