Mr George Brook on the Aeration of Marine Aquaria. 387 



be carried into the tank along with the stream. On the 

 other hand, the larger the stream the larger the air bubbles 

 carried along with it, and as these rise to the surface very 

 quickly, they do not give time for the water to absorb its 

 required oxygen. Thus it appeared that a very fine jet enter- 

 ing the water close to its surface would give a more beneficial 

 result. In order to try this I screwed off the vulcanite 

 nozzles and fitted an indiarubber stopper to the open end of 

 the jet. Through this a glass tube was introduced, sufficiently 

 long to reach the surface of the water. The end to form the 

 jet was then drawn out to a fine point, and arranged about 

 one-eighth of an inch above the surface of the water. By this 

 means a very fine stream always entered the tank, and along 

 with it an immense number of small air bubbles penetrated 

 quite to the bottom. Many of course rose to the surface 

 quickly, but the smaller ones remained so long in the water 

 as to be easily traced 5 or 6 feet from the jet. In this 

 manner less water was used in the daily circulation, and a 

 better result obtained. In less than a week's time it was 

 easily seen that the water presented a crystal appearance ifc 

 had never shown before. The small bubbles remained so 

 long in the water that time was given for all the oxygen to 

 be withdrawn that could be retained. Besides there was no 

 stirring up of the bottom, nor any signs of that turbulence 

 which is the necessary accompaniment of a comparatively 

 large jet. Later I adopted a form of filter and jet combined 

 (Fig. 3), which has been retained up to quite recently. This 

 is a simple arrangement, which proves very useful in case the 

 water has to be pumped direct from the sea, or if the water 

 should have become a little muddy from any cause. The 

 drawing will sufficiently explain itself. A is a cork cut in 

 grooves so as to allow the water to pass, and B represents 

 the carded cotton, which must be removed when dirty. I 

 have used various modifications of this arrangement, and 

 tried various substances through which to filter the water. 

 I find that carded cotton, washed before it is used in 

 fresh water, serves every purpose. Some months ago, how- 

 ever, it struck me that a modification of the form of 

 aspirator used in chemical laboratories should do even 

 VOL. viir. 2 B 



