268 



Article VII. 



Observations on the Arrangement and Use of the Bifilar 

 Magnetometer. By Wilhelm Weber*. 



[From the Resultate aus den Beobachtungen des niagnetischen Vereins im Jahre 

 J 837. — Herausgegeben von Carl Friedrich Gauss iind Wilhelm Weber. Got- 

 tingen, 1838.] 



After the full development in the preceding article of the prin- 

 ciple of the Bifilar Magnetometer, and of all that is essentially 

 necessary for its construction and application, an exact drawing 

 of the instrument will be particularly interesting. The drawing 

 (Plate XIV.) is so accui'ate that any skilfvd artist can w ork from it. 

 The following obsei-vations are added with a view of rendering 

 the drawing still more intelligible, and of facilitating the adjust- 

 ment of the instrument by other observers, as far as may be 

 done by such directions. 



1 . General Observations. 

 The height and other dimensions of the Gottingen astrono- 

 mical observatory, where the instrument figured has been esta- 

 blished, allowed of large size in the instrument, and therefore a 

 25lb. bar very powerfully magnetized was employed. At other 

 places it will perhaps be necessaiy to employ smaller dimensions, 

 and we shall notice at the conclusion the difference in the cost 

 produced by diminishing the size. Large dimensions are gene- 

 rally, however, more to be recommended for the bifilar than for 

 the unifilar, for the following reasons : 1st, because no pro- 

 portionate increase in the price is occasioned, as the principal 

 expense arises from the fine division of the circle and from the 

 mirror ; and since the latter is not attached to the end of the mag- 

 net bar, it is not requisite that its size should be increased with 

 that of the bar ; 2nd, because the enlargement of the instrument 

 does not require any considerable enlargement of the room ; 

 which would be the case with the unifilar, on account of the 

 experiments of deflection in the measurements of the absolute 

 intensity; 3rd, because the magnet bar need veiy rarely be re- 

 moved from the stirrup ; and therefore the size of the bar pro- 



* Translated by Mr. AVilliam Francis, and revised by Professor Lloyd and 

 Major Sabine. 



I 



