1820.] Current of Electriciti/ on the Magnetic Needle. 275 



Even glass, metal, and wood, interposed at once, do not 

 destroy, and indeed scarcely diminish the efiect. The disc of 

 the electrophorus, plates of porphyry, a stone-ware vessel, even 

 filled with water, were interposed with the same result. We 

 found the effects unchanged when the needle was included in a 

 brass box filled with water. It is needless to observe that the 

 transmission of effects through all these matters has never before 

 been observed in electricity and galvanism. The effects, there- 

 fore, which take place in the conflict of electricity are very 

 different from the effects of either of the electricities. 



If the uniting wire be placed in a horizontal plane under the 

 magnetic needle, all the effects are the same as when it is above 

 the needle, only they are in an opposite direction; for the pole 

 of the magnetic needle next the negative end of the battery 

 declines to the east. 



That these facts may be the more easily retained, we may use 

 this formula — the pole above which the negative electricity enters 

 is turned to the west ; under which, to the east. 



If the uniting wire is so turned in a horizontal plane as to form 

 a gradually increasing angle with the magnetic meridian, the 

 declination of the needle increases, if the motion of the wire is 

 towards the place of the disturbed needle ; but it diminishes if 

 the wire moves further from that place. 



When the uniting wire is situated in the same horizontal plane 

 in which the needle moves by means of the counterpoise, and 

 parallel to it, no declination is produced either to the east or 

 west; but an inclination takes place, so that the pole, next which 

 the negative electricity enters the wire, is depressed when the 

 wire is situated on the west side, and elevated when situated on 

 the east side. 



If the uniting wire be placed perpendicularly to the plane of 

 the magnetic meridian, whether above or below it, the needle 

 remains at rest, unless it be very near the pole ; in that case the 

 pole is elevated when the entrance is from the icest side of the 

 wire, and depressed, when from the east side. 



When the uniting wire is placed perpendicularly opposite to 

 the pole of the magnetic needle, and the upper extremity of the 

 wire receives the negative electricity, the pole is moved towards 

 the east ; but when the wire is opposite to a point between the 

 pole and the middle of the needle, the pole is most towards the 

 west. When the upper end of the wire receives positive electri- 

 city, the phenomena are reversed. 



If the uniting wire is bent so as to form two leo-s parallel to 

 each other, it repels or attracts the magnetic poles according to 

 the different conditions of the case. Suppose the wire placed 

 opposite to either pole of the needle, so that the plane of the 

 parallel legs is perpendicular to the magnetic meridian, and let 

 the eastern leg be united with the negative end, the western leg 

 with the positive end of the battery : in that case the nearest ' 



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