WHOLE VOL. SEA-LEVEL PRESSURES 441 



of many nations. The time of observation was noon of the meridian 135 E. 

 Isobars were drawn for every 4 millimeters, and interpolated values were 

 estimated to the nearest whole millimeter. In no case were interpolations 

 made where isobars were not drawn or were not supported by ship reports. 

 . Since these daily maps were not available before 1923, a different method 

 had to be employed for the years 1921 and 1922. The Kobe Imperial 

 Observatory publishes a 5-degree square representation of data for these 

 years over the North Pacific Ocean. In order to get readings at the particu- 

 lar intersections desired, these 5-degree square monthly means were plotted 

 on appropriate maps, isobars were drawn from them, and subsequently the 

 desired values were interpolated from these equal pressure lines. 



In the Atlantic Ocean the data from July 1922 through 1930 at Lat. 

 50 N., Long. 30 W. were read at the British Meteorological Office in 

 London. The remainder of the data were read from the British, the Nor- 

 wegian, and the United States Weather Bureau maps of the North Atlantic 

 by Mr. Namias. The time of observation in the Atlantic was noon Green- 

 wich meridian. 



15 



