Lenses and Waves

104 CHAPTER 3
pursued his thinking on the disturbing colors his configuration turned out to
produce.
The reality is that colors thwarted Huygens’ plan to design via theory a
configuration of spherical lenses that minimized the effect of spherical
aberration. It was not his own observation of those colors that made him
drop the project. He needed a Newton to point out that those colors were
inherent to lenses. And he only got the point when Newton made clear that
it was an aberration; a mathematical property inherent to refraction. Huygens
realized that his project was futile when he saw the ‘Abberationem
Niutonianam’. Disappointed, he stroke out the larger part of what was one
of the most advanced efforts in seventeenth-century science to do sciencebased
technology.
The ‘raison d’être’ of Dioptrica: l’instrument pour l’instrument
Huygens’ orientation on the telescope may explain the form and content of
Dioptrica, it does not explain it as such. Why did Huygens want to develop a
theory of the telescope? Why did he want to prove mathematically that his
eyepiece performed the way he knew by experience it did? Kepler’s motive
for creating Dioptrice had been his conviction that an exact understanding of
the telescope was needed for reliable observations. In the practice of midseventeenth-century
telescopy this need did not turn out to be as pressing as
Kepler had thought. Even when the telescope became an instrument of
precision, astronomers could go about it with a rather superficial
understanding of the dioptrics of the telescope.
Kepler’s point of view does not seem to have been Huygens’ main
motive to embark upon a study of the dioptrics of the telescope. In a preface
he wrote in the 1680s for Dioptrica, he expressed his surprise that no one had
explained the telescope theoretically. One would have expected this
marvelous, revolutionary invention to have aroused the interest of scholars.
“But it was far from that: the construction of this ingenious instrument was found by
chance and the best learned men have not yet been able to give a satisfactory theory.” 214
In this preface, Huygens did not explain what further use such a theory
would have. He wanted to explain the telescope and did not wonder whether
others also found this important. To Huygens, I believe, the dioptrics of the
telescope was a meaningful topic in its own right.
Huygens’ practical activities strengthen the impression that he was
fascinated by the instrument for its own sake. As we have seen, his interest in
telescopes went far beyond mere dioptrical theory. He made telescopes and
prided himself with the innovations he had made to the instrument as well as
to the craft. Yet, making telescopes seems to have been a goal in itself. 215
Despite his impressive discoveries around Saturn, Huygens never became a
telescopist. He did not – and could not and need not – make some sort of a
214
OC13, 435. “Sed hoc tam longe abest, ut fortuito reperti artificij rationem non adhuc satis explicare
potuerint viri doctissimi.”
215
Van Helden, “Huygens and the astronomers”, 148 & 158-159.