with Notes hi/ Mr. Faraday. 47 



phgenomena in question obey the laws of the collisions of 

 solids. The magnetism of rotation discovered by the cele- 

 brated Arago has already shown what influence motion has 

 in these phaenomena. Then slowly moving the magnet, it 

 may be introduced and removed from the spiral without 

 causing any sensible current. To obtain the maximum effect, 

 it is necessary that the magnetic pole should make its en- 

 trance or exit with great velocity. {Exp. Res. 136. 153. 258.) 



3. Introduce at the same time the poles of the magnet into 

 two equal spirals, having the same direction, and two contrary 

 currents will be obtained, which would destroy each other if 

 the poles of the magnet were of equal strength. But as the 

 north pole is in our latitudes more active than the south, the 

 effect obtained will equal the difference of the two currents, 

 and be in the direction of the greater force ; exactly as hap- 

 pens in the collision of solids. It results from this my expe- 

 riment, that henceforth we may ascertain at once with facility 

 which is the most powerful of two magnets, and how much 

 more active the north pole is than the opposite south pole of 

 the same magnet*. 



4'. In order to take advantage at the same moment of both 

 the poles of the same magnet, construct two spirals turning 

 in opposite directions, and place them as usual in connection 

 with the galvanometer. Then on introducing the poles of the 

 magnets, an effect will be obtained, equal to the sum of those 

 which could be produced by the poles separately. To mea- 

 sure the effect produced by these two spirals with a more 

 powerful magnet than the first, I was obliged to use a gal- 

 vanometer of only one-twentieth the sensibility of the first. 



6. I immediately perceived that this pair of spirals was a 

 valuable element capable of furnishing a mode of augmenting 

 without limit the efficacy of the instantaneous currents. I 

 therefore instantly constructed a second pair of spirals equal 



[* The statement that the north pole is in our latitudes more powerful 

 than the south is a mistake. The cause of the effects obtained by Signor 

 Nrgro will be found at p. 147 of my Exj). Research., and is dependent on 

 the inductive force of the earth, as a magnet, upon other magnets, as well 

 as upon soft iron. When a straight magnet is held in the dip, or even 

 vertically with its marked pole downwards, both poles are strengthened; 

 when held with its unmarked pole downwards, both poles are weakened. 

 And though when a horse-shoe magnet is held with both poles downwards, 

 as in Signor Negro's experiment, the marked pole is stronger than the un- 

 marked one, it is only because the two limbs are affected as the single magnets 

 just referred to, and the bend of the magnet being the upper part becomes 

 virtually a feeble south pole. If the horse-shoe magnet be held with 

 its poles upwards, then the contrary effect happens, and the unmarked 

 (usually called the south) pole becomes the stronger ; or if both poles «re 

 in equal relation to the magnetic dip, then both are e(|ually strong. — M.I<\] 



