WHOLE VOL. NOTES. NORTH AMERICA 4I 



UNITED STATES 



Authority. 



United States Weather Bureau, F. W. Reichelderfer, Chief ; Di- 

 vision of CHmate and Crop Weather, J. B. Kincer, Chief of 

 Division, Washington, D. C. 

 Hours of Observation. 



From November i, 1870, to August 24, 1872, observations were 

 made at 7'' 35"", 16" 35™, and 23** 35"", Washington time. 



From August 25, 1872, to October 31, 1879, observations were 

 made at y^ 35"", 16'' 35"*, and 23'', Washington time. 



From November i, 1879, to December 31, 1884, observations 

 were made at y^, 15*^, and 23^, Washington time. 



From January i, 1885, to December 31, 1886, observations were 

 made at y^, 15^, and 23^, 75th meridian time. 



From January i, 1887, to June 30, 1888, observations were made 

 at y^, 15*^, and 22*^, 75th meridian time. 



From July i, 1888, to December 31, 1937, observations were made 

 at 8" and 20*", 75th meridian time. 



From Januaiy i, 1938, to the present time, observations were 

 made at y\^ and 19-P, 75th meridian time. 

 Methods of Observation. 



(Taken from the Annual Meteorological Summaries, 1937.) 

 Pressure. 



Two mercurial barometers of the well-known Fortin cistern pat- 

 tern, or a modified form thereof, are furnished each station. 

 One of these, the station barometer, is used in making all 

 regular observations ; the other, the extra, is held in reserve 

 for use in case of emergency, except that monthly compara- 

 tive readings are made on the two instruments for purpose 

 of check upon the deterioration of either instrument. 



Each barometer, before issue to station, is compared with the sub- 

 standard at Washington, and a certificate-of-correction card 

 furnished showing the several constant corrections that must 

 be applied to the readings of the instrument in order to derive 

 therefrom the actual pressure of the air in standard units at 

 a specified elevation. Each observation as made, therefore, is 

 corrected by the application of the following : 



( 1 ) Correction of scale error, capillarity, etc. 



(2) Correction to standard gravity, comprising both latitude 



and altitude terms. 



