Practical observations on telescopes.

  • William Kitchiner
Date:
1815
Catalogue details

Licence: Public Domain Mark

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

    99/116 page 97
    . the temperature of which is much warmer than the open air, I usually take off the cap of the object end, and take out the eye-piece, and let the air pass through the tube for ten minutes ; and for at least the same space of time we must carefully avoid all stimulat¬ ing and bright objects ; so that the pupil may be in its most expanded state. When the eye is thus prepared, the sensibility of the visual organ will be much increased. I have also found it very advantageous to occasionally rest the eye for a few minutes : this will restore its irritability, which is soon exhausted when stimulated by an in¬ tensely bright object: and when a light is necessary to find an eye-piece, or rectify the instrument, to prevent the adjustment of the eye being disturbed, I use a small lantern, which gives a very faint light only on one side, and that may be made dark. For those who have not courage, or con¬ stitution, to brave the inclemency of mid¬ night frosts and damps, the most steady way of supporting a telescope within F
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