Now also a full explanation was first given why the highest tides take place at new and full moon: that is, when the moon stands between the sun and the earth; or the latter between the sun and the moon; as then the two celestial bodies unite their powers; while at half-moon the solar tide corresponding with the lunar ebb, or the lunar tide with the solar ebb, counteract each other. But even Newton explained the true theory of the tides only in its more prominent and general features, and the labours of other mathematicians, such as MacLaurin, Bernoulli, Euler, La Place, and Whewell, were required for its further development, so as fully to explain all the particulars of the sublime phenomenon. The reproach has often been made to science, that she banishes poetry from nature, and disenchants the forest and the field; but this surely is not the case in the present instance, for what poetical fiction can fill the soul with a grander image than that of the eternal restlessly-progressing tide-wave, which, following the triumphant march of the sun and moon, began as soon as the primeval ocean was formed, and shall last uninterruptedly as long as our solar system exists! Were the whole earth covered with one sea of equal depth, the tides would regularly move onwards from east to west, and everywhere attain the same height under the same latitude. But the direction and the force of the tide-wave are modified by many obstacles on its way, such as coast-lines and groups of islands, and it has to traverse seas of very unequal depth and form. Flat coasts impede its current by friction, while it rolls faster along deep mural coasts. From all these causes the strength of the tides is very unequal in different places. They are generally low on the wide and open ocean. Thus the highest tides at Otaheiti do not exceed eleven inches, three feet at St. Helena, one foot and a half at Porto Rico. But when considerable obstructions oppose the progress of the tide-waves, such as vast promontories, long and narrow channels, or bays of diminishing width, and mouths of rivers directly facing its swell, it rises to a very great height. Thus, at the bottom of Fundy Bay, which stretches its long arm between Nova Scotia and New Brunswick, the spring-tides rise to sixty, seventy, or even one hundred feet, while at its entrance they do not exceed nine feet, and their swell is so rapid as frequently to sweep away cattle feeding on the shore.