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 yourselfOne 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. Aglass 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： 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 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 its leaves the heather-bells， and the polypes of the sea， and the gnats above the summer stream.
I said just now， that happy was the sportsman who was also a naturalist. And， having once mentioned these curious water-flies， I cannot help going a little farther， and saying， that lucky is the fisherman who is also a naturalist. A fair scientific knowledge of the flies which he imitates， and of their habits， would often ensure him sport， while other men are going home with empty creels.
One would have fancied this a self-evident fact； yet I have never found any sound knowledge of the natural water-flies which haunt a given stream， except among cunning old fishermen of the lower class， who get their living by the gentle art， and bring to indoors baskets of trout killed on flies， which look as if they had been tied with a pair of tongs， so rough and ungainly are they； but which， nevertheless， kill， simply because they are (in COLOUR， which is all that fish really care for) exact likenesses of some obscure local species， which happen to be on the water at the time.
