126 ABSOLUTE OBSERVATIONS AXD ADJUSTMENTS. 



The highest and lowest readings noted at any time during the day were then entered as the 

 extreme values for the twenty-four hours, and the differences taken. Hourly, daily, and 

 monthly means were then finally computed. 



This set of tables is contained on pp. 130 to 141. 



Term Day Observations. 

 On certain selected days, called term days, a list of which is here given : — 



September J 5 1882. 



October 1 and 15 „ 



readings of the declinometer were made every five minutes from midnight up to 11.55 p.m., 

 Gottingen mean time, with the addition of certain other readings made for one previously 

 selected hour, as given in the following list, during which the instrument was read every 

 20 seconds. 



These observations having been reduced to absolute value and tabulated, form the tables 

 on pp. 166 to 223 ; they are also represented as plotted in curves forming plates 1 to 28. 

 No calculation of means or difi'erences have been made from them. 



HORIZONTAL INTENSITY (BIFILAR MAGNETOMETER). 



{See p. 123.) 



The scale value of this instrument and the temperature corrections of its magnet were 

 determined at Kew, and the latter was also re-examined on its return, but the corrections so 

 found were seen, by a preliminary reduction of the readings, to be very inadequate for the 

 purpose of reducing the observations made when the instrument was fixed in situ, and 

 measures were taken to deduce the true corrections from the observations themselves. 



The first step in the reductions was to find the mean scale reading for the hour from the 

 three observations, as in the case of the declination. 



These values were then extracted for the hours of 11 a.m., noon, and 1 p.m. (being the 

 period of least variation) on such days as the magnets were fairly steady, with the 



