🚀 go-pugleaf

In article <5761@tuegate.tue.nl> johan@blade.stack.urc.tue.nl (Johan Wevers)
writes:
>davids@spira.bri.hp.com (david sixsmith (contractor)) writes:
>>after all questions of lenses etc were well
>>understood by Newton - did noone have any idea why glass was transparent.
>
>He did have some difficulties with collor correction: Newton tought that it
>was impossible to give the focus point of 2 collors the same position.

This was actually the case given the limited types of glass which were
available to Newton.  The two-element achromat requires glasses with
different dispersion characteristics.

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 result was that Newton turned to reflector telescope design (which
doesn't suffer from chromatic abberations) and invented the modern
telescope.  Given the magnitude of Newton's accomplishments in optics
alone, I think he might be excused for not inventing borosilicates, too.

--
Phil Hees
hees@cubic.com