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210
The Fairy-Land of Science
·
Arabella B. Buckley
36
How
is
it
then,
that
if
all
these
different
waves
making
different
colours,
hit
on
our
eye,
they
do
not
always
make
us
see
coloured
light?
Because,
unless
they
are
interfered
with,
they
all
travel
along
together,
and
you
know
that
all
colours,
mixed
together
in
proper
proportion,
make
white.
I
have
here
a
round
piece
of
cardboard,
painted
with
the
seven
colours
in
succession
several
times
over.
When
it
is
still
you
can
distinguish
them
all
apart,
but
when
I
whirl
it
quickly
round
-
see!
-
the
cardboard
looks
quite
white,
because
we
see
them
all
so
instantaneously
that
they
are
mingled
together.
In
the
same
way
light
looks
white
to
you,
because
all
the
different
coloured
waves
strike
on
your
eye
at
once.
You
can
easily
make
on
of
these
card
for
yourselves
only
the
white
will
always
look
dirty,
because
you
cannot
get
the
colours
pure.
Now,
when
the
light
passes
through
the
three-sided
glass
or
prism,
the
waves
are
spread
out,
and
the
slow,
heavy,
red
waves
lag
behind
and
remain
at
the
lower
end
R
of
the
coloured
line
on
the
wall
(Fig.
7),
while
the
rapid
little
violet
waves
are
bent
more
out
of
their
road
and
run
to
V
at
the
farther
end
of
the
line;
and
the
orange,
yellow,
green,
blue,
and
indigo
arrange
themselves
between,
according
to
the
size
of
their
waves.
And
now
you
are
very
likely
eager
to
ask
why
the
quick
waves
should
make
us
see
one
colour,
and
the
slow
waves
another.
This
is
a
very
difficult
question,
for
we
have
a
great
deal
still
to
learn
about
the
effect
of
light
on
the
eye.
But
you
can
easily
imagine
that
colour
is
to
our
eye
much
the
same
as
music
is
to
our
ear.
You
know
we
can
distinguish
different
notes
when
the
air-waves
play
slowly
or
quickly
upon
the
drum
of
the
ear
(as
we
shall
see
in
Lecture
VI)
and
somewhat
in
the
same
way
the
tiny
waves
of
the
ether
play
on
the
retina
or
curtain
at
the
back
of
our
eye,
and
make
the
nerves
carry
different
messages
to
the
brain:
and
the
colour
we
see
depends
upon
the
number
of
waves
which
play
upon
the
retina
in
a
second.
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