Section III, 1919 [81] Trans. R.S.C. 



The Correction Factor of the Canadian Standard Anemometer and the 



Most Probable Maximum Velocity and the Possible 



Extreme Velocity in Gusts 



By J. Patterson, M.A,, F.R.S.C, Physicist to the Meteoro- 

 logical Service of Canada 



(Read May Meeting, 1919.) 



The Canadian Standard Anemometer 



The wind, velocities at the Canadian Meteorological Stations 

 are obtained from a Robinson anemometer, with cups 4" in diameter 

 on arms 6 ■ 72" long, measured to the centre of the cups. The revolving 

 system is mounted on ball bearings, is made of aluminium and weighs 

 1 lb. 10 oz. The anemometer registers each mile of wind on an anemo- 

 graph and the gearing is cut so that the velocity of the wind is three 

 times the linear velocities of the cup centres. 



The Dines pressure tube anemometer (described later) is also used 

 to measure wind velocities and as its corrections can be accurately 

 determined it was used as a standard with which to compare the 

 Canadian anemometer, and thus determine the correction, if any, of 

 the latter. 



Historical Note 



The factor three which expresses the relationship between the 

 velocities of the cup centres and the wind velocity was obtained by 

 Dr. Robinson in 1846^ when he designed the cup anemometer, and is 

 still used by instrument makers, no matter what the diameter 

 of the cups or the length of the arms may be. The accuracy of the 

 factor was unquestioned until about 1875, when experiments pointed 

 to this factor being too high. During the succeeding 20 years many 

 experiments were carried out to determine the factor accurately, and to 

 improve the instruments for measuring the velocity of the wind. The 

 principal experimenters were Dines^ in England, Marvin^, in the 

 United States and Wild*, in Russia. Their experiments indicated that 

 the factor depended on the relationship of the diameter of the cups 



1 Robinson, Rev. T. R. Trans, of the Roy. Irish Academy, 1850. Vol. XXII, 

 p. 163. 



2 Dines, W. H. Quar. Jour. Roy. Met. Soc. Vols. XIV and XVI. 

 » Marvin, U.S. M.W.R. Feb. 1889 and Jan., 1890. 



^Wild, H. Zeitschrift der oester Gesell, fur Met. Band VIII, p. 282, 1873. 

 Bulletin de I'Acad, St. Petersburg. Vol. XXIII, p. 176, 1876. 



