27S McAdie — New Units in Acro-2>fiysl('s. 



Abbreviations corresponding to others in the metric system 

 would be b, db, cb, mb. 



The new pressure base is found at a height of U)(i""" (y-tS 

 feet) above sea level, a level that is very convenient for many 

 reasons, which cannot be gone into here. 



The following short table may be found helpful in connec- 

 tion with the new system : 



7'o convert Pressure into Megadynes {C. G. S. Units). 



23 inches = "779 mgd. t -1 inch = -Ooa:] -01 = 



24 " r= -813 " j -2 " = -007 -02] 



25 " — -847 " I -3 " = -010 -03 )■ = -OOl 



26 " = -881 " i -4 " = -014 -04 j 



27 " = -914 •' i -5 " = -017 -05 "l 



28 " = -948 " i -6 " = -020 -06 )■ = "002 



29 " = -982 " : -7 " = -023 -07 J 



30 " = 1-016 " j -8 " = -026 -08/ _ 



31 " = 1-050 " 1 -9 " = 030 -09)" ~ '"^"^ 



Thus at Denver, elevation 5,291 feet, the mean barometer 

 reading is 24-708 inches. In the new unit this would be 

 •834 n'lgd. or 834,000 dynes. At New York, elevation 314 

 feet, the mean pressure is 29-695 inches, or 1,004,000 dynes. 

 Between the two stations, then, one readily perceives there is 

 a gradient of 170,000 dynes, or in round numbers 17 per cent. 



It will also be noted that the new system permits the widest 

 possible range and is entirely suitable for the needs of the 

 investigator at liigh levels, such for example as in the work 

 done during the past two years with ballon sondes, free bal- 

 loons and kites. Dr. W. JN^. Shaw, Director of the Meteoro- 

 logical Office, in a I'ecent paper* on the " Investigations of the 

 Upper Air" uses the new imit (see page 280) and rightly says : 

 " The reason for adopting this unit is that in the examination 

 of the results of the upper air, the actual number of inches or 

 millimeters in the pressure at any level is of little importance, 

 compared with the fraction of tiie atmosphere that is above or 

 below the level." 



It may not be generally known that recent observations have 

 brought out the fact that our atmosphere is practically in two 

 sections, a lower or troposphere and an upper or stratos])here. 

 Below 11 kilonjeters the atmosphere is in a disturbed condition, 

 convectional curi-ents are well marked, and cyclonic circulations 

 prevail. The decrease of temperature is nearly adiabatic, 

 although at times there are strongly marked inversions. In 

 the stratosphere tliere is a slight rise in temperature with iso- 



* The Free Atmosphere in the Region of the British Isles. M. 0. 202, 1909, 

 containing Report by W. N. Davis. See also Report by Gold and Harwood, 

 B. A. A. S. meeting at Winnepeg, 1909. 



