A Course of Practical Astronomy for Surveyors with the Elements of Geodesy

A Course of Practical Astronomy for Surveyors with the Elements of Geodesy

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1883 edition. Excerpt: ... shall only have to take into account the difference of the refractions at the two altitudes. The instrument is practically a telescope about 45 inches focal length, attached to a vertical axis round which it revolves, having been first clamped at a certain angle of elevation. The latitude must be known approximately, and a pair of stars selected which are of so nearly the same meridian zenith distance at that latitude that they will both pass within the field of view of the telescope without our having to alter its angle of elevation. As a rule, z and z must not differ by more than 50' at the most. If the axis is truly vertical and the telescope remains at the same vertical angle at the observation of both stars, then it is plain that the difference of z and z may be read by a micrometer in the eye piece. It is usual to observe only stars which pass within 25 degrees of the zenith. The telescope has a long diagonal eye piece with a micrometer in its focus, and the micrometer wire is at right angles to the meridian. There is a very delicate level attached to the telescope, and a vertical arc which serves as a finder. By reading this level at each observation we can detect and allow for any change in the angle of elevation of the telescope. The above is the merest outline of the principle of the instrument, and reference must be made to other works for the details of its construction. The method of using it is this: The latitude being already approximately known, a pair of stars is found from a star catalogue, both of which will pass within the field of view without altering the elevation, and which have nearly the same right ascension. The reason for this is that their transit may take place within so short an interval of time that the...
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Product details

  • Paperback | 46 pages
  • 189 x 246 x 3mm | 100g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236826272
  • 9781236826275