WHOLE \'0L. NOTES. EUROPE 47 



graph House, the new height being 46.4 m. above sea level. 

 xA.ccordingly, all means published since April 191 7 have been 

 decreased by .008 in. to reduce to the former height of 48.5 

 m. above sea level. All means therefore refer to a height of 

 48.5 m. above sea level. They have been reduced to 32° F. 

 but the correction for gravity by reduction to latitude 45° 

 has not been applied. 



Temperature. 



The monthly means of dry bulb temperature for 1841 to 1905 

 are taken from " Reduction of Greenwich Observations " 

 Parts III and IV, and for the remaining years, from " Green- 

 wich Magnetic and Meteorological Observations " Annual 

 Volumes. The revolving stand upon which are mounted the 

 dry and wet bulb thermometers employed for standardizing 

 the photographic temperature curves was first erected in 

 March 1841. The observations for previous months were 

 made with a thermometer suspended in a temporary manner. 

 The monthly means for the period April 1 841 -December 

 1847 ^^^ means of 12 symmetrically disturbed eye-observa- 

 tions and of 6 eye-observations for 1848. From 1849, the 

 monthly means are means of hourly values derived from 

 records of the photographic thermograph reduced by means 

 of the readings of the revolving stand dry -bulb thermometer. 

 In January 1899 the revolving stand was moved from its 

 position in the Observatory grounds to an open position in 

 the Magnetic Pavilion enclosure. The Magnetic Pavilion is 

 about 320 m. (350 yards) to the east of the Magnetic and 

 Meteorological Observatory. Minor changes in site occurred 

 in 1863 and 1846. 



Rainfall. 



The rainfall totals for 1841-1914 are taken from " British Rain- 

 fall 191 5 " Part I, pp. 36-37 and for the remaining years 

 from the Monthly Weather Reports of the British Meteoro- 

 logical Ofifice. Less reliable data for about 26 years earlier 

 than 1841 will also be found in "British Rainfall 1915." 

 The rainfall is measured daily at 9'', 15^^ and 21^ Greenwich 

 Mean Time in an 8" gage whose surface is 5 in. (12.7 cm.) 

 above ground. The continuous record of Osier's self-regis- 

 tering rain gage shows whether the amounts at 9'^ are to 

 be placed to the same or to the preceding civil day ; the 

 amounts thus adjusted refer therefore to the civil day (o^' 

 to 24'''). At the beginning of 1899, the gage was moved 



