« PreviousContinue »
convinced me that the colours are in themselves green, and derived rather from the vegetable than the mineral kingdom of the land. They are found in all rivers and lakes, and are visible whenever the water being by subsidence cleared of its grossest muddy, but not of its green vegetable particles; the formation of waves in them, as in seas, allows the light from within the fluid to emerge from. depths or thicknesses and at obliquities sufficiently great to shew the greens, or where by elevation, adequate extent of scene, and due obliquities of view are obtained.
In sailing down in the latitude in order to arrive at Barbados from the eastward, at the distance of about eighty leagues from the island, a portion of green water several leagues broad occurs, which can only be referred to some one of the South American continental rivers, perhaps the Oronoco. As from the white sands of the island of Barbados have long since been washed all particles capable of floatage, and except during land floods no waters flow from the island into the sea, the ocean there is blue to its margin, and this green water is passed through and not seen near the island. To the appearance of this green water is to be ascribed the supposed existence of land to windward of Barbados, of an island, the place of which in old maps has been laid down, and which has truly been called an imaginary island; but the green colours of seas are not derived from the shores or coasts, but from the waters of lands.
On the banks of Newfoundland the green colours at very considerable distances from land are exhibited. To the seas which cover the banks this green colour, and frequent fogs belong, and by these they are distinguished, and the approach to them ascertained. To the same cause both appearances are to be referred, the influx and commixture of coloured and of cold water from the continent of America, principally from the river of St. Lawrence and the lakes which feed it. To this influx and commixture and to the deposit of vegetable coloured materials which produce the green colours of the water, the formation of the banks themselves belongs, and the
accumulation of fishes thereon, deriving their sustenance from these same materials for which the particles of pure earths are by no means fitted. The phenomena thus happily illustrate and confirm each other. May not this floatage and deposit of vegetable materials be applied also to account for the formation of beds of coal undoubtedly composed of vegetable terrestrial matter, in a state clearly indicating such a previous condition of the materials from which they are derived, as can alone produce regular formations, such a pre-existing division of particles approaching to solution, as in their subsequent aggregation emulate crystalline arrangement, with rarely and only accidentally a few grosser fragments mixed and found therein? From beds of coal thus formed and existing below the level of the sea, one more argument is gained in favour of that system of geology, which refers so many existences on the earth to submarine formations, subsequently uncovered by the recess of the waters. Together with all the colours therefore exhibited in the distant ocean, seas near the coasts of large islands and continents exhibit also greens, dark, gravelly, and chalk white colours derived from the vegetable and mineral kingdoms of the land.
The colours of rivers, lakes, canals, and all inland basins of water, differ nothing from those of the ocean and seas; the reflected, obviously from the before mentioned properties of transparent bodies, which impart no colours to the reflections made at their first or surfaces of incidence, and because truly, the reflections of seas, rivers, and lakes are of the air incumbent on them, of the same body in all cases, and therefore are the same. These colours however, as well as those internal to land waters, are not so obvious to general observation as are those of the ocean and seas, in consequence of the generally greater expanse of these latter waters, their constant and larger undulations, and other circumstances of condition in land waters which it is proper to state.
When land waters have once become charged by torrents with various materials brought down into them, their colours are the colours of those mixtures, and only the colours of the grosser and
more copious materials are visible. These are first deposited. They are principally of the mineral kingdom. By their superior gravity they first subside, leaving the lighter vegetable particles to display their greens, at first partially and mixedly, afterwards more purely and distinctly, and subsequently more dilutedly, until by deposition of the last vegetable colouring materials in lapse of time, by rest in the reservoirs of the land, or dilution in the waters of the ocean even these disappear. These colours of inland waters are first a dark muddy hue speedily deposited, and succeeded by a colour resembling that of gravel, at first of darker, afterwards of brighter hues, mixed with yellowish and reddish tints, followed by lighter whites, allowing the greens to appear, but giving them a glaucous gray appearance; then succeed purer greens, then greens more and more dilute up to final evanescence. These internal gravelly colours so much resemble the whites of brighter clouds, that it requires nice observation, in the Thames particularly, to distinguish these colours, when derived and exhibited by reflection of the clouds, from the internal transmitted colours of land floods, or of materials again raised by the river itself from its own bed, by rushing during flood, over what had been deposited or left behind, during the quiet recess of ebb.
These internal gravelly colours so frequently occur within land to obscure the greens, that to them, to the small elevations of view, and to the want of adequate undulations, is to be ascribed the non-appearance of the relations of colour between rivers, lakes, and seas.
There is not a river, or a lake, or any basin of water however small but what, in the circumstances under which it exists, exhibits more or less to an eye duly posited and duly observant all the colours of the ocean, and of seas. I have repeatedly seen little pools of water in the open air, when ruffled by the wind, exhibiting at proper angles of observation, a blue as cærulean and intense as that of the ocean, and all the other colours of the atmosphere, and at proper depths all the varieties of interual dirty greens. In the Thames, and in the Canal in St. James's Park, at different times, from the bridge, and from differ
ent stations around, may be seen all the colours, internal or external, of the ocean, and of the seas of the coast.
From Story's Gate, the hour of observation being generally between one and five in the afternoon, the branch of the St. James's Canal east of the bridge is seen at small angles from its surface. Its colours are occasionally of all the varieties of dark slate, lighter slate, dirty gravel, bright gravel, gravel resembling the walks of the Park, with which it may immediately be cɔmpared, whites more or less bright, blues more or less intense, and all the colours which the clouds and vapours of the atmosphere high above or close to the horizon can exhibit. Occasionally along its extent, at the same time many of these various colours appear, being reflected from various parts of the horizon, and sometimes in still weather during the spring whilst the Canal appears white by low horizontal reflection, it will exhibit patches of slate colour derived from leafless trees or its banks intercepting the colours of the sky and substituting their own. In advancing to the bridge directly from the south, the western branch frequently and generally exhibits colours differing from those of the castern, principally darker colours from the va pours of the atmosphere in the neighbourhood of the sun, during those hours, or from clouds, whilst the eastern is generally resplendent with blue or with white. If from the bridge the water be viewed, near to the sloping bank directly under the bridge, the least depths show scarcely any colours, but as the depths increase, where there are at bottom white objects to reflect the light, the greenness becomes more and more visible, and of increasing intensity, as has been before observed of and con. cerning coloured and partially transparent bodies of various thicknesses.
If the Canal be looked at from the centre of the bridge along its course or length, the same greens will be exhibited of a more intense colour immediately under the spectator, of intensities diminishing as the distances of view increase, until at about distances on the water equal to triple the height of the eye above, if the water be not strongly agitated, the diminishing transmissions of light mixing with the in
creasing reflections, are by them obscured and finally and entirely cease, and reflections alone prevail, of all their various colours of blue, or white, or slate. In passing from the Palace to the Bridge, in a calm day, the still water of the western branch being seen very obliquely, frequently presents a surface of fluid metallic appearance, sometimes resembling quicksilver, at other times of a more leaden hue.
In passing from Story's Gate to the westward, crossing the Bridge, and returning towards the Horse Guards, the eastern branch will on one side exhibit one class of colours, and on the other side another; and in the same branch, whilst proceeding parallel thereto, I have remarked successively changes of colour throughout its whole length of blues, slates, and gravels, as the sky or moving dark or white clouds gave their colours to the surface. With the wind strong and westwardly, and with considerable undulations propagated throughout its whole length, the Canal puts on the colours of the seas of the coast when viewed sufficiently near from its eastern extremity, and exhibits glaucous greens and greens more or less pure, as its waters are more or less mixed with impuritics derived from the waters which flow into it, or excited by its own agitations. Το observe the greens the Canal must be closely approached; at a distance, and even when approached, its remoter parts exhibit the colours of the opposite sky or clouds. For the exhibition of these colours in the Canal the brighter spring months are most favourable. In June it becomes very generally filled with water plants, which considerably interrupt these appearances, and perplex an ordinary observer.
In the Thames all these colours of the Canal may be seen under due circumstances and proper angles of observation, subject, however, to more frequent interruption by intermixture of im. purities more immediately derived from the land, and more frequently and daily excited by its own flowing tides, which interfere with and obscure the greens.
With the green water of the Canal an experiment was made in the Laboratory of the Royal Institution, under the direction of Mr. Faraday, to determine whether the mixture of salt with fresh waters tended or not, to change the colour, or hasten