CONTENTS. 



Page 



Introduction — 



Position and Description of the Observatory, ix 



System of Observation and Personal Establishment, xi 



Magnetical Instruments — 



Declinometer — 



Description of the Declinometer, xii 



Values of the Scale Divisions, xiii 



Scale Reading for the Magnetic Axis, xv 



Correction for the effects of the Bifilar and Balance Magnets, xvi 



Correction for the effect of the Copper Ring or Damper, xvii 



Correction for the Non-Parallelism of the faces of the Plates of Glass in the Box, xviii 



Correction for the Torsion Force of the Suspension Thread, xviii 



Facts relating to the Suspension Threads, xix 



Accidental Sources of Error xx 



Adopted Scale Zeros xxi 



Time of Vibration of the Declination Magnet xxi 



Absolute Magnetic Declination xxii 



Unifilar Magnetometer and Observations of the Absolute Horizontal Intensity of the 

 Earth's Magnetism— 



Position and Description of the Instrument, xxiii 



Mode of Observation and Reduction, xxiv 



Observations of Absolute Horizontal Intensity, xxvi 



Bifilar or Horizontal Force Magnetometer — 



Description of the Instrument, xxix 



Adjustments and Values of Constants, xxxi 



Constants for Reduction after altering the Reading of the Torsion Circle, xxxiii 



Corrections for the effects of the Declination and Balance Magnets, xxxiv 



Time of Vibration of the Bifilar Magnet, xxxiv 



Mode of Observation, xxxiv 



Temperature of the Magnet, xxxiv 



Balance or Vertical Force Magnetometer — 



Description and Theory of the Instrument, xxxv 



Practical difficulties in Dr Lloyd's method of determining the Constants, xxxvi 



New method of determining the Constants (Note), xxxvi 



Another method (that used in this volume) of determining the Constants, • • • • xxxvii 



Values of Constants and Adjustments, xxxviii 



Time of Vibration of the Balance Needle, xxxviii 



