Blast from the past Measurement and morals in the early Transits of Venus

1. Blast from the past Measurement and morals in the early Transits of Venus Stephen Johnston Museum of the History of Science University of Oxford PHYSTAT 05 - Statistical problems in Particle Physics, Astrophysics and Cosmology Oxford, September 2005

2. The Choice The past is a foreign countryThey do things differently there - so it’s not directly comparable or relevant to today There’s nothing new under sun Doesn’t matter whether it’s 1769 or 2005, there are fundamental similarities in the predicament of the researcher

4. Benjamin Martin, A View of 17 Transits of the Planet Venus (1757)

5. ‘A Transitof thePlanet Venusover the Sun’s Disk is not only the mostrarebut also the most curiousPhaenomenonof the Heavens. And since themost Noble Problemin Nature, viz: theDimensionof theSolar System, is solvable only by it, & thereby renders it of the Greatest Consequence to Mankind, I concluded a proper Representation of all the Transits that happen in 1000 Years would prove no unacceptable Present to the Public.’ Benjamin Martin, 1757

6. Benjamin Martin (1705-1782) “The Great Retailer of the Sciences” Schoolmaster Author Lexicographer Itinerant lecturer Inventor Instrument maker Shopkeeper Publisher Entrepreneur

7. ‘A Transitof thePlanet Venusover the Sun’s Disk is not only the mostrarebut also the most curiousPhaenomenonof the Heavens. And since themost Noble Problemin Nature, viz: theDimensionof theSolar System, is solvable only by it, & thereby renders it of the Greatest Consequence to Mankind, I concluded a proper Representation of all the Transits that happen in 1000 Years would prove no unacceptable Present to the Public.’ Benjamin Martin, 1757

8. Benjamin Martin, Venus in the Sun (London, 1761)

9. Transits of Venus: • 18th-century challenges • One-day event in 1761 and 1769 • Global scattering of observers • Mix of established observatories and makeshift observing stations • International competition with nations at war • How to avoid error and inconsistency?

10. Captain James Cook (National Maritime Museum, Greenwich) Bark Endeavour (modern replica)

11. Tahiti, 1769 - through European eyes

12. Captain Cook in Tahiti: the Endeavour anchored off Fort Venus

13. Internal contact between Venus and the limb of the Sun

14. Transit observations by Cook and Green, Tahiti 1769 Philosophical Transactions (1771)

15. Transit observations by Cook and Green showing the ‘black drop’, Tahiti 1769, Philosophical Transactions (1771)

16. Samuel Dunn, ‘A Determination of the exact Moments of Time when the Planet Venus was at external and internal Contact with the Sun’s Limb’, Philosophical Transactions (1770)

17. Thomas Hornsby (1733-1810) 1760 - Fellow of Corpus Christi College, Oxford 1763 - Savilian Professor of Astronomy 1763 - Professor of Experimental Philosophy 1772 - Radcliffe Observer 1782 - Sedleian Professor of Natural Philosophy 1783 - Radcliffe Librarian Radcliffe Observatory Founded 1772

18. Thomas Hornsby and the Transits of Venus Observing: 1761 - Shirburn Castle, Oxfordshire (Earl of Macclesfield) 1769 - Tower of the Five Orders, Old Schools, Oxford Publishing (in Philosophical Transactions): 1763 - comparative analysis of 1761 transit 1765 - planning suitable stations for 1769, including South Seas 1769 - organising and reporting observing groups in Oxford 1771 - comparative analysis of 1769 transit

19. ‘It is well known to your Lordship, that the method practised by astronomers, in order to diminish the errors arising from the imperfections of instruments, and of the organs of sense, by taking the Mean of several observations, has not been so generally received, but that some persons, of considerable note, have been of opinion, and even publickly maintained, that one single observation, taken with due care, was as much to be relied on as the Mean of a great number.’ Thomas Simpson, 1756

20. ‘And the more observations or experiments there are made, the less will the conclusion be liable to err, provided they admit of being repeated under the same circumstances.’ Thomas Simpson, ‘A letter to the Right Honorable George Earl of Macclesfield, President of the Royal Society, on the advantage of taking the mean of a number of observations, in practical astronomy’, Philosophical Transactions, 49 (1756), 93

21. Solar parallax from Mars in opposition, 1751 Thomas Hornsby, ‘A Discourse on the Parallax of the Sun’, Philosophical Transactions, 53 (1763)

22. Solar parallax from Mars in opposition, 1751 - according to Lacaille Thomas Hornsby, ‘A Discourse on the Parallax of the Sun’, Philosophical Transactions, 53 (1763)

23. Planning for error reduction: Thomas Hornsby on the effect of solar altitude, 1765

24. Solar parallax from the transit of Venus, 1761 Thomas Hornsby, ‘A Discourse on the Parallax of the Sun’, Philosophical Transactions, 53 (1763)

25. Success in 1769 Thomas Hornsby, Philosophical Transactions (1771)

26. The solar system from Oxford; Thomas Hornsby (1771)

27. Thomas Hornsby’s calculation of solar parallax from the Transit of Venus, 1769, Philosophical Transactions (1771)

28. Thomas Hornsby transit calculations, 1769 (MHS Radcliffe MS 7)

29. ‘If Oxford be supposed only 5.0 W of Greenwich then….’

30. Hornsby juggling observations Ponoi and Norriton are dropped, then Cook is tried out as the only reliable witness from George’s Island (Tahiti)