Lenses and Waves

84 CHAPTER 3
In a letter of 11 January 1672, Oldenburg first made mention of Newton to
Huygens. 141 This ‘mathematics professor in Cambridge’ had invented a small
telescope in which the objective lens was replaced by a mirror. According to
Oldenburg it represented an object “without any color and very distinct in all
its parts.” 142 In his next letter of 25 January, Oldenburg sent him a drawing
and a detailed description, and asked Huygens’ opinion. 143 At the bottom of a
relatively wide tube a concave mirror reflected rays to a plano-convex ocular
lens via a small plane mirror. Huygens promptly sent Oldenburg his opinion
on the device. In the 81st issue of Philosophical Transactions (15 March, O.S.),
Oldenburg published Newton’s description of his reflector along with some
of Huygens’ comments. 144 In the meantime, Huygens had also sent a letter on
Newton’s telescope to Gallois, the editor of the Journal des Sçavans, who
published an extract of it in the issue of February 29. 145
Huygens spoke in the highest terms of Newton’s telescope. He
enumerated no less than four advantages over ordinary telescopes: a mirror
suffers less from spherical aberration, it does not ‘impede rays at the edge of
the glass due to the inclination of both surfaces’, there is no loss of light due
to internal reflections, and inhomogeneities in the material which affect
lenses play no part in mirrors. 146 Figure 34 The crossed out EUREKA.
In short, the reflector was a promising
device. The main obstacle for its success, already pointed out by Oldenburg,
was to find a durable material for making reflecting surfaces which lent itself
141
N.S. All dates are New Style unless indicated otherwise.
142
OC7, 124-125. “… qui envoye l’object à l’oeil, et l’y represente sans aucune couleur et fort
distinctement en toutes ses parties.”
143
OC7, 129-131.
144
OC7, 131 Huygens’ note a; 140-143.
145
OC7, 134-136.
146
OC7, 134-136 (to Gallois); 140-141 (to Oldenburg). In a note added to the description of Newton’s
reflector, Huygens calculated the difference of spherical aberration produced by a spherical lens and a
spherical mirror. The aberrations produced by a lens and a mirror with the same focal distance and
aperture are 28 to 3. Therefore, he concluded, the aperture of a mirror can be three times as large. OC7,
132.