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210
The Fairy-Land of Science
·
Arabella B. Buckley
79
Can
we
form
any
idea
why
the
crystals
build
themselves
up
so
systematically?
Dr.
Tyndall
says
we
can,
and
I
hope
by
the
help
of
these
small
bar
magnets
to
show
you
how
he
explains
it.
These
little
pieces
of
steel,
which
I
hope
you
can
see
lying
on
this
white
cardboard,
have
been
rubbed
along
a
magnet
until
they
have
become
magnets
themselves,
and
I
can
attract
and
lift
up
a
needle
with
any
one
of
them.
But
if
I
try
to
lift
one
bar
with
another,
I
can
only
do
it
by
bringing
certain
ends
together.
I
have
tied
a
piece
of
red
cotton
(c,
Fig.
21)
round
one
end
of
each
of
the
magnets,
and
if
I
bring
two
red
ends
together
they
will
not
cling
together
but
roll
apart.
If,
on
the
contrary,
I
put
a
red
end
against
an
end
where
there
is
not
cotton,
then
the
two
bars
cling
together.
This
is
because
every
magnet
has
two
poles
or
points
which
are
exactly
opposite
in
character,
and
to
distinguish
them
one
is
called
the
positive
pole
and
the
other
the
negative
pole.
Now
when
I
bring
two
red
ends,
that
is,
two
positive
poles
together,
they
drive
each
other
away.
See!
the
magnet
I
am
not
holding
runs
away
from
the
other.
But
if
I
bring
a
red
end
and
a
black
end,
that
is,
a
positive
and
a
negative
end
together,
then
they
are
attracted
and
cling.
I
will
make
a
triangle
(A,
Fig.
21)
in
which
a
black
end
and
a
red
end
always
come
together,
and
you
see
the
triangle
holds
together.
But
now
if
I
take
off
the
lower
bar
and
turn
it
(B,
Fig.
21)
so
that
two
red
ends
and
two
black
ends
come
together,
then
this
bar
actually
rolls
back
from
the
others
down
the
cardboard.
If
I
were
to
break
these
bars
into
a
thousand
pieces,
each
piece
would
still
have
two
poles,
and
if
they
were
scattered
about
near
each
other
in
such
a
way
that
they
were
quite
free
to
move,
they
would
arrange
themselves
always
so
two
different
poles
came
together.
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