Poiet.—A fish dinner such as you have just described, combined with one such as we have enjoyed to-day, might, I think, be made an interesting experimental lecture on natural history. The analogies of the different species and genera of fishes, so distinct in the form of their organs, are likewise marked in the appearance and taste of their flesh. The salmon and the char may be regarded as the generic types of the salmo. By trout, which have sometimes red and sometimes white flesh, they are connected with the grayling and hucho. By the grayling the trout is connected with the laveret, and by the laveret the genus salmo is connected with the carp genus. The char is immediately connected with the grayling, and laveret by the umbula. By the sea trout the salmon is connected with the trout; and by the hucho, with the pike and perch families.
Hal.—We will arrange a dinner of this kind in England, and by means of it follow the analogies of salt and fresh water fishes. But the time for our parting is almost arrived.—Let us drink a glass each of this old wine of the Danube to our next happy meeting, and go and take a last look of the Fall of Traun, whilst our carriages are preparing.
[They walk to the rock above the Fall of the Traun.]
Hal.—See, the cataract is now in great beauty; the river above is coloured by the setting sun, and the glow of the rosy light on the upper stream is beautifully and wonderfully contrasted with the tints of the cataract below. Have you ever seen any thing so fine?
Poiet.—The lights are beautiful; but I have certainly seen a finer combination of features in the Fall of the Velino, at Terni, though that water is not clear; but, even with this defect, it is certainly the most perfect of European falls. This cascade of the Traun, though not so elevated as that of Terni, and not so large as that of Schaffhausen, yet, from its perfect clearness, and the harmony of the surrounding objects, ranks high, as to picturesque effect, amongst the waterfalls of Europe; and the wonderful transparency of its pale-green water gives it a peculiar charm in my eyes, enhanced as it is now by the light of the glowing western sky; and the tints of the quadrant iris on its spray are not brighter than those of its stream and foam.
Orn.—We have now followed this water at least thirty miles, and wherever we have seen it, it has always displayed the same characters of clearness and rapidity—of green stream and white foam; and we have traced it from the snowy mountains of Styria to the plains of Upper Austria, where it serves to purify the darker Danube. How is it, that it has preserved its transparency, though so many of its tributary streams have been foul, either from the thunder storm, or from the sudden melting of snows?
Hal.—The three small lakes and the two larger ones, which are in fact its reservoirs, are the cause of this. The Gründtl See furnishes its principal stream, and this lake is fed by two others—Töplitz See and Lahngen See; and the tributary streams, which unite at Aussee, from Alten Aussee and Oden See, though one is blue and the other yellow, yet combine to give a tint, which is nearly the same as that from the stream of the Gründtl See, and which the river retains throughout its course Yet I have seen even this river very foul, but only in a part of its course, below Ischel. I was once at that place, when the thunder storm of a night having washed the dust of the roads into the river, it was extremely turbid from Ischel to the Traun See. It rendered the upper part of this large lake coloured; but, notwithstanding this, the river came from the lower part of it perfectly clear, and I caught fish in it there with a fly, which, at its entrance into the lake was quite impossible.
Poiet.—You, Halieus, must certainly have considered the causes which produce the colours of waters. The streams of our own island are of a very different colour from these mountain rivers, and why should the same element or substance assume such a variety of tints?
Hal.—I certainly have often thought upon the subject, and I have made some observations and one experiment in relation to it. I will give you my opinion with pleasure, and, as far as I know, they have not been brought forward in any of the works on the properties of water, or on its consideration as a chemical element. The purest water with which we are acquainted is undoubtedly that which falls from the atmosphere. Having touched air alone, it can contain nothing but what it gains from the atmosphere, and it is distilled without the chance of those impurities, which may exist in the vessels used in an artificial operation. We cannot well examine the water precipitated from the atmosphere, as rain, without collecting it in vessels, and all artificial contact gives more or less of contamination; but in snow, melted by the sunbeams, that has fallen on glaciers, themselves formed from frozen snow, water may be regarded as in its state of greatest purity. Congelation expels both salts and air from water, whether existing below, or formed in, the atmosphere; and in the high and uninhabited regions of glaciers, there can scarcely be any substances to contaminate. Removed from animal and vegetable life, they are even above the mineral kingdom; and though there are instances in which the rudest kind of vegetation (of the fungus or mucor kind) is even found upon snows, yet this is a rare occurrence; and red snow, which is occasioned by it, is an extraordinary and not a common phenomenon towards the pole, and on the highest mountains of the globe. Having examined the water formed from melted snow on glaciers in different parts of the Alps, and having always found it of the same quality, I shall consider it as pure water, and describe its characters. Its colour, when it has any depth, or when a mass of it is seen through, is bright blue; and, according to its greater or less depth of substance, it has more or less of this colour: as its insipidity, and its other physical qualities, are not at this moment objects of your inquiry, I shall not dwell upon them. In general, in examining lakes and masses of water in high mountains, their colour is of the same bright azure. And Captain Parry states, that the water on the Polar ice has the like beautiful tint. When vegetables grow in lakes, the colour becomes nearer the sea green, and as the quantity of impregnation from their decay increases—greener, yellowish green, and at length, when the vegetable extract is large in quantity—as in countries where peat is found—yellow, and even brown. To mention instances, the Lake of Geneva, fed from sources (particularly the higher Rhone) formed from melting snow, is blue; and the Rhone pours from it, dyed of the deepest azure, and retains partially this colour till it is joined by the Soane, which gives to it a greener hue. The Lake of Morat, on the contrary, which is fed from a lower country, and from less pure sources, is grass green. And there is an illustrative instance in some small lakes fed from the same source, in the road from Inspruck to Stutgard, which I observed in 1815 (as well as I recollect) between Nazareit and Reiti. The highest lake fed by melted snows in March, when I saw it, was bright blue. It discharged itself by a small stream into another, into which a number of large pines had been blown by a winter storm, or fallen from some other cause: in this lake its colour was blue green. In a third lake, in which there were not only pines and their branches, but likewise other decaying vegetable matter, it had a tint of faded grass green; and these changes had occurred in a space not much more than a mile in length. These observations I made in 1815: on returning to the same spot twelve years after, in August and September, I found the character of the lakes entirely changed. The pine wood washed into the second lake had disappeared; a large quantity of stones and gravel, washed down by torrents, or detached by an avalanche, supplied their place: there was no perceptible difference of tint in the two upper lakes; but the lower one, where there was still some vegetable matter, seemed to possess a greener hue. The same principle will apply to the Scotch and Irish rivers, which, when they rise or issue from pure rocky sources, are blue, or bluish green; and when fed from peat bogs, or alluvial countries, yellow, or amber-coloured, or brown—even after they have deposited a part of their impurities in great lakes. Sometimes, though rarely, mineral impregnations give colour to water: small streams are sometimes green or yellow from ferruginous depositions. Calcareous matters seldom affect their colour, but often their transparency, when deposited, as is the case with the Velino at Terni, and the Anio at Trivoli; but I doubt if pure saline matters, which are in themselves white, ever change the tint of water.
Orn.—On what then does the tint of the ocean depend, which has itself given name to a colour?