Unpublished paper, 'On the construction and use of single achromatic eye-pieces, and their superiority to the double eye-piece of Huyghens' by J B [Joseph Bancroft] Reade

Description

Reade suggests that it is impossible to make a telescope even approach to achromatism by employing the same object-glass with an astronomical and terrestrial eye-piece. This is because if the focus of the blue rays from the object-glass are thrown forwards, then a great over-correction will be produced for the astronomical eye-glass, and vice versa. It appears that the application of Huyghenian eye-pieces to refracting telescopes is incompatible with the conditions of achromatism throughout the entire range of magnifying power, and that in reflecting telescopes they unavoidably introduce dispersion, because they are not in themselves achromatic. Reade proposes to reduce these effects by substituting single achromatic lenses of corresponding magnifying power consisting of the crown-lens, and its correcting flint-lens, with their adjacent surfaces cemented together to avoid internal reflections and enable them to act as a single lens. The achromatic eye-pieces which he uses were made by Messrs. Tulley and Ross, and are described as single cemented triples. Annotations in pencil throughout.

Subject: Optics

Received 21 November 1839. Read 9 January 1840.

Written by Reade in Peckham [London].

Whilst the Royal Society declined to publish this paper in full, an abstract of the paper was published in volume 4 of Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London [later Proceedings of the Royal Society] as 'On the construction and use of single achromatic eye-pieces, and their superiority to the double eye-piece of Huyghens'.

Reference number

AP/23/39

Earliest possible date

12 November 1839

Physical description

Ink and graphite pencil on paper

Page extent

17 pages

Format

Manuscript