MAEINE AQUAEIUM, 11 



small tanks -which had been used for fresh water ; but 

 as it was necessary, during the unsuccessful experi- 

 ments with the brown and red sea-weeds, to agitate 

 and aerate the water, which had been rendered foul 

 from the quantity of mucus or gelatinous matter 

 generated during the decay of their fronds, until the 

 whole had become oxydized, and the water rendered 

 clear and fitted for another experiment, it was, there- 

 fore, for greater convenience, removed into a shallow 

 earthen pan, and covered, with a large glass shade to 

 protect the surface of the water, as much as possible, 

 from the dust and soot of the London atmosphere, 

 and at the same time impede the evaporation. In 

 this vessel then I had succeeded perfectly in keeping 

 a large number of beautiful living specimens in a 

 healthy condition up to the close of 1852. I therefore 

 gave instructions for the making of a small tank as a 

 more permanent reservoir, and one more adapted for 

 carrying on my observations and investigations on the 

 ceconomy and habits of the inhabitants. 



" From the experience I had obtained in my experi- 

 ments with the fresh-water tank, I was induced to 

 modify slightly the construction of this vessel ; thus, 

 at the back, or part towards the light, the framing 

 was filled with slate in the same way as the ends and 

 bottom ; for I had found that the glass, originally 

 employed, very soon became covered with a confer- 

 void growth which had an unpleasing appearance to 

 the eye, and in consequence of which I had been 

 .obliged to paint the glass on the exterior to prevent 

 this growth from increasing to too great an extent. 

 It was also an unnatural mode of illumination, as all 



