to retain its Magnetism after the Battery has been removed. 123 



all made from the same kind of iron ; one about six inches 

 in circuit, another about a foot, and the other four feet. 

 When connected with the battery they possess nearly equal 

 powers. When the contact is broken, — in the first case the 

 lifter falls off almost instantaneously ; in the second it does not 

 fall off', but requires a force of several pounds to separate it 

 a considerable time after the contact is broken ; the third re- 

 quires a much greater weight to separate the lifter when it 

 has been removed a considerable time from the battery. By 

 making one still longer, it is probable the retaining power 

 will be increased. ' 



The reason of this curious fact appears to be the following. 

 The molecules of the electric fluid acting on each other with 

 the same force, will obviously return to their natural position 

 most rapidly when the length of the circuit, through which 

 the action takes place, is diminished. If it be diminished till 

 the coercitive force of the iron be overbalanced by the ten- 

 dency of the molecules to return to their natural state of equi- 

 librium, from which they have been forced by the action of 

 the conducting wire, the electro-magnet will lose all its re- 

 taining power. 



Before I discovered this curious and, 1 believe, novel fact, 

 I was led to conclude that an electro-magnet had no power 

 in inducing permanent magnetism on hard steel, when the 

 magnetic circuit is completed by the lifter. The electro-mag- 

 net which I had used in all my experiments was the short 

 one of very soft iron, which scarcely possesses any retaining 

 power. With this magnet, though possessing a lifting power 

 of 50 or 60 pounds, I could scarcely induce the slightest mag- 

 netism, and was therefore naturally led to the conclusion that 

 an electro-magnet was deficient in this power. In repeating 

 the experiments with a different electro-magnet, (though still 

 by accident a very short one,) I always arrived at results al- 

 most negative. Mr. Children having stated to me that Mr. 

 Watkins communicated powerful magnetism by an electro- 

 magnet, induced me to re-examine the subject. When I dis- 

 covered the circumstance which modifies the retaining power, 

 it immediately occu rred to me that the same circumstance would 

 likely modify the power of inducing permanent magnetism. 

 Having arranged an un magnetized horse-shoe of tempered 

 steel, I began, as before, with the short magnet; and found 

 that scarcely any permanent magnetism was induced. Having 

 taken the next magnet in succession, and used it in the com- 

 mon way of magnetizing, a considerable degree of magnetic 

 power was induced : when I employed the magnet four feet 

 long, a much greater permanent effect was the result. The 



R2 



