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A Tubeless, or 'Aerial' Telescope

A Tubeless, or 'Aerial' Telescope.jpg Orbit and Phases of an Inferior PlanetThumbnailsThe Great Yerkes TelescopeOrbit and Phases of an Inferior PlanetThumbnailsThe Great Yerkes TelescopeOrbit and Phases of an Inferior PlanetThumbnailsThe Great Yerkes Telescope

From an illustration in the Opera Varia of Christian Huyghens.

Attempts were made to evade this unwieldiness by constructing them with skeleton tubes. or , indeed, even without tubes at all; the object-glass in the tubeless or "aerial" telescope being fixed at the top of a high post, and the eye-piece, that small lens or combination of lenses, which the eye looks directly into, being kept in line with it by means of a string and manœuvred about near the ground. The idea of a telescope without a tube may appear a contradiction in terms; but it is not really so, for the tube adds nothing to the magnifying power of the instrument, and is, in fact, no more than a mere device for keeping the object-glass and eye-piece in a straight line, and for preventing the observer from being hindered by stray lights in his neighbourhood. It goes without saying, of course, that the image of a celestial object will be more clear and defined when examined in the darkness of a tube.

Author
The Project Gutenberg EBook of Astronomy of To-day, by Cecil G. Dolmage Published 1910
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