samual jackson barnett elements of electromagnetic theory 1903英文版电力电磁电气工程教程教材电子版.docx
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samualjacksonbarnettelementsofelectromagnetictheory1903英文版电力电磁电气工程教程教材电子版
SamualJacksonBarnettElementsofElectromagneticTheory（1903）英文版电力电磁电气工程教程教材电子版下载
UNIVEKSITYOFCALIFOIu.IA
LIBEAKY
D3PAR2.IEIIT0?
CIVTL
GiftofLirs.EdwinH.Warnerfrom
herhusband
fslibrary.
January
1928
Library
UNIVERSITY
FCAUia’01*NIA
OFCIVILENGINEERING
UNIVERSITYor
DEPARTMENTOFCIVIL
CAL.IFOr?
MIA
ELEMENTSOF
ELECTROMAGNETICTHEORY
ELEMENTS
OF
ELECTROMAGNETICTHEORY
BY
S.
J.BARNETT,PH.D.
;/
ASSISTANTPROFESSOROFPHYSICS
INTHE
LELANDSTANFORD,
JR.,UNIVERSITY
gork
THEMACMILLANCOMPANY
LONDON
:
MACMILLAN&CO.,LTD.
1903
Allrightsreserved
tinsPeering
Library
Copyright,1903
BYTHEMACMILLANCOMPANY
Setup,electrotypedandprintedSeptember,1903
PRESSOF
THENEWERAPRINTINGCOMPANV.
LANCASTER.PA.
CORRIGENDA.
Page4,linei6,forunelectrified（sixthword}readelectrified
Page33
lme
io,/<?
rintensityreadtension
Page127,linei,forAd2readd2A
Page128,line
7,insert5.atbeginningofline.
Page130,line8,for5read6
..
Page203,lines
5,6-7,24,cancelisotropic
Page204,line\,forV2readVu
Page212,lines6-7,canceltheexpressioninbrackets.
Page216,lines27and30,cancel（39）and（40）
Page221,line28,for
VV2=
12rao/F12=
21
Page244,line29,for（9）read（a）
Page450,lines
18-19,substitutesmallbodieswithequaland
oppositechargesaremadetovibratesymmetricallywith
（ap-
proximately）simpleharmonicmotion
inastraight
lineabouta
fixedpoint,awavesystem
793211
DEDICATED
WITH
GRATITUDEANDAFFECTION
TO
MYREVEREDFRIEND
PROFESSORFRANCISH.
SMITH,
LL.D.
UNIVERSITYOFVIRGINIA
PREFACE.
InthistreatiseIhavetriedtopresent
insystematicanddefi-
niteforma
simple,rigorous,andthoroughlymodernintroduc-
tion
tothefundamental
principles
ofelectromagnetic
theory,
togetherwithsomeofthesimpleroftheirmoreinterestingand
importantnon-technical
applications.
Theworkmakesnopre-
tensetocompleteness,but
iswritten
fortheseriousstudentof
physics,whowillmakeliberaluseofmoredetailedtreatises,of
hand-books,andofjournals,asoccasiondemands.
Iamofcourseindebtedtomanybooksandmemoirs.
My
obligationsareespeciallygreat,asthemostcursoryexamination
ofthebookwillshow,totheworksofMaxwell,Heaviside,and
Poynting.
IamalsomuchindebtedtoProfessorA.G.Webster
fortheuseofanumberofexcellentdiagramsfrom
histreatise
onelectricaltheory.
S.
J.BARNETT.
STANFORDUNIVERSITY,CALIFORNIA
June,1903.
CONTENTS.
CHAPTER.
PAGE.
I.
GENERALELECTROSTATICTHEORY
i
II.
IDEALELECTRIC
FIELDSAND
CONDENSERSWITHHOMO-
GENEOUSDiELECTRICS
57
III.
STANDARDCONDENSERS.
CONDENSERSYSTEMS.
ELECTROM-
ETERS
122
IV.
ELECTRICFIELDSWITHTwoORMOREDIELECTRICS
139
V.
REVERSIBLETHERMAL
EFFECT.
ELECTROSTRICTION
168
VI.
ELECTRICABSORPTION.
ELECTRETS
176
VII.
COMPARISONOFDIELECTRICCONSTANTS.
SPECIFIC
INDUC-
TIVECAPACITY
192
VIII.
THE
ELECTRICCONDUCTIONCURRENT.
INTRINSIC
ELEC-
TROMOTIVEFORCE
199
IX.
ELECTROLYTICANDMETALLICCONDUCTION
228
X.
THERMALANDVOLTAICELECTROMOTIVEFORCES
246
XL
MAGNETS.
MAGNETOSTATIC
FIELDS
265
XII.
THEMAGNETICFIELDOFTHECONDUCTIONCURRENT
286
XIII.
ELECTROMAGNETICINDUCTION
332
XIV.
UNITSANDDIMENSIONS
415
XV.
CONVECTIONANDDISPLACEMENTCURRENTS.
THEGENERAL
ELECTRICCURRENT
424
XVI.
THE
FLUX
OF
ELECTROMAGNETIC
ENERGY.
ELECTRIC
WAVES
433
r
ELEMENTSOF
ELECTROMAGNETICTHEORY.
CHAPTER
I.
GENERALELECTROSTATICTHEORY.
V
electrificationbyContact.
PositiveandNegativeCharges.
Letoneendofaneboniterodandadrywoolenclothberubbed
01
ronglypressedtogetherandthenseparated
;andletasecond
roc
ndclothbetreated
inthesameway
:
Therubbedpartof
ea
.
cloth
willbefound,on
trial,
tobeattractedtowardthe
n
dpartofeachrod,whiletherubbedpartofeachclothwill
be
pelledfromtherubbedpart
oftheother
cloth,andthe
i
jdpartofeachrodfromtherubbedpartoftheotherrod.
.
.eseareexamples
ofelectricphenomena.
The
region
in
whichtheyaremanifested
iscalledanelectricfield
（
11）,and
mediumwhichpermeates
thisregion
airandaetherinthe
al
ecase
andthroughwhich
electric
influencesaretrans-
r
‘‘
xl
iscalledadielectric.
Thepartsoftheeboniteandwool
jedtogetheraresaidtobe
electrified,ortopossesselectric
‘rges.
Thetwopiecesofwoolenclotharesaidtohavelike
rges,
since
theywere
similarly
treatedand
sincewhat
is
.pelledfromoneisrepelledfromtheother,andwhatisattracted
towardone
isattractedtowardthe
other.
Similarly,thetwo
eboniterodsaresaidtohavelikecharges.
Butthewoolandthe
ebonitearesaidtohaveunlikeoroppositecharges,sincewhat
is
repelledfromoneisattractedtowardtheother.
I-L?
tEATSOFELECTROMAGNETICTHEORY.
Likeeboniteandwool,anytwodifferentsubstances,orpor-
tions
ofthesame
substance
in
different
physical
conditions,
exhibit
electricpropertiesafterintimatecontactand
separation.
Oneofthebodiesbehaves
likeeboniterubbedwithwool,the
otherlikethewool.
Anelectricchargelikethatofwoolaftercontactwithebonite
iscalledapositivecharge,andachargelikethatoftheebonite,
anegativecharge.
Thetermspositiveandnegativearejustified
bytheoppositepropertiesofthetwokindsofelectrification,but
thereisnoreasonexceptconventionand
resultingconvenience
whythetwotermsshouldnotbeinterchanged.
Inadditiontotheforcesbetweenelectrifiedbodies,forcesare
found
to
exist,
in
general,betweenan
electrifiedbodyandan
insulator
（
2）notelectrified（ChaptersIV.andVI.）.
2.
ConductorsandInsulators.
Electrificationby
Conduction.
Arodofeboniteelectrifiedatoneendexhibitselectricproperties
only
atthatend
;
whilearodofmetal,
heldbyan
ebonite
handleand
electrified
atone
end,becomes
electrified
atonce
（apparently）alloveritssurface.
Substanceslikethemetals,by
whichanelectricchargeis
distributedwithextreme
rapidity,so
astocomeintoastateofequilibriumwithin（usually）asmall
fractionof
asecond,
are
called
electricconductors.
A
body
chargedbyconnectionwithan
electrifiedbodythroughacon-
ductor,likethefarendofthemetalrodmentionedabove,
issaid
tobe
electrifiedbyconduction.
Substanceslikeebonite,overor
throughwhichanelectricchargeistransferredonlywithextreme
slowness,arecalledelectricinsulatorsornon-conductors.
Amongordinarymolecularsubstancesperfectinsulatorsand
perfectconductorsdonot
exist,nosuchsubstancecompletely
andforanindefinitetimepreventingalltransferofelectrification,
andallofferingmoreorlessobstructiontosuchtransfer.
There
iseveryreasontobelieve,however,thatfreeaether（a
"vacuum"）
andcleandrygasescontainingno
（electrolytically）
dissociated
moleculeshavethepropertiesofaperfectinsulator（ChapterIX.）.
GENERALELECTROSTATICTHEORY.
3
Amongsubstancespossessinghighconductivityarethemetals,
graphite,andsaltoracidsolutions
;amongthosewithhighin-
sulatingproperties
are（undissociated）gases,fusedquartz（cold
and
inthe
solid
state）,ebonite,cold
glass,
silk,andwool.
A
substancewhichisanexcellentinsulator
inonecondition,how-
ever,mayinanotherconditionhavethepropertiesofaconductor.
Thuscoldglass
isanexcellentinsulator,butasthetemperature
is
raised
itsinsulatingpropertiesdisappear.
Also,undervery
great
electric
stressthe
insulatingproperties
ofallmolecular
substancesbreakdown.
Abodycompletelysurroundedwithinsulators
is
saidtobe
insulated.
Aconductorcanbecompletelydischargedbybringing
itinto
contactatanyonepointwiththeinnersurfaceofahollowclosed
conductor
（
4）,suchasthewallsoftheroomwithinwhichthe
experiments
are
performed,
provided
there
areno
（insulated）
electrifiedbodieswithin.
Whenconnectedtothewallsofthe
room,ortheearth,theconductor
issaidtobeearthed.
From
aninsulatortheelectrificationcanbe
entirelyremovedonlyby
applyingaconductorateveryelectrifiedpoint,
e.g.,byimmers-
ing
itinaconductinggasorliquid.
3.
ElectrificationbyInduction.
Aninsulatedconductor,when
broughtnearanelectrifiedbody,
i.e.,intoanelectricfield,itself
becomes
electrified.
Examinedby
themethods
of
I,
the
chargesofthemoreremoteandnearerendsoftheconductorare
found
tobe
similarand
opposite,
respectively,
tothatofthe
originalelectrifiedbody.
Aconductorelectrifiedinthismanner
issaidtobeelectrifiedbyinduction.
Iftheconductor,while
still
insulated,
isremovedfrom
the
electricfield,allsignsofelectrification
disappear.
But
if,while
still
inthe
field,
it
isconnectedwiththewalls,orearthed,the
electrificationsimilartothatoftheoriginalchargedbodydisap-
pears,whiletheoppositeelectrificationofthenearendremains.
Iftheconductorisnowinsulatedandremovedfromtheoriginal
4
ELEMENTSOFELECTROMAGNETICTHEORY.
electricfield,thischargebecomesmoreevenlydistributedover
itssurface
（
42）.
In
thismanneranynumberofconductors
maybegivenchargesoppositetothatofagivenelectrifiedbody
without,asmaybeprovedbythemethodof
5,diminishingor
increasingthelatter’selectrification.
4-8.
Experiments
with
HollowClosedConductors.
Electric
Screens.
LetAdenoteaninsulatedhollowconductorhavinga
closelyfittingconductinglid,B,withaninsulatinghandle.
Let
Abeconnectedwithanelectroscope
orelectrometer
（Chapter
III.）,
C,bymeansofwhichanychangeinthe
state
ofelectri-
ficationofitsexterior（orinterior）surfacemaybedetected
;and
letAbekeptclosedexceptwhenanotherbody
isbeing
intro-
ducedint
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