Polybius, Histories

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Methods of Signalling

Aeneas, therefore, the writer of the treatise on tactics,

The improvement introduced by Aeneas Tactitus.

wished to correct this defect, and did in fact make some improvement; but his invention still fell very far short of what was wanted, as the following passage from his treatise will show.¹ "Let those who wish," he says, "to communicate any matter of pressing importance to each other by fire-signals prepare two earthenware vessels of exactly equal size both as to diameter and depth. Let the depth be three cubits, the diameter one. Then prepare corks of a little shorter diameter than that of the vessels: and in the middle of these corks fix rods divided into equal portions of three fingers' breadth, and let each of these portions be marked with a clearly distinguishable line: and in each let there be written one of the most obvious and universal of those events which occur in war; for instance in the first 'cavalry have entered the country,' in the second 'hoplites,' in the third 'light-armed,' in the next 'infantry and cavalry,' in another 'ships,' in another 'corn,' and so on, until all the portions have written on them the events which may reasonably be expected to occur in the particular war. Then carefully pierce both the vessels in such a way that the taps shall be exactly equal and carry off the same amount of water. Fill the vessels with water and lay the corks with their rods upon its surface, and set both taps running together. This being done, it is evident that if there is perfect equality in every respect between them, both corks will sink exactly in proportion as the water runs away, and both rods will disappear to the same extent into the vessels. When they have been tested, and the rate of the discharge of water has been found to be exactly equal in both, then the vessels should be taken respectively to the two places from which the two parties intend to watch for fire signals. As soon as any one of those eventualities which are inscribed upon the rods takes place, raise a lighted torch, and wait until the signal is answered by a torch from the others: this being raised, both parties are to set the taps running together. When the cork and rod on the signalling side has sunk low enough to bring the ring containing the words which give the desired information on a level with the rim of the vessel, a torch is to be raised again. Those on the receiving side are then at once to stop the tap, and to look at the words in the ring of the rod which is on a level with the rim of their vessel. This will be the same as that on the signalling side, assuming everything to be done at the same speed on both sides."