98 



NEGEETTI AND ZAMBRA, HOLBOEN VIADUCT, E.C., 



Negretti and Zambra think this Anemometer will meet a want often 

 expressed to them, viz., a simple self-acting Wind-gauge ; for with very little 

 more mechanical combination than a common direction vane, the Pendulum 

 Anemometer will give sufficiently accurate results for unscientific observers. 

 It has also the advantages of extreme simplicity, for beyond a little oil to the 

 moving parts and an occasional coat of paint for protection, it does not require 

 the least attention. Price, fig. 108, 660 



The simplest mode of mounting this Anemometer is to fib it on the top of 

 a flag-staff or mast 30 to 40 feet high, well sunk in the ground, strengthened 

 and supported by three or four wire rope stays, attached to small sunk posts in 

 the earth ; these wire ropes might be used as Lightning Conductors. Arms 

 with the letters N. E. S. and W. to show the direction of the wind as on fig. A 

 page 96 can be placed on the mast below the Anemometer. 



138. Lind's Anemometer or Wind 

 Gauge (fig. 109), invented in the year 1775, 

 for observing the pressure of the wind, con- 

 sists of a glass syphon, the tubes are parallel 

 to- each other, and each tube is of the same 

 diameter. One end of the syphon is bent at 

 right angles to the general direction of the 

 tubes, so as to present a horizontal opening 

 to the action of 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 of the tube 

 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 



FIG. 109. 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. At the base of 

 the instrument is a brass plate, upon which are engraved the principal points 

 of the compass, for indicating the direction of the wind. Price, 220 



The bend of the syphon is contracted internally to diminish the jumping 

 movement of the water produced by sudden gusts of wind. 



