70 



removal correction deduced in the manner illustrated in paragraph 

 198. In his letter the observer will give the value and algebraic sign 

 of the correction he proposes to use. 



182a. Vanable removal correction. — ^When extreme changes of 

 temperature, such as occur at different seasons of the year, taKen in 

 conjunction with considerable changes of elevation due to removal 

 of office, cause variations in the " removal correction " amounting to, 

 or exceeding 0.010 inch, it then becomes necessary to employ a 

 " variable removal correction," which is taken out for each observation 

 and which depends upon the temperature of the outside air. In 

 such cases this " variable " correction for different temperatures is 

 given in a special table on the back of Form 1059-Metl., and is used 

 for reducing the observations in the following manner : 



The barometric observations will be reduced practically the same 

 as heretofore (see par. 171), except that the proper " sum of correc- 

 tions " to be used at each observation will be taken from the table 

 mentioned above corresponding to the air temperature observed at 

 the same time. It is important to note that this temperature is the 

 dry-bulb reading in the instrument shelter, riot that of the attached 

 thermometer of the barometer. The " Sum of corrections " thus 

 taken from this supplemental table will be added algebraically to 

 the temperature correction in the usual manner, and the resulting 

 total correction applied to the barometer reading, and also entered 

 in the customary spaces on Form 1001, in the column headed " Total 

 correction," on pages 2 and 3. Finally, in entering the data on Form 

 1001-Metl., a supplementary column will be ruled adjacent to the 

 date column on the left. This column will be headed : " Removal 

 correction," and therein will be entered, from observation to observa- 

 tion, the particular value of the " Removal correction " from the table 

 given on back of Form 1059-Metl., corresponding to the " Sum of 

 corrections " employed in reducing the observations. 



Whenever 'new correction cards (Form 1059-Metl.) are furnished 

 to a station from the central office, the cards previously in use will 

 be destroyed. 



183. Comparative barometer readings. — ^The provisions of para- 

 graphs 118 to 121 will be observed in making comparative readings ; 

 the results will be tabulated and reported of Form No. 1027-Metl., 

 and the detailed instructions printed on the back thereof fully com- 

 plied with. Form No. 1027-Metl. will either be duplicated for the 

 station file, or a letterpress copy retained for the station record. 



Five comparative readings at intervals of hours, half hours, or 

 quarter hours will be made in accordance with the foregoing provi- 

 sions and on the occasions specified as follows : 



[a) When new barometers are received for the establishment of a 

 station, or, in general, whenever any serviceable Whether Bureau 

 barometer is received at station, by transfer or otherwise. 



{b) Regular monthly readings will be made on the 15th of each 

 month. When the 15th falls on a Sunday or holiday, the readings 

 will be deferred until the next regular working day. 



(c) Before and after removal of office or change in the location of 

 the barometers, also when a line of levels is not run, a set with the 

 station barometer in new office and extra in old office. (See par. 166.) 



{d) Before and after cleaning a barometer. 



