1. 1. Since Horrocks' observation of the 1639 Venus transit here only affords an entrance into what follows, details need not be given. Two variant holographs in fact exist of the text in which Horrocks wrote up his account of the transit, the well-known one published by Hevelius at Danzig in 1662 asVenus in Sole visaand a second (autograph, it would appear) now in Flamsteed's papers at the Royal Greenwich Observatory (Volume 68/C); the latter is unpublished in its Latin original, but was translated into English by A. B. Whatton in the middle of the last century asThe Transit of Venus over the Sun(London, 1859 ). The fullest secondary account of the topic publicly available is to be found in Chapter V (pages 72-103) of Betty M. Davis, "The Astronomical Work of Jeremiah Horrocks" (London M. Sc. thesis, 1967); but F. I. Lowe of Ecton, Northampton is currently engaged in studying the two texts of theVenusas part of a wider series of researches into the scientific and astronomical attainments and impact of Horrocks and his fellow mid-17th century north-countrymen. See also page 515 of W. Applebaum's article on "Horrocks, Jeremiah" in Scribner'sDictionary of Scientific Biography, 6 (New York, 1972): 514-16; and pages 375-6 of C. A. Ronan's semipopular 1975 Horrocks lecture on "Horrocks and Astronomy in his Time" (Journal of the British Astronomical Association, 86, 1976: 370-8).
2. 2. More fully,Astronomia Britannica: In qua Per Novam, Concinnioremq; Methodum,... quinq; Tractatus traduntur, (London, 1669 ). Newton's annotated copy of this is now in Trinity College, Cambridge (shelfmark NQ.18.36). To be precise, Newton's Latin scene-setting words are: 'poneAspectatorem in Terra,VVenerem acDCSolem sitq;ABVradius a Venere in Atmosphaeram versusABrefractus et producaturBVrecta adCpunctum in disco solari, et manifestum est quod radij a parte SolisCper locum Veneris (si modo obesset) adBvenientes refringentur etiam adA, adeoq; Venus apparebit obtegere locum disci solaris C'.
3. 3. See 1 above, and also pages 121-4 of Betty Davis' M. Sc. thesis on Horrocks. In hisVenusand other papers (see, for instance, page 164 ofHorroccii Opera Posthuma, London,11672/3) Horrocks gives good reasons for affirming that the solar parallax must be inconsiderable, but his appeals to the 'unity of nature' and Keplerian 'harmonies' - he supposes in particular that the planetary radii increase outwards from the Sun in proportion to their solar distances- in attaining his precise values for the parallax (on this compare page 251 of C. A. Wilson, "Horrocks, Harmonies, and the Exactitude of Kepler's Third Law", Studia Copernicana, XVI, Warsaw, 1978 , 235-59) were little to the taste of such later literal-minded astronomers as Flamsteed (who by precise observational triangulations thirty years afterwards further reduced the solar parallax to be some 10"-12" only). Newton, I may notice, already in late 1665 knew that 'M' Jeremy Horrox by his Observation of Venus in yeo concluds yeos horizontal parallax to be 15". Hypparchus, Ptolemy, Albategnius Ticho & c suppose it to be twixt 3' & 2'1/3. Kepler maketh it 1' (Cambridge University Library, MS Add. 3996, f.27r), but this information he took from reading Thomas Streete'sAstronomia Carolina(London,11661). His reactions to Horrocks'Venusitself -ifhe ever read it - are not recorded.
4. 4. It was the curious main thesis of Markham's, in his 'Postscriptum' (after page 244) to theAstronomia, that the nearer the planetVwas to the terrestrial observerA, thegreaterwould be the angular refraction by the atmosphere atBofVBintoBA- 'Quando verae altitudines [duorum Planetarum] conveniunt, tum fit per Refractionem ut altitudines apparentes ita discrepant, ut vicinior magis refringitur': which were it true (the reverse is the case), the horizontal parallaxEVAwould indeed, to the observer atA, largely be cloaked by the atmospheric refraction of the lightray passing fromVtoA. (Curtis Wilson has on pages 256-8 of his "Horrocks, Harmonies, and... Kepler's Third Law" traced the growth of this thoroughly mistaken notion from its birth in Wing's own 1663Almanack.).
5. 5. Inter aliamakes the strong point that, if the Earth possessed no refracting atmosphere, VenusVwould occlude a placeDon the solar disc (in line withAV) higher up on it than that,C, which it is seen to cover; whence refraction acts to increase the horizontal parallaxAVE- 'ducatur rectaAVet producatur donec cum Sole itidem occurrat inDet manifestum est quod si nulla esset refractio Venus appareret in loco Disci solarisDqui cum superior sit locoCmanifestum est quod refractio deprimit Venerem in Disco aeque ac Parallaxis atq; ita non minueret parallaxin sed augeret potius, quantum nempe angulusBVEest major ParallaxiAVE'.