12 Land Magnetic Observations, 1905-10 



for the land work for use with the boiling-point apparatus are graduated to 0.1 C. 

 The length of the mercurial column for this graduation is about 1 mm., so that 

 readings can be made by estimation to 0.01 C. 



Care of Instruments. 



Each observer is held responsible for his entire instrumental equipment and 

 upon delivery to him assures himself by careful and immediate examination that 

 it is complete and in first-class order in every detail, not only as regards the instru- 

 ment itself but also as to its miscellaneous accessories watch oil, shellac, brush, 

 adjusting pins, suspension material, glycerine, piece of chamois skin, pith, tissue 

 paper, etc., etc. The outfit is also frequently examined in the field. A mental 

 inventory and survey of each instrument case is made before leaving a station to 

 make sure that no part is left behind; the habit of doing this is quickly acquired 

 and frequently saves much worry and loss of time. At intervals of one or two 

 months or less, depending upon the nature of the region traversed, the instruments 

 are carefully cleaned and oiled with the highest grade of instrument or watch oil 

 and put in good adjustment. In case of alterations involving changes in instru- 

 mental constants, etc., memoranda, with full particulars and dates, are at once made 

 and transmitted to the Office. Accidents are reported promptly with full partic- 

 ulars as to damage; with the constant care exercised by the observers the number 

 of accidents has been very low, even under the rough traveling conditions not in- 

 frequently experienced. 



The magnets and needles of the various instruments are touched with the hands 

 as little as possible and, after use or handling, are always wiped with a clean piece 

 of chamois skin or with soft tissue paper; they are not allowed to touch each other 

 nor come in contact with iron or steel objects, and are kept in such cases and 

 positions as provided and indicated. The dip and intensity needles are wiped 

 with tissue paper both before and after observations and the pivots and agate 

 edges cleaned with pith. In reversing polarity of a dip needle the bar magnets 

 are drawn smoothly from center to ends of needle, as nearly parallel to the axis 

 of the needle as possible, and a sufficient number of strokes are taken to insure 

 good magnetization; in general ten strokes have been found sufficient. The needles 

 are remagnetlzed before beginning observations whenever some time has elapsed 

 between sets or the instrument has undergone transportation. The poles of the 

 intensity needles are, of course, never reversed and the weight in the loaded needle 

 is not disturbed after the constants have been determined, except for very good 

 reason. 



The chronometer and watches require great care; they are carried in leather 

 pockets close to the body, all possible precautions being taken to reduce jarring and 

 jolting to a minimum; they are wound regularly at about the same time each day. 

 Special care is exercised not to have any of the magnets near a timepiece, e. g., in 

 reversing polarity of dip needles, etc. 



