Star Distances.1


THE festal offering contributed by Prof. Oudemans to the Pulkowa celebration is an especially appropriate one. The incidents of the long parallax-campaign can scarcely be recapitulated without recalling, in connection with the name of Friedrich Struve, the quorum pars magna fui of Æneas. He it was who, in Sir John Herschel's opinion (Memoirs R. Astronomical Society, vol. xii. p. 442), made the first real impression upon the problem by showing that not one of twenty-seven circumpolar stars discussed in 1819-21 could possibly have an annual parallax amounting to half a second of arc. Thenceforward, astronomers knew what they had to expect. Sanguine hopes of meeting comfortably large, and properly periodical residuals among ordinary observations, were checked, if not extinguished. The changes of stellar position reproducing, according to the laws of perspective, the movement of the earth in its orbit, were perceived to be on a scale so minute that their satisfactory disclosure lay, for the moment, beyond the range of what was feasible. Success in the enterprise, it was evident, was conditional upon the employment of more perfect instruments than had heretofore been available with a precision and vigilance of which the very idea was absent from all but a few prescient minds. Sir William Herschel seemed to have anticipated the conjuncture when he declared in 1782 the case to be “by no means desperate,” although stellar parallax should fall short of a single second (Phil. Trans., vol. lxxii. p. 83). The memorable “triple event,”by which, almost sirnultaneously. at the Cape, at Königsberg, and at Pulkowa, his confidence was justified, is familiar to all readers of astronomical history. Its significance may be estimated from Bessel's admission that, until the yearly oscillations of 6I Cygni emerged from his measures in 1838, he was completely in the dark as to whether stellar parallax was to be reckoned by tenths or by thousandths of a second (Asir. Nach., No. 385).

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CLERKE, A. Star Distances.1. Nature 41, 81–82 (1889).

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