CHROMATIC ABERRATION • FREE-TRANSLATOR.COM • Definition of Chromatic aberration

... telescope was astonishing the world by its rapid development in the hands of Herschel, its unpretending rival was slowly making its way towards the position which the future had in store for it. The great obstacle which long stood in the way of the improvement of refractors was the defect known as "chromatic aberration." This is due to no other cause than that which produces the rainbow and the spectrum—the separation, or "dispersion" in their passage through a refracting medium, of the variously coloured rays composing a beam of white light. In an ordinary lens there ...

— A Popular History of Astronomy During the Nineteenth Century - Fourth Edition • Agnes M. (Agnes Mary) Clerke