DOC.
11
LECTURE ON ELECTRICITY
&
MAGNETISM
397
[4]In
contrast to
the
usage in
the
text, in
the
figure
e
=
e(x,y,z),
e1 =
e1(a,b,c).
[5]In
the
following
formula,
as
well
as
in many
instances
below, a subscript
1
denotes
a
dummy
summationindex.
[6]The
words "Hier
[...]
geben"
are
in Mileva EinsteinMaric's
handwriting.
[7]The quantities
df1
and
df2
below
denote
surface
elements; n1z
and
n2z are
the
angles
between
n1
and
n2
and the
zaxis.
[8]In
the
following
formula
dx
is
a
volume element and ds is
a
surface
element.
[9]The
words "einen
Spezialfall
des
sog." are
interlineated.
[10]These
remarks, as
well
as
the
ones
concerning
theoretical
constructs in
the
next
para
graph, may
derive from Pierre Duhem
(see, e.g.,
Duhem
1906).
See
Howard
1990 for
a
discussion
of Einstein's
reading
of Duhem.
[11]In
this
integral
the
integration region
K
is
the "continuum"
where
p
is
nonzero,
minus
a
sphere
with radius
R
around the
point
(a, b,
c).
[12]In
the
following integrals
the
integration region is
a
cylinder
of radius
R,
with its
upper
and
lower
surfaces
on
either
side
of the
charged
surface; a
factor of
rj0
(the
surface
charge
density) is missing
on
the
right side
of the
last
equality.
[13]A
minus
sign
is missing
in
the
lefthand side
of
the
following equation.
a
is the surface
charge density.
47c5
[14]The
last
equality
should
be C
=
jr.
[15]In
the
following equation
2a12
should
be
a\2.
[16]The
whole
line is
interlineated.
[17]In
the
last
three
equalities below,
a
minus
sign
should be added
on
the
left.
[18]In
the
second
equality below,
2d
A
should
be

2dAm.
[19]In the
following,
b1b2
should
be
b11b22
and
D
should
be
D2.
[20]A
minus
sign is
missing
on
the
right in
the last
equality.
[21]In the second
equality,
(a11

a22)
should
be
(a11

a12),
or, alternatively,
(a22

a12).
[22]In the formula
below,
2D' should be
(2D')2.
[23]In
the
following,
5
is
the distance between the
plates,
f
is
their
surface,
and
A(p
is
the
potential difference
between the
plates.
[24]The first
equality
should
be
0
=
2nE2j.
[25]The
"Schutzringelektrometer" (originally
devised
by
William
Thomson;
see
Thomson
1867b)
is
essentially
a
large condenser,
the
plates
of which
are
held
at different potentials.
The
potential
difference between the
plates
is
determined
by
measuring
the
force
on
a
loose
section
in
the middle of
one
of the
plates
(see
also the
figure).
For
more details,
see, e.g.,
Chwolson
1908, pp.
325329,
or
Graetz
1905b, pp.
6870.
[26]Thomson's
quadrant electrometer
(see
Thomson
1867b)
consists of
four
quadrants
(see
the
figure)
and
a
"needle"
(a piece
of aluminum
foil
or
something
similar)
that
hangs on
two
threads
above
or
inside them.
Opposite quadrants
are
usually
kept
at
the
same potential;
the needle
is
grounded
or
kept
at
a
fixed
potential.
A
potential difference
between the
pairs
of
quadrants, or
between the needle and the
quadrants
will
result
in
a
rotation of
the
needle.
For
more
details,
see,
e.g.,
Chwolson
1908,
pp.
318324,
or
Graetz
1905b,
pp.
6365.
See
also the
following
note
and Einstein's
description
of the instrument in
his
ETH student
notes,
H. F. Weber's
Lectures
on
Physics,
ca.
December 1897ca. June
1898
(Vol.
1,
Doc.
37),
pp.
156158.
[27]The
electrometer
is
treated
as a
system
of
two condensers,
each formed
by
a pair
of
quadrants
and the
part
of the needle that
lies
above the
pair
(or
inside of
it; see
the
figure).
In
the
expression
for the total electrostatic
energy
I,
P1
and
P2 are
the
potentials
of
the two
pairs
of
quadrants,
p
is
the
potential
of the
needle,
a

x
and
a
+
x
are apparently proportional to
the
area
of the needle above
(or
inside)
each of the
pair
of
quadrants,
and
k
is
a
constant.
The
derivative of
O
gives
the
torque D
that
is
exerted
on
the
needle.
[28]The
"Maschinchen"
is
Einstein's invention for
measuring
small
potential
differences
or
charges.
For
a description, see
Einstein
1908a
(Vol. 2,
Doc.
48).
A
charged
conductor
with