Practical observations on telescopes.

  • William Kitchiner
Date:
1815
Catalogue details

Licence: Public Domain Mark

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

    100/116 page 98
    9S doors, is by a clamp made to fasten on tins sashes when the top sash is put down : the object-end of the telescope is then in the open air, and out of reach of the undulating motion occasioned by looking through a medium of atmosphere which is undergoing a change of temperature, by the cold air rushing into the warm room. By this con¬ trivance we have almost all the steadiness of being on the ground without being ex¬ posed to the cold, 8cc. I must here endeavour to impress on the mind of my readers another most important observation : when they have done using the telescope, let the object-glass be taken out and laid in a dry warm place, for a suffix cient time to evaporate the damp air, which on dewy evenings too plentifully condenses on the object-glass ; and however closety the lenses constituting the object-glass are burnished into the brass cell, unless they are very carefully kept dry,, the damp air will penetrate between the glasses, and pro¬ duce a sort of fog, or sometimes an arbor¬
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