20 Land Magnetic Observations, 1905-10 



and so on. As little time as possible is allowed between determinations at the 

 two stations in order to minimize outstanding effects of corrections to common 

 epoch. With the number of determinations called for, this scheme of observation, 

 while of course not as good as simultaneous intercomparisons, can, with care, yield 

 results of value. 



Whenever possible, the practice is to secure with each instrument at least 

 twelve complete determinations of declination, six at each station; six complete 

 determinations of horizontal intensity, three at each station (one determination 

 consisting of two sets of oscillations and two sets of deflections at two distances) ; 

 and at least six determinations of dip with each needle, three at each station. 

 The observations are made for different orientations of the footscrews of the instru- 

 ments, preferably such that there will be an equal number of observations at each 

 station for footscrew marked A south, footscrew B south, footscrew C south. 

 The work for any one element is not completed on one day but distributed over 

 several days in order to minimize possible effect due to magnetic perturbations. 

 Where an exchange of stations is not practicable, the total number of determinations 

 for each element is at least as great as just stated. 



Particular care is used to see that the instruments are in good working order 

 and the requisite caution is exercised to insure the absence of disturbing influences 

 of whatever character. Before leaving the station, the computations are completed 

 far enough to make sure, at least, that no observational blunders have been made. 



Field Records and Computations. 



Records. The observations are recorded with a hard pencil (No. 4 grade in the 

 temperate and arctic regions, and No. 3 grade in the tropic regions) and entered at 

 once on the proper form, not kept on blank paper and afterwards copied on the 

 form. All computations are made in ink or inked over before the record is sent to 

 the Office. The various sheets, arranged in the following order, are fastened 

 together in the covers provided: (o) description of station; (b) sketch; (c) informa- 

 tion as to chronometer comparisons and corrections on standard time; (d) latitude 

 observations and computations; (e) azimuth and time observations and measure- 

 ments of angles; (/) azimuth and time computations; (g) magnetometer decli- 

 nation; (/?) dip circle compass declination; (z) oscillations; (7) deflections; (k) dip 

 observations; (/) dip circle intensity observations; (w) summary sheet. When 

 working in regions where the dip is within a few degrees of zero, particular care is 

 taken both in the correct designation of which end of the needle is the north-seeking 

 one, and in entering readings under properly headed columns for north and south 

 ends. 



The records are sent to the Office whenever a safe means of transportation offers. 

 First, however, the observer makes an abstract containing such observational means 

 and quantities as would be required for recomputation in case the original records 

 were lost in transmission to the Office. The various observation sheets invariably 

 give the day of the week in addition to that of month and year, thus: Mon. Nov. 15, 



