Lenses and Waves

90 CHAPTER 3
glasse but in ye difformity of refractions.” 168 Despite his doubts about the
true properties of different refrangibility, Huygens now recognized that the
disturbing colors in lenses are inherent to refraction. There is no word about
spherical aberration in his letter, and he may indeed already have realized at
this point that his project to design configurations to neutralize it had
become useless. Would this help account for the sharpening in his tone?
Newton partially granted Huygens both objections. He dropped the claim
that all colors are necessary to compound white light restricting it now to
sunlight. 169 In his reply of April 3 (O.S.), he strongly objected to Huygens’
claim that two primary colors are more easily explained, but he explicitly
refrained from proposing a ‘Mechanicall Hypothesis”. 170 As regards the actual
effect of chromatic aberration, he watered down his claim a bit. The rays that
are dispersed mostly
“… are but few in comparison to those, which are refracted more Justly; for, the rays
which fall on the middle parts of the Glass, are refracted with sufficient exactness, as
also are those that fall near the perimeter and have a mean degree of Refrangibility; So that
there remain only the rays, wich fall near the perimeter and are most or least refrangible
to cause any sensible confusion in the Picture. And these are yet so much further
weaken’d by the greater space, through which they are scatter’d, that the Light which
falls on the due point, is infinitely more dense than that which falls on any point about
it. …” 171
As a conclusion, Newton suggested a way to measure the chromatic
aberration of the extreme rays to verify his claims. Huygens accepted
Newton’s argument, but added that
“… he must also acknowledge that this abstraction [dispersion] of rays does not
therefore harm lenses as much as he seems to have wished to be believed, when he
proposed concave mirrors as the only hope for perfecting telescopes.” 172
Huygens was not, however, satisfied with Newton’s rebuttal concerning the
nature of white light and colors: “… but seeing that he maintains his opinion
with so much ardor, this deprives me of the appetite for disputing.” 173 Two
weeks later, he wrote to Oldenburg not to send Newton his last letter at all
and to tell him only that he did not want to dispute anymore. 174 Newton did
receive the letter anyhow and replied on 23 June (O.S.) by a more precise
reformulation of his theory, which was published in the 96th issue of
168
Newton, Correspondence I, 173.
169
Shapiro, “Evolving structure”, 224-225.
170
OC7, 265-266 and Newton, Correspondence I, 264-265.
171
OC7, 267 and Newton, Correspondence I, 266. In Opticks, he elaborated this argument a bit further and
mathematically, and reduced chromatic aberration to 1/250 of the aperture as contrasted to the original
1/50. Newton, Optical lectures, 429n15.
172
OC7, 302-303. “… mais aussi doit il avouer que cette abstraction des rayons ne nuit donc pas tant aux
verres qu’il semble avoir voulu faire accroire, lors qu’il a proposè les mirroirs concaves comme la seule
esperance de perfectionner les telescopes.”
173
OC7, 302. “…, mais voyant qu’il soustient son opinion avec tant de chaleur cela m’oste l’envie de
disputer.”
174
OC7, 315.