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    Re: Centerless Sextant
    From: George Huxtable
    Date: 2008 Jun 14, 16:37 +0100

    d walden asked
    
    Anyone have information about:
    http://mobius.mysticseaport.org/detail.php?t=objects&type=browse&f=maker&s=Hughes%2C+H.+%26+Son&record=2
    Micrometer quintant made by H. Hughes & Son, London
    
    INSTRUMENTS - QUINTANTS
    Micrometer quintant
    Hughes, H. & Son
    
     Micrometer quintant, brass frame, brass fittings, wooden handle. Stamped on 
    front of frame: "Registered Trade Mark/ (rising sun over the water)/ Husun/ 
    Gt Britain". Centerless sextant. Unusual and unsuccessful variation of 
    common sextant manufactured by H. Hughes & Son. An attempt to lessen the 
    weight and bulk to give the operator and easier celestial navigation 
    instrument to hold steady. Measuring to 136�.
    1953.3561
    
    ===========================
    
    and Gary LaPook added-
    I don't have any information about it but we had the opportunity to see it 
    at Mystic on June 6th.
    
    =============================
    
    Comment from George-
    
    What an interesting device! Thanks to d walden for bringing it to our 
    attention. I've never seen such a thing, or even heard of one, until now. 
    There isn't one in Peter Ifland's "Taking the Stars". It's frustrating that 
    the description and the picture from the Mystic website are so 
    uninformative. Is more detailed information available elsewhere, I wonder?
    
    Calling it a "quintant" is somewhat overstating the matter. Formally, it's 
    still a sextant, not a quintant until it reaches 144�, and this only reaches 
    136�. And even if the scale reaches that far, without trying it, it's hard 
    to be sure that any instrument remains functional up to the limit of its 
    scale, as often the field of view shrinks to an unusably narrow slot before 
    reaching that point.
    
    The one picture is so muddy and small (even when expanded) that I can't work 
    out what's going on, and where the optical path is, and even which way 
    should be up. Can anyone else do better, or recall it from a visit to 
    Mystic? Often, quintants were produced, not for navigating, but for nautical 
    surveyors and hydrographers to measure horizontal angles. In which case, 
    they would be sold without shades, and sometimes without a telescope; just a 
    peep. Is that the case with this one? Is that why its handle is at such an 
    odd-seeming angle?
    
    It's not surprising that the design failed to catch on. Presumably, without 
    a centre-pin, the design must have relied on the machining of the rail, or 
    rails, or grooves of the arc, and the wheels or rollers or balls that ran 
    along it, to define the angle. That must have been extremely demanding in 
    precision, if the device was to rival the precision of a normal sextant, and 
    I find it hard to believe that it could ever have done so. Perhaps that was 
    the reason for its short life.
    
    Willem M�rzer-Bruyns, now-retired director of the Amsterdam 
    Scheepvaartsmuseum, has recently spent some time on a research fellowship at 
    Greenwich, renewing their catalogue of navigational instruments, which has 
    been badly needed, and I hope his new volume will be published soon. Then, I 
    understand, he plans to do something similar for the Mystic museum, and 
    again, that seems to be much in need of doing. He is very careful and 
    methodical, and knows a lot about his subject. According to Willem, Mystic 
    holds the World's largest collection of octants, and the third largest of 
    sextants, after Greenwich and Mariners' Museum.
    
    George.
    
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 
    
    
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