78 



ADVERTISEMENT. 



In connection with the system of meteorological observations established by 

 the Smithsonian Institution about 1850, a series of meteorological tables was 

 compiled by Dr. Arnold Guyot, at the request of Secretary Henry, and the 

 first edition was published in 1852. Though primarily designed for meteoro- 

 logical observers reporting to the Smithsonian Institution, the tables were so 

 widely used by physicists that it seemed desirable to recast the work entirely. 

 It was decided to publish three sets of tables, each representative of the latest 

 knowledge in its field, and independent of one another, but forming a homo- 

 geneous series. The first of the new series. Meteorological Tables, was 

 published in 1893, the second, Geographical Tables, in 1894, and the third, 

 Physical Tables, in 1896. In 1909 yet another volume was added, so that the 

 series now comprises: Smithsonian Meteorological Tables, Smithsonian 

 Geographical Tables, Smithsonian Physical Tables, and Smithsonian Mathe- 

 matical Tables. 



The fourteen years which had elapsed in 1910 since the publication of the 

 first edition of the Physical Tables, prepared by Professor Thomas Gray, 

 had brought such changes in the material upon which the tables must be 

 based that it became necessary to make a radical revision for the fifth and 

 sixth revised editions published in 1910 and 1914. The latter edition was re- 

 printed thrice. For the present seventh revision extended changes have been 

 made with the inclusion of new data on old and new topics. 



CHARLES D. WALCOTT, 

 Secretary of the Smithsonian Institution. 

 June, 



