

PREFACE 



This collection of data is published in response to the need expressed 

 by the resolution passed b}^ the International Meteorological Con- 

 ference in session at Utrecht in September 1923. 



Most of the weather services of the world responded promptly to 

 the request for data and filled in and averaged the data on the forms 

 sent them, except in central Europe, where the outbreak of war inter- 

 fered. For most of the countries of Europe, however, it was possible 

 to extract the data in part up to 1937 from official publications in the 

 library of Harvard University and of the Blue Hill Observatory. We 

 are also indebted to Irving I. Schell for collecting and supplying some 

 of the missing data. 



The preparation of pressure data read from the international weather 

 maps at 10° intersections of the lines of latitude and longitude in the 

 Northern Hemisphere was undertaken for this publication by Jean A. 

 Gallenne and was near completion between the latitudes of 20° and 70°, 

 when the United States Weather Bureau began the preparation of re- 

 vised Northern Hemisphere weather maps from which the pressure 

 was read at 10° intersections for each day between 10° N. and 90° N. 

 and averaged by months. The Chief of the Weather Bureau has kindly 

 allowed us to publish these monthly means in place of those prepared 

 for us by Mr. Gallenne. However, the means for 10° N. and for 

 80° and 90° N. were derived from extrapolated isobars and hence can 

 be regarded as only an approximation of the true values. Moreover, 

 for these latitudes many days were missing, and for them no reliable 

 estimates could be made. 



In the additional data, the rainfall for the Caribbean area was fur- 

 nished by the United Fruit Company. 



The heights of the Rio de la Plata at Rosario were supplied by the 

 Direccion General de Meteorologia, Geofisica e Hidrologia, in Buenos 

 Aires. 



The heights of lakes in Africa, Bolivia, and the United States, and 

 the heights of the Nile River, were supplied by Sydney M. Wood, 

 C. E., who obtained them from official sources. 



As heretofore, meteorology is indebted to John A. Roebling for 

 providing the means for publication of the results. 



