LESSONS IN ELECTRICITY. 



337 



netlzlng Iho needle I hare supposed the rye- 

 end to be the last to quit tho marked end of 

 tho magnet ; that end of th.' needle is a south 

 pole. TJie end which la 4 quits the magnet 

 is always opposed in p'-larity to the end of 

 I ho magnet with which it lias been in contact. 

 BiMuglit near each other they mutually at- 

 iract, and thus demons. rate that they ate uu- 

 liki 1 p >!cs. 



You may perhaps learn all this in a single 

 hour; but spend seveial at it, if necessary; 

 an 1 remember, understanding it is not sulli- 

 cient : you mu^t obtain a manual aptitude in 

 addressing Nature. If you speak to your fel- 

 low-man, you are not entitled to use jargon. 

 Bad experiments nre juigon addressed to Na- 

 ture, and just as much tj be deprecated. A 

 manual dexterity in ill astral ing the interac- 

 titin of magnetic poles is of the utmost impor- 

 tance at tuis stage of your progress, and you 

 must not neglect attaining this power over 

 your implements. As yru proceed, more- 

 over, you will be tempted to do more than I 

 can possibly suggest. Thoughts will cccur 

 to you which you will endeavor to follow 

 out ; questions will arise which you will try 

 to answer. The same experiment may be 

 twenty things to twenty people. Having wit- 

 nessed the action of pole on pole through the 

 lr, you will perhaps try whether tbe mng- 

 pctic power is not to be screened off. You 

 use plates of glass, wood, slate, pasteboaid, 

 or gutta-percha, but find them all pervious to 

 this wondrous force. One magnetic pole nets 

 upon another through these bodies as if they 

 were not present. And should you become 

 a patentee for the regulation of fillips' com- 

 passes, you will not fall, as some projectors 

 have done, into the error of screening off the 

 magnetism of the ship by the inter position of 

 auch substances. 



If you wish to tench a class you must con- 

 trive that the effects which you have thus far 

 witnessed for yourself shall be witnessed by 

 twenty or thirty pupils. And here your pri- 

 vate ingenuity must come into play. You 

 will attach bits of paper to your needles, so 

 as to render their movements visible ot a dis- 

 tance, denoting the north and south poles by 

 different colors, say gieen and red. \ou 

 may also improve upon your darning-needle. 

 Take a strip of sheet-steel, the rib of a lady's 

 Hays will answer, heat it to vivid redness and 

 plunge it into cold water. It is thereby hard- 

 ened rendered, in tact, almost as brittle as 

 glass. Six inches of this, magnetized in the 

 manner of the darning-needle, will be better 

 aole to carry your paper indexes. Having 

 aeriireil such a strip, you proceed thus : 



Magnetize a small sewing-needle and deter- 

 mine its [>oles ; or, break half an inch or an 

 inch off your magnetized darning-needle, and 

 suspend it by a tine silk fibre. The sewing- 

 needle or the fiagment of the darning-needle 

 is now to be used as a test-needle to examine 

 the distribution of the magnetism in your 

 strip of steel. Hold the strip upright in your 

 left hand, and cause the test-needle to ap- 

 proach the lower end of your strip ; one end 

 is attracted the other ie repelled. Raise your 



needle along the strip ; its oscillations, which 

 at first weie quick, become slower ; opposite 

 the middle of the strip they cease enli ely ; 

 neither end of the needle is attracted ; above 

 the middle the test-needle turns suddenly 

 round, its other end being now attiacted. Go 

 through the experiment thoroughly ; yen 

 thus learn that the entire lower half cf'the 

 strip Attracts one end of the needle, while the 

 entire upper half attracts the opposite end. 

 Supposing the north end of your little reed-lc 

 to be that attracted below, you infer that tho 

 entire Ijwer half of your magnetized strip 

 exhibits south magnetism, while the enliio 

 upper half exhibits north magnetism. So 

 far, then, you have determined the distribu- 

 tion of magnetism in your strip of steel. 



You look HI this fact, you think of it ; in 

 its suggest iveness the value of the i xpc-i imeut 

 chiefly consists. The thought arises, " What 

 will occur if 1 break my ship of sled ncm&s 

 iu the middle ? Shall 1 obtain two magnet*,, 

 each possessing a single pole ?" Try the ex- 

 periment ; break your sliip of steel, and le&t 

 each half as you tested the whole. The mere- 

 presentation of its two ends iu succession tu. 

 your test-needle suffices to show you that 

 you have not a magnet with a single pole,, 

 that each half possesses two poles with aneiK 

 tral point between them. And if you again? 

 break the half into two other halves, you will 

 find that each quaiter of the original (strip ex.- 

 hibits precisely Ihe sanio magnetic dlsliibu-- 

 lion as the strip itself. You limy continue th* 

 breaking process ; no matter how small your 

 fragment may be, it still possesses two op-. 

 posite poles a"nd a. neutral point between them. 

 Well, your hand ceases to break vUieie hi cak- 

 ing becomes a mechanical impossibility : but 

 does the mind stop there ? No : you follow 

 the breaking process in idea when you can no 

 longer icalize it in fact ; your thoughts wan- 

 der amid the very atoms of your steel, and 

 you conclude that tach atom is a magnet, 

 and that the force exerted by the strip of steel 

 is the mere summation or lesullant of the 

 forces of its ultimate particles. 



Here, then, is an exhibition of power which 

 we can call forth cr cause to disappear at 

 pleasure. We magnetize onrstiip ot steel by 

 drawing it along the pole of a magnet ; we 

 can demagnetize it, or reverse its magnetism, 

 by properly drawing it along the same pole- 

 in the opposite direction. What, then, i- the 

 real nature of this wondrous change ? What 

 is it that takes place among the atoms of the 

 steel when thefcubstance is magnetized ? The- 

 question leads us beyond the legion of sense, 

 and into that of imagination. This faculty, 

 indeed, is the divining iod of the man of sci- 

 ence. Not, however, an imagination which 

 catches its creations fn,rn the air. but one in- 

 formed and inspired by fj'Cts, caj able </f seiz- 

 ing fiimly on a physical image as a principle, 

 of discerning its consequences, and of ('evising 

 means whereby these t\ recasts of thought may 

 be brought to an experimental test. If Mich 

 a principle be adequate to account for all the 

 phenomena, if from an assumed cause the ob- 

 served facts necessarily follow, wecail the as 



