proposed Improvejnents in the Magneto-electric Machine. 223 



Experiment 1. Take two bars of soft steel of any convenient 

 size, cut one of them in the middle, and bend the other into the 

 form of a horse-shoe magnet; temper both to the same colour, 

 magnetize them equallij, and try their powers in the following 

 manner : bring the two bars, as ^^___^ 



in the figure, to different di- 

 stances from the lifter A B, and 



ascertain their attractive power ; / \ A / \ b 



remove the bars and substitute / \ ■'^11 Fl^ 



the horse-shoe, and its power of 



attraction, and consequently its 



inducing power, will be found to SU UN" 



be much superior. Place the 



bars and horse-shoe in succession at the same distance from a 



revolving lifter, and the electricity induced on the coil will be 



found to be much greater, both in deflecting a needle and in 



decomposing water, with the horse-shoe magnet than with the 



equal bars. 



Hence the absurdity of using bar magnets instead of horse- 

 shoe ones to induce magnetism on soft iron, and thence voltaic 

 electricity on a coil. 



Experiment 2. Cut a bar of the same length as before into 

 three portions, bend one of the pieces into an arc, magnetize 

 the two parts, apply the arc to form a horse-shoe magnet as 

 Mr. Mullins proposes, repeat the previous experiment, and the 

 old horse-shoe magnet will be found to be much stronger than 

 the new one. 



It is easy to see how Mr. MuUins, in his experimental re- 

 searches, has been led into these errors. Horse-shoe mag- 

 nets, made by ignorant makers, are often left almost entirely 

 soft at the bending and only hardened towards the poles or ends, 

 from the old absurd notion that the magnetism was accurmi- 

 lated at the poles. The soft part of the circuit therefore, 

 possessing scarcely any coercitive power, is very much in the 

 same state with a piece of soft iron. Such a magnet may per- 

 haps be improved by cutting off the bending and supplying 

 its place by a properly magnetized arc. Another error into 

 which Mr. Mullins has fallen is not so easily accounted for : 

 he afiirms that the size of the arc is of no consequence. A 

 tempered steel wire would therefore be as good as an arc 

 formed of steel, two inches broad and half an inch thick. In- 

 stead then of recommending gentlemen who have horse-shoe 

 magnets applied to magneto-electric machines, to cut off the 

 bending, the wisest course will be to let them alone if they are 

 properly tempered, if not, to get them re-tempered and re- 

 magnetized. 



