CHAMBERS'S INFORMATION FOR THE PEOPLE. 



The force of the wind is measured by Anemom- 

 tters, of which some measure the velocity, by 

 the revolution of vanes, and 

 others the pressure. Of the 

 latter kind is Lind's Wind- 



fauge, represented in the 

 gure. When the instrument is 

 used, water is poured into the 

 tubes until the level in both 

 stands at the middle of the 

 scale. When no disturbing 

 force acts upon either column 

 of liquid, the level of both is 

 accurately the same ; but when 

 the mouth of the tube AB is 

 turned towards the wind, the 

 column in AB is pressed down- 

 wards, and that in CD rises 

 proportionably, and the differ- 

 ence of the heights of the two 

 columns gives the column of 

 water which the force of the 

 wind sustains, and from this 

 the pressure on a square foot is readily calculated. 



Dr Lind's 

 Anemometer. 



The following are a few velocities of wind, 

 translated into popular language : 7 miles an hour 

 is a gentle air ; 14 miles, a light breeze ; 21 miles, 

 a good steady breeze ; 40 miles, a gale ; 60 miles, 

 a heavy storm ; and 80 to 100 miles, a hurricane 

 sweeping everything before it We also add a few 

 comparisons of velocity and pressure : 5 miles an 

 hour is a pressure of 2 oz. on the square foot ; 10 

 miles, i Ib. ; 20 miles, 2 Ibs. ; 30 miles, 4^ Ibs. ; 40 

 miles, 8 Ibs. ; 51 miles, 13 Ibs. ; 60 miles, 18 Ibs. ; 

 70 miles, 24 Ibs. ; 80 miles, 32 Ibs. ; and 100 miles, 

 50 Ibs. During the storm in which the Tay 

 Bridge was destroyed (Dec. 1879), the rate of 

 velocity varied from 40 to 70 miles per hour, and 

 the maximum velocity during the heaviest gusts 

 was said to have reached 96 miles at Aberdeen. 

 Wind is most frequently measured by estimation. 



The estimate of the wind's force by the scale o 

 to 12, means that o represents a calm, and 12 a 

 hurricane. If such estimations be divided by 2, 

 and the quotient squared, the result will be the 

 pressure in pounds, approximately. 



Storms are violent commotions of the atmos- 

 phere, occurring in all climates, particularly in the 



tropics, and differing from other atmospheric dis- 

 turbances in the extent over which they spread 

 themselves, their- destructive power, and the sudden 

 changes which take place in the direction of the 



wind. Numerous attempts have been made to 

 reduce the phenomena of storms to general laws ; 

 but it is only quite recently that observations have 

 been sufficiently numerous and accurate to furnish 



