ic
-.-
...
.
..
..
,
.
-. .
.
. .
^..
. .
-:
,.
__
..
.
size
of
the
particle
radius
decreases,
extinction
for
<
2
decreases.
A
fifty
percent
increase
in
the
relative
radius
of
the
particles
appears
sdficient
to
produce
the
variation
In
the
ratio
of
selective
to
total
extinction
observed
by
Johnson
(1965).
observed
interstellar
extinction
curve
also
occurs;
at
xol
=
4.4
microas.
a
strong
armat
in
favor
of
graphAte.
For
the
first
time
thoro
is
structure
in
the
extinction
CUI'VO
and
ft
can
be
At
the
same
the,
the
A
maximum
in
the
The
aiithozs
feel
that
this
coincidence
provides
accounted
for
by
a
particular
substance,
possible
that
some
other
materfaf
could
have
the
same
signature
and
also
be
abundant
In
intorstellar
spaco
but
it
seems
improbable.
The
albedo
for
this
particle
size
distribution
is
some
what
larger
than
that
found
by
Wickramasingho
(1963)
and
nay
be
sufficiently
high
to
account
for
reflection
nebula
(van
Boutin,
1961).
inconsistant
with
the
observations.
It
seems
unlikely
that
a
particle
size
distribution
could
bo
forrnd
that
would
bo
satisfactory,
The
addition
of
n
diolectrfc
material
either
as
8
coating;
of
the
graphite
or
as
separate
amall
particles
could
easily
bring
up
tho
curve.
A
promising
"dielectric"
which
is
already
present
is
graphite
itself,
Graphite
1s
strongly
anisotropic,
optical
constants
Ensured
for
the
electric
vector
in
the
bqsrtl
planes,
When
the
electric
vector
is
perpendicular
to
the
basal
planes,
the
conductivity
is
at
letkt
100
tlmm
smaller
(Wickramssingbe
1963)
and
graphite then
acts
like
a
dielectric,
Since
grapate
%s
presumed
to
be
present in
the
fona
of
flakes
that
are
almost
randomly
oriented,
a
sizeable
proportion
of
the
fXakes
will present
thla
thin
dielectric
face
to
the
radlation,
index
of
refractSon
are uncertain
which
preciuaes
a
qiiaiitftatiYe
It
is
of
course
For
shorter
wavelengths,
the
calculated
curve
fs
Our
calculations
were
made
with
Both
the
ratio
of
crystal
axis
and
the
"dielectric"
calculation at-this
time.
Tbls
conjecture
could
bo
-2-
;
XERO
2
observationally
checked
by
polarization
measurements
at
I.-'
=
6
u",
of
iatorstollar
extinction
a
reversal
In
the
sign
of
mlarizrrtion
would
be
expected
when
the
"dielectric"
extinction
If
graphite
fa
asnuned
to
be
the
sole
caw30
L
exceeds
tbt
of
the
conducting
plane.
for
Interstellar
carbon
graim
it
bs
recently
been
pointed
aut
(Lam,
1866)
that
graphite
flakes
nag
grow
in
space
if
countering
effects
can
be
neglected.
The
exponential
whisker
growth
mechanism
(Soars,
1955)
was
shown
to
apply.
For
a
plate
of
10-'cm
thlckeness,
the
3
length
reaches
5
x
loe6
cm
in
6
x
10
gears
for
Hn
=
l/cm
and
6
x
lo7
years
for
NE
=
In
addition
to
the
proposal
of
Boyle and
Wickramasinghe
8
3
Grains
such
as
these
are
intornediate
in
strscture
and
1o/clt
.
uass
between
classical
grains
proposed
by
van
de
Hulot
(1948)
and
Platt
particles
(Platt
,
1950)
.
With
the
assumption
of
graphite
it
appears
that
It
will
be
possible
to
obtain
considerable
detailed
information
concerning
tho
particle
size
distribution
in
the
Interstellar
clo~~ds
between
w
and
any
particulnr star
by
means
of
rocket
observations
We
wishta
express
our.
gratitude
to
Nxw.
Jaylee
Burleg
for
interpreting
her
investigations
to
follow
the
calculatiom through
the
conzputer.
Theodore
P,
Stecher
Bertram
Donn
Goddard
Space
Flight
Center
Zatlonal
Aeronautics
8
Space
Administration
Greenbelt,
Maryland
I
I
I
i
I
1
i
i
I
1
REHEREHCES
Boggess
XIX,
A,
and
BorBpant
J.
1964,
Ap.
J.
-
140,
1636,
Cayrel,
P.
and
Schatwlaan,$.
1954,
Ann
d’Ap.
-
17,
555.
Dan,
8,
1965,
--
A.
3.
70,
320,
IiopXe,
P,
azd
Prrfc~~singhe,
f.
C.
1962,
Y.H.,
124,
417.
Hulst,
B,
C.‘van
de
1949,
Rech,
Obs,
Astr.
Utrecht,
-
11,
Part
Po
Hulst,
E,-C,
van
de
195%
Light
Scattering2
Small
Particles
Routen,
C.
J.
van
1901,
B.A.N.
-
16,
4609,
1.
Jobson,
ff.
L.
1965,
Ap.
J.,
141,
$23.
(Xew
Pork,
John
Wtley
L
Soas,
Inc.).
Platt,
Jo
Bo
1956,
Ap.
Je
z,
486.
Sears,
G,
W.
l956,
Acta/Met,
-
3,
301,
Taft,
E.
A.
and
mtilipp,
E.
R,.
1969,
Phy.
Rev,,
-
138,
A197.
Wicltramasinghe,
1963a,
--
M,N,
125,
87.
.*
..
.
t
.
c
..
.