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National Geographic : 1919 Sep
Contents
THE ISLE OF CAPRI Photograph by Edith P. Kingman FISHING IS ONE OF THE PRINCIPAL OCCUPATIONS OF THE MEN OF CAPRI Cultivation of the olive tree and of the vine are also profitable pursuits, but the inhabitants rely chiefly upon the annual tourists' crop for their livelihood. flict. At any rate, it shows that the great Archimedes, at least, had found some use for mirrors other than the usual one. THE USE OF MIRRORS BY THE ROMANS In imperial times the Romans had mirrors large enough to reflect the en tire person; they even had mirrors of glass backed with tin instead of quick silver. Although there are no references in ancient writings to the use of signaling by mirrors, such a simple and effective method surely must have been employed. A most significant thing is the old story of a mirror on the Alexandrian Pharos: "Alexander the Great placed on the top of the tower a mirror constructed with so much art that by means of it he could see the fleets of his enemies at loo leagues distance"; and, to enter still more into particulars, "a Greek named Sodorus, after the death of Alexander, broke the mirror while the garrison of the town was asleep." Now any tradition, no matter how dis torted, has its roots in truth; and this one leaves us with the feeling that there was a mirror on the tower. The most likely reason for its presence there is that it was used to signal with in day light hours; in other words, it was used for heliographing. Signaling was certainly a common military practice among the ancients. and ancient writers, such as Virgil, AEschylus, and Herodotus, frequently alluded to it. CODE MESSAGES OF THE ANCIENTS An interesting case of long-distance signaling by relaying is mentioned by Herodotus, in which it appears that cer tain tidings were sent to Xerxes in Asia by means of a line of beacon fires ar ranged through the Greek islands. The ancients went further than sim- 221
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