Descripiion of a Balance. 281 



the beam to a divided scale ; upon this index is screwed the 

 ball c, the office of which is to adjust the oscillation of the 

 beam, or in- other words to give it its required sensibility; 

 should the index not exactly coincide with the middle division 

 of the scale, it may be adjusted by turning the piece of wire d, at 

 the top of the beam. The lifting frame, efg h, is pressed up- 

 wards by an internal spring, its use being to lift the beam from 

 the agates, when not in use, or when weights are put into the scale 

 pans : this frame is lowered by the lever i, and is retained in 

 that position by turning the lever into the notch on one side. 

 At the bottom of the short stringed pan is a hook for the con- 

 venience of attaching substances whilst ascertaining their 

 specific gravities. The whole instrument is covered with a glass 

 case, and provided with a level for ascertaining the horizon- 

 tality of the agates, and with tweezers, and a box of platinum 

 weights from jJq of a grain up to 100 grains. The price of 

 this apparatus as manufactured by Mr. Robinson, of Devonshire- 

 street, Portland-place, is £6, with the beam and weights accu- 

 rately adjusted, or £4 when unadjusted. 



Art. VII. Oil the Magnetism impressed on Metals by Elect li- 

 cit t/ in Motion; read at the public Sitting oj" the Academy 

 of Sciences, 2d April, 1S21. By M. BioT. 



When the electric current, evolved from a voltaic battery, is 

 transmitted through any metallic bodies whatsoever, it gives 

 them instantaneously a magnetic virtue ; they become then 

 capable of attracting soft and unmagnetized iron. This 

 curious fact was discovered by M. Oersted. If we expose 

 to these metallic bodies, a magnetic needle, they attract 

 one of its poles, and repel the other, but only relative to 

 the parts of their surface to which the needle is presented. 

 Needles of silver or copper are not affected, but merely those 

 susceptible of being magnetized. These effects subsist only 

 under the influence of the electrical current. If we suspend the 

 circulalifon of the electricity, by brcakiirg oflT the communications 



