350 FRAGMENTS OF SCIENCE. 



standing it is not sufficient : you must obtain a manual 

 aptitude in addressing Nature. If you speak to your 

 fellow-man you are not entitled to use jargon. Bad 

 experiments are jargon addressed to Nature, and just 

 as much to be deprecated. Manual dexterity in illus- 

 trating the interaction of magnetic poles is of the 

 utmost importance at this stage of your progress ; and 

 you must not neglect attaining this power over your 

 implements. As you proceed, moreover, you will be 

 tempted to do more than I can possibly suggest. 

 Thoughts will occur to you which you will endeavour 

 to follow out : questions will arise which you will try 

 to answer. The same experiment may be twenty 

 different things to twenty people. Having witnessed 

 the action of pole on pole, through the air, you will 

 perhaps try whether the magnetic power is not to be 

 screened off. You use plates of glass, wood, slate, 

 pasteboard, or gutta-percha, but find them all pervious 

 to this wondrous force. One magnetic pole acts upon 

 another through these bodies as if they were not present. 

 Should you ever become a patentee for the regulation 

 of ships' compasses, you will not fall, as some projectors 

 have done, into the error of screening off the magnetism 

 of the ship by the interposition of such substances. 



If you wish to teach a class you must contrive that 

 the effects which you have thus far witnessed for your- 

 self shall be witnessed by twenty or thirty pupils. And 

 here your private ingenuity must come into play. You 

 will attach bits of paper to your needles, so as to render 

 their movements visible at a distance, denoting the 

 north and south poles by different colours, say green and 

 red. You may also improve upon your darning-needle. 

 Take a strip of sheet steel, heat it to vivid redness and 

 plunge it into cold water. It is thereby hardened ; 

 rendered, in fact, almost as brittle as glass. Six inches 

 of this, magnetised in the manner of the darning- 



