Our Astronomical Column

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    SOLAR PARALLAX FROM THE VELOCITY OF LIGHT.—Mr. D, P. Todd, of the American Nautical Almanac Office, publishes an interesting note upon this subject. Remarking that tie opposition of Mars in 1862, when the planet approached near the earth, and the experimental determination of the velocity of light in the same year, mark the beginning of a new era in the history of the determination of the solar parallax, he refers to the many values of this constant which have since been worked out, and the fact that although theoretically the better class of these determinations should yield values in consistent harmony with each other, there are at present singular and unaccountable discordances. Prof. Newcomb's mean value of the parallax, 8.848, he observes, was regarded with caution only because it was considered too small, the researches of Hansen, Leverrier, Stone, and Winnecke appearing to place the parallax considerably outside Newcomb's value. Within the last two or three years, however, Mr.Todd remarks that “the parallactic pendulum has swung quite to the lesser extremity of the arc until the true value of the solar parallax has appeared possibly below 8″.8, and that, too, with good reason.” But now there seems to be a slight gravitation towards a central value, and he thinks it is not possible to say that the mean equatorial horizontal parallax of the sun is so much as the hundredth part of a second different from the old figure, 8″.813 (27″.2 centesimal) adopted by Laplace in the Mécanique Céleste, and resulting from the early discussions of the transits of Venus in 1761 and 1769.

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    Our Astronomical Column . Nature 21, 331 (1880) doi:10.1038/021331a0

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