350 FRAGMENTS OF SCIENCE. 



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 

 illustrating 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 pres- 

 ent. Should you ever become a patentee for the regu- 

 lation 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 ren- 

 der 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 



