THE SPARK, ETC.] UNDULATORY FORCES. ELECTRO-MAGNETISM. 



257 



connection with frictional electricity, may be performed 

 similarly by means of the Rhumkorf coil ; and we shall 

 leave the choice of such to those of our readers who may 

 feel disposed to try them referring them to those we 

 have mentioned under the head of Frictional Elec- 

 tricity. 



We may here make a remark on some peculiarities in 

 reference to the appearance, (to. , of the spark produced 

 on charging a Leyden jar by means of a Rhumkorf coiL 

 The brilliancy of the spark, and the noise of the discharge, 

 are affected by the size of the jar, to some extent, but in 

 no comparison to that witnessed when frictional electricity 

 is employed. We have charged, successively, twelve 

 Leyden jars, each 28 inches high, and 50 inches in circum- 

 ference, by the hydro-electric machine* and a Rhumkorf 

 coil. The noise produced by the discharge of the jars, as 

 excited by the machine, was truly deafening ; whilst that 

 of the Rhumkorf discharge scarcely exceeded a sharp 

 rapping sound. Of course, the discharges and charges 

 of the Rhumkorf are produced continuously and succes- 

 sively, at a very rapid rate at least 200 per minute ; 

 whilst the machine charge did not exceed two in number 

 during that time. We have also remarked, that the 

 larger the jar charged by a Rhumkorl, the shorter is the 

 length of the spark ; but its lateral extension is, at the 

 same time, increased. Its mechanical and calorific effects, 

 however, do not seem to at all increase with the size of 

 the jars ; for a half-pint jar will perforate about the same 

 thickness of card as the large battery we have just 

 i ud. 



Numerous experiments, analogous to those included 

 under the head of Voltaic Electricity, may be repeated, 

 but on a very small scale with a Rhumkorf. We have 

 only succeeded in obtaining a most minute but brilliant 

 spark from carbon terminals similar to that produced by 

 charcoal points, forming the poles of a powerful voltaic 

 battery. We have rendered soft iron electro-magnets 

 attractive by the coil current; and feeble, but decided 

 decomposition of water, or of a solution of sulphate of 

 copper, may be produced. In this experiment we em- 

 ployed two pieces of platina wire as the poles of the 

 secondary coil. In repeating experiments of this kind, 

 the ordinary voltaic apparatus, like the frictional, may 

 be generally employed ; but, as we have already remarked, 

 care must be taken that the experimenter shall not receive 

 an accidental shock. 



As there are some interesting particulars attached, 

 generally speaking, to tho physiological effects of elec- 

 tricity, which are especially attractive to the general 

 reader, we will make a few observations on the subject. 

 The shock produced by frictional electricity has a sudden 

 and, of course, transitory effect ; because, the instant the 

 jar is discharged through the body of the person, the 

 effect can only bo repeated by a fresh-charged jar. The 

 shock from a voltaic battery, of high power, acts con- 

 tinuously on the muscles so long as the hands are in 



contact with the conducting wires ; and if from 100 cells 

 of Grove's battery, the effect is very painful. The 

 ordinary coil machine acts in a similar manner ; but being 

 more intense, the effect is still more powerful. The 

 physiological effects produced by the Rhumkorf coil, are, 

 of course, far greater. The writer accidentally received 

 a shock by the wire from the outer end of the coil falling 

 on his chest. The sensation experienced was such as to 

 create the idea that the whole of his body was a mass of 

 light : no pain was felt ; for the shock was so powerful as 

 to produce almost instantaneous insensibility. After 

 recovery, the digestive organs were considerably dis- 

 ordered for several days, and great languor and sickness 

 were felt for some hours. 



The best mode of receiving the shock from a Rhum- 

 korf, is to immerse two wires proceeding from the 

 terminals of the secondary coil, in separate basins filled 

 with river or spring-water. The hands can be dipped in 

 these ; and the force of the shock is much diminished by 

 the inferior conducting power of the liquid. 



In reference to further comparisons, or analogies, 

 between the effects generally produced by frictional and 

 voltaic electricity, and those afforded by Rhumkorf's coil, 

 we have already remarked that the latter affords a kind 

 of link for the two former ; and it may be useful to the 

 student if we enter into further details. 



The voltaic spark is continuous after being once pro- 

 duced (within certain limits) ; whilst that of the electrical 

 machine is intermittent. The spark of the Rhumkorf 

 holds a middle place. Again, the spark of the machine 

 exhibits but trifling heating effects; whilst that of the 

 voltaic battery affords us a greater amount of heat than 

 any other source with whicli we are acquainted. Now, 

 the two terminals of the secondary coil of a Rhumkorf 

 exhibit very different results. One is always intensely 

 heated, whilst the other remains comparatively cool.f 

 A voltaic battery, unless of enormous size as to the 

 number of its plates, rarely exhibits decided attractive 

 power on pith balls, or on the electroscope. The Rhum- 

 korf effects tliis result with ease, in a manner similar to 

 tho electrical machine. The Latter but feebly produces 

 chemical decomposition, as is the case with the Rhum- 

 korf; which, however, depends for its action on the 

 chemical decomposition going on in the battery, whence 

 it obtains its primary current. 



The electrical machine, even when of the largest size, 

 affects but slightly any piece of iron or steel, in respect 

 to the magnetic force ; whilst the voltaic battery affords 

 us a means of inducing magnetism to almost any extent 

 we please. The Rhumkorf holds an intermediate position 

 in this respect ; and in this and many other results which 

 our space prevents us enumerating, we may consider this 

 coil as the connecting tie between the various phenomena 

 and sources of electrical excitation and its effects ; and 

 as clearing away many difficulties which have liitherto 

 stood in the way of their complete generalisation. 



CHAPTER III. 

 MAGNETO-ELECTRIC INDUCTION. 



WB have considered it better to draw the attention of 

 our readers to the production of magnetic effects by 

 electric currents, before entering into tho discussion of 

 magneto-electric induction, because the apparatus em- 

 ployed, and tho phenomena manifested, will be more 

 readily understood by the perusal of our previous re- 

 marks. Hitherto, we have been drawing attention to 

 the fact, that currents of great quantity, such as are 

 produced by the voltaic battery, have, under certain 

 conditions, the power of inducing magnetic force. We 

 shall now show that magnetism can, by certain ar- 

 rangements, produce all the calorific, luminous, chemical, 

 and physiological results whicli may be obtained from the 

 voltaic battery, the electrical machine, or Rhumkorf's coil. 



VOL. I. 



See ante, p. 179. 



Magnetism and electricity have a mutual action on 

 each other. Wo noticed this when experimenting with 

 a spiral, at the end of which a voltaic battery was 

 placed, and to which a horse-shoe magnet was pre- 

 sented.]; The electrified spiral exhibits magnetic effects 

 just so long as the current from the battery passes by 

 it'; and such effects are exactly identical with those pos- 

 sessed by any kind of magnetised body. We have 

 shown, that if a current of electricity be passed, by means 

 of a wire, round a rod of iron, the latter at once ex- 

 hibits magnetic properties ; and, further, that these are 

 only produced when the current passes in a certain 

 direction. We shall now describe how, by using a 

 similar kind of apparatus, magnetism may induce ar 

 1 See ante, p. 255. : Ante, p. 248, \ A.nir, p. 249. 



2 L 



