THE ZooLoGistT—May, 1876. 4911 
beautiful manner, converted into a series of elliptically equated 
curves, which place before the eye in a strikiug way the cycles of 
years of hot and cold temperatures which mark our very variable 
climate. 
At or near the surface of the seas of our islands, where aquarium 
animals came from, the range, however, is very much less, the water 
being neither so hot nor so cold as the air, especially of the air in 
inland places, the temperature of our sea water being from 45° F, 
to 65° F., and having an average of about 60° F. This tolerably 
uniform temperature of the sea-water tends to give a similar uni- 
formity to the air immediately in contact with it, which accounts 
for the mildness of the climate at seaside places in winter. 
In the ‘ Engineer’ of October 15th last is an illustrated aquarium 
communication by me, but not signed, in which I have described 
the manner in which this uniformity is effected. The water is 
heated at the earth’s equator, and a surface-current of warm water 
flows towards both of its poles, and there becoming cold, it sinks 
and returns towards the equator in an under-current, the sinking, 
and therefore the primary cause of the motion, being caused by the 
behaviour of sea water under the influence of cold, as a consequence 
‘of the density which it acquires from the salts it holds in solution. 
Dr. W. B. Carpenter, who has devoted much attention to oceanic 
circulation, has also explained all this, and has testified to the 
correctness of the means which I have introduced in Aquaria to 
represent what Nature does. | 
Fresh water behaves somewhat differently to sea water when 
exposed to cold, but our rivers and other streams, and ponds, and 
lakes, similarly to the sea, do not have such great ranges of tem- 
perature as our air, and, to sum up on this point, it has been found 
that the best temperature for the sea and fresh water of Aquaria in 
which to keep British aquatic and non-lung-breathing animals is 
from 55° F. to 60° F. throughout the year. In winter this tem- 
perature might be easily maintained by means of fire, and in 
summer it might be kept down by refrigerating apparatus ; 
but without some such counteracting means of warming and 
cooling, an aquarium would injuriously follow the temperature of 
the atmosphere. It occurred to me, however, in the year 1854, 
by seeing what was done in the aquarium of the Regent's Park 
Zoological Gardens, where the sea-water reservoir was, and is, too 
small, and by the familiar domestic appliance of a cool cellar or 
