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Re: Chauvenet
From: Frank Reed CT
Date: 2004 Sep 21, 00:07 EDT
From: Frank Reed CT
Date: 2004 Sep 21, 00:07 EDT
George H wrote:
"To me, this was something of an eye-opener. [...] But I had thought that by the mid 1850s lunar predictions would have improved to the point at which errors in the predictions were negligible compared with the errors in the measurement. Not so, however, according to Chauvenet."
Don't forget that Lecky in "Wrinkles in Practical Navigation" talks about this very issue as a continuing weakness in the lunar distance method at that late date. Writing in about 1880, Lecky noted that the errors that might result from observation and instrument flaws are "independent of an additional error of from 6' to 8' due to a small uncertainty still existing in the place of the moon as given in the tables." That's 6 to 8 minutes of longitude error corresponding to about 0.3 minutes error in the Moon's position. In later editions, he adds a footnote commenting (after 1881) "this last error has practically ceased to exist. Commencing with 1883, the Naut. Alm. has employed Newcomb's corrections to Hansen's tables" etc.
Of course at any date after about 1850, lunars were obsolescent and very rarely used except in the navigation classroom. There is an irony to Chauvenet's nearly perfect method for clearing lunars. It was probably almost never used (outside the classroom). I would say it's a fair bet that more people will try clearing lunars by Chauvenet's method in this next decade of the 21st century than in any of the later decades of the 19th century.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"To me, this was something of an eye-opener. [...] But I had thought that by the mid 1850s lunar predictions would have improved to the point at which errors in the predictions were negligible compared with the errors in the measurement. Not so, however, according to Chauvenet."
Don't forget that Lecky in "Wrinkles in Practical Navigation" talks about this very issue as a continuing weakness in the lunar distance method at that late date. Writing in about 1880, Lecky noted that the errors that might result from observation and instrument flaws are "independent of an additional error of from 6' to 8' due to a small uncertainty still existing in the place of the moon as given in the tables." That's 6 to 8 minutes of longitude error corresponding to about 0.3 minutes error in the Moon's position. In later editions, he adds a footnote commenting (after 1881) "this last error has practically ceased to exist. Commencing with 1883, the Naut. Alm. has employed Newcomb's corrections to Hansen's tables" etc.
Of course at any date after about 1850, lunars were obsolescent and very rarely used except in the navigation classroom. There is an irony to Chauvenet's nearly perfect method for clearing lunars. It was probably almost never used (outside the classroom). I would say it's a fair bet that more people will try clearing lunars by Chauvenet's method in this next decade of the 21st century than in any of the later decades of the 19th century.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
