without them. M. Dollfus, again, has shewn that the specific weight of white ice is 871; that of blue ice 909; that of water being 1000; a result which confirms the preceding.

M. Durocher then affirms, "that the waters which flow from fields of snow and glaciers have a very decided sky-blue tint. When," he adds, "the detritus mingled with water are grey, they produce no other effect than to make the blue tint paler, and make it pass into dull blue." This assertion appears to me to be very rash, particularly when it is applied equally to the waters furnished by melted snow and those which come from the melting of glaciers. The former are more or less pure, but the colour varied, without, however, presenting the limpidity of that of springs. Thus, the little lake of Lioson, in the Canton de Vaud, fed by the snows of Tête-de-Moine, is of the most beautiful azure. The Bachalp-See, situate 2.275 metres above the sea, which receives the waters flowing from the snows of the Faulhorn, is of a yellowish-green.

Let us bestow a few words on the consideration of the waters which issue from glaciers. They are always charged with a considerable portion of mud, produced by the pulverisation of the fragments of rock which the glacier grinds down in its ceaseless progress. Thus, water taken from the surface of the Aar, at some metres from the glacier of the same name, contains, according to the experiments of M. Dollfus, 142 grammes of impalpable powder in a cubic metre of water. It is the same with the torrents which issue from glaciers. All of them roll along in a turbid, grey, milky, or dark stream, according to the nature of the pulverised rock. Hence the vulgar denominations of torrents, derived from the colour of their waters. The black water, which throws itself into the Rhone, near Martigny, in the Valais, comes from the glaciers of Trient and Buet. The white Lutschine derives its origin from the numerous glaciers which occupy the bottom of the valley of Lauterbrunn; and the black Lutschine comes from those of the valley of Grindelwald. Can it be true, as M. Durocher states (p. 445), that "the mud of glaciers has no other effect than to make the blue tint become paler, and pass into a muddy blue?" The Swiss geologist Ebel expressed the same idea thirty years ago: "the water of glaciers," he says,*" is of a whitish-blue, and the torrents which issue from them preserve this colour for many leagues, when other rivulets do not alter them by mixing with them." This, we perceive is the same opinion which M. Durocher has reproduced before the Academy. Nevertheless, I believe it to be incorThe waters which flow from glaciers have never appeared to me blue; this is also M. Agassiz's opinion, when he says (page 574 of his work on existing glaciers, which will be published speedily), It is the mud which gives the water of glaciers the milky tint which characterises them."

rect.

*Manuel au Voyageur en Swisse. 3d Ed., French Trans., tome ii., p. 521. Article GLACIERS.

In order to throw some light on the question, let us now consider the colour of the water of glaciers in a state of repose, where it is accumulated in great masses in the lakes of Switzerland. The lake of Geneva, fed principally by the waters of the Rhone, which come from all the glaciers of the Valais, is, it is true, of a beautiful azure blue; but the lake of Brientz, which receives the waters of glaciers exclusively, is of a very deep pistachio-green. This tint is equally striking, when we view it from the summit of the Faulhorn, that is to say, 2120 metres above its level, or only from a few metres above its surface. M. Bravais and myself have observed that, for entire weeks, this tint varies only very little, according to the light. The circumstance which proves decidedly that these tints are independent of the glacier origin of the tributaries is, that the lake of Thun, receiving its waters from the lake of Brientz, with which it communicates across the isthmus of Interlaken, is of a blue colour, sometimes equalling that of the lake of Geneva. The small Gelmersee, fed by the glaciers of the Geemerhorn, is pistachio-green, like the lake of Brientz. I may mention, besides, the lake of Kloenthal, in the Canton of Glaris. "One can scarcely distinguish it," says M. Raoul-Rochette, in his Lettres sur la Swisse,"from the meadow surrounding it; for its waters are of the same colour as the adjoining grass." This lake is fed by the glaciers of Glaernisch and the melted snow of Pragel. The small lake near the hospice of Grimsel is of a sombre tint; others are more or less blue; and this variability of hue proves that the character assigned by Ebel and Durocher to the waters of glaciers is subject to such numerous exceptions, that it loses all scientific value.

In order to finish this demonstration, let us turn our attention to the colour of the waters of glaciers when they make their escape in the form of rivers, from the lakes in which they have deposited the impurities with which they were charged. Nothing can equal the azure of the waters of the Rhone when they issue from the lake of Geneva; they form a striking contrast with the grey and muddy waves of the Arve, which comes directly from the glaciers of Chamonix. The only example cited by M. Durocher is of the same kind; he refers to the Otta-Elv, a river of Guldbrandsdal, a valley of Southern Norway. This river traverses four lakes in succession before receiving the tributary of Lougen-Elv. It is not therefore surprising that its waters, purified in passing through these four basins, contrast in their blue colours, with the waters of the Lougen-Elv; this is exactly the case of the Arve and Rhone at their junction below Geneva. Both of them come from glaciers; but the Rhone, grey like the Arve when it enters the lake of Geneva, is blue when it leaves it, because it is freed from its impurities. The Arve continues turbid, because it passes through no lake in its course. The following is the last fact we shall mention, as affording a still stronger proof that the blue colour is not inherent in the water of glaciers: At the top of the valley of Kandersteg (canton of Berne), 1568 metres above the

sea, is the small lake of Oeschinen; it is fed wholly by the waters which fall in numerous cascades from the glaciers of the Doldenhorn. This lake is of a deep green. Its outlet being subterranean, the waters pass through the ground as through a filter; they are limpid, transparent, shewing no trace of blue, of a sombre tint in deep places, and remind the spectator, in every point of view, of the pure and colourless waters where cresses grow, and the small rivers of Normandy inhabited by trouts. We perceive that, in this case, the waters furnished solely by glaciers, and after a very short transit, do not exhibit the blue tint either in a state of repose or motion.*

On the Colour of Water.

"I have," says Sir H. Davy, "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 greatest state of 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 from melted snows 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

* Comptes Rendus, No. 13, p. 545.

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 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 fine 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 Tivoli; but I doubt if pure saline matters, which are in themselves white, ever change the tint of water.-(Salmonia, by Sir Humphrey Davy, p. 198.)

John-Crow Vulture,* (Turkey-buzzard, Wilson; Cathartes aura, Vulture aura, Linn; Cathartes aura, Illiger.) Ann. pl. 151.†

The history of this species has been so ably written by Wilson and Audubon, that I shall do little more than touch on one or two disputed points in its economy. An excellent memoir of this vulture, communicated to me by my valued friend, Richard Hill, Esquire, of Spanish Town, affords some interesting particulars :—

"Notwithstanding it forms so common a feature in our landscapes, being seen every day and everywhere, on the mountain as well as on the plain, in the city as well as in the country, the Aura is not common to the West Indies. It exists in Cuba and Trinidad, but is unknown in Hayti, and in all the intermediate islands of the Caribbean chain. We are no doubt indebted for it to an accidental colony, blown over to us from Cuba, and Cuba itself owes it to some stray visitants from the neighbouring continent of Florida. Some similar fortuity imparted to us, in common with Cuba, from America, its naturalized hive-bee, which is said to have been at comparatively a late period an introduction into St Domingo.

"Those who ascribe the power which the vulture possesses of discerning from a distance its carrion food, to the sense of seeing or to the sense of smelling exclusively, appear to me to be both in error. It is the two senses, exerted sometimes singly, but generally unitedly, which give the facility which it possesses of tracing its appropriate food from far distances **** I shall relate one or two occurrences, which seem to me to be instances in which the sense of seeing and the sense of smelling were, sometimes separately, and sometimes unitedly, exerted by the vulture in its quest for food.

"A poor German immigrant who lived alone in a detached

* Length 25 inches, expanse 66, tail 91, wing from flexure 201, rictus 21%, arms 3, middle toe 21, claw 10.

†The above is extracted from an interesting volume on "The Birds of Jamaica," by Philip Henry Gorse and Richard Hill, Esquires, of Spanish Town, Jamaica, just published by Mr Van Voorst, London.