FRENCH SALT SELLERS. 361 



its passport, as formalty as if it had been a cask of 

 wine, or a suspicious stranger. French salt sellers 

 thus enjoy the height of protection ; they are 

 protected even from their colossal competitor, the 

 sea !' 



I do not know a prettier sight than that exhibited 

 by a health}' aquarium on a fine summer's day ; 

 the effect of the sunshine upon it being to cause 

 innumerable bubbles of oxygen that look like balls 

 of quicksilver to form on every weed, shell, and 

 smallest pebble. On looking through the transparent 

 sides of the vessel, small particles hitherto resting on 

 its base, may be seen slowly arising to the surface of 

 the water, each buoyed up by a miniature gas 

 balloon. The broad, ribbon like fronds of the ulva, 

 from the selfsame cause, float upwards, and reflect a 

 beauteous emerald hue upon all objects that lie 

 beneath ; while the glass bulb, placed in the tank as 

 before stated, to denote the density of the water, at 

 such a time belies its mission, and covered with 

 numerous argent globules, mounts gracefully in com- 

 panionship with the sea-weed, until shades of even- 

 ing approach, when its buoyancy gradually subsides, 

 and once more it falls to its original resting-place. 



Wherever the above phenomenon is apparent, rest 

 assured that the aquarium is in good condition. It 

 is, in fact, to the oxygen thus given out by the 

 plants and infant vegetation that the animals owe 

 their existence. If no algae were introduced, the 



