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Published online by Cambridge University Press: 15 September 2014
The art of figuring the lenses of a telescopic objective consists in correcting the spherical aberration by successive trials, until approximately aplanatic curves are obtained.
note * page 361 When u is less than unity, the refracted ray and radius vector lie on the same side of the normal, and the rays do not converge to or diverge from the pole. These constitute a family of parabolic or asymptotic curves, which, after describing a number of loops depending on the degree of the curve, go off to infinity.
note * page 362 This is the value found by putting r=x. See pp. 376–7, paragraphs 2 and 6.
note * page 363 Appendix, p. 377, § 5.