  Noting that the extensive astrometric observations of the double comet
Wirtanen (C/1956 F1) made by E. Roemer have never been published, I replicate
the contents of a fortuitously discovered copy of her measurement records of
the companion's offsets from the main mass in 1957-1959 and use with such data
by others to refine the fragmentation solution. The sublimation-driven
nongravitational acceleration is shown to essentially control the companion's
motion in the orbital plane. The fragmentation parameters derived by the author
in 1978 have now been improved and strong disagreement with the independent
results by Roemer is noted. The revised model is employed to predict the
positions of the companion on the plates exposed by Roemer on 25 September
1960, which she reported to show the principal nucleus but not the companion.
At my request, these plates have now been scanned and processed at the Lowell
Observatory, and the companion is found to be located at the predicted
position. The images of the main mass and the companion on one of the two
plates are displayed.
