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Manuel Johnson's Tide Record at St. HelenaThe astronomer Manuel Johnson, a future President of the Royal Astronomical Society, recorded the ocean tides with his own instrument at St. Helena in 1826-1827, while waiting for an observatory to be built. It is an important record in the history of tidal science, as the only previous measurements at St. Helena had been those made by Nevil Maskelyne in 1761, and there were to be no other systematic measurements until the late 20th century. Johnsons tide gauge, of a curious but unique design, recorded efficiently the height of every tidal high and low water for at least 13 months, in spite of requiring frequent re-setting. These heights compare very reasonably with a modern tidal synthesis based on present-day tide gauge measurements from the same site.Johnsons method of timing is unknown, but his calculations of lunar phases suggest that his tidal measurements were recorded in Local Apparent Time. Unfortunately, the recorded times are found to be seriously and variably lagged by many minutes. Johnsons data have never been fully published, but his manuscripts have been safely archived and are available for inspection at Cambridge University. His data have been converted to computerfiles as part of this study for the benefit of future researchers.
Document ID
20170007772
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Cartwright, David E.
(National Oceanography Centre Liverpool, United Kingdom)
Woodworth, Philip L.
(National Oceanography Centre Liverpool, United Kingdom)
Ray, Richard D.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
August 17, 2017
Publication Date
March 27, 2017
Publication Information
Publication: History of Geo- and Space Sciences
Publisher: Copernicus Publications
Volume: 8
Issue: 1
e-ISSN: 2190-5029
Subject Category
Oceanography
Report/Patent Number
GSFC-E-DAA-TN45571
Distribution Limits
Public
Copyright
Other

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