Abstract
MR. GILL'S EXPEDITION TO ASCENSION.—In address to the Royal Astronomical Society on April 8, 1857, “On the means which will be available for correcting the measure of the sun's distance during the next twenty-five years,” the Astronomer-Royal directed attention to a method of making observations for parallax, not applicable to the planet Venus, but applicable to Mars, namely, by “observing the displacement of Mars in right ascension when he is far east of the meridian, and far west of the meridian, as seen at a single observatory,” and he particularised the advantage of this method, and expressed his opinion that it is “the best of all.” The observations are not attended with the very great expense which is involved in the efficient observation of a transit of Venus, indeed if made at an established observatory need entail little or no cost; they may be conducted by a single observer or series of observers, in the latter case with a due regard to personal equation, and each observatory co-operating in the work, will furnish a result quite independent of the rest, so that the observer has the satisfaction of knowing that by the method recommended his own observations alone will give a value for the most important unit of measure in astronomy. The Astronomer-Royal confined his remarks to the observation of differences of right ascension, recommending as of the first consequence a firmly-mounted equatorial, and as advantageous though not absolutely necessary the chronographic method of transits first introduced by the American astronomers. The oppositions of Mars in 1860 and 1862 were referred to with regard to their relative advantages for such observations.
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Our Astronomical Column . Nature 16, 14–15 (1877). https://doi.org/10.1038/016014b0
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DOI: https://doi.org/10.1038/016014b0