Lenses and Waves

1677-1679 –WAVES OF LIGHT 207
have succeeded: “In this way I have made section MNO, and I have found
that the surfaces it makes have the same refractions as the surface gG, …” 147
After considering various ways of cutting the crystal, he concluded: “It
appears that it is not the disposition of the layers of the crystal that
contributes to the irregular refraction.” 148 Bartholin’s explanation and
Rømer’s objections thus lacked a foundation. A second EUPHKA followed:
“EUPHKA. The confirmation of my theory of light and of refractions.” 149
Huygens had proven that his was the only acceptable explanation of strange
refraction. Unexpectedly, Rømer had made it clear that Bartholinus’ law
could not be dismissed forthwith and that Huygens should produce decisive
evidence against it. In doing so, Huygens showed that his was the only
theory that could also explain strange refraction. Ergo, to take Rømer by his
own words, his principle of wave propagation was the only useful principle
in optics. On 12 August he continued the reading of his ‘Dioptrique’ at the
Académie.
Forced innovation
In the summer of 1679 Huygens showed himself an able measurer and
inventive experimenter. In a two-stage reaction to Rømer’s objections he
refuted Bartholinus’ law and confirmed his own ellipse construction. The
measurement and the experiment added a new, empirical element to his
study of strange refraction. It is remarkable that Huygens had not questioned
Bartholinus’ data previously. In 1672 he had improved Bartholinus’
measurements of the angles of the crystal by means of a more reliable
technique. 150 Yet, apart from the angle of the refracted perpendicular ray –
which Bartholinus had not provided – he had not measured any angle of
refraction. He had never measured the unrefracted oblique ray or any other
rays. That he developed the technique to measure the refraction of a ray only
in 1679 appears from the fact that this section of Traité de la Lumière was
inserted into the original manuscript. 151 Until that time his theory had
developed in an empirical void. He discovered the ‘law’ of strange refraction
by mathematical reasoning, not from precise observations as Buchwald
concluded from his study of Traité de la Lumière. 152 The empirical solidity of
the finalized theory was acquired only at the third stage of Huygens’ studies
of strange refraction, when he was forced by Rømer’s objections to take a
closer look.
147
OC19, 442. “De cette maniere j’ay fait la section MNO, et j’ay trouvè que les surfaces qu’elle a faites
avoient les mesmes refractions que la surface gG, …” On 3 November 1679 he wrote his brother: “I have
found means to grind and polish this crystal which was thought impossible, …” OC8, 241. “J’ay trouvè
moyen de tailler et de polir ce cristal ce qu’on croioit impossible,…”
148
OC19, 443. “Il paroit que ce n’est point la disposition des feuilles du cristal qui contribue a la refraction
irreguliere.”
149
OC19, 441. “EUPHKA. La confirmation de ma theorie de la lumiere et des refractions.”
150
Buchwald, “Experimental investigations”, 313-314.
151
OC19, “Avertissement”, 385.
152
Buchwald, “Experimental investigations”, 313 & 316-317 and Buchwald, Rise, 313.