iv CONTENTS. 



SECTION IV. 



OBSERVATIONS ON TERRESTRIAL MAGNETISM. 



PACE 



Description of the portable declinometer, D. 22 



Description of the transit theodolite 



General remarks on the methods of using the instruments 



Mode of determining absolute declinations 



Mode of making observations of vibrations 



Mode of making observations of deflections 



Mode of calculating horizontal force 



Determination of constants peculiar to the portable declinometer, D. 22 



Temperature coefficients of magnets 



Value of magnet scales .... 



Moment of inertia of the magnet, C. 32 . 



The constant P. . 



Magnetic moment of the magnet C. 32. . 

 Mode of making observations of inclination 

 Mode of computing the vertical and total force . 



Abstract of observations for magnetic declination, inclination, and force . 60 



Final values of the magnetic elements at each station . . . . . .61 



Observations of magnetic declination ..... . . 62 



Observations of magnetic inclination ..... . . . 75 



Horizontal intensity. Observations of vibrations 



Horizontal intensity. Observations of deflections .... 



SECTION V. 



OBSERVATIONS ON THE MAGNETISM OF THE SHIP. 



Description of the Monadnock . . .119 



Positions of the compasses . ... 

 Mode of swinging the ship . 



Corrections peculiar to the After Binnacle and After Ritchie Compasses . . 121 



Officers who observed the compasses ... . 



Mode of measuring magnetic force on board ship . ... 



Mathematical theory of the deviations of the compass .... . 123 



Correction of observed deviations for constant errors . . . . 129 



Observations for determining the deviations of the Admiralty Standard Compass . . 133 



Observations for determining the deviations of the After Binnacle Compass . .140 



Observations for determining the deviations of the After Ritchie Compass . . 147 



Observations for determining the deviations of the After Azimuth Compass . . 154 



Observations for determining the deviations of the Forward Alidade Compass . 160 



Observations for determining the deviations of the Forward Binnacle Compass . 167 



Observations for determining the deviations of the Forward Ritchie Compass . .174 



Mode of computing the coefficients A t , B t , C lt D,, E l . . . . .181 

 Values of these coefficients for each compass at each station ..... 182 



Probable errors of the values of the coefficients A,, B t , C,, D,, E, . . .184 



Computation of the constants A.,. -, , *, -?, and A ^, for each compass . .185 



x x x x x x 



Values of the coefficients 9(, 33, S, \ Q, for each compass at each station . . 1 1)1 



Table showing the values of the constants A. = % c , ~, , /, 9, *9, < and (?, 



x x x x x x 



for each compass . . . . . . . . . .193 



