Lenses and Waves

1690 - TRAITÉ DE LA LUMIÈRE 221
in French to join it with the first which is in this same language. This plan
has changed for it will remain in Latin.” 36
After the publication of Traité de la Lumière, Huygens continued to work
on the dioptrical treatise. In 1692, his plans changed once again after he had
read Molyneux’ Dioptrica Nova. Huygens’ notes on Dioptrica Nova survive. 37
Molyneux had treated telescopes better than anyone before, but had “little of
the things my treatise contains on this matter” 38 Huygens knew that he was a
better mathematician than the Irishman, and realized that he had still
something valuable to present in dioptrics. Some time after his reading of
Dioptrica Nova, he made a new (also the last) outline for his dioptrics: “De
Ordine in Dioptricis nostris servando” 39 He would leave out what Molyneux
had treated and emphasize his own strong points: the theories of spherical
aberration and magnification. He gave particular attention to his theorem on
the magnification produced by a given system of two lenses, the lens-formula
as it is called nowadays. 40 Huygens would prove it (instead of just stating it, as
Molyneux had done) and extend it to more complex systems.
‘De Ordine’ brought together scattered material ranging from the 1650s
to the early 1690s. In accordance with this scheme, Huygens ordered his
manuscripts and numbered the pages in red. 41 Roughly the set runs as
follows: the first part of Tractatus, with De Aberratione (without the rejected
parts) inserted after proposition twenty, propositions one and two of part
three of Tractatus, part two of Tractatus, various fragments of ‘De Telescopiis’.
It makes it clear that in the course of 40 years Huygens’ views on what
dioptrics was about had not changed: it was about telescopes. It had to
account for the working and improvement of telescopes mathematically.
Huygens did not live to see his dioptrical treatise through the press. In his
will he instructed De Volder and Fullenius to look over his “mathematical
writings” and “to edit as best they can whatever in it might be fit to
publish” 42 He explicitly named the ‘Dioptrika’ and three other treatises. De
Volder and Fullenius followed Huygens’ ordering pretty closely, so that the
1704 edition gives a good indication of his final idea of Dioptrica. 43
36
OC13, 754n4. “Commencement de ma seconde partie de la Dioptrique en francois pour la joindre a la
Première qui est en cette mesme langue. Ce dessein est changè car elle demeurera en Latin.”
37
OC13, 826-844.
38
OC10, 279. “… peu de ce que contient mon Traitè sur cette matiere.”
39
OC13, 770-778.
40
OC13, 773-774. The original version was: OC13, 186-197 and is treated in section 0.
41
Hug29, 101bis-205. 42
OC22, 775-776. “schriften van Mathematique” and “… ‘tgeen daerin soude mogen weesen bequaem
om gepubliceert te werden, hetselve willen besorgen ten besten sij sullen connen, …”
43
The editors of the Oeuvres Complètes chose not to follow the final ordering, but have attempted to make a
chronological reconstruction of Huygens’ dioptrical papers.