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    Peter Ifland's "Taking the Stars"
    From: Fred Hebard
    Date: 2003 Sep 1, 12:09 -0400

    I purchased this book, mostly to get a feel for the precision of older
    sextants.  It was a delight to read.  The pictures are spectacular.
    
    Dr. Ifland repeats the statement that the U.S. Naval Academy has
    discontinued its required course in celestial navigation.  Apparently,
    the course, which had been taught since the Academy was founded in
    1845, has been replaced with a modern equivalent, as people continue to
    maintain on this list that midshipmen are still instructed in celestial
    navigation.  But apparently they are not instructed as thoroughly or to
    such length.  At last these conflicting claims about the Academy
    abandoning instruction in celestial navigation appear to be clarified.
    
    Especially enlightening were the discussions of artificial horizons.
    Numerous devices were invented in the past, and Dr. Ifland appears to
    discuss the physical basis for all possible types of artificial
    horizons (Hopefully, some inventive soul will prove me wrong by coming
    up with a novel design). This discussion (which spans more than one
    chapter) should be of interest to all those interested in this subject.
    
    It was of interest to me that submariners were issued
    artificial-horizon sextants for use when surfaced because the conning
    tower frequently was too low to get an accurate view of the horizon.
    If the relatively stable platform of a submarine was difficult to use
    for an ordinary marine sextant, imagine the difficulties from a small
    yacht.  This would appear to recommend bubble sextants to yachtsmen.
    Certainly bubble sextants should be adequate for all those who rely on
    the Air Almanac and H.O. 249.  The one disadvantage I can see is that
    they could not double as stadimeters.
    
    As best as I can tell, the maximum precision of old pillar sextants was
    5 seconds of arc.  However, if they were circular sextants, this
    precision might be increased to about 1 second by repeated measurements
    around the circle.
    
    One quibble is that Dr. Ifland does not report the correct reading of
    most verniers which he illustrates.  For instance, the scale in Figure
    64 is measuring about 31d 37' or so, as best as I can determine, not
    31d 34'.  Likewise, the scale in Figure 65 measures 36d 15' or 16', not
    36d 17'.  In Figure 71, the scale reads 94d 9' 0" or thereabouts, not
    94d 9' 30".  These discrepancies could shake the confidence of a
    newcomer; I feel some degree of trepidation reporting them.  It's
    possible Dr. Ifland read the scale, then set the instruments down to
    photograph them, rather than reading the scale off the photographs.
    
    I was a bit disappointed that Dr. Ifland did not discuss further the
    merits of various telescopes.  The purpose of the various telescopes is
    still somewhat of a mystery to me.
    
    Overall, I was very pleased with "Taking the Stars," and recommend it
    highly.
    
    
    

       
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