Lenses and Waves

252 CHAPTER 6
A combination of several factors caused the almost complete rejection of
Huygens’ theory in the eighteenth century. 140 His account of rectilinear
propagation was generally thought to be inadequate, even by those who did
not follow Newton’s emission conception of light. The scope of the theory
was limited. In particular Huygens’ omission of colors was a drawback in
comparison with Opticks. In addition, the phenomenon on which Huygens’
theory was founded – strange refraction – was largely ignored during the
eighteenth century. Students of crystallography consulted Traité de la Lumière,
but only for his description of the crystal. 141 Only with the studies of Haüy,
Malus, and Wollaston the optical theory of strange refraction was
rediscovered. In some German textbooks Huygens’ theory was appealed to,
but adopted only in broad outline. 142 Huygens’ explanations of specific
phenomena such as rectilinear propagation were passed over. Hakfoort
explains this by the mathematical content of Huygens’ theory, that exceeded
the goals of books on natural philosophy, in which the nature of light was
customarily being discussed.
Hakfoort broadens his explanation of the neglect of Traité de la Lumière by
pointing out a disciplinary factor. Huygens’ mathematical treatment of
mechanistic causes eluded the capacities and interests of scholars dealing
with such explanatory theories. As had been the case previous to Huygens,
they resorted to qualitative explanations. Mathematicians, on the other hand,
continued to confine themselves to the behavior of light rays irrespective of
its underlying causes. According to Hakfoort, the eighteenth-century
disciplinary barriers between mathematics and natural philosophy, and the
lack of savants who successfully overcame them, caused Traité de la Lumière
to fall in neglect. 143 Opticks, on the other hand, had the advantage that it could
be read as an experimental theory of colors. Newton’s queries offered a
qualitative account of the nature of light and were adopted accordingly. This
would mean that the true ‘raisons de mechanique’ Huygens prided himself to
have established were an important factor in the neglect of his theory. What
Huygens considered as a comprehensible explanation eluded the savants of
the eighteenth century.
If Traité de la Lumière fell into oblivion, such was not the fate of Huygens’
oeuvre as a whole. Smith’s A Compleat System of Opticks is exemplary in this
regard. Whereas he ignored Traité de la Lumière – even for strange refraction
he adopted Newton’s account – his praise for Huygens’ accomplishments in
both practical and theoretical dioptrics was high. If Huygens was forgotten
as a mechanistic philosopher, he remained renowned as a mathematician. In
particular Horologium Oscillatorium earned him fame. In perfecting Galileo’s
science of motion, he was perceived as preparing the ground for Newton.
140
Hakfoort, Euler, 53.
141
Shapiro, “Kinematic optics”, 257.
142
Hakfoort, Euler, 119-126.
143
Hakfoort, Euler, 183-185.