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Telescope, consisting of a brass tube 3-1/2 in. long with an aperture of 2-3/4 in.; on its original brass tripod, with a serviceable altazimuth mounting.

The altazimuth can thus determine the altitude and azimuth of objects, hence the name.

This may be furnished either with an equatorial bearing for the telescope, or an altazimuth arrangement which permits both up-and-down and horizontal motions.

He himself, however, by much more exact observations, with an excellent altazimuth, reduced the alleged error from 20 minutes to only 4-1⁄2, or to 9⁄40ths of its formerly supposed value.

The instruments used were altazimuths, constructed under the direction of Prof. Mohn, specially for measuring the parallax of the aurora borealis.