LESSONS IN ELECTOICITT. 



Ing he will cause his boys to march at his 

 Bide with a profit and a joy, which the mere 

 exhibition of facts without principles, or the 

 appeal to the bodily senses and the power of 

 memory alone, could never inspire. 



As an expansion of the note at page 339 the 

 following extract may find a place here : 



4 ' It is well known that a voltaic current 

 exerts an attractive force upon a second cur- 

 rent, flowing in the same direction ; and that 

 when the directions are opposed to each other 

 the force exerted is a repulsive one. By coil- 

 ing wires into spirals. Ampere was enabled 

 to make them produce all the phenomena of 

 attraction and repulsion exhibited by mag- 

 nets, and from this it was but a step to his 

 celebrated theory of molecular currents. He 

 supposed the molecules of a magnetic body to 

 be surrounded by such currents, which, how- 

 ever, in the natural state of the body mutually 

 neutralized each other, on account of their 

 confused grouping. The act of magnetization 

 he supposed to consist in setting these mole- 

 cular currents parallel to each other ; and, 

 starting from this principle, he reduced all the 

 phenomena of magnetism to the mutual action 

 of ecletric currents. 



"If we reflect upon the experiments re- 

 corded in the foregoing pages from first to 

 last, we can hardly fail to be convinced that 

 diamagnetic bodies operated on by magnetic 

 forces possess a polarity * the same in kind 

 ns but the reverse in direction of, that ac- 

 quired by magnetic bodies.' But, if this be 

 the case, how are we to conceive the physical 

 mechanism of this polarity ? According to 

 Coulcoin'j's and Poisson's theory, the act of 

 magnetization consists in the decomposition 

 of a neutral magnetic fluid ; the north pole of 

 a magnet, for example, possesses an attraction 

 for the south fluid of a piece of soft iron sub- 



mitted to its influence, draws the said fluid 

 toward it, and with it the material particles 

 with which the fluid is associated. To ac- 

 count for diamagnetic phenomena this theory 

 seems to fail altogether ; according to it, in 

 deed, the oft used phrase, 'a north pole ex- 

 citing a north pole, and a south pole a south 

 pole/ involves a contradiction. For if the 

 north fluid be supposed to be attracted toward 

 the influencing north pole, it b absurd to sup- 

 pose that its presence there could produce re- 

 pulsion. The theory of Ampere is equally at 

 a loss to explain diamagnetic action ; for if 

 we suppose the pai tides of bismuth sur 

 rounded by molecular cui rents, then, accoid- 

 ing to all that is known of electro-dynamic 

 laws, these currents would set themselves 

 parallel to, and in the same direction as those 

 of the magnet, and hence attraction, and not 

 repulsion, would be the icsult. The fact, 

 however, of this not being the case proves 

 that these molecular curients are not the 

 mechanism by which diamagnetic induction 

 is effected. The consciousness of this, I 

 doubt not, drove M. Weber to the assumption 

 that the phenomena of diamagnetism are pro- 

 duced by molecular currents, not directed, but 

 actually excited in the bismuth by the magnet. 

 Such induced currents would, according to 

 known laws, have a direct ion opposed to those 

 of the inducing magnet, and hence would 

 produce the phenomena of repulsion. To 

 carry out tb" assumption here made. M. 

 Weber is obliged to suppose that the mole- 

 cules of diamagnetic bodies are surrounded 

 by channels, in which the induced molecular 

 currents, once excited, continue to flow with- 

 out resistance." Diam agnetism and Magne- 

 crystalhc Action, pp. 13G, 137. 



THE END. 



CONTENTS. 



.fttroductton 288 



JlUtoric Notes 288 



T>\-3 Art of Experiment 289 



KUiCtJ-ic Attractions 290 



I)is3>v-ry* of Conduction and Insulation 292 



T:i3 Electroscope &-3 



Electric an,l Non-Electrics 21)5 



Elactri-j R-pulsions 208 



Ftmlirnsatal Law of Electric Action 297 



Double or " Polar " Character of the Electric 



Force 290 



What is Electricity? 301 



Electric Induction 302 



The Electropho*-us 3"7 



Action of Points and Flames 308 



The Electrical Machine 309 



The Leyden Jar 314 



Franklin's Cascade Battery 317 



Leyilen Jars of the Simplest Form 318 



Itrnition by the Electric Spark 320 



Duration of the Electric Spark 3'J3 



Electric Light in Vacuo 324 



Lichtenberg's Figures 326 



Surface Compared with Mass 3-26 



Physiological Effects of the Electrical Discharge 328 



Atmospheric Electricity 3"<i8 



The Returning Stroke 330 



The Leyden Battery 888 



Appendix: An Elementary Lecture on Mag- 

 netism 334 



