Other rollers are, however, undoubtedly due to earthquakes or volcanic eruptions occurring in the bed of the sea. Many of the great and sudden waves which have caused devastation and great loss of life on the shores of western South America are referable to this cause. Observations to enable the focus of such a disturbance to be traced have generally been lacking, but it is probable that where the wave has been large the point of origin has not been far distant. In one notable instance the conditions were reversed. The point of origin was known, and the distance to which the resulting wave travelled could be fairly satisfactorily traced. This was the great eruption in the Straits of Sunda, in August 1883, which locally resulted in the disappearance of the major part of the island of Krakatoa, and the loss of nearly 40,000 lives, on the neighbouring shores of Java and Sumatra, by the huge wave which devastated them. The records of automatic tide gauges and the observations of individuals enabled the waves emanating from this disturbance to be followed to great distances. These waves were of great length, the crests arriving at intervals of about an hour, and moving with a velocity of about 350 miles an hour, were about that distance apart. The waves recorded at Cape Horn were apparently undoubtedly due to the eruption, and travelled distances of 7,500 miles and 7,800 miles in their course on either side of the south polar land. They were only 5 inches in height above mean level of the sea, while the waves recorded at places on the southern part of Africa, at a distance of about 5,000 miles from the scene of the eruption, were from 1 to 2 feet high, the original long waves being of an unknown height, but probably did not exceed 10 or 15 feet. No other such opportunity of testing the distances to which great waves may travel has ever occurred, and as such a catastrophe as gave rise to them could scarcely be repeated without similar loss of life, it may be hoped we shall not live to see another, interesting though the discussion of the numerous phenomena were. The movement of the particles of water due to the tide wave extends to the bottom of the deepest water, and doubtless plays an important part in keeping up a constant motion in the abysses, but the depth to which the action of the surface waves originating in wind reach is still but little known by observation. If, however, we study the contour of the bottom off the shores of land exposed to the full influence of the great oceans, we are struck by the very general rapid increase of slope after a depth of about 80 to 100 fathoms (500 to 600 feet) has been reached. It appears probable that this is connected with the depth to which wave action may extend, the fine particles brought down by rivers or washed from the land by the attrition of the breakers being distributed and gradually moved down the slope. When we examine banks in the open sea we find, however, that there are a great many with a general depth of from 30 to 40 fathoms, and the question arises whether this may not be the general limit of the power of oceanic waves to cut down the mass acted upon when it is fairly friable. The question has an interesting bearing on the subject of the ever-debated origin of coral atolls, for this is the general depth of many large lagoons; and granted that the sea can cut down land to this depth, we have at once an approach to the solution of the problem of the formation of bases of a suitable depth and material upon which the coral animal can commence operations. This question also awaits more light, and I merely offer this remark as a suggestion. It is, however, somewhat remarkable that in recent cases of volcanic islands piled up by submarine eruptions, they have all been more or less rapidly washed away, and are in process of further diminution under the surface. Observations on the mean level of the sea show that it constantly varies, in some places more than others. This subject has not yet been worked out. In some localities it is plainly due to wind, as in the Red Sea, where the suminer level is some two feet below that of winter, owing to the fact that in summer the wind blows down the whole length of the sea, and drives the water out. In many places, as in the great estuary of the Rio de la Plata, the level is constantly varying with the direction of the winds, and the fluctuation due to this cause is greatly in excess of the tidal action. In others the cause is not so clear. At Sydney, New South Wales, Mr. Russell found that during eleven years the level was constantly falling at about an inch a year, but by the last accounts received it was again stationary. The variations in the pressure of the atmosphere play an important part in changes of sea level. A difference of one inch in the barometer has been shown to be followed by a difference of a foot in the mean level of the sea, and in parts of the world where the mean height of the barometer varies much with the seasons, and the tidal range is small, this effect is very marked. Of any secular change in the level of the sea little is known. This can only be measured by comparison with the land, and it is a question which is the more unstable, the land or the water-probably the land, as it has been shown that the mass of the land is so trifling, compared with that of the ocean, that it would take a great deal to alter the general mean level of the latter. All the points connected with the sea that I have had the honour of bringing before you form part of the daily observation of the marine surveyor when he has the chance; but I cannot refrain from also mentioning other duties, which are indeed in the present state of our knowledge and of the practical requirements of navigation the principal points to which he has to pay attention, as it may explain why our knowledge on so many interesting details still remains very imperfect. Working as we do in the interests of the vast marine of Great Britain, the paramount necessity of good navigational charts requires that the production of such charts should be our principal aim. It is difficult for a landsman and difficult even for a sailor who has never done such work to realise the time that is necessary to make a really complete marine survey. The most important part, the ascertainment of the depth, is done, so to speak, in the dark-that is to say, it is by touch and not by sight that we have to find the different elevations and depressions of the bottom of the sea. In making a map of the land an isolated rock or hill stands up like a beacon above the surrounding land, and is at once localised and marked, but a similar object under the sea can only be found by patient and long-continued sounding, and may very easily be missed. When it is considered that marine surveying has only been seriously undertaken for about 100 years, with a very limited number of vessels, we shall, I think, understand how in the vast area of the waters, taking only those bordering the shores, many unsuspected dangers are yearly discovered. Very, very few coasts have been minutely surveyed, and, setting aside for a moment the great changes that take place off shores where sandbanks prevail, I should be sorry to say that even on our own coasts charts are perfect. Yearly around Great Britain previously unknown rocks come to light, and if this is the case at home, what are we to think of the condition of charts of less known localities! Our main efforts, therefore, are directed to the improvement of charts for safe navigation, and the time that can be spared to the elucidation of purely scientific problems is limited. Nevertheless, the daily work of the surveyor is so intimately connected with these scientific problems that year by year, slowly but surely, we add to the accumulation of our knowledge of the sea. The following Papers were read: 1. On Current Polar Exploration. By Col. H. W. FEILDEN.' 2. On a Recent Journey in the Valley of the Euphrates. This journey was undertaken for archæological reasons in order to see whether remains of Roman frontier works exist on the right bank of the Euphrates in a state of preservation similar to that of Severus's road to Melitene, explored by Messrs. Hogarth and Munro in 1891, Mr. Hogarth's party consisted of Messrs. V. W. Yorke and F. W. Green and Lord Encombe. The great river Euphrates' was seen first at Khalfat. Here and for 300 miles up it can be crossed only by ferry boats of singularly rude construction; and the process of crossing with horses in such craft is exciting. The upper course of the river is rarely navigated and only by skin-rafts and swimmers on skins partly filled with grain. The depth and precipitousness of its gorge cause the Euphrates to be a serious barrier, and no road can long follow either bank. From Khalfat to Samsat the party had to cut off a bend, passing through villages of settled Kurds, tamed by the possession of agricultural wealth, and imbued through contact with Arabs and Syrians with orthodox Islam. Above Samsat the gorge soon becomes impassable, and dangerous rapids begin. The party made straight across Taurus, meeting great difficulties from narrow paths on precipices and soft snow. Descending near Malatia they made their way past the junction of the northern and eastern forks, about whose names and respective claim to be the main stream there seems much error in maps. The natives call the northern fork Murad, not Kara Su, and consider it the main river. The name Frat is known, but little used. North of the junction, where the Kurdish mountains hang over the left bank, the scenery is very grand indeed. The party continued to follow the river up to Erzingan. The Kurds here are heretical and wilder than in the south. The Armenians are less servile than ordinary, but, being alive to the religious, social, and geographical difficulties in the way of independence, would gladly be left alone by agitators. There is little evidence of wanton oppression, least for religion's sake. Less is heard in the country than out of it of Kurdish tyranny. Armenians are well off in many respects, better in some than poor Moslems. Their condition is not improved, but the reverse, by irresponsible and otiose expressions of sympathy in Europe. Geographical considerations go far to preclude Armenia from becoming again a nation. Legionary camps were found at Samosata and Satala, but none at Melitene. A magnificent Roman bridge exists near Kiakhta and ruins of others, but no milestones or roadway connecting frontier forts, two of which were discovered. The reported walls along the bank south of Taurus were found to consist of ruins of an aqueduct. The river itself formed the most impassable of frontiers: it might well have seemed that the angel's vial must be poured out on the great river Euphrates, and the waters thereof dried up ere the way of the kings of the East could be prepared. 3. On Russian Armenia. By Dr. A. MARKOFF.2 4. Montenegro. By W. H. COZENS-HARDY. The old Montenegro, since the Berlin treaty, has nearly doubled in area. Montenegro, which lies near the sea, is made up of bare limestone mountains enclosing fertile basins, the average height of the country above the sea being 2,000 to 3,000 feet. The Zeta, flowing into the Lake of Scutari, is the chief river, but this part of the country is almost destitute of water, and the inhabitants are compelled to store snow for drinking. The small village of Cetinje, which forms the 2 Ibid. p. 469. Scot. Geog. Mag., 1894, p. 465. capital, lies in one of the mountain basins. In July 1893 the Montenegrins celebrated there the 400th anniversary of the establishment of the earliest Slavonic printing press, set up not far from Cetinje in 1493. In the new Montenegro to the north and west the geographical characteristics are quite distinct. Grassy downs, dense forests, and innumerable mountain streams are found, and there is excellent pasture for sheep. The two highest mountains are Kom and Durmitor, which are slightly under 9,000 feet high. The Montenegrins are divided into clans and communes, and possess an elaborate system of local government. At present Montenegro is emerging from an Homeric state of society, and its future depends on the ability of its people to adapt themselves to less warlike pursuits. FRIDAY, AUGUST 10. The following Papers were read: 1. On the Bathymetrical Survey of the French Lakes. By E. DELEBECQUE. As the result of the author's soundings in most of the French lakes, he has produced a series of sheets, published in 1892 and 1893 by the Ministère des Travaux Publics, under the title 'Atlas des Lacs Français.' The soundings were in every case made by means of a steel wire mounted on a graduated drum, the revolutions of which indicated the amount of wire payed out. The form of apparatus at first used was that of the Swiss Bureau Topographique, subsequently that of Belloc was employed, but finally one designed by the author and only weighing 4 kilogrammes was adopted. The position of each sounding was determined, either from angular measurements of the graduated mast of the boat taken from the shore, or by sextant bearings of objects on shore taken from the boat. A number of lakes have been sounded more roughly than those laid down in the atlas, and many observations of temperature and of the chemical composition of the water have been made. The atlas, which will be completed by the addition of maps of several lakes in the Jura and the Pyrenees, is only a part of a comprehensive work about to be published by the author. The lakes already mapped in the atlas are arranged as follows: Pl. 1. Lake of Geneva (the Swiss part sounded by M. Hörnliman, of the Bureau Topographique Fédéral) on the scale ʊʊʊ. Pl. 2. Lake of Bourget, scale oboo. Pl. 3. Lake of Annecy, scale goboo Pl. 4. Lake of Aiguebelette (Savoy), scale roboo Pl. 5. Lake of Paladru (Isère), scale Todo Pl. 6. Lakes of Brenets, St. Point, Romoray, and Malpas (Doubs), scale rodo Pl. 7. Lakes of Nantua, Sylans, and Genin (Ain), scale roboo Pl. 8. Lakes of Chalain, Dessus, Dessous, Marlay, La Motte, Grand Maclu, and Petit Maclu (Jura), scale Toboo: Pl. 9. Lakes of Saffrey and Petit Chat (Isère) and of La Girotte (Savoy), scale Too Pl. 10. Lakes of Issarlés (Ardèche), Bouchet (Haute-Loire), Pavin, Chauvet, Godivelle, and Tazanat (Puy-de-Dôme), scale ro000. In all cases the configuration of the lakes is expressed by contour lines at intervals of 5 or 10 metres, and the position of each sounding is shown by a dot. It was impossible to add the land contours on the same scale, as the French staffmaps do not show them with sufficient exactness. 2. On a Bathymetrical Survey of the English Lakes. By HUGH ROBERT MILL, D.Sc., F.R.S.E. Ten of the largest English lakes were sounded by the author, assisted by Mr. E. Heawood, Mr. Shields, and others, and the final discussion of the work enables the following tabular statement to be drawn up : There are two main types amongst these lakes, the shallow and the deep. The former, including only Derwentwater and Bassenthwaite, are the broadest of all the lakes, and they only average 18 feet in depth. The bed of these lakes may be roughly described as an undulating plain, grooved and ridged into shallow hollows, and low shoals running parallel to the long axis of the lake. The second, or deep type, the shallowest of which has an average depth of 40 feet, comprises all the other lakes. Ennerdale combines the characteristics of both types, conforming to the deep type in its upper, to the shallow in its lower reach. They are long, narrow, sometimes winding like Ullswater, or slightly curved in outline like Wastwater and Haweswater. The most characteristic lie in long narrow valleys with steeply sloping sides, and the slopes are continued under water with almost equal steepness, in some cases with greater steepness, and terminate in an almost flat floor. The typical form of this class of lake is thus a steepsided flat-bottomed trough, diversified along the slopes by the still steeper conical mounds of débris thrown down at the mouths of streams. 3. On the Currents of the Faeröe-Shetland Channel and the North Sea.1 By H. N. DICKSON, F.R.S.E. The physical observations made by the author on board H.M.S. 'Jackal,' on behalf of the Fishery Board for Scotland, during August 1893, were continued in November 1893, and in February and May 1894. The unusual atmospheric conditions during the year 1893 probably made the differences of temperature observed greater than the normal, and those of salinity less, at least during the earlier part of the work. The discussion of the observations leads to the following provisional conclusions:: 1. While the Atlantic current flowing over the Wyville-Thomson ridge attains its maximum velocity in winter, its speed is maintained during summer by the greater warmth of the upper layers of water in the Atlantic, and consequent higher level of the surface of that ocean compared with the Norwegian Sea. Passing over the ridge, the Atlantic current is cooled by mixture with the cold water of The paper is published in the Report of the Fishery Board for Scotland, 1894. 2 Brit. Assoc. Report, 1893, p. 835. |