[Illustration: Fig. 86.] =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|Common designation| | | lbs. | 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. | +-----------------------------------+