Page:The aquarium - an unveiling of the wonders of the deep sea.djvu/48

Rh the customary expression is, there are four hours' flood, four hours' ebb, and four hours' standing water. This peculiarity is seen with most distinctness at the time of spring-tide, but is liable to some variation from the influence of winds, &c. The water, more-over, does not lie for four hours, exactly at the same level; since there is more or less of a secondary tide, called the Gulder, which soon after the lowest ebb rises a little, and commonly falls again (but not invariably) towards the end of the four hours of standing water. This continuance of the recess of tide is very useful to the naturalist, since it allows him to prosecute his examinations for a much longer period at once; though, as a per contra, the long exposure to the air being more than some animals and plants could bear, they are compelled to reside at a lower level, and hence the low-water line around Weymouth is less rich in species than on other coasts where it is uncovered only a few minutes at each tide.

The first point to be attended to, is the procuring of living sea-weeds, the vegetable element in the combination which is displayed in an Aquarium. And this must naturally be the first thing, whether we are stocking a permanent tank, or merely collecting specimens for temporary examination, as we cannot preserve the animals in health for a single day, except by the help of plants to re-oxygenate the exhausted water. By their means, however, nothing is easier than to have an Aquarium on almost as small a scale as we please; and any visitor to the sea-side,