69 



VII. Summary of Special Instructions for Observers of the 

 Weather Bureau 



175. Station and extra haromMers. — It is the intention to keep each 

 station supplied as far as possible with two good barometers. The 

 names station and extra apply, respectively, to the one used in the 

 regular observations and the one held in reserve. Observers will 

 promptly report, by letter, any defect observed in either instrument, 

 giving full details as to its nature and probable cause. 



176. Exposure of harometers. — Observers will expose their barom- 

 eters and barographs in accordance with the provisions of para- 

 graphs 89 and 152. 



177. Cisterns of extra hwronieters. — When not in use the cistern of 

 the extra barometer may be screwed up so as to raise the level of the 

 mercury about halfway up the ivory point. The cistern should not he 

 filed nor the mercury forced to the top of the tube, except when the 

 barometer is to be moved. 



178. Elevation of barometers above sea level. — At the earliest prac- 

 ticable opportunity after establishing a new station or moving into a 

 new office the observer will ascertain and report, upon Form No. 

 1058-Metl. the elevation of the barometer above sea level. This 

 measurement should refer to the elevation of the lower end of the 

 ivory point of the barometer. Specific instructions in regard thereto 

 are given in paragraphs 161 to 166, and on the back of the form 

 mentioned. 



179. When observations are commenced at a new station and the 

 appropriate table of reductions to sea level has not, as yet, been 

 received from the central office, only the corrections given on Form 

 No. 1059-Metl. and for temperature will be applied to barometer 

 readings, and the results will be recorded on all forms required and 

 telegraphed in the usual manner until tables of reduction are 

 received. 



180. Regular haronietric observations. — Settings and readings of 

 the " station " barometer, as required by the instructions providing 

 for the regular observations of the station, will be made in accord- 

 ance with the provisions of paragraphs 97 to 100, and these readings 

 will be corrected for errors, as illustrated in the example given in 

 paragraph 171. 



181. Reduction of barometHc readings to sea level. — ^In reducing 

 barometer readings to sea level the special tables supplied each 

 station according to its elevation will be used. 



The temperature argument will be obtained by taking the mean of 

 the current and the previous 8 a. m. or 8 p. m. observation. For 

 example : Dodge City, Kans., March 1, 1905, temperature, 8 a. m., 

 33.7° ; 8 p. m., 45.4° ; the mean of these, 39.6°, is the temperature to 

 be used in reducing the 8 p. m. reading to sea level. 



182. Provisional removal correction. — ^When the elevation of the 

 barometer has been changed by removal or otherwise, and the 

 observer has ascertained with reasonable accuracy the new, that is, 

 the "actual elevation" (see par. 174), he will immediately report 

 the same to the central office, even if Form No. 1058-Metl. can not 

 be submitted at the same time. Furthermore, pending the receipt 

 of new copies of Form No, 1059-Metl., he will reduce his daily baro- 

 metric observations at the new location by the use of a provisional 



