The Vane
Fig. 86.
The instrument by which the wind’s direction is most generally noted, is the vane, or weather-cock, and all that need be said of it here is that the points north, east, south and west, usually attached to it, should indicate the true and not the magnetic directions; and that care should be taken to prevent its setting fast. Very complicated instruments are r
123. Lind’s Anemometer, or Wind-Gauge (fig. 86), invented so late as 1775, for showing the pressure of the wind, consists of a glass syphon, the limbs parallel to each other, and each limb the same diameter. One end of the syphon is bent at right angles to the limb, so as to present a horizontal opening to the wind. A graduated scale, divided to inches and tenths, is attached to the syphon tube, reading either way from a zero point in the centre of the scale. The whole instrument is mounted on a spindle, surmounted by a vane, and is moved freely in any direction by the wind, always presenting the open end towards the quarter from which the wind blows. To use the instrument, it is simply filled up to the zero point with water, and then exposed to the wind; the difference in the level of the water gives the force of the wind in inches and tenths, by adding together the amount of depression in one limb, and elevation in the other, the sum of the two being the height of a column of water which the wind is capable of sustaining at that time.
Table,
Showing the Force of Wind on a square foot, for different heights of the column of Water in Lind’s Wind-Gauge.
| Inches. | Force in lbs. | Common designation of such Wind. |
| 6 | 31·75 | A Hurricane. |
| 5 | 26·04 | A violent Storm. |
| 4 | 20·83 | A great Storm. |
| 3 | 15·62 | A Storm. |
| 2 | 10·42 | A strong Wind. |
| 1 | 5·21 | A high Wind. |
| ·5 | 2·60 | A brisk Wind. |
| ·1 | ·52 | A fresh Breeze. |
| ·05 | ·26 | A gentle Breeze. |
| 0. | 0. | A Calm. |
124. Modification of Lind’s Gauge.—Sir W. Snow Harris has effected a modification of Lind’s anemometer, with a view of obtaining a hand instrument for use at sea more especially. At present the force of the wind is estimated at sea by an arbitrary scale, suggested by Sir F. Beaufort, the late hydrographer; 0 being calm, 12 the strongest hurricane, and the intermediate numerals giving the varying strength of the wind. There has been a long-felt want of instrumental means for obtaining this data at sea, if merely for the sake of checking occasionally personal estimations, which may vary considerably among different observers. Harris’s wind gauge is intended to be held by hand, while facing the wind, and keeping it in proper position by attending to a spirit-level attached. When in position, and held firmly, the tube has to be opened to the wind by pressure of the thumb acting upon jointed levers, controlled by springs. The pressure of the wind moves the enclosed liquid; and by withdrawing the thumb, the tube is closed so as to keep the liquid in its position; the reading is then taken from its scale, either in pounds on the square foot, miles per hour, or the ordinary designations of wind, as light, fresh, strong, &c.
Fig. 87.
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