ADVERTISEMENT TO FOURTH REVISED EDITION. 



The original edition of the Smithsonian Meteorological Tables was 

 issued in 1893, and revised editions were published in 1896, 1897, and 1907. 

 A fourth revised edition is here presented, which has been prepared under 

 the direction of Professor Charles F. Marvin, Chief of the U.S. Weather 

 Bureau, assisted by Professor Herbert H. Kimball. They have had at their 

 disposal numerous notes left by the late Professor Cleveland Abbe, and 

 have consulted with officials of the U.S. Bureau of Standards and of other 

 Government bureaus relative to the value of certain physical constants 

 f nat have entered into the calculation of the tables. 



All errata thus far detected in the earlier editions have here been 

 corrected. New vapor pressure tables, derived from the latest experimental, 

 values by means of a modification of Van der Waals interpolation formula 

 devised by Professor Marvin, have been introduced. The table of relative 

 acceleration of gravity at different latitudes has been recomputed from a 

 new equation based upon the latest investigations of the U.S. Coast and 

 Geodetic Survey. These values have been employed in reducing barometric 

 readings to the standard value of gravity adopted by the International 

 Bureau of Weights and Measures, supplementing a table that has been 

 introduced for directly reducing barometer readings from the value of grav- 

 ity at the place of observation to its standard value. 



The new values of vapor pressure and of gravity acceleration thus 

 obtained, together with a recent and more accurate determination of the 

 density of mercury, have called for an extensive revision of numerous other 

 tables, and especially of those for the reduction of psychrometric observa- 

 tions, and the barometrical tables. 



Among the new tables added are those for converting barometric 

 inches and barometric millimeters into millibars, for determining heights 

 from pressures expressed in dynamic units, tables of gradient winds, and 

 tables giving the duration of astronomical and civil twilight, and the trans- 

 mission percentages of radiation through moist air. 



The tables of International Meteorological Symbols, of Cloud Clas- 

 sification, of the Beaufort Scale of Winds, of the Beaufort Weather Nota- 

 tion, and the List of Meteorological Stations, are among those extensively 

 revised. 



Tables for reducing barometric readings to sea level, and tables of 

 logarithms of numbers, of natural sines and cosines, of tangents and cotan- 

 gents, and for dividing by 28, 29, and 31, with a few others, have been 

 omitted from this edition. 



This reprint is from the electroplates that were employed in print- 

 ing the Fourth Revised Edition, after making certain minor corrections. 



Charles D. Walcott, 



Secretary. 



Smithsonian Institution, 

 June, 1924. 



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