A912 THE ZooLocist—May, 1876. 
under-ground back kitchen, that a much easier mode of equalising 
temperature in Aquaria might be used, and the various steps by 
which I reasoned_out and worked out such success as I then, and 
have since, attained, are described in a five-column communication 
I made to the ‘ Gardeners’ Magazine, and in pages 65 to 102 of 
the ‘Handbook to the Royal Westminster Aquarium,’ both pub- 
lished on the 22nd of January last, and both written during the 
week previously. The main principles involved in the water- 
circulating system in all public Aquaria constructed under my 
supervision, turn on the law governing the following facts:—If a 
quart of water at 100° F. be added to a quart at 50° F., the mixture 
of the two will be 75° F. If one at 100° F. be added to two at 
50° F., the result will be 66°6° F. If one at 100° F. be added to 
three at 50° F., the mean will be 62°5° F. If one at 100° F. be 
added to five at 50° F., the result will be 58°3° F.; and if the pro- 
‘portions be one to twenty, the mixture will be 52°3° F., and so on; 
the larger the proportion of the colder mass being to the warmer, 
the nearer the mean of the two masses will approach to the tem- 
perature of the larger mass. The entire thing is shown in the 
accompanying diagram, where B is a large under-ground, cool, dark 
reservoir, C is a pipe conveying water from B to the show-tank a, 
containing fishes or other animals, and P is a pipe conveying water 
from a to B. The six arrows indicate the direction in which the 
water flows. §E is a pipe to re-supply the water which evaporates. 
As this is an ideal representation, showing only results, all the 
machinery (as engines and pumps) giving these results, by moving 
the water, is omitted. 
Now let it be supposed that—which really would be the case in 
an English summer, without any circulation going on between 
A and B—the tank B would have its water at about 60° F., and a 
would have its water at about 75° F. On the circulation being 
established, and continued for some time, the water in A would 
become cooler, and that in B warmer, than before, and the mean 
temperatures of the two, varying according to the proportionate 
quantity of water in B, would be according to the seven following 
formulas :— 
No.l. A, 23 Bh aes result; 70° F. 
No. 2. a, 1; B, 1; result, 67°5° F. 
No. 8. a, 1; B, 2; result, 65° F. 
No. 4. a, 1; 3, 3; result, 63°7° F, 
