Geography

​Polybius says that there is a spring of potable water in the temple of Heracles in Gadeira, having a descent of a few steps down to the water, which reacts contrariwise to the tides of the sea, failing at high tide and filling up at ebb tide. And he attributes the cause to this: that the breath which escapes from the depths to the surface of the earth, when the surface is covered by the wave during the rises of the sea, is shut off from its proper exits of this kind; but turning back inwards, it blocks the passages of the spring and causes a lack of water; and when the surface is exposed again, proceeding in a straight course, it frees the veins of the spring so that it wells up abundantly. But Artemidorus, contradicting this and at the same time proposing a certain cause of his own, and also mentioning the opinion of Silanus the historian, does not seem to me to say things worthy of mention, since both he himself and Silanus are, as it were, laymen in these matters. Poseidonius, however, saying that this story is false, says that there are two wells in the Heracleium and a third in the city; and of those in the Heracleium, the smaller, when they draw water from it continuously, immediately fails and, when they cease drawing water, fills up again, while the larger, although providing water for drawing throughout the whole day, yet decreasing, just like all other wells, fills up at night when people no longer draw water; and since the time of filling up often coincides with the ebb tide, the antipathy has been vainly believed by the inhabitants. Now that this story has been believed, he too has said, and we ourselves have received it as a matter commonly talked about among marvels. But we used to hear that there are indeed wells, some in the gardens before the city and others inside, but because of the badness of the water in the city, cisterns of rainwater are prevalent; whether, however, any of these wells also exhibits the suspected antipathy, we do not know. As for the causes, if indeed these things happen in this way, one must accept them as in difficult matters. For it is plausible, on the one hand, that it is as Polybius says; and it is plausible, on the other hand, that some of the spring-feeding veins, being moistened from the outside, become slack and give a lateral discharge to the waters rather than squeezing them up along the ancient channel into the spring; and it is necessary that they be moistened when the wave overflows. But if, as Athenodorus says, what happens regarding high tides and ebb tides resembles inhalation and exhalation, there would be some of the flowing waters which naturally have their outflow to the surface through certain passages—the mouths of which we call springs and fountains—but through other passages are drawn back toward the depth of the sea; and, on the one hand, raising that sea up so that it floods, whenever what is like the exhalation occurs, they abandon their proper channel, but on the other hand, return again to their proper channel whenever that sea also takes its retreat.