🚀 go-pugleaf

In article <1992Oct05.144047.24467@cubic.com> hees@cubic.com (Phil Hees) writes:

>Newton, who first investigated dispersion (the dependence of the angle of
>refraction on the wavelength of the incident light), did consider using
>more that one lens to perform color correction.  Based on what might have
>been too hasty a study of the dispersion characteristics of various
>available glasses, he concluded that such correction was impossible.

The gory details are in the Opticks, Book One, Part I, Experiment 16.
Newton showed how one might correct for spherical aberration by using
two lenses with water in between them (in effect, therefore, three
lenses).  However, he reports

	"But by reason of this different Refrangibility [of colours],
	 I do not yet see any other means of improving Telescopes
	 by Refractions alone, than that of increasing their lengths..."

And, as Phil mentioned, he continues

	"Seeing therefore the Improvement of Telescopes of given
	 lengths by Refractions is desperate; I contrived heretofore
	 a Perspective by Reflexion, using instead of an Object-glass
	 a concave Metal..."

And the rest is history.