PECULIAEITY IN THE TIDES. 21 



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 in- 

 variably) 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 prose- 

 cute his examinations for a much longer period at 

 once ; though, as a ])er 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. 



COLLECTING SEA-WEEDS. 



The first point to be attended to, is the procui'ing 

 of living sea-weeds, the vegetable element in the com- 

 bination 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. 



