Lenses and Waves

238 CHAPTER 6
author, he has excited all the more those who wrote after him to resume it and to try to
find something better.” 84
This can hardly be read otherwise than as the outline of a program of
Cartesian physics. On the basis of the clear and comprehensible
philosophical foundation laid by Descartes’ followers would erect the
mechanistic science he himself failed to realize. At this moment, Huygens
does not tell that not long after his introduction to Cartesian philosophy
another protagonist of the new sciences would make an even deeper an more
decisive impression on him: Galileo. But first his reception Descartes’
teachings.
Undeniably, Huygens’ ideas about the ultimate nature of things have
always been uncompromisingly mechanistic. The question is, however, what
relevance these philosophical ideas for his science and when, and how, this
mechanistic framework was mobilized in his actual investigations. At what
moments did Huygens become a mechanistic philosopher, philosophizing
about the mechanistic causes of the phenomena? In Traité de la Lumière his
mechanistic thinking had a designate yet limited role of providing plausibility
of his hypotheses. His focus was on the derivation of the laws of optics. This
aspect of Huygens’ optics developed late in his career, probably not before
the late 1669s during his sojourn in Paris. In Huygens’ optics in general, La
Dioptrique formed the main point of reference, first as regards the dioptrics of
telescopes, then the mathematics and mechanics of refraction.
Responding to Descartes does indeed form a thread in Huygens’ optics,
but one that needs qualification. In the early decades of his career he
primarily responded to Descartes’ ideas and achievements insofar as they
pertained to the mathematical sciences. ‘Physique’, the consideration of
topics in mechanistic philosophy and the response to Descartes’ natural
philosophical conceptions, enters his oeuvre at a later stage, in the context of
his Académie activities. These qualifications of Huygens’ Cartesianism put
his famous confrontations with Newton in 1672 and 1690 in a different
perspective. The first, in 1672, concerned Newton’s theory of colors and has
been discussed in chapter 3. The second, around 1690, was Huygens’
reaction to Newton’s theory of universal gravity, and I will now discuss it
briefly. To do so, we have to go back to the late 1660s, when Huygens laid
the foundation of his ideas about the mechanistic cause of gravity.
The subtle matter of 1669
On one page in his notebook, probably between September 1667 and
February 1668, Huygens listed a series of statements about “… a matter very
84 OC10, 406. “Nonobstant ce peu de veritè que je trouve dans le livre des Principes de Mr. des Cartes, je
ne disconviens pas qu’il ait fait paroitre bien de l’esprit à fabriquer, comme il a fait, tout ce systeme
nouveau, et a luy donner ce tour de vraisemblance qu’une infinitè de gens s’en contentent et s’y plaisent.
On peut encore dire qu’en donnant ces dogmes avec beaucoup d’assurance, et estant devenu autheur tres
celebre, il a excitè d’autant plus ceux qui escrivoient apres luy a le reprendre et tacher de trouver quelque
chose meilleur.”