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Lot 342
DAWES, WILLIAM RUTTER (1799-1868, astronomer)
£400 - 500
US$ 670 - 840
Lot Details
DAWES, WILLIAM RUTTER (1799-1868, astronomer)
LONG AUTOGRAPH LETTER SIGNED ('WR Dawes'), to J[ohn] Heparth (1790-1868), mathematical physicist and journalist; beginning with an exposition of scientific methodology, Dawes considers the phenomenon of apparent projections and then defends his own observations against the idea that they afford only negative evidence of the subject; discusses at length the whole notion that an 'involuntary & unconscious change in the adjustment of the eye while intently expecting an occultation, would produce the rapid enlargement of the moon's edge, causing it to appear even behind the star while in fact it had not yet reached it'; provides the Royal Observatory's evidence of occultations and of the debates at the Royal Astronomical Society on the subject; rejects Heparth's interpretation of his [Dawes's] observation of the occultations of Jupiter; cites passages from reports by Sir James South and [George] Airy, the Astronomer Royal; and comes to the conclusion that 'no theory can be accepted as adequate to account for the phenomenon which does not extend to projections of from 4 to more than a dozen seconds' duration. It must also be admitted as a certain fact, that the instant of actual disappearance is the same to all observers, whether they see any projection or not...', 6 closely written pages, quarto, light brown stains to last page, recipient's note at head (in pen and ink) and (in pencil) in margins and across text and also with sidelines in pencil, Hopefield Lodge, Haddenham, Thame, 12 May 1860


  • ENTIRELY ABOUT ASPECTS OF OCCULTATIONS AND SCIENTIFIC METHODOLOGY. 'The term occultation is most frequently used to describe those relatively frequent occasions when the Moon passes in front of a star during the course of its orbital motion around the Earth. Since the Moon has no atmosphere and stars have no appreciable angular size, a star that is occulted by the moon will disappear or reappear very nearly instantaneously on the moon's edge, or limb. Events that take place on the Moon's dark limb are of particular interest to observers, because the lack of glare allows these occultations to more easily be observed and timed.' (Wikipedia).

    Dawes contributed papers to the Royal Astronomical Society on occultations, triple and double stars, planets, comets, the solar eclipse of 1836, photometry and instruments. He discovered the rotation of sunspots and invented the wedge photometer. 'Dawes contribution to double-star astronomy was enormous...[he]...was one of the leading observational astronomers of his time and "by 1860 probably the most skilled visual observer with a refracting telescope in the world"...His skill earned him the sobriquet "eagle-eyed"' (R.A. Marriott, Oxford Dictionary of National Biography). In 1865 Dawes established the non-atmospheric character of the redness of Mars.
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