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Article VI. 



On a new Instrument for the direct Observation of the Changes 

 in the Intensity of the Horizontal Portion of the Terrestrial 

 Magnetic Force"^'. By Carl Friedricii Gauss. 



[From the Resullafe aas den Beohachtiingen ties magnethchen Vercins im Jalire 

 1837. — Herausgegeben von Carl Fiiedricli Gauis unci Wilhelm Weber. Giit- 

 tingen, 1838.] 



AT is well kno^^■n that for the perfect determination of the ter- 

 restrial magnetic force at a given place, three elements are re- 

 quired ; and, in gcneial, the Declination, Inclination, and Inten- 

 sity are selected for the purpose. Although this choice is the 

 most simple in conception, it is not only allowable, but in many 

 respects it may be advisable, to adopt a different combination. 

 In practical as well as in theoretical respects, it is far more 

 advantageous to consider the horizontal portion of the terrestrial 

 force separately, and to imagine it in two elements, the direc- 

 tion (declination) and the intensity. If we add to these, as a 

 third element, — either the intensity of the vertical force, or the 

 inclination, — the intensity of the total force, if desired, may be 

 directly obtained. 



With respect to the two elements of the horizontal force, with 

 which alone we are here concerned, all the questions which 

 occur in regard to the declination are completely met by the 

 magnetometer which has been in use since 1833t. This instru- 

 ment serves Avith a certainty, convenience, and accuracy that 

 leaves nothing more to be wished ; not only for the determina- 

 tion of the absolute value of the declination, but also for follow- 

 ing its regular and accidental changes, from year to year, from 

 month to month, from hour to hour, — nay, from one minute to 

 the other. This magnetometer also determines, in absolute mea- 

 sure, the intensity of the horizontal portion of the earth's mag- 

 netic force, — which was, in fact, the object which first gave rise 

 to its construction : it does not, however, by any means, solve 

 this -^rohlem. jjerfectly in «// respects. 



The application of the magnetometer to determine the mag- 

 netic intensity is founded on a combination of several operations, 



* Transliitod by Mr. William Francis, and revised by Major Sabine and 

 Professor Lloyd. 



f Suientiiic Memoirs, part v. pp. 2.j e( acq. 



