A preliminary study about methods for harvesting energy from marine resources

1 1. HISTORICAL NOTES 1.1 Tides and tidal mills Ancient people from different ages showed several interests towards natural phenomena linked to the seas and the oceans, and they gave different explanations of them. The event related with seas that probably mostly stimulated the minds of the ancient philosophers and astronomers is the one of tides. The observation was suitable for all, as large expanse of land were periodically submerged by water, conditioning the life of people who lived in these areas: the changing level of water could create problems with boats, as it still does, or prevent the access to some areas of the shore. The first to give a partially correct interpretation of tides is probably the Greek explorer Phyteas, who travelled to the British Isles around 325 BC and was stunned by the higher intensity that tides had on the ocean rather than on the Mediterranean sea. The description of his voyage was well known in the past, but unfortunately it has been lost in the years. However, some writers and historians ascribed to Phyteas the relation of tides to the phases of the Moon. In the 2nd century BC Seleucus of Seleucia, a Babylonian astronomer, supposed that tides were due to the attraction of the Moon. He used also this explanation of tides to argument the Heliocentric theory of Aristarchus of Samos, which stated that the Earth rotated around its own axis which in turn revolved around the Sun. Pliny the Elder (23-79 A.D.), who made an important work of collection of previous scientific texts, in the second book of his Naturalis Historia made some important statements about tides: