20 THE AQUARIAN NATURALIST. 



ment of thin silk gauze of a blue colour, or by layers 

 of tissue-paper tinged blue and green, sometimes oiled 

 to make them more transparent; or coloured varnishes, 

 blue, and blue and yellow, mixed to the required tint, 

 will answer the same purpose. These materials should 

 be applied to the surface of the glass, or interposed 

 between the source of light and the water in such a 

 way, that the whole of the light which directly illu- 

 minates the aquarium may be tinted of the proper 

 colour. 



To such an extent has this plan succeeded, that 

 portions of red sea-weed, which had become thickly 

 mantled with the brown and green confervoid growths 

 above alluded to, and which had not exhibited the 

 least signs of vitality, on being placed in a small glass 

 jar, arranged with tinted and oiled tissue-paper, soon 

 lost the whole of this parasitic growth from its gra- 

 dually decaying, and being then consumed by the 

 mollusks j the fronds, assuming their deep crimson 

 hue, becoming perfectly clear, and throwing out new 

 shoots and leaflets. 



Sea-water may be preserved for a long period in a 

 perfectly efficient and healthy state under some cir- 

 cumstances without the introduction of growing vege- 

 tation, and this simply by exposing a very extended 

 surface to the action of the air, and at the same time 

 limiting its depth. 



The means whereby this may be accomplished, con- 

 sist in the employment of shallow circular stoneware 

 pans of about eighteen inches internal diameter by 

 five inches deep ; these are filled for about two inches 

 with water, the bottom is supplied with sand and 



