TABLE OF CONTENTS. 



ARTICLE IV. Observations on Terrestrial Magnetism and on tiie Deviations of the 

 Compasses of the United States Iron- Clad Monadnook during der 

 Cruise from Philadelphia to San Francisco, in 1865 and 1866. By 

 Wm. Harkness, M.D. Accepted for publication September, 1871. Pub- 

 lished April, 1873. 4to. pp. 225. With 2 Diagrams. 



Section I. Introduction. 











Introductory remarks . . . . 



1 



Plan of observation ....... 



1 



Instruments employed ....... 



2 



Section II. Descriptions of Stations. 





Philadelphia ........ 



4 



Gosport 











4 



St. Thomas 











5 



Isle Royal . 











5 



Ceara 











5 



Pernambuco 











6 



Bahia 











6 



Rio Janeiro 











6 



Monte Video 











7 



Sandy Point 











8 



Valparaiso . 











9 



Callao 











9 



Payta 











10 



Panama 











10 



Acapulco . . 











11 



Magdalena Bay 











11 



San Francisco 



• 







12 



Section III. Astronomical Observations. 





General remarks . . . • . 



13 



Observations of the sun for latitude .... 



13 



Observations of the sun for time ..... 



14 



Mode of determining true bearings .... 



26 



Observations of the sun for the determination of true bearings 



28 



Triangulation at Ceara ...... 



32 



Table of observed latitudes ..... 



34 



Errors of pocket chronometer, Fletcher, No. 906 . 



35 



Chronometer comparisons ...... 



36 



True bearings of objects used as azimuth marks 



36 



Section IV. Observations on Terrestrial Magnetism. 





Description of the portable declinometer, D. 22 



37 



Description of the transit theodolite .... 



37 



General remarks on the methods of using the instruments . 



38 



Mode of determining absolute declinations 



39 



Mode of making observations of vibrations 



42 



Mode of making observations of deflections 



44 



Mode of calculating horizontal force .... 



45 



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





Temperature coefficients of magnets .... 



50 



Value of magnet scales ...... 



50 



Moment of inertia of the magnet C. 32 . 



51 



The constant P. . 



53 



Magnetic moment 



of the 



magnet C. 32 







55 



