Lenses and Waves

102 CHAPTER 3
theory of spherical lenses he had developed earlier. As contrasted to
Descartes and others, his design for a better – or even perfect – telescope
did not start out with the ideal lenses of geometry, but with the ‘poor’ lenses
of actual telescopes. He did not avoid or explain away the defects of
spherical lenses, like Descartes or Hudde. He analyzed these defects in order
to take them into account and eventually correct them. Huygens’ design of a
perfect telescope was not based on the theoretically desirable, but on the
practically feasible.
Although craftsmanship preconditioned De Aberratione, Huygens did not
go the craftsman’s way as in his earlier inventions. He wanted to derive a
blueprint for an improved configuration on the basis of his theoretical
understanding of lenses. Instead of tinkering with lenses, he would be
tinkering with mathematics. He replaced the trial-and-error configuring of
lenses by mathematical design. Whether consciously or not, Huygens was
trying to bridge the gap between craftsmanship and scholarship. It was an
effort to make science useful for the solution of practical problems. An
advanced one, as the limitations and possibilities of the actual art of
telescope making were at the very heart of Huygens’ project. De Aberratione
can be seen as an early effort to do science-based technology.
How did Huygens set about it? He tried to understand mathematically the
technical problem of imperfect focusing and to solve it by means of his
theory. The configuration of lenses was the only part of the artisanal process
of telescope making he replaced by theoretical investigation. Colors he left
for crafty hands. Despite this close tie to practice, the subsequent elaboration
of the project was a matter of plain mathematics. He reduced the problem of
the imperfect focusing of spherical lenses to the mathematical problem of
spherical aberration. He then designed a configuration of lenses that
overcame the latter problem, assuming that it also solved the original
practical problem. It did not, for the test of his design brought to light an
additional technical problem that escaped his mathematical theory of lenses.
In a way, it was not just a test of his design but of his theory of spherical
aberration as well. The trial of 1668 can be seen as an empirical test of his
theory of spherical aberration – the first one, as far as the sources reveal.
Whether Huygens also saw it in this way may be doubted. His second design
of 1669 was founded upon the same theory. We do not know whether he
expected it to be free of colors, had it been realized. With hindsight, we can
say that the failure of Huygens’ project is an example of the fact that
technology goes beyond the mere application of science.
Huygens had remarked earlier that colors were a technical problem.
Minimizing their effects was a matter of craftsmanship and eluded
mathematical understanding. Unlike Barrow, Huygens was not inexperienced
with the craft of telescope making at all. With his diaphragm and his eyepiece
he had shown that he was quite capable of handling such technical problems.
The remark in his letter to Constantijn shows that he must have known, in a
practical way, much more of the properties of those disturbing colors than