We show how to use matrix methods of quantum mechanics to efficiently and
accurately calculate axially symmetric radiation transfer in clouds, with
conservative scattering of arbitrary anisotropy. Analyses of conservative
scattering, where the single scattering albedo is $\stackrel{~}{\omega}=1$ and no
energy is exchanged between the radiation and scatterers, began with work by
Schwarzschild, Milne, Eddington and others on radiative transfer in stars.
There the scattering is isotropic or nearly so. It has been difficult to extend
traditional methods to highly anisotropic scattering, like that of sunlight in
Earth's clouds. The $2n$ -stream method described here is a practical way to
handle highly anisotropic, conservative scattering. The basic ideas of the
$2n$ -stream method are an extension of Wick's seminal work on transport of
thermal neutrons by isotropic scattering to scattering with arbitrary
anisotropy. How to do this for finite absorption and $\stackrel{~}{\omega}<1$ was
described in our previous paper (arXiv:2205.09713v2). But those methods fail
for conservative scattering, when $\stackrel{~}{\omega}=1$ . Here we show that minor
modifications to the fundamental $2n$ -scattering theory for $\stackrel{~}{\omega}<1$
make it suitable for $\stackrel{~}{\omega}=1$ .