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    Re: Arificial Horizons and Tea
    From: Kieran Kelly
    Date: 2003 Jul 9, 11:45 +1000

    Bruce Stark is correct saying that a big advantage of tea is that it can
    be drunk. On expeditions in arid climates this is a vital consideration.
    However the other big advantage of tea is its weight compared to
    mercury. Mercury on Australian expeditions was often packed in 2lb
    flasks and they took several - a luxury on a pack horse where every
    ounce was vital.
    
    Also from practical experience in the Australian desert mercury is a
    nightmare to handle. It attracts dust and leaves as soon as it is
    decanted, immediately dulling the sheen. Cleaning mercury in the bush is
    a time consuming and frustrating process. If spilt it is impossible to
    recover which is a major advantage of tea. When a pannikin of tea is
    kicked over, and it inevitably is at least once on every expedition, the
    loss is not as great.
    
    At night I find it particularly difficult to get mercury back in the
    flask without spillage, especially if the pan is really full as it often
    is to enable low altitude shots. This often requires two hands to hold
    the pan and a lot of patience so it doesn't splash everywhere. Also
    using two hands there is nothing with which to hold the torch. This has
    been alleviated by head torches.
    
    While Bruce is correct that there is no difference between tea and water
    for sun sights I have not found water reflective enough for stars,
    however bright stars can be captured with a tea artificial horizon.
    
    Kieran Kelly
    
    
    
    
    
    
    -----Original Message-----
    From: Navigation Mailing List
    [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] On Behalf Of Bruce Stark
    Sent: Wednesday, 9 July 2003 11:15 AM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Arificial Horizons and Tea
    
    
    Kieran Kelly says that A. C. Gregory, the Australian surveyor and
    explorer, preferred a pannikin of black tea for his artificial horizon.
    I'd supposed the tea might prevent a reflection from the bottom of the
    container, if that was bright. Got to wondering if perhaps tea had a
    sheen that would make it show dim objects better. So, just now, I set
    out two similar containers. One had water, the other the same amount of
    strong black tea made with loose, rather than tea bag, tea.
    
    With the sun's reflection I couldn't tell if there was a difference in
    brightness. What I did notice was that the tea seemed to settle more
    quickly after being ruffled by a breeze. Switching the places of the two
    containers didn't change the effect, so it wasn't that the tea was less
    exposed.
    
    My quick experiment doesn't prove anything, and the effect, if there,
    was modest. Perhaps others will examine the merits of tea more
    carefully. According to Kelly, one of the reasons Gregory liked tea
    better than mercury was that he could drink it after the observation.
    
    Bruce
    
    
    

       
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