(This list does not include reprints of separate works, which are included in the former lists. These are mentioned in the commentary to the first edition. The present list includes either larger projects of editing Christiaan Huygens' collected works, or fragments from his letters or manuscripts which had not been published before.
1. Edtions of Huygens' collected works.
(a.) 's Gravesande's edition.
W.J. s Gravesande (ed.), Christiane Hugenii Zulichemii, dum viveret Zelemii toparchae, Opera varia quattuor tomis distincta: Primus continet Opera mechanica. Secundus geometrica. Tertius astronomica. Quartus miscellanea, 4 vols. (Janssonius vander Aa, Leiden, 1724) prefaced by a biography (in Latin) of Christiaan Huygens (no page numbers).
The same work occurs also with a title page dated 1751: W.J. s Gravesande (ed.), Opera mechanica, geometrica, astronomica et miscellanea, 4 vols. (Gerardus Potvliet, Henricus van der Deyster, Philippus Bonk and Cornelius de Pecker, Leiden, 1751). Apart from the title-page, the edition is identical with the Opera varia in the edition of 1724.
(b.) The edition by the Hollandse Maatschappij der Wetenschappen:
2. Editions of unpublished Huygens manuscripts and letters.
Manuscript material on and by Christiaan Huygens that has become available after the completion of the Oeuvres complètes:, cf. Vollgraff (1951), Van Maanen (1985) and Vermij & Van Maanen (1992):