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    Re: Henry's equal altitudes
    From: Henry Halboth
    Date: 2009 Apr 28, 20:19 -0700
    Hi Frank,

    A series of sights for Lat & Long, at a known position, was posted on 24 July 2005, including equal altitudes, primarily to demonstrate accuracy attainable,even on an indifferent sea horizon :-)

    Oh, and by the way. No offense intended, but not being a graduate of the Frank Reed School of Navigation (heaven forbid) and not being clairvoyant, I know nothing about what you may or may not know other than what you state in writing, emoticons notwithstanding. Again :-D

    Regards,

    Henry

    --- On Sun, 4/26/09, frankreed{at}HistoricalAtlas.com <frankreed{at}HistoricalAtlas.com> wrote:

    From: frankreed{at}HistoricalAtlas.com <frankreed{at}HistoricalAtlas.com>
    Subject: [NavList 8055] Henry's equal altitudes
    To: NavList@fer3.com
    Date: Sunday, April 26, 2009, 12:54 AM

    Henry Halboth, you wrote:
    "I am somewhat surprised at the time and space being devoted to the subject matter. Determination of Lar/Long at or by Noon Sight, also by the way Chronometer Error, has been around long enough to have grown a full beard. I alone have used it for over 60-years with generally good results and have previously posted current examples on this List."

    Yes, you did, and thank you for posting your results. There's nothing better than evidence from the field! I can't seem to find one of those posts right now. Maybe someone else could search the archive find the relevant message?? (thanks in advance)

    And:
    "The subject has been rather fully described and discussed by Raper, Bowditch, Lecky, and a host of others"

    What you are referring to is longitude by equal altitudes, generally using single altitudes on either side of noon, with no correction for motion of the observer (or changes in object declination) and no attempt to imrpove the fix by statistical means. Though "longitude by equal altitudes" is clearly the ancestor of the sorts of fixes we've been discussing, it is not the same thing.

    And you wrote:
    "- all of whom specify rather significant restrictions, or perhaps limitations, to its use, both as respects altitude and azimuth, which are apparently ignored by the present proponents of it as a universal panacea."

    Do you suppose it's just possible that I do in fact know about the limitations discussed by those authors?? :-) They refer to a very limited form of this observation. The limitations can generally be overcome using simple procedures that make it much more flexible, and in some ways, even easier. I've outlined my method for doing this, and others have their ideas. By the way, no one that I know of is calling this a "universal panacea" though one of GH's posts claimed that this was the case. Don't fall for his "straw man" arguments.

    You added:
    "One striking difference in the method as now proposed and that traditionally employed is the graphing technique advocated to obtain the altitude at LAN."

    The graphing technique, as commonly presented, is quite primitive. For example, a recent edition of Bowditch suggests that the navigator should 'fair a curve' through the points (or some similar language). What use is that? If you place some points on a graph in front of typical potential navigators, their curves rarely resemble parabolas and they would rarely lead to a useful solution of the problem. People have a tendency to draw smooth curves passing as close as possible to each data point, which is not correct. That's why one needs some more effective means of finding the axis of symmetry of the curve.

    But just to reiterate, you are completely correct that the equal altitudes method is the real basis for all of these things, at least from a certain point of view. And in some circumstances, it's just what the doctor ordered. I've got a USN Mark II sextant from 1945 that includes a complete table of instructions and basic almanac data that would have enabled a navigator with very basic skills to get a fix using this method. I'll attach some pictures. But to repeat, we can do much better than this today, and with very little extra effort.

    -FER



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