46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 79 



It was found in August 191 1 that there was an error of 10° F. 

 in the minimum thermometer owing to the condensation of 

 spirit at the top of the tube. The evaporation of the spirit 

 into the upper part of the tube appeared to have been going 

 on gradually since 1904. 



For the period January 1904 to June 1908 values of -K9^ + 

 15'') reduced to i( 7''+ 13^^ + 2 x 21^) by correction B are 

 shown. In July 1908 three observations each day were 

 taken and the values given from July 1908 until December 

 1920 representing true mean temperatures were obtained by 

 the formula ^(7'^+ 13^+ (2 X2i")). 



Jan. Feb. Mar. Apr. Ala> Jiiiif July Aug. Sept. Oct. Nov. Dec. 

 °F. ^(niax. + niin.) to i(7" + 13" + (2 X 21»)). 



A 0.2 0.1 0.1 0.4 0.8 1.0 1.4 1.1 0.8 0.4 0.0 0.2 



?.(9» + l.'i") to K"" + 13" + (2 X 21")). 

 + +--———-— — + + 



B 0.4 0.1 0.7 1.9 2.9 3.6 3.4 2.8 1.9 0.9 0.1 0.3 



Temperature data shown have been computed directly from the 

 original returns and are monthly and annual means in de- 

 grees fahrenheit for the period 1852- 1920. 



GREENWICH METEOROLOGICAL AND MAGNETIC 

 OBSERVATORY 



Authority. 



Meteorological Office, London, England. 



Site. 



The Meteorological and Magnetic Observatory is situated in 

 Greenwich Park, about I mile (0.8 kuL) south of the 

 Thames, on an elevated piece of ground sloping steeply to 

 the north and we.st and less steeply to the east and com- 

 manding extensive views of London, the Thames A'alley and 

 the plain of Essex. 



Pressure. 



The pressure means are taken from "Reduction of (ireenwich 

 Meteorological Observations, Parts 1 and II, 1854-1876" 

 and from " Greenwich Magnetical and .Meteorological Ob- 

 servations " Annual Volumes 1 877-1920. All means are de- 

 rived from hourly tabulations of the records of the photo- 

 graphic barograph standardized by eye observations of the 

 standard barometer after correction for temperature but not 

 for gravity or height above sea level. In April 1917 the 

 standard barometer was transferred to the New Magneto- 



