APP. N" IX.] SIAGNETICAL OBSEEVATIONS. 641 



was presented in the direction of the dip,— an attrac- 

 tion of 3^° when the bar was in an horizontal position, 

 — and a repulsion of 44° when the lower end was pre- 

 sented in a vertical direction. The great difference of 

 the deflective power of the upper and lower ends arises 

 thus : When the upper end of the bar was presented 

 to the N. end of the needle, it was attracted, and the 

 S. end thrown off to a distance of nearly 3 inches, and 

 into a position of such obliquity, that the effect of re- 

 pulsion on this end was trifling ; but when the lower 

 end, or north pole of the bar, was presented, the nortli 

 end of the needle being repelled, the south end approach- 

 ed the bar to within an inch and a half, and came into a 

 right-angular position to the attractive force, by which 

 the effect of the bar was doubled, the south pole be- 

 ing attracted as much as the north pole was repelled. 

 2. A steel bar, hardened at the ends, and very slightly 

 magnetised, being substituted for the iron bar, the 

 effects produced on the needle were varied. When 

 the north end of the steel bar, in the magnetic equa- 

 tor, was presented to the north end of the needle, the 

 repulsion was about 44° ; in the direction of the mag- 

 netic poles, the repulsion, with the south end depres- 

 sed, was only 13° ; but, with the south end elevated, 

 it was nearly 100°. Hence, magnetised steel is evident- 

 ly stronger in its polarity, when in the direction of the 

 dip or magnetic poles, than in any other position. 

 In these two experiments, it will be observed, the lower 

 end of the iron bar, when in a vertical position, and 

 the north end of the magnetised steel bar, when in the 

 position of the magnetic equator, had exactly the same 

 influence over the magnetic needle, each producing a 

 deflection from its natural position of 44°. If, there- 

 fore, the quantities of deflection of a magnetic needle, 

 freely suspended, be measures of the force of the po- 

 larities of any magnets presented to it at similar dis- 

 tances, and in the same jwsition, as is reasonable to 



