Practical observations on telescopes.

  • William Kitchiner
Date:
1815
Catalogue details

Licence: Public Domain Mark

Credit: Practical observations on telescopes. Source: Wellcome Collection.

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    perfection of reflecting telescopes, that the mirrors he truly parallel to each other, and also that the centres of them, together with the centres of the eye-glasses, be all in one direct line; viz. in^ the axis of the tube. Indeed, unless these particulars are attended to, the instrument will prove defective and faulty, even though the mirrors have the most exquisite figure possible given to them. That truly excellent artist, the late ingenious Mr. James Short, always took the greatest care to adjust and centre the metals of his telescopes. If the mir¬ rors are truly centred and adjusted to their best position, a fixed star, when the telescope is put out of focus, * should always appear, in reflecting telescopes, as a truly round circle of fire with a black spot exactly in its centre ; and when the telescope is adjusted to distinct vision, the star should appear, if the tele¬ scope is excellent, and the state of the un¬ favourable, exactly round, and totally free from all irradiations, or false rays and glare. Indeed I can assert, from experience, that
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