66 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 90 



Pressure Corrections to 24 Hours in Tenths of Millimeters 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 



K7 h +14 h +21") -1-1 +1 +1+1 —1 -1 -1 



K7 h +13 h + 21 h ) -2 -2 —2 -1 -1 -1 -1 -1 —1 -2 -2 -2 



J(7 h +13 h + 18 h ) +2 +3 +3 +3 +3 +2 +2 +2 +2 +2 +2 +2 



The height remained at 9 m until January 1928, when it was 

 lowered 3 m ; the values refer to the later height, 

 or 6 m. From June 1918 to December 1919 in- 

 clusive, the values were interpolated from contigu- 

 ous stations by differentiation. 



ISLA DE JUAN FERNANDEZ 



Authority. 



Robert C. Mossman. 



Temperature. 



The observations were made at various combinations of hours 

 but have all been reduced to the mean of :j(7 h + I4 h + 2i h + 

 2i h ) by corrections taken from Easter Island. From June 

 1923 to December 1928 the station was at a height of 345 m. 

 The somewhat large correction of +2? 5 applied to reduce 

 to 7 m was derived from an intercomparison of the mean 

 annual temperature ^(7 h + i4 h + 2i h -|-2i h ) at Isla Guafo. 

 Isla Mocha Oeste, and Juan Fernandez for the 10 years 

 1913-22 and the 5 years 1924-28, the latter period having 

 a mean o°i lower in both cases than in the former at Guafo 

 and Mocha Islands, which gives a plus correction of 2? 5 to be 

 applied to the Juan Fernandez observations. 

 It may be observed that a flat correction has been applied to all 

 the months, whereas at Easter Island one year's hourly 

 observations at two stations gave for 290 m the difference 

 between the upper and sea level stations, an annual difference 

 of +i?8 to reduce the higher station to sea level, the cor- 

 rections from August to February being +2°2 and from 

 March to July + 1°5, but it was considered safer in the 

 present instance to adopt the flat correction obtained in the 

 manner described. For a few months in which the data are 

 missing interpolated temperatures were derived from the 

 adjacent island stations of Chile by differentiation. See 

 notes on Chile. 



Precipitation. 



The rainfall data are but slightly affected by altitude from June 

 1923 to December 1928, since at Easter Island the two gages 

 gave practically the same results. 



