THE YOUNG SCIENTIST. 
didn't seem at all delighted, but turned up their 
noses, so to speak, at the delicacies offered 
them ! I could not make it out, and it was of 
no use to ask any of my friends about it, for 
they took no interest in my "pollywog" col- 
lections, as they called them. So I was left to 
my own conclusions, and child-like they were. 
I had been reading about fairies and fairy 
loi'e, and had become greatly interested in the 
accounts of the curious fairy circles that the 
Irish people reverence so much. So I made up 
my mind that in the woods or neighboring- 
fields there existed a fairy circle. The fairies 
thinking well of me, because I thought well of 
the birds, flowers and insects, had, during my 
absence, taken care of my tub of fish. And in 
truth some wonderful and silent powers com- 
bining together had been the means of saving 
my fish, as I found out in after years. In this, 
my first aquarium, there was a perfect balance 
of the three great powers — sunlight, oxygen, 
and carbonic acid gas, acting in harmony with 
the animal and plant life present. I had thus 
established one of the most perfect self-sustain- 
ing aquariums I have ever possessed. 
The philosophy of a self-sustaining aquarium 
is very simple when once understood. Its laws 
can never be changed, turned aside or gained 
by short cuts ; and this tub aquarium will give 
ns every rule that is required to run a self-sup- 
porting aquarium successfully. 
The proportions of the tub, seventeen inches 
across the top (inner measurement) and eight 
inches deep, was excellent for exposing a large 
surface of the water to the atmosphere, thereby 
enabling the water to absorb oxygen from the 
atmosphere. The depth of water was just 
right to allow sufficient light to pass into all 
parts of the tub, for the growth of the plants, 
and the situation was such that the sunlight 
was not in excess, so as to overheat the water. 
These were three very important conditions 
gained at the start. 
The green velvet-like substance that lined 
the tub, is one of the very best oxygenating 
plants known for an aquarium, and the num- 
ber of fish was rather under the proportion 
that could be sustained by the same amount of 
water and plant life. 
Without the green velvety lining, which 
consisted of a plant known as conferva, and 
which throws off large quantities of oxygen, 
the fish could not have existed in the tub over 
a week, and would have shown great distress, 
hugging the surface water for absorbed oxy- 
gen and breathing in air from above the sur- 
face of the water, till their lungs became dis- 
eased and in course of time, sickened and died. 
To prove that this conferva does produce 
oxygen in large quantities, take the fish out 
of the tub and place it in strong sunlight, to 
stimulate the conferva to grow and breathe 
more rapidly. In an hour's time a froth will 
be seen forming on the surface of the water 
and adhering to the side of the tub, and a 
slight hissing noise will be heard. Looking 
very closely into the water, strings of what 
seem like minute silvery beads may be seen 
streaming from the conferva. These bead- 
like streams are oxygen gas thrown off by the 
conferva in the act of breathing. The froth on 
the top is an accumulation of these beads or 
bubbles. The hissing noise is the bursting of 
the bubbles of oxygen — all going to prove that 
the water is thoroughly charged. 
If the reader should wish to prove that this 
gas is oxygen, it may be easily done by scrap- 
ing a little of the conferva off the side of the 
tub, and performing with it the curious and 
interesting experiment described in the Young 
Scientist for August, 1878. 
All animals breathe this oxygen, and cannot 
exist without it. As the minnows by opening 
and shutting their mouths cause the water to 
pass through their gills (which are their lungs) 
the oxygen held in suspension in the water, 
comes in contact with the carbon of their blood, 
and forms carbonic acid gas, which is poison- 
ous to animal life. 
As this gas is very easily dissolved in water 
it does not readily pass off in bubbles, but the 
water becomes so charged with it that if there 
was no provision made by nature for getting 
rid of this gas, all the fish and other aquatic 
animals would die. But strange as it may 
seem, if it were not for this gas, so poisonous 
to animals, all our beautiful flowers, trees, and 
aquatic plants would perish. It is this car- 
bonic acid gas that the conferva utilizes in 
breathing through the stonata or lungs, ex- 
haling that which is of no service to it (oxy- 
gen) but which the fish need to live on. And 
as it goes on, day and night, the plants per- 
forming silently miracles of work for their 
friends the fishes, and the fishes breathing out 
bountifully food for their neighbors the flora. 
How did the fish live without food? 
They did not ; Nature supplied them with 
the choicest diet. Over the tub grew a grape- 
vine; on the leaves of the vine, the cane, the 
