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BOSTON MEDICAL LIBRARY
IN THE
Francis A.Countway Library of Medicine
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' COMPLETE TREATISE
ELECTRICITY
I N
T H E O R Y AND P R A C T I C E i
WITH
ORIGINAL EXPERIMENTS^
B X
TIBERIUS CAVALLO.
LONDON:
Printcdfor EDWARD and CHARLES DILLY.
MBCCLXXVII.
THE SOCIETY CF APOTHECARIES
OF LONDON.
i
WILLIAM WATSON,
M. D. F. R. S. M. Br. Cur.
THIS
TREATISE
o r
ELECT RICITY
IS,
WITH THE GREATEST RESPECT, •
INSCRIBED
BY HIS
MOST OBEDIENT,
AND MOST HUMBLE SERVANT,
TIBERIUS CAVALLO.
Himim
THE
PREFACE
FI E defign of the following Treatife is, to prefent to the public a comprehenfive view of the prefent ftate of Eled:ricity, reduced into as fmall a compafs as the nature of the fcience would admit. It is divided into four parts^ in each of which are contained fuch particulars, as had lefs connection with the reft ; and the diftind: view of which, it was thought, might be a means of preventing a confufion of ideas in the minds of thofe readers, who before
A3 have
vi PREFACE.
have not been much converfant with the fubjed:.
The firft part treats qf the laws of , Electricity only ; /. e. of fuch natural laws concerning Electricity, as by innumerable experiments, have been found uniformly true, and are independent on any hypothecs. In this part, the Author has not de- fcended to any particulars, which were not clearly afcertained, or which were inconfiderable ; but he has, at the fame time, taken care not to omit any thing material, or which feemed to promife future difcoveries.
The fecond part is merely hypo- thetical ; relating not to faCts, but to opinions. The great improbabi- lity of moft of thefe hypothefes de- termined the Author to render this
4 part
PREFACE.
• •
Vll
part of his work as fhort as pofli- ble.
. The third part contains the prac- tical branch of Electricity. Here the Author has taken care to infert a defcription of all the new improve- ments in the apparatus ; which ferve to leiTen the expence of it, and at the fame time, to facilitate the per- formance of the experiments. As to the experiments themfelves, he has chiefly infifted on a {ew principal ones, which feemed moft neceffary to illuftrate, and confirm the laws of Eledricity *, omitting a great num- ber of others, which he has met with, as they appeared to be only variations of the former. He has however given an account of fome others, which, though not abfo-
A 4 ' lutely
:fc,
VIU
¥k E F A C E.
lutely neceiTary, feemed very deferv- ing of notice.
The fourth and laft part contains a brief account of the principal ex- periments, which have been made by the Author himfelf, in purfuance of vi^hat occurred to him in the courfe of his . ftudies in this branch of philofophy. In this part he has omitted to mention, not only thofe attempts, which did not produce any confiderable effe6l, but alfo the innumerable conjedlures he formed about them and others, not yet brought to the tell: of adual obferva-
o
tion.
The Author takes this opportunity
of acknowledging the obligations he
is under to feveral of his ingenious
2 ' friends,
PREFACE. ix
friends, for various experiments, and remarks, communicated by them ; and particularly to Mr. William Henly, who has done as much as laid in his power to inform him of every particular, v/hich he thought would enrich and embellifh the work.
It was deemed unnecefTary to point out thofe gentlemen, v/hofe experi- ments and obfervations introduced in this work, were before well known to the world ; for which reafon the Author has confined himfelf to the mention of the names of thofe per- fons, whofe experiments were new, or not commonly noticed by the writers on this fubjed:.
To
X PREFACE.
To render the Treatife more intelli- gible, andufeful, three copper-plates are added to it ; and a copious index of the particulars which are mod de-r ferving of attention.
THE
THE
CONTENTS.
PART I.
Fundamental Laws of Electricity.
C H A P. I.
page Containing the Explanation of fome Terms
principally ufed in EleSiridty. i
CHAP. II.
Of Eiledirics and ConduBors. 4
CHAP. III.
Of the two Elefiricities. 11
CHAP. IV.
Of the different methods of exciting Elec-- tries. 20
C H A p. V.
Of communicated Electricity. i()
CHAP.
*s\i C O N T E N T 1§.
C H A P. VI.
Of EleBn'dfy communicated to 'EleSiHcs. 4^.
CHAP. VII.
Of charged EleBrics^ or the Ley den Phial, ^§
CHAP. VIII.
Of atmofpherical EleSlricityt yo
C H A P. IX.
Advantages derived from EleSiricityi. 75
CHAP. X.
A compendious View of the principal PrO'
perties of Elediricity. ol
PART II.
Theory of Electricity*
C H A P. I.
The hypothefs of Pofitive and Negative
EleSiricity, 08
CHAP,
CONTENTS. xlli
CHAP. ir.
Of the nature of the eleBric Fluids jo8
CHAP. III.
Of the "Nature ofEleBrics and ConduSlors, 1 1 g
C HA P. IV.
Of the place occupied by the electric Fluid. 123
PART III.
Practical Electricity.
CHAP. I.
Of the ekSlrical Apparatus in general. 129
C H A P. II.
fheDefcription of fome particular eltSirical
Machines. 140
CHAP. III.
^he "particular Defcription of fome other necejfary Part of the ek^rical Ap-^ paratus. i6o
CHAP.
xlv . CONTENTS.
CHAP. IV.
TraSlical Rules concerning the Ufe of the eleStrical Apparatus^ and the per- forming of Experiments. ■ lyi
CHAP. V.
Experiments concerning ekclric Attrac--
tion and Repuljton. lyg
C H A p. VI.
Experiments on eleSiric Light. 207
CHAP. VIL
Experiments with the Ley den Phial. 228
C H A P. VIII.
Experiments with other charged EleSiric s. 264
CHAP. IX.
Experiments on the Infuence of Points^ and the ufefulnefs of pointed metallic ConduSlors to defend Buildings from the Effe6ls of Lightening. 273
CHAR X. |
|
Medical EleSiricity^ |
287 CHAP. |
CONTENTS. XV
C H A P. XI.
Experiments to be performed with the
electrical Battery. 291
CHAP. XIL
Promifcuous Experiments. 303
G H A P- XIIL
Further Properties of the Leyden Phial^
or charged EleSirics. 323
F A R T IV.
New Experiments in Electricity.
CHAP. I.
The ConJiruBion of the ekSirical Kite, and
other Injiruments ufed with it, 333
CHAP. II.
'Experiments performed with the eleSlrical
Kite. 344
CHAP.
xvi CONTENTS.
C H A P. III.
Experiments performed with the atmofphe^ rical EleBrometer^ and the EleBro^ meter for the Rain. 370
CHAP. IV.
Experiments made with the EleBrophorusy commonly called the Machine for ex-- hibiting perpetual Eledlricity. 380
C H A P. V,
Experiments on Colours. 390
CHAP. VL
-Promifcuous Experiments^ 394
^he Index, 405
INTRODUCE
INTRODUCTION.
ARTS and Sciences, like Kingdoms and Nations, have each In their turn, fome happy period of glory and fplendor. In which they more than ever attract the human atten- tion, and, by cafting a ftronger light thari at other times, become the favourite objedl and purfuit of the age i but thefe periods are foon over, and a few years of luftre and fame, are often overbalanced by centuries of oblivion* From undergoing this fate, fom© Sciences are however excepted, which, ow- ing to the vaft and neceflary extent of their ufe, and to the fruitfulnefs of their prpduc- tions, are ever fteuiiihlng ; and although once unknown, yet when fame had proclaimed their birth, or publlfhed their advancement, they never afterv/ards declined ; and though they grew old, yet never decayed. Of this kind is Eledricity, the moil plea- fmg, and furpriling, among all the branches
B of
ii INTRODUCTION.
of natural philofophy that ever were culti- vated by man. This Science, after it began to fhew the extent and generality of its power ; after it was known to be one of the greateft agents of nature, remained always in vogue, was profitably cultivated, irre- mittedly advanced, and is now brought to a ftate, in which, inftead of becoming fterile, it feems further to engage the general atten- tion, and to promife to its followers more munificent rewards. Optics, indeed, ihew many enchanting and ufeful properties, but concerning vifion only : Magnetifm exhibits the force of attraftion, repulfion, and pola- rity in that fubftance called a Magnet ^ Chy- miftry treats of the various compofitions and decompofitions of bodies ; but Electri- city, containing as it were, all, within its power, alone exhibits the effects of many Sciences, combines together different powers, and,by ftriking the fenfes in a particular and furprifing manner, affords pleafure, and is of ufe, to the ignorant as well as the Philo- fopher, the rich, as well as the poor. In Electricity, we are pleafed with beholding its penetrating light exhibited in numberlefs different f@rms ; v/e admire its attradion
and
INTRODUCTION. iii
and repulfion adiing upon every kind of body; we are furprifed by the fhock, terri- fied by the explofion and force of its bat- tery ; but when we conlider and examine it as the caufe of thunder, lightning, aurora borealis, and other appearances of nature, whofe direful eifedls we can in part imitate, explain, and even avert, we are then in- volved in a maze, that leaves nothing to con- template but the inexpreffible and permanent idea of admiration and wonder.
The earlieft account we have of any known electrical eifed: is by the famous ancient na- turalift, Theophrastus, who floriihed about 300 years before the prefent era. He tells us that amber (whofe Greek name is j^xsr^r^v, and from whence the name Eledricity is derived,) as well as the lyncurium *, has the property of attradling light bodies. This, and only this, was almoft all that was known of the fubjed:, for about fifteen centuries after Theophrastus, in which long period
* It hath heen in a manner proved, that the lyncurium of Theophrastus, is the very fame fubftancc that now goes under the name of Tourmalin, of which we (hall have cc- cafion to fpeak in the courfe of this treatife.
B 2 we
IV INTRODUCTION.
we find no mention in hiftory of any perfo^ having made any difcoveries, nor even any experiments in this branch of philofophy ; the Science remaining quite in the dark till the time of William Gilbert, an Eng- lifli Phyfician, w^ho lived about the twelfth century ; and who for his difcoveries in this new, and uncultivated field, may be juftly deemed the Father of the prefent Electri- city. He obferved, that the property of at- tradling light bodies, after rubbing, was not peculiar to amber, or the lyncurium ; but
that many other bodies pofTefTcd it as well as amber. He mentions a great number of thofe, together with many particularities, which, confidering the ftate of the Science at that time, may be deemed truly great and interefting.
After Gilbert, the Science advancing, although by fmall degrees, pafTed, as it were, from infancy to puerility ; many an excel- lent philofopher undertaking to examine na- ture in this walk. Such was Sir Francis Bacon, Mr. Boyle, Otto Guericke, Sir Isaac Newton, and moit of all Mr^ Hawkesbee, a perfon to whom we are
much
INTRODUCTION. v
much indebted for many important difco- veries, and a real advancement of Eledlri- city, Mr. Hawkesbee was the firft that obferved the great eledric power of glafs, a fubftancc, that, lincc his time has been gene- rally ufed by all Eled:ricians in preference to any other electric. He firfl remarked various appearances of the eleftric light, and the noife accompanied with it, together with a variety of phenomena relating to elecStric ;^ttra6lion, ^nd repulfion.
After Mr. Hawkesbee, the Science of Eleiflricity, however hitherto advanced, re- mained for about twenty years in a ftate of quiefcence, the attention of Philofophers be- ing at that time engaged in other philofo- phical fubjecSs, which, on account of the new difcoveries of the incomparable Sir Isaac Newton, were then greatly in repute. Mr, Grey was the firft after this period of oblivion to bring the Science again to light. Fie by his great difcoveries reintroduced it to the acquaintance of Philofophers, and from him the true flourifhing era of Eledri- eity may be faid to take its date.
B 3 The
vi INTRODUCTION.
The number of Eledtricians that hath been daily multiplying fince Mr. Grey, the difcoveries made, and the ufes derived from thefe till the prefent time, are matters really worthy of attention, and deferve to be admired by every lover of the Sciences, and well-wifher to the human race.
Whoever v^ould make himfelf acquainted v^ith the particular tranfadlions concerning thofe advances, fhould read the elaborate Hiftory of Electricity compiled by the learn- ed Dr. Priestley, a v^^ork that will inform him of v/hatever had been done relative to the fubjedt till its publication. I for my part muft forbear making any long hiftorical detail ; this Treatife being intended to give an account of the prefent ftate of Eled:ri- city, and not an hiftory of the fame. I fhall in general only obferve, that although the Science had, through the indefatigable attention of fo many ingenious perfons, and by the difcoveries that were daily produced, excited the curiofity of Philofophers, and engaged their attention ; yet, as the caufes of every thing, whether fmall or great, knovv'n or unknov/n, are feldom much at- tended
INTRODUCTION. vii
tended to, if their efFefts are not ftriking and jQngular ; fo Eled:ricity had, till the year 1746, been ftudied by none but Philo- fophers. Its attra<3:ion could in part be imi- tated by a loadftone^ its light by a phof- phorus; and, in jfhort, nothing contributed to make Eleftricity the fubjedl of the public attention, and excite a general curioiity, until the capital difcovery of the vaft accurnulation of its power, in what is called the Leyden Phial, was accidentally made, by Mr. MuscHENBROECK, in the memorable year 1 746. Then, and not till then, the ftudy of Electricity became general, furprifed every beholder, and invited to the houfes of Elec- tricians, a greater number of fpedlators, than ever were before afTembled together to ob - ferve any philofophical experiments whatfo- ever.
Since the time of this difcovery, the pro- digious number of Eleftricians, experiments, and new fails that have been daily pro- duced from every corner of Europe, and other parts of the world, is almoft incredi- ble. Difcoveries crouded upon difcoveries, improvements upon improvements, and the Science ever fince that time went on with fo
B 4 rapid
viii INTRODUCTION,
rapid a courfe, and is now spreading fo ama-. singly faft, that it feems as if the fubjed: would foon be exhaufted, and Eledricians arrive at an end of their refearches : but, alas ! the ne plus ultra is, in all probability, as yet at a great diftance, and the young Eled:ri-f cian has a vaft field before him, highly de- ferving his attention, and promifing further
difcoveries, perhaps equally, or more impor- tant than thofe already rpade.
A COM-
iiii I 1
Tim • — ' ___.^_^_^ . ^ :•-
A
COMPLE TE TREATISE
O F
ELECTRICITY.
PART !•
Fundamental Laws of Electricity*
CHAP. L
Containing the Explanation of fome Therms principally ufed in EleSlricity.
IF a perfon, holding with one of his hands a clean and dry glafs tube, rubs it with his other hand, alfo clean and dry, ftroking it alternately upwards and downwards 3 and after a few ftrokes prefents to it fmall light bits of paper, thread, metal, or any other fuVftancp, the rubbed tube will im- mediately attract them, and after a little time will repel thern, — prefently, attradl them again, and fo alternately continue this attrac- tion, and repujfion, for a confiderable time. If this tube be rubbed in the dark, and after having been rubbed, a finger be pre- fented to it at the diftance of about half an inch, a lucid fpark will be ^^tn between
the
z A COMPLETE 1^ R E A T I S E
the finger and the tube, accompanied with a fnapping noife ; the finger at the fame time receiving a pufh, as if it was from air if- filing with violence from a fmall pipe.
' In this experiment, the attradion, repul- fion, fparkling, &c. are the effeds of that unknown caufe called EleBricity ; and hence they are called eleBrlcal appearances. The rfafs tube itfelf is called the ele£iric\ and all ' bodies capable by any means of producing fuch effects, are called eleBrics ; and. as the rubbing awakes, as it were, in tnem the powder of producing eledlrical appearances,- they are therefore faid to be excited by the rubbinp*. The hand, or any other body rubbing an eled:ric, is called the rubber ^ zndi if inflead of the perfon rubbing the glafs tube, a machine be conftrudled capable hy ^ny means to excite an eledlric, this, will be aa ekclrical machine.
If at the end of the tube, oppofiteto that held by the hand, a wire of any length be tied, fufoendinp: a metallic ball at its end, and the tube be excited as before, the me-» tallic ball will, in this cafe, acquire all the properties of the excited tube, /. e. it
will
OF ELECTRICITY. 3
will attract, fparkle^ &c. like the tube it-- felf, the ele£lric virtue paffing through the wire to the ball : hence, the wire is faid to be a condudlor of eledtricity, and all fuch bodies capable of tranfmitting the electric virtue, like the above wire, are called con-- duel or s.
But, if inftead of the wire, a lilk firing be ufed in the above experiment, and the tube be excited as before, the ball v/ill in this cafe fhew no ligns of Eledtricity, the filk firing not permitting the eleftric virtue to pafs from the tube to the ball: hence the filk firing in this cafe, and all fubilances through which the eled;ric virtue cannot be tranfmitted, are called noit-condiiSlors.
A body reding intirely upon non-con- duftors is faid to be infulated y fo in the lafl experiment the metallic ball was infulated, for it was fufpended entirely by the filk firing, which is a non-condud:or.
What bodies are conductors, and what elec- trics, together with their particular proper- ties, as far as it is known, will be plainly laid down in the following Chapters.
CHAP.
4 A COMPLETE TREATISE
CHAP. IL
Of EleBrics and ConduBors.
TH E firft and principal maxim in Electricity is, that all the known bodies in nature are divided into two claffes, /. e. Eledtrics and Condudlors ; experiments ihewing, that whatever fubftance is a Con- dudior of Eled:ricity cannot be excited (hence Condudlors are alfo called non^eledtrics)^ and whatever fubftance can be excited is not a Condudor : (hence Ele^Srics and Nou-conducrr 2^(?r J- become fynonymus terms). This maxim, however, is not to be conlidered as ftriftly true and general , for in reality we know no fubftance that may be called ^ perfect Elec^ trie, nor any that may be called a perfed; Conductor ; the eleftric virtue finding fome refiftance in going through the beft Cpnduc-! tors, and being in part tranfqiitted through, or over the furface of moft, and perhaps all the Eledtrics. The lefs perfedl a Condudlor any fubftance is, the nearer it comes to the nature of an Electric; and, on the other hand, the lefs perfedl Elcdlrics come neareft to the nature of Condudtors. The limits of thefe
two
^ OF ELECTRICITY. 5
two clafies come fo far one within another, that there are many fubftances which may adlually be excited, and at the fame time are pretty good Condudors. If the reader be defirous to know thefe ambiguous fubftances, he muft feek for the worft Eledlrics among the Electrics, and for the worft Conducftors among the Condud:orSj excepting fuch on which the experiment cannot be made, as fluids, powders, See.
The two following lifts contain, in general, all the Eledlrics and Condudlors, difpofed in the order of their perfecflion, beginning in each lift with the moil perfect of their clafs. In this order, however, the reader muft not expeft a great exadlnefs ; that being imprac- ticable, when fubftances are fet under gene- ral articles, and at the fame time is of little, if indeed of any ufe whatever,
ELECTRICS.
Glafs, and all vitrification^, even thofe of metals.
All precious (lones, of which the moft tranfparent are the befl.
All
6 A COMPLETE TREATISE
Ail refins ^, and refinous compolitions* Amber. Sulphur. Baked wood.
All bituminous fubflances. Wax. Silk. Cotton.
All dry animal fubftances, as Jfeathers, wool, hairs, &c. Paper.
White fugar, and fugar-candy. Air. Oils.
Calces of metals and femimetals. The afhes of animal and vegetable fub-« fiances. The ruft of metals. All dry vegetable fubftances. All hard ftones, of which the befl: are the hardeft.
* Under the name of refins, I would be underftood to mean all fuch confident oily vegetable produ6lions that are inflam- mable, and not folublc in water ; gum-lac, therefore, and all fuch fubftances improperly called gums, are alfo meant under this article. See Macc^jer's Chemiftry, vol. I. chap, xi.
Many 3
OF ELECTRICITY. 7
Many of the above fubftances, and per- haps all, upon which the experiment can be made, when very hot, lofe their eledric pro- perty, and become abfolutely Conduftors ; fo red hot glafs, melted refm, hot air, baked wood made very hot, &c. become Conduc- tors of Eledricity.
It has been obferved, that glafs, efpecially the hardeft and befl vitrified, is often a very bad Electric, fometimes being quite a Con- dudor. Glafs veffels made for eledrical purpofes are often rendered very good Elec- trics by ufe and time, though they might be very bad ones when new.
A glafs velTel, out of which the air has been exhaufled, on being rubbed, (hews no iigns of eledlricity upon its external furface, but all the electric power appears within the veffel 'f ; and a glafs tube, or globe, with the air condcnfed in it, or full of fome con-
f Although a glafs vefTel exhauftcd of air fhews no iigns of cledricity without ; yet it has been obferved, that the eleflric power of a glafs cylinder is the ftronged, when the air within it is a little rarefied, i. e. fomewhat Icfs denfe than the external air. Sre L'EIIetiricifmo Artificiale of G. B. Beccaria, § 41 1.
da(5ting
« A COMPLEX fe TREATISE
dueling fubftance, is incapable of being e^-*
cited.
f . - • . '
C O N D U Q f O R S,
Gold. ' , : ..
Silver. ^
Copper.
Brafs.
Iron.
Tin,
Quickfilver.
Lead.
Semi-metals.
Ores, of which the bed are thofe that con- tain the metallic part in the greatell quanti- ty, and come neareft to a metalline ftate.
Charcoals, made either of animal, or vege-^ table fubftances.
The fluids of an animal body.
All fluids, excepting air and oils.
The efiiuvia of flaming bodies.
Ice.
Snow.
Mofl: faline fubfl:ances, of ' which the me- tallic falts are the beft.
Stony fubflances, of which the hardefl.arc the worft.
Smoak
OF ELE CTRIC IT Y. 9
Smoak.
The vapours of hot water.
Eledlricity pervades alfo vacuum, or the abfence of air caufed by an air-pump, al- moft as freely as the fubflance of a good Condudor.
Befides thefe, all bodies in v^hich more or lefs of fome of the above-mentioned Con- ductors are contained, are alfo proportion- ably Conductors ; thus, green vegetables, raw meat, &c. are Conductors on account of the fluids they contain.
From this principle it follows, that all Eledtrics before excitation fhould be well cleaned, dried, and fome made even very hot, in order to free them from every humi- dity, otherwife they are fo far from the na- ture of Eledtrics, that they become aCtually Conductors, on account of the moifture which they contain within their pores, or upon their furfaces.
In regard to the conducting power o£ charcoal, it mufl be obferved, that all char- coal will not conduct equally well, -here being forae that will hardly ccnduCt at
C alh
10 A COMPLETE TREATISE
all ; and ' fometimes it is in fuch a Hate, that it will affift the paiTage of a large quantity of eledric fluid along the fur- face, when it will not condud it any other way. This diiFerence, however, is not occafioned by the difference of the wood from which the coals are made, but by the degree of heat that is applied in the procefs of making them ; the befl: Conduc- tors being fuch as have been expofed to the greateft heat/^^
Whether the piece of wood in the procefs of coaling is fuffered to flame, or not, is quite immaterial ; and the continuance of the fame degree of heat has no apparent ef- fedl with refpecft to the conducing power of the charcoal.
It will not be improper to obferve in this place, the different changes from Conductor toNon-condu6tor, occafioned in the fame fub- ftance by different preparations. A piece of wool juft cut from a tree is a good Conduc- tor;, letit be baked, and it becomes an Elec-
* Se.*^ Dr. Priestley's fecond volume of Obfcrvations oa difFerciit Kinds of Air, Sec. xiv.
trie;
OF ELECTRICITY. ii
trie ; 'burn it to a cdal, and it is a good Con- dudor again ; laftly, let this coal be reduced to afhes, and thefe will be impervious to ekcSricity. Such changes are alfo obferva- ble in many other bodies 5 and very likely in
al| fubftances there is a gradation from the beft Conductors to the beft Non-condudlors of Eledtriirity.
CHAP. III.
Of the two EleBrictties.
IF, in the experiment, mentioned in the iirft chapter, the perfon that rubs the tube be infulated, /. e. be fet with his feet upon a cake of refin> a ftool, with glafs i^^ty or any other good Eledtric, fo that the com- munication between his body and the earth be cut off by means of Electrics ; and if in this fituation he rubs the tube with his hand as before ; this perfon, as well as the tube, will, in this cafe, appear eledlrified. If any light bodies be prefented to any part of his body, they will be attraded and repelled. If ano- ther perfon prefents his finger to him, a lucid fpark will follow, with a fnapping noife ; and, in (liort, this infulated perfon will fhew
C % every
12 A COMPLETE TREATISE
every fign of eledricity that the tube exhi- bits. But their eledricities are not the fame ; the eledricity of the tube being juft the re- verfe of the eledricity of the perfon, and their particular appearances are the folio win o-.
I. Whenever a light body infulated, as, for inftance, a fmall piece of cork fufpended by a filk thread, has been attraded by the tube, and afterwards repelled, if no conduding fubftance touches it in this ftate of re- pulfion, it will not be attraded by the tube again. The fame happens with the in- fulated perfon ; for when this light body has been once attraded by any part of his body, and afterwards repelled, it will not be at- traded again ; but if in this ftate of repul- lion the tube be prefented to it, it will then be attraded, and that violently by the tube ; and when repelled by the tube, it will be at- traded by the infulated perfon. Further, if two or more light infulated bodies, like the above-mentioned piece of cork, be feve- rally attraded by the tube, and when after- wards repelled, be bi^ought within a fmall diftance of one another, they will repel each other, and if well infulated, continue in this cledrified and repullive ftate for a conlidera-
blc
OF E L.E C T R I C I T Y. 13
ble time. The fame will happen, if they are prefented to the perfon inftead of the tube ; ^ they will alfo, after being once repelled by this, repel one another. But, if one, or more of thofe light infulated bodies be at- tracted and repelled by the tube ; and one or more others be attradled and repelled by the perfon, and afterwards both or all (/. e. fuch as were prefented to the tube, and fuch as were prefented to the infulated perfon] be brought within a fufficient diftance of one another, they will then, inftead of repelling, attract each other ; and inftead of continuing elec- trijfied, extinguifh at once every iign of elec- tricity. Thefe two eledlricities, therefore, are (as it was faid before) the one juft the con- trary of the other, the one attrading what the other repels ; and, as if one was an af- firmative, and the other a negative power, vv^hen equal quantities of each are fummed together, they balance each other^ and lofc every property.
2. Another chara6teriftic of each of the two eledricities, confifts in the appearance of thelF light. If a pointed body, as a needle, a wire, or the like, be prefented to. the ex-
C 3 cited
14 A COMPLETE TREATISE
cited tube in the dark, a lucid globule, like a ftar, will be feen upon the point ; but if this pointed body be prefented to the infu- lated perfon, then in the place of the ftar a lucid pencil appears, compofed of rays, feemingly iffuing from the point, and di- verging towards the perfon^^f-
3 . Laflly, in fome experiments (which will be hereafter particularly mentioned, and this property better explained) the electricity of the tube, when in the ad: of paffing from a body overcharged with it to another, either not eledrified, or poffefled of the contrary eiedricity, fhews an indifputable current from the former to the latter ; and the elec- tricity of the infulated perfon, when in the ac!3; of pafiing from a body overcharged with it to another, either not eleclrified, or pof- feffed of the contrary electricity, fliews clear- ly a current from the latter to the former.
Thefe two eleflricities are not onlv obferv- ed in the above-mentioned experirnentj, but
f This pencil of rays wIH;ippear better, if a pointed needle be prefented to the infulated perfon, at the dillance of about one inch from fome part of his body, while he is adually tub- bing the tube in the dark.
in
OF ELECTRICITY. i;
in feveral other cafes alfo ; and they al- ways accompany each other ; for when dif- ferent Eledrics are rubbed, fome will acquire one eled:ricity, and others will acquire the contrary ; the rubber, if infulated, fhewing at the fame time, figns of the eledtricity con- trary to that acquired by the excited eledlric : befides this, almoft all Ele6lrics may be made to fhew at pleafure the one or the other elec- tricity, according to the fubftance ufed for a rubber. Hence the following corollaries may be deduced : "viz. i . Whenever two different fubftances (being both infulated, or only that which is a Condudor) are rub- bed together, except they are both good Conductors, they will be both eledtrified, and one acquire the eledtricity contrary to the eledlricity of the other. 2, Almoft all the Electrics may be made to acquire, at pleafure, the one or the other eledricity, by ufing proper rubbers.
The firft of thefe two eledlricities, /. e.' that poffeffed by the glafs tube in the above experiment, as it was thought to be the conftant produdlion of rubbed glafs, was called the Vitreous EleSlricity ; and the
C 4 other.
^ 1
|6 A COMPLETE TREATISE
Other, as it was firft obferved to be pro- duced by refinous fubdances, was called
the Refmous EleBricity. The Vitreous Elec- tricity is alfo called Pqfitivey or Plus EkSiricityy for a reafon that will be conli- dered in the courfe of this Treatife ; and the Refmous is called alfo NegativCy or M/- nus Ele^ricity. A body, therefore, polTelTed of the Vitreous, Pofitive, or Plus Elecftri- city, is that which ihews fuch figns as the tube was faid to exhibit; and a body pof- felTed of the Refinous, Negative, or Minus Eledricity, is that which fliews fuch figns as the infulated perfon was faid to exhibit in the above-mentioned experiment.
In the following Table may be fcen what Eledlricity will be excited in different bo- dies, v/hen rubbed v/ith different fubflances. Smooth glafs, for infcance, will be found by this Table to acquire a Pofitive Eledricity, when rubbed v/ith any fubftance hitherto tried, except the back of a cat ; (by which I mean the f]<in of a cat while on the ani- mal alive) rough glafs will be found to ac- quire the Pofitive Eledricity, when rubbed with dry oiled filk, fulphur, 6i:c. and the Ne- gative
Rough glafs
Tourmalin
OF ELECTRieiTY 17
gatlve, when rubbed with woollen cloth, the hand, &c, and fo of the reft.
The back of a cat I Pofitive, | Every fubrtance with which it
1 I has been hitherto tried.
Smooth glafs \ Pofitlve f^^^^X Jubilance hitherto tried,
"' I except the back of a cat.
I Pofitive SDryoiled filk, fulphur, metals.
y ^Woollen-cloth, quills, wood, pa-
I Negatived per, fealing-wax, white-wax, J i the human hand.
Pofitive 2 Amber, air.*
Negative 5 Diamond, the human hand.
Pofitive j ^^^^'^> ^^^^» loadftone, leather, ^ hand, paper, baked wood.
Negative | Other finer furs,
Pofitive {Black filk, metals, black cloth. Negative { Paper, hand, hairs, wcafeFs fkin.
Pofitive 2 dealing wax.
Necrative 5 ^^^^'^' weafel's, and ferret's fkin^ I Ioadftone,brafs,filver, iron, hand!
Pofitive 5 Metals.
C Hare's, weafel's, and ferret's fkln. Negative j hand, leather, woollen cloth, C paper,
Pofitive jsilk.
Hare's icin
White filk
Black ffik
S«aling-wax
Baked wood
jSii
Negative < Flannel.
* /. e. By blowing with a pair of bellows upon it. By this means many Eledrics may be excited, and fome better if the air blown is hot, although, in both cafes, very little Eledlricity can be obtained.
The
iS A COMPLETE TREATISE
The preceding Table might have been much extended, had I chofen to bring into it all the minutiae attending this matter as far as it is known ; but this I have thought unnecelTary and impradicable, becaufe expe- riments of this kind are of fo nice a nature, that they require the moft fcrupulous atten- tion in making them ; and then their effeds
depend upon fo fmall and variable circum- ftances, that often the very fame Eledtric, rubbed w^ith the fame rubber, gives at one time figns of one Eleftricity, and at another time figns of the contrary. A very little alteration in the furface, a different degree of drynefs, and even a different application of the fame fubftances often occafions a differ- ence in the Electricity, I fhall only obferve in general, that as far as may be deduced from the greatefl number of experiments, it appears, that when the different fubflances are rubbed together, that whofe Eledtric power is the ftrongefl, in general acquires the Pofi- tive, and the other the Negative Electricity; and when two bodies, differing in the fmooth- nefs or roughnefs of their furfaces^ are rub- bed together, the fmootheft acquires the Po-^
fitive, and the rougheft the Negative Elec- tricity^
OF ELECTRICITY. 19
triclty. Thefe two qualities are often to be confidered both together 5 for except the two bodies are of the fame fubftance, as fmooth and rough glafs, white and black filk, &c. they generally differ in both, /. e. they have not the fame eledlric power, and at the fame time their furfaces differ in fmoothnefs. This rule, however, is not to be conlidered as a conftant and general one j; for, according to this principle, it fhouldfeem, that apiece of fealing wax when rubbed with the hand, or paper, would acquire a Politive ElecSri- city ; but this is contrary to experience.
In cafe that two eled:ric fubflances, equal in every refpedt, are rubbed together, it is to be obferved that the fubftance which fuf- fers the greatefl fridion acquires the Nega- tive, and the other the Pofitive Eledlricity, 5uppofe, for inftance, that a piece A of filk be drawn acrofs another piece of lilk B, in every refpedl equal to the former, fo that the furface of the whole piece A, /. e. of one fide of it, be fucceflively drawn over one part of the piece B, then A will acquire the Pofitive, and B the Negative Electricity. The reafon of this may probably be, becaufe the part
. of
f A COMPLETE TREATISE
of the piece B, over which the piece A has been drawn, has acquired a greater degree of heat ; for it has been obferved, that heat ra- ther difpofes bodies to be electrified Nega- tively.
C H A ?• IV.
Of the different Methods of exciting 'Eledlrics.
UBBING, as we obferved before, is the general mean by which all eleftric fubilances that are at all excitable, may be excited. .Whether they be rubbed with Electrics of a different fort, or Conductors, they always {hew figns of Eleftricity, and in general ftronger when rubbed with Con- dudlors, and weaker when rubbed with Electrics. But befides fridion, there are other means by which fome Elecftrics may be caufed to fhew eleilric appearances, thefe are by melting, or pouring a melted Eledlric into another fubftance 5 and by heating or cooling. The particulars obferved by uiing the firft of thefe two methods are the fol- lov/ing :
If
O F ELECTRICITY. 21
If fulphur be melted in an earthen veffel, and left to cool upon Condudlors : if taken out of the veffel, when cold, it will be found ftrongly eledlrical ; but not at all fo, if it be left to cool upon Eledrics.
If fulphur be melted in glafs veffels, and afterwards left to cool, they will both ac- quire a ftrong Eledtricity, the fulphur Nega- tive, and the glafs Pofitive, whether they be left to cool upon Eledlrics or Conduc- tors ; however, they always acquire a ftronger power in the former cafe than in the latter, and a ftronger flill, if the glafs veffel is coated with metal. It is remarkable that the ful- phur acquires no electricity till it begins to cool; its power increafes in proportion as it contracts, and is the ftrongeft when in the ftate of greatefl: contraction ; but then the electricity of the glafs veffel is at ihQ> fame time the weakeft.
If melted fulphur be poured into a veffel of baked wood, it acquires a Negative, and the wood a Politive Eledtricity ; but if it be poured into fulphur, or rough glafs, it acquires no fenfible eleCtrlcity, .
Melted
22 A COMPLETE TREATISE
Melted fulphur poured into a metal cup> and there left to cool, fhews no figns of Eledricity whilft in the cup ; but if they are feparated, they will then appear ftrongly cledrified, the fulphur Pius, and the cup Minus. If the fulphur is again replaced in the cup> every fign of Eledlricity will va- nifh ; but if, whilft they are feparate, the Electricity of either of them is taken off^ they will both, on being replaced, appear poflefled of that Electricity which has not been taken oiF.
Melted wax, poured into glafs, or wood, acquires a Negative Electricity, and leaves the glafs or wood Poiitive. But fealing-- vfax poured into fulphur, acquires a Poll-* tive Electricity, and leaves the fulphur Ne-» gative.
Chocolate, freifh from the mill, as it cools in the tin pans in which it is received, becomes ftrongly eleCtrical : when turned out of the pans, it for fome time retains this property, but foon lofes it by handling. , Melting it again in an iron ladle, and pouring it into the tin pans as at firft, will for once, or twice, renew the power ; but, when the
raafs
OF ELECTRICITY. 23
liiafs becomes very dry, and powdery in the ladle, the Elediricity is revived no more by fimple melting ; but if then a little olive oil be added, and mixed well with the cho- colate in the ladle, on pouring it into the tin pan, as at firft, it will be found to have completely recovered its eledlric power •-f-
Now that we are fpeaking of melted Elec- trics, it will not be improper to obferve, that it fometimes happens, that fome eledlric fub- ftances, by being melted and left to cool, ac- quire ^n ele<Strical power, which they retain for a confiderable time, often for months to- gether, efpecially if they are preferved free from dampnefs and duft. Such effects have fometimes induced Eledtricians to think, that fome bodies are pofleiTed of a permanent or perpetual Eledlricity, which is as inherent in their fubflance as the magnetic power of a loadftone : in truth, however, no fuch fub- flance has yet been found ; and although ro- fin, fulphur, amber, and fome other Elec- trics, fhew figns of Eledricity for a confi-
f The above remark on chocolate, together with the method of reftoring its power by means of olive oil, is a recent diico- very of my friend Mr, W. Henly, F. R. S.
derable
[24 A COMPLETE T Pv E A T I S E
detable time after they have been rendered eledlrical, yet their power is continually di- minilhing till it quite vanifhes. It is re- markable, however, that fulphur, reiinous, and bituminous fubftances, retain in general the eledtric power much longer than glafs, or any other Eledlrics ; the reafon may be, that they do not attradt moifture like glafs and other fubftances.
The property of exhibiting electrical phoe- nomena, by means of heating and cooling, was firft obferved in a hard femi-pellucid foffil, known under the name of Tourma- lin;};. This ftone, which is generally of a deep red, or purple colour, and feldom ex- ceeds the lize of a fmall walnut, is common ifi feveral parts of the Eaft Indies, and efpe- cially in the Ifland of Ceyldn, Its properties in regard to Eledlricity are the following :
I. The Tourmalin, while kept in the fame degree of heat, fhews no figns of Elec-^ ' tricity, but it will become eledlrical by in-
X This ftone is called a/cl^ifitnc^ier hy the Dutch 9 from its property of attra<Sling the alhes, when layed near the fire. Lin- neus calls it /af:s fkdricus. See his Flora Zcylonica.
creafing
O F £ L E C T R I C I T Y. 2;
creafing or diminifliing its heat, and ftronger in the latter than in the former circum- ftance,
2. Its Electricity does not appear all over its furface, but only on two oppolite fides, which may be called its poles, and they al- ways lay in one right line with the centfcr of the ftone, and in the diredion of its ftrata; in which direction the flone is ab- folutely opaque : though in the other, femi- tranfparent.
3. Whilfl the Tourmalin Is heating, one of its fides (diflinguifhed by A) is eledri- .fied plus, and the other fide B minus. But when it is cooling, A is minus, and B plus*.
4^ If it be heated, and fuffered to cool without either of its fides being touched, then A will appear pofitive, and B nega- tive, all the time of its heating or cooling,
* From this law may be eaCIy deduced, that if one fide of the ftone, in feme circumftance or other, is growing hot, while the other is cooling, then both fides will appear pof- fefiedof the fame eledlricity at the fame time ; and if only one fide changes its degree of heat, while the other remains th« fame, then the former fide only will appear eledrificd.
D 5. If
i6 A COMPLETE T R E A T I S E^
5. If this ftone be excited by fricfliony like any other Eleftric, then each of its fides, or both at once, may be made Pofitive.
6. If the Tourmalin be heated or cooled upon fome other infulated body, that body wilf be found eledrified as well as the ftone, and poffefTed of the Eledlricity contrary to that, acquired by that lide of the ftone which was laid upon it,
7. The Elefcriclty of each fide, or of both^ may be reverfed by heating or cooling the Tourmalin in contad; with various fubftan- ces ; fo if it is cooled, or heated in contact with the palm of the handv that fide of it, which would have been pofitive if cooled in the open air, is now negative • and ihat^ which would have been negative, is bow polidve.
8. If a Tourmalin be cut into feveral parts, each piece will have its politive and negative poles, correfponding to the poiitive and nep-ative fides of the ftone from which
o
it was cut.
9. Thefc
OF EL ECTRIC ITV. ^j
g. Thefc propertied of the Tourmalin are aifo obfervable in vacuo, but not fb ilrong as in the open aii\
16. If this ftbrie be covered all oVer with fbme eleftric fubftance, as fealing-v^ax, oil, &c. it v^ill in general fhow the fame ap-^ pearances with this coating, as without it,
ii. Mr. WiLLtAM Canton hath kte^ ly obferved a very vivid light to appear upon the Tourmalin, while heating in the dark : he can by this determine, which end of the ftone will be pofitive, and which negative. Further, when the ftdhe is ftrcngly excited^ it emits very ftrong flafhes from the pofitive 16 the negative eiid, in the dark -f .
12. In the iafl place, it is rerharkablc
that the power of the Tourmalirl is fbme-^
*times injured by the aftioti of a ftfong fird^
fometinieS improved, dnd fometimes not stt
ail afFedted by it. The laws, however, of
\ The Brifilian emerald ^r. Canton has obferved 10 have slU ib this property of emitting light, whilft heating in the dark*
D a theft
2i A COMPLETE TREATISE
thefe uncertain eiFeds have not yet been afcertained.
The mofl of the above properties, which tvere iirft obferved, and thought peculiar to the Tourmalin, have been found to be- long to almoft all hard precious ftones, they being alfo made eledtrical by heating and cooling, and have their pofitive and nega- tive fides laying in the diredlion of their flrata or cryftals ; and, in fhort, as far it as has been obferved, they have been found to adt exactly like Tourmalins.
We fhall laftly obferve, in this chapter of excitation, that whenever an Electric is rub- bed with another infulated fubftance, al- though it acquires an eledlric power, and fhows eledlrical appearances, yet that power is very weak ; and in order to obtain a con- liderable Eledlricity, it is neceffary that the rubber fhould have a regular communication with the earth, by means of good Con- dudors*
CHAP.
OF ELECTRICITY. 29
C H A P- V,
Of Communicated Ele5}rkify.
IN the preceding Chapters we have confi- dered Eledlricity no further than in re- refped: to its quality ; we have remarked the differences between the Pofitive and the Negative, and have noted which bodies, and by what means, they could acquire this property. — But now a vaft profpeil is open- ing to cur view, full of extraordinary ap- pearances ; and v/e are to couiider in this Chapter, not tlie mere kind of Eleftricity^ but its numerous effects; Under the title of Communicated Elediricity falls almoff all that is known of the fubjedt; the paffage of this virtue from one body to another is what caufes its light j by being communi- cated to other bodies, we fee its attradion j by its quick tranfition it is that it- melts metals, deftroys animal and vegetable life j^ and, in fhprt, it is by this communi- cation that the Science is at all known jind cultivated. In order, therefore, to pre^s
P 3 . i'^^Yt
$0 A COMPLETE TREATISE
ferve perfpicuity, and diftindion in defcribing fuch a multitude of fads, I fhall employ more chapters on this fubjed;, and arrange in each fuch particulars as feem mod pro- per to be placed together, at the fame time contriving to reduce the whole into as few principal heads as it is poffible^ without con- fulion.
Whenever Electricity is by any means fuperinduced on a body, it is there con- fined only by Ele6lrics, and remains with that body a longer or a fhorter time, ac- cording as the Eiedrics that confine it are more or Icfs perfedt. A glafs tube, for in- ftance, when rubbed, acquires a quantity of that pov^er, whatever it is, which we call Eledlricity, That Eleftricity remains, and is perceivable upon the glafs, infomuch as it is furrounded by the air, which is an Elec- tric ; and as the air is in a more or lefs per- fed ele(5ric ftate, fo that virtue is retained upon the glafs longer or fliorter ; and be- jcaufe the air is never a perfed Eledric, there- fore the excited tube can never preferve^the
acquired Eledricity perpetually, but it is con-r
tinually
OF ELECTRICITY. 31
tinually imparting fome of it to the contigu- ous air, or the condudling particles that float in that element, 'till at laO: it quite lofes its power. If a finger, or any other Condu(ftor be prefented towards an excited Eledlric, it will receive a fpark, and in that fpark part only of the Elediricity of the Electric ; but why not all ? Becaiife the excited Eledric being a Non-condudor, cannot convey the Xleftricity of all its furface to that iide, to which the Conduftor has been prefented. Hence, if a conducting fubftance be fuccef- lively prefented to different parts of an ex- cited Eled:ric, it will receive at twcvy ap- proach a fpark, w ithout repeating the exci - tation, 'till all the power of that P^leftric is €xhaufl:ed, and then a new excitation is ne- ceffary in order to revive it.
Whenever a Condudor communicatine with the earth is exhibited at a convenient diflance to an excited Electric, it acquires on that exhibited fide an Eledrici ty con- trary to that pofTelled by the Eieftric : this Eledricity increafes the nearer it is ap- proached, and at lafl, as there is an eap-er at- tra<3:ion between Poiltive and Negative Elec-
D 4 tricity,
J2 ACOMPLETE TREATISE
tricity, the Condu£lor receives a fpark from the Eledlric, and fo the balance is reftored. If this Condudor does not communicate with the earth, but is infulated, and ap- proached to the excited Eledlric as before, then not only that fide of it which is towards theEledric, but the oppolite alfo, will appear eledlrified ; with this difference, however, that the fide, which is expofed to the influ- ence of the Eledlric, has acquired an Eledlri- city contrary to that of the excited Electric, and the oppofite fide an Eledricity of the fame kind with that of the Eledric. Thefe two different Eled:ricities of the Condud:or increafe as it comes nearer to the Eledric, and at laft the former receiving a fpark from the latter, becomes throughout polfeiTed of the fame Eledlricity with the Ele(5lric, from which it has received the fpark. All thefe effeds will happen in the fame manner, if be- tween the excited Eledlric and the approach- ed Condudtor there is interpofed fome other eledlric fubflance befides air ; as for inflance, a thin plate of glafs, rofin, fealing-wax, 6cc. but then a fpark can never come from the excited Eledlric to the Condudlor, ex- cept it forces, or burils its way through
th«
O F E L E C T R I C I T Y. jj
the interpofed Eleftric, as it always does through the air. This difplacing of the air is what caufes the noife that attends a fpark, and that noife is more or lefs loud in pro- portion to the quantity of Eleftricity, and to the reiiftance it meets with in its paf- fage.
An infulated Conductor having received the Elecflricity from an excited Eled:ric, (in Vv^hich ftate it is faid to be eledrified by communication) will ad: in every reipedt like the excited Eledric itfelf, except, that when it is approached by another Conduftor communicating with the earth, the former gives one fpark to the latter, and by that dif- charges all its Eledlricity. The reafon why an eledlrified Condu(ftor lofeth its Electricity all at once, when touched with another Con- ductor communicating with the earth, and not part of it only, like the excited Elec-» trie, is, becaufe the EleClricity belonging to the v/hole of the Condu£tor is eafilycon- du<fted through its own fubflance, to that fid^, to which the other ConduClor is pre- fented. Hence it appears that, in general^ the Eledlricity difcharged from an ekclrified
Con-
^ A COMPLETE TREATISE
Conductor is much more powerful, than when difcharged from an Eledlric ; for the Conductor may acquire a great quantity of Ekclricity from an Electric, by receiving fpark after fpark, and afterwards if touched, difchairge it all at once, and not by little and little as it was received.
If an infulated Condudlor be touched with another Conductor ele£lrified, it will acquire part of the Electricity belonging to the elec- trified Conduftor, and afterwards each will faow ilgns of it. The Eledlricity in this cafe will net always be equally divided be-^ tween the two Conductors, nor will it keep any proportion to the quantity of matter in each contained ; but will obferve the follow- ing laws.
1. If two infulated Conductors, that in refpeCt to their external furfaces are equal and iimilar, and both, or only one electri- fied, are touched together, the EleCtricity will be equally divided among them.
2. If their furfaces are equal and diffimilar, as for inftance a fquare foot of tin foil in
one
OF ELECTRICITY 35
(>nc piece, and another fquare foot of it cut In a long flip^ then that body, whofe fur- face has a greater exteniion, will acquire more Ele£lricity than the other*
J. Laftly, if their furfaces are unequal and fiiflimilar, the Electricity that each acquires after the contact, feems pretty clear from experiments, and in confequence of the above two laws, to be in a cgmpound proportion of their furfaces, and the extenlions of the fame,
The eledric fpark (/. e. a fcparate quantity ,of Eleftricity) will go a greater or lefs dif- tance through the air, in order to reach a Condudor, according as its quantity is greater or lefs ; as the parts from which it flies ofF^ and on which it ftrikes, are more fharp or more blunt, and as the Condudlor is more or lefs perfect. The noife together, and the light with which the fpark is attended, is greater or lefs, according as the Electricity is greater or lefs ; as the parts from which it flies, and on w^hich it ftrikes, are more blunt jor more fharp, and as the Condudor is more prlefsperfedt. Thus, for infcance, a iharp point- ed
$6 A COMPLETE TREATISE
ed body will throw off Eledricity to^and receive it from a greater diftance^ than a body of any other fhape ^ but then that paffage occalions no noife, and but little lights for, in this cafe, the Elecftricity does not come in a feparate large body, but by little and little, or rather by a continuate flream.
It is remarkable in the cafe of points throw- ing oiF, or receiving Eledricity, that a cur- rent of air is fenfible at an electrified point, which is always in the diredion of the point, whether the Eledricity is pofitive or negative.
The eledric fpark, taken upon any part of a livinn* animal body, caufeth a difagree- able fenfation, which is more or lefs trou- blefome, as the fpark is ftronger or weaker, and the part, upon which it is taken, is jnore or lefs delicate.
A large quantity of Electricity, pervades the fubflance of a Condudor of a qonfidera- ble length, with a furprifing and impercep- tible velocity ; but a fmall quantity of it | ha§ been found to take fome little time in . \ paffing
OF ELECTRICITY. 37
pafling through a long, and lefs perfed: Con- ' dudor.
Bodies, pofTefled of the fame Eledtricity, whether pofitive or negative, repel each other. But bodies, poiTefled of different Eledrici- ties, attradl each other ; and there is no elec- tric repulfion, but between bodies poiTefTed of the fame Electricity, nor eledric attrac- tion but between bodies poifeiTed of dif- ferent Eledlricities, /. e. between bodies politively, and bodies negatively, eledlrified \.
Eledricity, ftrongly communicated to in- fulated animal bodies, quickens their pulfe, and promotes their perfpiration. If it is communicated to infulated fruits, fluids, and in general, to every kind of bodies that are adlually in a ftate of evaporation, it alfo
X This law, 1. e. that there is no cle6lric attraftion, except between bodies poncfled of difFerent Eledlrlcicics, will, perhaps, appear paradoxical upon obferving, that an excited Eledric attrafts fmall bodies, which never were by any means made electrical before ; but the paradox will foon vanifh, if whae has been faid above be confidered, 1. e. that when Conduftors, and indeed Eledrics too, come near an electrified body, they become adtually pofTelTsd of a different Eledtricity. But this will appear much clearer from the experiments that are to be mentioned hereafter.
in-
A COMPLETE TPvEATISfe.
increafeth that evaporation^ and that iri i greater or lefs degree, as thofe bodies ar^ more or lefs fubjed: to evaporate of them- felves, as the velTels, that contain the fame^ afe Coftdudors or Eleftrics, and as the;^ have a greater or lef^ furface expofed to the open air §i
By increaling the perfpiration of vegeta-^^ bles, Eledricity promotes their growth ; it having been found, after feveral experiments^ that fuch plants, which have been often, and long electrified, have fhewed a more lively and forward appearance, than others of the fame kind that were not eledtrified.-
When Eledricity is communicated to in-^ fulated veiTels, containing water, that is ac^ tually running from a pipe, the eifedts will^ as far as may ingrofs, be deduced from ex- periments, obferve the following laws;
** I. The electrified ftream, though it di-^ ^^ vides, and carries the liquid further, is
§ Although it has been by fome pretended, that Fle^lrldfry caufed feveral fubftances to evaporate through the pores of glaft, and metals, yet that could never be obferved, though many ac- curate experiments were made for that purpofe ; befides, this J)retended evaporation, feems on all accounts exceedingly imr- probablc.
^* neither
OF ELECTRICITY. 5^
** neither fenfibly accelerated nor retarded^ ^^ when the pipe through which it iffues i^ ^ not lefs than a line in diameter.
^* 2. Under this diameter, if the tube is ** wide enough to let the liquid run in a con- ** tinned ftream. Electricity accelerates it a *' little, but lefs than a perfon would ima- *^ gine, if he judged by the numbers of jets ** which are formed, and by the diftance to *^ which they go.
*^ 3. If the tube be a capillary one, front ** which the water only drops naturally^ ^^ the eledlrified jet not only becomes a con- *^ tinned ftream, and even divided into fe- *^ vera! flf earns, but is alfo conliderably acce^ ^Merated; and the fmaller the capillary *^ tube is, the greater^ in proportion, is the ** acceleration.
"^^ 4. So great is tlie effeft of the ele<^ric ^^ virtue, that it drives the water in a con- ^* ftant ftream out of a very fmall capillary ** tube, out of which it had not before beeil *^ able even to drop.'^^
The eledlric virtue has been found not to fee affedled by, or afFed:, the magnetic virtue
of
40 A COMPLETE TREATISE
of a loadftone ; neither is it affeded by heat or cold ; fince, an iron bar made red hot, or any conducing fubflance hard frozen, when eledrified, attrads, repels, gives fparks, &c. in the fame manner as in its natural temperature. Eledric attradion is obferva- ble alfo in vacuo, where it ads nearly at the fame diftance, as in the open air ^ and eledric fubftances may alfo be excited in vacuo.
Lajflly, we fhall conclude this chapter with remarking two peculiarities, refpeding ex- cited and communicated Eledricity. The firft of thefe is, that if the face, or any part of the body, is prefented to an excited Elec- tric, it will feel as if a wind wa5 blowing, or rather, as if a fpider*s web was drawn over it, whereas this is feldom produced bj communicated Eledricity. The other particular confifts in this, that if the noftrils are prefented to an excited Eledric, they will be affeded by a fmell, much refembling that of phofphorus; but communicated Eledricity does not occafion any fuch fenfaticn, except when a large quantity of it does fuddenly pafs from one body to another.
GHAR
OF ELECTRICITY;
49
CHAP. VL
Of Ekifricity communicated to EIe5irks^
S the Eledric Virtue can be fuperin- duced on Conductors by eommunica-- tion, fo may it alfo be communicated to Elec- trics : the difference however is, as might be expelled, very remarkable ; for when one fide of a Conductor is prefented to an eledri- fied body, the Eledricity will inftantly per- vade its whole fubftance, on account of its conducting nature ; whereas when an Ele6lric is prefented to another Eledtric excited, or to an electrified Conductor, it will with fome difficulty acquire any Electricity, becaufe its fubftance is impervious to that virtue, and in order to make it acquire fome, it muft be feveral times, and in different parts, touched with the electrified body. That it is as dif- ficult to deprive an EleCtric of its acquired Electricity, as it is to fuperinduce it on its furface, I think might eafily be fuppofed ; for the very fame quality, which caufeth it to acquire that power flowly (namely its be- ing a Non-conduCtor) makes it alfo part with
E
It
'50 A COMPLETE TREATISE
it flowly ; and, in order abfolutely to deprive the Eledric of its acquired Eledricity, it muft be touched feveral times, and in almoft every part of its furface, with foine conducing fub- ftance.
In the preceding chapter we oblerved, that when an infulated Condudor is prefented to an eledrified body, it acquires, on the part neareft to that body, a contrary Electricity ; and on the oppofite part, an Electricity of the fame kind with that of the eleClrified body ; we alfo obferved that thefe two Elec- tricities increafe, as the Condudor comes near to the eledrified body, and that when the Condudor is arrived within the ftriking dif- tance of that body, a quantity of Eledricity flies off from the latter; forces its way through the intermediate air, and, ftriking upon the former, renders it throughout pofTefled of the fame Eledricity. Thefe effeds are in a cer- tain degree alio obfervable when an Eledric, inftead of a Condudor, is prefented to an eledrified body ; for the eledric will alfo ac- quire on different fides, contrary Eledricities : thefe Eledricities increafe, as the diftance de- creafes ; but, if at laft a fmall quantity of
Elec-
OF ELECTRICITY. 5t
Eledricity is communicated to the Eledric, that Eledlric will not become throughout pof-^ felled of one Eledricity, but will ftill, in fome cafes, fiiew different Electricities on different fides, and in fome circumftances many re- peated changes from pofitive to n^g^^^ve Elec- tricity may be obferved upon the fame Elec- tric, as will appear from the following expe- rimxCnt.
If the end of a pretty long glafs tube be prefented to a body eledrified, for inftance pofitively, the tube will be found electrified pofitively alfo for the fpace of one or two inches at that end ; but, beyond that fpace, v/ill be found two or three inches electrified negatively; after that, another pofitive Elec- tricity will appear, and fo alternately, a pofi- tive and a negative zone will follow one ano- ther, always weaker and weaker in power, till at laft they quite vanifh. Now the caufe of thefe effects is always to be deduced from the two above-mentioned principles, i, e, the non-condu£ting quality of an Eledric, and the property of bodies in general to acquire an Electricity contrary to that pofl^efled by another contiguous cleCtrified body : fo in the
E 2 above
52 A COMPLETE TREATISE
above experiment, that end of the tube which was prefented to the body eledrified pofitivcly, before it received any Ele£lricity from that body, appeared negative on the part prefented to it, but after it had received fome Eledri- city, appeared to be pofitive no further than that Eledricity could be fpread over its fur- face, but beyond that place a part of the tube appeared to be negative, on account of its contiguity to the part electrified pofitively ; after that, another place appeared to be pofi- tive, becaufe of its contiguity to the part elec- trified negatively, and fo of the fubfequent changes ; and the pofitive Eledtricity of one part of the tube cannot mix with the adjoin- ing negative part fo as to prevent thefe ap- pearances, becaufe the non-condu6ling quality of the glafs will always hinder fuch an effect from taking place*
If to one fide of an Ele£tric fufficiently thin, as for inftance a pane of common win- dow-glafs, a plate of fealing-wax, &c. be communicated one Electricity, and to the op- pofite fide be communicated the contrary, that plate in that cafe is faid to be charged^ and the two Electricities can never come together, I except
OF ELECTRICITY. 53
except a communication of condu£ting fub- flances be made between both fides, or the Eledric be broken by the power of elednc attradion. When the two Eledricities of a charged EIed;ric are by any means united, and therefore, their power deftroyed, that Elec- tric is then faid to be difcharged, and the adt of union of thefe two oppofite powers is, for a reafon hereafter to be mentioned, what is called the ekSiric Shock.
In order to avoid the difficulty of commu- nicating Electricity to an electric plate, it is cuftomary to coat the fides of it w4th fome conducting fubftance, as tin foil, gilt paper, &c. by which means the charging and dif- charging becomes very eafy ; for w^hen the Electricity is communicated to one part of tiic coating, it is immediately fpread through all the parts of the Eled;ric that are in contact with that coating, and when the EleCtric is to be difcharged, it is fufficient to make a con-*- daCting communication between the coatings of both fides, in order to difcharge entirely ihe Electricities of that Electric.
E ^ It
54 A C O M P L E T E T R E A T I S E
It will be readily underdood why the coat- ings of both fides of an Elc<flric ihould not come very near one another towards the edge of the plate, for then a communication be- tween the fame coatings is ready at hand, and although they do not abfolutely touch one another, yet when they are eledrified, the Electricity will eafily force a paiTage through the air, and, by paffing over the furface of the Electric from one coating to the other, ren- ders it incapable of receiving any charge^.
By means of charged Eledrics, we may fee a difplay of the greateft powers of Elec-p tricity ; we can accumulate this power, and ufe it advantageoufly in different experi- ments. By confidering the properties of a charged Eledric, we become further and better acquainted with this fcience, than by any other means, and for the enumeration of thefe properties the following chapter is employed.
* The property of conducting the Elcdlricity over the furface is fo remarkable in feme kinds of glafs, that they arc on this account abfolutely unfit for the purpofe of charging and difcharging.
CHAP.
OF ELECTRICITY, 55
CHAP. VII.
Of charged Ele£lricsy or the Leyden Phial.
F a glafs plate, whether fmooth, or rough, is coated with fome coadudling fub- ftance on both fides, fo that the coatings do not come fo very near the edge of the glafs, as to render it unfit to be charged, and if to one of thofe coatings be commu- nicated fome Eledricity, the other coating, while communicating with the earth, or with a fufficient quantity of conducing bodies, acquires by itfelf an equal quantity of the contrary Electricity; but if whilft one fide is acquiring Eledtricity, the oppofite fide does not communicate with the earth, or with a fufficient qiiantity of condudling fubftances, the glafs cannot be charged. Now the reafon why when one fide of the glafs is receiving one Electricity, the op- pofite fide acquires the other, is the fame as obferved in the preceeding chapter, /. e. the property of bodies to acquire an Eled:ri- city contrary to that poflefled by a contigu- ous eledrified body ; and the caufe, that
E 4 hinders
56 A COMPLETE TREATISE
hinders thefe two Eleftricities from mixing together, is the interpofition of the glafs plate, which is impermeable to Electrici- ty *; but if the charge is too high, and the glafs plate too thin, then the great attrac- tion, between the two different Eledrics, forces a paffage through the glafs, difcharges it, and renders it unfit to receive another charge.
Thefe effects happen in the fame manner if the glafs be not in the form of a plate, but in any other fliape whatfoever, provid- ed it is fufRciently thin, it being not the form, but the thicknefs of the glafs, that makes it more or lefs fit to be charged : and the thinner it is, the greater charge it is capable of receiving j for the ftronger in proportion is
* This remarkable property of Eieflricity was firft obferved at Leyden with a bottle containing fome water, which ferved for the infide coating, and the undcfigned apphcation of the hands on the outfide ferved for another coating. A bottle coated on the infide and outfide for tliepurpofe of being charged, has from thence been called the Leyden Phial^ other wife an ele^ric Jar ; and the charging and difcharging in general, of coated glafs, has been called the L.^ydcn Experiment.
the
OF ELECTRICITY. 57
the power of the Eledricity of one fide, to caufe a contrary Electricity on the oppofite fide.
How thick a glafs plate or other Ele£fcric Ihould be, to become incapable of being charged, hath not yet been afcertained.
If a coated glafs plate, or phial, after being charged, be infulated, and only one of its fides be touched with fome Condudor, that fide will not part with its Eledricity, becaufe the Electricity of one fide exifts in confequence of the contrary Electricity on the oppofite fide, and both, by their mutual attrad:ion, confine one another upon the fur- face of the glafs. In order therefore to dif- charge that glafs, both its coatings muft be touched at the fame time, and connected with the earth : or by means of fome Con- ductor a communication muft be made be- tween them, and in this cafe the difcharge is laid to be made through that Conductor.
When, in order to difcharge a jar, one of its coatings is touched firft with a Conductor, as for inftance, with one end of a chain,
nothing
SS A C O M P L E T E T R E A T I SE
nothing particular in that cafe will appear ^ ; but as foon as the other end of the chain comes within a fufEcient diftance of the other coating, a fpark will be feen between the end of the chain, and that coating, ac- companied with a noife, &c. juft as when an excited Eledric, or an eledirified Condud:or is made to communicate V\^ith another Con- dudor ; but the power, the light, and the report is in general much greater than that of a fpark taken from a body fimply elec- trified.
It IS remarkable that the fpark occafioned by the difcharge of charged Eledrics, al- though it is more den(e^ more powerful, and makes a greater report, yet is not fo long as the fpark drawn from an eledrified Con- dudor.
* If one coating of a charged jar communicates with the earth while the other coating is expofed to the free air for fome time, the charge of that jar will be filently and gradually diflipated ; for while the Eledricity of one fide goes to the earth, the Eledricity of the other is com- municated to the air, which, as we obferved before, is never a perfeft Electric.
When
OF ELECTRICITY. 59
When the difcharge of a jar is made through the body of a living animal, it oc- cafions a fudden motion by contracting the mufcles, through which it pafles, and gives a difagreeable fenfation, for which reafon the effed; of difcharging an eledric jar has been generally called the eleSiric Shock.
The force of the eledric fliock, occafioned by glaffes of the fame thicknefs, is greater or lefs in proportion to the quantity of coat- ed furface, and the height of the charge. Upon this principle, the power of the faid {hock, by increafing the quantity of coated glafs, may be augmented at pleafure, provid- ed means be ufed powerful enough to charge it.
A number of coated jars conneded toge- ther in fuch manner that their whole force maybe united, and ad: like one jar, conftitutes what is called an electrical Battery. This battery is the moft formidable, and entertain- ing part of an eledrical apparatus, and by its ufe many wonderful efFeds are produced, but as the performing of thefe belongs
rather
* /
6o A COMPLETE TREATISE
rather to the pradical, than to the prefent part of this Treatife, I ihall only enumerate theiTL in this place, and referve further par- ticulars for the third part of this work.
In making the difcharge of an ele£lric jar it is furprizing to obferve with w^hat quick- nefs the Electricity performs the circuit from one fide of the glafs to the other. It has been found to employ no perceivable time in going through a Condudler of feveral miles, which connedicd the two coatings of a phial.
The force and noife of an elcdric fhock is not affeded by the inflexions of the Con^ dudor, through which it goes, but it is fen- iibly weakened by its length ; hence when the circuit, /. e. the communication be- tween the two fides of the electric phial, is made by one perfon touching one fide with one hand, and the oppofite lide with the other, the fhock is flronc;er than when the circuit is formed by many perfons together joining hands.
That
O F -E L E C T R I C I T Y, 6r
That the Electricity finds fome obiln,i6iiou in going through even the beft Condu61:ors, appears evident, from this, that in fome cafes it vvrill prefer a fliort paffage through the air, to a long one through Condudors, even the moft perfed:. This obltrudtion is greater ia that place, where the Conductors, forming the circuit, do not lie in perfeCt contad: ; and if the circuit being compofed of Conductors of different natures, the EleCtricity be obliged to pafs from one Conductor to another lefs per- fect, the obftriiCtion is ftill greater. If the interruption of a circuit be made in w^ater, on making the difcbarge (notwithuanding that the water is a Conductor) a fpark will be feen in it, w^hich never fails to agitate the water, and often breaks the veiTel that, contains it.
A ftrong fhock, fent through an animal or a plant, puts an end to animal as well as to vegetable life. If the circuit be interrupted by one or m.ore ElcCtrics, or imperfect Conductors, of a moderate thick- nefs, the eleCtric fhock will break them, and in fome circumftances difperfe them in every direction, and in fuch a manner as if the
force
62 A COMPLETE TREATISE
force proceeded from the center of every one of the interpofed bodies *.
A ftrong fhock, fent through a flender piece of metal, makes it inftantly red-hot, melts it, and if the fufion is perfed, reduces it into globules of different magnitudes. If the me- tal be inclofed between ^pieces of glafs, the Ihock, by melting It, will force it Into the fubftance of the glafs, fo that afterwards it cannot be taken off without fcraping part of the glafs w^ith it. In this experiment the glaffes are fhattered to pieces, and it is feldom that they refifl the force of a flrong fhock.
If the glalTes, inclofmg the metal, be prefTed by heavy weights, then a remarkable fmall fhock is capable often not only to raife the weight, but to break fuch thick glaffes, that otherwife require the force of a large battery.
* In feveral inftances the effedt of a (hock upon an interpofed.' body is evidently greater on that fide of it which communicates with that coating of the jar or battery, that is pofTefled of the pofitive Eledricity. But of this more will be faid hereafter,
2 Thick
OF ELECTRICITY. 63
Thick pieces of glafs may be alfo broken into innumerable fragments by only fending a fhock over a fmail part of their furface, which are preffed by weights, without the interpofi- tion of any metal. When thefe pieces of glafs are not broken, they are marked by the explofion with the moft lively prifmatic co- lours, which lie fometimes confufed, and fometimes in their prifmatic order. The co- loured fpot is evidently formed by thin plates or fcales, in part feparated from the furface of the glafs ; and it generally occupies the fpace of about one inch in length, and half an inch in breadth.
In melting wires of the fame metal by the eleftric fhock, it muft be obferved, that the forces required for that purpofe muft be great- er or lefs according as the lengths or thicknelTes of the wires are greater or lefs, but they are far from bearing any dire(fl proportion to the xjuantity of metal ; for if a wire of a given length and diameter be barely melted by a large battery, a wire of equal length and twice the fubftance, would perhaps take ten fuch batteries to produce the fume effed upoa it.
When
64 A C O M P L E 1^ E 7^ R E A T I S £
When a moderate fhock* is fent through an imperfect metal (efpecially if the circuit is formed by feveral pieces, as by a chain), a black duft, in the form of fmoke, will be feen to proceed from the metal, which is thought to be fome of the metal itfelf partly calcined, and, by the violence of the explofion, forced from it.
If fuch circuit, or part of it, be laid upon a piece of paper, glafs, or other Non-condudlor, this, after the explofion, w^ill be found ftained w^ith fome indelible marks, and often {hew evident figns of having been burnt. A long and permanent track may be marked upon glafs, and fome other bodies, by the eledtric explofion, If the interruption of the circuit be made upon its furface.
What Is more remarkable, In confidering the efFeds of Eledrieity on metals, is, that it revivifies their calces, and, like a true phlo- gillic procefs, when an explofion is made be—
* By a moderate (hock here, I mean, one that is not able to raeh the metal through which it pafles,
tween
OF ELECTRICITY- 65
tween two pieces of the fame, they, in part, return into their metalline form.
Ahhoiigh we obferved, in the fifth chapter, that Electricity and Magnetifm did not inter- fere with one another's adion, yet that mud not be underftood in general, and w^hen a large force of Eledricity is meant ; for this is capable not only of deftroying the virtue, orof reverfmg the poles of a magnetic needle, but even of giving it that virtue. When the charge of ten, eight, and even a lefs number of fquare feet of coated glafs is fent through a 1 fine fewing-needle, it will often give it polarity, fo that it will traverfe when laid on water*. It is remarkable that if the needle be ftruck, lying eaft and weft, that end of it which is entered by the fhock, will after- wards point north ; but if the needle be ftruck, lying north and fouth, that end
* A fmart ftroke of a hammer will make a needle magnetic : but they fliould always be tried before th^ experiment: for many fmall needles will traverfe upon water, without the ele(3:iic ihock, gr the ftroke of th«- hammer.
©f
66 A COMPLETE TREATISE
of it which lay towards the north, will, in any cafe, point north ; and the needle will acquire a llronger virtue in this, than in the former cale.
That the electric fpark fliould kindle in- flammable fubftances, I think might be ex- pected, when its power has been confidered n many circumftances, in which it has been obferved to a£t as a moft penetrating and ex- traordinary hre. In firing feveral lubftances a fmall flaock is fufficient ; and inflammable fpirits may be fired even by a fpark proceed- ing from an eled:rified Conduclor. \
If the moderate charge of a large battery is difcharged between two fmooth furfaces of metals, or femi-metals, lying at a fmall diftance from each other, a beautiful fpot will be marked upon them. This confifts of one central fpot, and fome concentric circles*, which are more or lefs diftind, and more or
* The central fpot as well as the circles lie at a little * diftance from one another ; and they are compofed of dots and cavities, indicating a true fufion.
lefs
OF E L E e T R I e I T Y. 67
iefs in number, according as the metal upon which they are marked, requires a Iefs or greater degree of heat to be melted, and as a greater or Iefs force is employed.
If the expldfion of a battery^ iffiiing from a pointed body^ as the point of a needle, be repeatedly taken-iipon the plain furface of a piece of metal fituated at a little diftance from the point, or if iffuing froiii the furface, be t^ked ilpon the point, that metal will be marked with a coloured fpot, confifting of all the prifmatic colours difpofed in circles, and evidently formed by fcales, or thin plates of the metal feparated by the force pf the ex- plofion'^%
. When the difcharga of a battery is made by bringing the ends of two Condudlors, communicating with the infidcj and the out- fide of the battery, in contact with^ or at a little diftance from the furface of feveral con- dueling fubftances, as water, raw raeat^ &c#
* For further particulars concerning thoft circles^ fee the PhlL Tranf. vol. LVIII.
68 A COMPLETE TREATISE
it is obfervable that the Eledricity, Inftead of entering thofe fubftances, goes over their fur- face, and in a lucid feparate body reaches from Conduftor to Condudor ; fometimes it prefers a much longer paflage over the furface, to a fhorter one through any fubftance. In this cafe the explolion never fails to give a concuffion to the body, over whofe furface it paffes.
The explofion, taken in different kinds of air, ads in general like any phlogiftic pro- cefs*.
Befides the above-mentioned properties of charged glafs, there are a few more obferved,. which as yet have neither been fujSiciently inveftigated, nor fo far purfued as to be re- duce under any general laws. They afford a great field for fpeculation, and feem more intimately connected with the nature of Elec- trics in general ; but it feems not proper to make any general conclufions from the fads
* See Dr. Priestley's fecond vol. of Obfervations on different Kinds of Air, fee. XIII.
2 already
OF ELECTRICITY.
already known, at leaft fo as to be Inferted in this part of the prefent treatife. I Ihall there- fore employ a chapter for the hiftory of the fame, in which I Ihall relate the principal, and more promifing experiments hitherto made, and take notice of the heft conjedures offered for their explanation. This chapter will be found at the end of the third part, in which place, I think, it will be more accept- able to my readers, particularly fuch, who have not been much converfant with Elec- tricity, and therefore require firft the defcrip- tion of the eledrical apparatus, and the know- ledge of the experiments neceffary to prove the fails recited*
F3 CHAP
70 A COMPLETE TREATISE
CHAP. VIII.
Of Atmofpherical Ek&rkity.
WHOEVER has remarked the nu- merous properties of Eledricity already mentioned, and has confidered their extenfive power, will, I doubt not, be grcc^-t- ly furprifed, when he compares the ftate, in which the Science remained half a century ago, with that in which it is at prefent ; but his wonder will ftill increafe, when he is told that Electricity is not only to be obferved by rubbing an Ele^Slric, or warming a Tour- malin, but that it has been found to exift in the ciir, rain, and clouds:, that thunder and lightning have been difcovered to be its effeds ; and that In fhort whatever has the appearance of fire, or of any thing extra- ordinary in the atmofphere, and upon the earth, has been attributed to Electricity*
That the cfredts of Eledricity bore a great refemblance to thunder and lightning, had been feveral times remarked by philofophers, and efpecially by the learned Abbe Nollet j
but
OF ELECTRICITY. 71
but that they fliould actually be found to be cfi^edl-s of the fame caufe, and that the phe- nomena of Electricity fhould be imitated by lightning, or thofe of lightning by Electri- city, was neither thought poffible, nor fuf- peCted, till the celebrated Dr. Franklin made the bold aflertion, and the French phi- lofophers firft, and afterwards Dr. Frank- lin proved the fad: by undeniable argument3 in the year 1752.
The fimilarlty of lightning and EleClricity is not to be remarked in a few appearances only, but it is obfervable throughout all their numerous efFeCls, and there is not a fingle phenomenon of the one, but may be imitat-* ed by the other. Lightning deftroys edifices, animals, trees, &c. ; lightning goes through the heft Conductors, which it meets in its way, and, if its paflage is obftruded by Elec- trics, or lefs perfect Conductors, it rends them, and difperfes them in every direction ; lightning burns, and melts metals and other fubftances ; a ftroke of lightning often dif- turbs the virtue of a magnet and gives pola- rity to ferruginous fubftances ; and all thefe cffeds, as has been obferved above, may be
F 4 pro-
72 A C O M P L E TE TREATISE
produced by Eledricity. But independent of the great fimilarity exifting between light- ning and Electricity ; what fully proves their identity is, that the matter of lightning may be adlually brought down from the clouds by means of infulated and pointed metallic rods^ or by eledrical kites, and with it any known electrical experiment may be per- formed.
Clouds, as well as rain, fnow and hail, that fall from them, are almofl always elec- trified, but oftner negatively than pofitively ; and the lightning, accompanied with the thun- der, is the effect of the EleCtricity, which, dart- ing from a cloud, or a number of clouds, highly electrified, ftrikes into another doud, or elfe upon the earth, in which cafe it pre- fers the moft lofty and pointed places, and by this ftroke produces all thofe dreadful efFeCts, that are known to be occafioned by light- ning.
The air, at fome diftance fromhoufes, trees, mafts of fhips, &c. is generally eleCtrified pofitively, particularly in frofty, clear, or foggy weather ; but how the air, the fogs,
and
O F E L E C T R I C I T Y. 73
and the clouds become ele<3:rified has not yet been afcertained, although feveral conjedures have been offered. ^'
After that Eledriclty, and the matter of lightning were found to be the fame thing, philofophers began to fufpedt the adion of Electricity to be where it had before been lef& imagined, and not without reafon endeavour- ed to reconcile to it feveral other natural ap- pearances. The aurora borealis, or northern light, was foon attributed to Eledricity, on obferving that by this that flaming light may be imitated*, and that the aurora borealis, when very ftrong, has been known to difturb the magnetic needlef , which is alfo an effe£t of Electricity.
* The late Mr. Canton frequently coUefted Elec- tricity in a confiderable degree, during the time of aa aurora borealis. His apparatus for that purpofe confided of an infulated fifhing rod, ereded on the top of his houfc, and having a wiretwifted round.
t See the Phil. Tranf. vol. LIX. page 88.
The
74 A COMPLETE TREATISE
The accentions, that are often feen in the atmofphere (commonly called Jailing Stars) are thought to be electrical appearances. The fame is alfo fuppofed to be the caufe of fuch other meteors like white clouds, that often appear by night-time, particularly in hot cli- mates. Befides thofe phenomena, water- Ipouts, hurricanes, whirlwinds, and even earthquakes have been attributed to EleClri- city. But now, perhaps, the reader will think philofophers too extravagant, in going fo far with Ele6lricity. Such thoughts feera at firft fight to be extravagancies, but if it be confidered, that they do not appear to con- tradi6l the known laws of nature, that they are not aflertions abfoiutely void of proofs, add that they are the thoughts of great phi- lofophers, then, I think, they may be ad- mitted at le.^-ft io far as to be tried on proper occafions, and to be confidered as the moft plaufible conjectures yet offered in explana- tion of the moft furprizing phenomena of nature*.
* For further conjectures fee Dr. Franklin's Letters, and Dr. Priestljly's Hift. ofEIedl. Part I. per. X, fee. XIL
CHAP,
OF ELECTRICITY, 75
CHAP. IX,
Advantages derived from EleSlricity.
NATURE, ever wife and admirable in her a6lions, feeras to follow a certain fimilarity in her works with a conformity of operations, and from the fimpleft to the moft complicated of her objedls an analogy is obfervable, which, as it is wonderful to be confidered, fo it is inftruftive and ufeful. It is on account of this analogy, that whenever a difcovery is made in any part of natural philofophy ; whenever a fcience is advanced, we not only attain to the knowledge of that fmgle law, or particular fcience, but at the fame time acquire means in general of in- veftigating the operations of nature with fomewhat more certainty and accuracy, and by purfuing that analogy we are enabled to make further difcoveries, and to improve every branch of knowledge. How far Elec- tricity has contributed towards this purpofe, I think it unneceflary to be further proved, when its aftion has been fhown to be fo general, and fo powerful, as to perform what I no
76 A COMPLETE TREATISE
no art can operate. But, befides the field that Eleftricity has opened for further difco- verles, and the fatisfaftion of that curiofity, which before attended the contemplation of fo many wonderful phenomena as have been explained in this fcience, there are two great advantages derived from Ele6tricity ; the one is a defence againft the direful effe6ts of lightning, and the other a remedy for many diforders incident to the human bo- dy.
In order to guard edifices or fhips from being damaged by lightning, it was judici- oufly propofed, by Dn Franklin, to raife a metallic Condu6tor fome feet above the high- eft part of the building, and continue it down the wall till it penetrated fome feet into the ground ; by this means the houfe could never receive any damage, for whenever the light- ning fhould happen to fall upon it, it is evi- dent that the Condu6tor, being of metal, and higher than any part of the building, would certainly attraft it, and by conducing it to the ground, hinder that building from re- ceiving any damage, for it is known that Electricity always ftrikes the neareft and
beft
OF ELECTRICITY. 77
beft Conduftors, that it meets within its way.
«
The reafonablenefs and truth of this afler- tion has been confirmed by numberlefs fafts, and the praftice of raifmg fuch Conduftors has been found exceedingly ufeful, particu- larly in hot climates, where thunder-ftorms are very frequent, and the damages occafion- ed by the fame, too often experienced.
In regard to the conftru6t:ion of fuch Con- ductors there have been fome controverfies among Electricians ; and the moft advanta- geous manner of ufing them has not, with- out a great many experiments, and but very lately, been afcertained. Some philofophers have afferted that fuch Condu6lors fliould terminate in a blunt end, that they might the lefs invite the lightning from the clouds ; for a blunt end will not attract Ele6tricity from fo great a diftancc as a fharp point. But fome other philofophers have thought a pointed termination to be much preferable to a blunt one, and their aflertion feems,on the following accounts, founded on much better realbn- ing.
A fharp-
fS A COMPLETE TREATISE
A fharp-pointed Condu61or, it is true, will attra6l EIe6lricity from a greater diftance than a blunt one, but at the fame time, will attract and condu6l it by little and little, or rather by a continued ftream, in which manner a re-* markably fmall Conduftor is capable of con* du6ling a very great quantity of Ele6lricity ; whereas a blunt terminated Condu6lor attracts the Ele6lricity in a full feparate body, or explofion, in which manner it is often made red-hot, melted, and even exploded in fmoke, and by fuch a quantity of Electricity^ as perhaps would not have at all afFe6ted itj if it had been fharply pointed.
A fharp-pointed Condu6tor, certainly, in-* vites the matter of lightning eafier than a blunt one, but to invite, receive, and conduct it in fmall quantities never endangers the Condu6tor ; and the obje6t bf fixing a Con- ductor to a houfe, is to prote6t the houfe from the effefts, and not the Condu6tor from tranfmitting the lightning.
It is an obfervatlon much in favour of fharp- pointed Conductors, that fuch fteeples of churches, and edifices in general, that are
ter-
OF ELECTRICITY, 79
terminated by pointed metallic ornaments, have never, or very feldom, been known to be (Iruck by lightning, whereas others that have flat or blunt terminations, and have a great quantity of metal in a manner infulated on their tops, are often ftruck by it, and it is but feldom that they efcape without great damage.
Befides thofe confiderations, a fliarp-point- ed Conduftor, by the fame property of attract- ing Ele6lricity more than a blunt one, may actually prevent a ftroke of lightning*, to do which a blunt-en ded one is abfolutely inca- pable.
A Conductor therefore to guard a building, as it is now commonly ufed in confequence of feveral confiderations, and experiments, fhould confift of one iron rodf about three
* This and other properties of pointed Conduflors will be made to appear very evidently by experiments.
t Copper would do much better than iron fur a Con- dudor ; it being a more perfeft Condu<5tor of Electricity, and at the fame time not being fubjeft to contradl ruft like iron.
quarters
8o A COMPLE TE TREATISE
quarters of an inch thick^ faftened to the wall of the building, not by iron cramps, but by wooden ones. If this Conduftor was quite detached from the building, and fup- ported by wooden pofls at the diftance of one or two feet from the wall, it would be much better for common edifices, but it is more particularly advifable for powder-magazines, powder-mills, and all fuch buildings as con- tain combuftibles ready to take fire. The upper end of the Condu6lor fhould be termi- nated in a pyramidal form, with the edges, as well as the point, very fharp*; and if the Condu6lor is of iron it fhould be gilt, or painted for the length of one or two feet. This fharp end fhould be elevated above the higheft part of the building (as above a flack of chimnies, to which it may be faftened) at leafl five or fix feet. The lower end of the Condu6lor fhould be driven five or fix feet into the ground, and in a direflion leading from the foundations; or it would be better to connect it with the neareft piece of water,
* This pyramidal termination of the Conduflor is an improvement of an ingenious Eledrieian, Mr, Swift at Greenwich.
if
bF ELECTRICITY; St
if any be dt hand. If this Conductor, on iaccourit of the difficulty of adapting it to the form of the building, cannot conveniently be made of one rod, then care fhould be takeri, that where the pieces iheet, they be tnade to come in as perfect contact with one another a§ poffible ; for as we obferved before, Electricity finds cbnfiderable obftruc- tion where the Condudor is interrupted.
For ari edifice of a moderate fizd one Con- ductor, in the manner already defcribed, is perhaps fufficient ; but, in order to fecure a large building from fuftaining any damage by lightning, there iliould be two, three, or more Condu£lors| in proportion to the extent of the building.
On board {hips a chain has often been ufed for this purpofe, which, oft account of its pliableneff^, has been found very convenient, and eafy to be managed among the rig- ging of the veflel ; but as the Electricity finds a great obfl:ru(3:ion in going through the feveral links, for which reafon chains have been adtually broken by the lightning, fo their ufe has now been almoft intirely
G la^d
.82 A COMPLETE TREATISE
laid afide, and in their ftead, copper wires a little thicker than a goofe quill have been fubftituted, and found to anfwer very well. One of thefe wires fhould be elevated two or three feet above the higheft maft in the veflel ; this fhould be continued down the maft, as far as the deck, where, by bending, it fhould be adapted to the furface of fuch parts, over which it may moft conveniently be placed, and, by continuing it down the fide of the vefTel, it fhould be always made to communicate with the water of the fea.
In regard to perfonal fecurity in cafe that a thunder-ftonn were to happen while a perfon is in a houfe not furnifhed with a proper Condudlor, it is advifeable not to fland near places where there is any metal, as chimnies, gilt frames, iron cafements, or the like ; but to go into the middle of a room, and endeavour to ftand or fit upon the beft Non-condudor that can be found at hand, as an old chair, a flool, &c. '^ It is " flill fafer (fays Dr. Franklin) to bring *^ two or three matralTes or beds into the ^* middle of the room, and folding them up ^* double, put the chair upon them j for they
^^ not
it
€i
OF ELECTRICITY. 83
"^^ not being fo good ConduQors as the walls, " the lightning will not choofe an interrupt^ ^' ed courfe through the air of the room and *^ the. bedding, when it can go through a *' continued better Conductor, the wall. But *' where it can be had, a hammock or *' fwinging bed, fufpended by filk cords, *^ equally diftant from the walls on every *' fide, and from the ceiling and floor above " and below, affords the fafefl fituation a a perfon can have in any room what- ever, and what indeed may be deemed quite free from danger of any ftroke by *' lightning.'*
If a florm was to happen whilft a perforl is in the open fields, and far from any build- ing, the bed thing he can do is to retire within a fmall diftance of the higheft tree or trees he can get at ; he muft by no nieans go quite near them, but fhould flop at about fifteen or twenty feet from their outermofl branches ; for if the lightriing fhoiild fall thereabout, it will very probably flrike the trees ; and in cafe a tree was to be fplit, he is fafe enough at that diftance frgm it* ,
G 2 In
84 A COMPLETE TREATISE
In regard to the other great ufe of Elec- tricity, /. e. its application as a medicine, there have been fo many opinions proy and contra^ and the event in general of the in- numerable trials has been fo precarious, that to give a juft eftimate of its power feems to rne very difficult. The innumerable cures performed by the application of Eledlricity, that are related by feveral writers, feem to re- prefent it as a panacea for every diforder : on the other hand, the unfucceisfulnefs of other attempts^ and which (although feldom recorded) are the more numerous, Ihow its inefficacy, and inutility : if therefore a de- cifion Ihould be given on the refult of all thofe cafes, Electricity fhould be confidered as the moft ufeful, and uielefs remedy in the whole materia ?nedica.
In order however to fatisfy more fully the curiofity of the reader about this important fubjed, I Ihall here fubjoin two cafes, in one of which, related by Dr. Hart of Shrewfbury, the application of Eledricity proved very pernicious, and the other is a moft remarkable inftance of its good efFed. In regard to the firft cafe it is thought by I fome,
O F E L E C T R I C I T Y. 85
fome, that Ele<3:ricity was injudicioufly ap- plied ; but of the veracity and juft treatment of the fecond the reader can have no doubt, for it was executed by the celebrated Dr. Watson, a gentleman, who is both an ex- cellent phyfician, and one of the greateft
JEledricians.
»
CASE 1/
*^ A young girl, about fixteen, whofc *' right arm was paralytic, on being ele£tri- *^ fied the fecond time, became univerfally ^^ paralytic, and remained fo about a fort- *^ night, when the increafed palfy was re- *' moved by medicines, which her cafe indi- ^^ cated ; but the firft difeafed arm remained " as before : I fhould have mentioned too, ^' that this arm was greatly wafted, in com- " parifon to the other. However, notwith- *' ftanding the former bad accident, I had a ^' mind to try the efFe£t of Eledricity on her ^* again, which we renewed ; and, after ** about three or four days ufe, fhe became ^^ the fecond time univerfally paralytic, and ^* even loft her voice, and with difficulty ^' could fwallow. This confirmed me in my
G 3 *^ opinion.
86 A COMPLETE TREATISE
*' opinion, that the eledrical Ihocks had og'- ^' cafioned thefe fymptoms.— We therefore *^ omitted it, and the girl, though fhe grew " better of her additional palfy, for fo I call " it, remained as bad as before of her
'' firft^'^
CASE II.
A girl belonging to the Foundling Hof-^ pital, aged about feven years, being firft feifed with a diforder occafioned by the worms, was at laft, by a univerfal rigidity of the mufcles, reduced in fuch a ftate, that her body feemed rather dead than alive. After that other medicines had been inefFedtually adminiftered for about one month, fhe was at laft eledtrified intermittedly for about two months, after which time fhe was fo far re- eovered, that fhe could, without pain, exercife every mufcle of her body, and perform every aftion as well as before fhe had the diftemper-f^.
♦ Phil. Tranf. Vol. XLVIII. t Phil. Tranf. Vol. LIII.
Wheu
OF ELECTRICITY. 87
When I afk perfons that have tried Elec- city upon themfelves, or upon others, it is ten to one, but they inform me, that it affords fome reHef in fome diforders, but it is not a remedy to be depended on, or to be ge- nerally ufed ; for patients, they fay, do not like to fubje6l themfelves to a long, uncer-^ tain, and (on account of the fhocks) trou- blefome treatment ; befides, the ele6lrical machine vsrill not always a6l w^ell, and the turning of the wheel, for the fpace of an hour or longer, is not a very pleafmg employment even for a fervant.
To all thefe objeftions, a philofopher would anfwer, that it is not every diforder, nor every temperament that requires an equal, or perhaps any application of Electricity. That Ele6tricity has been of great benefit in many cafes, where the application of other medicines has failed, is beyond doubt, and, if two or three equivocal cafes be ex- cepted, there is no inftance of its having ever done any harm : its inefficacy in feveral cafes is in a great meafure to be attributed to the injudicious application of it, indeed more than to any other caufe ; for, in general,
G 4 this
88 A COMPLETE TlREATISE
this remedy has been adminifteted either by Eledricians, who were not phyficians, or by phyficians, who were little if at all Ikilled in Eleftricity. In regard to the trouble, &c. attending its adminiftration, jjt would be as ridiculous to alledge it in proof of its want of utility, as it would be to degrade thq knowledge, and advancement of Ele^ricity on account of the expences that attend thq purchafe of an ele6lrical apparatus. For 4 few pence a man may be hired? who will work the machine as long as it is neceflary^ and be thankful for the employment ; but, i^ order to obviate this inconvenience, an elec- trical machine, to work by wind, by water, or by a horfe, might be eafily confl:ru^:ed, with an infulated floor, or room ; and with fuch a machine a vaft number of patients might be very conveniently eleclrified.
After all thefe difquifitions, that the read- er may form a juft idea of the medical ufe^ of Eleftricity, I fhall in ihort give thq refult of what feems well authenticated by fafts and reafoning under the following pa- ragraphs, and referve the pra6tical ufe for the third part*
The
OF ELECTRICITY. 89
The certain efFe6ls of Electricity, when ic.ommunicated to the human body, are a pro-.; mption of the infenfible perfpiration, an in? creafe of the circulation of the blood,* an4 an increafe of gUndukr fecretion.
Thefe efFcjEls have been found always con- ftant ; they may be proved by feveral experi- ments independaqt of phyfical cafes; and I think there is no body^ who will deny that fuch promotions are not only beneficial, buf: abfolutely neceffary for many diforders.
In regard to the obfervations made by phy-? ficians in the application of this remedy^ it muft be acknowledged that among the dif- ferent cafes, there are feveral, which are related by perfons of great veracity; they feem to be w^ell authenticated, and therefore their refult fhould be carefully confidered. Thefe fafts fhow that Eleftricity, except it be adminiftered to perfons afFe6led with the venereal difeafe, or to pregnant women, ge- nerally gives fpme relief at leaft, if it doe§
* It has been found by very accurate experiments that Elciflricity, communicated to the human body, increafes the circulation of the blood about one fixth.
not
90 A COMPLETE TREATISE
not efFe6t a total cure. For the apoplexy, the palfy, the dropfy, coldnefs in the feet, fiftula lacrymalis, rheumatifm, mortification, amaurofis or gutta ferena, and in fhort for all other diforders occafioned by obftruftians, or contra6tions, Ele6lricity has been found beneficial*.
It has often been obferved in paralytic cafes, that the patients have in general re- ceived fome relief after being ele6lrified four or five days; but that afterwards, finding nothing further could be obtained, they dif- continued the application of this remedy, and in fhort time relapfed.
In regard to this, it might be obferved, that in fome cafes, there are two kinds of
* Abundance of phyfical cafes, in which Ele<n:ricity has been applied, may be met with in ahuoft every writer on Eleftricity, but efpecially in Jallabert's Experimenta Eleftrica, LovETT'sSubtil Medium proved, Wesley's Defideratum, or Eledricity made plain and ufeful, Ferguson's Introduftion to Electricity, and Becket's EfTay on Eleftricity. Some cafes in which Eleftricity has been fuccefsfully applied for the amaurofis are alfo related in the 5th Vol. of the Medical EfTays of the College of Phyficians in London.
ob-
OF ELECTRICITY. 91
obftru6lion, or diforders to be confidered ; one that is the immediate occafion of the diftemper, and the other which is in confe- quence of the firft. When an obftru6lion, howfoever originated, happens in any part of the body, and continues any confiderablc time, it caufeth not only a bad habit in the functions depending on that part, but occa- fions a deftru6lion of feveral duds, and even a disfiguration of the folids. Now as for the firft kind of obftru6lion, it is eafy to fuppofe that Ele6lricity, judicioufly applied, will prove beneficial, but to expe6l that it fhould cure the fecond feems quite ridicu- lous. Therefore, from this confideration as well as from the daily experience, we may deduce that Ele6lricity can have very little $fFe6l in cafes of long ftanding.
Laftly, I muft beg of my readers to ex- cufe me if in the prefent chapter I have been too long, and particular : this comprehend- ing one of the moft ufeful parts of the fci- ence of Eleftricity, I imagined it could not be treated too fully. Sciences are fo far in- terefting as they are ufeful; and it is for the ufe, and benefit of human kind that Philofo- phers labour.
CHAP-
9* A COMPLETE TREATISE
CHAP. X,
^07itaining a compendious view of the principal properties of EleBricity.
AFTER the laws hitherto eftabllihedia the fcieace of Eledricity have been exhibited at large, and the particulars re- lating to each have been fufficiently confider-i ed, it will not be amifs to Ihow in how fmall a compafs thofe laws may be reduced, and how narrow is the foundation of all what has hitherto been done,
I doubt not but this recapitulation will prove very ferviceable to thofe, who are novices in Electricity, as by getting in me- mory a few particulars, they will not only reconcile all that has been faid before, but alfo be enabled thcmfelves to explain moft of the following experiments, and to underftand the application of the hypothefis, of which yjt fhall next proceed to treats
All the natural bodies are divided into two clafles, /• e. Electrics and Conduftors.
Ele6tric§
OF ELECTRICITY. 93
Eledrics are fuch as may by fome means be excited, fo as to produce Eledrical ap- pearances, but Condudors are fuch as can- not be excited by themfelves, /. e. without the interference of an Eledric: further, eledrical fubftances will not tranfmit Electri- city, whereas the fubftance of Condu6lors is pervaded by it.
Ele6lrics may be excited three ways, /. e. by fri6lion, by heating and cooling, and by melting, or pouring one melted fubftance into another.
When two different bodies, except they are both Conductors, are rubbed together, they will both (provided that which is a Conduc- tor be infulated) appear ele6trified, and pof- feffed of different Ele6tricities ; fo when a piece of fmooth glafs is rubbed with an in* fulated piece of leather, it acquires one kind of Ele6lricity, called the vitreous, pofitive or plus Electricity ; and the infulated leather ac- quires the other, called the refinous, negative or minus EleCtricity.
The
|4 A COMPLETE TREATISE
The difference between thefe two Eleftri- cities confifts principally in the appearances of their light, and in the phenomena of at- tra6tion and repulfion*
When the pofitive Ele6l:ricity is entering a pointed body, it caufes the appearance of a lucid ftar or globule on that point ; but the negative Ele6lricity fhows a lucid pencil of rays feeming to iffue from the extremity of the pointed body.
Bodies, poffefled of the fame Electricity, repel each other ; but bodies, poflefTed of dif- ferent Ele6lricities, attra6l each other.
Whenever bodies of any kind come with- in the fphere of action of an ele6lrified body, except they are very fmall, and infulated, they become a6tually poffefled of the Elec- tricity contrary to that of the ele6lrified body, to which they are prefented.
No Ele6lricity can be obferved upon the
furface of any eleftrified body, except that
furface is contiguous to an Ele6tric, which
2 Eledric
OF ELECTRICITY. 95
Eleftric can fome how or other acquire a contrary Ele6i:ricity at a little diftance. Otherwife, — no Ele6lricity can appear upon the furface of any eleftrified body, except that furface is oppofite to another body, which has a6lually acquired the contrary Electricity, and thefe contrarily eleftrified bodies are feparated by an Ele6lric *.
If
* On confidering this principle, it may be afked, why any Eleftricity can be obferved upon the furface of an cledrified body, that is infulated at a confiderable diftance from other Conduftors ? Or, which is the Ele6lric, that h contiguous to the furface of an eleflrified Con- duftor, or excited Eledric, and which has aftuaJly ac- quired a contrary Eledricity at a little diftance from the faid furface ? To this queftion is anfwered, that the air is in general the Eleftric, which is oppofite to the furface of any eleftrified body, which being not a perfect Conduc- tor, does eafily acquire a contrary Eleftricity on a ftratum of its fubftance, that is at a little diftance from the elec- trified body; and in confequence of this ftratum, it ac- quires another ftratum contrarily eleftrified, and at a little diftance from the former ; to this, other ftrata fucceed alternately poflefled of pofitive and negative Eleflricities, and decreafing in power until they vanifli. This afler- tion is eafily proved by feveral experiments, that are to be dcfcribed hereafter, but efpecially by the experiment of the glafs tube, mentioned in the Vlth chapter, which (hows that, in general, when an Eledric, fufiiciently
denfe.
96 A COMPLETE f REATISE
If the repuirioii exifting between bodies pdflefled of the fame kind of Ele6]tricity be excepted, all the other eleflrical phenomena are occafioned by the paflagc of Electricity from one body to another;
A corifiderable qiiantity of EleSEricity exifts in the atitiofpllere, arid it is certainly employed for fome gteat actions of nature*
Hitherto Ele6lricity has riot been found con- cerned in any fermentation, evaporation, or coagulation, although the clouds, the rain*, the hail, the fnow and the fogs, are almoft always eleStrifiedi
Thefe few laws, well confidered, will be found to contain almofl: all that is known of the fubje6l, and if properly applied, they may explaiti moft of the experiments that follows
Befides what has be^n faid in this part of the prefent Treatife, there are feveral other
denfe, is prefented to an elecflrified body, it acquires fuc- ceffive zones, or ftrata of pofuive and negative Eledri- city,
maxims,
\ I
OF ELECTRICITY; 5^
tnaxims, rules, &c. to be , known in Elec- tricity ; but as thefe refpe^l the real pra6tice^ fo they v/ill be occafionally ihferted in other places, that feem better adapted to their re- ception*
H PART.
g8 A COMPLETE TREATISE
PART IL
Theory of Electricity.
CHAP. I.
T^ke Hy pot he/is of Fojitive and Negative
Eledlricity.
IT is the bufinefs of Philofophy to colled the hiftory of appearances, and from thefe to deduce fiich mechanical laws, as may either be themfelves of immediate ufe, or lead to the difcovery of other fadts more interefting and neceflary for the happinefs of human kind. After a number of fuch conftant ap- pearances, which are called natural laws, have been eftablifhed, and confirmed by a fufEci- ent number of experiments, it is then proper to invefligate the caufe of thofe efFedts, which if it is once difcovered, and its mode of a6ling is afcertained, puts an end to the trouble of experimental inveftigation, and renders the application of its effe6ls certain, and determinate.
V
Caufes
OF ELECTRICITY. 99
Caiifes and effects are fo Intimately con- nected and dependant on each othef, that throughout the fyftem of nature we every where difcover a feries of energies, which whilil they are depending on, and derived from, their preceding terms, are at the fame time the caufes of their fucceeding ones. But what'^is the firft caufe of all the reft, which being not the efFeft of any preceding, may be called the fource of all, and the firft term in the feries ? In contemplating this fource, the mind is loft in wonder, and, after we are advanced a few fteps, we find that a cloud obftrud:s our further progrefs, and, from continuing our inquiry and contemplation, nothing more can be derived but an argu- ment to prove the imbecility and fhortnefs of our underftanding. It is certain that feries either finite or infinite, are not only pofiible but evidently neceffary and exifting ; and as far as we can difcern the works of nature are all depending ; but is the feries of natural caufes finite or infinite ? This how- ever is not the fubjedl of the prefent Trea- tife, and all I meant to deduce is, that, after the laws of Eledlrlcity have been con-
H 2 fidered,
300 A C O A'l P L E T E TREATISE
fidered, it is neceiTary that we fhould go a little further, and inveftigate, if poflible, the immediate caufe of that property in nature, or confider the mofl: probable conjectures that have been offered on this fubjed:, by the knowledge of which we may explain all the known eled:rical appearances, and adapt their effeds to our purpofes with fomewhat more certainty and precifion.
The vaft number of hypothefes that have been framed in explaining the ele6lrical phenomena from the infancy of the Science to the prefent time may be eafily imagined by confidering the great number of labour- ers, and the difcoveries that have been pro- duced without intermiffion in this field of wonders. It would be not only and end- lefs work to relate all the hypothefes hither- to offered, but alfo an ufelefs one, when they have been evidently contradicted by feveral experiments, and- after they have all given place to the hypothcfis of a fingle eledric fluid, which generally goes under the name of Dr. Franklim^s, That although this hypothefis explains all the known electrical appearances, it is however not a demonftrable
truth.
OF ELECTRICITY. loi
truth, but the moft probable fuppofition, I confefs, and in order that a due diftincSion might be preferved between the knowledge of fads, and the fuppofition of their imme- diate caufe, I have feparated the former from the latter, and followed that method which feemed more philofophical and in- ftrudive ; but now to make further apolo^ gies for admitting this hypothefis at a time when numberlefs experim^ents fpeak clear in its favour, would be doing an injury to the philofophical world in general, and efpecially to the ingenious philofophers that propofed and improved it. I fliall therefore, wathout further preamble, lay it down as it is now commonly and reafonably admitted ; and fhall ufe it in the explanation of the fol- lowing experiments.
All the phenomena called Eledrical ^re fuppofed to be effeded by an invifible fubtile fluid exifting in all the bodies of the earth. It is fuppofed alfo that this fluid is very elaftic, /. e. repulfive of its own particles, but attradive of . the particles of other matter.
H 3 When
102 A COMPLETE TREATISE
When a body does not fhow any elecElrical appearances it is then fuppofed to contain its natural quantity of electric fluid (but whether that quantity bears any proportion to the quantity of matter in general, or not, is uncertain), and therefore that body is faid to be in its natural^ or non-eleSirified Jiate : but if a body fhows any electrical appearances, it is then faid to be electrified, and it is fup- pofed that it has either acquired an additional quantity of eledric fluid, or that it has lofl fome of its natural fhare. A body having received an additional quantity of eledlric fluid is faid to be overcharged^ or pofitively eleSirified^ and a body that has loft part of its natural quantity of eleCtric fluid is faid to be undercharged^ or negatively ekoirified.
From hence it appears, why the terms pofitive and negative, or plus and minus, Eledricity came to be ufed ; for the firfl: fig- nifies a real plus, or fuperfluity, and the fecond a real minus, or deficiency of the quantity of eledtric fluid proper to a body.
By
li
OF ELECTRICITY.
IC3
By this hypothefis, which is analogous to the other phenomena of nature, the electrical appearances are eafily explained, and there is not a fingle experiment that feems to contradict it. Firft it appears that when an eleCtric and a conducting fubftance are rub- bed together, the Electricity is not then pro- duced, but by the aClion of rubbing one body, pumps, as it were, the eleCtric fluid from the other*, hence if one becomes over- charged
* By what mechanifm one body extrafts the eleiSric fluid from the other is not yet known. The celebrated Father Beccaria fuppofes that the aftion of rubbing increafeth the capacity of the Eleflric, /. e. renders that part of the eledlric, which is actually under the rubber capable of containing a greater quantity of electric fluid; hence it receives from the rubber an additional fharc of fluid, which is manifefted upon the furface of the Electric when that furface is come out of the rubber, in which ftate it lofes, or, as it were, contadls its capacity. Signior Beccaria's experiment to prove this fuppofition is the following. He caufed a glafe plate to be rubbed by a rubber applied on one fide of the plate, while it was turn- ing vertically, and holding at the fame time a linen thread on the other fide of the plate juft oppofite to the rubber, he obferved, that the thread was not attraded by that part of the glafs, which correfponded to the rubber, but by that which was oppofite to the furface of the glafs,
H 4 that
104 A COMPLETE TREATISE
charged with it, or pofitively eledrified, the other muft neceffarily be undercharged, or eleftrified negatively, except its deficiency be fupplied by other bodies communicating with it. From hence alfo appears the reafon, why when an eleftric is rubbed with an infulated rubber it can acquire but httle ele6lricity, be- caufe in that cafe the rubber not communicat- ing with other Condu6lors can fupply the ele6lric with only that fmall quantity of fluid, which belongs to itfelf, or which it collefts, from the contiguous air,
Electric attra6tion is eafily explained ; for this does not exift, except between bodies differently eleftrified, which muft certainly attraft each other, . on account of the attrac- tion exifting betwen the fuperfluous eleftric fluid of the bodies eleftrified pofitively, and the undercharged matter of the bodies elect- trified negatively,
that had jufl: come out of the rubber ; which fhows that the fluid, acquired by the glafs plate, did not manifeft its power until the furface of the glafs was come out of the rubber. But, query, in what manner does the glafs aug* ment its capacity of holding the eledric fluid by the adlioa of the rubber ?
As
OF ELECTRICITY. 105
As to the repulfion exifting between bo- dies poflefled of the fame Electricity ; in or- der to underftand its explanation thorought- ly, the reader mufl: be reminded of the principle mentioned in the preceding part, which is, that no Electricity, /. e. the elec- tric fluid proper to a body can neither be augmented nor diminifhed upon the furface of that body, except the faid furface is con- tiguous to an EleClric, which can acquire a contrary Eleftricity at a little diftance ; from whence it follows that no Electricity can be difplayed upon the facing furfaces of two bodies that are fufficiently near one another, ^nd both poflefTed of the fame Electricity ; for the air that lays between thofe contiguous furfaces has no liberty of acquiring any con- trary Electricity. This being premifed the explanation of eleClric repulfion become? very eafy. Suppofe, for inftance, that two fmall bodies are freely fufpended by infulated threads, fo that when they are not eleClrified they may hang contiguous to one another. Now fuppofe thofe bodies to be EleCtrified either pofitively or negatively, and then they muft repel one another, for either the increafed
or
jc6 A COMPLETE TREATISE
or dlminiflied natural quantity of ele6lric fluid in thole bodies, will endeavour to difFufe it- felf equally over every part of the furfaces of thofe bodies, and this endeavour will caufe the faid bodies to recede from each other, fo that a quantity of air may be in- terpofed between their furfaces, fufficient to ^acquire a contrary Ele6lricity at a little dif- tance from the faid furfaces. — Otherwife. — If the bodies, poiTefled of the fame Ele6lri- city, do not repel each other, fo that a fuffi- cient quantity of air may be interpofed be- tween their furfaces, the increafed quantity of electric fluid, when the bodies are elec- trified pofitively, or the remnant of it, when the bodies are electrified negatively, by the above principle, cannot be difFufed equally throughout, or over the furfaces of thofe bodies ; for no Electricity can appear upon the furfaces of bodies in conta6l, or that are very near one another. But the ele6lric fluid, by attracting the particles of matter, endeavours to diff'ufe itfelf equally through- out, or over the furfaces of thofe bodies ; therefore the faid bodies are, by this endea- vour, forced to repel one another.
I think
OF ELECTRICITY, i^j
I think It is unneceffary to infift further upon the above explanation ; for the princi- ple, upon which it depends, feems univerfal and clear, fo that it may be eafily applied to explain ele6lric repulfion in general, as well as the repulfion between the above-men- tioned two bodies.
The charging of coated glafs, and other Ele6trics, as well as the other phenomena of Eleflricity, may alfo be eafily accounted for, by the above-mentioned hypothefis of Elec- tricity ; but, I think it unneceffary to enu- merate, and account for all the particulars in this place, as we fhall have occafion to fpeak of them in the explanation of the ex- periments in the third part.
CHAP-
io8 A COMPLETE TRE ATI SE
C HA P. IL
Of the Nature of the elcBric Fluid.
TH E human mind, never fatisfied, after the caufe of fome efFeds has been dif- covered, or only guefled at, attempts to in- veftigate fome more intimate quahty, and even the origin of that fuppofed caufe^ making further fuppofitions, and framing other hypothefes, which, by the courfe of things, muft certainly be lefs probable than the former. This unlimited endeavour to ac- quire knowledge is often too ridiculous to be purfued on account of its abftrufenefs, and uncertainty, efpecially when the fceps immediately preceding the fubje£b in hand have but a fmall degree of probability. It is from hence that Philofophers have fre- quently fpent a great deal of time, and trou- ble in attempting to difcover the properties and caufes of what exifted only in their own imaginations. Sometimes, however, when ^ fuppofed exiftence comes fo very near to truth, that the moft fceptic Philofopher hefi- tates not to confefs the probability of it, or vy^hen he can invent no argument to evince 2 the
OF ELECTRICITY. 109
the contrary, then it is not only allowable, but neceflary for the bufinefs of Philofophy, to purfue the inquiry further, and if no- thing elfe can be afcertained, at lead to pro- pofe fome further conjectures upon the former hypothefis. This now is the cafe in the fcience of Eledricity, and after we have re- related the moft plaufible hypothefis as yet offered, L e. that of a fingle elaftic fluid, we come in this place to confider the elfence of this fluid, in order, if poffible, that we might attain to, at leaf!:, fome probable con- jedure, refpeding its materials.
When nothing more than elet^lric attrac- tion and repulfion had been obferved. Elec- tricians fuppofed that thefe were effefted by a kind of un<5luous effluvia proceeding im- mediately from the eleftrified body ; but. when the light, the burning quality, the phofphoreal fmell,*&c. was perceived to be produced by excited Ele6lrics, then it was naturally fuppofed, that the ele6lric fluid was of the fame nature with fire. This opi- nion has prevailed much among feveral Phi- lofophers, and it is from hence, that the ele6tric fluid has been commonly called Elec- tric
no A COMPLETE TREATISE
trie Fire. Befides this fuppofed identity of the ele6tric fluid, and the element of fire, there have been two other opinions concern- ing the eflence of this fluid ; it having been thought by fome to be the ether of Sir Isaac, Newton, and by others (whofe opinion feems to be the mofl probable) to be a fluid fui generis^ i. e. different from all other known fluids.
In order the more regularly to examine thefe conje6lures it will be neceflary to pre- mife fomething in regard to the nature of fire, at leaft fo. much as is fufiicient for the prefent purpofe.
The element of fire may be confidered in regard to its fpring, to the different ftates of its exiflence, and to its effedls. In regard to its origin ie is commonly fpecified under the names of Celeftial, Subterraneous, and Cu- linary Fire ; underftanding by the firft, that, which proceeds from the fun, and by being difperfed throughout the univerfe, gives life, and motion to almoft every thing that exifls ; by the fecond, that, which is the caufe of volcanos, hot fprings, &c. and laftly, under
the
O F E L E C T R I C I T Y. iir
the name of Culinary Fire, underftanding that, which is commonly produced upon the earth, by burning feveral fubftances, Thefe diftin6lions however are little if at all ufe- ful, for whatever be the origin of fire, its ef- fects are always the fame.
In refpe6t to the different ftates of Its ex- iftence, the Chymifts know only two ; the firft obvious one, and indeed that, to which only is given the name of Fire, is that ac- tual agitation of the particles of that ele- ment, which produces the complex idea of lucid, hot, &c. that is commonly under- ftood under the name Fire ; and the other ftate is the real principK^ of fire exifting as a conftituent principle in feveral, and per- haps all fubftances ; or, that matter, whofc particles, when agitated in a peculiar and violent manner, produce the common fenfible fire.
This, which we may call fire in an un- a<5tive ftate, is the Phlogijion of the Chymifts, and is that, which when united in a fuflScient quantity with other fubftances, renders them inflammable. That this principle does real-
4 ly
ju A COMPLETE TREATISE
ly exift, is beyond a doubt ; we may trans- fer it from one body to another ; we may render a body inflammable, which in its own nature is not fo, by fuperinducing on it the phlogifton ; and we may reduce a body, na-^ turally inflammable, to a fubfl:ance not in- flammable by depriving it of its phlogifton.
Now the electric fluid, as far as we can determine, bears but a very fmall refem- blance to the above-mentioned two ftates of fire ; for although it exifts in different bo- dies, as the phlogifton, yet when we com- pare its other attributes with thofe of fire, we then immediately perceive it to be not the fame, but a diff'erent principle. In the firft place if they were both the fame thing, they ftiould be always together, and when-* ever fiich a quantity of fire exifts, there the fame quantity of ele6tric fluid fhould be found, but this is contrary to experiments j for a piece of metal or other fiibftance may acquire a great degree of heat without ap- pearing at all eledrified, and on the other hand may be ftrongly eledtrified without ac- quiring by it any fenfible degree of heat, or any addition to its phlogifton. Secondly
fire
OF ELECTRICITY. 113
fire penetrates every known fubftance, and an exceedingly fmall quantity of it is difFufed alike throughout bodies of every kind, whereas the eleftric fluid pervades only Con- duftors*. Thirdly the eledric fluid goes through a very long Condudtor in a fpace of time almoft inftantaneous, but fire is very flowly propagated. I might enumerate fe- veral other improprieties attending this hy- pothefis of the famenefs of fire, and the elec- tric fluid, but thofe already mentioned are, I think, fufficient to induce my readers to fuppofe otherwife.
Dr. Priestley, on obferving that the ele6lric explofion taken in different kinds of air, a6ts, in general, like other phlogiflic procefles, fuppofes that the eled:ric mat- ter either is, or contains, phlogiftonf . In regard to this, I would obferve that there is no neceffity of fuppofing the eledlric mat-
^ Here may be obferved that heat pervades more ea-« iily the fubftance of fome good Conduiftors of Eledricity; but the rule however is far from being general.
f Obfervatlons on different Kinds of Air, vol. 11. ffc. XIII.
I ter
114 A COMPLETE TREATISE
ter either to be, or contain phlogifton, on that account ; for the phlogifton, in this cafe, may, by the force of the Eledric ex- plofion, be extricated, either from the furface qf the Condu6tors, between which the ex- plofion is taken, or from particles of hetero- geneous matter floating in that air, in which the explofion is made.
In regard to the fimilarity between the effects of fire, and the effects of the electric fluid, it will be very obvious to rem.ark that although fire is in feveral inftances produced by the ele6lric fluid, yet we fhould never confound the one with the other, and con- fider them both as the fame thing ; for it is well known thict fri£lion produces fire, and it is by no means furprifing that the eledtric fluid, by the rapidity of its motion, through fubflances, that in fome manner cbftrudl its paflage, fliould generate light, heat, rare- fadlion, and the other eff^eds of fire*.
* Fere it is proper to obferve that the eleciric fluid fhows no efFefts of fire, except when it goes through fome medium that obftrucls its free paflage.
Mr.
OF ELECTRICITY. 115
Mr. HenLy, in confequence of feveral very inlerefting experiments, that lie has lately made, fuppofes, that, although the elec- tric fluid may be neither phlogifton nor fire, yet that it is a modification of that element, which, while in a quiefcent ftate, is called Phlogifton, and when violently agitated is called Fire. We conftantly obferve (fays he) L that if two bodies are rubbed together, w^hich have an equal quantity of phlogifton. (w^hich is the cafe with bodies of the famaC kind, as glafs and glafs, metal arid metal, &c») they acquire either very little, or no Eledricity at all. 11. That as one of the bodies has a greater quantity of phlogifton than the the other, fo they acquire a greater quantity of Electricity, as when glafs is rubbed with metal. III. That a certain de- gree of friction produces Electricity, and that a more violent friBion produces Jtre, but no Electricity, as maybe obferved by rub- bing together two pieces of baked w^ood, of glafs, &c. IV. And that in general bo- dies, poflefled of a greater quantity of phlo- gifton, give the eleCtric fluid to bodies that have lefs of it, /. e. they acquire the negative
I 2 Elec-'
ii6 A COMPLETE TREATISE
Electricity, when rubbed with bodies that have a lefs quantity of phlogiftoiA
From thefe obfervations we gather, that the ele6lric fluid, and fire, are produced by fimilar operations, and are both extradited from bodies abounding with phlogiflon : and hence, he concludes, that, the phlogifton, the electric fluid, and fire, are only different modifications of the very fame element ; the firft being its quiefcent fl:ate of exifl:ence ; the fecond its firft aftive, and the laft its more violent ftate of agitation : like fermen-
* Mr Henly, in order to try what Ele£tiicity different fubdances will acquire, infulates them upon flicks of fealing, wax, and rubs them againft his woollen coat, or waiftcoat. In this manner he has tried a vafl number of vegetable, animal, mineral, and artificial fuhflances ^ and he has difcovered a very remarkable circumftance, which is, that, fuch fubftances, which have a great quantity of phlogifton, as vegetable fubftances, and particularly the hot, aromatic plants and feeds, &c. give the ele(5lric fluid ; that is, they acquire the negative Eleftricity when rubbed againft woollen cloths ; and, that fuch fubftances, w^ich have but little phlogifton (as moft animal fubftances) acquire the elccSlric fluid from the faid cloths, /. e. they are electrified pofitively.
tation
O F E L EC T R I C I T Y. 117
tation producing firft wine, fecond vinegar, iaftly putrefadion,
I fhall only obferve further on this inge- nious hypothefis, in order to {how its great degree of probability, that it is fo very aaa- logous to the other operations of nature, and at the fame time fo clear, and fimple, that I think it can hardly be difregarded by the moft prejudiced Philofopher.
As to the identity of the Eleflric, and the ethereal fluid, it feems to me quite an improbable, or rather a futile, and infignifi- cant hypothefis ; for this ether is not a real, exifting, but meerly an hypothetical jiuid^ fuppofed by different Philofophers to be en- dued with different properties, and to be an element of feveral principles. Some fup- pofe it to be the element of fire itfelf, others make it the caufe of attraQion, others again derive anirnal fpirits from it, &c. but the truth Is, that not only the effence, or pro- perties, of this fluid, but even the reality of its exiftence is abfolutely unknown.
I 3 Ac-
ji8 A COMPLETE TREATISE
According to Sir Isaac Newton's fup- pofition, this ether is an exceedingly fubtle, and elaftic fluid, difperfed throughout all the univerfe, and whofe particles repel the parti- cles of other matter. But on this fuppoiition the eledric fluid is different from ether ; for although the former is fubtle, and elaftic like the latter, yet (as Dr. Priestley obferves) it is not repulfive like the ether, but attrac?- tive of all other matter.
CHAP-
OF ELECTRICITY. 119
CHAP. III.
Of the Nature of EleBrics and ConduBors.
TH E remarkable difference exifling be- tween the two claffes of bodies in re- gard to Eledricity, /. e. Eledrics, and Con- ductors, naturally induces an Eledrician to inquire what is that principle in bodies, or by what mechanifm fome fubftances become capable of tranfmitting the eleftric fluid, whilfl: others are impervious to it ?
In regard to the explanation of thefe two remarkable properties, there have been, as might be expected, feveral conjed:ures of- fered, but except one probable hypothefis, there is nothing as yet afcertained. When the catalogue of Electrics and Condudors was very Ihort and imperfect, it was fup- pofed that, the only two conducing princi- ples were metals, and water ; and that all fubftances were nearer, or further from the nature of a perfect Conductor, in proportion as they contained a greater or lefs quantity of the above principles in their compofition.
1 4 Wood,.
120 A COMPLETE TREATISE
Wood, for inftance, was fuppofed to be a Conductor only on account of the water it contained within its pores ; accordingly, it was obferved, that the greater quantity of moifture the wood contained, the better Con- du£tor it proved to be, and on the contrary, that it adted more like an Electric, in pro- portion as it was freed from its moifture. But when water itfelf was obferved to be a bad Condudor, and hot air, and charcoal to be good Condudlors, efpecially the latter, which fubftances, it is well known, contain no water nor metal, at leaft not in fuch a quantity as is fufEcient to change a non- condudling fubftance into a Conductor, then, the former fuppofition was laid afide, and another was offered by Dr. Priestley, in his fecond volume of Obfervations on the different Kinds of Air*, which feems to be well founded.
The Dodtor, confidering what the princi- ple is, which Condudors pofTefs in common, and finding one of their common ingre-
* See. XIV-
dients
OF ELECTRICITY. lar
dients to be the phlogifton, deduces from thence, that the conduding quality is abfo- hitely owing to the phlogifton. " Had there " been (fays he) any phlogifton in water, I *' fhould have concluded, that there had " been no conducting power in nature ; but " in confequence of fome union of this ^' principle with fome bafe. In this, metals, *^ and charcoal exadlly agree. While they *^ have the phlogifton, they conduct; when *^ deprived of it they will not condud.'*
And in a note to this paragraph he fub- joins.
" Having fince found, that long agitation " in the pureft water injures air, fo that a " candle will not burn in it afterwards, ** which is precifely the eff'ed of all phlo- " giftic procefles, I now conclude that the " maxim, fuggefted in this paragragh, is uni- " verfally true,"
This hypothelis feems very ingenious and probable ; and, till any other more plaufible be offered, or experiments contra-
did
122 A COMPLETE TREATISE
didi it, I think we may fafely make ufe of it in purfuing our eledlrical inveftigations, and endeavour to reconcile to it the phenomena already difcovered in Electricity,
CHAP-
OF ELECTRICITY. 123
C H A P. IV,
»
Of the Place occupied by the eleSlric Fluid.
BEFORE we quit the hypothetical part of this Treatife it may be proper to fay fomething concerning the refidence of the eledric fluid either natural to a body, or fuperinduced on it. That the eledtric fluid, proper to a body when in its natural fl:ate, is equally diffufed throughout all its fubftance, I think no one will deny ; becaufe that fluid is attradive of the particles of all other matter, and the particles of other matter are attradive of the eledric fluid; and as this attradion is in proportion to the quantity of homogeneous matter, any quantity of matter will certainly attrad a quantity of eledric fluid proportionable to itfelf ; there- fore, the eledric fluid mufl: be equally dif- fufed throughout all the parts of that portion of matter. This propofition, however, will take place only in fpeaking of Condudors, for it is founded upon the fuppofition, that the eledric fluid, proper to a body in its natural fl:ate, does freely pervade that fub- ftance ;
124 A COMPLETE TREATISE
ftance ; but whether this Is a fa6l refpeding Eledrics or not, hath not hitherto been af- certained. As far as may be judged from experiments, I ihould fuppofe this rule to hold good with Eled:rics alfo, and my fup- pofition is founded upon the following rea- foning. All the Eledrics, when made very hot, become Condudors* ; in that ftate, there- fore, the above rule muft hold good, /. e. the eleftric fluid, proper to their quantity of matter, muft be equally difFuffed through- out their fubilance ; and as all the Ele(!lrics in nature, before they became fuch (w^e may fuppofe) w^ere Condudors ; in that ftate they certainly had their proper fhare of fluid. Now as they afterwards cool and become Eledrics, it fhould feem that the change of their nature could not aft^e£t the equal diffu- fion of the eledric fluid, which took place, whilft they were in a conducting ftate. In confequence of this confideration, the diff'er- ence between a Conductor and a Non-con-
* As this propofition has been found (rue in all the experiments hitherto made, I think it may be copfidered very properly, as a general law in the fcience pf Elec- tricity.
dudor,
OF ELECTRICITY, 125
du£tor5 in regard to their natural quantity of eledric fluid, is, that in the former, the fluid may eafily move, whereas in the latter, it is confined in its pores. But it may be afked, whether a quantity of eledric matter contains as much eleftric fluid as an equal quantity of condu6ling matter ; a piece of rofin, for inftance, when melted, docs it contain more, lefs, or the fame quantity, of ele6lric Fluid as when cold ? To this queftion I can give no fatisfadory anfwer ; for, by the experiments hitherto made, nothing certain has been de- termined. Dr. Priestley, in order to af- certain this matter, made the following expe- riment. He made a piece of glafs red-hot (in which Hate it is a Condudor) and plac- ing it upon an infulated piece of copper, left it in that fituation till quite cold {/• e. till it became an Eledric), but in air the time of its cooling no Eledricity of any kind was perceived, either in the copper or glafs, which would have certainly been the cafe if the piece of glafs had contained either more or lefs fluid when in an Eledric, than when in a conduding ftate *. This experi-
* Hiftory of Eleftricity p. 716. — Experiments of a fimilar nature are met with in Beccaria's Elcftricifmo Artificials
4 meat
126 A COMPLETE TREATISE
ment feems to give a decifive anfwer to the above queftion ; but v^hen the experiments, mentioned in the firft part, of melting an ele6lric fubftance into another, and other fads of a fimilar nature, are duly confidered, they feem to make the anfwer again difficult^. It muft therefore be confefled, that this mat- ter remains as yet unfettled, and nothing but further experiments, and the difcovery of other fa6ls, can determine any thing fatif- fadory about it.
In refped to the place occupied by the eledlric fluid fuperinduced on a body, it has been thought, by feveral ingenious perfons, that, when a body is eledrified, all the fu- perfluous fluid, or all the deficiency of it, in cafe the body is electrified negatively, refides as a kind of atmofphere all around the body; to this atmofphere they attribute the phof- phoreal fmell, and that tickling fenfation
* The wax chandlers, in forming their mafs in (licks, &c. find it fo ftrongly attraftive of duft, &c. that they are obliged to ufe great caution in keeping it at a fuiBcient diftance from the charcoal fire, over which they work, left it fhould (as it fometimes happens) cover itfelf with ajfhes, and thus fpoil the work,
produced
OF ELECTRICITY. 127
produced by an excited Eledric, and they even fuppofe that thefe atmofpheres may be made vifible. But to this aflertion it is anfwered by others, that if the Electricity communicated to a body did refide round it like an atmofphere, it fhould qertainly repel the air contiguous to that body ; but this is not the refult of experiments j for it has been found that the eledtric atmofphere, however denfe, if it does at all exift, has no efFed; upon the air contiguous to the elec- trified body, nor has the motion of the air, even a violent wind, any efFed: upon the at- mofphere. In regard to the above-mentioned fenfations of phofphoreal fmell, &c. it is thought that they are only occafioned by the electric fluid entering or going out of the fkin in a very fubdivided manner.
From what may be deduced from experi- ments, it appears that, although the electric fluid is tranfmitted through the fubftance of Condudors, yet no communicated Eledtrici- ty can be obferved within a fufRciently nar- row cavity of an eledrified body ; befides if two bodies of the fame fize and figure, but of different denfities, are eledrified together, 2 and
128 A COMPLETE TREATISE
and afterwards feparated, they will acquire each the fame quantity of Eledricity, i.e. the Eledricity that they acquire will be propor- tional to their furfaces, and not to their re- fpedive quantities of matter.
We may laflly conclude that the Electrici- ty, communicated to a body, lies not difFufed throughout the fubftance of that body, but on that furface of it, which is contiguous to a free Eledric, /. e. to an Eledric, that is not fur- rounded by an homolougous Eledricity,
tART.
OF ELECTRICITY. 129
PART III.
Practical Electricity.
C H A P. I.
Of the eleSirical Apparatus in general.
HITHERTO we have treated of Elec- tricity only theoritically, having noted what has been found uniformly certain re- lative to this fubje£l, and having exhibited a view of the moft probable conjedlures offered in explanation of eledrical appearances ; but Electricity being a fcience, that requires a more pradical management, than perhaps any other branch of natural philofophy, it is neceflary, that we fhould now treat of it practically, and give the beft direClions we are able, both in regard to the conftru6lion of the neceflary apparatus, and to the per- formance of the experiments, not only requi- fite in proving the foregoing Propofitions, but fuch alfo, as are pleafing and entertain- ing.
K In
130 A COMPLETE TREATISE
In this part of my work the reader will perhaps find more novelty, than he expefts ; for confidering the number of books that have been lately publifhed on this fubje6l, one would imagine that all the experiments poffible to be exhibited with an eledrical machine, and its appendages, . have already been defcribed. The cafe however is much the contrary, for not only the old experi- ments have been diverfified, but a variety of new ones have been invented, and even the principal part of the apparatus has under- gone feveral changes, and improvements.
In order the more regularly to proceed in the defcription of the eledrical apparatus, it will not be improper to divide its parts into three clafTes, confidering in the firft, the in- ftruments neceflary to produce Eledricity ; in the fecond, thofe proper to accumulate, retain, and employ it ; and laftly, thofe ne- cefTary to meafure its quantity, and afcertain its quality.
The principal inftrument to produce Elec- tricity, is the eled:rical Machine, /. e. a ma- I chine
OF ELECTRICITY. 131
chine capable by any means, of exciting an Eledric, fo as to produce eledtrical appearances. The conftrudion of thofe machines from their firft invention to the prefent time, has undergone fo many changes, and their forms have been fo much varied, that it vv^ould be very difficult, and even tedious to defcribe thofe only, which are moft frequently in ufe. Every maker, and almoft every Elec- trican conftru6ls his own machines in a manner different from the reft, and as new fa6ls, or long pradice points out fome im- perfedions, the Electrician is ready to con- trive a new method to correct the preceeding errors. Indeed the rapid advance of the fcience is moftly owing to this change^ and variety of conftru£tions ; for whether cafual, or defigned^ a new conftru6tion has generally either produced fome difcovery of importance, or expofed Ibme defeat in the apparatus, and management of the fame.
That the reader might be left at the liber- ty of choofing the form of his machine, I fhall in this chapter lay down the moft ne- cefTary rules to conftrud eledlrical machines in general, and fhall referve for the next chap-
K 2 ter
132 A COMPLETE TREATISE
ter the particular defcription of fome ma- chines, that are the moft ufeful, and which contain all the improvements hitherto made.
The principal parts of the machine are the Eledric, the moving Engine, the Rubber, and the prime Condudor, /. e. an infulated Conductor, which immediately receives the Eledricity from the excited Electric.
The Eledlric was formerly ufed of differ- ent fubftances, as glafs, rofin, fulphur, feal- ing-wax, &c. and of different forms, as cy- linders, globes, fpheroids, &c. This diver- fity then obtained on two accounts, firfl, be- caufe it was not afcertained, which fubftance or form would anfwer befl, and fecondly, on account of producing a negative, or pofitive Electricity, at the pleafure of the operator; for before the Eledricity of the infulated rubber was difcovered, fulphur, rough glafs, or fealing-wax, was generally ufed for the negative Eledricity. At prefent, fmooth glafs only is ufed ; for when the machine has an infulated rubber, the ope- rator may produce pofitive or negative Elec- tricity at his pleafure, without changing the
Eleftric.
O F E L E C T R I C I T Y. 13^
Eledric. In regard to the form of the glafs thofe commonly iifed at prefent are globes, and cylinders. The moft convenient fize for a globe. Is from nine to twelve inches diameter, they are made with one neck, which is cemented * to a flrong brafs cap in order to adapt them to a proper frame. The cylinders are made with two necks, they are ufed to the greateft advantage without any axis, and their common fize is from four inches diameter and eight inches long, to twelve inches diameter and two feet long, which are perhaps as large as the workmen, can conveniently make them. The glafs generally ufed is the beft flint, though it is not yet abfolutely determined, which kind of metal is the beft for electrical globes, or cy- linders. The thicknefs of the glafs feems immaterial, but perhaps the thinneft is pre- ferable. It has often happened that glafs
* The beft cement for eleclrical purpofes Is made with two parts of rofin, two of bees-wax, and one of the powder of red okre, Thefe ingredients are melted, and mixed together in any veflel over the fire ; and afterwards kept for ufe. This kind of cement fticks very faft, arid is much preferable to rofin only, as it is not fo brittle, and at the fame time infulates equally well.
K 3 globes,
134 A COMPLETE TREATISE
globes, and cylinders, in the a6l of whirling, have burft in innumerable pieces, with great violence, and with fome danger to the by* ftanders, Thofe accidents are fuppofed to happen when the globes, or cylinders, after being blown^ are fuddenly cooled. It will therefore be neceflary to enjoin the workman to let them pafs gradually, from the heat of the glafs-hpufe, to the atmofpherical tem-* perature.
It has been long queftioned whether a coating of fome electric fubftance as rofin, turpentine, &;c- on the infide furface of the glafs, has any efFed: to increafe its eledrical power ; but now it feems pretty well deter- mined, that if it does not increafe the power of a good glafs globe or cylinder, at leaft it does confiderably improve a bad one. I have feveral times put a coating of rofm on the infide furface of phials and tubes, and have conftantly found, that the worft of them received fome improvement by it.
The mofl: approved compofition for lining glafs globes, or cylinders, is made with four parts of Venice turpentine, one part of
rofm
OF ELECTRICITY. 135
rofin and one part of bees-wax. This com- pofition mud be boiled for about two hours over a gentle fire, and muft be kept ftirring very often : afterwards it is left to cool, and referved for ufe. When a globe or cy- linder is to be lined with this mixture, a fuf- ficient quantity of it is to be broken into fmall pieces, and introduced into the glafs ; then, by holding the glafs near the fire, the mixture is melted, and equally fpread over all its internal furface, to about the thicknefs of a fixpence. In this operation care muft be taken, that the glafs be made hot gradually, and be continually turned, fo as to be heated equally in all parts, otherwife, it is apt to break in the operation.
In refped: to the Engine which is to give motion to the Electric; multiplying wheels have been generally ufed, which, properly adapted, might give the Eled:ric a quick motion, while they are conveniently turned by a winch. The ufual method is, to fix a wheel on one fide of the frame of the ma- chine, which is turned by a winch, and has a groove round its circumference* Upon the brafs cap of the neck of the glafs globe, or
K 4 one
136 A COMPLETE TREATISE
one of the necks of the cyUnder, a pulley is fixed, whofe diameter is about the third or fourth part of the diameter of the wheel ; then a firing or ftrap, is put over the wheel and the pulley, and by thefe means, when the winch is turned, the globe or cylinder makes three, or four, revolutions, for one revolution of the wheel. There is an incon- venience generally attending this conftruc- tion, which is, that the firing is fometimes fo very flack, that the machine cannot work. To remedy this inconvenience, the wheel Ihould be made moveable with refpeft to the Ele6lric, fo that by means of a fkrew it might be fixed at the proper diftance ; or elfe the pulley fhould have feveral grooves of different radiufes on its circumference.
It has been cuflomary v^ith fome, to turn the cylinder fimply with a winch, without any accelerated motion ; but that feems not fufficient to produce the greatefl Electric power, the glafs is capable of giving; for the globe or cylinder fhould properly make • about fix revolutions in a fecond, which is more than can be conveniently done with the winch only. This method however, on ac- 4 count
O F E L E C T R I C I T Y. 137
count of its fimplicity, and eafy conftruc- tion, fhould not be difregarded, and it may- be conveniently ufed, when no very great power is required,
Inftead of the pulley and the firing as above defcribed, a wheel and pinion, or a wheel, and an endlefs fkrew, has-been alfo ufed. This conftrud:ion anfwers perhaps as well as any other ; but, it muft be con- llrudled with great nicety, otherwife, is apt to make a difagreeable rattling, and without frequent oiling, foon wears away by the great fridion of its own parts.
The next thing belonging to the Eledrical machine neceflary to be defcribed is the rubber, which is to excite the Eledric, The rubber, as it is now made, is nothing more than a filk cufliion fluffed with hair ; and over this cuihion is put a piece of leather, on which fome amalgam* has been rubbed
* This amalgam has been found to excite fmooth glafs the mod powerfully of any thing yet tried. Any metal, diflblved in quick-filver, will perhaps do equally well, but the amalgam generally ufed, is made with two parts of quick-filver and one of tin-foil, with a fmall quantity of powdered chalk, mixed together until it become a mafs, like pafte.
fo
I3ft A COMPLETE TREATISE
fo as to ftick as faft as poffible to the leather. Sometime ago it was generally ufed, and it is now cuftomary alfo, to make the rubber of red bafil fkin ftufFed with hair ; but the filk one, as above defcribed (which is an improvement of Dr. Nooth) is much pre- ferable. If this filk cufhion, on account of adapting it to the furface of the glafs, is to be fixed upon a metal plate, then care Ihould be taken to make the plate free from fharp points, edges, or corners, and it fhould be as much as poffible concealed, or covered with filk. In fhort to conftrud the rubber properly, it muft be made in fuch a manner, that the fide of it, which the furface of the glafs enters in whirling, may be as perfedl a Condudlor, as it can be made, in order to fup- ply Electricity as quick as poffible, and the oppofite part fhould be as much a Non-con- dudor as poffible, in order that none of the fluid accumulated upon the glafs, may return back to the rubber, which has been found by experiment to be the cafe, when the rubber is not made in a proper manner.
The
OF ELECTRICITY. 139
The rubber fhould be fupported by a fpring, by which means it may eafily fuit any inequalities, that may be found on the furface of the glafs, and by a Ikrew it may be made to prefs harder or fofter, as occa- lion may require. It fhould alfo be infulated in whatever manner is moft convenient, for whenever infulation is not required, a chain or wire, &c. may be occafionally hung upon it, and thus communicate with the earth or with any other body at pleafure j whereas, when there is not a contrivance for infula- ting the rubber, many of the moft curious experiments in Electricity will never be per- formed with the machine.
We come now to confider the prime Con- ductor, or firft Conductor, which is nothing more than an infulated conducting fubftance furnifhed with one, or more points at one end, in order to colleCt the EleCtricity im- mediately from the EleCtric. When the Conductor is of a moderate fize, it is ufual to make it of hollow brafs, but when it is very large, then, on account of the price of the materials, it is made of pafte-board co- vered with tin-foil, or gilt paper. The
Conductor
I40 A COMPLETE TREATISE
Condu6tor is generally made cylindrical, but let the form be what it will, it fliould always be made perfectly free from points, or fharp edges ; and if holes are to be made in it, which on many accounts are very con- venient, they fhould be well rounded, and made perfe6lly fmooth. Further, that end of the prime Condu6lor, which is at the greateft diftance from the Eleflric, ought to be made larger than the reft, as the ftrongeft exertion of the electric fluid in efcapingfrom the ConduCior is always at that end.
It has been conftantly obferved, that the larger the prime Conductor is, the longer,, and denfer fpark can be drawn from it, and the reafon of this is, that the quantity of Electricity, difcharged in a fpark, is nearly proportional to the fize of the Condud:or ; on this account the prime Cpndudtor is now made much larger, than what was formerly ufed. Its fize, however, may be fo large, that the diffipation of the Ele6lricity from its furface, may be greater than what the Eledric can fupply ; in which cafe fo large a Con- dudor would be nothing rnore than an un- weildy, and difagreeable incumbrance.
Before
OF ELECTRICITY. 141
Before we quit the electrical machine it fliould be obferved, that, befides the above- mentioned parts, it is neceflary to have a ftrong frame to fupport the Eledtric, the rubber, and the wheel. The prime Con- dudor fhould be fupported by ftands with pillars of glafs, or baked wood> and not by filk firings, which admit of continual mo- tion. In Ihort, the machine, the prime Conductor, and any other apparatus adlually ufed, fhould be made to fland as fleady as poflible, otherwife many inconveniences will arife.
Befides the Electrical machine, the Elec- trician fhould be provided with glafs tubes of different fizes, a pretty large flick of feal- ing-wax, or a glafs tube covered with feal- ing-wax, for the negative Ele6lricity. He fhould at leaft, not be without a glafs tube about three feet long, and one inch and a half in diameter. This tube fhould be clofed at one end, and at the other end fhould have fixed a brafs cap with a ftop cock, which is ufeful in cafe it fhould be required to con- denfe, or rarefy the air within the tube.
The
142 A COMPLETE TREATISE
The beft rubber for a tube of fmooth glafs is the rough fide of black oiled filk, efpeci- ally when it has fome amalgam rubbed upon it; but the beft rubber for a rough glafs tube, a ftick of baked wood, fealing-wax, or fulphur, is foft new flannel.
The inftruments neceflary for the accu- mulation of Eledtricity, are coated EIe6lrics, among which, glafs coated with Condu6lors obtains the principal place ; on account of its ftrength it may be formed into any fhape, and it will receive a very great charge. The form of the glafs is immaterial with refpeft to the charge it will contain ; its thicknefs only is to be confidered, for the thinner it is the higher charge it is capable of receiving ; but it is at the fame time more fubjeft to be token by the force of ele6lric attra6lion ; for this reafon therefore, a thin coated jar, or plate may be ufed very well by itfelf, and it is very convenient for many experiments ; but when large batteries are to be conftrudled, then it is neceflary to ufe glafs a little thick- er, and care fhould be taken to have them perfectly well annealed. If a battery is re- quired
OF ELECTRICITY. 143
quired of no very great power, as containing about eight or nine fquare feet of coated glafs, I (hould recommend to make ufe of common pint, or half-pint phials, fuch as apotheca- ries ufe. They may be eafily coated with tin-foil, fheet-lead, or gilt paper on the out- fide, and brafs-filings on the infide, they occupy a fmall fpace, and on account of their thinnefs, hold a very good charge. But when a large battery is required, then thefe phials cannot be ufed, for they break very eafily, and for that purpofe cylindrical glafs jars of about fifteen inches high, and four or five inches in diameter are the moll con- venient-.
When glafs plates or jars, having a fufKci- ently large opening, are to be coated, the beft method is to coat them with tin-foil on both fides, which may be fixed upon the glafs with varnifh, gum- water, bees-wax, &c. but in cafe the jars have not an aperture large enough to admit the tin-foil, and an inftru- ment to adapt it to the furface of the glafs, then, brafs-filings, fuch as are fold by the pin-makers, may be advantageoufly ufed, and they may be ftuck with gum-water,
bees-
144 A COMPLETE TREATISE
bees-wax, &c. but not with varnifh, for this is apt to be fet on fire by the difcharge, as will appear in the latter part of this work. Care muft be taken that the coatings do not come very near the mouth of the jar, for that will caufe the jar to difcharge itfelf. If the coating is about two inches below the top, it will in general do very well ; but there arefome kinds of glafs, efpecially tinged glafs, that, when coated and charged, have the property of difcharging themfelves more eafily than others, even when the coating is five or fix inches below the edge. There is another fort of glafs like that, of which Florence flafks are made, which, on account of fome unvitrified particles in its fubftance, is not capable of holding the leaft charge ; on thefe accounts therefore, whenever a great number of jars are to be chofen for a large battery, it is advifeable to try fome of them firft, fo that their quality, and power may be afcer- tained.
Electricians have often endeavoured to find fome other Ele6lric, which might anfwer better than glafs for this purpofe, at leaft be cheaper; but except Father Becgaria's
method,
OF ELECTRICITY. 145
method, which may be ufed very well, I do not find that any remarkable difcovery has been made relating to this point.
Father Be CCA Ri A took equal quantities of very pure colophonium, and powder of marble fifted exceedingly fine, and kept them in a hot place for a confiderable time, where they became perfectly free from moifture; he then mixed them, and melted the com- pofition in a proper veffel over the fire, and when melted poured it upon a table, upon which he had previoufly ftuck a piece of tin- foil, reaching within two or three inches of the edge of the table ; this done, he endea- voured with a hot iron to fpread the r^ixture all over the table as equally as poffible, and to the thicknefs of one tenth of an inch ; he afterwards coated it with another piece of tin-foil reaching within about two inches of the edge of the mixture ; in fhort, he coated a plate of this mixture like a plate of glafs. This coated plate, from what he fays, feems to have had a greater power than a glafs plate of the fame dimenfions, even when the weather was not very dry : and if ic is not fubjed to break very eafily by a fpontaneous
L difcharge.
146 A COMPLETE TREATISE
difcharge, I think it may be very conveni- ently ufed ; for it doth not very readily at- tract moifture, and cqnfequently may hold a charge of Electricity better, and longer than glafs ; befides, if broken, it may be repaired by a hot iron ; but glafs, when broke, can never be repaired.
When a jar, a battery, or jr^ general a coated Electric, is to be difcharged, the ope- rator fhould be provided with an inftrument called the difcharging Rod, which confifts of a metal rod foraetimes ftraigbt, but more
. ' ' ■ ■ ^"^ -1X1 I
commonly bended in the form of a C : they are made alfo of two joints fo as to open like a kind of compafles. This rod is furnifhed with metal knobs at its extremities, and has a non-condu£ting handle, generally of glafs or baked wood fattened to its middle. When the operator is to ufe this inftrument, he holds it by the handle, and touching one of the coated fides of the charged Eledlric with one knob, and approaching the other knob to the other coated fide, or fome conduding fubftance communicating with it, he com- pletes the communication between the two fides, and difcharges the Eledric*
The
OF ELECTRICITY.
H7
The inflruments to meafure the quantity, and afcertain the quality of Ele(0:ricity are commonly called BdeSirometers^ and they are of four forts, i ft. the fingle Thread, 2d. the Cork, or Pith-balls, 3d. the Quadrant, and, 4th. the difcharging Eledrometer *. But a particular defcription of the fame will be found in the third chapter of this work.
Befides the apparatus above defcribed there are feveral other inftruments ufeful for vari- ous experiments, but thefe will be defcribed occafionall)^. The Electrician, however, ought to have by him not only a fingle coated jar, a fingle difcharging rod, or in fhort, only what is neceffary to perform the common experiments, but he fhould provide himfelf with feveral plates of glafs, with jars of different fizes, with a variety of different
* The fecond fort of Elecflrometer, /. e, the cork-balls Electrometer W2s invented by Mr. Canton^ ; the dif- charging Eledrometer was invented by Mr. Lane, and hath been improved by Mr. Henly : another on a different principle by Mr. Rinnersley; and the quadrant Elec- trometer, which is of lateft invention, is a contrivance of Mr. Henly.
L 2 inftruments
148 A COMPLETE TREATISE
inftruments of every kind, and even tools for confl:ru6l:ing them ; in order that he may readily make fuch new experiments, as his curiolity may induce him to try, or that may be publifhed by other ingenious perfons, who are purfuing their refearches in this branch of philofophy.
CHAP,
OF ELECTRICITY. 149
CHAP. 11.
T^he defcrtption of fome particular eleSlrical
Machines.
IN this chapter I fhall prefent the reader with the particular defcription of three ele6lrical machines, which, I think, will be very acceptable after the general account of their conftru6lion, which has already been given. The firft of thefe is that defcribed by Dr. Priestley, in his Hiflory of Elec- tricity*; where a drawing of the fame may be feen, and which, on account of its extenfive ufe, may be defervedly called a univerfal ele6lrical Machine.
The bafis of this machine confifts of two oblong boards, which are kept in a fituation parallel to one another, about four inches afunder, by two fmall pieces of board proper- ly adapted to that purpofe. Thefe boards, when fet horizontally upon a table, and there fixed by faftening the lower of them
* Part V. fee. XL
L 3 with
ISO A COMPLETE TREATISE
with iron cranks, form the fupport of two perpendicular pillars of baked wood, and of the rubber of the machine. One of the pil- lars, together with the fpring fupporting the rubber, Aides in a groove, which reaches almoft the whole length of the upper board, and, by means of fcrews, may be placed at any required diftance from the other pillar, which is fixed, being let through a mortice in the upper board, and ftrongly fattened to the lower. In thefe two pillars are feveral holes for the admittance of the fpindles of different globes, and as they may be fituated at any diftance from one another, they may be adapted to receive not only globes, but alfo cylinders, or fpheroids of different fizes. In this machine, fays Dr. Priestley, more than one globe or cylinder may be ufed at once, by fixing them one above the other in the different holes of the pillars, and by adapting to each a proper pulley, they may be whirled all at once, and their power unit- ed in order to increafe the Electricity ^' ; but
in
* When feveral globes are ufed at once, and their power united, it has been found by experiment, that the Elec- tricity
4C
OF ELECTRICITY. 151
in this confl:ru6lion I do not think that differ- ent rubbers can be conveniently applied to them all ; which is a capital imperfe6lion.
*^ The rubber confifts of a hollow piece " of copper, filled w^ith horfe-hairj and covered v/ith a bafil fkin. It is fupport- ed by a focket, which receives the cylin^ drical axis of a round and flat piece of " baked wood, the oppofite part of which *' is inferted into the focket of a bent fteel fpring. Thefe parts are eafily feparated, fo that the rubber, or the piece of wood that ** ferves to infulate it^ may be changed at *' pleafure. The fpring admits of a two- ^^ fold alteration of pofition. It may be ei- ^^ ther flipped along the groove, or moved '' in the contrary direction (the groove being wider than the fcrew which fattens the fpring), ^' fo as to give it every defirable ^^ pofition with refpe£t to the globe or cy«
trk:ity does riot increafe in proportion to their number, although it is more, than what may be produced by d fingle globe. However, as the friftion, and the difficulty of working the ritachine lacreafes in proportion to the number of globes or cylinders, fo I think that one good large cylinder is preferable to many of them.
L 4 *' lindeif
152 A COMPLETE TREATISE
*' Under ; and it is, befides, furniflied with ^' a fcrew, which makes it prefs harder or *^ lighter, as the operator choofes/'
The wheel of this machine is fixed to the table ; it has feveral grooves, for admitting more firings than one, in cafe that two or three globes, or cylinders are ufed at a time ; and as it is diffengaged from the frame ^ of the machine, the latter may be fkrewed at different diftances from the former, and thus fuited to the variable^ length of the firing.
The prime Condudor is of hollow copper, made in the fhape of a pear, fituated with its neck upwards, and with its bottom or rounder part upon a fland of baked wood ; and an arched wire proceeds from its neck, having an open ring at its end, in which fome fmall pointed wires are hung, that by playing lightly upon the eledric colle6l the eledtric fluid from it.
This machine notwithflanding that it has feveral imperfections, is yet a very good in- vention J but except different globes, or cy- 2 linders.
I
OF ELECTRICITY. 153
linders, or feveral of thofe at once are re- quired to be ufed, I think a great deal of the work may be fpared, and the machine might be made more fimple, and concife.
Next to Dr. Priestley's machine I fhall defcribe another, which was invented by Dr. Ingenhousz, and which for its fimpli^ city, and concifenefs, makes a fine contrail with the former.
This machine confifts of a circular glafs plate about one foot diameter, which is turn- ed vertically by a winch fixed to the iron axis that pafles through its middle, and it is rubbed by four cufhions, each about two inches long, fituated at the oppofite ends of the vertical diameter.
The frame confifts of a bottom board, about a foot fquare, or a foot long and fix inches broad, which, when the machine is to be ufed, may be faftened by an iron crank to the table. Upon this board two other flender, and fmaller ones are raifed, which lie parallel to one another, and are faftened together at their top by a fmall piece of
wood.
154 A COMPLETE TREATISE
wood. Thefe upright boards fupport in their tniddle the axis of the plate, and to them the rubbers are fattened;
The Condudor is of hollow brafs, and from its extremities branches are extended^ which coming Very near the extremity of the glafs, colled: the Eledtrlcity from it.
The power of this tnachine is perhaps more than a perfon would judge by looking at it* It may be objedled that this con- ftruftion will not eafily adrnit of the rub- bers being infulated, nor confequently be adapted to a great variety of experiments ; but at the fame time it muft be allowed, that it is very portable, that it is not very liable to be out of order, and that it has a power fufficiently ftrong for phyfical purpjfes ; on which account it may be conveniently ufedi
The laft machine, that I am to defcribe, is that reprefented in fig. i of plate 2 which has all the improvements hitherto made, ex- cept that it is not capable of admitting dif- ferent kinds, or more than one Ele^ric, but
whichj
OF ELECTRICITY. 155
which, indeed, it feems not to ftand in need of. The eledric power of fuch a machine I think is equal to what may be obtained by any other conftrudion, and at the fame time its fize being neither remarkably large, nor at all inconvenient, renders it, I think, the completeji machine hitherto contrived*.
The frame of this machine confifts of the bottom board A B C, which, when the ma-^- chine is to be ufed, is faftened to the table by two iron cranks, one of which appears in the figure near C. Upon the bottom board are perpendicularly raifed two ftrong wooden pillars K L, and A H, which fupport the cylinder, and the wheel. From one of the brafs caps of the cylinder F F, an axle of fteel proceeds, which pafles quite through a hole in the pillar K L, and has on this fide of the pillar a pulley I fixed upon its fquare extremity. Upon the circumference of this pulley there are three or four grooves, in or- der to fuit the variable length of the ftring
* Thefe machines are made, and fold, by Mr. George Adams, in Fleet-ftreet, London, philofophical inftru- ment-maker to hisMajefty.
a by
156 A COMPLETE TREATISE
a b^ which goes round one of them, and round the groove of the wheel D. The other cap of the cyHnder has a fmall cavity, which fits the conical extremity of a ftrong fkrew, that proceeds from the pillar H. The wheel D, which is moved by the handle E, turns round a ftrong axle, proceeding from almoft the middle of the pillar K L.
The rubber G of this machine is on each end two inches fhorter than the cylinder (/. e. the cylinder exclufive of the necks), and it is made to rub about one fourth part of the cylinder's circumference ; it confifts of a thin quilted cufhion of filk, fluffed with hair, and faftened by filk firings upon a piece of woodj which is properly adapted to the furface^^^ of the cylinder. From the upper extremity of the cuihion proceeds a piece of oiled filk, that covers almoft all the upper part of the cylinder ; and to the lower extremity of the cufhion, or rather of the piece of wood, to which the cuftiion is tied, a piece of leather is faftened, which is turned over the cuftiion, /. e. ftands between it and the furface of the cylinder. Upon this leather, which reaches from the lower to almoft the upper extremity
of
OF ELECTRICITY,* 157
of the cufhion, fome of the above-defcribed amalgam is to be worked, fo as to be forced as much as poffible into its fubftance. This rubber is fupported by two fprings, fkrewed to its back, and from which it may be eafily unfkrewed, when occafion requires it.' The two fprings proceed from the wooden cap of a ftrong glafs pillar*, perpendicular to the bottom board of the machine. This pillar has a fquare wooden bafis, that Aides in two grooves in the bottom board ABC, upon which it is faftened by a fkrew. In this manner the glafs pillar may be faftened at any required diftance, and in confequence the rubber may be made to prefs harder or lighter upon the cylinder. The rubber in this manner is perfe6lly infulated, and when infulation is not required, a chain with a fmall hook may be hanged to it, fo as to have a regular communication with the piece
* This glafs pillar as well as the glafs feet of infu- lating ftools in general, fhould be covered with varnifh, or rather with fealing-wax, otherwife they infulate very im- perfeftly, on account of the moifture, that they attraft from the air, in damp weather.
of
158 A COMPLETE TREATISE
of leather, the chain then falling upon the table, renders the rubber uninfulated.
Fig. 2 reprefents the prime Condu£tor AB belonging to this machine. This is of hollow brafs, and is fupported by two glafs pillars varnifhed, that by two brafs fockets are fixed in the board C C. This Conduftor receives the ele6lric fluid through the points of the coUeftor L, which are fet at about half an inch diftance from the iurface of the cylinder of the machine.
If the handle E fig. i of the wheel, be turned (and on account of the rubber it fhould be turned always in the direction of the letters a b c) this machine, ftanding in the fituation, that is reprefented in the figure, will give pofitive Electricity, /. e. the prime Condu6lor will be eled:rified pofitively, or overcharged with ele6lric fluid ; for by the a6lion of rubbing, the cylinder pumps as it were the fluid from the rubber, and every other body properly conne6ted with it, and gives it to the prime Condu6tor, But if a negative Electricity is required, then, the chain muft be removed from the rubber I and
OF ELECTRICITY. 159
^nd hung to the prime Gonduftor ; for in this cafe the Eledricity of the prime Con- dudor will be communicated to the ground-j and the rubber remaining infulated, will ap- pear ftrongly negative. Another Coiidudor equal to the Conductor A B fig. 2. may be ponnedted with the infulated rubber, and then, the operator may obtain as ftrong ne- gative Eledricity from this, as he can pofi*^ tive from the Condu6lor A B fig. 2^
CRAP-
^^..
s
160 A COMPLETE TREATISE
CHAP. III.
T^he f articular Defcription of fome other ne-^ cejfary Parts of the electrical Apparatus.
FIG 4. rcgrefents a Hand fupporting the eledrometers D D C C. B is the bafis of it made of common wood. A is a pillar of wax, glafs, or baked wood* To the top of the pillar, if it be of wax or glafs, a circular piece of wood is fixed, but if the pillar be of baked wood, that may conftitute the whole. From this circular piece of wood proceed four arms of glafs, or baked wood, fufpending at their ends, four ele6lrometers, two of which D D are filk threads about eight inches long, fufpend- ing each a fmall downy feather at its end. The other two electrometers C C are thofe with very fmall balls of cork, or of the pith of elder, and they are conftruded in the following manner, a b is 2l flick of glafs about fix inches long, covered with fealing- wax, and fliaped at top in a ring : from the lower extremity of this Hick of glafs pro- ceed
OF ELECTRICITY. i6i
ceed two fine linen threads "^ c c about five inches long, each fufpending a cork, or pith ball d about one-eight of an inch in diameter. When this eledrometer is not eledlrified^ the threads c c hang parallel to each other, and the cork balls are in contadt; but when ele6lrified, they repel one another, as repre- fented in the figure. The glafs ftick a b ferves for an infulating handle, by which the ele6lrometer may be fupported, when it is ufed without the ftand A B.
Another fpecies of the above ele(^rometef is reprefented in fig sd, which confifts of a linen thread, having at each end a fmall cork ball. This ele6lrometer is fufpended by the middle of the thread on any Condu6lor proper* for the purpofe, and ferves to Ihew the kind^ and quantity of its Eledricity*
Fig 7th. reprefents Mn Henly\s qua- drant eledrometer fixed upon a fmall ftand, from which it may be occafionally feparated and fixed upon the prime Conductor, or ia
* Thefe threads fliould be wetted in a weak folution of fait.
M any
i62 A COMPLETE TREATISE
any other place at pleafure. This ele6lro- meter confifts of a perpendicular ftem form- ed at the top like a ball, and furnlfhed at its lower end with a brafs ferrule, by which it may be fixed in one of the holes of the prime Condu6lor, or in its proper fland, as occafion requires. To the upper part of the ftem, or pillar, a graduated ivory femicircle is fixed, about the middle of which is a brafs arm, which contains a pin, or the fmall axis of the index. The index confifts of a very flender ftick, which reaches from the center of the graduated femicircle to the brafs ferrule, and at its lower extremity^ is faftened, a fmall cork ball, nicely turned in a lathe.
The propereft wood, for the purpofe of making the pillar and index of this ele6lro- meter, is box, and this pillar and index fhould be well rounded, and made as fmooth as poflible. When this ele6lrometer is not eleftrified, the index hangs parallel to the pillar, as in fig. 7 ; but when it is eledlri- fied, the index recedes more or lefs, accord- ing to the quantity of Eledricity, from the
ftem;
OF ELECTRICITY. 163
ftem ; as reprefented on the prime Gon- dudor E fig. 24
The main of Mn Lane's dlfcharging Elec* trometer, confifts in a brafs ball about one inch and a half in diameter,; fcrewed to a brafs graduated rodi and adapted to a proper frame, fo that it may be fet at any required diftance from the pririie Condudlor, or the knob of an eledtric jaf i The principal ufe of this ele£trometer is to let a jar difcharge by itfelf through any proper circuit, without ufing any difcharging-rod, or removing any part of the apparatus ; and to give fhocks nearly of the fame ftrength. Suppofe for inftance, that the above-mentioned brafs ball be fet at half an inch diftance from the prime Conductor, and that a coated jar be fituated fo as to touch the prime Condu£tor with its knob, and to have its outfide coating com- municating with the above-mentioned brafs balL Now it is evident that the circuit, from the outfide to the infide of the jar, is inter- rupted only between the prime Conductor and the brafs ball, which lie half an inch afunder j therefore when the jar is charging, and th^ charge is become fo high as to ftrike through
M 2 half
i64 A COMPLETE TREATISE
tialf an inch of air, the jar will difcharge itfelf, and by keeping the brafs ball at the fame diftance from the prime Conductor, and charging the jar fucceffively, the fhocks will be of the fame flrength.
This ele(3:rom€ter is, however, fubject to a great inconvenience, which is, that the fur- face of the brafs ball is often deprived of its fmoothnefs by the force of the explofion, in which cafe it becomes unfit for ufe. The principal ufe for which this ele6lrometer is intended, /. e. to give fhocks of the fame ftrength, may be more elegantly obtained by the above-defcribed quadrant eleftrometer, which fufFers no damage by the difcharges ; '^hence, I think, that a delineation, and ^ more particular defer ipt ion of the difcharging elec- trometer is unnecefTary.
Fig. 5th reprefents Mr. Henly's univer- fal difcharger, which is of a very extenfive ufe, and is compofed of the following parts, A is a flat board fifteen inches long, four inches broad, and one thick, or thereabous, which forms the bafis of the inflrument^ B B are two glafs pillars cemented io two boles upon
the
OF ELECTRICITY. 165
the board A, and furnifhed at their top witli brafs caps, each of which has a turning joint, and fupports a fpring tube, through which, the wire D C Aides : each of thefe caps is compofed of three pieces of brafs, coniie<fted fo,that the wire DC,befides its Aiding through the focket, has two other motions, viz. an horizontal and a vertical one. Each of the wires DC, DC is furnifhed with an open ring at one end, and at the other end has 'a brafs ball D, which, by a Aiort fpring focket, is Aipt upon its pointed extremity, and it may be removed from it at pleafure. E is a ftrong circular piece of wood five inches in di- ameter, having, on its furface, a Aip of ivory inlaid, and furniflied with a fl:rong cylindri- cal foot, which fits the cavity of the focket F, which is faftened in the middle of the bottom board, and has a fcrew G, which ferves to fatten the foot of the circular board E at any required height. H is a fmall prefs belonging to this inftrument; it confifts of two oblong pieces of board, which may be preATed againft each other by means of two fcrews aa : the lower of thefe boards has a cylin- drical foot equal to the foot of the circular board E. When this prefs is to be ufed, it is
M 3 fixed
|66 A COMPLETE TREATISE
fixed Into the focket F, in the place of the circular board E, which muft, iji that cafe, be removed.
Fig. nth is an eledric jar coated with tin- foil on the infide and outfide, within three inches of the top of the cylindrical part of the glafs, having a wire with a round brafs knob A at its extremity. Thi$ wire pafles through the cork * D, that flops the mouth of the jar, and at its lower end, is bended fo as to touch the infide coating in feveral places.
Fig* I cth reprefents a battery compofed of fixteen jars coated in the infide and outfide with tin-foil, which all together contain about twelve feet of coated glafs. About the middle of each of thefe jars is a cork that fufiains a wire, which at the top is faftened round, or foldered to the wire E knobed at each end, which conne(3:s the infide coatings of four jars J and by the wires F F F the jnfidp coat-
* When corks are ufed to flop ejedric jars, they (hould be made very dry, and clipped in melted bees- wax or varniflied,
ings
OF ELECTRICITY. 167
ines of all the fixteen jars are conne(3:ed to- gether. Each of the wires F has a ring at one end, through which, one of the wires E pafles, and the other end has a brafs knob. If the whole force of the battery is not required, one, two or three rows of jars may be ufed at pleafure; for as each of the wires F F F is moveable round the wire E, which paiTes through its ring, and refts upon the next, wire E, it may be eafily removed from that, and turned upon the contrary wire E ; and thus the communication between one row of jars and another may be difcontinued at plea- fure. See the figure.
The fquare box that contains thefe jars is of wood lined at the bottom with flieet-lead or tin, and has two handles on two oppofite fides, by which it may be eafily removed. In one fide of the box is a hole, through which, an iron hook B pafles, which com- municates with the metallic lining of the box, and confequently with the outfide coating of all the jars. To this hook is faftened a wire, the other end of which is connected with the difcharging rod.
M 4 The
|68 A COMPLETE TREATIS.E
The difcharglng rod confifts of a glafs handle A, and two curved wires B B, which move by a joint C, fixed to the brafs cap of the glafs handle A. The wires B B are pointed, and the points enter the knobs DD, to v/hich they are fcrewed, and may be un- fcrewed from them at pleafure. By this con- ftru£tion we have the opportunity of ufing the balls or the points, as occafion requires ; and as the wires are moveable by the joint C, they may be adapted to fmaller or larger jars at pleafure.
The battery, reprefented in the plate, Is a fmall one .in comparifon to thofe now fre- quently ufed, and much too weak for the purpofe of fome experiments, hereafter to be defcribed. But I thought it fufficient to give an idea of its conftruftion ; and, when a large battery is to be conftru£led, I would recom- mend rather to make two, three, or more fmall ones as reprefented in the plate, than 4 fingle large battery, which is heavy, and, on feveral accounts, inconvenient. The force of feveral fmall batteries may be eafily united by a wire or a chain, and thus they may be
made
OF ELECTRICITY. 169
made to adl in every refped like a large
one.
F in fig. 2. is a circular brafs plate hung on the prime Conductor by a chain, and rett- ing in an horizontal pofition. Underneath this, there is another plate P parallel, and equal to the former (but it would be better if it was a little larger), which is fupported by a fland H of brafs, having alfo a foket to receive the foot of the plate, and a fcrew G to fix it at diiferent diftances.
D in fig. 2. is a fly made of fmall brafs wires fixed in a cap of brafs alfo, which is to be put upon the pointed wire K, that h fcrewed to the prime Conductor, upon w^hich it muft fl:and in equiUbrio, like the needle of a compafs. The other ends a^ b^ r, d of the wires are pointed and bent all one way*
N. B. whenever hereafter I mention the prime Condudor, I mean the prime Conduc- tor naked, that is, without the parallel brafs plates F P, without the fly D and its Sup- porting pin K, without the eledrometers E, and even without the knobed rod I B, which
is
170 A COMPLETE TREATISE
is fcrcwed to it occafionally ; except the con- trary is exprelTed.
It is highly requifite for an Eledrician to have by him feveral infulating ftools, or ftands, they being very neceflary for feveral experiments. The beft materials to conftrudt thefe are glafs covered with fealing*wax, and baked wood *• A large ftool, proper to infu- late a chair upon, or two, three perfons ftandlng, may be made with a ftrong board, about two feet and a half fquare, and may be fupported by four feet of glafs, or baked wood, about eight inches long. But fmall ftands are better made with one foot or pil- lar, and all of baked wood or glafs, without any condu6ting fubftance in their conftruc- tion. Drinking-glafles, either varnifhed, or in part covered with fealing-wax, anfwer this purpofe very well.
* The wood (hould be baked very well, even till It be- comes quite brown, it then being in the beft ftate fot infulation ; and to make it ftill better, i, e. to defend it from mofture, it may be (lightly varniftied as foon as it comes out of the oven, or elfe boiled in linfeed oil ; but in this cafe, after boiling, it (hould be made hot again, and then it is fit for ufc.
CHAP,
O F E L E e ' |
Y. |
173 |
C H A |
< |
«• the he |
PraBical Rules concer: |
^^ |
|
tr teal Apparatus y ai |
||
periments. |
LJ.x\^ . w
IT often happens l are at a lofs to affign experiments do not fucceed with them as defcribed in the Treatifes on Eledricity. Sometimes they are in pofleffion of very good inftruments, but, by reafon of fome circum- ftance or other, unattended to, they are quite ufelefs in their hands. This indeed can be remedied by nothing but practice, and it is by long life, that the Eledrician, as well as the Practitioner in any art or fcience, be- comes fo good an Operator, as to ufe his inftruments to the beft advantage. A few rules are however very neceflary to guide him in his operations ; and although thefe alone are infufficient to make a perfon a complete practical Electrician, yet, when accompanied with the actual management of the apparatus, they facilitate the ufe of it, and render the performance of the experiments more accu- rate and expeditious*
The
J70 A Complete treatise
is fcr
tr^The firft thing that the young ElciflTician {hoiild obierve, is, the prel'ervation, and care, of his inftruments. The eleiil:rical machine, the coated jars, and in ihort every part of the cleOrical apparatus, fhould be kept clean, and as free as poflible from dull, and moifture.
When the weather is clear, and the air
dry, efpecially in clear and froftv wenther,
the elei^ical machine will always worK: well.
But when the weather is very hot, the
electrical machine is not lb pov, erful : nor
in damp weather, except it be brought
into a warm room ; and the cylinder, the
ftands, the jars, &c. be made thoroughly dry.
Before the machine be ufed, the cylinder fhould be tirtl wiped very clean with a foft hnen cloth, that is dry, dean, and warm ; and afterwards with a clean hot flannel, or an old filk handkerchief; this done, if the winch be turned, when the prime Conductor, and other inftruments, are removed from the elc<i!brical machine, and the knuckle be held at a little diftance from the furface of the 2, cylinder.
OF ELECTRICITY. 173
cylinder, it will be foon perceived that the eledric fluid comes like a wind from the cylinder to the knuckle, and, if the motion be a little continued, fparks, and crackling will foon follow. This indicates that the machine is in good order, and the Electrician may proceed to perform his experiments. But, if, when the winch is turned for fome time, no wind is felt upon the knuckle, then the fault is, very likely, in the rubber, and to remedy that, ufe the following diredions : By unfcrewing the fcrews on the back of the rubber, remove it from its glafs pillar, and keep it a little near the fire, fo that its filk part may by dried ; take now a dry piece of mutton fuet, or a little tallow from a candle, and juft pafs it over the leather of the rubber, then fpread a fmall quantity of the above-defcribed amalgam over it, and force it as much as poffible into the leather. This done, replace the rubber upon the glafs pillar ; let the glafs cylinder be wiped once more, and then the machine is fit for ufe.
Sometimes the machine will not work well becaufe the rubber is not fufficiently fupplied with electric fluid ; which happens
when
174 A COMPLETE TREATISE
when the table, upon whieh the machine ftands, and to which the chain of the rubber is conneded, is very dry, and confequently in a bad conducing ftate. Even the floor and the walls of the room are, in very dry weather, bad Conductors, and they cannot fup- ply the rubber fufficiently. In this cafe the beft expedient is, to connect the chain of the rubber, by means of a long wire, with fome moift ground, a piece of water, or with the iron work of the water-pump ; by which means the rubber will be fupplied with as much eledric fluid as is required.
When a fufEcient quantity of amalgam has been accumulated upon the leather of the rubber, and the machine does not work very well, then, inftead of putting more amalgam, it will be fufficient to take tlie rubber off, and to fcrape a little, that, which is already upon the leather.
It will be often obferved, that, the cylinder^ after being ufed fome time, contracts fome black fpots, occafioned by the amalgam, or fome foulnefs of the rubber, which grow continually larger, and greatly obftrud: its I eledric
OF ELECTRICITY; 175
cledric power. Thefe fpots muft be care- fully taken off, and the cylinder muft be frequently wiped in order to prevent its con- trading them.
In charging eledric jars in general, it muft be obferved, that not every machine will charge them equally high. That ma- chine, whofe ele(9;ric power is the ftrongeft, will always charge the jars higheft. If the coated jars, before they are ufed, be made a little warm, they will receive, and hold the charge the better.
If feveral jars are connected together, among which there is one, that is apt to difcharge itfelf very foon, then the other jars will alfo foon be difcharged with that ; although they may be capable of holding a very great charge by themfelves. When eledlric jars are to be difcharged, the Elec- trician muft be cautious left, by fome cir- cumftance not adverted to, the fhock fliould pafs through any part of his body; for an unexpe(^ed fliock, though not , very ftrong, may occafion feveral difagreeable accidents.
In
176 A COMPLETE TREATI SE
In making the difcharge, care muft be taken that the difcharging rod be not placed on the thinneft part of the glafs, for that may caufe the burfting of the jar. /
When large batteries are difcharged, jars will be often found broken in it, which burft at the time of the difcharge. To remedjr this inconvenience Mr. Nairne fays he has found a very effectual method, which is, never to difcharge the battery through a good Condu6tor, except the circuit be at leaft five feet long. Mr. Nairne fays that, ever fince he made ufe of this precaution, he has difcharged a very large battery near a hundred times without ever breaking a fmgle jar, whereas before he was continually break* ing them. But here it muft be confidered that the length of the pircuit weakens the force of the fhock proportionably ; the higheft degree of which is in many experi-' ments required.
It is advifeable when a jar, and efpeclally a battery has been difcharged, not to tpuch its wires with the hand, before the dif^ charging rod be applied to its fides a fecond.
OF ELECTRICITY. 177
and even a third time ; as there generally remains a refiduum of the charge^, which is fometimes very confiderable.
When any experiment is to be performed, which requires but a fmall part of the apparatus, the remaining part of it fhould be placed at a diftance from the machine, the prime Conductor, and even from the table, if that is not very large. Candles, particularly, fhould be placed at a confiderable diftance from the prime Condudlor, for the effluvia of their flames carry off much of the eledric fluid.
Laftly the young Eledrician fhould be cautioned not to depend on firft appearances in Electricity. A new phenomenon may juflly excite his curiofity : it is laudable to remark it, and to purfue the hint ; but at the fame time even the doubtful affertion of
* This refiduum is occafioned by the Electricity, that, when thejar is charging, fpreads itfelf over the uncoated part of the glafs near the coating, which will not be difcharged at firft, but gradually returns to the coating after the firft difcharge,
N a nevr
178 ACOMPLETE TREATISE
a new fa£t fhould never be made, till after a number of fimilar and concurring experi- ments* Ele6lricity is a fcience that often deceives the fenfes, and the rtioft experienced Electrician frequently finds himfelf miftaken in things, which perhaps he may have before confidered as the moft certain.
CHAP-
OF ELECTRICITY. 179
CHAP. V.
Experiments concernmg eleSlric AttraSiion^ and
Repuljion.
Experiment I.
*
The eleSirified Cork ball Ele£tro meter.
WHEN the ele6lrical machine is put in order, and the prime Conductor is fet fo, that the points of the colledor are about half an inch from the furface of the cyhnder, fix at the end of the prime Con- ductor the knobed rod I B fig. 2. and hang on it the electrometer with the cork balls fig. 3. The balls will now touch one ano- ther, the threads hanging perpendicularly, and parallel to each other. But if the cy- linder of the machine be whirled by turning the winch E, then the cork balls will repel one another, and more, or lefs, according as the Electricity is more, or lefs power- ful.
Na In
l8© A COMPLETE TREATISE
In this experiment the glafs cylinder ex« trading the eledric fluid from the rubber, jhrow8 it upon the pointed wires of the coj- ledlor, and in confequence upon the prime Condudor, and the eledrometer ; which are all connedled together : and as bodies over- charged with eledlric fluid will always re- pel qach other, fo the cork balls mufl fepel each other.
If the eledrometer be hung to a prime Gondu£lor negatively ele6lrified, /• e. con^ neded with the infulated rubber of the ma- chine, the cork balls will alfo repel each other ; for bodies, undercharged, will repel each other, as well as bodie? oyercharged w^tli eledric fluid.
If, in this fl:ate of repulfion^ the prime Conduftor is touched with fome condu6ting fubftance not infulated, the cork balls will immediately come together; for the elev^triq fluid fuperinduced upon the prijne Conduc-^ tor, and the eleftrometer communicating with it, will be carried away to the ground by that condu6Ving body; To that in this
cafe
OF ELECTklCITY, iSt
cafe the prime Condu6lof can never be over- charged, nor can it be Undercharged^ if con- nected with the rubber; for its deficiency of fliiid is fupplied through that condu6ling body, with which it has been touched. Biit if inftead of the cotidudfcing fubftance, the prime Coridudtor is touched with aii eledtric, ^s for iriftance a ftick of fealiiig-wax, k piece of glafs, &C. theii the bofk balls will continue to repel each other; becaiife thfi eledric fluid caiinot be coridudted throiigfi that eledlric ; herice we have an eafy me- thod of determining what bodies ate Con- dudtdrs, and what electrics.*
This eledrical tepumori li alfb fli^wn by the quadrant eledtrometef, v^ith a largd downy feather; or the like ; for if thefe b6 Connected \^ith the prime Condu6tor, and the winch be turned, the electrometer will raife its index, and the feather by the diver- gency of its down, will appear fwelled in k beautiful mahtiero
* This method in grofs will do very well ; but wheti the conducting power of fluids or other like fcodies, and the degree of that power is to be afcertainei, then re- tourfe muft be had to other means more nice, and accvi- )fate.
N 3 Ex-
182 A COMPLETE TREATISE
Experiment II.
AttraSlton and Repuljion of light Bodies.
Conned with the prime Condudor the two parallel brafs plates F, P, as reprefented in fig. 2. at about three inches diftance from one another, and upon the lower plate put any kind of light bodies, as bran, bits of paper, bits of leaf-gold, &c. then work the machine, and the light bodies will foon move between the two plates, leaping alternately from one to the other with great velocity. If, inftead of bran or irregular pieces of other matter, fmall figures of men or other things cut in paper, and painted, be put upon the plate, they will generally move in an ered: pofition, but will fometimes leap one upon another, or exhibit different pof- tures, fo as to afford a pleafing fpedtacle to an obferving company.
In this experiment both the attradion, and repulfion of Eledrlcity are obferved at the fame time : for when the upper plate F> which communicates with the prime
Con-
OF ELECTRICITY. 183
Condudor, is eledrlfied, the fmall bodies placed upon the lower plate, together with that plate, by being within the fphere of a6lion of the electrified upper plate, become adually pofFefled of a contrary Eledricity, leaving their proper quantity of fluid in the lower plate, or the other conducing bodies, that communicate with it. But bodies dif- ferently eledlrified attra6t each other ; there- fore the plate F, attra6ts thofe light bodies. Now as foon as thefe bodies touch the plate F, they become inftantly poflefled of the. fame Ele6lricity with the plate, and will therefore be immediately repelled to the lower plate, which is actually electrified with the contrary Ele6tricity, and by touching the light bodies, affifts in repelling them again to the upper plate ; and thus the plates continue to a6l upon the light bodies alter- nately.
That the light bodies cannot be attracted by the upper plate, except they become firfl: poflTefTed of a contrary Ele6tricity, may be obferved as follows. Put the faid light bo- dies upon a clean, and dry pane of glafs ; then take off the brafs plate P, with its ftand
N.4 G,
1^4 A COMPLETE TREATISE
G, and in Its fiead put the pane of glafs^ holding it by one corner ; this done let the wheel of the machine be turned, and you will fee that the light bodies are not attrad- ed by the brafs plate F ; for in this cafe they have no opportunity of parting with their proper quantity of fluid, and confequently can not acquire the contrary Ele6lricity* But if to the under fide of the pane of glafs, on which the light bodies are placed, a finger or any other conductor be prefented, then, the light bodies will be inftantly at- tra6:ed by the plate F, and will leap be-- tween the glafs and plate, in the fame man- ner as between the two plates ; for thefe bodies now depofit their fluid upon the up- per furface of the glafs plate, whilfl: the un- der furface depofits its fluid upon the finger, or other condudlor, that has been brought near it*. If this experiment be continued the glafs will foon be charged.
* If the above experiment be made with a prime Con- duiElor negatively eletflrified, the effedl will be the fame, only the Electricities of the plates are reverfed ; /. e. the upper plate is electrified negatively, and the under plate, by being in the atmofphere of the upper one, is pofitively elec* trifled.
ExPE*
OF ELECTRICITY, 185
Experiment III.
^he Flying-feather^ or Shuttk-^cork.
The phenomena of eleftric attraction and repulfion may be reprefented alfo with a glafs tube, or a charged bottle, and fome of them in a manner more fatisfa6lory, than with the machine.
Take a glafs tube (whether fmooth, or rough, is not material), and after having rubbed it, let a fmall light feather be let out of your fingers at the diftance of about eight or nine inches from it. This feather will be immediately attraded by the tube, and will Hick very clofe to its furface for about two or three feconds, and fometimes longer ; after which time it will be repelled, and if the tube be kept under it, the fea- ther will continue floating in the air at a confiderable diftance from the tube, without coming near it again, except it firft touches fome conducting fubftance ; and if you manage the tube dexteroufly you may drive
the
i86 A COMPLETE TREATISE
the feather through the air of a room at your pleafure.
The reafon of this experiment is obvious ; for when the feather is eledrified, it cannot approach the tube again, except it firft touches fome condudling body, becaufe it cannot part with its Electricity when float-^ ing in the air, and therefore cannot acquire a contrary Electricity : confequently it muft remain in a Hate incapable of being again attracted by the excited tube.
If it be afked, why, when the feather is at firft attracted by the tube, it fticks for fo confiderable a time to its furface before it is repelled, the anfwer is, that the feather being an eleCtric, requireth fome time before it acquires any confiderable quantity of Elec- tricity.
There is a remarkable circurnftance attend- ing this experiment, which is, that if the feather be kept at a diftance from the tube by the force of eledric repulfion, it al- ways prefents the fame part towards the tube : — You may move the excited tube 4 , about
OF ELECTRICITY. 187
about the feather very fwiftly, and yet the fame fide of the feather will always be pre- fented to the tube. The reafon of this phe- nomenon is, that the equilibrium of the ele6lric fluid in the parts of the feather, being once difturbed, cannot eafily be reflored ; be- caufe the feather is an eledtric, or at leaft a very bad Condudtor. When the feather has acquired a quantity of Eledtricity from the tube, it is plain that by the adlion of the excited tube, that fuperinduced eledricity will be in the greateft part forced on that fide of the feather, which happens to be at firfl the farthefl from the tube ; hence that part will always afterward be repelled the fartheft.
This experiment may be agreeably varied in the following manner : A perfon may hold in his hand an excited tube of fmooth glafs, and another perfon may hold an ex- cited rough glafs tube, a flick of fealing- wax, or in fhort another ele£lric negatively eledrified, at about one foot and a half diftance from the fmooth glafs tube : a fea- ther now may be let go between thefe two differently excited eledtrics, and it will leap
alter-
i88 A COMPLETE TREATI9E
alternately from one elcdric to the other ; and the two perfons will feem to drive a Ihut- tie-cork from one to the other, by the force of Eledlricity*
Experiment IV.
^he fmall tnfuldted Body.
Tie a fmall body^ as for inftance a light piece of cork, to a filk thread about eight inches long, and holding the thread by its end, let the fmall body hang at the diftance of about eight inches from the fide of the prime Conductor ele6lrified. This fmall body, if the eleftrification of the Condudlor is not ftrong, will not be attracted ; for, being infulated, it cannot^ by depofiting its fluid upon, or receiving it from another bo*" dy (when the prime Conductor is eledlrified negatively), become contrarily electrified. But if a finger or any conducing fubllance be prefented to the fide of the fmall body which is fartheft from the prime Condudlor, then the fmall body will immediately move toward the prime Coiiduftorj for it lias* I depo-
OF ELECTRICITY. i
depofited its own fluid upon, or acquired fome (in cafe the conductor is negatively eledrified) from the body prefented to it; and when this body has touched the prime ConduiSor it will be inftantly repelled from it, on account of the repulfion exifting be- tween bodies poflefled of t|ie fame kind qf Eledricity,
Indeed, if this Infulated body be very near to the prime Condu<5tor, or the prime Con- ductor ftrongly eledrified, then the fmall body will be attraded without prefenting to it ar^y conducting fubftance ; but in this cafe its natural quantity of electric fluid will be either repelled into the contiguous air, or crouded on the part of the body, which is fartheft from the prime Conductor, if the Conductor is eleCtrified pojitively ; but if it is electrified negatively ^ then the addi- tional quantity of fluid, neceflary to render the fmall body overcharged, will be acquired from the air, or the natural fluid belong- ing to that body will be all crouded on that fide of it, which is neareft to the prime Con-^ ^uCtor.
If
190 A COMPLETE TREATISE
If this fmall body, inftead of the filk, be fufpended by a linen thread it will be at- tracted at a much greater diftance, than in the other cafe ; for now the eledric fluid will eafily be conduced by the thread, paffing upwards, or downwards according as the prime Conductor is eledlrified, W2;. ne- gatively, or pofitively.
Experiment V. :,
The eleSlric Well.
Place upon an eleftric flool a metal quart mug, or fome other conducing body nearly of the fame form and dimenfion ; then tie a fhort cork ball eledrometer of the kind reprefented fig. 3,* at the end of a filk thread proceeding from the ceiling of the room, or from any other proper fupport, fo that the eledrometer may be fufpended with- in the mug, and no part of it may be above the mouth j this done eledrify the mug by
* Inftead of the eleilrometer there may be ufed any Other kind of fmall conducing body ^ but that feems beft adapted to fuch experiments,
giving
OF ELECTRICITY, 191
giving it a fpark with an excited ele6lric or otherwife, and you will fee that the eleftro- meter, whilft it remains in that infulated fituation, even if it be made to touch the fides of the mug, is not attracted by it, nor does it acquire any Eledricity ; but, if whilft it ftands fufpended within the mug, a Conductor, ftanding out of the mug, be made to communicate with, or only pre- fented to, it, then, the eledlrometer acquires an Ele6lricity contrary to that of the mug, and a quantity of it, which is proportionable to the body, with which it has been made to communicate ; and it is then immediately attracted by the mug.
The reafon why in this experiment the eledtrometer contracls no Electricity whilft fufpended intirely within the cavity of the mug, is, becaufe the Eledricity of the mug ads upon the eledrometer on all fides, and this has no opportunity of parting with its fluid, when the mug is eledrified pofitively ; nor of receiving any, when the mug is eledrified ^ negatively. But, as foon as any Conductor communicates with it, the elec- trometer becomes immediately pofTefTed of
the
192 A COMPLETE TREATISE
the Electricity contrary to that of the mug ; for if the mug be eledrified pofitively, the fluid belonging to the eleftrometer will be repelled to that body, which communicates with it ; and which, being out of the mug, cannot be afFeded by its Eledricity ; and if the mug is eledrified negatively, it will at- tradl the fluid of the eledlrometer, which actually receives an additional quantity of it from that conducting body, with which it communicates. The eledtrometer therefore, becoming always poiTefled of a contrary Elec- tricity, muft aecelTarily be attracted,
If, by raifmg the filk thread a little, part of the electrometer, /. e. of its linen threads, are lifted juft above the mouth of the mug, the balls will be immediately attracted ; for then, by the aCtion of the EleCtricity of the mug, it will acquire a contrary EleCtricity by giving to, or receiving the electric fluid from, the air above the cavity of the mug.
It has been fuppofed by fome, that the electrometer in the above experiment (or any other fmall infulated body), hanging in the cavity of an eleCtrified velTel, or the
like;,
Of ELECTRICITY.
like, i5 not attbfled by the fides of the veffel, becaufe the attradioii of Ele6lricity, beiiig aS the fquares of the diftances in- verfely^ cannot afFedt the eledrometer one way riiofe than another ; it being demon- ftrable that, if td every point of a fpherical concave furface;, eqlial centripetal forces are dlredtedj decreafing aS the fquares of the diftances from thofe points, a fmall body fituated any where within that furface, would remain therei without being attracted one Way more than another*.
But to this it may be replied, that, the derhdnftratioii of the above-mentioned pro- pofition, if it is applicable to fpherical, or cyliridrical concave furfaces, cannot, how- ever, be applied to every kind of irregular Cavities, with which (if they exceed not a certain fize) the kbove experiment fucceeds ^s wellj as \^^ith the cjrlindrical cavity of the mug.
Iri fhort, in this experiment, when the mug is eledrified pofitively, it is fuppofed^
* Newton's Principia book t prop. LXX.
O L That
194 A COMPLETE TREATISE
L That the fuperinduced fluidv taking place upon the external furface> occafions the con- tiguous air to depofit its fluid upon a fub- fequent quantity o£ air,: and this overcharged air occaRons a contiguous circle, 'or quantity of air, to depofit its fluid upori its fub- fequent or next adjacent circle, and fo on. 11. That none of the fuperinduced fluid can exift upon the internal furface of the mug, and therefore, infulated bodies intirely fuf- pended therein, can acquire ijo ele£tricity, becaufe the internal/ air has no opportunity of parting with its own fluid, except a fmall quantity about the mouth of the mug, where, accordingly, a little Eledricity is, ob- fervable. When -the mug is eledtrified, ne- gatively, then it,is fuppofed I, That the de- ficiency of fluid. in the mug is only on its extcrjaal furface; for the air, C'Qjitiguous to this furfiice, by acquiring an additional quan- tity of eledric fluid from the next ftratum of air, may become ele6lrified pofitively. II. That the internal furface of the mug is not undercharged, becaufe its contiguous air, being furrounded by the mue^, cannot be- come overcharged, by acquiring an addition- al quantity of fluid, except a frnall quantity 4.* , . towards
OF E' L E C T R I C I T Y. 195
towards the mouth of the mug, where, ac- cordingly, a little Electricity is obfervable.
Experiment VL
To dijiingutjh the ^lalify of Elecfricity In elec^
trijied Bodies.
Before we proceed further, it is neceifary, that we {hould defcribe fome pra6lical me- thod of diftinguifhing the. quality of the Eledtricity in an electrified body, which is abfolutely neceflary for the right perform- ance of the enfuing experiments. To do this, different methods may be followed, which however are all founded, either upon the eledric attraClion, and repuliion, or upon the different appearances of the elec- tric light. To find out the quality of Elec- tricity by the different appearances of its light, is a very convenient, and fure me- thod ; but the phenomena of attradion and repulfion, afford one much more general, and eafy ; for fometimes the quantity of Ele6lricity to be obfcrved is fo very fmall, that it will give no light, though it may be flill capable of attradling or repelling.
O 2 The
ig6 A COMPLETE TREATISE
The general method to prove whether the Eledricity of a body, eledrified either by excitation, or communication, is negative, or pofitive, is, to bring it pretty near to an elciflrified eledrometer D or C fig. 4, and oblerve whelher the body attracts or repels it ; for if the ele(flrometer is electrified po- fitivcly, and the eleftrified body repels it, then you may conclude that the body is alfo eledrified pofitively ; becaufe bodies, poflefled of the fame kind of Ele6lricity, repel each other ; but if the body prefented attradts the Eleclrometer, then it muft be eleftrified negatively, becaufe there is no electric attradion between bodies, unlefs they are differently eledlrified ; and as the eledlrometer is known to be electrified pofi- tively, the body is confequently eleClrified negatively^
This may be alfo done by eledrifying the electrometer negatively ; but then the efi'eCts are juft the contrary, /. e» the eleCtrified body, if negative, will repel the eleClrometer, and if pofitive, will attraCt it.
In
OF ELECTRICITY.
197
In this experiment, however, it miift be obferved, that, if the Eledtricity of the elec- trified body is much ftronger, than that of the ele6lrom.eter, or the Ele6tricity of the latter flronger, than that of the former, and the eleftrified body be brought very near the eledrometer, then, they wall attra6l one another, notwithftanding they are pofTe fled of the fame kind of Electricity. Suppofe,,for inllance, that one of the electrometers C is pofitively eleCtrified, fo that its cork balls may diverge about half an inch, and a glafs tube ftrongly excited be brought near it ; when this tube is a foot diftant, or more, the electrometer will be a little repelled by it ; but if the tube be brought nearer, the cork bails, that before diverged half an inch, will now converge till they are in contact, and appear, as they actually are, unelec- trified ; becaufe the adlion of the excited tube has repelled their fuperfluous fluid through the threads up to the remoteft part of the electrometer. If the tube be pre- fented ftill nearer, the balls will then be at- tracted by it, becaufe the ftronger EleClricity of the tube repels not only their fuperin-
O 3 duced>
'\
I
198 A COMPLETE TREATISE
duced, but alfo their natural quantity of fluid up the threads, &c. and therefore the balls, becoming negatively eledrified, , in\u(l neceflariiy be attra6led by the tube.
But Ihould a more precife methods than the abov^ be required to determine the qua- lity of the Electricity of an eleftrified body, the following may be ufed. Firft ele6lrify one of the eledrometers C, placed upon the ftand fig. 4, either politively, or negatively, at pleafure : touch it, for inftance, with an excited glafs tube, fo that its balls may re- pel, and ftand about two inches diftant from one another ; then touch the other eleftro- meter C with the eleftrified body, that you defire to examine, fo that it may be pof- feffed of the fame degree of Eleflricity : Laftly, take either of the two electrometers by the top of the glafs handle ^, difengage it from the arm of the ftand, and bring it near the other electrometer ; if then, the balls of one electrometer repel thofe of the other, you may conclude that they are pcf- fefled of the fame kind of EleCtricity ; but if they attract each other, you may con- clude that they were eleCtrifed with con- trary
OF ELECTRICITY. 199
trary Ele^lricities > arid as you know the Eledlricity of that electrometer, which was firft eledlrified, you will alfo know the Electricity of the other ele6lrometer, i. e. of the eledrified body, with which it was touched.
The above experiment may be alfo made with the fmgle-thread electrometers; for if they are brought near to one another,' when their feathers are electrified, they will, if poffefled of the fame EleCtricity, repel, or if pofleffed of contrary Electricities, attraCt each other.
Experiment VIL
The infulated metallic Rod.
Infulate in an horizontal pofition a me- tallic rod about two feet long, having blunt ends, and to one of its ends fufpend an Electrometer, like that reprefented fig. 3, then bring within three or four inches, diftance of its other end an excited glafs tube. On the approach of .the tube, the balls of the electrometer wiH open, and if
O 4 you
aco A GOMPLETfi TREATISE
you prefent towards th^m a body pofitively eledrified, you will perceive, that they di- verge with pofitiye Electricity. If the tube is removed, the balls come together again, and nQ Eleclricity remaips ix\ them, or in the metallic rod. But if w^hile the tube is near one end of the rod and the balls di- verge with pofitive Electricity, the other end of the rod, viz. that, ftom which the ekiSlrometer hangs be touched with fome conductor, the corlf balls will corne imme- diately together, and they will remain fo when the Conductor has been removed ;— • remove now the excited glafs tube, and tl^e balls will immediately diverge with nega- tive Eledlricify, which fhows that the rod remains undercharged, /. e, eledrified nega? lively.
The reafon of this experiment is, that the repelling power of the excited tube driving the fluid of one end of the rod to its other end, 7. e. to that, with which the eledlrometer is connected, renders this end eledrified pofi- tively; but in fa6l the lube cojnmunicates no Electricity to the rod. It only difturbs the equable diffufiQa of it§ fluid ; i^ cpnfg-
quence
pF ELECTRICITY. 201
guence of thi?, the eledrometer, hanging to the overcharged end of the rod, muft neceflarily appear to be dedrified pofitively; but when the tube is removed, then the eledrometer appears again uneledtrified : for the fluid, which had by the adion of the tube been driven to one end of the rod, flow retires to its former fituation, and leaves the rod with the eledrometer une- |ei6lrified.
In the fecond cafe, v/hen the balls of the eledrometer diverge with politive Eleflricity, if that end of the rod is touched with fome Condud;or, all its fuperfluoys fluid, which is no other, than that belonging to the op- pofite end of the rod, will be couimuni- cated to that body, with which the rod is touched, and therefore the eledroqieter re- mains uneledrified : but now in fad: the rod has loft fome of its natural quantity of fluid ; for if the end of it, that is fartheft from the Excited tube, remains in its natural ftate, the other end is undercharged ; confe- quently, when the tube is removed, the fmall quantity of fluid, that remains in the rod \viU diffufe itfelf uniformly through it ; but
this
202 A C 6'M P L E T E T R E A T I S E
this quantity of fluid is lefs than that, na- turally inherent in the- rod ; the rod will therefore remain undercharged, and hence the balls of the electrometer diverge with ne- gative Eledricity.
As this experiment is the bafis, or key, of feveral other, I fhall infifl on it a little longer, and to render its explanation more intelligible, and clear, I fhall make ufe of the following diagram,
A B.
Let the above-mentioned infulated rod be reprefented by the line A B. When this rod is in its natural ftate (in refpedt to Elec- tricity), then the ele6lric fluid belonging to it, is equally diffufed throughout the rod. But v;hen the excited tube is brought with- in three or four inches diftance of one of the ends, for infl:ance B, then the fluid, be- longing to that end, will be driven to the end A, which end therefore becomes over- charged, and the end B undercharged, yet the rod has no more eledric fluid now, than it had before; and when the tube is
re-
OF ELECTRICITY. 203
removed to fome diftance from the rod, the fuperfluous fluid, repelled to the end A, returns to its former place, /. e. to the end B, and the equilibrium in the rod is reftored* But if when the fluid in the rod is repelled to the end A, this end be touched, the fluid repelled thither will immediately be conducted away by the body, that touched it, and will leave the end A of the rod, in a natural ftate ; but at the fame time the end B, is un- dercharged ; therefore, when the tube is re- moved, part of the natural fluid, belonging to the end A, will go to the end B, and thus the whole rod will remain undercharged, /• e. negatively eledrified.
If the above experiment be made with an eledtric negatively electrified, for inftance a rod of fealing-wax, inftead of the excited glafs tube, then the apparent Eledlricities in the rod will be juft the reverfe of what they were before ; for in this cafe, that end of the rod, to which the eledlric has been prefented, willbe overcharged, and the oppofite end undercharged, which oppofite end, if touched in this ftate with fome conduding fubftance, will acquire fome of the eledric .fluid from
that
2C4 A COMPLETE TREATISE
that fubftance, and when, after that fubftance has been removed, the excited electric is alfo removed, the rod w^ll remain overcharged.
In making this experiment, care muft be taken that the end of the rod be very blunt, and that the electric be not very powerfully- excited, otherwife a fpark may pafs from this to the rod, which renders the experiment precarious.
Experiment VIIL
The two infulafed metallic Rods.
Take two rods of metal each about a foot long, furnifhed with knobs at both ends, and, either by filk lines, or by infulating ilools, infulate them, fo that they may ftand horizontally in one direction, and at about half an inch diftance from one another. To the middle of each of thefe rods hang an electrometer like that reprefented fig. 3. — This done, take an excited glafs tube and bring it to about three inches diftance from the knob of one of the rods ; on doing which the eledrometers of both rods will appear eledrified : keep the tube in that fitu^tion for I about
OF ELECTRICITY. 205
about two feconds, then remove it. The rods now will remain ele<9trified, as appears by the eledrometers, the firft, viz. that to which the excited tube had been prefented remaining negative, and the other pofitive.
The reafon of this phenomenon is, that when the tube was near the end of one of the rods, the adtion of its fluid, repelling the fluid of that rod, caufed it to pafs in a fpark to the other contiguous rod, on which account, when the tube was removed, the firft rod, having loft fome of its natural fluid, remained undercharged, and the other rod, acquiring the fluid loft by the former, became over- charged.
In this experiment if inftead of the glafs tube, an electric negatively excited be brought near the end of one rod, then that rod will be eledlrified pofitively, and the other negatively ; for the adion of this electric, producing juft the contrary tStdi of the glafs tube, inftead of repelling the fluid of the firft rod into the fecond, attracts that of the fecond into the firft.
In
2c6 A COMPLETE TREATISE
In this experiment, tiie ele£lric does not communicate any Ele&icity of its own ; but only difturbs the equilibrium between the fluid of the rods.
CHAP.
OF E L E C T R I C I T Y. 207
C H A P; VI.
Experime''4s. on. eleBric Light.
TH E following experiments reijuire to be made in the dark ; for although the eledric light in feveral circumflances may be feen in the day-light, yet its appearance in this manner is very confufed, and that t!ie Eledrician might form a better idea; of its different appearances, it is abfolutely neceffary to perform fuch experiments in a aa,rkened room. ^
Experiment L
i^he Star and Penal of eleSiric Light.
\¥hen the eledrical machine is^ in,- good, order, and the prime Condu6lor, is. iltiiated with the colled:or fufKciently near the glafs cylinder (which fituation I fhall call hereafter its proper place), turn the winch, and. you will fee a lucid ftar^ja^t each of the points of the colledor. This ftar is the conftant ap- pearance of the eledric fluid that is entering ^ EPl^t* At the fame time you wjll fee a ftrong light proceeding from the rubber, and^
fpreading
268 A eOkPLETE TREAtl SE
fpreading Itfelf over the furface of the cy- linder ; and if the excitation of the cylinder is very powerful, denfe ftreams of fire will proceed from the rubber, and darting round almofthalf the circumference of the cylinder, will reach the points of the colle<ftor *•,.
If the chain of the rubber is taken off, and a pointed body, as for inftance, the point of a needle or a pin, is prefented to the back of the rubber, at the diftance of about two inches^ a lucid pencil of rays will appear to proceed from the point prefented, and di- verge towards the rubber. This pencil is the conftant appearance of the eledric fluid ifluing from a point ; and in fa£t it noW comes out of the point, in order to fupply the rubber, which is conftantly exhaufted by the cylinder in motion.
If another pointed bod,y be prefented to the prime Conductor, it will appeal illuminated with a ftar j but if a pointed wire or other
* If the prime Conduftor is removed, the denfe ftreams of fire will go quite round the cylinder 3 reaching from one fide of the rubber to the other.
pointed
OF ELECTR I G I T Y. 209
pointed conducting body be connected > with the prime Condudor, it .will throw out a pencil of rays ; for the prime Condu6lor being overcharged, the fluid departing from it mufl, agreeably to theJaw,^ form. , a pencil on that point from which it flies ofl^, and a fl:ar, on that point, which it enters ''^.
From this experiment may be learned ^he method of diflinguifliing the quality of the Electricity of an eledrified tody, by t^e 'ap- pearance of the eledtric light ; for if a^neeotei fc or any other pointed body be prelented/iii
nq * It may be. afked, why the eledrlc fluid entering a^' point, caufeth the appearance of a ftar^^ and when going out of the point caufeth the appearance pf a brufli of rays.? In anfwer to this (jueftion, F. BEccAkiA fuppofes,* tWat the ftar is occafioned by the difficuhy, withrwliich *the ekcftric fluid is extricated from the air, which .is an eke* trie 5 fuppofe, forinftance, that a pointed wire is.prefent- ed to a body pofitively eleftrified, the electric fluid is firft from that body communicated to the air between it "and the wire, and then the wire muft extricate it from that air. The brufii, he fuppofes, to be occafioned by thq force, with which the eledtric fluid, going out of a point, runs through the contiguous air, to that which is more remote from it, /. e, ti^ dividing the contiguous air, and not by affixing itfelf to it,
P the
5iio A COMPLETE TREATISE
the dark tvlth the point towards a body ftrongly eledrified, it will appear illuminated with a ftar, when that body is eledrified pofitively, and with a pencil or brufh, when it is eledrified negatively.
Experiment IL
Drawing Sparks.
Let the prime Conductor be fituated in its proper place, and eledrify it by working the machine J then bring a metallic rod with a round knob at each end, or the knuckle of a finger, within a proper diftance of the prime Condudtor, and a fpark will be {^en between that, and the knuckle, or knobed wire. The longer, and ftronger fpark is drawn from that end of the prime Conduc- tor, which is fartheft from the cylinder, or rather from the end of the knobed rod I B> fixed at its end B, fig. 2. ; for the eledric fluid feems to acquire an impetus by going through a long Condudor, when eledlrified by a powerful machine *.
* Thereafon of this, I think, is, becaufe that end of the prime Conduftor is lefs influenced 'by the atmofphere of the excited cylinder.
This
OF £ L E G T R I C I T Y. ail
This fpaf k (which has the fame appearance whether drawn from a prime Gondudior po- fitively, or negatively eledrified) appears like a long line * of fire, reaching from the Con- dudlor to the oppofed body, and often (par- ticularly when the fpark is long, and differ- ent conducing fubftances are near the line of Its direction) it will have the appearance of being bended to fharp angles in different places, exactly refembling a ilafh of light- ning. Notwithflanding, however, this ex« tended appearance, which is imputed to the quick palTage of the luminous matter, the eledtric fluid, palling from one body to ano- ther in a fpark, is reafonably thought to pro- ceed in a feparate, and nearly globular body.
The dire£i:ion of the fpark often deceives the moft experienced Eleftrician^ it feeming fometimes to proceed from one place, and at other times under the fame circumftances to proceed from the oppofite. When the prime Condudor is electrified pofitively, the fpark
^ It often darts bruflies of light fide- ways in every direxftion.
P 2 rauft
%i2 A COMPLETE TREATISE
muft certainly proceed from it, and go to the body prefented ; and when the prime Con- duclor is eledrified negatively, the fpark muft proceed from the body prefented, and go to the Condudlor. This, however, we learn by reafoning from other experiments ; for the real direction of the fpark in the above experiment, is much more rapid in its motion, than to admit its form, much lefs its dired:ion to be perceived by our eyes.
Experiment III.
, The el/Brk Light, jiajhing between two
inetallic Plates.
Let two perfons, one ftanding upon an in- fulated ftool, and communicating with the prime Conductor, and another ftanding upon the floor, each hold in one of his hands a metal plate in fuch a manner, that the plates may ftand back to back in a parallel fitu- ation, and about two inches aftinder. Let the winch of the machine be turned, and you will fee the flaflies of light between the two plates fo denfe and frequent, that you may eafily diftinguifti any thing in the room. By this experiment the eleftric light is exhibited 4 in
OF ELECTRICITY, 213
in a very copious, and beautiful manner, and it bears a ftriking refemblance to lightning.
Experiment IV,
To Jire inflammable Spirits.
The power of the eledlric fpark to fet fire to inflammable fpirits, may be exhibited by feveral different methods, but more eafily thus : Hang to the prime Condudlor a fhort rod having a fmall knob at its end, then pour fome fpirits of wine, a little warmed, into a fpoon of metal * ; hold the fpoon by the handle, and place it in fuch manner, that the fmall knob on the rod, may be about one inch above the furface of the fpirits. In this fituation if, by turning the winch, a fpark be made to come from the knob, it will fet the fpirits on fire.
This experiment happens in the very fame manner whether the Conductor is eledrified
* The readied way to warm the fpirits for this experl- ment, is to fet it on fire with a candle when it is in the fpoon, and after it has burned for about two feconds, to blow it out with your breath, In this ftate it will be found very ready to take fire, even by a fmall fpark.
P 3 pofitively
214 A COMPLETE TREATISE
pofitively or negatively, /. e. whether the fpark be made to come from the Condudor, or from the fpoon ; it being only in confe- quence of the rapid motion of the fpark that - the fpirits ave kindled,
>
It will be perhaps fcarce necelT^ry to re- mark, that the more inflammable the fpirits are, the more proper they will be for this experiment, as a fmaller fpark will be fufE-j* cient to inflame them ; therefore rectified fpirit of wine is better than common proof fpirit, and aether better than either.
This experiment may be varied diff^erent ways, and may be rendered very agreeable to a company of fpedators ; a perfon, for inftance, ftanding upon an eleftric fl:ool, and communicating with the prime Gondudor, may hold the fpoon with the fpirits in his hand, and another perfon, ftanding upon the floor, may fet the fpirits on fire by bringing his finger within a fmall diftance of it. Inftead of his finger, he may fire the fpirits with a piece of ice, when the experi- ment will feem much more furprifing. If the fpoon is held by the perfon ftanding upon
the
O F E L E C T R I C I T Y. , 215
the floor, and the infulated perfon brings fome conducing fubftance over the furface of the fpirits, the experiment fucceeds as well.
ExPERIxMENT V^
Tihe artificial Bolonian Stone illuminated by the eleSiric Light.
The moll curious experiment to (hew the penetrability of the eledric light, is made with the real, or more eafily, with the artifi- cial Bolonian ftone, invented by the late Mr. J. Canton. This phofphorus is a calcareous fubftance generally ufed in the form of a powder, which has the property of abfbrb- ing light, when expofed to it, and after- wards to appear lucid when brought into the
dark *.
Take
* The method of making this phofphorus is as follows, ** Calcine fome common oyfter (hells" (if they are old, and half calcined by time, fuch as are commonly found upon the fea fliore, they are, as Mr. W. Canton obferves, fo much the better), " by keeping them in a good coal ** fire for half an hour ; let the pureft part of the calx be •* pulverized, and lifted ; mix with three parts of this •' powder one part of the flowers of fulphur ; let this
P 4 *' mixtura
2i6 A COMPLETE TREATISE
Take fome of this powder/ and, by means ^of fpirits of wine, or aether, Hick it all over the infide of a clear glafs phial, and flop it with a glafs ftopper, or a cork and fealing- wax. If this phial be kept in a darkned room (which for this experiment muft be very dark) it v^^ill give no light, but let two or three ftrong fparks be drawn from the prime Condudor, when the phial is kept at about two inches diflance from the fparks, fo that it may be expofed to that light, and this phial will receive that light, and after-:
*^ mixture be rammed into a crucible of about an inch **^ and. a halfin depth, till it be almoft full ; and let it be *' placed in the middle of the fire, where it muft be kept *' red-hot for one hour at leaft, and then fet it by to ^^ cool : when cold, turn it out of the crucible, and cut- ting or breaking it to pieces, fcrape off, upon trial, the brighteft parts ;, which, if good phofphorus, will be a white powder, and may be preferved by keeping it in a dry phial wiih a ground ftopple." If this phofphorys, whether in the phial or not, be kept in the dark, it will give no light, but if expofed to the light either of the day, or of any thing clfe, and after- wards brought into a dark place, it will then appear lucid for a confiderable time. For farther properties of thisi phofphorus, fee the. Phil. Tranf. Vol. LVIIL;
wards
OF ELECTRICI T Y, 21;
wards will appear illuminated for a confider-* able time.
This powder may be ftuck upon a board by means of the white of an egg, fo as to reprefent figures of- planets, letters, or any thing elfe at the pleafure of the operator, and thefe figures may be illuminated in the dark, in the fame manner as the above-defcribed phial.
A beautiful method to exprefs geometrical figures with the above phofphorus, is to bend fmall glafs tubes of about the tenth part of an inch diameter, in the fhape of the figure defired, and then fill them with the phofphorus powder. Thefe may be illu- minated in the manner defcribed, and they are not fo fubjed: to be fpoiled, as the figures reprefented upon the board frequently are*
The beft method of illuminating this phofphorus, and was that Mr. W. Canton generally ufed, is to difcharge a fmall eledric jar near it.
EXPERI-
ai8 A COMPLETE TREATISE
Experiment VI. The luminous ConduSfor.
Fig. 6. Plate I. reprefents a prime G)n- du£lor invented by Mr. Henly, which fhews clearly the direftion of the electric fluid pafling through it, from whence it is called the luminous ConduBor. The mid- dle part E F of this Condu£lor is a glafs tube about eighteen inches long, and three or four inches in diameter. To both ends of this tube the hollow brafs pieces F D, B E, are cemented air-tight, one of which has a point C, by which it receives the eleftric fluid, when fet near the excited cy- linder of the electrical machine, and the other has a knobed wire G, froni which a ftrong fpark may be drawn j and from each of the pieces F D, B E, a knobed wire pro- ceeds within the cavity of the glafs tube. The brafs piece F D, or B E, is compofed of two parts, /. e. a cap F cemented to the glafs tube, and having a hole with a valve, by which the cavity of the glafs tube may be exhaufted of air ; and the ball D, which
is
O F E L E C T R I C I T Y. 219
is fkrewed upon the cap F. The fupporters of this inftrument are two glafs pillars faftened in the bottom board H, like the prime Condudlor reprefented fig. 2. When the glafs tube of this Condudor is exhaufted of air by means of an air pump, and the brafs ball is fkrewed on, as reprefented in the figure, then it is fit for ufe, and may ferve for a prime Gondudor to an ele£lrical machine.
If the point C of this Conduflor is fet near the excited cylinder of the machine, it will appear illuminated with a ftar ; at the fame time the glafs tube will appear all illu- minated with a weak light ; but from the knobed wire, that proceeds within the glafs from the piece F. D, a lucid pencil will ifTue out, and the oppofite knob will appear illu- minated with a ftar, which, as well as the pencil of rays, is very clear, and difcernible among the other light, that occupies the greateft part of the cavity of the tube.
If the point C, inftead of being prefented to the cylinder, be connected with the rub- ber of the machine, the appearance of light
within
/
220 A COMPLETE TREATISE
within the tube will be reverfed ; the knob which communicates with the piece F D ap- pearing illuminated with a ftar, and the op- pofite with a pencil of rays ; becaufe in this cafe the diredion of the eleftric fluid is juft the contrary of what it was before ; it then going from D to B, and now coming from B and going to D.
If the wires within the tube E F, inftead of being furnifhed with knobs, be pointed, the appearance of light is the fame, but it feems not fo ftrong in this, as in the other cafe.
Experiment VII.
T^he conduSling Glafs Tube.
Take a glafs tube of about two inches diameter, and about two feet long; fix to one of its ends a brafs cap, and to the other a ftop-cock, or a valve ; then by means of an air-pump exhauft it of air. If this tube be held by one end, and its other end be brought near the eledrified primq Conduc-" tor, it will appear to be full of light,, when- ever
OF ELECTRICITY, 221
ever a fpark is taken by it from the prime Conductor ; and much more fo, if an eledric jar be difcharged through it.
This experiment may alfo be made with the receiver of an air-pump ; take^ for in- ftance, a tall receiver clean and dry, and through a hole at its top infert a wrire, v\^hich muft be cemented air tight. The end of the w^ire, that is within the tube, muft be pointed, but not very fharp ; and the other end muft be^fi^rnifhed with a knob. Put this receiver upon the plate of the air pump, and exhauft it. If now the knob ^f the wire at the top of the receiver be touch- ed with the prime ,Condud:or% every fpark will pafs through the receiver in a denfe and large body of light, from the wire,- to the plate of the air-pump.
* When any thing Is to be touched with the prime Condudtor, that is not very portable, as the air-pump above mentioned, the communication between the former and the latter, may be made by means of a rod furnifhed with an eledtric handle, or the like.
ExPE-
%11 A C O M P L E T E TREATISE
Experiment VIIL
T&e Aurora Borealis.
Take a phial nearly of the Ihape and fizc of a Florence flaffc ; fix a ftbp^cock or a valve to its neck, and exhauft it of air as much as it is poffible with a godd air-pump. If this glafs is rubbed in the common man- ner ufed to excite eledtrics, it w^ill appear luminous within, being full of a flaftiing light, which plainly refembles the aurora borealis, or northern light. This phial may alfobemade luminous by holding it by either end, and bringing the other end to the prime Condudor ; in this cafe all the cavity of the glafs will inftantly appear full of flafhing light, which remains in it for a con- fiderable time after it has been removed from, the prime Conductor.
Inftead of the above-defcribed glafs veflel, a glafs tube, exhaufted of air and hermeti- cally fealed, may be ufed, and perhaps with better advantage. The moft remarkable cir- cumftance of this experiment is, that if the 2 phial,
OF ELECTRICITY. 223
phial, or tube after it has been removed from the prime Condudor (and even feveral hours after its flafliing light hath ceafed to appear), be grafped with the hand, ftrong flaihes of light will immediately appear within the glafs, which often reach from one of its ends to the other.
The caufes on which this experiment de- pends are two ; fir ft the conduxfling nature of the vacuum, and fccond the charging of the glaft I for when one fide of the glals phial is touched with the prime Condudor, the ele<Stric fluid, comaunicated'id- the out-* fidefurface of one fide of the phial, caufeth the natural fluid belonging ifo ' the infide furface to depart from its place, and go to the oppofite fide of the phial ; and this fluid, pafling throUgh the vacuum, caufes the light within the phial, which light is more or lefs fubdivided, according as the vacuum is lefs or more perfedt. Now, that part of the phial, which has touched the prime Condudlor, is adually charged ; for its out- fide furface has acquired an additional quan- tity of electric fluid, and the infide furface has loft part of its own j but as the outfide
of
224 A COMPLETE TREATISE
of the phial has no coating, therefore, whea it is removed from the prime Condu6lor, and it is not grafped with the hand, or other Conductor, the charged part ot the glafs can be difcharged only gradudly ; that is, whilft its outfide furface is commuriicaring its fuperfluous fluid to the contiguous air,, the infide furface acquires the eledric fluid from the other end of the phial, which fluid paffing through the vacuum, caufes that flafh- ing, which is obferved for fo confiderable a time. If the phial is grafped with the hand, its difcharge. is accelerated, hence the flaflies within the phial appear more denfe and co- pious, yet it cannot be difchargei^ all at once by this operation, becaufe the hand cannot touch every part of the glafs at once.
ExPERIxMENT IX.
cr
^he vifib.le eleSiric Atmofphere.
G I fig. 2. Plate II. reprefents the re- ceiver with the plate of an air-pump. In the middle of the plate I F, a fhort rod is fixed, having at its top a metal ball B nice- ly polilhed, whofe diameter is nearly two
inches.
OF ELECTRICITY, 225
inches. From the top of the receiver, ano- ther rod A D with a like ball A proceeds, and is cemented air-tight in the neck C ; the diftance of the balls from one another being about four inches, or rather more. If, when the receiver is exhaufted of air, the ball A be electrified pofitively, by touching the top D of the rod A D with the prime Conductor or an excited glafs tube, a lucid atmofphere appears about it, w^hich although it confifts of a feeble light, is yet very con- fpicuous, and very well defined ; at the fame time the ball B has not the leaft light. This atmofphere does not exift all round the ball A, but reaches from about the middle of it, to a fmall diftance beyond that fide of its furface, which is towards the oppofite ball B. If the rod with the ball A be elec- trified negatively, then a lucid atmofphere, like the above defcribed, will appear upon the ball B, reaching from its middle to a fmall diftance beyond that fide of it, that is to- wards the ball A ; at the fame time the ne- gatively eleftrified ball A remains without any light.
m6 a complete treatisi:
The Operator in this experiment, muft be careful not to eleftrify the ball A too much, for then the ele6lrlc fluid will pafs in a fpark from one ball to the bther, and the experi- ment will not have the defired efFe^^t. A lit- tle pra6lice, however, will render the operation very eafy and familiar*
By this elegant experiment, which is of the celebfated F, Beggaria, we have an ocular demonftration of the theory of a fmgle ele£lric fluid ; we fee that Elec- tricity confifts of one uniform, homogeneous fluid, and not two, viz. the vitreous, and refinous, as fome have fuppofed ; for if the pofitive, and negative Eledricity were two difl:in6l fluids attractive of one another, there fhould, in the above experiment, always ap- pear two atmofpheres, /. e. one about the ball A, and another about the ball B ; for when the ball A is overcharged with either fluid, it fliould fhew that fuperfluous fluid on its furface, and this fluid fliould attrad towards the ball A, an atmofphere of the contrary fluid from the ball B, But this, as we obferved before, is not the cafe j for
the
O F E L E C T R I C I T Y^ %2^
tlie appearance of the lucid atmofphere is always on one ball, namely, that which is overcharged with the eledric fluid ; thus when the ball A is eledrified pofitively, the fuperfluous fluid is vifible on that part of it, which is neareft to the ball B, becaufe B being in a contrary ftate of Ele6lricity, en- deavours to attraffc it ; but, when the ball A is eledlrified negatively, it will attra6t the fluid proper to the ball B, which fluid on that account appears upon the furface of B, jufl: in the a£l of leaping to the ball A*
In order to remove an error, that has been adopted by feveral writers on Elec- tricity, it will be not amifs in this chapter to mention, that the eledlric light has all the prifmatic colours, as well as the light of the fun. This may be eafily experienced by viewing an eledric fpark through a glafs prifm*.
* Sec Dr. Priestley^s Hiftory of EIe£lricity, part VIIL fee, XIIL n> XH.
Q^a CHAP-
228 A COMPLETE TREATISE
CHAP. VIL
Experiments with the Leyden Fhiah
Experiment L
Of charging^ and difcharging a Phial in
general.
T.k. a .cated jar, as D E fig. « P.ate I, and place it upon the table near the prime Condudor, fo that the knob of its wire, and that only, may be in contact with it : fix the quadrant ele6lrometer E fig 2, upon the prime Conductor, and then turn the winch of the machine. You will obferve, that as the jar is charging, the index of the eledlrometer will rife gradually as far as 90^, or thereabouts, and then reft : when this happens you may conclude, that the jar has received its full charge. If now you take a difcharging rod, and holding it by the glafs handle, apply firft one of its knobs to the outfide coating of the jar, and then bring the other knob near the knob of the wire of the jar, or near the prime Con- 4 du6tor,
OF ELECTRICITY. 229
dudor, that communicates with it, you will hear a report, and fee very vivid fparks be- tween the difcharging rod, and the conduc- ing fubffances, communicating with the fides of the jar. This operation difcharges: the jar. If, inftead of ufmg the difcharging rod, you touch the outfide of the jar with one hand, and bring the other hand near the wire of the jar,> the fame fpark and re- port will follow, but now you will feel a fhock, which affedls your wrifts, elbows^ and, if ftrong, your breaft alfo^. If a number of perfons join hands, and the firft of them touches the outfide of the jar, and the laft touches the wire communicating with the infide, they will all feel the ihock, and precifely at the fame perceivable tirae^ This fhock bearing • no refemblance to any fenfation otherwife felt, cannot confequently be defcribed, arid in order that a perfon may form a juft idea of it, he muft abfolutely feel it.
* A fliock may be giveri to any fingle part of the t)ody, if that part only be brought into the circuit* ;
CLs The
zy) A COMPLETE TREATISE
The reafon of the charging of the phial, or jar in this experiment, is, that When a foperfluous quantity of electric fluid is forced upon the infide furface of the glafs, it caiifeth an equal quantity of fluid, naturally inherent in the glafs, to depart from the oppofite furface, in confequence of the re- pulfion natural to the particles of theelec^ trie fluid, which repulfion is exerted even through the glafs ; ohe fide therefore of the glafs remains overtbarged, and the other undercharged ; as foon therefore as the com-* municatjon between the two fides of the jar is compleated, the fuperfluous fluid on pne fide of the glafs flies violently to the other fide, and the rapidity of its motion oc- cafions tiie fpark, the report, &c.
< ■ ■
If :the coated jar /rbe held by the wire communicatiiig with MS'infide> and the out- fide coating be prefented to the prime Con- du6lor, it will be charged as^ readily as in the other method, but with this difi^erence, that in this cafe the outfide will be pofitive, and the infide negative.
We
OF ELECTRICITY. a^i
We have fuppofed above, that the prime Condudor was eledtrified pofitively ; but if the experiment be repeated, when thfe Con- dud:or, by being connefled with the rubber of the machine, is electrified negatively, the jar would in the fame manner be charged, except that in this cafe the fide that touches the prime Condudlor, would be eledlrified negatively, and the oppofite fide, pofi- tively.
Experiment XL
T'o Jhew that an infulated Jar cannot be
charged.
Set a coated jar upon an eledric ftool ; conneft its wire, or its outfide coating with the prime Conduflor, and turn the winch of the machine. You will then obferve, that the index of the quadrant ele£lrometer, placed upon the prime Conductor, foon rifes to 90^, feemingly fhewing that the jar is charged. Then remove the eledric ftool with the jar from the prime Condu£lor, and either with a difcharging rod, or with your hands, en-
0^4 deavour
232 A COMPLETE TREATISE
deavour to difcharge the jar, and you will find, that it is not charged ; for no fpark, no fhock, nor any other phenomenon of charged glafs, will appear.
The reafon why in this experiment the infide of the jar could acquire no additional electric fluid, and therefore the jar could ac- quire no charge, is becaufe the outfide could not ^t the fame time part with its own fluid, its communication with the earth being cut off by the eledric flool. But repeat this experiment with only this variation, that, by means of a chain or otherwife, the out- fide of the jar be made to communicate with the table, and you will then find, that the jar will be charged ; for in this cafe the fluid, naturally inherent in the outer furface of the jar, can readily be repelled through the chain, &c. into the table.
If a jar be infiilated, and one fide of it, inftead of being connefted with the earth, be connected with the infulated rubber, whilft the other fide communicates with the prime Conductor, the jar will be alfo charged, and perhaps in a more expeditious manner ;
for
O F E L E C T R I C I T Y. 233
for whilft the rubber exhaufts one fide, the other fide is fiipplied by the prime Con- du6tor. In this manner it is fhown, that the jar is charged with its own fluidy /. e. the natural eledtric fluid of one of its fides, is, by the adion of the machine, thrown on the other fide.
Experiment III.
^he preceding BiXperiment diverjified.
To make the above experiment in a cleareri and more fatisfa£tory manner, place the jar upon the fl:ool as before, and with its wire, not in contact, but at about half an inch diftanceifrom the prime Conduftor, hold the knob of another wire at fuch a diftance from the outfide coating of the jar, as the knob of the tjar is from the prime Gondud:or, then let the winch of the machine be turned, and you will obferve, that whenever a fpark comes from the prime Condudor to the wire of the jar, another fpark pafTes from the outfide coating of the jar to the knob of the wire prefented towards it; which Ihews, that as a. quantity of electric fluid is entering the infide of the jar, an equal quantity of it is
leaving
5i34 A COMPLETE TREATISE
leaving the outiide* In this manner the jar becomes charged.
If inftead of the knobed wire, a pointed one be prefented to the outfide of the jar, it will appear illuminated with a ftar ; and if inftead of prefenting any wire to the jar > a pointed wire be conne£led with its coating, it will appear illuminated with a brufh of rays (/. e. by throwing the eledric fluid into the air), which will laft as long as the jar is charging.
If the knob of another jar be prefented to the outfide coating of the infulated jar in the above experiment, it will alfo be charged ; for the fluid, going put of the outfide coatiag of the firft jar, /. e. that ftanding upon the ftool, will go in the infide of the other jar, and caufe the fluid, inherent to the outfide of that jar, to depart from its place *•
Ex-
* It IS cafy to underftancJ from this experiment, how fevcral phials may be connefted together, fo that they may be charged all at once, with nearly the fame trouble as one is charged. It muff, however, be obfervcd, that when fcvera] jars arc fo connedcd, that the infide of one
com«
OF ELECTRICITY^ a^s
Experiment IV.
Tojhow that the Charge of a Jar^ or Glafs in general does not rejide in the coating.
Take a naked phial, and for a coating on the outfide ftick a piece of tin-foil with a little tallow, or bees-wax, fo that it can juft adhere to the glafs ; and for an infide coating ufe fmall leaden fhot^ or quickfilver j laftly, infert through its neck a knobed wire com- municating with the fhot, or quickfilver. — This done hold the phial thus coated by its outfide coating, and charge it, by prefenting its knobed wire to the prime Condudor. When it is charged turn it upfide down, and let its wire, and quickfilver, or fliot fall in a glafs receiver ; then remove its outfide coating alfo.. In this operation the phial does not lofe its charge, and if you examine the quickfilver or fhot, you will find that it contains no more ElcjiStricity, than any other like conducing infulated body, which has
communicates with the outfide of another, &c. they can- not be charged fo high, nor fo eafily, as otherwife ; the difficulty increafing nearly in. proportion to the number of the jars.
been
236 A COMPLETE TREATISE
been in contad with the prime Condudor, would contain. Replace the outfide coating again upon the phial, pour the ftiot or quickfi.lver again into it, or any other con- du£ting liibnance, theii touch with one'hand the outfide coating, and with the other, by introducing a finger or a wire, touch thd infide non-ele£tric, and you will feel a fliock, which will convince you, that the glafs has loft very little of its charge by the operation above mentioned.
The fame experiment may be more con- veniently made by laying a pane of glafs upon a metal plate, and covering an equal part of the upper furface with tin-foil, having -a filk thread fattened to one of its fides, by which it may be eafily taken ofF^ when the glafs is charged, and as eafily re- placed, when required. <
r 'k r ■
m
Experiment V. '' ^"^^'^'^
To prove that the eleSiric Fluid does not expel , the Air contained in a PhiaL . ., .~
Through a hole made in the cork" that flops a coated phiil, introduce a fmall glaf^
tube
/
OF E L E C T R I C I T Y. 237
tube open at both ends, and of about one thirtieth part of ah inch in diameter ; bend that part of the tube, that is out of the phial in an horizontal fituation, and with bees-wax faften the cork fo, that no air can get in or out of the phial, except it paffes through the glafs tube; laftly, put a fmall drop of red wine, or ink, in the horizontal part of the tube, fo that it may be eafily moved through it by the leaft rarefadion, or condenfation of the air within the phial. If this phial thus furnifhed be charged, by conneding the prime Con- dudtor with its wire, the drop of liquor in the glafs tube will not be ftirred from its fitu- ation, which fhows that the eledric fluid, immitted into the phial, does not exclude- any of the air, that the phial contains. If the phial be difcharged, the drop of liquor in the tube will be often pufhed a little out of its place, and afterwards return to its former fituation, which £hows, that on mak- ing the difcharge, the air within the phial was a little difplaced, or rarefied. This how- ever is to be imputed to fome fpark, that generally happens within the cavity of the phial, on account that the wire is not
in
238 A COMPLETE TREATISE
in perfe<^ conta6l with the infide coat-
ing*.
Experiment VI.
T!he courfe of the ekSiric Fluid in the 'Dif charge rendered vijible by the Star^ and Pencit.
Whena jar Is charged, take a difchargingrod having its ends pointed, /. e. the difcharging rod reprefented in fig. lo. Plate I, without its knobs, and keep it as reprefented, fig. 1 1. that is, in fuch a fituation, that one of its points C may be at about one inch diftance from the knob A, and the other point B, at an equal diftance from the outfide coating of the jar j by thefe means the jar will be dif- charged filently, and if its infide be eledri- fied pofitively, you will fee, that the point Q of the difcharging rod, is illuminated with a ftar, and the point B with a pencil ; becaufe.
* Having repeated this experiment with a fmall phialj whofe charging piece (as we may call it) was a produc- tion of the infide coating, which was of one piece of tin- foil, ftuck to the glafs with bees-wax, in confequence of which no fpark could happen within the phial, I found that the drop of liquor in the glafs tube, was not ftiirei either in charging, or difcharging*the phial.
ia
OF ELECTRICITY, 23^
in this cafe, the eledric fluid, going from the infidc to the outfide of the jar, enters the point C, and iffues from the point B. But if the jar is eledrified negatively on the infidCr and confequently pofitive on the outfide, then the pencil of rays will appear upon the point C, and the flar upon the point B ; for in this cafe the eledric fluid paflTes from the outfide to the infide of the jar*
N. B. This experiment, as well as any ether, in which the ele6lric light is to be ob- ferved, requires to be made in the dark.
Experiment VII.
The Courfe of the ele5lric Fluid in the Dif- charge Jhown by the Flame of a Wax-taper^
Remove the circular piece of wood E from the univerfal difcharger, reprefented fig. 5. Plate I. Fix the wires D B, D C, fo that their knobs D D may be about two inches diftance of one another ; and upon the focket F fiix a piece of wax taper lighted, fo that its flame may be jufl: in the middle between the knobs D D. Having difpofed the apparatus in this manner, if you conne6l, by means of 2 a chain
240 A COMPLETE TREATI SE
a chain or otherwife, the outfide of a charged jar with one of the wires C, and bring the knob of the jar to the other wire C, you will obferve, that on making the difcharge, which muft pafs between the knobs D D, the flame of the wax taper is always driven in the diredion of the eledric fluid, that is, it will be blown upon the knob of that wire, which communicates with that fide of the jar, which is negatively electrified.
In this experiment the jar muft have an exceeding fmall charge, juft fufficient to pafs through the interval in the circuit ; which experience will prefently determine : other- wife the experiment will not fucceed, or be perhaps rendered equivocal ^.
* Ifitbeafked, why this experiment does not fucceed with a great explofion as well as with a very fmall one, the anfwer is, that when ajar highly charged, is brought near one of the wires of the univerfal difcharger, it creates an atmofphere about the knob of the faid wire, which at- mofphere difturbs the flame of the wax taper, before the aclual difcharge ; befides the eledlric fluid in a great ex- plofion, by its elaftic nature, pafles through the flame of the wax taper too fwiftly, for to communicate to it any vifible motion ; in the fame manner as a bullet, difcharged by a piftol againft an open door, makes a hole through the door, without (hutting it.
Ex-
OF ELECTRICITY. 24.1
Experiment VIII.
^he Courfe of the eleSiric Fluid in the Difcharge^ rendered confpicuous by the Motion communis cated to a pith balh
Bend a card length-ways, over a round ruler, {o as to form a channel, or femicircular groove^. Lay this card upon the circular board E of the univerfal difcharger reprefented fig. 5, of Plate L and in the middle of it put a pith ball of about half an inch diameter ; then at equal diftances, about half or three quarters of an inch from the cork ball, lay the two brafs knobs D D. The card being perfectly dry, and rather hot, if you connedt, by means of a chain or otherwife, the outfide of a charged jar, with one of the wires C, and bring the knob of the jar to the other w^ire C, you will obferve, that on making the difcharge, which muft pafs between the knobs DD, and over the card, &c, the pith
* Inftead of the card, a piece of baked wood may be cut in that (hape, and painted over with lamp-bl ck and oil i which will anfwer better than the card, it being much more fteady, and not fo liable to attradt oioifture.
f ...
R ball
^42 A COMPLETE TREATISE
ball is always driven in the diredlion of the eledric fluid, /. e. it is pufhed towards that knob, which communicates with the negative iide of the jar.
It muft be obferved that in this experi- ment the charge of the jar muft be juft fuf- ficient to pafs through the interval in the circuit ; the card, or piece of baked wood, muft be very dry and clean ; and in fliort the difpofition of the apparatus, and the per- formance of this curious experiment, require a degree of nicety, that can only be obtained by pradice. Without great precaution, it fomethues fails ; but when the Operator has once got it to fucced, and follows exa6lly the fame method of operation, he may be fure, that the event of the experiment will be conftantly as above defcribed.
Experiment IX.
The hey den Vacuum.
Fig. 8 and 9. of Plate I. reprefent a fmall phial coated on the outfide about three inches puthe fides with tin-foil ; at the top of the neck of this phial, a brafs cap is cemented,
having
OF fe t E C t R I C I T Y. 243
having a hole with a valve, and from the cap a v^ire proceeds a few inches within the phial, terminating in a blunt point. When this phial is exhaufted of air, a brafs ball is fcrewed upon the brafs cap^ which is cemented into its neck, {o as to defend the valve, and prevent any air from getting into the exhaufted glafs *• This phial exhibit^ clearly the diredioa of the electric fluid, both in charging and difcharging ; for if it be held by its bottom, and its brafs knob be prefented to the prime Conductor pofi-^ tively eledrified/ you will fee that the ele(3:ric fluid caufeth the pencil of fays to proceed from the wire within the phial, as reprefented fig. 9. and if it is difcharged, a ftar will ap- pear in the place of the pencil, as reprefented in fig^ 8. But if the phial is held by the brafs cap, and its bottom be touched with the prime Condudor, then the point of the wire on, its infide, will appear illuminated w^ith a fl:ar^ when charging, and with a pencil^ whea difcharging. If it be prefented to a prime
* The .infide of this phiaf requires no costing, because as the electric fluid pervades vacuum, it can pafs freely from the wire to the furface of t!^e exhaufted glafs, with- out the help Qf a non-eleitric coating,
R a Coa^
I
244 A COMPLETE TREATISE
Condudlor electrified negatively, all thefe appearances, both in charging, and dif-* charging, will be reverfed.
This experiment of the Leyden vacuum, together with the tvsro preceding ones, namely the feventh and eighth of this chap- ter, are inventions of Mr. Henly, and they exhibit an ocular demonftration of the hypo- thefis of a fmgle electric fluid.
Experiment X*
^0 pierce a Card^ and other Suhjiances njuitk
the eleSlric Explojion.
Take a card, a quire of paper, or the cover of a book, and keep it clofe to the outfide coating of a charged jar ; put one knob of the difcharging rod upon the card, quire of paper, &c. fo that between the knob, and coating of the jar, the thicknefs of that card, or quire of paper, only is in- terpofed ; laftly by bringing the other knob of the difcharging rod near the knob of the jar, make the difcharge, and the eledric matter, rulhing through the circuit from the
pofi^
OF ELECTRICITY. 245
poiitive, to the negative furface of the jar, will pierce a hole (or perhaps feveral) quite through the card, or quire of paper *• This hole has a bur raifed on each fide, except the card, &c. be preffed hard between the difcharging rod and the jar ; which fhows that the hole is not made in the diredlion of the paflage of the fluid, but in every diredtion from the center of the refifting body.
If 'this experiment be made with two cards, inftead of one, which however mull be kept very little diftant from one ano- ther ^f*, each of the cards, after the explofion, will be found pierced with one or more holes, and each hole will have burs on both furfaces of each card,
* The hole, or holes, are larger or fmaller, accord- ing as the card, &c. is more damp, or more dry. It is remarkable that if the noftrils are prefented to it, they will be afFefted with a fulphureous, or rather a phofpho-
real fmdi, juft like that produced by an excited Elec- tric.
f This may beeafily effe£ted by bending a little one of the cards,
R 3 * If
ft46 A COMPLETE TREATISE
If inftead of paper, a very thin plate of glafs, rafin, fealing-wax, or the like, be in- terpofed between the knob of the difcharging rod, and the outfide coating of the jar, on making the difcharge, this will be broken in feveral pieces.
Small infe^ls may alfo be killed in this manner ; they may be held between the out- fide coating of the jar, and the knob of the difcharging rod, like the above card ; and a fhock of a common phial fent through them^ will inftantly deprive them of life, if they are pretty fmall ; but if larger, they will be affected ia fuch a manner, as to appear quite dead on firfl receiving the flroke, but will, after fome time, recover : this, however, depends on the quantity of the charge fenf: through them.
]ExPEr
OF ELECTRICITY. 247
Experiment XL
To Jhew the Effect of the Shock fent over the Surface of a Card or other Subjiances.
Put the extremities of two wires upon the lurface of a card, or other body of an elec- tric nature, fo that they may 1>6 iii one di- reftion, and about one inch diftance from one another; then, by connecting ane of the wires with the outfide of a charged jar, and the other wire with the knob of the jar, the (hock will be made to pafs over the card or other body.
If the card be made very dry, the lucid track between the wires will be vifible upon the card for a confiderable time after the explofion. If a piece of common writing paper be ufed inftead of the card, it will be torn by the explofion into very fmall bits.
If inftead of the card, the explofion is fent over the furface of a piece of glafs,
R 4 this
248 A COMPLETE TREATISE
this will be marked with an indelible tfack, which generally reaches from the extremity of one of the wires to the extremity of the other. In this manner the piece of glafs is very feldom broken by the explofion. But Mr. Henly has difcovered a very remark- able method to increafe the effect of the ex- plofion upon the glafs ; which is by preffing with weights that part of the glafs, which lies between the two wires, (/. e. that part, over which the fhock is to pafs). He puts firfl: a thick piece of ivory upon the glafs, and places upon that ivory- a weight at plea- fure, from one quarter of an ounce, to fix pounds : The glafs in this manner is gene- rally broken by the explofion into innumera- ble fragments, and fome of it is abfolutely reduced into an inpalpable powder. If the glafs is very thick and refills the force of the explofion, fo as not to be broken by it, it will be found marked with the moft lively prifmatic colours, which are occafioned by very thin laminas of the glafs, in part fepa- rated from it by the fhock. The weight laid upon the glafs is always fhook by the ex- plofion, and fometimes it is thrown quite
off
OF ELECTRICITY. 249
off from the ivory ^. This experunent may be mod conveniently made with the univerfal difcharger. Fig. 5. of Plate I.
Experiment XIL
To Jhew the DireSlion of the eleSiric Fluid in the Difchaf^g'i by caiijing the Shock to go over the Surface of a Card.
Difpofe the apparatus in the manner de- fcribed in the preceding experiment, but vvuth this ditFerence, that inftead of laying the extremities of both wires upon the fame fide of the card, one of them be placed under the card ; then fend a fliock through the faid wires, as in the preceding experiment, and you will obferve, that the ele£tric fluid will run over that furface of the card, upon which lies the extremity of that wire, which is connected with the po- fitive fide of the jar j and in order to pafs
* If fmall reprefentations of houfes, &c. be laid upon a board, placed on the piece of ivory ; that, being (hook by the explofion, will give a very natural idea of an earthquake
to
250 A COMPLETE TREATISE
to the extremity of the other wire, it will break a hole through the card juft over the extremity of that wire, which is conneded with the negative fide of the jar.
This excellent experiment, which fhows the diredlion of the eleftric fluid in the difcharge of a jar, is a difcovery of Mn Lul- LiN of Geneva.
N. B. With very large jars, this experi- ment has been obferved to pierce feveral holes, and in fuch manner as to render the experi-- ment not fatisfadory.
Experiment XIIL
^ofwell the Clay^ and break fmall Tuber with the ele6lric Explojion,
Roll up a piece of foft tobacco-pipe clay in a fmall cyhnder C D fig, 4. Plate II. and infert in it two wires A, B, fo that their ends within the clay may be about a fifth part of an inch from one another. If a {hock be fent through this clay, by con-
neding
OF ELECTRICITY. ^51
^e6ling one of the wires A, or B with the out fide of a charged jar, and the other with the infide, it will be inflated by the fhock, /. e. by the fpark, that palTes between the two wires, ai)d after the explolion will ap- pear as reprefented fig, 5. If the fhock fent through it is too ftrong, and the clay not very moift, it will be broken by the explofion, aud its fragment fcattered in^very fdiredion.
To make this experiment with a little va- b riation, take a piece of the tube of a tobac- co-pipCv about one inch long, and fill its bore with moift clay, then infert in it two wires, as in the above rolled clay, and fend a fhock through it. This tube will not fail to burft by the force of the explofion, and its fragments will be fcattered about to a great jdiftance,'
If inftead of clay, the above-mentioned tube of the tobacco-pipe, or a glafs tube, (which will anfwer as well) be filled with any other fubftance either eledric, or non- pledric inferior to rnetal, on making the dif-
charge,
25a ACOMPLETE TREATISE
charge, it will be broken in pieces with nearly the fame force.
This experiment is the invention of Mr. Lane, F. R. S.
Experiment XIV.
Tojhow the Courfe of the eleSfrtc Fluid by the fpontaneous Difcharge.
Take a coated phial of a fmall fize, and if the naked part of it, /. e. from its out- fide coating to the cork, is very dry, breathe upon it once or twice, fo as to render it flightly damp ; then holding the phial by its outfide coating, prefent its knob to the prime Conductor, while the machine is in a6lion, and you will fee, that after the phial has received a fmall charge, a beautiful brufh of rays w^U proceed from the cork, which, after going a little way into the air, turns its courfe towards the outfide coating of the phiaL If the phial, inftead of the prime Conductor, be prcfented to the infu* lated rubber, then the brufh, inftead of pro- ceeding from the cork, will iffue from the
outfide
O F E L E C T R I C I T Y. 253
outfide coating, and dire6l its courfe towards the cork or wire of the phial ; fhowing be- yond a doubt the truth of the hypothefis of a fingle eledric fluid*
This experiment, which Is of Mr. Hen- Ly, requires a nicety of operation, without which it will not fucceed as above defcribed. The quantity of moifture upon the phial, and the quantity of Eleftricity communi- cated by the machine, muft be of a de- gree, which nothing but practice can deter-^ mine*
Experiment XV.
To make the eleElric Spark vifible in Water.
Fill a glafs tube of about half an inch diameter, and fix inches long, with water, and to each extremity of the tube adapt a cork, which may confine the water ; through each cork infert a blunt wire, fo that the extremities of the wires within the tube may be very near one another ; laftly con- ned one of thefe wires with the coating of a fmall charged phial, and touch the
other
^54 A COMPLETE TREATISE
other wire with the knob of It ; by which means the fhock will pafs through the wires, and caufe a vivid fpark to appear between their extremities within the tube. In per- forming this experiment care muft be taken, that the charge be exceedingly weak, other- wife the tube v/ill burit.
C fig. 14. Plate II. reprefents a common drinking glafs almoft full of water. A B are two knobed wires fo bent, that their knobs may be within a little diftance of one another in the water. If one of thefe wires be conne6i:ed with the outfide coating of a pretty large jar, and the other wire be touch- ed with the knob of it; the explofion which muft pafs through the water from the knob of one of the wires to that of the other, will difperfe the water, and break the glafs with a furprifmg violence. This experi- ment is very dangerous if not condu6led with great caution.
ExPE-
OF ELECTRICIT Y. 255
Experiment XVL
To prove that the eleSiric Spark difplaces^ and rarifies the Air.
Fig. 3. Plate IT. reprefents an inftrument, which the inventor, Mr. Kinnersley, calls the eleBrical Air l^hermometer^ it being very ufeful to obferve the efFefts of the eledlric exploiion upon air. The body of this ther- mometer confifts of a glafe tube A B, about ten inches long, and nearly two inches dia- meter ; and clofed air-tight at both ends by two brafs caps. Through a hole in the up- per cap, a fmall tube H A, open at both ends, is introduced in fome water at the bottom B of the large tube. Through the middle of each of the brafs caps, a wire F G, E I is introduced, having a brafs knob within the glafs tube, and by Aiding througk the caps, they may be fet at any diftance from one another. This inftrument is, by a brafs ring G, faftened to the pillar of the wooden ftand C D, that fupports it. When the air within the tube A B is rarefied, it will prefs upon the w^ater at the bottom of I the
256 A COMPLETE TREATISE
the tube, which will confequently rife in the cavity of the fmall tube ; and as this water rifes higher or lower, fo it fhows the greater or lefs rarefadtion of the air within the tube A B, which has no communication with the external air.
If the water, when this inftrument is to be ufed, is all at the bottom of the large tube, /. e. none of it is in the cavity of the fmall tube ; it will be proper to blow with the mouth into the fmall tube, and thus caufe the water to raife a little in it, where, for better regulation, a mark may be fixed.
Bring the knobs G I of the wires I E, F G into contact with one another, then connedl the ring E, or F with one fide of a charged jar, and the other ring with the other fide, by which operation a fhock will be made to pafs through the wires F G, I E, /. e. between the knobs E I. In this cafe you will obferve, that the water in the fmall tube, is not at all moved from the mark ; which fliows, that the paflage •of the eledlric fluid through Condudors fuf- 3 ficiently
OF ELECTRICITY. 257
ficiently large, occafions no rarefadlion, Gor dilplaces the air about them.
Put the knobs G, I a little diftant from one another, and fend a fhock through them as before, and you will fee that the fpark between the two knobs, not only difplaces, but rarefies confiderably the air ; for the water will be fuddenly pufhed almoft at the top of the fmall tube, and immediately it will fubfide a little, as for inftance as far as H, which is occafioned by the fudden dif- placing and replacing of the air about the place, where the fpark appeared within the tube A B. After that the water has fubfided fuddenly from the firft rifing^ it will then gradually, and flowly come down to the mark, at which it flood before the explo- fion ; which is the effedl of the air that was rarefied, and which gradually returns to its former temperature.
If this experiment be made in a room, where the degree of heat is variable, then proper allowance muft be made for this cir- cumftance, in eftimating the event of the experiment ; for the elcdrical air thermo-
S meter
2S^ A COMPLETE TREATISE
meter is afFedled by heat, or cold in generaf, as well as by that caufed by an electric fpark.
Experiment XVII.
To jire Gtm-powder.
Make a fmall cartridge of paper, and fill it with gun-powder, or elfe fill the tube of a quill with it ; infert two wires, one at each extremity, fo that their ends within the quill, or cartridge, may be about one fifth of an inch from one another ; this done, fend the charge of a phial through the wires, and the fpark between their ex- tremities, that are within the cartridge, or quill, will fet fire to the gun-powder. If the gun-powder be mixed with fteel filings it will take fire more readily, and with a very fmall fhock.
ExPE-
or E L E C T n I C / T Y. ^s^
ExPERiMENt XVIIL To Jinke Metals info Glafs^
Take two jQips of common window-glafs kbout three inches long, and half an inch^ wide^;^ put a fmall flip of gold, filver, or brafs leaf> between them, and tie them to- gether, or elfe prefs them together between^ the boards of the prefs H) belonging to the univerfal difcharger fig. 5, Plate T, leaving a little of the metallic leaf out between the glafles at each end ; then fend a fhock through this metallic leaf, and the force of the explofion will drive part of the metal into fo clofe a contact with the glafs, that it cannot be wiped off, or even be afFedl- ed by the common menftrua, which other- wife would diflblve it*
. In this experiment the glafTes are often (battered to pieces, but whether they are broken of not, the indelible metallic tinge will always be found in feveral places, and fometimes through the whole length of both glafles.
5 2 Expfi^
^ ^6o A COMPLETE TREATISE
Experiment XIX.
^0 Jiain the Paper^ or Gtafs.
Lay a chain, which forms a part of the circuit between the two fides of a charged jar, upon a fheet of white paper, and if a fhock be fent through it, the paper will be found ftained with a blackifli tinge at every jundure of the links. If the charge be very large, the paper, inftead of being ftained with fpots, is burnt through. If the chain be laid upon a pane of glafs, inftead of paper, the glafs will often be found ftained with fpots in feveral places, but (as might be expeded) not fo deep as the paper. ,
« If this experiment be made in the dark, a fpark will be feen at every jundure of the links; and if the links are fmall, and the fliock pretty ftrong, the chain will appear illuminated like a line of fire ; which ftiows that the electrical fluid meets with fome re- fiftance in pafling from one link of the chain to another.
ExPE-
OF E L E C T R I C I T Y. a6r
ExPERIiMENT XX.
^he lateral Exphjion.
If a jar be difcharged with a difcharging rod, that has no electric handle, the hand that holds it, in making the difcharge, feels fome kind of Ihock, efpeciaily when the charge is confiderable. — In other word^. A perfon or any conducing fubftance, that Is conneded w4th one fide of a jar, but forms no part of the circuit, will feel a kind of fhock, /. e. fome efFed of the dif- charge. This may be rendered vifible in the following manner. Connect with th6 outfide of a charged jar a piece of chain; then difcharge the jar through another cir- cuit, as for inftance with a difcharging rod in the common way, and the chain that communicates with the outfide of the jar, and which makes no part of the circuit, will appear lucid in the dark, /. e. fparks will appear between the links ; which fhows that the eleftric fluid, natural to that chain,' muft by fome means have been difturbed. This chain will alfo appear luminous, if it
S 3 is
262 A COMPLETE TREATISE
is not in conta<5l with the outfide of the jar, but only very near it ; and on making the difcharge, a fpark will be feen between the jar> and the end of the chain near it, This eledtrical appearance out of the cir- cuit of a difcharging jar, is that, which we Call the lateral Explofion^ arid to make it appear in the moft confpicuous mannef obferve the following method, which is of Dr. Priestley,
When a jar is charged and ftands upon the table as ufual, infulate a thick metallic rod, and place if fo that one of its ends inay be contiguous to the outfide coating p£ the jar ; and within about half an inch of its other end, place a body of about fix or feven feet in length ; and a few inches in breadth ; then put a chain upon the ta- ble, fo that one of its ends may be about one inch and a half diflant from the coat- ing of the jar ; at the other end of the chain apply one knob of the difcharging fod, and bring the other knob to the wir§ of the jar in order to make jthe pxplofiop. On making the difch^rge in this manner^ a ftfong fpark will be feen J)ct\YCcn xhp
..^
OF ELECTRICITY. 263
Infulated rod, which communicates with the coating of the jar^ and the body near its extremity, w^hich fpark does not alter the ftate of that body in refpe£l to Electricity ; hence it is imagined that this lateral fpark flieg from the coating of the jar, and returns to it at the fame inftant, allowing no per- ceptible fpace of time, in which an eledro- meter can be afFedled. Whether this lateral explofion is received on fiat and fmooth fur- faces, or upon fharp points, the fpark is aU ways equally long and vivid.
The caufe of this phenomenon feems to be the interruption in the circuit, made by introducing bad Conductors into it ; for, as this interruption is greater or lefs, fo the^ lateral explofion 13 more or Icis confiderablc.
S 4 CHAP-
1
264 A COMPLETE TREATISE
CHAP. VIIL
Experiments with other charged EleSirics.
^ H A T the experiments made with other charged electrics, are fimilar to thofe made with charged glafs, is very evi- dent : fmce it has been obferved above in the Firft Part, and alfo in the experiments already defcribed, that the property of being charged, of exploding, &c. is not inherent in glafs, as glafs, but, as being impervious to the electric fluid ; and in confequence, it muft be com- mon to all fuch fubftances, which like glafs, are impervious to that fluid : therefore, under the title of experiments with other elec- trics, I mean to defcribe experiments, not of a different nature from the above mentioned,, but only the manner of coating, and ufing, other electrics, which are not fo manageable as glafs ; but at the fame time, have fome peculiar advantages. Thefe methods I fhall reduce to three, /. e. firft, that of making the noble experiment of charging a plate of air j fecondly, the method of coating refinous fubftances ; and laftly, a method of trying other eledrics, that are in a fluid ftate.
O F E L E C T R I C I T Y, 265
Experiment L
To charge a Plate of Air.
Take two fmooth circular boards, quite plain, and each about three or four feet in diameter; coat one fide of each with tin- foil, which Ihould be palled down, and burniflxed, and turned over the edge of the board. Thefe boards muft be both infulated, parallel to one another, in an horizontal po- fition ; they muft be turned with their coat- ed fides towards each other, and fhould be placed in fuch a manner as to be eafily re- moved to, or from each other ; to do which, it will be proper to fix to one of the boards, a ftrong fupporter of glafs, or baked wood, and to fiifpend the other by filk firings from the ceiling of the room ; from whichj by a proper pulley, it may be lowered or raifed, fo as to be at any diftance required from the lower board, which may be placed upon the table.
When thefe boards are placed in the man- ner above defcribed, and at about one inch ^iftance from one another, they may be ufed
exactly
^66 A COMPLETE TREAT f S E
exadtly as the two coatings of a pane of glafs. If one of the boards is conneded with the eledrified prime Conductor, and the other be left infulated, they will receive no charge, agreeable to the fecond experiment of the preceding chapter, and if after fome time you touch them, you will receive only a fpark from the upper board, in confequence of its being canne6:ed with the €led:rified prime Conduftor. If, whilft one of the boards is receiving Eleftrioity, the other commuriri-r cates with th€ earth, then, the plate of air between th^m will be charged, like a coat€d plate of glafs ; for that board, which com-r jnunicates with th^ earth, will acquire an Eledricity contrary to that of th^ other board ; and if you tPtich them, /. e, make a communication between them, they will ex^ plpde, give the fhock, &e* fimilar to a charged jar.
In this experiment; it cannot be expeded, that fuch an explofion, and with fuch a force will be produced, as by an equal furface of coated glafs ; for here the coatings cannot be brought fo near one another as to render them capable of a high charge, becaufe the
plate
O F E L E C T R I G I T Y, 26?
plate of air being much lefs compact than glafs, may be eafily broken by the force of the charge, /. e, it may eafily difcharge itfdf. ^Jqtwiihfl;^^diIlg, however, that a plate of air is riot capable of receiying a very high charge, yet this experiment ha§ a great advantage, v^hich is, tha;t here we may fee what preffes bet\yeen the two coatings either in charging, or difcharging the plate of air, and we may jntr.Q((^ijLce feveral things into the fubliance of this coated electric, which produce feveral remark^tle^ appearances. By this experiment the true ftate of thie earth, when covered by eleclrified cloijds, rtiay be rjeprefented exceed-* ingly well ; and feveral meteors, that happen in that ft ate, ancj which are thought to be effe£ls of Eleftricity, may be imitated ; fuch ^s watpr-fpQuts *^ Sind whirlwinds^ hefides
f It was fometime ago doubted whether the caufe of water-fp JUts could be attributed to Eledlricity, or not ; but at prefent it feeqns pretty well afcertairied that they are elec* Jrical phenomena 5 it having been lately obferved (befides other reafons) that a fla/h of lightening was feen at the time that a watier-fpojut v>^2s brokeji, and difappeared. See Captaiti Cook's Voyage round the Wprld during the Yearns 1772 — 3-—^ — 5, by Mr. G. Forstlr^ F. R. S. ypL L p. 190.
the
68 A COMPLETE TREATISE
the well-known eleftrical phenomena, thunder and lightening.
In order to reprefent a water-fpout, as it is often obferved at fea, place the two boards at about two inches diftance from one another ; put a large drop of water about the middle of the loweft of them, and fix a metallic ball, or any other piece of metal, that is fomewhat fpherical *, to the upper board, juft oppofite' to, and at about half an inch diftance from the furface of the water. If in this fituation the upper board be eledlrified, whilft the lower communicates with the earth, the water, which reprefents the fea, will be attracted by the metallic ball, which reprefents a cloud,' and rifing nearly in a conical body, will af- ford a pretty good reprefentation of the water-fpout f.
The
* The metallic covering of fome kind of coat buttons anfwers exceedingly well, and may be parted on the tin- foil coating of the board.
f The knob of a charged bottle being brought near the water in a metal plate, or common earthen ware fawcer, fhows this experiment In a fimple, and beautiful manner. If a large drop of water be placed upon the knob of an infulated charged bottle, and the knob of ano- ther
OF ELECTRICITY, 269
The appearance of a whirlwind is but fel- dom, and by chance to be obferved. The bran between the two plates F, P fig. 2, Plate I, is often whirled like the duft in a whirlwind ; but there is no certain rule, that I know, for producing this phenomenon.
In order to fucceed in this experiment, Mr. Becket direds to place the boards above mentioned, about four or five inches afunder, and to put fome bran, and very fmall bits of paper about the center of the lower board. If in this fituation the upper board be con- nedled with the eledrified prime Condudor, and the lower be either conneded with the ground, or with the rubber of the machine, the bran, and bits of paper will be attraded, and repelled, alternately, by the boards. " But (fays Mr. Becket *) the moft furpriz-. *^ ing appearance in this experiment, and ^' what gives it the moft exadl refemblance
ther bottle charged with the contrary Ele(5lricity be brought near the drop of water, It will be fquirted away in a curious manner, particularly if the coating of the infu- lated bottle be touched at the fame time. * In his Eflay on Eledricity, p, 141.
4 '' of
i^o A COMPLETE: TREATISE
** of a whirlwind^ is that lometimes, whefl *^ the Eledficity is very ftrong, a quantity of " the paper and bran will accumulate in one *' place, forming a kind of column between " the boards^ and fuddenly acquire a fwift '^ horizontal motion^ moving like a whirlirrg ** pillar to the edge of the boards, and from *^ thence fly off and be fcattered about the *' room- to a confiderable diftance. I own *' I am entirely at a lofs to account for this ** extraordinary appearance— I call it extra- *^ ordinary, becaufe it but feldom occurs/ and ^' feems to depend either on a certain degree " of attraction, quantity of the bran, or dif- *^ tance between the boards; and I could ^^ feldom get it to fucceed perfedly but by ^' accident.'*
The phenomena of thunder and lightening^ are exhibited at the' fame time by a f]p6nta-i^' neous difchargeof the plate of air, which may be eafily produced by fetting- the boards at about an inch diftance from each other, and eledrifying them ftrongly*
ExPE-
OF ELECTRICITY. afi
Experiment II.
To c6at refinous Erle^rics.
The beft method to coat fuch eledrics, as rofiri, fealing-wax, &c, that can eafily be melted, is firft to put a circular piece of tin- foil, about two inches lefs in diameter thari' the plate you intend to make, upon a marble table; then, to pour over it the ele£tric juft itielted. This may be fpread and flattened by prefling it with a pane of glafs, or any thing, that is even, and fmooth ; afterwards, another piece of tin-foil equal to the former is to be ftuck upon the eledrlc, which may be done by prefljng it gently with a hot iron ; and then the plate, which may be eafily feparated from the marble table, will be fif for ufe.
Experiment III.
To infulate fluid File5lrics.
Take a large earthen difh, flat at the bot-^
tom, and ftick within it a piece of tin-foil
about an inch fhorter than the flat part of
the difh all around, and through a fmall hole
I made
X]z A COMPLETE TREATISE
made in the bottom of the difh, introduce a flender wire, which muft communicate with the tin-foil; then pour into the difh fome melted tallow, Or other electric fubftances, that you defire to try; laftly, let a round brafs plate ^y equal to the tin-foil, ftuck in the dilh, and either proceeding from a glafs arm, or from the prime Condu£lor, juft touch the furface of the eledric in the difh, and let it fland parallel, and oppofite to the tin-foil ftuck in its bottom. In this manner the plate of liquid eledric is coated, and may be eafily fubjedled to experiments.
Plates of other confiflent electrics, that can- not eafily be melted, may be coated in the fame manner as a plate of glafs ; and fome of them will be found to anfwer as well, if not better than glafs.
* The brafs plate F fig. 2 of Plate I may be very ufe-. ful for this purpofe*
CHAP.
OF ELECTRICITY. 273
CHAP. IX.
Experiments on the injluence of Points^ and the ufefulnefs of pointed metallic ConduSiors^ to defend Buildings from the effects of Lighten-* ing.
MY reader in the courfe of this work muft have obferved in feveral of the experiments already defcribed, the remark- able property, that points have, both of throwing off, and rtctiYmg flently the elec- tric fluid ; but in this chapter I Ihall defcribe fome more curious experiments of this kind, by which the influence of points, in refpeft to Eledlricity, may be better underftood, and which may, in a more particular manner, de- monflrate the utility of metallic Conductors to houfes, or piles of building, in order to preferve them from the damage often occa- fioned by a fl:roke of lightening, which is one of the greateft benefits that mankind has received from the fcience of Eledricity.
EXPE-
274 A COMPLETE TREATISE
Experiment L
To difcharge a Jar Jilently.
When a large jar is fully charged, which would give a terrible fhock, put one of your hands in conta6t with its outfide coating; with the other hold a fharp-pointed needle, and keeping the point directed towards the knob of the jar, proceed gradually near it, until the point of the needle touches the knob. This operation difcharges the jar in- tirely, and you will either receive no Ihock at all, or fo fmall a one, as can hardly be perceived. The point of the needle there- fore has filently, and gradually drawn all the fuperfluous fluid from the infide furface of the eledlric jar.
Experiment II.
Drawing the EleSirictty from the prime Con--
duSlor by a Point.
Let a perfon hold the knob of a brafs rod at fuch a diftance from the prime Condudlor, that fparks may eafily fly from the latter to the former, when the machine is in motion.
Then
OF ELECTRICITY. 275
Then let the winch be turned, and while the fparks are following one another, prefent the fliarp point of a needle at nearly twice the dif- tance from the prime Condudior, that the knobed rod is held ; and you will obferve that no more fparks will go to the rod ; — - remove the needle intirely, and the fparks will be feen again ;— prefent the needle, and the fparks difappear ; Vv^hich evidently (hows that, the point of the needle draws o^ filently almoft all the fluid, that the cylinder throws upon the prime Gondudtor.
If the needle be fixed upon the prime Con- dudor with the point outward, and the knob of a difcharging rod, or the knuckle of a finger be brought very near the prime Coh- du£tor, though the excitation of the cylinder may be very ftrong, yet yoti will perceive that no fpark, or an exceeding fmall one can be obtained from the prime Condu^or.
Experiment III,
T!he eleStric Fly.
Fix the fly defcribed in the third chapter. Upon the prime Conductor, as reprefented by
276 A COMPLETE TREATISE
D fig. 2 of Plate I, then turn the winch of the machine, and the fly will immediately begin to move round, in an horizontal pofi- tion, and in the diredion of the letters abcdy i. e. contrary to the direction of the points of the wares. If the experiment is repeated with a Conductor negatively eledrified, the fly will turn the fame way as before, viz. in the direction of the letters abed. The rea- fon of this experiment depends upon the re- pulfion exifling between bodies poflefled of the fame Electricity ; for whether the fly is eledirified pofitively or negatively, the air oppofite to the points of the wires (on ac- count of the points eafily tranfmitting Elec- tricity) acquireth a ftrong Electricity, ana- logous to that of the points, and therefore, the air and the points mufl: repel each other. This explanation is confirmed by obferving that the above fly not only does not move in vacuo ; and even if placed under a clofe re- ceiver, it will turn but for a little while, and then flop ; for the quantity of air contained in the receiver, may become readily, and
equally eledrified *•
ExPE-
* If, when the fly under the clofc receiver is flopped, you put the end of a linger on the outfide of the glafs, oppofite
to
OF ELECTRICITY. 277 >
Experiment IV.
T!he eleSlrified Cotton.
Take a fmall lock of cotton, extended in every dire£tion as much as conveniently can be done, and by a linen thread about five, or fix inches long, or by a thread drawn out of the fame cotton, tie it to the end of the prime Condudor ; then let the winch of the ma- chine be turned, and the lock of cotton, on being eledlrified, will immediately fwell, by repelling its filaments from one another, and will ftretch itfelf towards the neareft Con- dudlor. In this fituation let the winch be kept turning, and prefent the end of your finger, or the knob of a wire towards the
to one of the points of the fly, this will move again briflc-
ly : and by altering the pofition of your finger occafion-
ally round the glafs, you may continue its adion a con-
fiderable time, vi%, till moft of that part of the glafs is !l|
charged. In this cafe, when the finger is applied on the
outfide of the receiver, the glafs lofing part of its natural
eledric fluid from the outfide (/. e. if the fly is eledlrified
pofitively, or vice verfa^ if negatively) receives the fluid
of the electrified air on its infide furface ; hence this air is
put in a ftate of being again eledrified by the point of the
fly, which renews the motion of the fly,
T 3 lock
278 A COMPLETE TREATISE
lock of cotton, which will then immediately move towards the finger, and endeavour to. touch it; but take with the other hand a pointed needle, and prefent its point towards the cotton, a little above the end of the fin- ger, and you will obferve the cotton immedi- ately to fhrink upward, and move towards, the prime Conductor.- — Remove the needle, and the cotton will come again towards the finger.- — Prefent the needle, and the cotton will fhrink again ; which clearly fhows, that the needle, being fharp pointed, draws off the eleftric fluid from the cotton, and puts it in a ftate of being attraded by the prime Conduftor, which could not be efteded by a wire having a blunted end, or. a round ball for its termination.
Experiment V.
T^he eleBrified Bladder.
Take a large bladder well blown, and cover it with gold, filver, or brafs leaf, flicking it with gum-water ; fufpend this bladder at the end of a filk thread, at leaft fix or feven feet long hanging from the ceiling of the room, and electrify the bladder, by giving it a
flrong
OF E L E C T R I C I T ¥• 27^
flrong fpark with the knob of a charged bottle ; this done, take a knobed wire, and prefent it to the bladder when motionlefs ; and you will perceive, that as the knob ap-» proaches the bladder, the bladder alfo moves towards the knob, and when nearly touching it, gives it the fpark, which it received from the charged phial, and thus it becomes un- ele6lrified. Give it another fpark, and, in- ftead of the knobed wire, prefent the point of a needle towards it, and you will perceive that the bladder will not be attracled by, but rather recede from the point, efpecially if the needle be very fuddenly prefented to- wards it. This is one of Mr. Henly's ex- periments.
Before we proceed to the practical ufe of pointed Conductors to buildings, in order to defend them from lightening, which is nothing more than the proper application of the preceding experiments, it w^ill be proper to fay fomething in explanation of the above property of points, the caufe of which has occafioned feveral controverfies. In order to this, it fhould be remembered, that the dedric fluid, fuperinduced upon an infulated
T 4 hodjy
iSo A COMPLETE TREATISE
body, is confined upon that body by the air, which furrounds it ; further, that Eledricity, by being continually communicated to the air, which is never a perfedt eledric, is gradually diffipated, from whence follows this very evident principle, /• e. that as a greater or lefs quantity of air is contiguous to a given quantity of eleftrified furface, fo that furface lofeth its Electricity fooner or later. Suppofe for inftance, that a pointed needle is fixed upon the prime Conduftor ; mark a dot upon any part of the prime Condudlor, which may be nearly equal to the point of the needle, and then ele£lrify the prime Con- ductor. Now it is evident to bare infpection, that although the point of the needle, and the dot, &c. are of equal furfaces, yet the forriier is expofed to a quantity of air, which almoft entirely furrounds it, and which is vaftly greater, than the air contiguous to the latter ; hence, the Eledricity, communicated to the prime Conductor, is diffipated more eafily from the point of the needle, than from the dot, or any other part of the prime Conduc- tor. Befides, the air about the point may more eafily be moved, in confequence of the electrical repulfion, than at any other part
of
OF ELECTRICITY. ^ti
of the furface of the prime Condudor, and new air, /. e. uneledrified air, pafles more frequently by it, which taking always part of the Eledricity of that body promotes alfo its diffipation.
In the fame manner may be underftood, why the Electricity is more eafily diffipated at fharp edges and corners, than at flat ones ; for as the furfaces of bodies in general are more or lefs plain, fo they are expofed to a lefs or greater quantity of air, and participate more or lefs of the nature, and properties of points.
When the pointed body is negatively elec- trified, it is for the fame reafon, that it ac- quires the ele£tric fluid through the point, eafier, than through any other part of its furface ; /. e. becaufe the point exhibiting the leaft furface to the greateft; quantity of free air, has the greateft number of particles of air, from which it can extrad the eledric fluid ^.
* For a more particular explanation of the the above- mentioned property of points, fee Beccaria's Artificial Eledricity.
EXPE-
282 A COMPLETE TREATISE
Experiment VI. .
The Thunder^houfe.
Fig. I of Plate II is an inftrument repre- fenting the fide of a houfe, either furnifhed with ^ metallic Conductor, or not; by which both tlie bad effeds of lightening ftriking upon a houfe not properly fecured, and the ufefulnefs of metallic Conductors, may he clearly reprefented. A is a board about three quarters of an inch thick, and fhaped like the gable-end of a houfe. This board is fixed perpendicularly upon the bottom board B, upon which the perpendicular glafs pillar C D is alfo fixed in a hole about eight inches diftajit from the bafis of the board A. A fquare hole I L M K about a quarter of an inch deep, and nearly one inch wide, is made in the board A, and is filled with a fquare piece of wood, nearly of the fame di- menfions. — I mention, nearly of the fame dimenfions, becaufe it muft go fo eafily into the hole, that it may drop off, by the leaft fhaking of the inftrument, A wire L K is fattened diagonally to this fquare piece of
wood.
OF ELECTRICITY. 283
wood. Another wire I H of the fame thick- nefs, having a brafs hall H, fcrewed on its pointed extremity, is faftened upon the board A ; fo alfo is the wire M N, w^hich is (haped in a ring at O. From the upper extremity of the glafs pillar CD, a crooked wire pro- ceeds, having a fpring focket F, through which a double knobed wire flips perpen- dicularly, the lower knob G of which falls juft above the knob H. The glafs pillar D C muft not be made very faft into the bottom board ; but it muft be fixed fo as it may be pretty eafily moved round its own axis, by which means the brafs ball G may be brought nearer or farther from the ball H, without touching the part E F G. Now when the fquare piece of wood LMIK (which may reprefent the fhutter of a window or the like) is fixed into the hole fo, that the wire L K ftands in the dotted reprefentation I M, then the metallic communication from H to O, is complete, and the inftrument reprefents a houfe furnifhed with a proper metallic Con- ductor ; but if the fquare piece of wood LMIK is fixed fo, that the wire L K ftands in the diredion L K, as reprefented in the
figure,
284 A COMPLETE TREATISE
figure, then the metallic Condudor HO, from the top of the houfe to its bottom, is interrupted at I M, in which cafe the houfe is not properly fecured.
Fix the piece of wood L M I K, fo that its wire may be as reprefented in the figure, in which cafe the metallic Condud:or HO is difcontinued. Let the ball G be fixed at about half an inch perpendicular diftance from the ball H, then, by turning the glafs pillar D C, remove the former ball from the latter ; by a wire or chain conned the wire E F with the wire Q^of thejar P, and let another wire or chain, fattened to the hook O, touch the outfide coating of the jar. Conned the wire Qj/vith the prime Condudor, and charge the jar; then, by turning the glafs pillar DC, let the ball G come gradually near the ball H, and when they are arrived fufficiently near one another, you will ob- ferve, that the jar explodes, and the piece of wood L M I K is pufhed out of the hole to a confiderable diftance from the thunder- houfe. Now the ball G, in this experiment, reprefents an eledrified cloud, which when it
is
I
OF ELECTRICITY. 285
is arrived fufficiently near the top of the houfe A, the Electricity ftrikes it, and as this houfe is not fecured with a proper Conductor, the explofion breaks part of it, /. e. knocks off the piece of wood I M.
Repeat the experiment with only this vari- ation, viz. that this piece of wood I M is futated fo, that the wire L K may ftand in the iituation I M ; in which cafe the Con- du<3:or H O is not difcontinued ; and you will obferve, that the explofion will have no effed upon the piece of wood L M ; this re- maining in the hole, unmoved ; which fhows the ufefulnefs of the metallic Conductor.
Further ; unfcrew the brafs ball H from the wire H I, fo that this may remain pointed, and with this difference only in the apparatus repeat both the above experiments ; and you will find that the piece of wood I M is in neither cafe moved from its place, nor any 'explofion will be heard, which not only de- monftrates the preference of Condudors with pointed terminations to thofe with blunted ones, but alfo fhows that a houf^, furnifhed with fharp terminations, although aot fur- nifhed
286 A COMPLETE TREATISE
nifhed with a regular Conduftor, is almofi fufEciently guarded againft the effects of lightening.
To prove farther the preference of pointed Conductors to bkmt ones, the experiment of the eledrified cotton {viz. the fourth experi- ment of this chapter) may be eafily repeated with this apparatus^ by which it may be fhown, that a pointed Conductor, filcntly drawing off the eledric fluid from the fmall clouds near it, which are reprefented by the cotton tied to the wire of the ball G, repels them, and may thus in fome cafes, perhaps^ actually prevent a ftroke of lightening, where- as the blunted Conductor facilitates it. Small feathers may alfo be tied near the knob d which, by repelling one another, may exhibit a better reprefentation of an eledrified cloud ; and in fhort, with a little contrivance, the above- defcribed apparatus, commonly called the thunder -^houfe^ may be adapted to reprefent the principal phenomena of lightening, toge- ther with feveral circumftances preceding^ or following it<
CHAP.
O F E L E C T R I C I T Y. 2S7
CHAP. X.
Medical EleSlrkity.
WHEN we mentioned the ufes of Eledricity in the Firft Part of this Treatife, we obferved that Eleftricity had been found beneficial in many diforders, oc- cafioned by obftru£tions, in which a promo- tion of the infenfible perfpiration, and of glandular fecretion was neceffary, or an ad- ditional impetus required to be given to the common courfe of the fluids in the human body. We alfo confidered the different opi- nions relating to this fubjeft ; in this chapter therefore, nothing remains but to defcribe a pradtical method of applying Elec- tricity to the human body, when affefted with different diftempers.
The promotion of the infenfible perfpira- tion is produced by fimple electrification ; a patient therefore, on whom this effed: is to be produced by Eledricity, fhould be in- fulated in the mofl convenient fituation, and by being conneded with the prime Conduc- 2 tor
288 A COMPLETE TREATISE
tor of the machine, he fliould be kept elec- trified as long, and often, as his phyfician: may think proper. Shocks in this cafe, and even fparks, fhould be avoided ; for though they may not be actually injurious, yet they are by no means pleafmg fenfations j efjpecial- ly to a fick perfon.
In cafes of partial obftrudions, as rheu- matifm in the knees, fhoulders, &c. ftrong Iparks may be drawn from the afFeded part, and fometimes fmall 'Ihocks may be very proper*
In fome cafes, w^here fliocks may be thought neceffary, they fhould be confined to that part only, which is affeded with the diforder, and fhould never be too flrong; a number of fmall fhocks (as for inftance, from a half-pint phial fully charged) having been found to be more beneficial, than large ones. In order to confine the fhock to one part of the body only, as for inftance to the knee, tie a wire or a chain round the legt a little below the knee, and put another chain round or in contad with the thigh, a little above the knee j laftly conned one of 4 thefe
OF ELECTRICITY, 289
thefe chains with the outfide coating of the jar, and tie the other to one of the wires of the difcharging rod. Now, when the jar is charged, if you bring one knob of the difcharging rod, near the knob of the jar, the fliock wnll be fent through the knee, as defired. The wives may alfo be faftened on each fide the knee, by filk firings, afiid the fhock fent from one fide of it to the other, if needful. If the quadrant elec- trometer is fixed upon the prime Condu6lor, and the Operator obferves to difcharge the jar always when the Index Is arrived to a given degree, the fhocks will be precifely of ' the fame ftrength.
A very ufeful Inftrument to cure the
tooth-acht is reprefented fig, 6, Plate 11.
It confifts of two wires A E, BE, fixed
in two holes in the piece of baked wood
H. Thefe wires from C to D, and G
to F are bended in a plane Inclined to
the reft of the wires ; their extremities D E,
- F E, being again bended towards one ano-
■ther, and in the plane of C A G B. The
'extremities A B of the wires are bended la
a ring, Wheq this inftrument is to be ufed,
U it
290 A COMPLETE TREATISE
it muft be applied in fuch a manner, that the afFeded tooth may be embraced pretty firmly by the two wires at E, which being flexible, may be adjufted fo as to receive teeth of different fizes ; then the end A, or B of one of the wires, by means of a chain or a wire, muft be connected with the out- fide of a charged jar, and the end of the other wire with the knob of the jar, fo as to make the fhock pafs through the wires of the inftrument, and in confequence through the tooth. A fingle fliock, fent through an af- fected tooth in this manner, will often cure it inftantaneoufly ; it is however proper to fend always two or three fhocks through it.
CHAP^
OF ELECTRICITY. 291
CHAP. Xh
Experiments with the eleSlrical Battery.
The force of accumulated Electricity, great as it appears by the experiments performed with a fmgle coated jar, is very fmall whea compared with that, which is produced by a number of jars connetled together ; and if the efFefts of a fmgle jar are furprifmg, the prodigious force of a large battery is certain- ly aftonifhing. To obferve that the metals, even the moft purified platina, which refifts •the greateft efforts of chemic fire, are a6lual- ly, and almoft inftantaneoufly rendered red- hot, and fufed : to fee animals deftroyed, and to hear the loud report of a large elec- tric battery, are things that always produce a kind of terror in the mind of an attentive obferver. Experiments of this kind fhould be conducted with great caution, and the Operator ought to be attentive, not only to the bufinefs in hand, but alfo to the per- fons, who may happen to be near him, pro- hibiting their touching^ or even coming too uear any part of the apparatus ; for if a
U 2 miftake
292 A L Q M P L E T E TREATISE
miftake in performing other experiments m^y be difagreeable, thofe in the difcharge of ^ Jarge battery may be attended with worfe confequences#
When a battery is to be charged, jnftead pf a large prime Condu(5lor, a fmall one i§ much more corjivenient ; for, in this cafe, the diflipation of the Ele<3;ricity is not fo confiderable. The quadrant elecflrometefii which {hows the height of the charge in the; battery, may be fixed either upop the prime Condudor, or upon the battery, in whicl^ latter cafe, it fhould be placed upon a rod proceeding from the w^ires of the jars, and if the battery be very large, it fhould be elevated two or three feet above them*
The index of the eleftrometer in charging a large battery will feldom rife fo high fis 90°, becaufe the machine cannot charge a bat- tery fo high in proportion, as a fingle jar. Its limit is often about 60^ or 70^, more or jefs in proportion to the fize of the battery, and the force of the machine.
EXPE-
8t liLtC f tl C It Y. 293
fexpERIMElSit li
^Ae melt JVires.
Cohried: witK the liook, communicating "ivith the oiitfide coating of a battery, con- taining at leaft thirty fqiiare feet of coated furface, a witei that is about drie fiftieth ][)art of ah inch thick, ahd about two feet long j the other end of it muft be faftened to one 6nd of the difcharging rod j this done, charge the battery; arid then by bringing the difcharg- ing rod healr its wires, fend the explofidn through the fniall wire, which, by this means, will bd made red-hot, And melted, fo as to fall upon the floor in different glowing pieces. When a wire is melted in this man- ner, fparks are frequently feen at a confide- rable diflance from it) which are red-hot particle^ of the metal, that by the violence of the explofiori are fcattered iri all dire£hion$. If the force of the batter;^ is very greatj; i^he wire will be intirely difperfed by the ^xplofion, fo that none of it can. be after- wards found* ^
Us H
29+ A COMPLETE TREATISE
By repeating this experiment with wires of different metals, and the fame force of ex- plofion, it will be found that fome metals are more readily fufed than others, and fome not at all effeded ; which fhows the difference of their condudling power. If it be required to melt fuch particles of metals, that cannot eafily be drawn in wires, as ores, grain gold, &c. they may be fet in a train upon a piece of wax ; this train may be inferted in tlie circuit, and an explaiion may be fent through it^ which, if it is fufficiently ftrong, will melt the im^e tall ic particles, as well as the wires : or, if the quantity to be tried be large enough, it may be confined in a fmall tube of glafs.
la rmeking wires x)f a confid^i^aible length, it is often obferved that when the force of the explofion is juft fufficknt io rendj^g; tl^e wire red-hot, the rednefs begins firfl: frojn one end of -it, namely that which communicates with the pofitive fide of the battery, and from thepce gradually proceeds to the other end. This is another oculai- demonftr^tion of the theory of a fingle eledlric fluid. .; -
4
If
OF ELECTRICITY.
295
If a wire is ftretched by weights, and a fhock is fent through it, which renders it juft red-hot, the wire, after the explofion, will be found confiderably lengthened. If a wire is melted upon a piece of glafs, the glafs, after the explofion, will be found marked with all the prifmatic colours*
Experiment IL
"To Jhow that the eleBric Fluid prefers a Jhort PaJJage through the Air^ to a long one through good ConduBors.
Bend a wire about five feet long in the form reprefented by fig, 1 1, Plate II, fo that the parts A, B may come within half an inch of one another ; then conne£l the extremi- ties of the wire with the hook of the battery, and the difcharging-rod, as diredled in the preceding experiment, and fend the charge of a battery through it. On making the ex- plofion a fpark will be feen between A and B, which fliows that the eledlric fluid choofes rather a fhort paflage through the air, than the long one through the wire. The charge however, does not pafs intirely through A
U 4 and
29^ A COMPLETE TREATISE
and B, but part of it goes alfo through the wire, which may be proved by putting a flender wire between A and B; for on mak- ing the difcharge with only this addition in the apparatus, the fmall v/ire will be hardly made redr-hot, whereas if the large wire A D B be cut in D, fo as to difconti- nue the circuit A D B, the fmall wire will be melted, and even exploded by the fame fhock, that before made it fcarcely red-hot. In this manner (fays Dr. Priestley, who is the inventor of this experiment) may the conducing power of different metals be tried, ufmg metallic circuits of the fame length and thicknefs, and obferving the difference of the palfage through the air in each.
Experiment III.
"To make Globules of Metals.
Take a very flender wire, and put it in a glafs tube, about one quarter of an inch in diameter ; then fend the charge of a battery through it, and the wire will be melted, and reduced in globules of different fizes, which are found flicking on the infide furface of the glafs tube, and they may be eafily fepa-
rated
OF ELECTRICITY, 297
rated from it at pleafure: thefe, upon exami- nation, will all be found hollow, and are little more than a mere fcoria of metal.
It muft be obferved in making this experi- ment, that the charge of 'the battery muft neither be too high, nor too weak ; for in the former cafe the wire will be reduced in pieces exceedingly fmall, or rather exploded in fmoak, and in the latter cafe it will be im- perfedly fufed, fo that its pieces will be large, and irregular.
Experiment IV.
"The Fairy Circles.
Fix upon each of the knobs DD of the univerfal difcharger, fig. 5, Plate I, or upon the wires that fupport the knobs, if the knobs are removed, a flattifh, and fmooth piece of metal, or femi-metal (watch-cafes are very fit for this purpofe), fo that their furfaces may come fo near each other, that the battery may be difcharged through them ; then connedl one wire of the difcharger v/ith the outfide of the battery, and the other wire, by the help of the difcharging rod, with the infide of it,
fo
298 A COMPLETE TREATISE
fo as to make the difcharge, which will occafion the fpot, and circles defcribed in the Firft Part of this Treatife, upon the furface of each of the pieces of metal fixed upon the difcharger.
Thefe circles have hitherto been exhibited upon the furface of no other fubftances but metals, and they are found to be marked more diftinctly upon fuch metals, as melt with the leaft heat. The -moft beautiful of thefe rings are produced by a number of dif- charges from a large battery, every part of the apparatus remaining exactly in the fame fituation. If the pieces of metal receive the explofion in vacuo, the fpot formed on them is very irregular, and confufed.
I Jhave given tt^efe ipot^ the ' appellation of Fairy Cirjcles^ on account that they bear fome refemblance to the fpots fo called, wjiicji are often obfcrved upon the grafs in th^e fields, Thefe, which we may call natural Fairy Circles in the fields, it has been thought to be effe£led by lightening, on account of their bearing fome refemblance to the above-men- tioned circles produced by Eledricity ; the
fuppofition.
OF ELECTRICITY. 299
fuppofition, however, feems not very proba- ble ; for the fpots in the fields, called Fairy Circles, have no central fpot, no concentric circles, neither are they always of a circular figure ; and, as I am informed, they feem to be rather beds of mufhrooms, than the effeds of lightening.
ExPERIxMENT V,
To mark coloured Rings on Metals.
In order to exhibit coloured rings upon tlhe furface of metals, place a plain piece of any of the metals upon one of the wires of the univcrfd difcharger, and upon the. other wire fix a fharp-pointed needle with the point jufl: oppofite to the furface of the metal ; then connect one wire of the difchatger with the
outfide of a battery, and the other with the
.... .J,
difcharging-rod, &c- In this manner, if ex- plofions are repeatedly ient either from the point to the piece, of metal, or from the latter to the:f©i2mery t^LcyfwiHigradual}^^ mark the furface. 06 the piece cxf metals oppofite to the point, ;mth circles confiiting of all the prif- matic colours ; which are evidently occafion-
ed
3C0 A GOMPLEfE I^REATISE
ed by lamina; of the metal, raifed by the force of the explofions.
Thefe colours appear fooner, arid the fiiigs are clofer to one another, when the point is nearer to the furface of the metal. The num- ber of rings is greater orlefs, according as the point of the needle is more fharp or more blunt ; and they are reprefented equally well upon any of the metals.
The point of the heedle h alfo coloured to a confiderable diftance, the colours upon it returning in circles^ though not very diftinfl- ly. This is an experiment of Dr. Priest- ley.
Experiment VL
Tie Rarthquakei
The appearance of the earthquake, as f e-- prefented with the explofion of a battery, is cccalioned by the concuflion given to fe veral fubftances by the explofion palling over their furfaces. To give a reprefentation of the impreflion made upon houfes by the earth- quake, fmall fticks, cards, or the like may be I piaeed
P F ELECTRICITY. 3or
placed upon the furface of the body, oyer -^hich the exploijon is to be traofmitted, fq a,s to ftand very light. Thefe flicks, &c, y/ill never fail to be Ihook; and often be thrown dowfi by the e^plofipn.
It is remarkable that an explofion will not pafs over the fame length of furface of all bodies, though jthey are equally good Con- jdudlors. Water, ice, wet wood, raw fle/b, and moft of the animal fluids, are the beft to njake thi^ remarkable ejcperin^ent; to do which nothing more is required, than to infert part of the furface qf the faid ful^ftances into the cjrcuit of the two fides of a battery ; a chain for inftar^ce communicating with thp outfide, njay be placed fq as nearly tq touch the fur- face of a quantity of w^ater, and at B.\>Qut eight or nine inches diftant * from another chain, fituated alfo very near the furface of the water, and communicating with one end of the dil- charging-rod. If the ends of the chains touch the water, the experiment will happen in the farne manner.
^ The diftance, at which an explofion will ftrike over the furface of the above-mentioned fubftances is much greater, than that it can ftrike through in air only.
The
ff-^.
302 A COMPLETE TREATISE
The report. In this experiment, is much louder than when the explofion pafles through the air only. The concuffion given to the water by the explofion pafling over its furface, is not only fuperficial, but afFeds its whole body ; and if the hand is kept deep under its furface, whilfl: the explofion pafTes over it, the concuffion may be very fenfibly felt.
The fpark, that In this experiment pafles over the furface of the water, feems to bear a great refemblance to the balls of fire, that have fometimes been feen over the furface of the fea, or land, in time of an earthquake ; and hence it feems very probable, that thofe balls of fire arc.eledrical phenomena.
CHAP.
OF ELECTRICITY. ^oj
CHAP. XIL
Promifciious Experiments.
Experiment I.
T^o JIdow that Smoak^ and the Vapour of hot Water are Conductors.
LE T a cork ball ele6lrometer be luf- pended about four or five feet above the prime Conductor, then turn the winch of the machine very gently, and you will find, that the balls of the electrometer will not diverge. Put upon the prime Conduc- tor a wax taper * juft blown out, fo that its fmoak may afcend to the cle£trometer ; then turn the winch again, and the balls of the eledlrometer will immediately feparate a little with the fame force of Eledtricity from the prime Conductor : which fhows that fmoak is a Conductor in a fmall degree.
* A green wax taper is the beft for this experiments
In
•.9-'' '■
3P4r
A COMPLETE TREATISE
In the fame manner, by placing a fmall veflel with hot water upon the prime Con- ductor, inftead of the wax taper, it may be proved, that its vapour is alfo a Conduftor ; but inferior in itsi conducting power, to the fmoak. This experiment is an invention of Mr. He>jly.
EXPEIIIMENT IL
7'a prove that Glafs and other EleSirics become QonduSiorSy when they are made very hot.
Take a fmall glafs tube of about oqe twentieth of an inch in diameter, and above a foot long ; clofe it at one end, and in,- troduce a wire into it, fo that it may be extended through its whole length : let two or three inches of this wire project above the open end of the tube, and there faften it with a bit of cork ; tie round the clofed end of the tube, another wire, which will be feparated from the wire within the tube only by the glafs interpofed between thera* In thefe circumflances endeavour to fend a ihock through the two wires, /. e. the v^ire
in-
OF ELECTRICITY. 305
inferted in the glafs tube, and that tied on its outfide, by connecting one of them with the outfide, and touching the other with the knob of a charged jar, and you wull find that the difcharge cannot be made, unlefs the tube be broken ; becaufe the circuit is interrupted by the glafs at the end of the tube, which is interpofed between the two , wires. But put that end of the tube, to which the wire is tied, into the fire, fo that it may become juft red-hot, then ^en- deavour to difcharge the jar again through the wires, and you will find that the explo- fion will be eafily tranfmitted from wire to wire, through the fubftance of the glafs, which, by being made red-hot, is become a Conduftor.
In order to afcertain the conducing qua- lity of hot refinous fubftances, oils, &c. bend a glafs tube in the form of an arch C E F D fig. 7, Plate II ; and tie a filk ftring G C D to it, which ferves to hold it by, when it is to be fet near the fire; fill the middle part of this tube with rofin, fealing- wax, &c. then introduce two wires A E, B F through its ends, fo that they may
X touch
3c6 A COMPLETE TREATISE
touch the rofin, or penetrate a little way in it. This done, let a perfon hold the tube over a clear fire, fo as to melt the rofin within it ; at the fame time, by connediing one of the wires A, or B with the outfide of a charged jar, and touching the other with the knob of the jar, endeavour to make the difcharge through the rofin, and you will obferve that, while the rofin is cold, no fliocks can be tranfmitted through it; but. it becomes a Conductor, according as it melts, and when totally melted, then the fhocks will pafs through it very freely.
Experiment III.
To/bow that hot Air is a Conduct or.
Eledrify one of the cork-ball electrome- ters, fufpended upon the ftand fig. 4 of Plate I, or eledrify the prime Condudlor with the quadrant ele6lrometer ; then bring a red- hot iron within a fufficient diftance of the eledlrometer or prime Condudor, and you will find that they fopn lofe their Eledricity, which is certainly conduded by the hot air contiguous to the iroa j for if the expe- riment
OF ELECTRICITY^ 307
riment be repeated with the lame iron, when cold, /. e. by bringing it within the fame diftance of the electrified Electrometer or prime Conductor, their EleCtricity will not be conducted away as before.*
The above experiments may reafonably induce us to fufpeCt, that feveral fubftances, which are ranged among Conductors, would become eleCtrics if they were brought into a colder temperature ; and that all the elec- trics become Conductors, when they are heat-* ed in a very high degree.
* It has been often obferved, that a battery may be ,
difcharged by introducing a red-hot iron between tv^o knobs interpofed, and ftanding at fome diftance from each other in the circuit : but if, inftead of iron, there be introduced a piece of i^ed- hot glafs between the knobs, (the diftance between them remaining as at firft) the battery cannot be difcharged : whence we may infer that either hot air is not fo good a Condudlor as has been imagined, or elfe, that air heated. by iron (perhaps from its ignited particles) is ftronger with refpect to its con- du(£ting power, than when heated by the red-hot glafs. |
X 2 ExPE-^
308 A COMPLETE TREATISE
Experiment IV.
To ekcirify the Air of a Room.
The air furrounding the electrical ma-» chine when in ufe, and contiguous to every highly electrified body, always acquires a portion of Eledricity, which it retains for a confiderable time. A very expeditious method, however, to eledrify the air, is to fix two or three needles upon the prime Conductor, and to keep it ftrongly eledtri- fied for about ten minutes- If afterwards an electrometer be brought into the air fur- rounding the apparatus, it will plainly {how that the air has acquired a confiderable quantity of EleCtricity, which it will retain even after the apparatus has been removed into another room. To eleCtrify the air ne- gatively, conneCl the pointed needles with the rubber when infulated ; and make a com- munication by a chain or wire, from the prime Conductor to the table.
Another method of electrifying the air, \z to charge a large jar, and infulate it :
• then
OF ELECTRICITY. 309
then connect a fharp-pointed wire, or a number of them, with the knob of the jar ; and make a communication from the outfide coating to the table. If the jar be charged pofitively, the air of the room will foon become ftrongly eleftrified pofitively like- wife : but if the jar be charged negatively, the air will become alfo negative. A charg- ed jar being held in one hand, and the flame of a candle infulated, and held in the other, being brought near the knob of the jar, will alfo foon produce the fame ef- fed.
ExPERIxMENT V.
T!he Atmofphere of Smoak.
Take a brafs ball or any piece of metal that is free from points or edges, of about three or four inches diameter, and infulate it upon a narrow ele6lric ftand ; then give it a fpark with the knob of a charged phial, and immediately prefent to it a wax taper juft blown out and fmoaking, The fmoak in this cafe will be attracted by the eledrified body, and by encompaffing that
X 3 body.
310 A COMPLETE TREATISE
body, will form a kind of atmofphere about it* This atmofphere will remain for a few fcconds, and afterwards, beginning from the bottom, will gradually vanifh, until at laft, intirely departing from the electrified -body, it goes off in a flender column, that foon rarefies, and diffufes itfelf into a confiderable fpace.
This experiment will not fucceed unlefs it be made in very dry weather, and in a room, where the air is not agitated : care muft alfo be taken, that in blowing out the taper, and prefenting it to the electrified body, the air be difturbed as little as pof- fible.
This phenomenon has induced fome phi- lofophers to fuppofe, that the EleClricity of &n electrified body, refided about it, /. e. refted upon its furface like an atmofphere, which, they thought, v^^as made very evident by the fmoak. But this appearance, when duly confidercd, is far from proving any fuch eleCtric atmofphere, and the caufe of it may be very eafily explained in the fol- lowing manner. The fmoak is attraCled by
the
OF ELECTRICITY, 311
the eleftrified body in the fame manner, and for the fame reafon, that other bodies are at- trafted by it. It remains fufpended about that body, and cannot all come into contadt with its furface, on account of the elafticity of its particles. It remains fo long fufpend- ed about the electrified body, and is not im- mediately repelled, becaufe it is a bad Con- ductor, and acquires Electricity very flowly ; but having acquired a fufficient quantity of Electricity, it begins to quit the eleClrified body, and afcending in the air, extends itfelf into a large fpace, in confequence of the repulfion exifting between its own eleCtrified , particles.
Experiment VI. -
ToJIjew that Metals conduSi the eleSiric Fluid through their Suhjiance.
Take a wire of any kind of metal, and cover part of it with fome eleCtric fubftance, as rofin, fealing-wax, &c. then difcharge a iar through it, and it will be found, that it conducts as well with, as without the eleClric coating. This proves that the elec-
X 4 trie
21% A COMPLETE TREATISE
trie fluid pafles through the fubftance of the metal, and not over its furface. A wire con- tinued through a vacuum is alfo a convincing proof of the truth of this obfervation.
Experiment VII.
^&e deSiriJied Cup and Chain.
Infulate a metallic cup, or any other con- cave piece of metal ; and place within it a pretty long metallic chain, having a filk thread tied to one of its ends. To the han- dle of the cup, or to a wire proceeding from it, fufpend a cork-ball ele6lrometer ; then cle£trify the cup by giving it a fpark with the knob of a charged phial, and the balls of the eledrometer will immediately diverge. If, in this fituation, one end of the chain be gradually raifed up above the top of the cup, &c. by the filk thread, while the lower end of the chain remains in it, the balls of the ele6lrometer will converge a little ; and more or lefs in proportion to the elevation of the chain above the top of the veflcl ; which proves that the Electricity of the cup and chain together is more denfe^
when
OF ELECTRICITY. 313
when thefe bodies are in a compad, than when they are in a more extended form. A more eafy method to fhew this property of Electricity, is that ufed by T. Ronayne, Efq. which is- as follows : He excites a long flip of white flannel, or a filk ribband^ by rubbing it with his fingers ; then by ap- plying his hand to it, takes off as many Iparks B^ the excited ele6tric will give ; but when tUe flannel, &c. has loft the power of giving any more fparks in this manner, he doubles, or rolls it up ; by which operatioa the contracted flannel, &c. appears fo ftrong- ly eledrical, that, it not only gives fparks to the hand brought near, but ir throws out fpontaneous bruflies of light, which appear very beautiful in the dark.
Experiment VIII.
Tojbow the Courfe of the eleSlric Fluid by the Flame of a Wax-taper.
Fix at that extremity of the prime Con- ductor, which is the remoteft from the ma- chine, a brafs rod fix inches long, having on its extremity a brafs ball about three- fourths
.4
314 A COR4PLETE TREATISE
fourths of an inch in diameter, and let the winch of the machine be moved. If in this fituation the flame of a wax-taper be pre- fented to the above-mentioned brafs ball, it will be blown almoft horizontally, and in a dire6lion from the ball, that is, in the di- re6lion of the eled:ric fluid. If a wire with a like ball be fixed to the infulated rubber, the flame of a wax-taper, prefem^^^to this ball, will be blown alfo in the dirtction of the €le&ic fluid, that is, it will be blown upon the ball, fhowing the true courfeof the ele6:ric fluid in a very fimple and convincing manner.
Experiment IX*
T'o jhow the eleSlric AttraBion^ and Repulfion by the eleSlric Lights
Fix a pointed wire upon the prime Con- ductor, with the point outward, and ano- ther like wire upon the infulated rubber; then let the winch of the machine be turned, and the points of both wires will appear illuminated, viz. the former with a brufh, and the latter with a fl;ar. In this fituation,
take
OF ELECTRICITY. 315
take an excited glafs tube, and bring it fide- way of the point of the wire fixed upon the prime Conduftor, and you will fee, that the brufh of rays ilTuing from the point, is turned fideway, /. e. is repelled by the at- mofphere of the tube ; and if the excited tube be held juft oppofite to the point, the brufh will intirejy vanifh, becaufe both the tube and the point are ele6lrified pofitive- ly. If the excited tube be brought near the point of the wire fixed upon the rubber, the ftar upon it will turn itfelf towards the tube ; for this wire, being electrified nega- tively, will attrad theelcdric fluid of the ex- cited tube.
If this experiment be repeated with an excited fl:ick of fealing-wax, or any other ' electric, negatively ele6lrified, inftead of the glafs tube, it will be found, that the brufh proceeding from the wire fixed upon the prime Condudor, will turn itfelf towards the excited wax, &c. and the flar upon the point of the wire negatively eledrified, will be diverted from it, or intirely fuppreffed, if the excited ftick of fealing-wax be brought jufl oppofite to the point.
EXPE-
3i6 A COMPLETE TREATI SE
Experiment X.
I'/je ele^rtfied Capillary Syphon.
Let a fmall bucket of metal, full of water, be fufpended from the prime Condudlor, and put in it a glafs fyphon of fo narrow ex- tremity, as the water will juft drop from it. If in this difpofition of the apparatus the winch of the machine be turned, the water, which, when not eledrified, only dropt from the extremity of the fyphon, will now run in a full ftream, which will even be fubdivided into other fmaller ftreams ; and if the experiment be made in the dark, it will appear beautifully illu- minated.
Experiment XL
T/je eleElriJied Bells.
Fig. lo of Plate II, reprefents an inftru-
ment . having three bells, which are caufed
to ring by the power of eledric attraction
and repulfion. B is a brafs piece furnifhed
4 with
OFELECTRICITY. 317
with a hook, by which It may be fufpend- ed from the rod proceeding from the extre- mity of the prime Condudtor A. The two bells C, and E are fufpended by brafs chains, but the middle bell D, and the two fmall brafs clappers between C D, and D E, are fufpended by filk threads. From the con- cave part of the bell D a brafs chain pro- ceeds, which falls upon the table, and has a filk thread F at its extremity. The appa- ratus being difpofed as in the figure, if the cylinder of the machine be turned, the clap- pers will fly from bell to bell with a very quick motion, and the bells will ring as long as they are kept ele6trified.
The two bells C and E, being fufpended by brafs chains, are firft eledtrified, hence they attra6l the clappers, communicate to them a little Eledlricity, and repel them to the unele6lrified bell D, upon which the clap- pers depofit their Eledlricity, and then run again to the bells C, E, from which they acquire more Eledlricity, &c. If by holding the filk thread F, the chain of the middle bell be raifed from the table ; the bells, after ringing a little while, will flop, becaufe the
bell
3i8 A CO M PLETE TREATISE
bell D remaining infulated, will foon become as ftrongly eledrified as either of the other two bells, in which cafe the clappers, hav- ing no opportunity to depofit the Eledri- city that they acquire from the bells C, E, muft confequently flop.
If this experiment be made in the dark, fparks will be feen between the clappers and the bells.
Experiment XII.
Hhe Spider feemingly animated by Ele^ricity.
Fig. 9 of Plate II, reprefents an eledric jar, having a wire C D E fattened on its outfide, which is bended fo as to have its knob E, as high as the knob A. B is a fpider made of cork with a few fhort threads run through it, to. reprefent its legs. This fpider is faftened at the end of a filk thread, proceeding from the ceiling of the room, or from any other fupport, fo that the fpider may hang mid-way between the two knobs A, E, when the jar is not charged. Let the place of the jar upon the 2 table
OF ELECTRICITY. 319
table be marked; then charge the jar by bringing its knob A in conta6l with the prime Condu6tor, and replace it in its marked place. The fpider will now begin to move from knob to knob, and continue this mo- tion for a confiderable time, fometimes for fe- veral hours.
The infide of the jar being charged po- fitively the fpider is attracted by the knob A, which communicates to it a fmall quan- tity of Electricity ; the fpider then be- coming poflefled of the fame Ele6lricity with the knob A, is repelled by it, and runs to the knob E, where it difcharges its Ele6lricity, and is then agaih attracted by the knob A, and fo on. In this manner the jar is gradually difcharged ; and when the dif- charge is nearly compleated, the fpider fi- nilhes its motion.
Experiment XIII.
The Spiral Tube.
Fig. 13 of Plate II, reprefents an inftru- ment compofed of two glafs tubes C D, one
within
320 ACOMPLETETREATISE
within another, and clofed with two knobed brafs caps A, and B. The innermoft of thefe tubes has a fpiral row of fmall round pieces of tin-foil, ftuck upon its outfide fur- face, and laying at about one thirtieth of an inch from each other. If this inftru- ment be held by one of its extremities, and its other extremity be prefented to the prime Conductor, every fpark that it receives from the prime Condu£lor, will caufe fmall fpark to appear between all the round pieces of. tin-foil ftuck upon the innermoft tube, vsrhich in the dark affords a pleafing fpefta- cle ; the inftrument appearing encompafled by a fpiral line of fire.
The fmall round pieces of tin-foil are fometimes ftuck upon a flat piece of glafs A B C D fig. 12, fo as to reprefent curve lines, flowers, letters, &c. and they are il- luminated after the fame manner as the fpiral tube ; i. e. by holding the extremity C, or B in the hand, and prefenting the other extremity to the prime Conduftor, when the machine is in motion.
EXPE-
OF ELfiCTRICITY. 321
Experiment XIV*
T!he dancing Ballso
Fix a pointed wire upon the prime Con^ Hudlor, with the point outward ; then takd a glafs tumbler, grafp it with your hands, and prefent its infide furface to the point of the Wire upon the prime Condudlor, while the machine is in motion ^ the glafs in this manner will foon become charged; for its infide farface acquires the EIe£lricity from the point, and its outfide lofes its natural quantity of eledtric fluid through the hands, which ferve as a coating,— This done put a few pith balls upon the table and cover them with thig charged glafs tumbler. The balls will immediately begin to leap up along the fides of the glafs, as reprefented fig. 15, Plate II, and will cdntinue their motion for a confiderable time.
In this experiment the pith balls are at- tracted and repelled by the ele£tric fluid fuperinduced upon the infide furface of the glafs, which they gradually conduct to the
Y table
322 A COMPLETE TREATISE
table or other condudling body upon which the glafs is fet ; at the fame time that the outward furface of the glafs acquires the eleftric fluid from the contiguous air.
CHAR
OF ELECTRICITY. 323
CHAR XIII.
Farther Properties of the Leyden Phial^ or
charged Ele5lrics.
TH E properties of charged eledrics, plain as they may appear at firft fight, and conformable to the commonly eftablifh- ed theory of Electricity, are yet, when at- tentively confidered, far from being intirely imderftood, fo as to require no further expe- riments, or leave no doubt in the mind of the fpeculative Electrician. The firft quef- tion, that naturally occurs, in confidering a charged phial, is where does the fuperin- duced ele£tric fluid refide ? — Is it lodged in the fubftance of the glafs, or in the air con- tiguous to the furface of the phial ? In the firft cafe, if the eleCtric fluid penetrates a certain quantity of the fubftance of the glafs, it follows that a glafs plate may be given fo thin, that the eledtric fluid may freely pervade its fubftance*. If fuch a
plate
* I have often blown glafs balls, fo thin that then thicknefs was lefs than one-fix hundredth part of an inch,
Y 2 and
y.\ A COMPLETE TREATISE
plate can be made, it will be eafy , from thence, to determine how far can the electric fluid penetrate the fubllance of the glafs, when charged in the ufual manner. In the fecond cafe, if the eledric fluid refides in the air contiguous to the glafs, it muft repel that air^ /. e. a glafs bottle fliould contain lefs air when charged, than when in its natural ftate j but this is contrary to experience.
The late Mr. Canton charged fome thin glafs balls of about an inch and a half la diameter, having tubes of about nine inches in length, and afterwards fealed them her- metically. If thefe balls, when they were cold, were prefented to an eledrometer, they fliewed no fign of Ele£tricity ; but if they were kept a little while near the fire, they then appeared ftrongly eledrical, and pof- fefled of that kind of Electricity, with which their infide had been charged. Mr. Canton difcovered farther, that if thefe balls are kept under water, they retain their virtue
and have always obferved, that they were capable of re- ceiving a charge, which they retained for a confiderabl^ ^imci if they were liot made very hut,
for
OF ELECTRICITY. 325
for a confiderabk time, even for feveral years ; but if they are often ufed, their powir is foon exhaufted. It is obvious to remark, that the Electricity, which appears upon the outfide of thefe balls, when they are rendered hot, /. e. when the glafs is Tendered a Conductor by the heat, is not that Electricity, which properly conftitutes the charge, but the fuperfluous Eiedricity of their infide*.
As for the Electricity, which conftitutes the charge, it being juft fufficient to balance the contrary EleCtricity of the oppofite fur- face of the glafs, it will lofe its power, as foon as it is arrived to that furface, which in the cafe of the above-mentioned
* If a charged jar be infulated, and difcharged with an infulated difcharging rod, after the difcharge both the fides of the jar, together with the difcharging rod, will be found polTeiied of the Electricity contrary to the Electricity of that fide of the jar, which was touched laft before the difcharge ; which (hows that one fide of a charged elec- tric may contain a greater quantity of Elecftricity than that, which is fufficient to balance the contrary Elec- tricity of the oppofite fide. This redundant Electricity (hould be carefully confidered in perforn^ing experiments gf '^delicate nature.
Y 3 balls.
326' A COMPLETE TREATISE
balls, it actually reaches, before it can hQl Upon the eledrometer.
The moft remarkable phenomena pro- duced by charged electrics, are exhibited with flat plates of glafs, jointly charged, like a fingle coated plate. If two glafs plates, having plain furfaces, be placed one upon the other, and their outward furfaces be coated with tin-foil, in the ufual manner of coating a fingle plate for the Leyden ex- periment, and then be charged, by prefent- ing one coating to the prime Conductor, and communicating the other with the earth, the plates (which we Ihall call A, and B) after having been charged, will adhere very firmly to one another, and if feparated. A, viz. that, whofe coating was prefented to the prime Condudor, will appear pofitive on both fides, and B negative on both fides. If thefe plates are laid in contact as before they were charged, and are difcharged by making a communication between the two coated fides, they will be found ftill to ad- here to one another after the difcharge, and if feparated, they will appear ftill elec- trified, but with this remarkable difference,
viz.
OF ELECTRICITY. 327
^z. that now A is negative on both fides, and B pofitive on both fides. If thefe plates, after being difcharged, be feparated in the dark, flafhes of light are perceivable between their internal furfaces. By laying the plates together, touching their coatings and feparating them fucceffively, the flafhes may be obferved for a confiderable number of times, diminifhing by degrees, until they quite vanifh^
Father Beggaria explains thefe and other fimilar phenomena of charged, as well as of excited eledrics by the following princi- ple, which he diftinguifhes by the name of 'vindicating EkSiricity. When two bodies, cither a Conductor, and an eleftrified ele6lric, or two contrarily and equally eledrified elec- trics are joined together, they adhere to each other, and their Electricities difappear; but as foon as they are feparated, the electrics re- cover their Eledlricities*. How far this prin- ciple can be of ufe to explain the phenome- na of charged glafs, &c. I will not take upon me to determine. It would exceed
* See Beccaria's Artificial Electricity, Part. II. fee. VI. Y 4
too
328 A COMPLETE TREATISE '
too far the limits of my work, if I were to enumerate, and account for all the particu- lars. When the principle is exprefled, the ingenious reader may eafily apply it to ex- plain the efFeds. I -iihall only mention an obfervation of Mr. Henly relative to this fubjeft, which feems not conformable to Father Beccama's theory, and with that I fhall conclude this part of my work. Says Mr. Henly in one of his papers prefented to the Royal Society, in which he defcribes the above-mentioned experiments of the two glafs plates, " Crown-glafs, that is ^^ the glafs commonly ufed for fafh win- *' dows, though fo much thinner, fucceeds *' in this experiment as well as the plate- *' glafs ; but what is very remarkable, the ^* Dutch plates, when treated in the fame *^ manner, have each a pofitive and nega- *' tive furface, and the Eledricitv of both fur- *' faces, of both plates, is exchanged for the ^* contrary Eledricity in the difcharge. If a '' clean, dry, uncoated plate of looking-glafs be placed between the coated looking-glafs plates, or between the plates of crown- ** glafs, it appears, after charging, to be ne- ^' gatively eleftrified on both fides ; but if it
' • ^^bc
i6
OF ELECTRICITY. 329
f * be placed between the Dutch plates, it ac- f^ quires, like them, a pofitive Eleftricity on 5' one furface, and a negative Ele£lrjicity oiii ** the other.'*
In another paper, Mr. Henly further obferyes, that if the Dutch plates are fepa- rated immediately after being charged, they will then ad like two plates of looking- glafs, /. e. one of them will be pofitive, and the other negative on both fides; but if . a little time be allowed before the plates be feparated, the experiment will conftantly fuc- ceed as above.
PART,
330 A COMPLETE TREATISE
PART IV.
New Experiments in EleSiricify.
TH E laws of Eleflricity, together with the experiments neceflary for their demonftration, having already been defcribed, in as compendious a manner as could be done, without obfcurity, I fhall in the lafl Part of this work relate fuch new experi- ments, and obfervations, as I have made during the courfe of about two years, in which time I have purfued the Science of Electricity with a particular view to difco- ver, if poffible, the unknown caufe of fe vera! eledrical phenomena, efpecially thofe relative to atmofpherical Eledlricity.
The firft inftrument that I made ufe of, to obferve the Eledricity of the atmofphere, was an electrical kite, which I had conftruCted, not with a view to obferve the Electricity of the air, for this, I thought, was. very weak and feldom to be obferved ; but as an inftru- ment, which could be occafionally ufed in
time
OF E L E C T R I C I T Y. 331
time of a thunder-ftorm, in order to obfervc the Eledricity of the clouds. The kite how- ever being juft finifhed, together with its firing, which contained a brafs wire through its whole length, I raifed it the 3 ift^f Auguft 1775, at feven of the clock in the afternoon, the weather being a little cloudy, and the wind juft fufficient for the purpofe. The ex- tremity of the (Iring being infulated, I ap- plied my fingers to it, which, contrary to my expectation, drew very vivid, and pun- gent fparks : I charged a coated phial at the firing feveral times ; but I did not then ob- ferve the quality of the Eleilricity, This fuccefsful experiment induced me to raife the kite very often, and to keep it up, for feveral hours together, thinking that if any periodi- cal Eledricity, or any change of its quality took place in the atmofphere, it might very probably be difcovered by this inilrument. In the following two Chapters I (liall defcribe the conftrudion of the electrical kite VvMth its appurtenances, and fhall tranfcribe the m.ofl remarkable part of my journal, relative to the kite, /. e. defcribing fuch experiments only, which are more remarkable, and do not hap- pen very commonly ; for although I have
ufed
33^ A COMPLETE TREATISE
ufed my kite, fometimes ten, and more times in a week, and at any hour of the day or jiight, yet as the greateft part of thofe experi^ ments are only of life to confirm a few laws of atmofpherical Eleftricity, I fhall leave their particular detail, and fhall only fubjoin thofe laws at the end of the fecond chapter.
CHAP-
OF ELECTRICITY. 333
CHAP. I.
the confiruSlion of the eleSirical Kite, and other Injiruments ufed with it.
THE firft eledrical kite, that I con- ftrufted, was feven feet high, and it ; was made of paper with a ftick or ftraiter, I and a cane bow, like the kites commonly ufed j by fchool-boys. On the upper part of the I ftraiter I fixed an iron fpike, projeding about I a foot above the kite, which, I then thought, was abfolutely necefTary to collect the Elec- tricity, and I covered the paper of the kite with turpentine, in order to defend it from
11, the rain. This kite, perfedt as I thought it pto be, in its conftrudion, and fit for the expe- riments, for which it was intended, foon S manifefted its imperfedtions, and after being raifed a few times, it became quite unfit for farther ufe; it bein*^ fo large, and confe- quently heavy, that it could not be ufed, except when the wind was ftrong, and then after much trouble in raifing and drawing it in, it often received fome damage, which foon obliged me to conflrudt other kites upon a different plan, in order to afcertain which I method
334 A COMPLETE TREATISE
method would anfwer the beft for my pur- pofe. I gradually leflened their fize, and varied their form, till I obferved upon trial, that a common fchool-boy's kite, was as good an eleftrical kite as mine. In confe- quence of which I conftrudted my kites in the moft fimple manner, and in nothing dif- ferent from the childrens kites, except that I covered them with varnilh, or with well boiled linfced oil, in order to defend them from the rain, and I covered the back part of the ftraiter with tin-foil, which however has not the leaft power to increafe its Eledricity. I alfo furnifli the upper extremity of the ftraiter with a flender wire pointed, which, in time of a thunder-ftorm, may perhaps draw the Electricity from the clouds, fomewhat more effedually ; but in general, I find, as it will appear in the account of the experi- ments, that it does not in the leaft affedt the Ele6lricity at the ftring. The kites, that I generally have ufed, are about four feet high, and little above two feet wide. This fize, I find, is the moft convenient, becaufe it renders them eafy to be managed, and at the fame time they can draw a fufficient quantity of ftring. As for filk or linen kites, they require a good 3 deal
OF ELECTRICITY, 335
deal of wind to be raifed, and then they arc not fo cheap nor fo eafy to be made, as paper kites are. The firing fometimes breaks, and the kite is loft, or broken, for which reafon, thefe kites fhould be made as cheap and as fimple as poffible.
The firing is the moft material part of this apparatus ; for the Eled:ricity produced is more or lefs, according as the ftring is a bet- ter, or a worfe Conductor. The ftring, which I made for my large kite, confifted of two threads of common twine twifted together with a brafs wire between the ftrands. This ftring ferved very well for two, or three trials, but on examination, I foon found that the wire in it was broken in many places, and it was continually fnapping; the metallic continuation therefore being fo often inter- rupted, the ftring became foon fo bad, that it aded nothing better than common twine without a wire. I attempted to mend it, by joining the broken pieces of wire, and work- ing into the twine, another wire, which proved a very laborious work ; but the remedy had very little effect ; the wire breaking again after the firft trial, which determined me to
adopt
336 A COMPLEX £TREATISi:
adopt other methods ; and after feveral experi« ments, I found that the heft ftring was one^ which I made by twifting a copper thread '^ with two very thin threads of twine. Strings like this I have ufed for the greateft part of my experiments with the kite, and I find theni to be exceedingly ufeful^ and fit for the pur- pofe. Silver or gold thread would do much better, to twifl: with the twine, becaiife they are much thinner than copper thread, and iri confequence the ftring would be much lighter; but at the fame time it is to be confidered, that gold or filver thread is much dearer than copper thread.
»
I have attempted to render the twine d good Conductor of Electricity, by covering it with conducing fubftances, as lamp-blacky powder of charcoal, very fine emery, and other fubftances, mixing them with diluted gum-water ; but this method improves the ftring very little, and for a very fhort time ; for the faid conducing fubftances are fooni
* I mean fuch a thread of copper as is ufed for trim- mings, &c. in imitation of gold threads^ \A?hich are nothing more than filk or linen threads covered with a thin lamina ©f copper.
rubbed
OF ELECTRICITY. 337
rubbed ofF of the twine. Mr.NAiRNE inform- ed me, that he had ufed to foak the firing of his eledrical kite in a flrong folution of fait, which rendered it a good Condu6lor, fo far as it attrad:ed the moifture of the air. In confequence of this information I foaked in fait w^ater a long piece of tw^ine, and by raif- ing a kite with it, I found that it condu6led the Ele6lricity pretty well, but I thought it much inferior to the above-defcribed firing with the copper thread : befides, the falted firing in wet weather not only leaves part of the fait upon the hands of the Operator, and In confequence renders them unfit to manage the refl of the apparatus, but it marks a white fpot w^herever it touches the clothes.
In raifing the kite when the weather is very cloudy and rainy, in which time there is fear of meeting with great quantity of Eledlricity, I generally ufe to hang upon the firing A B fig. 8, Plate II, the hook of a chain C, the other extremity of which falls upon the ground. Sometimes I ufe another caution befides, which is to fland upon an infulating llool; in which fituation, I think, that if any great quantity of Eledricity, fuddenly dif-
% charged
338 A COMPLETE TREATISE
charged by the clouds, ftrikes the kite, it can-^ not afFed: much my perfon. As to infulated reels, and fuch like inftruments, that fome gentlemen have ufed for to raife the kite, ^without danger of receiving any lliock ; fit for the purpofe as they may appear to be in theory, they are yet very inconvenient to be managed. Except the kite be raifed in time of a thunder-ftorm, there is no great danger for the Operator to receive any lliock. Al- though I have raifed my ele6lrical kite hun- dreds of times without any caution v^diatever, I have very feldom received a few exceedingly flight fhocks in my arms. In time of a thunder-ftorrii, if the kite has not been raifed before, I would not advife a perfon to raife it while the ftormy clouds are juft overhead ; the danger in fuch time being very great, even with the precautions above mentioned : at that time, without raifmg the kite, the Eleftricity of the clouds may be obferved by a cork ball Electrometer held in the hand in an open place, or if it rains, by my eledtro- meter for the rain, which will be defcribed hereafter.
When
OF ELECTRICITY. 339
When the kite has been raifed, I generally introduce the firing through a window in a room of the hoiife, and fallen it to a ftrong filk lace, the extremity of which is generally tied to a heavy chair in the room. In fig. 8, bf Plate III, A B reprefents part of the firing of the kite, which comes within the room j G reprefents the filk lace; DE, a fmall prime Conductor, which, by means of a fmall wire, is connected with the firing of the kite ; and F reprefents the quadrant electrometer fixed upon a (land of glafs, covered with fealiilg- wax, which I ufed to put near the prime Con-* dudlor, rather than to fix it iri a hole upon the Condud:or, becaufe the firing A B fometimes jfhakes fo as to pull tHe prime Coridudtof dovv'n, in which cafe the quadrant eledroiiie- ter remains fafe upon the table, otherwife it would be broken, as I have often experienced before I thought of this method. G repre- fents a glafs tube about eighteen inches long, with a knobed wire cemented to its extremity, which inftrument I ufe for to obferve the quality of the Electricity, vvhen the Eledlri- city of the kite is fo ftrong, that I think it hot fafe to come very near the firing. The
Z 2 method
340 A COMPLETE TREATISE
method is as follows I hold the inftrument by that extremity of the glafs tube, which is the fartheft from the wire, and touch the ftring of the kite with the knob of its wire, which being infulated, acquires a fmall quan- tity of Eledricity from it, which is fufhcient to afcertain its quality w^hen the knob of the inftrument is brought near an eledrified elec- trometer. Sometimes, when I raife the kite in the night time, out of the houfe, and where I have not the convenience of obferv- ing the quality of its Eledricity by the at- traction and repulfion, or even by the appear- ance of the electric light, I make ufe of a coated phial, which I can charge at the ftring, and when charged, put into my pocket, wherein it will keep charged even for feveral hours*. By making ufe of this inftrument,
I am
* The conftruflion of this phlal is as follows. BeHdes the coating on the infide and outfide that this phial has, like any other of the fame kind, a glafs tube open at both ends is cemented into its neck, and proceeds within the phial, having a fmall wire faftened to its lower extremity, which touches the infide non-eleclric coating. The wire with the knob of this phial is cemented into another glafs tube, which is nearly twice as long, and fmaller tten the
tub«
OF ELECTRICITY. 341
I am obliged to keep the kite up no longer than it is neceflary to charge the phial, in order to obferve the quality of the Ele6tricity in the atmofphere ; for after that the kite has been drawn in, and brought home, I can then examine the Eledtricity of the infide of the phial, which is the fame as that of the kite.
When the Eledlricity of the kite is very ftrong, I fix a chain, communicating with the ground, at about fix inches diftance from the firing, which may carry off its Eleftri- city, in cafe, that this fhould increafe fo much, as to put the byftanders in danger.
tube cemented into the neck of the phial. The wire Is cemented fo, that only its knob projefls out of one end, and a fmall length of it out of the other end of the tube. If this piece with the wire be held by the middle of the glafs t^be, it may be put in or out of the tube, which is in the neck of the phial, fo as to touch the fmall wire at the lower extremity of it, and that without difcharging the phial, if it is charged, I have kept fuch a phial charged for fix weeks together, and probably it would keep much longer, if it were to be tried. The ingenious young Elec- trician may make ufe of fuch a phial for feveral diverting purpofes.
Z 3 Befides
342 A COMPLETE TREATISE
Befides the above-defcribed apparatus, I have occafionally ufed fome other inflru- ments, which I have often varied, according as fome particular experiments required*; but as they are of no great confequence, I ihall omit to defcribe them. It is only neceffaryi before I enter into the narration of the princi- pal experiments performed with the kite, to give ah idea of the- ftandard of my quadrant electrometer, which may, very probably, Ihew the fame intenfity of Ele6:ricity under a nilmber of degrees different from the other inftrument of the fame kind. When the kite is flying, and the apparatus is difpofed as in fig. 8, of Plate III, I bring, under the extremity E of the prime Conductor, a little bran, held upon a tin plate, and obferve, that when the index of the electrometer is at ten degrees, the prime Conductor begins to attra6t the bran at the diftance of about* three fifths of an inch, when the index is at twenty degrees, the prime Condudlor attrads the bran at the diftance of about one inch and a quarter, when the index is at thirty degrees, the bran begins to be attrad at the diftance of two inches
and
O F E L E C T R I C I T Y. 343
and one fifth. Thefe diftances vary as the weather changes its degree of drynefs, but in frofty weather^, I obferve them conftantly as above.
Z 4 CHAR
•
344 A COMPLETE TREATISE
CHAP. IL
Experiments performed with the electrical
Kite.
Eptember the 2d, 1775- The weather being very cloudy, and aftually rain- ing, the kite was railed at eight o'clock P. M. with two hundred yards of firing, which had a brafs wire through its whole length. The wind was from the fouth and very ftrong. The Electricity at the ftring was negative, and juft fufficient to charge a half-pint phial fo as to give a fhock fen- fible to the elbows. The kite, after being up for about one hoijf., fell to the ground, having its paper, which was not properly varnifhed, almoft intirely torn off by the violence of the wind and the rain.
September the 14th. The kite was
raifed with a ftrong north wind at half paft
three P. M. The Eledricity was pofitive,
and pretty ftrong, the index of the eleftro-
3 meter
OF ELECTRICITY. 345
meter being generally about 20^*. The weather was rather cold, and very thick clouds were gradually approaching the ze- nith. The kite was pulled down at half paft four P. M.
N. B. At night the aurora borealis was very ftrong, and feveral flafhes of lighten- ing were feen near the horizon towards the north.
September the 23d. A fmall kite was raifed at half paft ten o'clock in the mornings and it was kept up for eleven hours fuc- ceffively, viz. till half paft nine P. M. The ftring, which was only a common twine without a wire, was conftantly elec- trified pofitively although in a very fmall degree. About nine o'clock the Electricity appeared ftronger, fo that a fmall phial, charged at the ftring, gave a pretty fenfible fhock. The weather was very clear, and
♦ The index of the eleftrometer in general raifes higher or falls lower, according as the kite comes nearer to, or goes farther from the zenith 3 the length of the ftring remaining the fame.
warm J
346 A COMPLETE TREATISE
warm ; but in the night no aufora borcalis, or any other ele<3:rical appearance was per- ceived* The wind was eaft by fouth, and fo weak that the kite was kept up with great difficulty*
0<3:ober the loth, 1775- The weather being clear, and the wind blowing ftrong from the fouth weft, the kite was raifed at eleven o^clock A. M. with ninety yards of firing, which had a copper thread twifted in*^. The wind, during the experiment, increafed and decreafed feveral times, and the Eleftri- city, which was pofitive, as it appeared by the index of the Eledtrometer, alfo increafed and decreafed. At noon the violence of the wind caufed the kit? to fall. At half paft four o'clock, the wind being a little more moderate, the kite was raifed again. The Electricity was alfo pofitive, and feemed ra- ther ftronger than it had been in the morn- ing. The weather at this time was cloudy j the clouds appearing much thicker near the horizon, than about the zenith. The kit^
* Such {Irino; as this was ufed in all the following ex- periments.
OF ELECTRICITY. 347
was pulled down at half paft five o'clock^ and at half after feven was raifed again ; every phenomenon continuing the fame. At eight o^clock, while I was pulling the kite in, I infulated the firing when only thirty- five yards of ir were out, and was fur- prifed to find that now the Ele6lricity was as flrong as it had been, when all the firing was out, which wa3 ninety yards long. It mufl: hov/ever be remarked that at this time a few flalhes of lightening were feen among the clouds, which vv^ere pretty thick about the horizon. At a quarter paft eleven o'clock, the kite was raifed again, which was the fourth time of raifing it that day ; the weather then being very clear, and the wind the fame as in the afternoon. The Eledtricity was very weak, but conftant- ly pofitive. The kite was pulled down aftep having being up a few minutes only.
Odober the i6th. At about two P. M. a thick fog being juft cleared up, the wea- ther became clear, and the wind began to blow from the fouth fouth wxft. The kite was raifed with on© hundred and twenty yards of ftring, and it was kept up no
longer
348 A COMPLETE TREATI SE
longer than a quarter of an hour. The Eledricity was pofitive and pretty ftrong ; the index of the eledirometer being about 15^. At half paft three o'clock the kite was raifed again, the weather being very little cloudy. At half paft four o'clock the clouds became very thick, and in a fhort time began to rain, which increafed the Elec- tricity of the kite v.athout changing its qua- lity ; the index of the electrometer arriving to 20^. The kite was pulled down at five o'clock.
0£lober the i8th. After having rained a great deal in the morning and night before, the weather became a little clear in the afternoon, the clouds appearing feparated, and pretty well defined. The wind was weft, and rather ftrong, and the atmofphere in a temperate degree of heat. In thefe circumftances at three P. M. I raifed my electrical kite with three hundred and fixty feet of firing. After that the end of the ftring had been infulated, and a leather ball, covered with tin-foil, had been hanged to it, I tried the power, and quality of the Elec- tricity, which appeared to be pofitive and
pretty
OF ELECTRICITY. 34,
pretty ftrong. In a fhort time a fmall cloud paffing over, the Eledricity increafed a little ; but the cloud being gone, it decreafed again to its former degree. The firing of the kite was now fattened by the filk lace to a poft in the yard of the houfe, wherein I live, which is fituated near Iflington, and I was repeatedly charging two coated phials, and giving fhocks with them ; — while I was fo doing, the Eledricity, which was Hill pofitive, began to decreafe, and in two or three minutes time it became fo weak, that it could be hardly perceived with a very fenfible cork ball ele£tr6meter. Obferving at the fame time that a large and black cloud was approaching the zenith (which, no doubt, caufed the decreafe of the Eledricity) indicating imminent rain, I introduced the end of the firing through a window, in a firfl floor room, wherein I fattened it by the filk lace to an old chair. The quadrant eledrometer was fet upon the fame window, and was, by means of a wire, conneded with the ftrlng of the kite. Being now three quarters of an hour after three o'clock, the Eledricity was abfolutely unperceivable ; however in about three minutes time it be- came
550 A COMPLETE TREATISE
came again perceivable, but now upon trial was found to be negative; it is therefore plain that its flopping was nothing more than a change from pofitive to negative, which was evidently occafioned by the ap- proach of the cloud, part of which by this time, had reached the zenith of the kite^ and the rain alfo had began to fall in large drops.-^The cloud came farther on ; — the rain increafed, and the Electricity keeping pace with it, the electrometer foon arrived to 15^. Seeing now, that the Eledricity was pretty ftrong, I began again to charge the two coated phials, and to give fhocks with them ; but the phials had not been charged above three or four times, before I perceived that the index of the eledlrometer w^as arrived to 35^, and was keepirig ftill increafmg. The fliocks now being very fmart, I defifted from charging the phials any longer, and confidering the rapid ad- vance of the Eledricity, thought to take off the infulation of the firing, in cafe that if it ihould increafe farther, it might be filently conduced to the earth, without caufing any bad accident by being accumulated in the infulated firing. To effedt this, as I had I no
OF ELECTRICITY. 351
no proper apparatus near mej I thought to remove the filk lace, and faften the firing itfelf to the chair ; accordingly I difengaged the wire that connected the eleftrometer with the firing ; laid hold of the firing ; un- tied it from the filk lace, and faflened it to the chair ; but while I efFeded this, which took up lefs than half a minute of time, I received about a dozen, or fifteen very* flrong fhocks, which I felt all along my arms, in my breafl, and legs; fhaking me in fuch a manner, that I had hardly power enough to effe£l my purpofe, and to warn the people in the room to keep their diflance. As foon as I took my hands off the firing, the Electricity (in confequence of the chair being a bad Conductor) began to fnap between the firing and the fhutter of the window, which was the nearefl body to it. The fnappings which were audible at a good dillance out of the room, feemed firfl ifochronus with the fhocks, which I had re- ceived, but in about a minute's time, oftner, fo that the people of the houfe compared their found to the ratling noife of a jack going v/hen the fly is off. The cloud now v/as jufl over the kite; it was black, and
w^ell
352 A COMPLETE TREATISE
well defined, of almoft a circular form, its diameter appearing to be about 40^; the rain was copious but not remarkably heavy. As the cloud was going off, the electrical fnapping began to weaken, and in a fhort time, became unaudiable. I went then near the ftring, and finding the Eleftriclty weak, but ftill negative, I infulated it again, thinking to keep the kite up fome time longer ; but obferving that another larger, and denfer cloud was approaching apace towards the zenith, and I had then no proper apparatus at hand, to prevent every poffible bad acci- dent, refolved 10 pull the kite in ; accord- ingly a gentleman, who was by me, began pulling it in, while I was winding up the firing. The cloud was now very nearly over the kite, and the gentleman, who was pulling in the firing, told me, that he had received one or two flight fhocks in his arms, and that if he were to feel one more, he would certainly let the firing go, upon which I laid hold of the firing and pulled the kite in as fafl as I could, without any farther obfervation ; being then ten minutes after four o'clock.
N.B.
OF ELECTRICITY.
353
N. B. There was neither thunder or lightening perceived that day, nor indeed for fome days before or afterwards.
November the 8th, 1775. The wind being north \l^ftj and juft fufficient, the kite was raifed at three quarters paft eleven A. M. with one hundred and twenty yards of firing. The Ele£lricity was pofitive and weak ; the weather being cloudy. At noon the clouds grew thicker, and the Ele£tricity quite vanifhed ; however in a few feconds it returned, and from this time it evidently kept increafing and decreafmg, according as the clouds became thinner or thicker. At forty minutes after one o'clock the Eleftricity vanifhed again ; a thick cloud then covering almoft the whole hemifphere ; but as a little rain began to fall, the Electricity re- turned, and it was ftill pofitive. At three quarters paft three o'clock the clouds began to grow thin, and the Electricity increafcd a little ; but at this time I was obliged to pull the kite in. The index of the electrometer in this experiment feldom arrived to 6^.
A a ' No-
354 A COMPLETE TREATISE
November the i6th. The weather being very clear and frofty, the kite w^as raifed at a quarter paft ten A. M* with one hun- dred and twenty yards of firing. The Elec- tricity was pofitive and pretty ftrong, the index of the electrometer g^ng from 9^ to 15^, raifing as the wind blew ftronger, and the kite was more elevated, and vife verfa. At a quarter paft three o'clock the wind, which was north north weft, intirely failing, the kite fell.
November the 17th. The weather being exceedingly damp, and the fog fo denfe, that the houfes at about a quarter of a mile diftance could not be diftinguifhed, the kite was raifed at two P. M. with one hundred and ten yards of ftring, while it was rain- *ing, but very little. The Eledricity was pofitive, and fo weak that the cork balls of an electrometer diverged about three quarters of an inch. The wind being very violent I was obliged to pull the kite in, after having been up for about live minutes.
De-"
OF ELECTRICITY. 355
December the 5th. 1775. The weather being equally cloudy, and the wind weft by north, and hardly fufficient, the kite was raifed at a quarter paft three P. M. with one hundred and twenty yards of ftring. The Eledlricity was pofitive and fo weak, as to caufe the cork balls of an ele6lrometer to diverge about an inch. At a little after four o'clock the kite was pulled in ; and at eight o'clock in the evening it was raifed again. At this time the Ele6lricity was much ftronger than in the after- noon, but conftantly pofitive. The weather clearing up, the clouds were driven away by the wind, which was now a little ftronger than in the afternoon. At forty minutes after eight o'clock the fky was clear, the moon and ftars appearing very bright ; except that a few thin clouds were yet to be feen near the horizon. The index of jhe eledtrometer was now going from 15^ to 20^. At ten mi- nutes after nine o'clock the kite was drawn in.
A a 2 N. B.
356 A C O M P I, E T E TREATISE
N. B. No aurora borealis was to be feen.
December the 20th. The weather being cloudy and hazy, the kite was raifed at three quarters after ten o'clock A, M. with one hundred and forty yards of ftring. The Eleftricity was pofitive and pret- ty ftrong, the index of the eleftrometer going from 16^ to 21^. At half paft one, P* M. the weather growing a little clearer, I pulled the kite down, and after having interpofed a filk ribband between its loop and the extremity of the ftring, fo as to infulate the kite, I raifed it again with the fame length of ftring, and after I had infulated the lower extremity of the ftring, I obferved that the intenfity of the Electricity, as it appeared by the index of the eleClrometer, was, as nearly as could be determined, the fame as before, /. e. when the kite was not infulated with refpe£l to the ftring.
At two o'clock P. M. 1 pulled the kite
down, and found upon obfervation, that the
filk ribband had contraded na moifture, fo
4 that
OF ELECTRICITY. 3^7
that the kite was perfedly infulated by It. This experiment of infulating the kite I have often repeated at other times, and have always met with the famefuccefs ; hence it appears, that it is the firing and not the kite, which in general c6lle£ls the Elediricity from the air. The kite therefore in ge- neral is only ufeful to extend the firing high into the open air.
January the 4th, 1776. The froft hav- ing been very hard during the day and night before ; the wind began to blow very ftrong from the fouth at two o'clock A. M. which occafioned a fudden thaw and a co- pious rain. At eight o'clock A. M. in which time the kite was raifed, the hemifphere appeared like a uniform dark canopy, under which feveral fmall, irregular, and darker clouds were running very faft ; the rain was conftant, but^ not remarkably heavy. As foon as the firing of the kite was in- fulated, the Eledricity, which was negative, began to fnap from it, to the flmtter of the window and other bodies near ; the index of the eledrometer arrived to 40^. and it would have certainly gone farther, if the ap-
A a 3 paratus
358 A COMPLETE TREATISE
paratus had been drier ; but the air was fo damp, that it was almofl impoffible to keep any part of the apparatus fufficiently free from moifture. The Ele6lricity however, gradually decreafed, fo that at ten o'clock A. M* at which time the kite was pulled in, the index of the electrometer w^as at a lit- tle above 12^. The coated phials in this experiment were charged furprilingly quick; three or four feconds of time being fuffi- cient to charge two half-pint phials com- pletely.
January the i ith. The ground was covered
with ice and fnow, and the atmofphere was
fo hazy, that the houfes at a mile diftance
could not be perceived. The wind was fouth
eaft by fouth, and juft fufficient to raife the
kite, which was raifed at three o'clock P. M.
with one hundred and twenty-four yards
of firing, and kept up till half an hour
after midnight. When the kite was firfl
raifed it began to thaw, but as foon as
it vv^as dark it began to freeze again very
hard. The Electricity was pofitive, and
pretty flrong, the index of the eledrometer
being about I3^* At half paft four o'clock
4 I let
O F E L E C T R I C I T Y. 359
I let out thirty-four yards more of firing, fo that all the firing the kite now had, was one hundred and fifty-eight yards. With this addition of firing the Eleclricity increafed, fo that the index of the electro- meter arrived to 17^. At half after five o'clock the wind began to increafe, and the Ele£lricity to decreafe, until the index of the eledrometer arrived to 6^* At three quarters pad fix o'clock the index of the eledtrometer was about 13^, and at feven o'clock it arrived to 20^ ; the wind being now quite eafl. At one quarter pafl feven o'clock the index of the eledrometer was about 25^. From this time the wind and the Eledlricity began both to decreafe, fo that at nine o'clock the index of the eledrometer was about. 10^. At eleven o'clock the wind in- creafed. At twelve o'clock the wind was very flrong, and the index of the elec- trometer was about 6^. At half pafl twelve o'clock the index of the eledrometer w^as between 3^, and 4^ ; but the wind being grown very violent, the firing broke very near the window, and was loft with the kite.
A a 4 N. Ba
36o A COMPLETE TREATISE
N. B. A few minutes after the kite was loft, it began to fnow copioufly.
January the 26th. The froft being very intenfe as it had been for about three weeks, and adually fnowing, I raifed the kite with feventy yards of ftring ; but before the firing was infulated it ceaied to fnow and the weather began to clear up, and foon became very ferene. The Ele£lricity was pofitive, and very ftrong, the index of the elecirometer being about 32^, At eleven o'clock the ftring broke, and the kite fell, after having been up for above three quarters of an hour.
February the 17th, 1776. The weather being cloudy, rainy, and fo hazy, that the houfes at half a mile diftance could not be difcerned, the kite was raifed at three quar- >ters paft eleven o'clock A, M. with one hundred and feventy-five yards of ftring. The wind was pretty ftrong ; the Electricity was negative, and alfo ftrong, the index of the eledrometer being about 20^. In about five minutes time the rain ceafed, the wind
weakened,
OF ELECTRICITY. 361
weakened, and fhifted a little towards the fouth, and the Electricity changed from ne- gative to pofitive. The index of the elec- trometer was now about 15^. In two or three minutes time it began to rain again, and continued fo for the greateft part of that day ; the wind became very weak, and the Electricity changed again from pofitive to negative, and continued fo till half an hour after noon, at which time the wind be- came fo weak, that I was obliged to pull the kite in.
February the igth. The fky being full of pretty well defined clouds, and the wind weft north weft, the kite was raifed at half paft three o'clock P. M. with one hundred and feventy-five yards of firing. The Elec- tricity was pofitive and ftrong, the index of the electrometer going from 10^ to 20^. At three quarters paft three o'clock a denfe clqud pafTed over the kite, which occafioned the index of the electrometer to defcend to 4^. As . the cloud went away, the elec- trometer elevated its index. At four o'clock the kite was pulled down.
April
362 A COMPLETE TREATISE
April the 8th, I776, The weather was clear and the northern light very ftrong. The kite was raifed for a few minutes at nine o'clock P. M. with one hundred and feventy-five yards of firing ; the wind being north north weft and pretty ftrong. The Elec- tricity was pofitive, and, as I could judge, the index of the electrometer would have arrived to 15^
May the 15th, 1776. The weather being cloudy, and the wind north; the kite was raifed at three o'clock P. M. with one hundred and feventy yards of ftring. The Electri- city was at firft exceedingly weak, and, as I imagine, (for I had not time to examine it) pofitive. But a denfe cloud pafling over the kite, the Eledlricity vanilhed, and as a few drops of rain fell, a very weak nega- tive Electricity appeared, which foon in- creafed, fo as to caufe the index of the eleClrometer to arrive to 15^. The rain however, in a few minutes, ceafed,- and the Electricity gradually decreafed and va- niftied. A very weak pofitive EleCtricity im- mediately took place ; but as another denfer
cloud
OF ELECTRICITY. 363
cloud pafled over, and a few very fmall drops of rain fell, the pofitive Eledricity vaniftied, and the negative took place. The cloud and rain foon went off, and the Electricity became again pofitive, and continued fo till the kite was pulled down. According as the clouds, which pafled continually over the kite, were thinner or thicker, fo the Electricity was more or lefs intenfe, fometimes caufing the index of the electrometer to arrive to 5^, and at other times being fcarce per- ceiveable with the cork ball electrome- ter. At five o'clock the kite was pulled in ; the weather being then pretty clear, and the index of the eleCtrometer at 3^. The wind, during this experiment, was llronger or weaker according as the clouds which pafled over were thicker or thinner. At half paft: feven o'clock in the evening of the fame day, the kite was raifed again, with the fame length of firing, the wind being then rather fi:rong, and the weather pretty clear. The EleCtricity was pofitive, and the index of the eleCtrometer flood at 10^; but as fome clouds came from the north, the EleClricity began to decreafe, and by eight o'clock, it juft feparated the balls of an
eleCtro--
364 A C O M P L E T E T R E A T I S E
electrometer, the hemifpuere being then intirely covered by clouds. At half paft eight o'clock the kite was pulled down, the clouds over the kite being then very thin, and the index of the eledrometer at 5^.
June the 4th, 1776. The weather being cloudy and the wind on the fouth fouth weft, the kite was raifed at one o'clock P, M. with one hundred and feventy yards of ft ring. The Eledricity was pofitive, and the index went from i^ to 7^. At three quarters paft one o'clock the clouds began to be diffipated, and the Eledricity incre'afed a little. At two o'clock the kite was puUed in.
June the 17th. The weather being cloudy, and the wind fouth weft, the kite vv^as raifed at five o'clock P. M. with one hundred and feventy yards of ftring. The Electricity was pofitive, and the index of the eleftrometer w^ent from lo*^ to i6^. In this experiment the clouds, whether thicker or thinner, feemed to have no effed upon the E.ledricity of the kite. At a quarter paft fix o'clock the kite was pulled in.
June
OF ELECTRICITY. 365
June the 20th. The weather being cloudy and the wind eaft, and juft fufficient, the kite was raifed at three quarters paft three P. M. with one hundred and feventy yards of firing. The Eledlriclty was pofitive, and the index of the electrometer flood about 8^. At five o'clock the v/eather began to clear up, and the Eledricity to increafe, fo that in half an hour's time the index of the eledrometer arrived to 17^; and at fix o'clock it flood at 25^. But the wind fuddenly failing about this time, the kite fell.
January the 8th, 1777. The weather being frofly and clear, and the wind north, and pretty flrong, the kite was raifed at four o'clock P. M. with one hundred and feventy yards of firing. The Eleftricity was pofitive and flrong, the index of the eledlrometer being at 36^. The fpark taken from the fmall prime Conductor, was remarkably pungent in this experiment ; although it was hardly a quarter of an inch long. At a quarter pafl five o'clock the kite was pulled in.
Gcjieral
366 A COMPLETE TREATISE
General Laws^ deduced from the Experiments performed with the eleSlrical Kites »
I. The air appears to be eleftrified at all times ; its Electricity is conftantly pofitive, and much ftronger in frofty, than in warm weather^; but it is by no means lefs in the night, than in the day-time f .
II. The prefence of the clouds generally leflens the Electricity of the kite; fometimes it has no efFedt upon it; and it is very feldom that it increafes it a little.
* My obfervations upon the Elecflricity of the atmof- phere, h:ave been made in almoft every degree of tempe- rature, from 15'' to 8c^ of Farenheit's Thermo- meter.
f In all my experiments it happened only once, that the ftring of the kite gave no figns of Eledlricity ; it was one afternoon, when the weather was warm, and the wind fo weak that the kite was raifed with difficulty, and could hardly be kept up for a few minutes ; in the evening however, tlie wind, which in the day-time had been north weft, fhifted to the north eaft, blowing a little ftronger, I then raifed the kite again, being half paft ten o'clock, and obtained, as ufual, a pretty ftrong pofitive Eledri- city,
IIL When
OF ELECTRICITY. 367
IIL When it rains, the Eledricity of the kite is generally negative, and very feldoni pofitive.
IV. The aurora borealis feems not to afFe£l the Electricity of the kite.
V. The eleftrical fpark taken from the firing of the kite, or from any infulated Condudor connected with it, efpecially when it does not rain, is very feldom longer than a quarter of an inch, but it is exceedingly pungent. When the index of the eledrometer is not higher than 20^, the perfon that takes the fpark, will feel the efFed: of it in his legs ; it appearing more like the difcharge of an eledtric jar, than the fpark taken from the prime Conduftor of aneledrical machine.
«
VI. The Ele6lricity of the kite is in gene- ral ftronger or weaker, according as the firing is longer or fhorter, but it does not keep any exad proportion to it ; the Eledricity, for inftance, brought down by a firing of a hundred yards, may raife the index of the eledrometer to 20^, when with
double
368 A COMPLETE TREATISE
double that length of firing, the index of the eledrometer will not go higher than 25^.
^ \^II. V/hen the weather is damp, and the Electricity is pretty ftrong, the index of the eledlrometer, after taking a fpark from the firing, or prefenting the knob of a coated phial to it, rifes furprifingly quick to its ufual place ; but in dry and warm weather, it rifes exceedingly flow.
Thefe few laws are in fhort the deduction of all my experiments performed with the kites, during the courfe of about two years. How far they may be of ufe, or may coincide with the obfervations of other experimenta- tors, I will not pretend to fay. My expe- riments have been performed at Iflington, and perhaps the refult of fimilar ones may be different at other places, efpecially under different climates; I wifh, therefore, that they may be accurately repeated in other places, and their refult may be compared together, in order to determine, if poffible, fomething fatisfadory, relative to the caufe
of
OF ELECTRICITY. 369
of that perpetual Eledricity, which exifts in the atmofphere, and which, very probably, occafions the Eledricity of the clouds.
I'
B b CHAP.
370 A COMPLETE TREATISE
CHAP. III.
Experiments performed with the Atmofpherical Ele£lro?neter^ and the Electrometer for the Rain.
IG. I, of Plate III, reprefents a very limple inftrument, which I have con- trived for the purpofe of making obferva- tions on the Eledricity of the atmofphere, and which on feveral accounts feems to be the mofl: ufeful for that purpofe. A B is a common jointed fifhing-rod without the laft, or fmallefl: joint. From the ex- tremity of this rod proceeds a flender glafs tube C, covered with fealing-wax, and having a cork D, at its end, from which a pith ball eledbrometer is fufpended. H G I is a piece of twine faftened to the other extremity of the rod, and fupported at G by a fmall firing F G. At the end I of the twine, a pin is faftened, which, when pufhed into the cork D, renders the eledrometer E uninfulated.
When
OF ELECTRICITY. 371
When I would obferve the Eledricity of the atmofphere with this inftrument, I thruft the pin I, into the cork D, and holding the rod by its lower end A, project it out from a window in the upper part of the houfe, into the air, raifing the end of the rod with the electrometer, fo as to make an angle of about 50^ or 60^ with the ho- rizon. In this fituation I keep the infl.ru* ment for a few feconds, and then pulling the twine at H, I difengage the pin from the cork D, which operation caufes the firing to drop in the dotted fituation K L, and leaves the electrometer infulated, and elec- trified, with an Electricity contrary to that of the atmofphere. — This done I draw the infl:rument into the room, and examine the quality of the EleCtricity, without obfl:rudion either from wind, or darknefs.
With this infl:rument I have made ob- fervations on the EleCtricity of the atmof- phere, feveral times in a day for feveral months, and from them I have deduced the following general obfervations, which
B b 2 feena
372 A COMPLETE TREATISE
feem to coincide with thofe made with the eledrical kites.
L That there is in the atmofphere at all times a quantity of Eleftricity ; for, when- ever I ufe the above-defcribed inftrument, it always acquires fome Electricity.
II. That the Eledricity of the atmofphere, or fogs, is always of the fame kind ; namely, pofitive ; for the ele£lrometer is always ne- gative, except when it is evidently influenced by heavy clouds near the zenith ; as it appears by the obfervations made the 19th of Odober in the following fpecimcn of the journal.
III. That in general the ftrongeft Eledtri- city is obfervable in thick fogs, and alfo in frofty weather ; and the weakeft, when it is cloudy, warm, and very near raining : but it does not feem to be lefs by night, than in the day.
IV. That in a more elevated place the Electricity is ftronger than in a lower one ; for having tried the atmofpherical electrome- ter
OF ELECTRICITY. 373
ter both in the ftone, and iron gallery on the cupula of St. PauFs Cathedral, I found that the balls diverged much more in the latter, than in the former lefs elevated place ; hence it appears, that, if this rule takes place at any diftance from the earth, the Electricity in the upper regions of the atmofphere muft be exceedingly flrong.
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OF E L E C T R I C I T Y, 375
The ele£lrometer for the rain, in princi- ple, is nothing more than an infulated in- ftrument to catch the rain, and by a pith ball eledrometer to fhew the quantity and quality of its Eledricity.
Fig. 2, of Plate III, reprefents an inftru- ment of this kind, which I have frequently ufed, and after feveral obfervations, have found to anfwer very well. A B C I is a ftrong glafs tube about two feet and a half long, having a tin funnel D E cemented to its extremity, which funnel defends part of the tube from the rain. The outfide fur- face of the tube from A to B is covered with fealing-wax ; fo alfo is the part of it v/hich is covered by the funnel. F D is a piece of cane, round which feveral brafs wires are twifted in different direcftions, fo as to catch the rain eafily, and at the fame time to make no refiftance to the wind. This piece of cane is fixed into the tube, and a flender wire proceeding from it, goes through the bore of the tube, and commu- nicates with the ftrong wire A G, which is thruft into a piece of cork faftened to the
B b 4 end
376 A COMPLETE TREATISE
end A of the tube. The end G of the wire A G, is formed in a ring, from which I fufpend a more or lefs fenfible pith ball elec- trometer, as occafion requires.
This inftrument is fattened to the fide of the window frame, where it is fupported by ftrong brafs hooks at C B, which part of the tube is covered with a filk lace, in order to adapt it better to the hooks. The part F C is out of the window, with the end F a little elevated above the horizon. The re- maining part of the inftrument comes through a hole in one of the lights of the fafh, within the room, and no more of it touches the fide of the window, than the part C B.
When it rains, efpecially in paffing fhow-^ ers, this inftrument, ftanding in the fituation above defcrihed, is frequently eleftrified, and by the diverging of the electrometer, the quantity and quality of the Eledricity of the rain may be obferved, without any danger of a miftake. With this inftrument I have obferved that the rain is generally, though not always, eled:rified negatively, and fometimes fo ftrongly, that I have been
abl^
OF ELECTRICITY. 377
able to charge a fmall coated phial at the wire AG.
This inftrument fhould be fixed in fuch a manner^ that it may be ealily taken ofF from the window, and replaced again, as occafion requires ; for it will be neceflfary to clean it very often, particularly when a fhower of rain is approaching.
I fhall conclude this chapter with the de- fcription of a pocket eleftrometer fig. 5 and 6, of Plate III, that I have lately con- ftrudled, and which on feveral accounts feems preferable to thofe of the moft fenfible fort now in ufe. The cafe, or handle, of this eleiSrometer is formed by a glafs tube about three inches long, and three tenths of an inch in diameter, half of which is covered with fealing-wax. From one extremity of this tube, /. e. that, without fealing-wax, a fmall loop of filk proceeds, which ferves occafionally to hang the electrometer on a pin, &c. To the other extremity of the tube, a cork is adapted, which, being cut tapering on both ends, can fit the mouth of the tube with either end. From one
extremity
378 A COMPLETE TREATISE
extremity of this cork, two linen threads proceed, a little fhorter than the length of the tube, fufpending each a little cone of pith of elder. When this eledlrometer is to be ufed, that end of the cork, which is oppo- lite to the threads, is pufhed into the mouth of the tube ; then the tube forms the in- fulated handle of the pith eled:rometer as reprefented fig. 6, Plate III. But when the eledlrometer is to be carried in the pocket, then the threads are put into the tube, and the cork flops it, as reprefent- ed fig. 5. The peculiar advantages of this electrometer, are, its convenient finall fize, its great fenfibility, and its continuing longer in good order than any other I have yet feen.
Fig. 4, of Plate III, reprefents a cafe to carry the above-defcribed electrometer in. This cafe is like a common tooth -pick cafe, except that it has a piece of amber fixed on one extremity A, which may occafionally ferve to eleftrify the ele6lrometer negatively, and on the other extremity it has a piece of ivory faftened upon a piece of amber B C. This amber B C ferves only to infulate the
ivory,
OF ELECTRICITY. 379
ivory, which, when infulated, and rubbed againft woollen cloths, acquires a pofitive Eledrlcity, and it is therefore ufeful to elec- trify the eledrometer pofitively.
CHAP.
S8o A COMPLETE TREATISE
CHAP. IV.
Experiments made with the EleSlrophorus^ com- monly called a Machine for exhibiting p^r-- petual EleSiricity.
IN fig. 9, of Plate III, there are reprefent- ed fome Plates, commonly called, the Machine for exhibiting perpetual Eledricity, or the EleSirophorus. This machine confifts of two plates, one of which B, is a circular glafs plate covered on one fide with fome fulphureous or refinous electric, moft com- monly with a compofition made of equal parts of rofin, flielWac, and fulphur ; the other plate A, is a brafs plate, or a board covered with tin-foil, which is nearly of the fame dimenfions as the eledric plate, and it is furniflied with a glafs handle I, which, by means of a brafs or wooden focket, is fcrewed into its center. This machine is the in- vention of an Italian philofopher (Mr. Volt A of Como), and its ufe is the fol- lowing.
Firft,
OF ELECTRICITY. 381
Firft, the plate B is excited, by rubbing its coated fide with a piece of new white flannel, and when excited as much as poflible, is fet upon the table with the coated fide up- permoft ; fecondly, the metal plate is laid upon the excited eledric, as repreiented la the figure ; thirdly, the metal plate is touched with the finger or any other Conductor, which, on touching the plate, receives a fpark from it. Laftly, the meta! plate A, being held by the extremity of its glafs handle I, is feparated from the ele6lric plate, and, after it is elevated above that plate, it will be found ftrongly eledrified with an Eledricity con- trary to that of the eledric plate, in which cafe it will give a very ftrong fpark to any Con- du6lor brought near it- By fetting the metal upon the electric plate, touching it with the finger, and feparating it fucceffively, a great number of fparks may be obtained apparently of the fame ftrength, and that without exciting again the eledtric plate. If thefe fparks are repeatedly given to the knob of a coated phial, this will pre- fently become charged.
The
382 A COMPLE TE TREATISE
The adlion of thefe plates depends upon a principle long ago difcovered, "viz. the power that an excited eledric has to induce a con- trary Eledricity in a body brought within its fphere of adion ; the metal plate therefore, when fet upon the excited electric, acquires a contrary Electricity by giving its electric fluid to the hand, or other Condudlor that touches it, when fet upon a plate pofitively eledlrified, or acquiring an additional quantity of fluid from the hand, &c. when fet upon a plate eledlrified negatively.
As to the continuance of the virtue of this electric plate, when once excited without repeating the excitation, I think, there is not the leaft foundation for believing it perpetual, as fome gentlemen have fuppofed ; it being nothing more than an excited eledric, it muft gradually lofe its power by imparting con- tinually fome of its Eledricity to the air, or other fubdances contiguous to it. Indeed its Electricity, although it could never be proved to be perpetual by experiments, lafts a very long time, it having been obferved to be pretty ftrong feveral days, and even weeks 4 after
O F E L E C T R I C I T Y. 383
after excitation. The great duration of the Eledricity of this plate, I think, depends upon two caufes : firft, becaufe it does not lofe any Eledricity by the operation of put- ting the metal plate upon it, &c. and fecond- ly, becaufe of its flat figure, which expofes it to a lefs quantity of air in comparifon with a flick of fealing-wax, or the like, which being cylindrical, expofes its furface to a greater quantity of air, which is continually robbing the excited electrics of their virtue.
The firft experiments that I made, relative to this machine, were with a view to difcover which fubflance would anfwer beft for coating the glafs plate, in order to produce the greateft effedc. I tried feveral fubflances either fimple or mixed, and at laft I obferved, that the flrongeft in power, as well as theeafieft, I could conftruct, were thofe made with the fecond fort of fealing-wax ^',
fpread
* It is remarkable that fometimes they will not ail well at firft, but they may be rendered very good by fcraping with the edge of a knife the (hining, or glofly furface of the wax. This feems analogous to the well -known pro- perty of glafs, which is, that new cylinders or globes,
m^de
384 A COMPLETE TREATISE
fpread upon a thick plate of glafs *. A plate that I made after this manner, and no more than fix inches in diameter, when once excited, could charge a coated phial feveral times fuccejHively, fo ftrong as to pierce a hole through a card with the difcharge. Some- times the metal plate, when feparated from it, was fo ftrongly eledrifiedi that it darted ftrong flafhes to the table, upon which the eledtric plate was laid, and even into the air, befides caufing the fenfation of the fpider's web upon the face brought near it, like an cledric ftrongly excited. The power of fome of my plates is fo ftrong that fometimes the electric plate adheres to the metal, w^hen this is lifted up, nor will they feparate even if the metal plate is touched with the finger, or other Condudtor.
made for ele£trical pnrpofes, are often very bad eleflrics at firft, but that they improve by being worked, /.£. by hav- ing their fuiface a httle worn. Paper alfo has this pro- perty.
* I have lately feen fo»ie of thofe plates confl:ru<!flcd by Mr, G. Adams, which aSed exceedingly well; and they were made with a compofition of two parts of (helf* lac, and one part of Venice turpentine, without any glafs plate.
4. If,
OF ELECTRICITY. 3S5
If, after having excited the fealing-wax, I lay the plate with the wax upon the table, and the glafs uppermoft, /. e. contrary to the common method, then, on making the iifual experiment of putting the metal plate on it, and taking the fpark, &c. I obferve It to be attended with the contrary Eledricity, that is, if I lay the metal plate upon the eledric one, and while in that fituation, touch it with an infulated body, that body acquires the pofitive Eledricity, and the metallic, removed from the electric plate, appears to be negative; whereas it would become pofitive, if laid upon the excited wax. This experiment, I find, anfwers in the fame manner, if an eledlric plate is ufed, which has the fealing- wax coating on both fides, or one of Mr* Adams's, which has no glafs plate.
If the brafs plate after being feparated from, be prefented with the edge toward the wax, lightly touching it, and thus be drawn over its furface, I find that the Eledricity of the metal is abforbed by the fealing-wax, and thus the eledric plate lofes part of its power ; and if this operation is repeated five
C c Of
386 A COMPLETE TREATISE
CT fix times, the eledric plate lofes its power intirely, fo that a new excitation is neceflary in order to revive it.
if, inftead of laying the eleftric plate upon the table, it is placed upon an electric ftand, fo as to be accurately infulated, then the metal plate fet on it, acquires fo little Electricity, that it can only be difcovered with an electrometer ; which fhows, that the Electricity of this plate will not be confpicu- ous on one fide of it, if the oppofite fide is not at liberty either to part with, or acquire more of the eleCtric fluid. In confequence of this experiment, and in order to afcertain how the oppofite fides of the eleCtric plate would be affeCted in different circumftances,
I made the following experiments.
»
Upon an eleClric Hand E fig. 9, Plate III, 1 placed a circular tin plate, nearly fix inches in diameter, which by a flender wire H com- municated with an electrometer of pith balls G, which was alfo infulated upon the eleCtric ftand F. I then placed the excited eleCtric plate D of fix inches and a quarter in diame- ter, upon tlui tin plate, with the v/ax upper-
mofl,
OF ELECTRICITY, 387
moft, and on removing my hand from it, the eleftrometer G, which communicated with the tin plate, /. e. with the under fide of the eledric plate, immediately opened with negative Electricity, If, by touching the electrometer, I took that Electricity off, the electrometer did not afterwards diverge. But if now, or when the eleCtrometer diverged, I prefented my hand open, or any other unin- fulated Conductor at the diftance of about one or two inches, over the eleClric platen vvithbut touching iti then the pith balls diverged, or if they diverged before, came together; and immediately diverged again with pofitive Electricity ;-^I removed the hand, and the balls came together; — approached the hand, and they diverged ; and fo on.
If while the pith balls diverged with ne- gative Electricity, I laid the metal plate, hold- ing it by the extremity K of its glafs handle, upon the wax, the balls came, for a little time, towards one another, but foon opened again with the fame, /. e. negative Elei2:ri- city;
C c 2 If
388 A COMPLETE TREATISE
If whilft the metallic reded upon the elec- tric plate, I touched the former, the elec- trometer immediately diverged with pofitive Electricity, which if, by touching the eledro- meter, I took off, the electrometer continued without divergence. — I touched the metal plate again, and the electrometer opened again ; and fo on for a confiderable number of times ; until the metal plate had acquired its full charge. On taking now the metal plate up, the electrometer G inftantly diverged with flrong negative EleCtricity.
1 repeated the above- defcrlbed experiments with this only difference in the difpofition of the apparatus, /. e. I laid the eleCtric plate D with the excited fealing-wax upon the circular tin plate, and the glafs upper- moft ; and the difference in their refult was, that where the EleCtricity had been pofitive in the former difpofition of the apparatus, it now became negative, and vice verfa ; except that, when 1 firft laid the eleCtric plate upon the tin, the eleCtrometer G diverged with negative EleCtricity as well in this, as in the other difpofition of the apparatus.
I re-
OF ELECTRICITY. 389
I repeated all the above experiments with an electric plate, which befides the fealing- wax coating on one fide, had a ftrong coat of varnifh on the other fide, and their refult was fimilar to that of thofe made with the above-defcribed plate*
As to the explanation of thefe experi- ments, they feem to depend upon thefe two well known principles, viz. that a body brought within the fphere of adion of an electrified body, does a<3:ually acquire the contrary Eledricity ; and that the exift- ence of one kind of Electricity upon the furface of a fubftance whatever, caufes the exiftence of the contrary Electricity upon fome other fubftance near it.
Cc3 CHAR
/
390 A COMPLETE ^TREATISE •
^ CHAP. V.
Experifnenfs on Colours.
HAVI;NG accidentally obferved than ar^ eledric fliock fent over the furface of a card, marked a black ftroke upon a. red fpot of the card, I was from this in- duced to try what would be the efFeft of fending fhocks over cards painted with dif- ferent water colours ; accordingly, I painted feveral cards with almoft every colour I had, and fent fhocks * over them, when they were very dry ; making ufe of the uni- verfal difcharger fig. 5, Plate I. The efFeds were as follow*
Vermillion wa5 marked with a ftrong black track, about one tenth of an inch wide. This ftroke is generally fingle as reprefented by A B fig. 7, of Plate III; fometimes it is divided in two towards the
* The force geneirally employed was the full charge of onefoot and a half of coated gl^fs.
mid-
OF ELECTRICITY. 391
middle, like E F; and fometimes, particu- larly when the wires are fet very diftant from one another, the ftroke is not con- tinued, hut interrupted in the middle, like G H. It often, although not always, hap- pens, that the impreliion is marked ftrongr er at the extremity of that wire, from which the electric fluid iflues, as it ap- pears at E, fuppofing that the wire G communicates with the pofitive fide of the jar ; whereas the extremity of the ftroke, contiguous to the point of the wire D, is neither fo ftrongly marked, nor furrounds the wire fo ranch %s the other extr^mi^ ty E-
Carmine received a faint and (lender Im- preflion of a purple colour,
Verdigrife was fhook off from the fur- face of the card, except when it had been mixed with ftrong gum-water, in which cafe it received a very faint impreffion.
White lead was marked with a ftrong black track, r^ot fo broad as that on vcrmil- Bon.
C 9 4 Red
392 A COMPLETE TREATISE
Red lead was marked with a faint mark much like carmine.
The other colours, I tried, were orpi- ment, gambodge, fap-green, red-ink, ultra- marine, Pruffian blue, and a few others, which were compounds of the above; but they received no impreffion.
It having been infinuated that the ftrong black mark, which Vermillion receives from the eledric fhock, might poffibly be owing to the great quantity of fulphur contained in that mineral, I was induced to make the following experiment. I mixed toge- ther equal quantities of orpiment, and flower of fulphur, and with this mixture, by the help, as ufual, of very diluted gum- water, I painted a card ; but the eleflric fhock fent over it, left not the leafl: im- preffion.
Defirous of carrying this invefligation on colours a little further, with a particular view to determine fomething relative to the
proper-
OF ELECTRICITY. 39^
properties of lamp-black and oil % I pro- cured fome pieces of paper painted on both fides with oil colours, and fending the charge of two feet of coated glafs over each of them, by making the interruption of the circuit upon their furfaces ; I obferved that the pieces of paper painted with lamp-black, Pruffian blue, vermillion, and purple brown, w^ere torn by the explofion, but white lead, Naples yellow, Englifh ochre, and verdi- grife remained unhurt*
The fame fhock fent over a piece of pa- per painted very thickly with lamp-black and oil left not the leaft impreffion. I fent the Ihock alfo over a piece of paper un- equally painted with purple brown, and the paper was torn where the paint laid very thin, but remained unhurt where the paint
* It has often been obferved, that when the lightening has flruck the mafts of ftiips, it has paffed over fuch parts of the mafts, which were covered with lamp-black and tar, or painted with hmp-black and oil, without the leaft injury, at the fame time that it has (hiverec^ the un- coated parts, in fuch a manner as to render the mafts ufe- lefs. For a particular account of fuch fafts, fee the Phil. Tranf. Vol. XLVIII and LXVII.
was
394 A COMPLETE TREATISE
was evidently thicker. Thefe experiments I repeated feveral times and with foniQ little variation, which naturally produced dif-. ferent efFedsj however, they all feem to point out the following propofition.
!• A coat of oil paint, over any fubftance, defends it from the effects of fuch an electric fhock, as would otherwife injure it ; but by no means defends it from any electric ihock whatever, IL No one. colour feems prefer- able to the others, if they are equal in fub- ftance, and equally well mixed with oil ; but a thick coating does certainly afford a better defence, than a thinner one.
By rubbing the above-mentioned piecess of paper, I find that the paper painted with lamp-black and oil is more eafily excited, and acquires a ftronger Eledricity, than the papers painted with the other colours ; and perhaps on this account it may be, that lamp- black and oil might refift the fhock fome-j what better than the other paints.
It is remarkable, that vermillion receives the black impreflion, w^hen painted with Hn-
feed
OF ELECTRICITY, 395
feed oil, nearly as well as when painted with water. The paper, painted with white lead and oil, receives alfo a black mark ; but its nature is very lingular. The track, when firft made, is almoft as dark as that mark- ed on white lead, painted with water, but it gradually lofes its blacknefs, and in about one hour's time (or longer, if the paint is not frefh), it appears without any darknefs, and when the painted paper is laid in a proper light, appears only marked with a colourlefs track, as if made by a finger-nail. I fent the fhock alfo over a piece of board, which had been painted with white lead and oil about four years before, and the explofion marked the black track upon this alfo ; this track however was not fo ftrong, nor vanifh- ed fo foon as that marked upon the painted paper, but in about two days time it alfo va- piflied intirely.
CHAP.
396 A COMPLETE TREATISE
CHAP. VL
Promifawus Experiments.
OBferving that a ftrong fpark may be obtained from the metal plate belong- ing to Mr. Volta's machine, defcribed in the fourth chapter of this Part, when not the leafl: fpark can be obtained from the eledric plate itfelf, I was naturally induced to make ufe of the above-mentioned metallic plate, to difcover the Eledricity of very weak electrics ; which otherwife would be either incbfervable, or fo fmall as not to permit its quality to be afcertained. Accordingly I con- ftrudled feveral fuch plates of different fizes, beginning from that of a common metal button faftened upon a ftick of fealing-wax, and by ufing them, I obtain a very fenfible Electricity from the hairs of my legs, when ftroked, and of my head, or any part, that I have tried of my body, or the head of almoft any other perfon.
In
OF ELECTRICITY.
397
In this manner I obtain fo ftrong fparks from the back of a cat, a hare's fkin, a rabbit's fkin, a piece of flannel, or of paper, that I can prefently charge a coated phial with either of thofe, and fo ftrongly, as to pierce a hole through a card with its difcharge.
I have often obferved that, when ftroking a cat with one hand, and holding it with the other, I feel frequent fmart pricklings on different parts of that hand, which holds the animal. In thcfe circumftances, very pungent fparks may be drawn from the tips of the ears of the cat.
Smooth glafs rubbed with a rabbit's fkin, dry and warm, acquires, I find, the nega^ the Eledlricity ; but if the fkin is cold, the glafs is excited pofitively. Sometimes fmooth glafs may be excited negatively with new white flannel, clean and dry, and alfo with a hare's fkin.
Obferving the flrong eledric power of new white flannel, I thought that a piece of it, rolled round the globe of an eleftrical
4 ma-
398 A COMPLETE TREATISE
machine, would perhaps give a ftronger Electricity to the prime Condudor, than the glafs itfelf. In order to try the truth of my fuppofition, I tied a large piece of flannel, dry and wariii, round the globe of the ma- chine, and for a rubber, I applied the palm of my hand, then turned the winch, firft flowly, and afterwards brifkly ; but con- trary to my expedation, the Ele£lricity at the prime Condudor, although pofitive, was fo weak, that the index of the quadrant electrometer was not moved from its per- pendicular fituation. Surprifed at this events I refolved to take off the apparatus; but I was more furprifed, when, on removing the flannel from the globe, the former appeared fo ftrongly pofitive, that it darted feveral fparks to my arm, and other contiguous bodies, and the latter remained fo ftrongly negative, that the eledlrometer upon the prime Conductor inftantly elevated its index to about 45^^. This experiment being feveral times repeated, produced always the fame efi'ea.
Having had occafion to coat a ten ounce phial, for the Leyden experiment, I ftuck
the
OF ELECTRICITY. 399
the brafs filings on the infide of it, with varnifh, agreeable to the diredions given by fome writers on Electricity. This phial remained about a week unufed, but it happened that whilfl: I was charging and difcharging it for fome experiments, on making a difcharge, it exploded with a greater noife than ufual, the cork with the wire being at the fame time blown out of the neck of it. Being intent upon the main experiments in hand I omitted to exa- mine this phenomenon ; — I replaced the cprk into the neck of the phial, and went on charging and difcharging it again ; but it had not been charged above three or four times more, when, on making a difcharge, the varnifh that ftuck the brafs filings, was in a flame, which burnt the under fide of the cork, and occafioned a good deal of fmoke and flame to come out of the phial. Some days after, this experiment was re- peated in the prefence of three gentlemen, well verfed in Electricity, when the cork with the wire, was alfo pufhed out of the neck of the phial ; but the varnifh was this laft time fo far burnt, that the brafs filings were almoll all dropped to the bottom of the phial, I and
400 A COMPLETE TREATISE
and they had their colour changed by the combuftion.
In making fome experiments, of a nature rather different from Eledricity, I acciden- tally obferved, that when I agitated fomc quickfilver in a glafs tube hermetically feal- ed, and in whofe cavity the air was very much rarefied, the outfide of the tube ap- peared fenfibly eledrified ; its Eledtricity however was not conftant, nor, as I firft thought, in proportion to the agitation of the quickfilver. Being defirous of afcertain- ing the properties of fuch tubes, I conftrudt- ed feveral of them, and by means of two cork ball electrometers, obferved their pro- perties ; but as they all agree in regard to the chief points, I fhall only defcribe one, which is the beft of them. This tube is reprefented by fig. 3, of Plate III. Its length is thirty- one inches, and its diameter is little lefs than half an inch. The quickfilver in it may be about three fourths of an ounce, and in order to exhauft it of air, I clofed it while the quickfilver was boiling in its op- pofite end.
Before
OF ELECTRICITY. 401
Before this tube is ufed, I make it a little warm, and clean it ; then holding it nearly horizontal, I let the quickfilver in it, run from one end of the tube to the other, by gently, and alternately elevating and de- preffing its. extremities. This operation im- mediately renders the outfide of the tube eledlrical, but with the following rem.ark- able property, "uiz. that end of the tube, where the quickfilver actually ftands, is pofi- tive, and all the remaining part is negative. If by elevating this pofitive end of the tube a little, I let the quickfilver run to the oppofite end, which was negative, then the former inftantly becomes negative ; and the latter ' pofitive. The pofitive end has always a ftronger Eledricity than the negative. If when one end of the tube, for inftance A, is pofitive, /. e. when the quickfilver is in it, I do not take off that Eledricity, by touch- ing it ; then on elevating this end A^ fo as to let the quickfilver run to the oppofite end B, it appears negatively eledrified in a very fmall degree. If by deprefTmg it again it be rendered pofitive a fecond time, and that pofitive Electricity is neither taken off,
D d then
402 A COMPLETE TREATISE
then on elevating this end A again, it ap- pears to be pofitive in a fmall degree : but if whilft it is pofitive, its Electricity be taken off, then on being elevated, it appears ftrong- ly negative.
When about two inches of each extremity of this tube is coated with tin-foil as it ap- pears in the figure, that coating aflifts to render the Electricities at the extremities of the tube more confpicuous, fo that fometimes they give fparks to a Condudtor brought iiear.
In regard to the conftruCtion of fuch tubes (which I have made of feveral lengths, from nine to thirty-one inches) it is obfervable that fome will a£t very well, while others will hardly acquire any Electricity at all, even when they are made very hor, I ani not yet thoroughly fatisfied in refped to this difference, but fufpeCl that the thicknefs of the glafs is more concerned, than any thing clfe, it appearing that a tube, whofe glafs is about one twentieth of an inch thick, anfwers better than either a thicker or a thinner cnc.
Ilhall
OF ELECTRICITY.
403
I fliall laftly finifli this Treatife with men- tioning two remarkable difcoveries lately made in Eleffcricity, which, as they came to my notice after a great part of this work had already been printed, could not be con- veniently inferted in any other place. The firft of thefe difcoveries is of Mr. Koestlin> who (as he fays in his Latin Differtation of the EfFedts of Electricity upon fome organic Bodies) has found that both animal and vege- table life is retarded by negative eledlrification. The other difcovery is of Mr. Aghard, at Berlin, who, in the month of January 1776^ obferved, that water froze, to the twentieth degree below the freezing point of R e a u m u r 's thermometer (which anfwers to the thirteenth degree below o of Farenheit's fcale) was an ele<Sric. He tried his experiments in the open air where he found that a rod of ice two feet long and two inches thick, was a very im- perfect Conductor when Reaumur's thermo- meter was at fix degrees below o, and that it would not in the leafl conduct, w^hen the thermometer was at 20^. By whirling a fpheroid of ice in a pr3p^r machine, he even eleftrified the prime Condudor fo as to
D d 2 attra6^
440 A COMPLETE TREATISE, &c.
attraft, repel, give fparks, &c. The ice, that this gentleman made ufe of, was free from bubbles of air, and quite tranfparent ; to pro- duce which, he ufed to fet a veflel, contain- ing diftilled water to be frozen, upon the window of a room, which was rather warm with refpeft to the ambient air, where the water began to freeze on one fide of the veffel, while on the other fide it was ftill liquid.
THE
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1
THE
INDEX.
A
y^IRconi^Tiki or much rarefied obftruds excitation, 7. a current of it from eledlrified points, 36. eledrified, 72,
eleclrified artificially,. 308. receiving a charge, 265. heat«
.ed by red-hot iron, a condu6lor, 306. heated by red-hot
glafs a very bad conductor, 307* ^/«^?^^7/» defcribed, 137.
Animals the elFedls of Eledricity upon them, 36, 37, 61. 86. Apparatus^ ele^rical dtCcribcd^ 129. 160. Atmo/phere^ its Eledricity, 70. of fmoke, 309. eledrical, vi-
fible in vacuo, 224. Atmo/phericalKXtoinzityj 70. electrometer, 370. Attra8ion eledric, between bodies diifcrently eledrified, 37,
its caufe, 104. Aurora borealisy an eledlrical phenomenon, 73. imitated, 22;t.
. B
Battery y eleSlricaU 59. its conftruftioa, 142* 166. experi- ments performed with it, 291. Bdls^ iUSiricaU 316.
D d 3 Black
4o6 INDEX-
Black dujl raifed from metals by eledrical explofions. 64. Black Jirokes marked upon colours, 390, J^r^/yJS' of electric light, 14. 207.
Capillary tubes t\tz\.x\^^^j 39, 316.
C^?r^ pierced with the electric cxplofion, 244.
Cement for electrical purpofes, 133.
Charcoal its properties, 9.
Charging and di/c barging mgQTiQtdX^ 52, 53. 57. aglafsjar,
175. 228. a battery, 176. other electrics, 271. Charged eleSiricSf 5^* 55*
Chocolatey its Electricity, 22. its power reftored, 23. Circles marked upon metals by electrical explofions, 66, 299.
fairy, 297. Clouds generally electrified, 72. their influence upon the kite,
366.
Coatings 53. glafs 143. a plate of air, 265. other electrics, 271, 272.
Cohefion between electrified bddiesof the electrophorus, 384.
Colours^ prifmatick, marked by electric explofions upon metals, 67. 299. ditto upon glafs, 62. 248. experiments upon, 390.
Communicated Elecincky, 29. 31. 49,
Compofition for lining glafs globes or cylinders, 134.
Conductor, primCy 132. 139. luminous, 218.
Condudorsy 3. a table of, 8. their nature, 119. obftructing the paflage of Electricity, 61. metallic to defend build- ings, 76.'
Cup electrified, 312.
Cujhiony or rubber, 137.
D
Difeafes cured by Electricity, 90, Di/c barging rody 1 46 , 1 6 8 .
Dujlf black, raifed from metali by electrical explofions, 64,
Eartk*
i
INDEX.' 407
Earthquakes^ thought to be effects of Electricity, 74. imi- tated, 249. 300.
'EhSiric atmcfpherey whether it does exifl: or not, 126. the af- fection of bodies immerged in it, 31. 94. does not exclude the air, 236.
i.le5irk fluids lOi, its nature, 108. its place, 123. a fing!e fluid, 226. its courfe fljewn, 238, 239, 241. 249. 252.
Eleclric lights in vacuo, 218. 220. 2 22. its prifmatic colours,
, 227. peculiarly penetrating, 215. 247.
EleSlric fpark^ I. 36. Ihoclc, 53. 59. attraction and repulfion, 37. 104. fly, 169. 275. ilar, 14. 207. pencil, I4. 207. well, 190.
EJeftrical air thermometer, 255. apparatus, 129. battery, 59. 142. 166. bells, 316. machines, 2. 132. 149. fpider, 318.
Electricity^ 2. pofitive Or plus, and negative or minus, 16. 102. vitreous, i5.refinous, 16. perpetual, 23. 380. rendered more confpicaous by contracting the electrified bodies, 3 1 2. produced different ways, 20. communicated to conductors, 31. communicated to electrics, 49. hypothefis of, lOl. per- vading the fubftance of Conductors, 311. acquires an im* petus, 210. atmofpherical, 70 not confpicuous within the cavities of electrified bodies, 127. 190. firing inflam- mable fubllances, 66, 213. 258. melts metals, 62. thecaufe of thunder and lightening, 71. promotes vegetation, 38. promotes evaporation and the circulation of the blood, 37, 86. negati've retards animal and vegetable life, 403. of the air, 72. of the kite, 344. 366. of the clouds, rain, fnow^ and hail, 72. not produced by fermentation, evaporation or coagulation, 96. applied as a remedy for feveral difeafcs, %\. different produced by different rubbers, 16. vindicating,
327- Eledricities the two, 1 1. their particular appearancrs, 12.
EU^rics 2. a table of, 5. become condudlors when mad*
D d 4 very
4c8 I N D E X.
very hot, 7. 304. 306. their nature, 119. refinous and fluid, coated, 271.
Electrometer, 147. fingle thread, 160. pith or cork ball, 160. difcharglng, 163. quadrant, 1 61. atmofpherical, 370. for the rain, 375. for the pocket, 377. llandard of that ufed with the eledrical kite, 342.
Ele&rophorus-i 380.
Enjaporation increafed by Eledricity, 38. does not produce - Eledricity, 96.
Excitation, 2. by rubbing, 20. by heating and cooling, 20. 24. by melting, 20, 21. encreafed by the amalgam, 137.
Experiments, eleSIrical, concerning attraftlon and repulfion, 179, on elcdlric light, 207. .with the Leyden phial, 228. with other charged eledlrics, 264. on the influence of points, and the ufe of metallic Condudlors, 273. with the cledrical battery, 291. promifcuous, 203. with the cledricai kite, 344. with the rain and atmofperical eledlro* metej:, 370. with the electrophoius, 380. on colours, 390.
Fairy rings, 297.
Falling ftar, thought to be an Electrical phenomenon, 74.
Fermentation does not produce Electricity, 96.
Fire its origin, no. different dates of its exiflence, iii. its
refemblance to the electric fluid, 112. Fly, ele^rical, 169. 275. Fogs electrified^ 72. ftrong Electricity in time of, 374.
Gla/s, the beft for electrical purpofes, 133* fometimes a con- ductor, 7. 144. globes and cylinders, 133. vefl^el exhaufted, 7. vefTel with the air condenfed, 7. tube 141. exhaufted con* ducting tube 220. containing quickfilver, 400* thinncft ac- quires the (Irongeft charge, 56. 142.
4
Hail
INDEX. 409
H Hail electrified, 72.
«
Hypothejis of Electricity, i o i .
Hurricanes thought to be effects of Electricity, 74,
I
Ice an electric when froze very hard, 403. In/ulate, 3. the conflruction of (tools to, 170. Infulated metallic rods to attract the Electricity from the clouds, 72.
K
Kite^ ele£iricaU to attract the Electricity of the clouds, 72. its conftruction, 333. experiments made with it, 344. propo- fitions deduced from the experiments made with it, 366. conflruction of its firing, 335.
L
Leyden phial, 56. its coating, 143. bodies without the circuit effected with the explofion of it, 26. its two fides contrarily electrified, 55. its fpontaneous difcharge, 142, 179. inca- pable of becoming charged when infulated, 231. its redun- dant Electricity, 325. experiments performed with it, 228. to put into the pocket when charged, 340.
Leyden 'vacuum, 242.
Lightening, an electrical phenomenon, 71. imitated, 270. its effects avoided, 76. 82. 273%
Z//;»/;7(7;^/ conductor, 218.
M
Machines eleSlrical, 2. their conftruction in general, 132. the defcription of fome particular ones, 149. for exhibiting perpetual Electricity, 380.
Magneti/m
410 INDEX.
Magnetijm not efFecting Electricity, 39. given by the electric exploHon, 65.
il/^^/V^/ Electricity, 84. 287.
Metallic CortiiuSiorsy 76. their conftruction, 77. their ufe exem- plified, 282.
Metals conduct the electric fluid through their fubftance, 31 1. melted by Electricity, 293. calcined and revivified by the electric explofion, 64. ftruck into glafs by the electric ex* plofion, 259. coloured rings marked upon them by repeated explofions, 67. 299. circles marked on them by the cxplo* fion, 66. 297. in part reiift the paflage of the electric fluid, 61, 295. the difference of their conducting power in which manner afcertained, 294. 296,
Minus 9 or negative Electricity, 16.
N
Negati've EleSlricityf 1 6,
Nort'ConduSlors. 3. the fame as electrics, 4,
Non-elet^ricSf \. ,
P
Paper^ quire of, pierced with the electric explofion, 244.
Pencil of rays, 14. 207.
Perpetual Electricity, 23. the machine for exhibiting it, 308.
Perfonal fecurity in time of a thunder- dorm, 82.
Phofphorusy Mr. Canton's, defcribed, 215. illuminated by Electricity, 215.
Phlogijion, its exiftence, iii. the caufe of the conducting quality in bodies, 1 2 1 .
Polarity deflroyed, reverfed, and given to needles by the electric explofion, 56,
Pofiti've or plus Electricity, 16.
Pointed bodies their influence, 35. 273. their properties exem- plified, 275. 282. their properties explained, 279. acurrcnt Gf air from them when electrified^ 36.
Prime
INDEX. 4n
Prime conJu^off 132. its conftruction, 139. luminogs, 218.
R
Rain generally electrified, 72, the electrometer for the, 375.
Repulfion electrical, i. 94. its caufe, 105.
Rejiduum of the charge, 177.
Refinous Electricity, i6.
Rings fairy y 297.
Rubbery 2. its conftr action for an electrical machine, 137. for aglafstube, 142. for fealing-wax, &c. 142. different Elec- tricity produced by different, 16. its Electricity diiftrent from that of the electric, 15.
Rulesy practical, 171.
S
halted firing for the kite, 337, threads for electrometers, i6i.
Sealing-nuax excited by melting, 22.
Shocky electric, 59. weakened by the length of the conductor, 60. deftroying animal and vegetable life, 61. melting metals, 6z. calcines metals, and revivifies their calces, 64. acting like a phlogiflic procefs upon different kinds of air, 68. given to one or more perfons, 229. fmall ones are better for phyfical purpofes, 288.
Sn9wo electrified, 72.
Sparky electric, 210. its effects upon an animal body, 36. fhorter and flronger from charged electrics than from elec- trified Conductors, 58. vifible in water, 61. 253. difplaces and rarefies the air, 255,
Spider electric, 318.
Stary electric, \j^. falling thought to be an electrical pheno- menon, 74.
Sulphur excited by melting, 21, 22*
TJ!fi9ry of Electricity, 98.
2 Thunder
412 I N D £ 4C.
Thunder an electrical phenomenon, 71. imitated, 270.
Thunder- houfey 282.
Tourmalin^ its properties, 24. its properties found in other
precious ftones, 28. 9"a^^ glafs, 141. conducting, 220. fplral, 319. containing
quickfilver, 400.
V
Vacuunty 9. 40. Leyden, 242.
Vegetables deftroyed by the electrical explofion, 61. their vege- tation promoted by electrification, 38. their vegetation re- tarded by negative electrification, 403.
Vitreous Electricity, 15.
W
Water running from a pipe electrified, 38. 316. the fpark vifi- blein it, 61.
Water-fpouty an electrical phenomenon, 74, 267. imitated, 268.
Well ehBricy 190.
Whirlwind thought to be an electrical phenomenon, 74, imi- tated, 269.
Wind from electrified points, 36. from excited electrics, 40.
FINIS.
ERRATA.
Page 1 8. 1. 10, for the difFerent read different 152. J. g* for fkrewed read fcrewed 154. I. 21. for plate 2. read FhtelL 184. 1. irfor G read H. 242. ]. 2 2, » for puthe read up the 257. 1. 10. for as for inftance r^^^ for inftance ^64. 1. i\. for other electrics read other charged
electrics 267. 1. 7. for prefles read pafTes 27 J. 1. ig. for to infulate fluid electrics read to coat
fluid electrics 276. 1. 21, for and even read but even 341. 1. \%. for the r^^^ that
366. 1. 8. for clouds generally read clouds, if it does
rain, not generally
Publiilied by Edxvard and Charles Dilly,
I. An Essay towards a Syftem of Mineralogy: By Axel Frederic Cronstedt» Tranflated from the original Swedifh, with Notes by Guftavon En- geflrom. To which is added, a Treatife on the Pocket Laboratory, containing an eafy Method, ufed by the Author, for trying Mineral Bodies ; written by the Tranflator. The whole revifed and corrected, with fome additional Notes, by Emanuel Mendes Da Costa. The Second Edition, to which is added an Appendix, in One Volume 8vo, price bound 6s.
II. An Eafy Method of Assaying and Classing Mineral Substances, containing plain and eafy In- ftrudions for any Perfon to examine the Produ6is of his own Land, or fuch as are obvious in Excurfions or Travels in foreign Countries, without having a complete chemical Apparatus. To which is added, a Series of Experiments on the Fluor Spatofus, or Sparry Fluor ; abftradcd from the Memoirs of the Royal Swedifti Aca- demy of Sciences for the Year 1771. By John Rein- HOLD FoRSTER, LL.D. and F, R.S. price is. 6d.
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