PREFACE 



TO THE FOURTH EDITION. 



To PROF. SPENCER F. BAIRD, 



Secretary of the Smithsonian Institution. 

 SIR, 



I TAKE pleasure in transmitting herewith the completed fourth edition 

 of Guyot's Smithsonian Meteorological and Physical Tables. 



A new arrangement of the tables composing the third edition of this 

 book has allowed the insertion of quite a large number of new and 

 useful tables: 



Series I., containing the Thermometrical Tables, has remained un- 

 changed. 



Series II., containing the Hygrometrical Tables, has been enlarged by 

 an addition to Table vn. The Psych rometrical Tables of Dr. Guyot 

 (pp. 108, 109) are based upon Regnault's modification of the formula of 

 August ; which have been extended so as to include differences of 29. 5 

 in temperature between the wet and dry bulb thermometers. 



Series III., containing the Barometrical Tables, has remained un- 

 changed. 



Series IV., containing the Hypsometrical Tables, is now limited to the 

 first twenty-six tables of the same series in the former edition, and as a 

 new section remains unchanged. 



Series V. is partly new and partly old, seventeen of the remaining 

 forty-four tables of the old series IV. having been retained as they were. 

 Of the remainder, some have been discarded as of no further value 

 others have been re-calculated from more recent data ; and others are 

 entirely new. The series now contains three sets of tables of Geographi- 

 cal Measures, as follows : 



a. For containing the most important measures of length used for 

 indicating altitude; containing forty-nine tables. 



(xi) 



