Description: Dawes (William Rutter, astronomer, 1799-1868) Long Autograph Letter signed to John Heparth, mathematical physicist and journalist, 6pp., 4to, Hopefield Lodge, Haddenham, Thame, 12th May 1860, an exposition of scientific methodology, Dawes considers the phenomenon of apparent projections and then he defends his own observations against the idea that they afford only negative evidence and discussing occultations, the Royal Observatory's evidence of occultations etc., folds, slightly browned. ***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. In 1865 Dawes established the non-atmospheric character of the redness of Mars..
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