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termination of the exact moment of the shock, and it is highly desirable that such a simple instrument shall be extensively employed throughout the world in the investigation of these phenomena. Professor Abbe suggests that earthquakes are not beyond the reach of the Army Signaloffice predictions.—7 C, X., 444.

RECENT VOLCANIC PHENOMENA IN ICELAND. During the past winter attention was directed in Norway to the falling of dust from the atmosphere, which at first was supposed to be of meteoric origin; but Professor Kjerulf decided that it was more likely to have been disseminated from some active volcano. The precise source was unknown; but from the direction of the wind, and the known conditions, it was suspected that some volcano in Iceland was concerned. This surmise has been confirmed by the more recent advices from that country, which report a very remarkable series of volcanic phenomena, first commenced by earthquakes, then followed by an eruption accompanied by dust and ashes. On March 29, 1875, the fall of the ashes was so excessive that it covered the eastern country sides, Jökuldal especially, with a coat six inches in thickness, and all that day, although elsewhere it was bright and sunny, the people were in absolute "pitch” darkness. Fountains and rivulets were dammed by the ashes, and every mountain stream ran dark and muddy between banks covered with drifts of ashes. The farmers fled out of the ash-covered country with their cattle, in search of pastures not yet destroyed by the scorice, but with what chance of saving their live stock does not appear.

There is no calculating the extent of this calamity, nor its effect upon the habitable portions of Iceland, although from present appearances it threatens to be extremely widespread.-3 A, May, 22, 1875, 649.

THE FIGURE OF THE EARTH. Mr. Hind, of Nova Scotia, calls attention to the fact that the equatorial bulge of the earth's surface may have been much larger in earlier geological epochs than at the present day, and that Captain Clarke's and General Schubert's investigations, according to which the earth's equator is an ellipse and not a circle, favor the idea that in these earlier epochs this ellipticity must have assumed the nature of a gradual change in the figure of the earth, in virtue of which a vast equatorial undulation has progressed with extreme slowness in an easterly and westerly direction.-12 A, X., 166.

TYDERGROUND TEMPERATTRES. The sixth report of the committee on underground temperatures states that they have made a very interesting series of observations in the great well of La Chapelle, at Paris. There was a tolerably regular increase of temperature at the average rate of one degree Fahr. for every ninety-four feet, except for the very last portion of the well, where a sudden increase appeared to take place, giving a rate of about one degree for every twenty-five feet. A very elaborate calculation has been made by the engineers in charge of the well, which has shown that a large portion of this sudden increase of temperature must be attributed to the heat generated by the operation of boring the well. The total weight of the tool employed by them is 3000 kilogrammes, and the quantity of work converted into heat at every fall of this great weight through a distance of fifteen inches is sufficient to raise the temperature of the lower portion to nearly 100° Fahr., which heat is retained at the bottom of the well for many days, owing to the feeble conducting power of the surrounding rocks. - Report Brit. A880C., 1873, 252.

“ICE care" YEAR DOBSCHAT. Dr. Joseph A. Krenner, of the National Museum of Bnda-Pesth, gives an account of a visit to the famous ice care near Dobschan, in the spring of 1873. It is located in the “ Goellnitzer” valley, and is excavated in triassic limestone. From the entrance the trend of the cave is downward, a large mass of stratified ice, partly transparent, partly translucent, forming the floor of the higher and larger portions, while numerous stalactites and stalagmites of ice (the former hollow) ornament the ceiling and walls, forming at times exceedingly picturesque groups. Frozen waterfalls are found near the lower portions of the cave. The ice which serves as a floor is so compact and so smooth as to furnish excellent skating. The water that does not freeze runs off to the lower portions into a mass of débris, and appears as a spring on the side of the mountain containing the cave. A number of observations give the mean temperature of the cave at -0.86° C., while outside it was +3.53° C. Dr. Krenner states various reasons why the temperature can remain so low, and thus render possible the persistence of ice, as follows: The cave has only one very small entrance, from which it runs downward throughout its entire extent; the water that is not frozen has an opportunity to flow off without stagnating, or melting the ice; the position of the entrance is such that the sun never reaches it, therefore it must be comparatively cool; a current of cold air passes upward through the cave, tending to produce low temperature.

THE DEPOSITION OF FINE SEDIMENTS.

Dr. T. Sterry Hunt states, in reference to the question of the deposition of fine mud in the Mississippi, that the deposited matter requires from 10 to 14 days to subside; but that if sea-water or salt or sulphuric acid be added to the turbid water it becomes clear in from 12 to 18 hours. Thus is explained the rapid precipitation that occurs when the river water mixes with the salt waters of the Gulf of Mexico. The cohesion of water diminishes when it holds saline matter in solution, as was said by Guthrie and was verified by Dr. Hunt. He found that the addition of eight parts of chloride of calcium to 1000 parts of water reduces the size of drops to one ninth, and the precipitation of suspended clay is made very rapid when a strong solution of salt is employed. — 12 4, X., 277.

SO-CALLED TIDES IN GREAT LAKES. The qnestion of the so-called tides in the greater lakes of North America is likely to receive some elucidation from the researches of Dr. Forel, of Lausanne, who has for several years been investigating what are known as the seiches of the Lake of Geneva, this term being applied locally to a certain oscillatory movement occasionally seen to occur on the surface of the lake. Forel agrees with previous observers in

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attributing the phenomenon to variations in the atmospheric
pressure; and it is believed that it will be found to occur in
all large bodies of water.

His investigations have led him to the conclusion that the
seiche is an oscillatory undulation, having a true rhythm, and
that the phenomenon is not occasional, but constant, though
varying in degree. The duration of a seiche is a function of
the length and depth of the section of the lake along which
it oscillates; this duration increases directly with the length
and inversely with the depth of the lake. The instrument
he has devised for the investigation of the phenomenon is a
“tide measurer.”—12 A, June 17, 1875, 134.

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SECULAR CHANGES IN THE LEVEL OF THE OCEAN. Professor Schmick has called attention to the fact that his theory of the existence of regular periodical changes of the level of the sea, and especially of a secular movement from the northern to the southern hemisphere, is apparently supported by the conclusion of the astronomer Nyren. The latter has shown that the latitudes of all well-determined observatories in the northern hemisphere have slightly diminished since accurate observations began. This phenomenon is, according to Schmick, easily explained by the hypothesis that the water of the Southern Ocean is now about perhaps two fect deeper than it was a hundred years ago, which hypothesis accords precisely with the conclusion to which he was led by the entirely different course of reasoning published by him some years ago in his works on floods, etc. Gaea, XI., 29.

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TIDES OF THE EASTERN ALEUTIANS AND THE NORTII PACIFIC.

In the appendix to the United States Coast Survey Report for 1872, now in press, is a report by Mr. W. H. Dall on the tides, currents, and meteorology of the Eastern Aleutian region and the Northeast Pacific, accompanied by explanatory diagrams. Mr. Dall's observations on the oceanic currents, which are here tabulated and discussed up to the date of the report, are of special interest, as being the first series undertaken with a direct view to the solution of the problems in question, and result in the proof of there being a reflexed northerly arm of the great easterly North Pacific current, de

nominated by him the Alaska current, which had previously been surmised from isolated observations and theoretical considerations. Mr. Dall has been able to determine the rate and dimensions of several portions of this current, and the maximum, minimum, and mean annual temperature. The existence of definite oceanic currents in the eastern half of Behring's Sea is shown to be very doubtful. Some important generalizations on the relations of the Pacific and Behring's Sea tides to each other are made, and the peculiarities of the compound tides of this region are graphically indicated by diagrams in a new method, original with the author, and possessing some interest for those studying these problems. The report is accompanied by numerous hydrographic memoranda, and tables of meteorological, current, and tidal observations.

ORIGIN OF OCEAN CURRENTS. Mühry, in a paper on the origin of ocean currents, states that a difference of temperature in the equatorial and polar regions of the ocean is not sufficiently powerful alone to bring about the great hydrodynamic effect attributed to it, viz., the existing phenomena of latitudinal circulation. This latter is largely a result of the rotation of the earth, although the thermal circulation is frequently of great importance. He finds that the latitudinal oceanic circulation is to be considered as a duplicate one, that is, resulting from two causes working in the same direction, the one being the general diminution of gravitation toward the equator, and the other the general elevation of temperature, with its consequent expansion of the sea-water, each circulation existing by itself, independently of the others. The difference of density due to a difference in the saltness of water, according to Mühry, has no influence in the formation of currents.-Zeitschrift für Meteorologie, IX., 282.

THE CIRCULATION OF OCEAN CURRENTS. Dr. Carpenter calls attention to the researches on ocean currents and deep-sea temperatures of Lenz, who accompanied the Russian exploring expedition of Kotzebue in 1823–26, and made a large number of observations of temperatures of the ocean water with thermometers whose indications were

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