A complete treatise of electricity in theory and practice : with original experiments

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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.

B b 3 The

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ft; VO

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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PXATE.IIL.

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B

i

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T.da'ollv d<il!'

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Jh"Xod^e Sa/7p.

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

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