Lenses and Waves

224 CHAPTER 6
corners but that these dispersing waves are too weak to produce light. 57 This
argument was, of course, elaborated in the first chapter of Traité de la
Lumière. 58 At the beginning of 1690, Traité de la Lumière was printed and he
sent some copies to England. 59 Huygens wrote Fatio on 7 February 1690 that
he was anxious to know what Newton thought of his “… explanations of
refraction and of the phenomena of Iceland crystal, but I am not quite sure
whether he understands French, …” 60 He would not live to see Newton
entirely reject the idea of light waves, and ignore his explanation of strange
refraction, in the queries appended to Opticks.
With Traité de la Lumière now published, we may ask what Huygens
thought he had published. The hesitations about titles and languages suggests
that Huygens was not sure anymore of the status of his wave theory. Did it
still belong to his ‘Dioptrique’? He had written it in French, the language
used at the Académie. But French was also the language of the particular
topics discoursed of there, issues in physics and so on. Latin, on the other
hand, was the language he used for mathematical topics. 61 His doubts about
translating it might also indicate that he was doubting whether it still
belonged to the mathematical science of optics. At the very last moment
Huygens decided to publish it as an independent treatise in French, under
the title Traité de la Lumière. In so doing, he cut through the umbilical cord of
his wave theory, thus withdrawing it from the realm of mathematics.
Huygens had put, so to speak, his theory of light in the milieu of the Paris
Académie and the post-Cartesian debates proliferating there. Through the
decoupling of Traité de la Lumière from ‘Dioptrique’ he focused attention on
the wave theory, that is, on the explanation of the laws of optics instead of
their application to the behavior of rays. The title he chose, Traité de la
Lumière instead of Dioptrique, suggests that the treatise had switched from a
correction of La Dioptrique to a rebuttal of Le Monde. However, its stated aim
was much more modest:
57
OC21, 475.
58
Cohen argues that one of the reasons Huygens was urged to publish Traité de la Lumière was to guarantee
his priority regarding the theory of wave propagation. Cohen, “Missing author”, 32.
59
Cohen explains that a series of Traité de la Lumière exist that was issued by the publisher Vander Aa with
the author’s name spelled out on the title page: “Par Monsieur Christian Huygens, seigneur de Zeelhem.”
The other copies of Traité de la Lumière, including the large-size edition Huygens also printed to distribute
among acquaintances, only have the author’s initials on the title page: “Par C.H.D.Z.”. Cohen assumes
that the title page was altered just after printing had begun. The reason may have been that Huygens had
used the title ‘Lord of Zuylichem’ in earlier publications and wanted to prevent confusion by used a
neutral ‘D.Z.’. Since the death of their father, Constantijn formally was ‘Lord of Zuylichem’. Cohen,
“Missing author”, 33-35.
60
OC9, 358. “… Explications de la Refraction et des phenomènes du cristal d’Islande, mais je ne suis pas
bien assurè s’il entend le François, …”
61
After his move to Paris in 1666 Huygens began writing more and more in French, with the exception
however of his works on mathematics. Illustrative are his 1672 notes on strange refraction, where – as we
have seen above – he switched between both languages accordingly. Huygens’ use of languages
corresponds with what seems to be a general pattern. Halfway the seventeenth century, the vernacular had
begun to replace Latin in scholarly writings, especially in France and England. The notable exception are
mathematical texts, which remained to be written in Latin well into the nineteenth century. A systematic
study of the use of languages in scholarly writings would be well worth pursuing.