1. 1854. Notices Scientifiques, vol. i 491–491.
2. Outlines of Astronomy 232–232.
3. Astronomie Populaire, vol. ii 396–396. Since this was written I find that Bessel considered that the vibrations of the tail of Halley's comet, observed by him, indicated the action of a polar force. Arago has made no mention of this hypothesis, apparently because he doubted the results on which it was founded