The Iceland spar navigation theory has been around for quite a long time, but the Royal Society has published an article that gives it more weight.
http://rspa.royalsocietypublishing.org/content/early/2011/10/28/rspa.2011.0369
I noticed this RS study last month and thought it serendipitous that I had just encountered a reference to the polarizing crystal in Thomas Pynchon's mind boggler 'Against the Day' (p.250):
Sometime before the first report of it in 1669, calcite or Iceland spar had arrived in Copenhagen. The double-refraction property having been noticed immediately, the ghostly mineral was soon in great demand among optical scientists across europe. At length it was discovered that certain "invisible" lines and surfaces, analogous to conjugate points in two-dimensional space, became accessible throught carefully shaped lenses, prisms, and mirrors of calcite, although the tolerances were if anything even finer than those encountered in working with glass, causing artisans by the dozens and eventually hundreds to join multidudes of their exiled brethren already wandering the far landsscapes of madness.
"So," the Professor had gone on to explain, "if one accepts the idea that maps begin as dreams, pass through a finite life in the world, and resume as dreams again, we may say that the paramorphoscopes of Iceland spar, which cannot exist in great numbers if at all, reveal the architecture of dream, of all that escapes the network of ordinary latitude and longitude...."
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