CONTENTS. 



SECTION IV. 



OBSERVATIONS ON TERRESTRIAL MAGNETISM. 



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 

 Final values of the magnetic elements at each station . 

 Observations of magnetic declination .... 

 Observations of magnetic inclination .... 

 Horizontal intensity. Observations of vibrations 

 Horizontal intensity. Observations of deflections 



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SECTION V. 



OBSERVATIONS ON THE MAGNETISM OP THE SHIP. 



Description of the Monadnock ....... 



Positions of the compasses . . .... 



Mode of swinging the ship ..... . . 



Corrections peculiar to the After Binnacle and After Ritchie Compasses 

 Officers who observed the compasses ...... 



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



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



Correction of observed deviations for constant errors .... 



Observations for determining the deviations of the Admiralty Standard Compass 

 Observations for determining the deviations of the After Binnacle Compass . 

 Observations for determining the deviations of the After Ritchie Compass 

 Observations for determining the deviations of the After Azimuth Compass . 

 Observations for determining the deviations of the Forward Alidade Compass 

 Observations for determining the deviations of the Forward Binnacle Compass 

 Observations for determining the deviations of the Forward Ritchie Compass . 

 Mode of computing the coefficients A v B v G v B u E t . 

 Values of these coefficients for each compass at each station . 

 Probable errors of the values of the coefficients A v B v C v D v E x . 



Computation of the constants A v 



and , for each compass 



Values of the coefficients 3(, 33, S, ©, (S, for each compass at each station 



P aP / Q aQ 



Table showing the values of the constants A 1 ■. 

 for each compass 



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