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    Re: "Latitude"questions
    From: Brooke Clarke
    Date: 2003 Sep 26, 17:26 -0700
    Hi Doug:

    Here is the idea:
    http://americanhistory2.si.edu/surveying/object.cfm?recordnumber=758935

    The passage you quoted was:

    " . . observer would then reverse the scope 180* on the verticle plane . . "

    Where today we would say "in the verticle plane", not axis.

    Have Fun,

    Brooke


    Royer, Doug wrote:
    Thanks for the replies on this matter Brooke and Mitch.I now understand what
    1900 has to do with 1896 and can see what was being conveyed.
    After reading your reply of the "Meridian Scope" I did a search to find
    pictures or details of one but came up dry.I still can not visualise what it
    looks like and how one would rotate it 180* on its verticle axis and still
    be able to view the star with the objective lens in the proper place.
    
    -----Original Message-----
    From: Brooke Clarke [mailto:brooke@pacific.net]
    Sent: Friday, September 26, 2003 14:18
    To: Navigation Mailing List; doug.royer@REMEC.COM
    Subject: Re: "Latitude"questions
    
    
    Hi Doug:
    
    I don't have the book so can only give my opinion.
    
    A "meridian  scope" is one that only has a single axis of rotation
    aligned East - West and is always looking in the North - South plane
    containing the local longitude.  This is the type of scope at Greenwich
    at 0 degrees longitude.  You just set the elevation of the scope to
    match that declination of a star and make a hack when it crosses one of
    the reticule lines.  If it takes a star, say 1 minute of time to cross
    each reticule line, then the scope could be inverted between each time
    hack.  Treating the even and odd hack marks as two different time series
    would allow some scope alignment errors to be corrected.
    
    The Photographic Zenith Telescope (PZT) was used for many decades to set
    the master clocks of the USNO and other time standard locations.  It has
    a more complicated way to eliminate errors.
    
    Most, but not all, stars are in a fixed location on the celestial
    sphere.  But the Earth precesses just like a gyroscope and also
    wobbles.  This causes the apparent position of a star to change, so to
    accurately point to a star you need to know where it was on a given
    epoch date and how much the Earth has precessed and wobbled since then.
    
    Have Fun,
    
    Brooke Clarke, N6GCE
    http://www.pacificsites.com/~brooke/Nav.shtml
    
    Royer, Doug wrote:
    
      
    I am reading my copy of the book "Latitude" and have some questions on 2
    subjects I ran across.
    On pages 61 thru 64 a method for the "telegraphing of correcting longitude"
    useing a telegram is explained.All well and good.For those who don't have
    the book here is a short explaination of the method.Each station used to
    relay the time was equiped with a chrono,telegraph key,telescope that would
    rotate 180* on it's verticle axis and a cylendrical record.At every 2 sec.
    of time the chrono would cause a tick to be recorded on the record as would
    every minute be recorded as a double tick.The observer would then use the
    special telescope and observe a celestial body's movement  in the
        
    reticle.As
      
    the body crossed a series of lines in the reticle the observer would
        
    depress
      
    a telegraph key which would also record a tick on the record.Then the
    observer would then reverse the scope 180* on the verticle plane and repeat
    the proceedure to cancel certain errors and allow corrections to be
        
    computed
      
    for others.I cannot visualize this scope.Can anyone help?
    On pages 84 and 85 it states that in 1896 the rules governing the
    nomemclature of variable stars were inconsistant at the time.The locations
    of the stars were expressed by R.A. and Declination.All well and good so
    far.Here's where I get lost:"in Seth Chandler's system the designation of a
    variable star was obtained by dividing by ten the number of secounds in its
    R.A. during the year 1900".
    As like Forrest Gump I can say "I am not a smart man" but this statement
        
    has
      
    me totally baffled! Can someone in the list please explain what is being
    conveyed as I don't understand what 1900 has in common with 1896.
    Thanks for any insights you can give me.
    
    
    
    
        
    
    
      
       
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