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    Dollond's back sight attachment
    From: Frank Reed
    Date: 2010 Apr 13, 17:24 -0700

    I missed out on most of this discussion about back-sight lunars a few weeks ago while I was prepping for the first navigation class I was doing. I apologize if this has already been discussed. I've seen some general descriptions of Dollond's attachment but I can't picture it. Has anyone found any photos of an instrument so equipped? Did this add onto a traditional back horizon glass? Or replace it? And what became of it? Thanks to George and everyone else for pointing out the experiments on Cook's voyage. I had run through that book of observations three or four times looking at probably three dozen different sets of lunar observations and never noticed any of those high-angle back sights (that actually would be just about even money odds for hitting one by chance since they appear to have been about 3% of the hundreds of lunars taken by the astronomers on that lunar-filled voyage). But was that the end of it? Maskelyne wrote about the Dollond device as the solution that would finally make back sights useful for lunars navigation. Wales and Bayley dutifully experimented with the technique. And then it seems to have disappeared completely. Did Dollond license his patent to anyone? Did Wales report to Maskelyne that the device did not live up to their expectations? Was it merely too little, too late?


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