No CrossRef data available.
Published online by Cambridge University Press: 15 September 2014
In designing a telescope for a particular class of observations, it was found desirable to have a field-bar in the focus of the object-glass, and, at the same time, to have an image of that object-glass exterior to the eye-lens. These desiderata cannot both be got by the achromatic arrangement of two lenses made of one material; they are combined in the ordinary four-lens eye-piece.