Credit: ©The Royal Society
    Image number: RS.15669

    A 'universal measure'

    Date
    10 October 1664
    Creator
    Unknown, Artist
    Object type
    Archive reference number
    Manuscript page number
    p3
    Dimensions
    height (page): 190mm
    width (page): 152mm
    Description
    Diagrams from Christian Huygens's letter to Robert Moray concerning the problem of a 'universal measure', namely determining the length of a seconds pendulum. In this letter, Huygens discusses suspending different shapes from a cord: right-angle isosceles triangles, circles and ellipses. This was a topic of interest to the Royal Society, and William Brouncker in particular. Huygens worked out a general solution to determining the centre of oscillation in early October 1664, which was printed in Horologium oscillatorium (1674) (see Correspondence of Henry Oldenburg, ed. Hall and Hall, vol. 2, 268n8).

    The letter was read at the meeting of the Royal Society on 19 October 1664. Henry Oldenburg sent an extract to Robert Boyle on the next day, 20 October. These diagrams are reproduced in the extract at EL/OB/18/003.
    Object history
    At the meeting of the Royal Society on 19 October 1664, ‘Sir Robert Moray produced a letter of Monsieur Huygens to himself, which was read, containing, 1. A new observation of Jupiter, in whose disk the shadows of two of his satellites had been seen at Rome. 2. An account of watches with two springs so moved, that whilst the small weight is wound up by the great, it ceaseth not to have just the same force to make the balance wheel, on which it immediately hangs, turn. 3. A speculation of his own, in which, by searching for simple pendulums, isochrone to triangles and other figures, he had met with considerable propositions, which he affirmed to conduce to the establishing of the universal measure. It was ordered, that the several experiments specified in this letter should be tried, and Mr. Hooke take care thereof’ (Birch 1:476).
    Related fellows
    Christiaan Huygens (1629 - 2006, Dutch) , Natural philosopher
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