CONTENTS. 



INTRODUCTION 



Observations proposed ............... 1 x 



MAGNETICAL OBSERVATIONS- 

 ABSOLUTE DECLINATION . . ' . . . . . . . . . . . . X 



Description of the Declinometer ............. z 



Adjustments and observations .............. xi 



Experiments to determine zero of the magnetic scale ........... xil 



Adjustments of tfie alt-azimuth instrument . . . . .... . . . . xii 



Observations to determine the absolute declination . .. . . " , . . . . xiii 



Calculation of the observations . . . . . . . . . . .'.'.", xiii-xr 



DIURNAL VARIATION OF THE DECLINATION ............. XT 



The instrument used, and mode of observation ............. XT 



Comments on the observed results . . . . . . . . ,. . . . XT! 



TABLE I. Hours of the day at which the declination magnet attains its easterly and westerly elongation! .... XTil 



TABLE II. Diurnal arcs described by the declination magnet between its several elongations . . , . . ' . XTii 



HORIZONTAL FORCE . . . . . t . . . . ." . . . " .* . . xviii 



Description of the unifilar magnetometer . ........... xviii 



Description of the vibration apparatus . .. . . .". . . . . . xriii 



Formulas of reduction, and calculation of the constants . . . . . . . . . . xix-xxi 



Mode of observing, and explanation of the observations .... . . .. . . . xxi 



Value of the scale division .............. xxii 



ri 



Value of p- without weights .............. xxii 



U 



Value of p with weights . . . . . . . .'. "*"". . . xxiii 



Value of 13 . V . rxi* 



a a' 



Values of -jg- XX!T 



Values of T and T . . . ^. \ ^.' XXT 



Value of K . . . . . - . . ., . . .. . . . '. XXT 



Observations to determine the temperature correction . .......... xxr-xxvil 



Calculation of the temperature co-efficient . . . . . . ... . . . xxvii 



Localities and observers ,. . . . . . . . . . . . . . xxTii 



IJJCLINATION ................. xxvii 



Description of the inclinometer . . . . . . ". . . . . . . . xxTii 



Mode of observation . . . . . . ...... . . . . . Txriii 



Determination of tht correction IM to defective pwot*, Sfc. * 



