Shortly, we may define the action of the earth's magnetism on the iron of a ship as follows: The earth being surrounded by a magnetic field of force differing greatly in intensity and direction in the regions from the North Pole to the Equator and the Equator to the South Pole, the ship's magnetic condition is largely dependent upon the direction of her head whilst building and the part of that field she occupied at the time; partly upon her position in the magnetic field she traverses at any given time during a voyage.

For the reasons I have given, magnetic charts are a necessity for practical purposes and in the following order of value. That of the magnetic declination or variation which is constantly in use, especially in such parts of the world as the St. Lawrence and the approaches to the English Channel, where the declination changes very rapidly as the ship proceeds on her course. Next, that of the dip and force, which are not only immediately useful when correcting the ship's compass, but are required in the analysis of a ship's magnetism both as regards present knowledge and future improvements in placing compasses on board.

If astronomers have for a very long time been able to publish for several years in advance exact data concerning the heavenly bodies, is it too much to hope that magneticians will before long also be able to publish correct magnetic charts to cover several years in advance of any present epoch? If this is to be done within reasonable time there must be a long pull, a strong pull, and a pull all together of magnetic observers in all lands, and accumulated data must also be discussed.

On Magnetic Instruments for Travellers.

Travellers in unsurveyed countries, if properly instructed and equipped, can do good service to science by observing the three magnetic elements of declination, inclination or dip, and force at as many stations as circumstances will permit; hence the following remarks.

For the purpose of making the most exact magnetic survey the best equipment of instruments consists of the well-known unifilar magnetometer, with fittings for observing the declination, and a Barrow's dip circle. To some travellers these instruments might be found too bulky, and in some regions too delicate as well as heavy to carry.

Of suitable instruments made abroad, those used by M. Moureaux in his survey of France may be mentioned, as they are of similar type, but much smaller and lighter than the instruments above mentioned.

Another form of instrument, called an L.C. instrument, for observing both the inclination and total force, is shown in the instrument before you. Originally designed for observations on board ships at sea where the ordinary magnetic instruments are unmanageable, it has also been found to give satisfactory results in a land survey, where greater accuracy is expected than at sea. Thus, during a series of observations extending from the north side of Lake Superior to the southern part of Texas last year, comparisons were made between the results obtained with an L.C. instrument and those of the regular unitilar magnetometer and dip circle, when the agreement was found satisfactory.

I am therefore of the opinion that a traveller furnished with a theodolite for land-surveying purposes, but fitted with a reversible magnetic needle, can at any time he observes a true bearing obtain a trustworthy value of the declination. Dismounting the theodolite from his tripod, the latter will serve for mounting an L.C. instrument with which to observe the inclination and force. Thus, by adding to his ordinary equipment an instrument weighing in its box about 21 ib., he can obtain valuable contributions to terrestrial magnetism, and at the same time give useful assistance to geological investigations.

Concluding Remarks.

Although a great subject like terrestrial magnetism, even to exhibit our present knowledge of the science, cannot be brought within the compass of an address for it requires a treatise of many pages I have brought some of the

broad features of it before the Section in order to show its connection with Geography.

I also entertain the hope that geographers will become more interested in a subject so important to pure science and in its practical applications, and that it will become an additional subject to the instruction which travellers can now obtain under the auspices of the Royal Geographical Society in geology, botany, zoology, meteorology, and surveying.

There is a wide field open to observers, and where results often depend so much upon locality we require to explore more and more with the magnetic needle. To look over the great oceans and think how little is being done for terrestrial magnetism is a great matter for regret. Yet even there we may begin to be hopeful, for the United States Coast and Geodetic Survey authorities are making arrangements to fit out its vessel with the necessary instruments for determining the magnetic elements at sea.

We wish them all success; but I must again remind you that although we cannot compel observers to start, there is room for them and to spare.

I would fain make some remarks on the prevailing ignorance of sound geography in many quarters, and on the defective methods of teaching the science; but I feel that the subject is placed in very able hands, and will be fully discussed elsewhere during the present meeting.

The following Papers were read :—

1. The recent West Indian Eruptions.1

By TEMPEST ANDERSON, M.D., B.Sc.

2. The Economic Development of West Africa. By E. D. MOREL.

Although West African affairs are engaging more and more attention, the public as a whole continues to display a curious indifference to that part of the world. Yet there are urgent reasons why a manufacturing nation like ours should show keener interest in one of the greatest raw material-producing countries in the world, of which we possess some 700,000 square miles, inhabited by 30,000,000 people. The author of the paper protests against the indifference of the public: the extent of British commercial interests in West Africa is ignored by most, and the future potentialities of the country are insufficiently appreciated. The chief factor which determined the Powers to assume the liabilities they have in tropical Africa was due to the belief that raw material is necessary to an industrial and manufacturing nation, and that each nation must find new markets for the consumption of home manufactures, markets which will pay for such manufactures in raw material. It follows, therefore, that the economic development of tropical Africa is the principal aim which each Power has in view. How can that economic development be best pursued in a manner profitable to the people of Europe and to the people of Africa? If it is to be permanently successful, it must be profitable to both.

The paper goes on to point out that two political conceptions utterly divergent and antagonistic, yet both alike concerned with the economical development of tropical Africa, and therefore both alike arising from the cardinal factor which led to the partition of tropical Africa among the Powers-are before the world. The adoption of one or the other conception will decide the future of European effort in the black man's country The two conceptions are defined as Coercion and Commerce: the former is characterised as a revival in aggravated form of the old culture system of the Dutch East Indies, which had to be abandoned

The subject-matter of the lecture appeared in the Geographical Journal for March 1903.

2 Printed in full in the West African Mail, September 18 and 25, 1903.

owing to the ruin and exhaustion it brought with it. This system is at present in operation in a large portion of tropical Africa. It is based upon the repudiation, or rather the ignoring, of native rights of land tenure; upon the definition of all land not actually built over or cultivated for food-stuffs as vacant'; and upon the appropriation of all such land and the produce yielded by it. It tends towards the enslavement of whole peoples and brings inevitable ruin in its train. Arguments are adduced to show that, apart from its moral side, this conception is antagonistic to the development of all legitimate European aims in tropical Africa, and that if it is morally pernicious it is also practically short-sighted and injurious, and should be resisted to the uttermost.

The other conception has, the author contends, notwithstanding many material obstacles, produced results which are obvious and visible to all. It is based upon the recognition that the inherent rights of a native of tropical Africa to his land and the produce thereof are the necessary accompaniments of all successful and permanent development work in the interests both of the European and the negro. The commercial instincts of the negro are notorious, his adaptability remarkable; the theory that he will not work is untenable in face of the positive results of his labours in the millions of pounds' worth of produce shipped home annually to Europe from West Africa. He merely requires instruction and guidance to prevent wastage and destruction of economic products due to want of knowledge in the preparation and collection of the raw material. An urgent necessity is the careful study of native land tenure as an important factor in economic development, the theory of 'vacant' lands being often misleading and open to grave abuses.

The paper then discusses the best means of improving native industries and helping the native to construct new ones, laying particular stress upon the great importance of extending the growth of cotton in, and promoting its export from, the tropical African provinces of the Empire. Reference having been made to various measures which might with advantage be taken by Government to secure these ends, the opinion is expressed that the only right and practical ideal which should govern European action in tropical Africa (which is, and must always remain, a black man's country, where the European cannot colonise and can only supervise) is to teach the native to take pride in his property; to guarantee him from molestation in his ownership of his property; to assist him in developing the raw products his fertile soil yields for his own advantage and ours; to make it clear to him that we look upon him, not as a fool, still less as a brute, but as a partner in a great undertaking which, if properly conducted, will confer lasting benefit upon his race and the white over-lords who have established themselves in his midst.

FRIDAY, SEPTEMBER 11.

:

The following Papers and Report were read :

1. The Influence of Ice-melting upon Oceanic Circulation.1

By Professor O. PETTERSSON.

The circulation of oceanic waters has been ascribed partly to physical causes, such as the heating of surface waters in tropical and the cooling in polar regions, partly to mechanical causes, such as the influence of the prevailing winds. The latter is at present regarded as the chief motive power of the currents of the sea. In either case the vis movendi must be the effect of a thermodynamic cycle of the free heat in the atmosphere or in the hydrosphere. On the mechanical hypothesis it is obvious that the primary effect is the generation of surface-currents (windcurrents) of great intensity, and that the intensity of motion must decrease with the depth. The general conviction at present is that the movement of the bottom

The Paper will probably appear in extenso in the Geographical Journal.

waters of the ocean is extremely slow (vide G. Schott's description of the results of the German Valdivia expedition).

In 1878 the author pointed out that a great-and probably the greatest-part of the oceanic current system must be due to another cause, viz., the thermodynamic cycle of latent heat, consisting in the formation of ice in polar regions and the melting of ice in sea-water at lower latitudes.1 In Petermann's Mitteilungen,' 1900, Heft I. and II., he calculated the energy generated by the melting of ice in the sea between Iceland and Jan Mayen to be about 400,000 horsepower, which energy is employed in accelerating the movement of the waters of the East Iceland polar current, which makes its way from the sea between Iceland and Jan Mayen towards the Färoes, there to dip under the current of Atlantic water which sets in between the Shetlands and the Faroes, and ultimately vanishes into the Atlantic depths in the shape of a submarine waterfall over the Iceland-Faroe and W. Thomson bank. The energy set free on the melting of ice in sea-water is expended on raising the water from the submerged part of the ice to the surface, and may be likened to a waterfall where the water, instead of descending, arises from below to the surface. The heat necessary for this melting is supplied from undercurrents of warm Atlantic water, which exist wherever the melting of ice goes on in the ocean. One part (in the case referred to about) of this warmer and salter water mixes with the ice-water and forms the polar surface-current, while the greater part (here about 3) is cooled to a temperature approaching the temperature of equilibrium between ice and salt water, and sinks to the bottom, there to form the layer of cold water which is known to exist in all oceans. The temperature and the salinity of this bottom water depend upon the relation between the quantity of ice which is melted and the amount of warm water supplied by the undercurrent. In the Atlantic Ocean the temperature is a little below or above +2°, which shows that the warm water here is in excess of the ice. In the Norwegian Sea the bottom temperature is about 1.4° C., which is the lowest existing on the globe. This shows that the warm water supplied by the Atlantic current is just sufficient to melt the ice which is brought down along the coast of Greenland by the polar current. It is inferred from this that the state of this part of the sea is in a very unstable equilibrium, which may account for the instability of the climate of the northern countries of Europe and the great variations in the extension of the ice in this sea. In the Polar Sea we meet with the startling fact, discovered by Nansen, that the bottom temperature is higher than in the Norwegian Sea, or above -0.9° C. This is explained by the fact that the ice in the polar sea flcats in a layer of cold water diluted by the admixture of river-water from Siberia. Thereby the access to the ice of the warm and salt undercurrent, which Nansen discovered at about 200 m. depth, is more or less prevented. The ice-melting in the polar sea thereby becomes less intense, the surface of the sea is filled with ice-floes and pack-ice, which must be carried out into the Norwegian Sea or the Atlantic in order to melt. Therefore the cooled bottom layer has a higher salinity and temperature than in the adjacent Norwegian Sea.

The influence of the thermodynamic cycle of latent heat upon oceanic circulation is characterised by the following circumstances:

1. The seat of the accelerating force is localised in the meeting places of the ice-currents of polar origin with warm currents. The most important of these places are the seas between Iceland and Jan Mayen, W. of Spitzbergen, S.E. of Newfoundland, and the ice girdle encircling the Antarctic Sea.

2. In all such places warm undercurrents are found to exist under the ice. The melting process is maintained chiefly at the cost of the heat stored up in the waters of the undercurrent. The system of currents and undercurrents of the Norwegian Sea is represented on a chart prepared by the author.

3. The warm water of the undercurrent, which in the northern hemisphere is denoted by the name of Atlantic' water (alias Gulf Stream water), is modified by

Öfvers. Kgl. Vetenskaps-Akademiens Forhandl., 1878, No. 2, p. 61, and On the Properties of Water and Ice (Vegaexpeditionens iakttagelser, Stockholm, 1883).

1

its contact with the ice into Arctic' water. One part of this Arctic water consists of Atlantic water diluted with ice-water. This kind of water rises to the surface and contributes to the maintenance of the polar currents. The other and greater part consists of Atlantic water, which has given up its surplus of heat and sunk to the bottom, there to form the great cold bottom layer of the oceans.

4. The warm undercurrents always follow the trend of the deepest isobathic lines, while the ice-currents only exist over shallow parts of the sea. As soon as an ice-current leaves the coast-bank and takes its way over a deep part of the ocean, its ice is exposed to melting by the warm undercurrent, which is attracted by the ice and maintained by the energy set free at the melting process.

5. The above-mentioned chart shows a remarkable example of how north-going warm currents and undercurrents are deviated to the west in the Norwegian Sea, in spite of the powerful influence of the earth's rotation.

6. The metamorphosis of Atlantic water into Arctic water involves also a biological change. The foraminifers, &c., of the Atlantic die out (as already shown by Sir J. Murray) in contact with the cold water and sink to the bottom, there to form calcareous deposits. Consequently the course of the warm undercurrents can be traced up to the highest latitudes by a surplus of CaO in the bottom sediments.

7. The author's experiments with exact measurements in the Skagerrack and the Baltic show that the motion of the deeper layers there is by no means insignificant or slow, as it is judged to be by the advocates of the wind-theory,' but is, as a rule, stronger than that of the surface water. How far this holds with regard to the deeper parts of the oceans remains to be investigated. Therefore current measurements in the Atlantic at depths of 800-4000 m. are a pressing desideratum in oceanography.

8. As the accumulation of polar ice varies with the season, and is influenced by terrestrial (meteorological) as well as cosmical phenomena (radiation, &c.), it is evident that the current system set in action by the cycle of latent heat must show periodical variations with the seasons and also periodical or non-periodical variations of longer duration. Are there any indications of such variations in the movement of the undermost layers of the sea? The author's experience is that there are such indications, and this discovery has led him to propound the present theory.

9. The Antarctic Ocean presents the grandest example of ice-melting and of variations in ice-melting. It must be borne in mind that the energy liberated by ice-melting in the ocean is proportional to the depth of the submerged part of the ice. From an iceberg 500 m. in depth the melting of one kilogram of ice will produce an amount of work equal to 7 kilogram-metres. Great outbursts' of icebergs from the Antarctic are known to happen from time to time (Russell). Such outbursts, which carry icebergs down to low latitudes in the Indian Ocean, may exercise influence upon the climate of India, Australia, &c., as thereby part of the warm area of the ocean from which the water evaporates, which ultimately falls as monsoon rain upon the coasts of these countries, may be encroached upon by cold polar water. It is a matter worth notice that the last great 'outburst' from the Antarctic and the last great droughts of India fall within the same period of years (1891-1898). By means of regular surface observations on board of liners crossing the Indian Ocean and a few series of deep soundings along the 60th and 100th meridians such yearly variations in the hydrographic state of the Indian Ocean as can be of meteorological interest might be ascertained.

In order to put the theory of the influence of ice-melting to a test the author has carried out a series of experiments so arranged as to correspond as nearly as possible to the natural conditions of the Norwegian Sea, and has compared the results with the actual results of the Norwegian and Swedish hydrographic research in this part of the ocean in 1900. A description of the last experiment of the series, carried out by Mr. J. W. Sandström, assisted by Miss A. Palmquist, is given in the next paper.

1 It is evident that in the course of oceanic circulation there must be a transition of Atlantic water into Arctic water, and vice versa. The first-named metamorphosis is effected by the ice-melting process.