3. Note on Clapeyron's Formula. By Professor Dewar. 4. Note on the Specific Gravity of Ocean Water. By During the cruise of the Challenger the specific gravity of the surface water was observed daily while at sea, and that of water from the bottom and intermediate depths as often as opportunity offered. These observations were almost entirely confined to the region between the parallels of 40° N. and 40° S. latitudes, which, including as it does the regions of the equatorial calms, of the trade winds, and to a certain extent of both the northern and southern westerly winds is decidedly the most interesting field for such investigations. Many valuable observations have been made by other observers, and I have availed myself more especially of the series of observations made by Lenz during Kotzebue's voyage to the Pacific and back. His observations were almost entirely confined to the surface water. The density of sea water depends on the amount of salt which it contains, on its temperature, and on the pressure to which it is subject. Away from the disturbing influences of the shore, the water of the ocean is subject to comparatively slight variations in saltnesss, so slight indeed that different waters may without sensible error be assumed to be equally affected by changes of temperature and pressure. As the remarks which are offered in the present paper have reference to the salinity or concentration of the water, the specific gravities have all been reduced to their value at 60° F., the unit being that of distilled water at its temperature of maximum density. The pressure is that of one atmosphere. There are two meteorological causes which affect the saltness of the sea; the one is the formation of vapour and the precipitation of it as rain, and the other is the freezing of the water and melting of the ice thus formed. Vast quantities of solid matter, chiefly carbonate of lime and silica, are removed from the water by living organisms, and these substances form the chief components of the solid matter brought down in solution by rivers. Although this is VOL. IX. 2 P a very important cause of the transmigration of rock, it does not sensibly affect the specific gravity of the sea-water, because only a very limited amount either of silica or of carbonate of lime can be in solution at any one time. The general distribution of saltness, as indicated by the specific gravity of the water at a common temperature of 60° F. at the surface, is shown on a chart on which localities of equal saltness are connected by lines, and the spaces between successive lines coloured distinctively. The vertical distribution is shown in diagrams in sections along certain lines of route, the depths at which the same saltness is observed being also connected by lines. The variations of saltness at the surface on the lines of section are further shown by curves having for ordinates the reduced specific gravity, and for abscissæ degrees of latitude or longitude according to circumstances. These diagrams show at once how great are the differences in the saltness of the water in different depths and at different localities on the surface, and it must be remembered that we are here considering bona fide ocean water, litoral waters so much influenced by the drainage of the land being reserved for separate treatment. Looking at the chart we see that specific gravities above 10270 occur in three localities only-namely, in the trade-wind regions of the North and South Atlantic, and of the central South Pacific. In the North Pacific the specific gravity was nowhere as high as 1.0265, whereas large tracts both of the North and South Atlantic reached 1.0275. The greater part of the year 1873 was passed in the North Atlantic, and the central part was crossed on the homeward voyage. On the eastern side and in the track of outward bound ships, the maximum of 1·02763 was reached in latitude 24°. In the central part the maximum was 1.02768 in latitude 25°, and in the western part it was 1.02743 in 27°30'; so that between the meridians of 20° W. and 70° W. the line of maximum saltness would appear to run nearly due east and west, with a slight northerly inclination towards the west. In the central South Atlantic the maximum of 1.02768 was observed in latitude 17°26', and in the western part 1.02783, in latitude 15°15', so that here also the line of maximum saltness would appear to have a slight northerly trend. Between these two lines the specific gravity falls off until a minimum of 1.0260 is reached at about 3° N. latitude, and following the equator from east to west the specific gravity appears to increase pretty steadily. In the Central Pacific the maximum saltness is observed in latitude 18° S., where the specific gravity is 102725; in the north the maximum is 1·0263, in latitude 22° N. The minimum of 1.02488 was found in latitude 7°26′ N. In the Western Pacific the series of observations was not so continuous, there being a considerable gap between latitude 15° S. and 2 S.; the northern portion, however, is complete. Here, again, the absolute maximum is in the south, reaching 1·0268, in 22°30° S.; in the north the maximum is 1·0263 in 22° N., but the dense water of the Southern Pacific penetrates into the northern part of the ocean, giving another and higher maximum of 1.0266 in lat. 2' N. The actual maximum observed was 1.0242 close to Humboldt Bay, in New Guinea. Other very low specific gravities were observed occasionally even at considerable distances from the coast; but the fact that there was frequently drift-wood floating about, and that the light water was confined to a stratum of 10 to 20 fathoms thickness, showed that we had here to do with shore water. If the general run of the curve be followed, the oceanic minimum will be found to occur about 10° N., marking 1.0258. The saltness, which increases on both sides of the equator until a maximum is reached in the trade wind districts, decreases again towards the poles and the whole of the ocean to the southward of latitude 40° S., has a specific gravity below 10260, and for the greater part below 1.0255. In the neighbourhood of ice in summer great and sudden variations are frequently observed, the specific gravity amongst loose park ice frequently falling as low as 1·0240. Confining our consideration, then, in the meantime, to the surface, we find that the maxima in the Southern Pacific and Atlantic are situated nearer the equator than those in the northern parts of these oceans; that the maxima in the Atlantic are higher than the corresponding ones in the Pacific; and that the maximum maximorum occurs in the South Atlantic about latitude 15° S. The equatorial minima in both oceans are to the northward of the equator; and from all these facts we see how intimately the concentration of the sea-water is connected with the distribution of the trade winds. If we turn now to the consideration of the vertical distribution of density, we see that the influence of atmospheric conditions does not cease when we leave the surface. In the trade-wind districts we find the excessive concentration extending to greater or less depths, according to the ocean which we are considering, and, as might have been expected, this effect is much more sensible in the Atlantic than in the Pacific. In the Atlantic, again, the amount of concentration is much greater in the northern than in the southern portion, while in the Pacific the reverse is the case. The great amount of concentration in the North Atlantic is doubtless due chiefly to the form of its basin. The south-east trade which blows with a preponderating force drives constantly fresh supplies of water in to the northern basin, where a large portion of it is kept constantly circulating by the prevailing winds in a region where the atmosphere is ever greedy of moisture. This circulation, assisted by the yearly oscillations of temperature, bring about a constant concentration of the deep waters, and at the same time, as I have pointed out, a heating of the deeper waters by convection. The effect of this concentration of the water is to render it heavier than an equal bulk of water further to the south, and consequently it forces its way southwards along the bottom. This under outflow from the North Atlantic was conjectured by Captain Tizard from a consideration of the temperature of the deep water of the western basin of the South Atlantic, and a glance at the vertical section of the Atlantic is sufficient to show the great likelihood of its existence. From a consideration of this section it would appear probable that at some position about 40° north latitude a tolerably uniform density of from 1.0265 to 1.0270 will be found, and, indeed, in the neighbourhood of the Azores the following bottom specific gravities were observed: 750 1675 1000 900 Depth in fathoms, Specific gravity at 15.56, Although we find that in all tropical and temperate regions the temperature of the water is highest at the surface, and decreases as the depth increases, we do not by any means invariably find the highest specific gravity at the surface, nor does it decrease regularly with increasing depth. The water is usually least salt at between 500 and 1000 fathoms from the surface. The maximum specific gravity at any locality is frequently observed at depths of from 25 to 150 fathoms from the surface, and it is not unusual to find besides the normal minimum between 500 and 1000 fathoms, a second minimum at 25 or 50 fathoms from the surface. These maxima and minima are caused in some cases by currents, and in others are the evidence of past wet or dry seasons. In the Southern Ocean the surface specific gravity varies between 1.0240 and 1.0250, being nearly constant at 1·0250 in localities free from ice; it increases, however, with the depth, the bottom specific gravity being usually 1.0255 or 1.0256. The following Gentlemen were elected Foreign Honorary Fellows, to fill up the vacancies caused by the death of Adolphe Theodore Brongniart and of Christian Gottfried Ehrenberg: ALPHONSO DE CANDOLLE, Geneva. Professor CARL GEGENBAUR, Heidelberg. The following Gentlemen were elected Ordinary Fellows of the Society: JOHN MURRAY. WALTER NOEL HARTLEY, Chemical Demonstrator, King's College, London. WALTER WELDON, F.C.S., London. Monday, 29th January 1877. Professor KELLAND, Vice-President, in the Chair. The following Communications were read : 1. Note on the Manganese Nodules found on the Bed of the Ocean. By J. Y. Buchanan. The manganese nodules occur in greater or less quantity all over the ocean-bed, and most abundantly in the Pacific. They occur of all sizes, from minute grains to masses of a pound weight, and even greater, and form nodular concretions of concentric shells, round a nucleus, which is very frequently a piece of pumice or a shark's tooth. Their outside has a peculiar and very characteristic mammillated surface, which enables them to be identified at a glance. When freshly brought up they are very soft, being easily |