NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dip observations by Carnegie Institution
From: Bruce J. Pennino
Date: 2013 Jun 12, 19:22 -0400
From: Bruce J. Pennino
Date: 2013 Jun 12, 19:22 -0400
Bruce
Hello:
For his terrestrial magnetism measurements, William
J. Peters was concerned about accurate location using CN on the oceans of the
world. For the cruises he was on, Galilee cruises 11 and 111, and Carnegie
Cruise 1V, I believe they traveled over 350,000 nm from Alaska to the Antarctic,
Japan to San Francisco and all over the Pacific. The cruise reports
(summaries) are available online. The Galilee and Carnegie were ships
that were altered/designed for measuring the earth's magnetic
field. Observations on refraction were made over 10 years from about
1907 to 1917. The height of eye for most of the measurements was either 18
ft or 24 ft. From the refraction data with several devices, Peters
concluded that the equation for dip of the horizon is 0.89 sqrt Hgtof Eye
ft. This compares to 0.97 sqrt H ft as found in the Nautical Almanac or
everywhere else.
My very limited theodolite measurements of
dip from land seems to agree with the value of 0.89 (more or less
considering scatter especially below eye height of 25 ft). Peters
recommends against refraction measurements at eye heights below 18
ft. I'm still gathering and checking my dip measurements, but will
eventually give the data to the NavList community. I'm herewith asking the
NavList community to look at one or two of their best observations
from known locations and heights (above 16-20 ft if possible) and determine if
their "fix" would be closer to the true location if smaller dip were used.
I'm particularly hoping that Jeremy could do this from his ship. I've tried
using my own data and I've come to no definite conclusion because of my own
scatter/technique. By the way, at eye height below 14 ft, even
with much scatter in the data, dip = about 0.8 sqrt H feet....... I
think.
Bruce
----- Original Message -----From: Richard B. LangleySent: Monday, May 20, 2013 9:13 AMSubject: [NavList] Re: Dip observations by Carnegie Institution
Paper extracted from the "book" and attached. -- Richard Langley On 2013-05-19, at 8:36 PM, Paul Hirose wrote: > > Bowditch (volume 1, 1984) mentions the results of 5000 dip measurements > at sea by the Carnegie Institution. I haven't found the source document, > but in 1918 a Carnegie scientist, Willliam J. Peters, summarized 3031 > dip observations in "Results of Dip-of-Horizon Measurements Made on the > Galilee and Carnegie, 1907-1917." [Terrestrial Magnetism and Atmospheric > Electricity, volume 23, number 2 (June 1918), page 47] > > A scan is online at archive.org: > > http://archive.org/details/journalofgeophys22ameruoft > > To download (not view online), click "HTPPS" in the "View the book" box. > The article begins on page 261 of the document. > > Peters says the visible horizon was never more than 2.4 minutes above or > 2.0 minutes below the geometric horizon. He concludes dip tables that > ignore temperature are sufficiently accurate for navigation. > > -- > > > > : http://fer3.com/arc/m2.aspx?i=124098 > ----------------------------------------------------------------------------- | Richard B. Langley E-mail: lang{at}unb.ca | | Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ | | Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3 | | Fredericton? Where's that? See: http://www.fredericton.ca/ | -----------------------------------------------------------------------------Attached File: 124103.peters_dip-of-horizon_june_1918.pdf (no preview available)
: http://fer3.com/arc/m2.aspx?i=124103
