and $220 \pm 30$ km s$^{-1}$, respectively. The discovery of transverse (clockwise) motion, with no radial motion, was unexpected.

The total flux density of component N-1 hardly changed, and the difference images shown in Figures 2 and 5 clearly show the negative-positive residuals characteristic of a moving source with constant flux density. In contrast, the negative-positive signature of proper motion is not present in the case of S-1 (see Figures 2 and 6) because during the same period there was the strong brightening previously discussed that dominated the difference image.

A Precession Model for IRAS 16547-4247
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We believe that it may be possible to understand the distribution of almost all the identified sources as well as the clockwise precession as the result of ejecta from a precessing jet of stellar origin. The gently curved and antisymmetric distribution of the radio components strongly suggests such a model. The basic idea is that the jet itself is not observed directly (because of the lack of radial motion in the outflow). Rather the observed sources are the result of the jet interacting with the ambient medium. We describe this model in simple empirical terms. We assume that the axis of symmetry is 