'A Description of an Instrument for Dividing a Foot into Many Thousand Parts, and Thereby Measuring the Diameters of Planets to a Great Exactness, &c' HOOKE, Robert (1635-1703) Illuminating the World

HOOKE, Robert (1635-1703). 'A Description of an Instrument for Dividing a Foot into Many Thousand Parts, and Thereby Measuring the Diameters of Planets to a Great Exactness, &c' [in:] Philosophical Transactions, No. 29 [together with:] Philosophical Transactions, No. 25. London: Printed by T[homas] N[ewcomb] for John Martyn, Printer to the Royal Society, and are to be sold at the Bell a little without Temple-Bar, 1667. Two complete single issues, quarto (225 x 172mm); pp. 449-274 and 541-556 [folding plate] (very good; some light even browning throughout; bound in modern marbled-paper wrappers). A pivotal moment in the history of science: William Gascoigne's invention of the micrometer, communicated here by Richard Towneley and Robert Hooke in two issues of the Philosophical Transactions for 1667 (nos 25 & 29). Inspired by the work of Johannes Kepler, Gascoigne studied astronomical phenomena from the 1630s until his early death in 1644. Around 1638 Gascoigne devised his micrometer, consisting of two fine wires brought closer together or further apart by means of a screw of known pitch. Together with the focal length it is possible to calculate the size of astronomical objects with this set-up. In 1666, the French astronomer Adrien Auzout wrote to the Royal Society to describe his own micrometer, which was similar in design to Gascoigne's. Gascoigne's collaborator Richard Towneley, who was in possession of a micrometer of Gascoigne's design, wrote a strongly worded letter to Society, published in the 25th number of the Philosophical Transactions [offered here]. Towneley claimed Gascoigne's priority and gave a brief description of the instrument, an example of which he then sent to London. Hooke created his own version of the micrometer and wrote a thorough description, published in No. 29 [also offered]. Perhaps the most significant feature of Hooke's description is the remarkable engraving of the micrometer, which reveals aspects of its design not covered in the text. Moreover, the engraving is a piece of paper engineering in its own right: it shows two aspects of the design by means of an ingenious flap, which allows exterior and interior views. The micrometer was immediately put to use by Hooke and, more importantly, John Flamsteed, who used one extensively in the creation of his masterpiece Historiae coelestis, begun in 1676. In various forms, the micrometer has been central to precision astronomer ever since, and has transformed scientific understanding of the nature of celestial objects.