4914 THE ZooLocist—May, 1876. 
of a. The water rises through c at an even temperature, exactly 
as it would if rising from a natural well, or spring, whether the 
spring be cold or hot, as in nature, and we can so increase the 
speed of the flow through c that the fluid is not allowed time to 
become unduly warm or cold in a. We know by many years of 
observation in the Observatory at Greenwich, that at a depth of six 
feet below the ground there, the mean daily range of the ther- 
mometer is less than one degree, while at the surface it is. often 
twenty degrees. These facts, and the results to be deduced from 
them, are alike incontrovertible. We also know, from Bunsen’s 
tables, how much atmospheric air in solution water will retain when 
not under pressure at varying temperatures, and it is also known 
that it is upon the presence of such air in solution that the value 
of the water for aquarium animals proper mainly depends. It is 
true that, as Mr. Kent states, the quantity of air injected into a 
under the conditions No. I may be increased by accelerating the 
flow, but that does not diminish or increase the temperature, and 
that is the primary thing. It is also true that some local circum- 
stances may affect these results, such as a very equable and mild 
climate, or an aquarium building of extreme temperatures either 
way, or the use of tanks which are very shallow or very high, 
which increase or diminish the surface absorption of air, but, as 
giving general and broad results, the figures just quoted may be 
depended upon, and they were true in their results at the Man- 
chester Aquarium, which Mr. Kent cites as a contradiction to my 
theory. This, under Mr. Kent’s supervision, containing show-tanks 
aggregating 150,000 gallons, the amount in animal life was no 
greater than, if so great as, is contained in the Crystal Palace Aqua- 
rium of only 20,000 gallons in the show-tanks. Even in the reserve- 
tanks in the latter place we often keep almost as much living food 
alone, in the shape of prawns, shrimps, crabs, mussels and oysters, 
all of which tend to sully the water, and which themselves have to 
be fed, as were kept in all the Manchester Aquarium, which has no 
reserve-tanks. There is no truer test of the amount of healthy 
organic life in an aquarium, of the kind which admits of manual 
feeding, than is to be found in the quantity of food consumed. 
Mr. Kent told me that in the vast aquarium at Manchester, con- 
taining show-tanks collectively of 150,000 gallons, and a reservoir 
of 50,000 gallons,—total, 200,000 gallons,—the food amounted ‘to 
no more than £40 or £50 a-year, But in the Crystal Palace 
