67 



station elevation." In case, therefore, an office is moved to new 

 quarters and the elevation of the barometer is thereby changed, a 

 proper correction will be applied to the barometric readings in the 

 new location that will reduce the observed readings to the pressure 

 appropriate to the " station elevation," notwithstanding changes and 

 removals. The pressure thus ascertained will be designated " station 

 pressure." 



169. The " station elevation " for a station in operation January 

 1, 1900, is its elevation above sea level on that date. For stations 

 closed before 1900, or subsequently established, the elevation will be, 

 in general, the elevation above sea level of the zero point of the 

 barometer at the date of closing or opening the respective stations. 



170. Reduction of current observations to a " station elevation " in 

 accordance with the foregoing plan w^ill, therefore, be required only 

 when changes are made in the elevations of the barometers. In all 

 such cases the Instrument Division of the central office will furnish 

 a new copy of the barometer correction card (Form No. 1059— 

 MetL), in which a " removal correction," based on the change made 

 in the elevation of the barometers, will be combined with the correc- 

 tions for local gravity, scale errors, etc. The " sum of corrections " 

 thus determined, together with the " correction for temperature," 

 will be applied to all recorded readings of barometric pressure, and 

 the result will be regarded as the pressure of the air appropriate to 

 the station in question. 



171. The following example will elucidate the complete correction 

 of observed barometer readings : 



Observed barometer reading (attached thermometer, 76.5°) 30.287 



Correction for temperature (Table I) —0.131 



Sum of corrections, Form No. 1059-Metl -f-0. 032 



Total correction —0. 099 



Station pressure 30. ISS 



The " total correction," as shown above, will be entered on Form 

 No. lOOl-MetL, and applied to the " observed " reading, deriving 

 thereby the pressure of the air appropriate to the adopted elevation 

 of the station ; this result will be recorded on Form No. 1001-Metl., 

 in the columns for " station pressure." 



172. The barograph will be adjusted and corrected to correspond 

 with the " station pressure " ascertained as shown in the above ex- 

 ample. See also paragraph 153. 



173. All pressure observations made at a station and reduced 

 according to the foregoing plan are therefore strictly comparable 

 with each other, all being reduced to the adopted elevation. Fur- 

 thermore, a change of elevation or removal of office does not necessi- 

 tate a new table of reductions to sea level; that is, all observations 

 will be reduced to sea level, when required, by one and the same 

 table of reduction, namely, that based on the adopted elevation of 

 the station. 



174. Nornenclature. — The following nomenclature, embracing baro- 

 metric terms, will be used, as far as practicable, in the correspond- 

 ence, records, and publications of the Weather Bureau : 



Actual elevation. — The height of the zero points of the barometers 

 of a station above sea level. 



