page_title: Ramsden surveying instruments
section_title: The zenith telescope
hierarchical_section_title: Ramsden surveying instruments / The zenith telescope
caption_attribution_description: English: The zenith telescope constructed by Jesse Ramsden in 1802. Used to determine the latitude of stations of the Principal Triangulation of Great Britain.
context_page_description: The Ramsden surveying instruments are those constructed by
  Jesse Ramsden and used in high precision geodetic surveys carried out in the period 1784 to 1853. This includes the five great theodolites—great in name, great in size and great in accuracy—used in surveys of Britain and other parts of the world. Ramsden also provided the equipment used in the measurement of the many base lines of these surveys and also the zenith telescope used in latitude determinations.
context_section_description: The zenith telescope constructed by Jesse Ramsden in 1802 which was used to determine the latitude of many stations of the Principal Triangulation of Great Britain. This portable instrument was designed to bring observatory precision to fieldwork. The outer frame stood about 12 ft (3.7 m) tall and the telescope mounted on an inner frame was 8 ft (2.4 m) long. The telescope was restricted to observations within a few degrees of the zenith in order to prevent errors due to refraction. A complete description of the instrument is given by Pearson.
caption: Ramsden's zenith telescope.
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