INSTRUMENT FOR MEASURING MAGNETIC ATTRACTIONS, &C. 257 



needle, in one experiment 10°, and in another 14° or 15°. (2.) The 

 bar, freed from magnetism, and the shock of the battery received 

 on the lower end of it, it repelled the needle 16°. (3.) A dis- 

 charge taken from the outside of the jars, the lower end of the bar 

 being connected with the positive electricity, gave a repelling 

 power of 15°. 



Exp. 3. — The bar was now placed horizontally, pointing east and 

 west by the compass, consequently in the magnetic equator. In 

 this position, the discharge of an electrified jar sent through it, 

 produced no magnetism whatever, and the effect of the battery 

 was scarcely perceptible. The slight deviation of the needle, in- 

 deed, after one discharge of the battery, is to be attributed to some 

 accidental circumstance ; probably the bar was not accurately in 

 the magnetic equator. 



12. A bar of iron possessing some magnetism, has its pola- 

 rity diminished, destroyed, or inverted, if an electric discharge 

 be passed through it, when it is nearly in the position of the 

 magnetic axis, provided the south pole of the bar be down- 

 ward ; while its magnetism is weakened or destroyed, if it re- 

 ceive the shock when in the plane of the magnetic equator. 



Exp. 1. — The bar, No. 1., having such a magnetic influence as to 

 produce a deflection of the compass needle of 10°, was placed in 

 the direction of the magnetic axis, north pole upward. A shock 

 from the battery being then passed through it, the whole of its 

 magnetism was found to be dissipated. The discharge of one jar 

 on the bar, when slightly magnetised, with its north pole upward, 

 had a similar effect ; only in some instances, the magnetism, 

 though weakened, was not wholly destroyed. 



Exp. %. — The bar being in the plane of the magnetic equator, and 

 having such polarity as to produce 10° deflection of the needle, had 

 a charge of the battery passed through it, by which its power on 

 the needle was reduced to 2°. The shock of a single jar, produced 

 in some degree a similar effect. 



13. Iron 



