glaucus-or the wonders of the shore(格劳高斯)-第37章
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rapid succession to the surface all over the vessel； and this process goes
on uninterruptedly as long as the rays of the sun are uninterrupted。
〃Now these globules consist of PURE OXYGEN； given out by the
plants under the stimulus of light； and to this oxygen the animals in the
tank owe their life。 The difference between the profusion of oxygen…
bubbles produced on a sunny day； and the paucity of those seen on a
dark cloudy day； or in a northern aspect； is very marked。〃 Choose；
therefore； a south or east window； but draw down the blind； or throw a
handkerchief over all if the heat become fierce。 The water should
always feel cold to your hand； let the temperature outside be what it
may。
Next； you must make up for evaporation by FRESH water （a very
little will suffice）； as often as in summer you find the water in your vase
sink below its original level； and prevent the water from getting too salt。
For the salts； remember； do not evaporate with the water； and if you left
the vase in the sun for a few weeks； it would become a mere brine…pan。
But how will you move your treasures up to town？
The simplest plan which I have found successful is an earthen jar。
You may buy them with a cover which screws on with two iron clasps。
If you do not find such； a piece of oilskin tied over the mouth is enough。
But do not fill the jar full of water； leave about a quarter of the contents
in empty air； which the water may absorb； and so keep itself fresh。 And
any pieces of stone； or oysters； which you send up； hang by a string from
the mouth； that they may not hurt tender animals by rolling about the
bottom。 With these simple precautions； anything which you are likely
to find will well endure forty…eight hours of travel。
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What if the water fails； after all？
Then Mr。 Gosse's artificial sea…water will form a perfect substitute。
You may buy the requisite salts （for there are more salts than 〃salt〃 in
sea…water） from any chemist to whom Mr。 Gosse has entrusted his
discovery； and； according to his directions； make sea…water for yourself
One more hint before we part。 If； after all； you are not going down
to the sea…side this year； and have no opportunities of testing 〃the
wonders of the shore；〃 you may still study Natural History in your own
drawing…room； by looking a little into 〃the wonders of the pond。〃
I am not jesting； a fresh…water aquarium； though by no means as
beautiful as a salt…water one； is even more easily established。 A glass
jar； floored with two or three inches of pond…mud （which should be
covered with fine gravel to prevent the mud washing up）； a specimen of
each of two water…plants which you may buy now at any good shop in
Covent Garden； Vallisneria spiralis （which is said to give to the Canvas…
backed duck of America its peculiar richness of flavour）； and Anacharis
alsinastrum； that magical weed which； lately introduced from Canada
among timber； has multiplied； self… sown； to so prodigious an extent； that
it bid fair； a few years since； to choke the navigation not only of our
canals and fen… rivers； but of the Thames itself： （34） or； in default of
these； some of the more delicate pond…weeds； such as Callitriche；
Potamogeton pusillum； and； best of all； perhaps； the beautiful Water…
Milfoil （Myriophyllium）； whose comb…like leaves are the haunts of
numberless rare and curious animalcules：… these （in themselves； from the
transparency of their circulation； interesting microscopic objects） for
oxygen…breeding vegetables； and for animals； the pickings of any pond；
a minnow or two； an eft； a few of the delicate pond…snails （unless they
devour your plants too rapidly）： water…beetles； of activity
inconceivable； and that wondrous bug the Notonecta； who lies on his
back all day； rowing about his boat…shaped body； with one long pair of
oars； in search of animalcules； and the moment the lights are out； turns
head over heels； rights himself； and opening a pair of handsome wings；
starts to fly about the dark room in company with his friend the water…
beetle； and （I suspect） catch flies； and then slips back demurely into the
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water with the first streak of dawn。 But perhaps the most interesting of
all the tribes of the Naiads； … （in default； of course； of those semi…human
nymphs with which our Teutonic forefathers； like the Greeks； peopled
each 〃sacred fountain；〃） … are the little 〃water…crickets；〃 which may be
found running under the pebbles； or burrowing in little galleries in the
banks： and those 〃caddises；〃 which crawl on the bottom in the stiller
waters； enclosed； all save the head and legs； in a tube of sand or pebbles；
shells or sticks； green or dead weeds； often arranged with quaint
symmetry； or of very graceful shape。 Their aspect in this state may be
somewhat uninviting； but they compensate for their youthful ugliness by
the strangeness of their transformations； and often by the delicate beauty
of the perfect insects； as the 〃caddises；〃 rising to the surface； become
flying Phryganeae （caperers and sand… flies）； generally of various shades
of fawn…colour； and the water… crickets （though an unscientific eye may be
able to discern but little difference in them in the 〃larva；〃 or imperfect
state） change into flies of the most various shapes； … one； perhaps； into
the great sluggish olive 〃Stone…fly〃 （Perla bicaudata）； another into the
delicate lemon…coloured 〃Yellow Sally〃 （Chrysoperla viridis）； another
into the dark chocolate 〃Alder〃 （Sialis lutaria）： and the majority into
duns and drakes （Ephemerae）； whose grace of form； and delicacy of
colour； give them a right to rank among the most exquisite of God's
creations； from the tiny 〃Spinners〃 （Ba 塼 is or Chloron） of incandescent
glass； with gorgeous rainbow…coloured eyes； to the great Green Drake
（Ephemera vulgata）； known to all fishermen as the prince of trout…flies。
These animals； their habits； their miraculous transformations； might give
many an hour's quiet amusement to an invalid； laid on a sofa； or
imprisoned in a sick…room； and debarred from reading； unless by some
such means； any page of that great green book outside； whose pen is the
finger of God； whose covers are the fire kingdoms and the star kingdoms；
and it
