71 



184. Except in the case of the regular monthly readings, observers 

 will forward special comparative barometer readings with a letter of 

 transmittal, giving any pertinent remarks relative to the condition 

 of the instruments, the occasion for making the readings and other 

 particulars that may enable the central office to understand more 

 fully the matter under consideration. 



185. Barometers not to he changed. — Barometers Avill not be 

 changed in location nor one instrument substituted for another 

 without authority from the central office, unless the circumstances are 

 such that immediate action is necessary. Neither the " station " nor 

 the " extra " instrument will be loaned without authority. 



186. Changes in the location of barometers, especially when the 

 elevation is changed, as in the removal of an office, should be made 

 at the end of the month, if practicable, and the station barometer 

 will be moved in the interval between the last observation of one day 

 and the first observation of the following day. The foregoing will 

 also apply, as far as practicable, when a new barometer is substituted 

 for the station instrument. 



187. Authority to clean haroTmeters. — Authority to clean barome- 

 ters will be granted only in special cases, and applications therefore 

 should be made with due consideration of the provisions of para- 

 graph 116. Unless otherwise provided for, only one barometer will 

 be cleaned within any given month, and then just after the regular 

 monthly comparative readings have been made. The set of readings 

 required, after cleanmg^ may be made the same or the following day, 

 preferably the latter. The specific instructions for cleaning barome- 

 ters, paragraphs 124 to 144, will be carefully observed. 



188. Requisition for mercury. — Mercury will be furnished to sta- 

 tions only on special requisition, which will be made when the 

 mercury is needed for immediate use in connection with the author- 

 ized cleaning and repairing of barometers. 



189. Impure mercury. — Mercury of an impure character that has 

 been removed from barometers, or otherwise acquired on station, 

 should be carefully preserved, and in quantities of from a half pound 

 to a pound or more will be forwarded by mail to the central office, 

 in strong bottles or other suitable receptacles, securely wrapped in 

 proper packing material to prevent breakage. The stopper of the 

 bottle should fit tightly and be strongly tied and sealed if practicable. 

 The mercury is easily reduced to great purity at this office by distil- 

 lation, etc. The package should be marked " Instrument Division." 



190. Mercury not to he removed. — ^When an unserviceable barome- 

 ter is returned to this office the mercury will not be removed except as 

 provided for in paragraph 151, and if not returned to Washington 

 with the instrument, will be disposed of as specified in paragraph 189. 



191. Barographs. — The winding and regulating of barograph 

 clocks, the changing of sheets, and the adjustment of pens to stand- 

 ard pressures, will be attended to in accordance with the provisions 

 of section (B), "Care and Use of Barographs," paragraphs 153-160. 



192. Time ei^or checked. — The barograph will be checked for time 

 error at 12 noon, each day, in the manner explained in paragraph 

 158. 



193. Hourly readings. — Detailed instructions for compiling and 

 transcribing records from barographs are given in circular A, instru- 

 ment division. 



