a machine that shows either the course or velocity of the wind. (See also the article Wind-Gauge.)

The machine which shows the course of the wind, or from what point of the compass it blows, consists of an index moving about an upright circular plate, like the dial of a clock, on which the 32 points of the compass are drawn instead of the hours. The index, which points to the divisions on the dial, is turned by a horizontal axis, having a trundle-head at its external extremity. This trundle-head is moved by a cog-wheel on a perpendicular axis; on the top of which a vane is fixed, that moves with the course of the wind, and puts the whole machine in motion. The whole contrivance is extremely simple; and nothing required in the construction, but that the number of cogs in the wheel, and rounds in the trundle-head, be equal; because it is necessary, that, when the vane moves entirely round, the index of the dial also make a complete revolution.—An anemoscope of this kind is placed in one of the turrets of the queen's palace. The anemoscope, calculated for indicating the force or velocity of the wind is the same with what most writers call an anemometer; and we have accordingly described one of those machines under that article. We shall here add another, contrived by the late Mr. Pickering, and published in the Philosophical Transactions, No. 473. This anemoscope is a machine four feet and a quarter high, consisting of a broad and weighty pedestal, a pillar fastened into it, and an iron axis of about half an inch diameter fastened into the pillar. Upon this axis turns a wooden tube; at the top of which is placed a vane, of the same materials, 21 inches long, consisting of a quadrant, graduated, and fitted with an iron rim, notched to each degree; and a counterpoise of wood, as in the figure, on the other. Through the centre of the quadrant runs an iron pin, upon which are fastened two small round pieces of wood, which serve as moveable radii to describe the degrees upon the quadrant, and as handles to a vellum or sail, whose pane is one foot square, made of canvas, stretched upon four battens, and painted. On the upper batten, next to the shod rim of the quadrant, is a small spring which catches at every notch corresponding to each degree, as the wind shall, by pressing against the sail, raise it up; and prevents the falling back of the sail, upon lessening of the force of the wind. At the bottom of the wooden tube, is an iron index, which moves round a circular piece of wood fastened to the top of the pillar on the pedestal, on which are described the 32 points of the compasses. The figure of this machine is given on Plate XXXIII. fig. 3, where a is the pedestal; b, the pillar on which the iron axis is fitted; c, the circle of wood, on which are described the 32 points of the compasses; e, the wooden tube upon its axis; f, the vellum; g, the graduated quadrant; h, the counterpoise of the vane. The adjoining figure represents the vellum, which takes off: a is the plane of the vellum; b, the spring; cc, the wooden radii; dd, the holes through which the pin in the centre of the quadrant goes. Its uses are the following.

1. Having a circular motion round the iron axis, and being furnished with a vane at top, and index at the bottom, when once you have fixed the artificial cardinal points, described on the round piece of wood on the pillar, to the same quarters of the heavens, it gives a faithful account of that quarter from which the wind blows. 2. By having a vellum or sail elevated by the wind along the arch of the quadrant to a height proportionable to the power of the column of wind pressing against it, the relative force of the wind, and its comparative power, at any two times of examination, may be accurately taken. 3. By having a spring fitted to the notches of the iron with which the quadrant is shod, the vellum is prevented from returning back upon the fall of the wind; and the machine gives the force to the highest blast, since the last time of examination, without the trouble of watching it.

The ingenious contriver of this machine tells us, that he carefully examined what dependence may be had upon it, during the storms of February 1743-4, and found that it answered exceedingly well; for that, in such winds as the sailors call violent storms, the machine had six degrees to spare for a more violent gust, before it comes to a horizontal position. It is certainly tainly to be depended upon in ordinary weather, the velum being hung so tenderly as to feel the most gentle breeze. There is however reason to fear, that the exposing the anemoscope to all winds for a continuance, must disorder it, especially irregular blasts and squalls. It may not therefore be amiss, in violent weather, for the observer to take the tube with its vane and velum in his hand, in order to know the force of the wind; and when he has finished his observations, to carry the machine into the house, till the violence of the storm is abated, when it may be placed in its former situation.