88 Transactions of the Kansas 



necessary to produce in the ball of known weight the observed deflections, and for 

 convenience made the following table : 



For deflection of 1 centimetre, force = .73 gramme. 

 " " " 2 '■ " 1.46 grammes. 



" 3 " " 2.19 



'• 4 " " 2.92 



******* 



" 60 •' " 43.80 



Having this table of pressures, the next question is to find the wind's velocity 

 corresponding to each of them. There are several empirical formulas, which might 

 be applied to the solution of a problem such as this, but one proposed by Welsbach 

 seems to be the most reliable. It is for the action of an unlimited stream, either of 

 water or air, and by giving suitable values to some of its factors it affords an easy 

 solution to the problem in hand. I do not know that it has ever before been applied 

 in this way, but I find the results obtained agree very closely with those derived 

 from a formula computed by Colonel James for the British Board of Trade. The 

 formula is this : 



2s: 



Fy, 



in which P is the pressure of the wind, z a term dependent on the shape of the 



v^ 

 body exposed to the wind, -^ the height due to the velocity v, F the exposed area^ 



y the density of the air. The value of z has been found from experiment to be 

 about 0.64, so transposing the equation to find the value of v^ we have, 



„» 2g P 



' ~ .64 Fy ' 



from which the numerical value of v can be easily found, as those of g, P, F and a 

 are known. It must be observed that the value of z varies with the barometric 

 height, making it necessary to read the barometer for each set of observations. It 

 is now easy to construct another table, as follows : 



For deflection of 1 cen., velocity = 3.9 m. per h. 



2 " " 5.51 " 



3 " " 6.74 '• 



4 " ■' 7.80 " 



ti: * :i: * iH :Jc * 



60 " " 30.2 " 



Finally these values are substituted in the columns of deflections observed, and a 

 mean obtained which represents the wind's velocity for the fifteen minutes of obser- 

 vation. 



After making a large number of experiments as above described, I learned these 

 facts regarding the anemometer at the Kansas University: First, that it never reg- 

 isters too much ; and second, that for small velocities it does not register enough. 

 This is due to the fact that a gentle wind, whose strength, however, is sufficient to 

 deflect the ball, will fail to move the cups sometimes for many minutes. 



The following figures will show results obtained by both methods. The first col- 

 umn contains the velocities determined by the deflected ball, and the second those 

 determined for the same time by the anemometer. 



5.6 m. per h. 

 10.5 

 11.68 

 13.5 

 13.7 

 14.7 

 15. 



per ti. 15. m. per h. 



14.88 

 16. 

 18.15 

 18.39 

 19 2 

 26.14 



