1. Constantyn Huygens to Christiaan Huygens, Letter 2405, 25 October 1685, Oeuvres complètes de Christiaan Huygens, ix (The Hague, 1901); hereafter: OC, 36.
2. Christiaan Huygens to Constantyn Huygens, Letter 2404, 23 October 1685, OC, ix (The Hague, 1901), 35.
3. Leiden University Library, Special Collections, Ms. Huygens 45, Letter 2122, fol. 2v, Nicolaes Hartsoeker to Christiaan Huygens, 12 April 1678. Hartsoeker asked Huygens whether he would be able to accompany him to Paris. See, OC, viii (The Hague, 1888), 70-71
4. and Stroup Alice, A company of scientists: Botany, patronage, and community at the seventeenth-century Parisian Royal Academy of Sciences (Berkeley, 1990), 203.