DOC.
11
LECTURE ON ELECTRICITY
&
MAGNETISM
253
algebraically;
in
other
words:
the
quantity
of
electricity
of
a system
of
bodies
is equal
to
the
sum
of the
quantities
of
electricity
of the
system's
individual bodies.
This
principle
can
be
further
extended,
given
the character of
our
experience
with
electrified
bodies.
If
bodies with
quantities
of
electricity
e1
&
e2
are brought
into contact
with
one
another, then,
in
general,
their electric
state will
change.
But their
action at
a
distance
on a
third
e. q.
ea
will not
change
upon
the
contact,
and
so
the
sum
of the
electrical
quantities
will not
change
either.
(Important
law
of the
constancy
of the
sum
of
quantities
of
electricity, an exception
to which has
never
been
found.)
We
endow
these
two laws with
a tangible, physical
meaning
by imagining
that the
substrate for the
quantity
of
electricity
is
some
sort
of indestructible
matter,
which,
however,
must
be
thought
of
as
being present
in
a positive
and
a negative
modification,
because
the
experiments
alluded
to
above show
the
existence
of
positive
as
well
as
negative
electrical
quantities
(in
the
case
of attractive
forces).
One
more thing
has to be
added
to
complete
what has
been
said
so
far,
for there
is
no way
to
decide
which
sign
to ascribe to
a specific given
electrical
quantity,
because the
[p. 5]
interaction between
two
e.
q.
only
makes it
possible
to
decide whether the
two have
to
be
assigned
like
or opposite signs.
But
all
that
is needed, therefore, is to fix
the
sign
in
a
specific
case
(glass
rubbed
with wool
is
positive),
in
order
to
fix
signs
for
all
other
quantities
of
electricity.
In
completing
what has
been
said
about the
auxiliary
representation
of
positive
and
negative electricity,
it
should be added that
one
imagines
that the interactive
forces act
between the electricities and
are
transferred
from
them
to
the carriers of
electricity
(bodies)
to which
they
are
bound. We further
complete
the
picture
by
the
assumption
that
not
only
the
algebraic sum
of the electrical
quantities,
but
also
the
sum
of the
electricities
of
each
of
the
signs
is
constant-a
proposition
that
is
part
of the
picture
and
that
cannot
be either
directly
confirmed
or directly
discomfirmed
by
experiment.
The
action
of
a system
of electric
masses
(e1 e2
....)
on a
pointlike quantity
of
electricity
(e).
An electrical
quantity
e1(x y
z)
exerts
the
force
K
on
a
quantity
of
electricity
e(a, b,
c).[4]
We
have
g
ee
i,
where
=
(x-a)2
+
(y-b)2
+
(z-c)2.
The direction
cosines
of
this force
are
x-a
y-b
z-c
r
r r
so
that
its
components are
Previous Page Next Page