470 



ELECTRICITY. 



I 1 -. ;x-l: 



ftl be- 

 ii tc oulumn. 



Pi ATr 



IV. 



Application 

 I' t!,<: co- 

 lumn to dc- 

 i ermine 

 the con- 

 ducting 

 pneis of 

 Indie*. 



-.. .1- increU to a/left the )>old K-nf electrometer, it applied 

 to one extremity when the column i- in this ute, the 

 effect will be instantly perceived at the other end. 

 In order to restore quickly the >t.;te of the divergen- 

 ciev the finger.-, should he Inid n both extremiti 

 t!ie column together, aiul then removed at the same 

 instant, when the original state of divergency will he 

 restored. By means of the third electrometer P, l)e 

 Luc has shewn that the negative effect goes on increas- 

 ing from the zinc to the cop|>er end of the column, 

 while the positive effect increases from the copper to 

 the line extremity, so that the electric state of each in- 

 termediate point is the sum of the corresponding terms 

 of two in verse progressions represented by determined, 

 though, in some respects, variable numbers. \\ In n 

 the divergencies at both extremities are equal, there is 

 no divergency at C, which is in a neutral state. When a 

 communication is made with the ground at B, the elec- 

 trometer at C diverges with positive electricity in the 

 came degree as it did before at A, and the divergence 

 of A is now nearly double. It is now found that the 

 whole column is in a positive state increasing towards A, 

 excepting the very extremity B, which is neutral from 

 rmninunicating with the ground. When the commu- 

 nication with the ground is made at A, the electric 

 states of the column are all reversed. The electrometer 

 C being now negative, and equal to that at B in the 

 insulated state of the column, the negative state increases 

 towards B, A being neutral. When the glass tube TU 

 is filled with water, suspended as in the Figure, the co- 

 lumn being insulated, the electrometers continue in the 

 state of equal divergence ; but when the hook of the 

 wire 8 is disengaged from the silk thread, and fixed to the 

 hook 5, the circulation of the electric fluid through the 

 glass tube is so rapid, that the divergences in the electro- 

 meters entirely cease, and return only when the extre- 

 mity of the wire 8 is again lifted up. In this way 

 De Luc tried the conducting powers of various bodies, 

 which are reduced to slips or rods, and kid on the hooks 

 5, 6. The rods are first laid upon two brass wire 

 brackets 12, 12, fixed on the front of the instrument, and 

 they are taken up by two glass hooks covered with 

 sealing wax, in order that they may be placed on the 

 hooks 5, 6, without disturbing the electrical state of the 



column. As these substances have more or lest a con- DeKripmc 

 ducting quality, they diminish in dillereiit degrees the I^ltni.v- 

 divergence of the cli . -troineter, by transmitting more """""Y""' 

 or less of the electric fluid from A to B. In this way 

 De Luc iiiiide .1 MTV cu:..m-> e\|K;rimcnt. A thin slip 

 of deal cut along the fibres was applied to the column, 

 and almost no divergence rciimined in the electrometer, 

 while another slip of the same wood, and of the same 

 thickness and breadth, but cut across, produced much 

 less diminution in the divergence. 



De Luc has likewise applied his column to the pur- And to de- 

 pose of determining the nmlatng qualities of bodies, terminc die 

 These bodies lihould he placed upon the bracket 1 12, I _', 

 and after being allowed to n main there a little time, they 

 should be breathed upon, in order that the moisture of 

 the breath may dissipate any electricity they contain, 

 mid conduct it to the ground As soon as the moisture 

 is e\.iporated, the body must be taken up with insulated 

 hooks, and then applied to the column upon the hooks 

 5, 6. A naked glass rod, placed in this way upon the 

 hooks, sensibly diminishes, in a short time, the diver- 

 gency of the electrometer. In tin's way De Luc found 

 that sealing-wax was the best electrical varnish, but that 

 the finest kind was not the most perfect insulator. 



In converting this instrument into an aerial dec- UM of thr 

 troscope, as DC Luc calls it, for observing the electrical column as 

 changes which take place in our atmosphere, he em- *" "I 

 ployed the apparatus connected with the gold ball | 

 17, which we have already described. When the ball 

 17 was suspended without the apparatus at 21, 2'2, it 

 often stuck to the large ball 1 8 ; but when the horizon- 

 tal silver wire 21 is so adjusted to the position of the 

 suspending wire 16, 17. that the two meet, the very in- 

 stant before the ball 17 strikes the ball 18, the sudden 

 jerk which is thus produced effectually prevents the 

 sticking of the ball. As the strikings of the ball 1 7 are 

 disturbed by the least shaking motion, De Luc found it 

 necessary to place the instrument in a glazed box, and 

 his apparatus was then ready for use. The following 

 observations made on the 10th of May, will show the 

 nature of the observations which our ingenious author 

 made with his electroscope, after having placed some 

 additional columns for the purpose of increasing its 

 power. 



The striking.* of the balls having ceased on the 1 4th of 

 Ma}', and on other subsequent days, De Luc was induced 

 to think of connecting the ball 1 8 with the negative ex- 

 tremity of the columns, in order to observe if the stri- 

 kings would thus be more numerous ; and it occurred 

 to him, at the same time, that, by quickly changing the 

 connection of the ball for that with the ground, and in- 

 versely, be would be enabled to discover variations in 

 the electric state of the ground, by comparing, in a short 

 time, it* effect on the striking* with that of the nega- 



tive extremity of the columns. This he accomplished 

 by means of the insulating pillars 27, 27, and by chan- 

 ging the position of the brass wire '29, he was enabled, 

 in a moment, to form u communication cither with the. 

 ground, or with the negative end of the columns. The- 

 following oVervations, made on the 26th, 27th, and 

 28th of May, will show the kind of information 

 which the column affords, when the ball is connected 

 with the ground, or with the negative extremity of the 

 columns. 





