WIND TABLES. XXIX 



the greatest definiteness of application is the duodecimal scale introduced into 

 the British navy by Admiral Beaufort about 1800. 



Table 39 is taken from the Observer's Handbook of the Meteorological 

 Office, London, edition of 191 7, and the Marine Observer's Handbook of 

 Meteorology, edition of 1930. The velocity equivalents in meters per second 

 and miles per hour are based on extensive observational data collected by 

 Dr. G. C. Simpson and first published by the Meteorological Office in 1906. 

 Several other sets of ecjuivalents have been published in different countries. 

 For a history of this subject see " Rept. loth Aleeting International Meteoro- 

 logical Committee," Rome, 1913, Appendix VII (London, 1914), and a paper 

 by G. C. Simpson on " The velocity equivalents of the Beaufort scale," Pro- 

 fessional Notes No. 44, Air Ministry, ^Meteorological Office, London, 1926. 



Simpson points out that the Beaufort scale has been used by sailors for 

 many generations to describe the effect of the air in motion on ships and their 

 rigging, and upon the sea. With change in the rig of ships there still remains 

 the effect of wind upon the surface of the sea, and to this has been added the 

 effect upon objects on land. 



Finally, it became desirable to interpret wind force on the Beaufort scale 

 in terms of wind velocity as measured by the anemometer. For this purpose 

 experiments with the anemometer both on land and on sea were made. The 

 results showed considerable discrepancies in the velocity equivalents of winds 

 indicated by different numbers on the Beaufort scale, but Simpson attributes 

 these discrepancies to differences in anemometer exposures during the tests. 

 For example, the Meteorological Office equivalents represent velocities mea- 

 sured by an anemometer not less than 10 meters above the ground level, while 

 the Deutsche Seewarte equivalents represent velocities measured by ane- 

 mometers as ordinarily exposed. 



Simpson proposed a scale of equivalents about midway between those 

 determined by the Meteorological Office and by the Seewarte, respectively, 

 and this compromise scale was adopted by the Commission for Synoptic 

 Weather Information of the International Meteorological Organization at 

 its meeting in Zurich in 1926, with the proviso that the velocity equivalents 

 correspond on land with the wind speed at a height of approximately 6 meters 

 above a level surface. Since, however, the International Commission for Air 

 Navigation has taken as the surface wind that measured at a height of 10 to 

 15 meters above the ground, it has seemed best in these tables to continue 

 to adhere to the British Meteorological Office equivalents, which are based 

 on the equation F = 0.836 V5^, where B is the Beaufort number representing 

 the wind force, and V is the velocity equivalent in meters per second. 



The velocity equivalents adopted by the Commission for Synoptic Weather 

 Information, referred to above, expressed in statute miles per hour, correspond 

 very closely to the values in Table 39 expressed in nautical miles (knots) per 

 hour. 



