174 



rxix i. \T..I:V ro&OXa- KI.K.TKICIT v. 



[TUB KLKTBJO HP*KK. 



mall portion of air, together with the vapour of bisul- 

 phite of carbon. This u easily dime, by placing a little 

 cotton wool, moistened with nrad, on the screw. The 

 air, ruhiug in, will take a portion of tin- rapour with it 

 Tin- rweiver u again to be exhausted, after doting the 

 crew. If the ipark be then paused, a fine lavender- 

 ; n-d discharge will take place ; a port ion t>f thu vit|>oiir 

 will be decomposed ; a bright Hash of l>lno lij,'ht will be 

 MOD ; and sulphur will be deposited on the inside of the 

 glass receiver. 



Experiment J. By similar mean*, the vapour of 

 ether, benzole, camphine, alcohol, and other volatile 

 liquids, may be introduced ; and each will produce a cha- 

 racteristically coloured .park. 



Experiment 8. Besides volatile liquids, various gases, 

 such as oxygen, nitrogen, carbonic acid, hydrogen, <tc., 

 may be employed. ThU is best done by filling a bladder, 

 ..Inl with a good stopcock, with the gas, and screw- 

 ing the worm into the scruw-hole of the air-pump, 

 through which air is admitted into the receiver. The 

 stopcock of the bladder should at first be closed, until 

 the air in the receiver lias been exhausted ; a small 

 quantity of gas may then bo admitted by opening the 

 stopcock. The spark is then passed as before, and some 

 pleasing effects may thus be obtain. 1. 



We must caution the experiment r. however, as to the 



employment of coal gas, or pure hydrogen ; as, if the ro- 



r happen to contain air, or if the gas be mixed with 



air in the bag, the electric spark may cause its ignition, 



and an explosion may ensue. 



fiment 9. A very ready mode of trying these 

 experiments in a vacuum, may be found in an ordinary 

 barometer tube. A glass tube, thirty-six inches long, 

 and a Quarter of an inch in diameter, is to be sealed at 

 one end, and through this a platinum wire is to be passed, 

 so that one end may be inside, and the other outside of 

 the tulxj. The latter is to bo filled, at its open end, with 

 mercury ; and the finger being placed on the hole, so as 

 to prevent the escape of the metal, the tube is to be in- 

 serted into a small vessel containing mercury. The 

 finger may then be removed from the tube, and a portion 

 of the metal will run out into the cistern. The height 

 of mercury remaining in the tube, will correspond with 

 that of an ordinary barometer, and a vacuum will be left 

 at the top of the tube. The platina wire is then to be 

 connected with the conductor of the machine, and any 

 liquid or gas can easily be passed up to the vacuum por- 

 tion of the tube, by means of its open 

 end. We first employed this ar- 

 rangement for experiments with a 

 Khuuikorff coil machine, and found 

 it extremely convenient ; because, 

 excepting the presence of a slight 

 amount of mercurial vapour, a per- 

 fect vacuum is readily obtainable. 

 Fig. 7 represents an apparatus of 

 this kind. 



We shall have again to refer to this 

 arrangement when we explain the 

 cause of the Aurora Borealis ; but 

 we may just remark, that the elec- 

 trical discharge in a vacuum, pre- 

 sents many points of resemblance to 

 the phenomena we have named. 



The reader, on repeating the ex- 

 periments we have suggested, will 

 at once perceive the truth of what 

 we before stated that the colour and 

 intensity of the electric spark de- 

 pend on t "f lli" medium 

 u the glu* lube, con- through which it passes : and having 

 sf illustrated this /act, we may now 

 suggest a variety of experiments, 

 i ] .resent the spark as it panel 

 between conductor*. A great num- 

 ber of ingenious devices have been 

 arranged for this purpose. 

 Experiment 10. Paste, on a piece of window-glass, 

 some small dots of tinfoil, in the manner illustrated in 



t- m of that metal ; c, 

 the Ttcuum ; <i, the 

 platinum wire ; nd 

 i, i rinit-ound to 

 nppart the tube in a 

 Trtlul pueiliun. 



>. so that a continuous and equi-distaut series may 

 pass from one end t>. r\ t . a, 



other : attach to one end a - 



wire, connected with the |c? o o o <?o oo oO <? 

 earth, and present the op- 

 posite end to the conductor of the machine. At each in- 

 terval bet ween the pieces of tint, i will pass as the 

 electricity breaks from one to the other through the air. 

 Any device may thus be made luminous by the electric dis- 

 charge ; and an illustration of one of them arrangements 

 is found in Fig. 9. >, f . g 



A brass itiiob . 

 should bo attached 

 to that end which 

 is presented to the 

 conductor, for rea- 

 sons we shall pre- 

 . explain. 



,.<(!< 11. A very pretty mode of showing the 

 electric spark, is that of threading, alternately, glass 

 beads, with pieces of cork covered with tinfoil, on a silk 

 thread previously varnished. One end of this is to be 

 connected with the earth; and the opposite one, being 

 nated with a brass ball, is to be presented to the 

 conductor of the machine. As the spark passes, each 

 bead will appear luminous. A thread of upwards of 100 

 feet long was frequently used with the hydro-electric 

 machine, when many hundred sparks, passing over the 

 whole length, produced a most brilliant effect. 



Experimeiit 12. Those of our readers who possess a 

 three-feet plate machine, may moke a very elegant ar- 

 rangement for exhibiting the spark passing inside egg- 

 shells. Four or six egg-shells are attached to each other, 

 so that a copper wire may pass through the end of each. 

 The wires are separated, at the centre of the egg, by a 

 thin thread of silk being tied to each, so as to preserve 

 the mechanical continuity of the chain whilst the elec- 

 trical continuity U broken. Oil presenting one end of 

 the arrangement, by means of a knob, to the conductor, 

 each egg will be beautifully illuminated as the spark 

 passes between the wires inside it. The arrangement is 

 illustrated in Fig. 10. 



In each of the experi- 

 ments suggested, we have 

 recommended, that one end 

 of the apparatus should 

 have a brass ball attached 

 to it ; or, what will do ; 

 equally as well, one of cork, 

 covered with tinfoil; and 

 that tliis ball should be held 

 at a small distance from the 

 conductor. This plan has 

 the effect, apparently, of 

 (what we shall coll, for want 

 of a better term) giving an 

 impetus to the charge. If j 

 any of the arrangements we ' 

 have described are placed 

 in direct contact with the. 

 conductor, the effect is Very a it the conductor of the machine; 

 feeble. * U a dUcharger, through which 



This leads us to remark fo^r'e^.tb'r^Rh'.'iii^hlhetpar'k 



On the result which points pasce*; eisawircconm-ctinif them 



have on the passage and %*& &? "- 



character of the electric 



spark. When any pointed object is presented to an 



clertriscd surface, the spark does not pass in the manner 



wo have previously spoken of, but becomes conv. 



into a brush-like form; hence the term "electric 



brush." 



Experiment 13. Present a penknife, or pointed brass 

 rod, to within a short distance of the conductor of ilm 

 machine. A peculiar hairy-like spark will be produced, 

 having an appearance illnstratediu Fig. 11. 



Points have exactly an opposite effect on the electric 



. to that of round and even substances. They tend 



to diffuse the force; and hence the conductor of the 



electric machine is always well rounded and polished ii> 



Fig. 10. 



