This would indicate that from August to November, 1884, the pole of the earth had approached Berlin more closely by 20 to 30 feet than in the time from March to May.

This conclusion was fortified by the examination of other data, obtained from the observations made at Pulkova by Nyrén.

Here, then, was evidence of a comparatively rapid change in latitude. New observations were undertaken at Berlin, Potsdam, Prague, and Bethlehem, Penn. (all by Talcott's method), and all agreed in showing plus and minus changes in latitude for the years 1888-'90.

There were still some doubters. Moreover it was decided to critically test the matter by sending an expedition to the Sandwich Islands, which is 180 degrees (nearly) in longitude from Berlin. If it was known the latitude of Berlin increased, then a point in the northern hemisphere 180 degrees away from Berlin should simultaneously show a decrease in latitude, for if the pole moves toward Berlin it must move from the point on the other side of the earth.

Our own Government joined in the effort. Marcuse of Berlin and Preston of Washington spent more than a year on the Sandwich Islands observing for latitude, while at the same time observations were continued at Berlin, Prague and Strassburg in Europe, and at Rockville, Bethlehem and San Francisco in the United States. The results of all these observations have been published, and show, without a chance of error, that the earth's axis is moving, that the latitudes at the Sandwhich Islands increased when the latitudes in Germany diminished and vice versa.

The law of the change was eagerly and industriously sought for by some of the ablest mathematical astronomers of the world. They first worked on the idea that the changes must conform to the 305-day period of Euler, combined with an annual change due to causes set forth by Sir W.

Thomson, and which I have previously mentioned. None of these investigations have given a satisfactory formula for the prediction of the latitude of any place.

In 1891 Dr. S. C. Chandler, of Cambridge, Mass., began his investigation of the problem. He remarks:

"I deliberately put aside all teaching of theory, because it seemed to me high time that the facts should be examined by a purely inductive process; that the nugatory results of all attempts to detect the existence of the Eulerian period (of 305 days) probably arose from a defect of the theory itself, and that the entangled condition of the whole subject required that it should be examined afresh by processes unfettered by any preconceived notions whatever. The problem which I therefore proposed to myself was to see whether it would not be possible to lay the numerous ghosts in the shape of various discordant, residual phenomena pertaining to determinations of aberration, parallaxes, latitudes and the like, which have heretofore flitted elusively about the astronomy of precision during the century, or to reduce them to some tangible form by some simple consistent hypothesis. It was thought that if this could be done a study of the nature of the forces as thus indicated, by which the earth's rotation is influenced, might tend to a physical explanation of them."

Dr. Chandler proceeded to examine his own work with the Almucantar at Cambridge, the observations of Küstner, Gyldén, Nyrén, the Washington observations and others. He found that they all seemed to indicate that the pole of the rotation axis was moving from west to east about the axis of figure of the earth in a period of 427 days. Other observations did not seem to confirm this period. Finally he made an elaborate analysis of 33,000 observations between 1837 and 1891, and the result was an empirical law which can be announced as follows:

The pole of the rotation axis of the earth moved with its greatest velocity about the pole of the axis of figure about the year 1774; the period then was 348 days. The velocity has diminished with an accelerated rate since then. In 1890 the period was 443 days. The distance of one pole from the other was about 22 feet 0.22".

Further elaborate examination of this material developed the exceedingly important and interesting result that the changes in latitude were the sum of two periodic fluctuations superposed on each other. One had a period of about 427 days and an amplitude of 0.12" The second had a period of a year with an amplitude that was variable between .04" and .20"

Sometimes these two fluctuations worked together, giving a total range of .33", and at times they conspired against each other, reducing the range to a minimum of a few hundredths of a second. He compared his theory with the observations, and the result was in the main exceedingly satisfactory.

His conclusions were attacked as to the 427-day term. The annual term could be explained as due to meteorologic causes.

Professor Newcomb, however, in March, 1892, explained in a paper communicated to the Monthly Notices of the Royal Astronomical Society that in deducing the Eulerian period of 305 days the earth, as we have remarked, was considered absolutely rigid; that when the effect of the mobility of the oceans and of the lack of perfect rigidity of the earth were taken into account, the mathematics required a time of rotation of the true pole about the axis of figure longer than the previously accepted 305 days. Making certain assumptions Newcomb obtained a period of 443 days.*

which Dr. Chandler has lately published is that the fluctuation with a period of 427428 days is a circular one, as theory seems to demand, while the annual fluctuations appear elliptical in character.

An exceedingly interesting and important confirmation of the Chandlerian period of 427 days, or about 14 months, was lately announced by M. Tisserand. Examination has been made of the tide records of the Helder in Holland. These are kept with great accuracy. It has been found that between 1851 and 1893 these tide records show a variation in the average sea level indicating a 14-month period. The greatest divergencies are very small, only 14 mm.= inch about, but they appear unmistakably and are what theory would demand.

In a letter recently received from Dr. Chandler he states that he finds that the annual part of the polar motion is an ellipse three or four times as long as broad, and he expresses the law of the motion of the pole in this ellipse as that the areas described from the centre are proportional to the times.

We can conclude safely, therefore, that no large changes of latitude have taken place for many thousands of years; in fact, in geologic times, that there is no adequate proof of progressive changes in the latitude of any place; but finally that very small periodic changes have occurred, and they are such as can be and are observed.

The feeling is growing in the minds of those who have given the subject close attention that we shall find that many and various causes enter into the problem of determining the law of changes. It will, no doubt, take many years of careful observation to obtain the data necessary to fully test Dr. Chandler's or any other hypothesis.

The scientific men abroad are discussing the advisability of establishing several observatories at various places on the earth's surface, for the purpose of collecting the data.

Ultimately Dr. Chandler's formula, or a slight modification of it, may be proved correct, and with it we may be able to state what the latitude of any place will be at any time.

The lecture was followed by some illustrations showing that revolving bodies preferred to revolve about their shortest axis or around the axis about which the moment of inertia was a maximum.

Charts and diagrams were exhibited showing the results of observations made at Pulkova, Prague, Berlin, Strassburg, Bethlehem and the Sandwich Islands, etc.

These results were compared with the deductions from Chandler's formula and shown to agree therewith to a remarkable extent.

The preliminary results of the observations made at Columbia College from May, '93, to July, '94, were exhibited.

The lecturer threw on the screen illustrations of several forms of Zenith Telescopes and described the new form made by Wanschaff, of Berlin.

COLUMBIA COLLEGE.

J. K. REES.

CURRENT NOTES ON PHYSIOGRAPHY (VII.).

AREA OF LAND AND WATER.

PROFESSOR H. WAGNER, of Göttingen, contributes to the April number of the Scottish Geographical Magazine an abstract of his recent studies on the land and water areas of the globe for successive latitude belts. He contends that Murray's figures, published in the same magazine for 1886 and 1888 and based on Bartholemew's maps, are inaccurate to a significant extent. Wagner's measures of the better known lands between 80° north and 60° south latitude is 51,147,100, against Murray's 51,298,400 square miles. Taking 250,000 for lands yet undiscovered in the Arctic regions, and 3,500,000 for Antarctic lands, the total

land area of the globe would be 55,814,000 square miles. Wagner finds confirmation of his figures in the results independently obtained by K. Karstens, who has recently made a new reckoning of the area and mean depth of the oceans.

THE FLY-BELT IN AFRICA.

THE remarkable control over the occupation of Africa, exercised by the little tse-tse fly, whose bite is fatal to horses and cattle, leads to the introduction of cheaply constructed narrow-gauge railways across the belt of country dominated by this pest. The Portuguese district, next south of the Zambesi river on the east coast, with its capital at the little settlement of Beira, attains some commercial importance from its relation to Mashonaland and the gold district of the interior; but in order to connect the two, a railway a hundred and twenty miles long has been made to bridge the fly-belt.' The coast exhibits a combination of equatorial and tropical rainfall, having high temperature and heavy rain from October to April, but from June to September 'the weather is almost pleasant.' At Beira the scarcity of water in the dry season threatened a few years ago to be a serious question, as a supply had to be brought from the upper course of the rivers at a considerable cost; but "in 1893 a Scotch plumber was imported, and all anxiety on this score came to an end," as he made galvanized iron tanks in which rain water could be gathered and stored from the roofs (Scot. Geogr. Mag., April, '95).

COLD AND SNOWFALL IN ARABIA.

THE ordinary association of heat with the dryness of deserts tends to give the impression that Arabia has no cold weather. Nolde's account of his expedition into the Nefud desert of the Arabian interior, latitude 28 north, altitude 3,000 feet, tells of the severe cold that he experienced there in

February, 1893. The days were warm and pleasant; but the nights cooled to -5° or -10° C; the changes of temperature being extremely sudden. For example, on February 1, at noon, the thermometer read +5°.5, with a cool wind; at 2 o'clock, +6°, at 4, 7.5°; then came a rapid rise to 25.5°, for which no special explanation is given. Just after sunset there was a sudden fall of thirty-three degrees, to -8°; and the minimum of the night was -11°. The cold and blustering wind caused much discomfort in traveling. The greatest surprise that Nolde met was on February 2, when a storm clothed the Nefud far and wide with a sheet of snow several inches deep, making it resemble a Russian steppe rather than an Arabian desert. The Bedouins, however, said that snowfall there was very unusual. (Globus, 1895, No. 11.)

CENTRAL AMERICAN RAINFALL.

PROF. M. W. HARRINGTON shows in an article under the above title (Bull. Phil. Soc. Washington, xiii., 1895, 1-30) that the northeast slope of Guatemala and Honduras has rainfall maxima in June and October, following the zenithal passages of the sun and a moderate winter maximum in January, ascribed to the encroachment even in these low latitudes of cyclonic areas from the westerly winds of the temperate zone. This gives an interesting repetition of the case of northern India, as described by Blanford. The rainfall on the southwest slope of Central America has maxima in June and September-October, corresponding to the two zenithal passages of the sun. The July-August minimum is faintly marked, while that of January and February is very low and for a time almost rainless. It is noteworthy that the zenithal rains here are often accompanied by strong squally winds from the southwest, suspected of being occasional extensions of the southeast trade wind across the equator into our

hemisphere. It may be remarked that the association of these winds with the counter current that runs eastward in the Pacific a little north of the equator confirms the suggestion that the equatorial counter currents in general are caused by the extension of the trade winds of one hemisphere across the equator into the other hemisphere. They are thus deflected from a westward to an eastward course, and hence locally produce eastward currents.

THE METEOROLOGISCHE ZEITSCHRIFT.

THE thoroughness so characteristic of German scientific work appears in this excellent journal, the leader of its class, with its able original articles, its rich variety of notes and its exhaustive bibliographic reviews. Originally established thirty years ago by the Austrian Meteorological Society, and edited successively by Jelinek and Hann, of Vienna, it was enlarged eleven years ago by further assistance from the German Meteorological Society, when Köppen, of the naval observatory at Hamburg, became associate editor; his place being lately taken by Hellman of the Prussian Meteorological Institute at Berlin. Dr. Hann,

however, still retains his position as leading editor and is a frequent contributor to the pages of the journal. One of his latest essays (January, 1895) is on the rainfall of the Hawaiian Islands, in which he brings together all available material, and discusses it more completely than has hitherto been done. Dutton's explanation of the considerable rainfall on the southwest slope of Hawaii is quoted with acceptance. A meteorological peculiarity of these islands seems to be that their richer windward sides, sloping to the northeast with a plentiful rainfall, are on a large part of the coast with difficulty approached from the sea on account of the cliffs that have been cut along the shore by the strong surf from waves driven by the trade winds.

FOEHN-LIKE EAST WINDS IN AFRICA.

DANCKELMAN, who for some years has made a special study of African meteorology, contributes a note on the foehn-like east winds felt on the southwest coast of Africa, about the southern tropic (Met. Zeitschr., January, 1895). In the interior, temperatures above 27°C are unknown in the winter (April to October); but on the coast in this season, maxima over 30°, and even as high as 39°, are reported, east winds and low humidity occurring at the same time. As so high a temperature cannot be ascribed to heat from the interior, Danckelman explains it as the result of the dynamic warming of the wind during its descent from the interior highlands.

This

is only one more illustration of the importance of adiabatic changes of temperature in meteorological phenomena; the Swiss foehn and our western chinook, the extraordinary foehn-like winds of west Greenland, the 'hot winds' of India and of Kansas, as well as the ordinary warm or hot southerly cyclonic winds, or 'siroccos,' all owing a greater or less share of their high temperatures to the heat developed by compression during the descent of air from higher to lower levels.

THE AMERICAN METEOROLOGICAL JOURNAL.

THE American Meteorological Journal, conducted for a number of years by Professor Harrington at Ann Arbor, and since 1892 edited by R. DeC. Ward and published by Ginn & Co., Boston, is an able exponent of the science of the atmosphere for this country. The closing number (April, 1895) of the eleventh volume opens with a note by the editor, reviewing the recent work of the journal, and making an excellent showing for its continuation. Its original articles make it of value to the investigator; its notes and reviews place much important material before the general student; and its more elementary or educational articles

must prove useful to the teacher, for in spite of a recent assertion to the effect that the meteorological aspects of geography are well taught in our schools, there is room for much improvement in this direction. The April number contains notes on signs of a recent change of popular opinion concerning the effect of cultivation on rainfall in Iowa, the proceedings of the last meeting of the New England Meteorological Society-the only society of the kind, we believe, in this country-and diagrams of a curiously curved storm track from the Pilot chart of the Hydrographic office; reviews of the Blue Hill (Mass.) observations for 1893, of Ley's new work on clouds, and of a new Danish series of monthly pressure charts for the North Atlantic. The editor contributes an account of Swiss studies of thunderstorms, and a description of meteorological work in India and Australia. The wind known as the southerly burster,' as felt at Sydney, has recently been studied in a prize essay; it recalls in many particu

lars the northers' of our Texan coast.

NOTE ON CROLL'S GLACIAL THEORY. A BRIEF article by the undersigned (reprinted in Amer. Met. Journal for April from the Trans. Edinb. Geol. Soc., vii., 1894, 77-80) suggests a common explanation for three forms of geologically recent climatic change, namely, the glaciation of many northern lands, the expansion of many interior lakes, and the production of wadies by water action in the now dry Sahara. Accepting Croll's theory of the coincidence of glacial conditions with long aphelion winters during periods of great orbital eccentricity, it is argued that the chief cause of snowy precipitation at such times must be the greater activity of cyclonic processes, then intensified by the stronger general circumpolar circulation, in turn accelerated by the increased winter contrast of polar and equatorial temperatures;