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    Re: USn BuShips Mark II sextant telescope.
    From: Frank Reed
    Date: 2010 Nov 29, 20:37 -0800

    Hi Bill. You wrote:
    "I suggest that the specification may have called for a telescope giving an erect, wide field image of x3 powers and may not have emphasised brightness of image. "

    Sounds plausible to me.

    Both the Germans and the Japanese came late to the game of international imperialism as well as ocean-voyaging. From the German navigation documents and navigation textbooks that I've looked at it (minimally, since I can only read a little German without a dictionary, digital or otherwise, open all the time), the Germans at least were innovative and eager to use the latest best practices of navigation. They had no centuries-long traditions of navigational practice to weigh them down. The Americans, on the other hand, were very slow to adopt the "new navigation" and continued to shoot time sights for longitude and meridian sights for latitude well into the middle of the 20th century. Old navigators taught new navigators so the "old navigation" prevailed. And why not? It worked. Note that these "old navigation" methods are primarily daytime sights. You shoot the Sun when it bears nearly east in the morning for longitude, and in the south at noon for latitude, and again in the west in the afternoon for longitude. Since they were almost always shooting the Sun, large apertures were not required at all. I'm not saying they never shots star. They did --but those sights were not critical. The war, of course, created an entirely new generation of celestial navigators, almost wiping the slate clean, and the "new navigation" was soon nearly the only navigation practiced. Since it depended on twilight star sights, it was recommended shortly after the war (from what Joel Jacobs once said on NavList) that new sextants should immediately be equipped with telescopes with much larger apertures and corresponding mirrors.

    Also, even with lunars back in the 19th century, the primary "other body" was usually the Sun. Magnification mattered, but aperture did not. So we find these thin 8x and 12x telescopes in the old sextant boxes. They often have that same "straight tube" appearance that you see in the 3x telescope on the USN Mk II.


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