same proportion to this pond that the millions of fish bear to the
ocean."

"I say, Jack!" cried Peterkin, waving his hand; "come here, like a good
fellow. Ralph is actually talking philosophy. Do come to our
assistance, for he's out o' sight beyond me already!"

"What's the matter?" inquired Jack, coming up, while he endeavoured to
scrub his long hair dry with a towel of cocoa-nut cloth.

I repeated my thoughts to Jack, who, I was happy to find, quite agreed
with me. "The best plan," he said, "will be to put very few animals at
first into your tank, and add more as you find it will bear them. And
look here," he added, pointing to the sides of the tank, which, for the
space of two inches above the water-level, were encrusted with salt,
"you must carry your philosophy a little further, Ralph. That water has
evaporated so much that it is too salt for anything to live in. You
will require to add _fresh_ water now and then, in order to keep it at
the same degree of saltness as the sea."

"Very true, Jack; that never struck me before," said I.

"And, now I think of it," continued Jack, "it seems to me that the
surest way of arranging your tank so as to get it to keep pure and in
good condition will be to _imitate_ the ocean in it; in fact, make it a
miniature Pacific. I don't see how you can hope to succeed unless you
do that."

"Most true," said I, pondering what my companion said. "But I fear that
that will be very difficult."

"Not at all," cried Jack, rolling his towel up into a ball and throwing
it into the face of Peterkin, who had been grinning and winking at him
during the last five minutes--"not at all. Look here. There is water
of a certain saltness in the sea; well, fill your tank with sea-water,
and keep it at that saltness by marking the height at which the water
stands on the sides. When it evaporates a little, pour in _fresh_ water
from the brook till it comes up to the mark, and then it will be right,
for the salt does not evaporate with the water. Then there's lots of
seaweed in the sea; well, go and get one or two bits of seaweed and put
them into your tank. Of course the weed must be alive, and growing to
little stones; or you can chip a bit off the rocks with the weed
sticking to it. Then, if you like, you can throw a little sand and
gravel into your tank, and the thing's complete."

"Nay, not quite," said Peterkin, who had been gravely attentive to this
off-hand advice--"not quite.