and Vegetable Life on Carhonate-qf-Lime Waters. 147 



consisted of four small crucian carp with a gold carp. Several 

 freshwater moUusks, principally Planorbis corneus and Limneus 

 palustris, were also introduced to act as scavengers and consume 

 the decaying vegetation. The tank was loosely covered with a plate 

 of glass, so as to allow of a free admission of the external air, and 

 at the same time keep out a great deal of the soot and dust of the 

 London atmosphere and impede the too rapid evaporation of the 

 water. As the Trichomanes were stated to delight in shade, a thin 

 muslin bhnd was placed over the covering glass. 



The aquarium was located in a window-way having an eastern 

 aspect, but, being surrounded within a few yards by the high walls 

 of adjoining houses, the direct rays of the sun only reached it for 

 about three hours in the morning during the months of June and 

 July. It was established in January 1851, and has not since been 

 disturbed, except by occasional supplies of distilled or rain-water, 

 to replace the loss in volume arising from evaporation. It had 

 been my custom to weed out the excessive growth of the Vallisneria 

 during the summer, and also to remove some of the flaky deposit of 

 calcareous matter from the surface of the glass nearest the light ; 

 but as I considered that such disturbances might interfere with the 

 course of the investigation, these operations were discontinued. 



The results that have been obtained from this investigation dur- 

 ing the years 1861 and 1862 are as follows : — 



degrees of hardness, or grains of lime- 

 salts, per imperial gallon, in terms 

 of carbonate of lime. 



The amount of calcareous matter dissolved will be seen to have 

 steadily decreased during the spring and summer months, from 

 its maximum in March 1861 and February 1862 to its minimum 

 in July 1861 and August 1862, and then to have increased as 

 steadily during the autumn and winter months. 



Part of this hardness, however, unquestionably arose from the 

 presence in the water of other salts of lime besides the carbonate. 



