128 



ABSOLUTE OBSERVATIONS AND ADJUSTMENTS. 



■were generally noted in tlie journal, and also by comparison of daily means for adjacent days 

 at tte time of the adjustment. The values finally adopted were as follows : — 



Table 10. 

 Corrections for change of zero produced by lifting of the Magnet of the Balance 



Magnetometer. 



The assumption was then made that the change in the scale readings was proportional 

 between the different shiftings of the zero and a table drawn up giving a suitable propor- 

 tionate correction for every day (with the exception of January 5, when the instrument was 

 bodily disarranged, and on May 25th, when the balance of the magnet was entirely altered). 



These corrections being applied to the daily means, 5-day averages of both scale readings 

 and temperature were calculated and the results plotted in a curve ; measurements were then 

 made from this curve and a final temperature correction of ^ 1° centigrade = ±4*5 scale 

 divisions found. 



The 5-day means and their corresponding temperatures were then again copied and the 

 new temperature correction applied ; another plotting of the second set of 5-day means was 

 then performed and the smoothing of this curve afforded materials for a better estimation of 

 the effects of the re-adjustment of the magnet. Finally a table was drawn up giving 

 corrections to be applied to the daily readings of the magnetometer so as to bring them into 

 one uniform continuous series. 



The means of the tri-horary readings were then taken, copied out, reduced to temperature 

 0°, and corrected for adjustment. The same reductions were also applied to term day 

 readings. 



A selection was then made of corrected and reduced scale readings for the times at which 

 absolute determination of the vertical force had been computed by Captain Dawson from his 

 unifilar and dip observations, and from these the following table was prepared for 

 converting scale readings into absolute units. 



Table. 11. 



