XLIV. Description of an electrometer invented by Mr. Lane; with an account of some experiments made by him with it: In a letter to Benjamin Franklin, LL. D. F. R. S. [ M* ] Received Auguft,, i f 07* XLIV. Defcription o f EleBrometer in­ vented by Mr. Lane; w ith an A ccount o f fam e Experim ents made by him w ith it >' In a Letter to Benjamin Franklin, F .R .S . Alderfgate-Street, Oftober 15* s i r , Read Nov. j 6,T O E I N G employed in fome eleftri- * 767* | j cal enquiries about the beginning of the year 1762, it occurred to me, that many experi­ ments on this fubjeft might be made with a much greater degree of ptecifion, i f we could determine, with any tolerable accuracy, the comparative quan­ tity of elettric fluid, with which, for any given ex­ periment, the coated phial is impregnated. An inftrument, which I have contrived for this purpofe, may not improperly be called an Electro­ meter. 1 have herewith fent you a drawing thereof [ T a b . X X .] with the machine * to which 1 have fixed it. * This portable machine is the contrivance o f Mr. Read, mathematical indrument maker at K^nightlbfidgc ̂ ncar^ on. M m m 2 Figure D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 C 45a J F igure i . A . T h e cylindrical glafs o f the m achine, ufed inftead o f a globe. T h e cylindrical part o f the glafs is fix inches in length, and fixteen in circumference. r : % f i * • HfI Z’i n fli118p V ̂ *?$ * k * dwk B. T h e wheel, at every turn o f w hich the cylindri­ cal glafs revolves four times! * C . T h e conductor. D . T h e coated phial, E . A brafs wire loop, pafling through the wood w ork to a tin plate, on w hich the coated phial Hands. F . T h e pillar o f the Electrom eter m ade o f w ood, bored cylindrically about 4 o f its length, and rendered eleCtrical, by being long* baked in an oven, and then boiled in. p n % d oiL and again kaked;^ A t firft the pillar was m ld e o f brafs, which, though it ferved very well to determine the eleCtric ftroke for medical purpofes, yet was defective in m any experiments] as the ta­ ble thereby became a ready co n d u cto r.' - G . Bra$ work, having its lower part inclpled within the bofe o f th e pillar. H . A fCteW, * which pafles through the brafs w ork near the bottom, * and fixes ft in the pillar. * ^ groove for the ferew H to move in, yvhen th e Electrometer is moved higher or lower, as the diffbreht heights o f different condenfing phials may require. ! ̂ ’ v • § ; ; , A well poliflied hemifpherical piece o f brafs, fixed to the conductor* L, A D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 t M3 J , , L. A fteel fcrew,; pafling through the top of the brafs work, whofe threads are diftant nearly u(\) of an, inch from each other. M . : A well polifhed fphericaj, piece of brafs, fixed to the fcrew L, apd oppofite to K. T he poliih of K and IVf. will often tbe: deftroyed by large eledrical explofioi^s, and it ftiould'iagain be reftored, particularly, wh^re the experiments require accuracy. N . A fcale, ?with divifions equal to each turn of the 3f{i fcrew. - \ . . :r ] . ;; \H . : • ; O . ; A circular plate fixed to, and moving with the fcrew, pointing at each turn to the divifion upon th e fcale. This plate is alfo divided into tw elve,; to denote the parts of each turn. T he principle, on which the Elqdrometer ads. is very: Ample, being; merely th is; the coated phjaf is hereby crender#ed incapable of accumulating and re- taining 'any more than a certain quantity of the £le$ric fluid, for any intended experirpent, w hen a metallic;,pr non-eledric communication ? is*, made from the fcrew H to the, wire, lpop E of |h p , may chine, and that quantity w ill be proportionate to, ; the diftance of, K and . M * from each other,, «and ppnfe- queptly the exploflon and ftroke thereby he * re­ gulated^; v/ ; j ? v+hSivr ( Thus if a perfon holds a «wire faftened to the fcrew H in one hand, and another wire fixed to the loop E in the other, he will perceive no ftroke, if. K and M are in contad, notwithft^nding thp cylin­ drical glafs A ads ftrongly. But if„ by turning the fcrew L, the ball M is diftant from K part of 3. anV D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 C 454 J an inch, a very fmall ftroke will b6 perceived, w ith ah explofton from K to M J; &nd if K and M are diftant one inch frotlveach other, the quantity o f the etedtric fluid, at the tim e o f the explofion^W tllbe ihcreafed loO 'titnes r for example, i t appfeaVs by experiment, that; if the expiofioh happens after 4 ttirns o f-th e wheel B / w h e n : ;M is diftant frdm K o f an inch; or 1 turn o f th e fdfew ; the fame will happen at 8 turns o f the w heel; w hen M and K ’are diftant 2 turns 0 f; f h e ^ r d w y m r VT- o f an inch 5 and if K and M are diftant 3 turns o f the fcrew, the turns of the Wheel WiH be 12 at the tiihe o f the explofion * the fame proportion will conti­ nue fo far as the diftance o f K and M is equal to the condenfing power o f the coated phial w ithout wafting. By wafting, I m ean when the phial is fo fully charged; that part o f the efleQ$c fluid efckpes frotn the m o u th o f die boftl&f far fto ftfth e ‘condu ft^ f into th e air, or to fodi e adjacent non-eledtric,v T h e dum ber Of ttirns Of th e wheet;^W henr K and M are at any of th e abo^e distances,'' Will be m dre or left id proportion to:th e ftate: o f die aif^ th e dyflridtical glafs; the^cuftiion agaihft which' t h e l!glafsr 4 ifhfU nt By. experiment it alia appears, that the quantity o f eleCtric fluid, at every explofion, will be propor­ tionate to the quantity of coated glafs, either as to the fize of the coated phial, or to the number of phials added, t o r example, if the phial D has half of the coating on each fide of the glais taken off, the explofion will happen after half the number of turns of the wheel, at any o f the above diftances * and if a phial, with twice the quantity of coated glafs, is employed inftead of D, the number of turns of the wheel will be double; the feme will happen if two coated phials, each equal to D, are ufed 5 and if three phials, the number o f turns will be triple, ccc, T?he phial D, ufed, in the following expei'imentF, contains about-80 fquare inches of coating on the infide, and tilfo on the outfide of the gla&; , the mouth being flopped with wood, prepared like the pillar, and the coating not too near the mouth of the phial,* to prevent the eleCtric fluid’s wafting, and thereby the phiafm ay be more fully charged.. As K is part of the conductor, and of M the elec­ trometer, the diftance; between them is the diftance of the electrometer from the conductor ^ whence it will be readily underftood, when I relate the diflance of the electrometer, in any experiments, For ex­ ample, the electrometer at 20, that is, M, is 20 turns of the ferew diftant from K, or of an inch. T hat lightning and electricity are qf very near affinity, it not the fame, evidently appears from the many difeoveries you have m ade; and as the follow­ ing experiments tend to confirm the fame, as well as 7 to D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 f 4 5 6 1 to iiluftrath the tlfe'Of^he eleflrom cfcrj11 hope they will not b h unacceptable,: r j n f l 1 0 . ' : n u n t'd EXPERIM ENT 1\ i 1; q£II (T ilJ“i£iC|" 3n[« II €*>lcra^V> 1U1 , ,)-iv 1 •?'; %ii$l£JCf A piece o f moift tobacco-pipe clay, rolled cylin* drically, a>fig. 2. about an inch in length, and about 2 or y3o- o f an inch in diameter, having a piece o f wire thruft into each end, b b, diftant about ilL. o f an inch from each other, w ith the folid clay between, and the end o f one o f the wires, fixed to the loop of the machine E , and the other fixed to the fmall fcre'w of the eledtrometer H , will, w ith an explofion at 20 of the eledtrometer, be inflated as in fig, 3. or i f the clay is too dry, of the quantity erf* eledtricity too great, it will b u r f t‘in pieces,: leav­ ing only the clay concave hear the erids of* th e w ires; and though the experim ent will in appearance differ, yet it vfili always leave evident figns o f an ex- plofive power, or fudden rardfadtion/ eXceptihg when the wires in the d a y are at too great a d iftan ce' from each other y then the eledtric fluid will'only run over its rnorft furface. If, inftead o f clay, a mucilaginous vegetable pafte is ufed, as wheat-flowef a M water,' &c, th e e x p e rim e n t will appear the fahie. ExPR RIM feN T'IL [Take a piece o f com m on tobacco-pipe^ hard- baked, as ufed for fmoaking, about ah infch in length ; filh the bore w ith clay, and put wires* into daeh end, as in fig, z , which applied fn the 1 fame m anner to the machine, will burft into many pieces, at D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 C 4:57 3 at 2Q of the qledrom eter; fometimes the pieces will be driven near ten feet from the machine. , **v 1 . •• vi 4 V I 1 I « ' - 'J* ' * Experiment III. A fmall fquare piece of Portland ftone, with holes drilled each end fo as to admit the wires, was in like manner burft in pieces, when a fecond coated phial was added to increafe the ftroke* T h e iron cramps in ftone buildings are fitttilar to the wires, and when a building is ftruck by light*' ning produces a fimjlar effect. I obferved, that when the tobacco pipe, of ftone* was damp, the experi­ ment fucceeded better than when d r y ; and I fre- qpendy found, that fither, of .them,, afte r̂ ^eing fifft dipped ip water,' would be broken with a le fsp p lo - fion than before. Tjiis |pb^eryatipn is different from the received ppinicjn p P many, not well acquainted with ^bc- tricityi thgt lightning k ie fs likely to k o m tichief af^ t^r a t flipper of rain |h a n before, f ' fo Far ma^ be truej that the rain, will bring down feme of the li^htningt and aifo render thatched bouies, .&