I HAVE just returned to England from H.M.S. Porcupine, having accompanied the dredging expedition as far as Lisbon. In reading the back numbers of NATURE, I notice in that for July 28 an account of an extraordinary mirage in the Firth of Forth on July 22. A reference to my journal shows me that on the same day we were dredging on the Portuguese coast, within sight of the Ferilhoe and Berlinga Islands, about forty miles north of Lisbon. The bearings of these islands and their exact distance, calculated by the aid of the known height of the lighthouse, gave us, of course, an exact position, which our “dead reckoning” also confirmed. Several solar observations, both for latitude and longitude, were taken by two of the officers during the day, both of whom always arrived at the same result, but this was so widely different from our position as previously determined by two other methods, that we were forced to the conclusion that there was a very false horizon. It was the only instance of the kind during the month I was at sea.
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CARPENTER, W. Mirage. Nature 2, 296 (1870). https://doi.org/10.1038/002296c0