42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO5 



(3) Correction for removal — a correction applied if any 



change has been made in the elevation of the barom- 

 eter, to reduce the readings to the elevation adopted 

 in 1900. (However, at a very few stations the eleva- 

 tion of 1900, or the original elevation of a station 

 opened since 1900, has been replaced as the "station 

 elevation" by an actual elevation since established.) 



Corrections i, 2, and 3 are constant for any one station and are 

 combined in a single sum. 



(4) Correction for the temperature of the scale and mer- 



curial column. 



In the pressure columns of this part the values presented are 

 those at the station elevations of the barometer cisterns, 

 which are at various heights above the ground level, but 

 usually less than 100 feet. On the other hand, daily weather 

 maps and most other pressure data issued by the Bureau 

 indicate sea-level pressures. 



The monthly mean pressures given in the summary are deducted 

 from the corrected observations of pressure at 7 : 30 a. m. 

 and 7 : 30 p. m., 75th meridian time, by taking the mean 

 thereof and applying thereto a correction to reduce to the 

 mean of 24-hourly observations. At several Alaska stations 

 and at Honolulu the mean is printed uncorrected. The ex- 

 tremes are determined, wherever possible, from the baro- 

 graph trace. 

 Temperature. 



The temperature of the air at 7 : 30 a. m. and 7 : 30 p. m., 75th 

 meridian time, is obtained by the use of the whirled dry-bulb 

 thermometer.- The latter is a part of the whirled psy- 

 chrometer and is mounted in the thermometer shelter adopted 

 in 1885. The means of these observations are given in the 

 columns headed 7: 30 a. m., and 7 : 30 p. m., respectively. 



The maximum temperature is obtained by the use of the Negretti 

 and Zambra mercurial thermometer, having a constriction in 

 the bore of the tube below the scale. The minimum tem- 

 perature is obtained by the use of the ordinary Rutherford 

 alcohol minimum thermometer. Both instruments are read 

 and the values recorded twice daily, at 7 : 30 a. m. and 7 : 30 

 p. m., 75th meridian time, and are set twice daily at 7 : 30 

 a. m. and 7 : 30 p. m. The extremes given in the summaries 



