Mathematical consideration is given to the symmetry of free molecular ‰ows through the pipe of an arbitrary shape. In the previous paper (I), it was shown that the diŠuse re‰ection based on a stochastic model conserves the symmetry if and only if it obeys cosine law. To explore whether a specular re‰ection conserves the symmetry, a new framework including both the stochastic and deterministic models was developed. Using this uniˆed framework it immediately follows that the specular re‰ection

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... serves the symmetry, even when arbitrarily mixed with the cosine law re‰ection. In contrast with the stochastic model, the deterministic model allows innumerable symmetry-preserving re‰ection rules.