For a long time, in countries where the tides show a large rise and fall in certain waters, thought has been devoted to the exploitation of the power brought into action by this phenomenon. Anyone interested in the problem will be familiar with the names of Passamaquoddy, Cobscook, Petit-Codiac, San José and Mezen bays, and the Severn, Abervrach and Ranee estuaries. All these stretches of water have been, as some still are, the subject of investigations carried to very different stages, with a view to building barrages to hold the water brought up by the tide, and plants to collect power from its return.