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 temper

ature.

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 A, X., 277.

SO-CALLED TIDES IN GREAT LAKES.

The question 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

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.

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 feet 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.

TIDES OF THE EASTERN ALEUTIANS AND THE NORTH 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, bas 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

carefully corrected for the influence of the pressure of the water. Lenz deduced the important conclusion that there is at and under the equator a belt of water cooler than the water to the north and south of it, the existence of which is explained on the principle that there must be a flow of warm surface water from the equatorial regions toward either pole, and which must be accompanied by a corresponding flow toward the equator in the lower regions of the ocean, so that at the equator itself, where the two deepsea currents meet, cool water rises to the surface. This principle has been independently propounded by Dr. Carpenter to explain the cold band between the Gulf Stream and the United States coast, and justifies him in the statement that his own researches during the past ten years have but afforded a confirmation and elaboration of Lenz's doctrine of oceanic circulation.-12 A, X., 170.

NEW GENERALIZATION IN OCEAN PHYSICS.

A new generalization of much importance in reference to ocean physics has lately been derived from the observations of the Challenger in the Malay Archipelago during her recent passage from Cape York to Hong-Kong. The seas vis ited, we are told, consist of a series of sunken lakes or basins, each surrounded and cut off from the neighboring seas by a shallower rim or border. There is a general oceanic circulation down to a depth equal to that of the border, and the temperature gradually decreases from the surface to this level. The entire mass below, however, having no communication with the outer water, and consequently no circulation, remains at nearly the same temperature as that flowing over the floor of the rim; or, in other words, the water coming along the floor of the ocean from the antarctic seas, which is found in all the deep open channels, can not obtain admission through or over the rim.

On this account the bottom temperature depends entirely upon the altitude of the encircling rim. Thus, in Torres Strait, with a depth of 2450 fathoms, and a rim reaching within 1300 fathoms of the surface, the body of water below that depth has a steady temperature of 35°. The Sulu Sea, which is 2550 fathoms deep, with a rim reaching within 400 fathoms of the surface, has a temperature to its bottom

as high as 50°. The Molucca Passage, however, is open to the depth of 1200 fathoms, and the China Sea to that of 1500 fathoms.-12 A, Dec. 31, 1874, 174.

INFLUENCE OF WINDS UPON THE TIDES.

In the appendix to the recent volume of the report of the United States Coast Survey, Mr. Ferrel presents a revision of his discussion of the tides of Boston Harbor, in which, among other matters, he investigates the effect of winds and barometric pressure on the height of the tides. After comparing the actual observations with the ordinary formula for computing the heights of the tides, certain residuals remain, which may possibly be in part explained as due to the influence of the winds and the barometer. He shows that this influence varies very much in different parts of the world. Thus, at Boston, a rise of an inch in the barometer is followed by a fall of seven and one-third inches of water. At Brest, however, for the same change in pressure, the change in the water is fourteen and one-ninth inches, and at Liverpool eleven and one-tenth inches, while at London it is only seven inches, being even less than the value obtained for Boston. The direct effect of atmospheric pressure is probably to a large extent inextricably complicated with the influence of the winds. Mr. Ferrel suggests as an explanation that when the barometer is rising we usually have clearing weather on the New England coast, with westerly winds, which tend to lower the sea level; they consequently more than counteract the direct effects of inertia and friction. When the barometer is falling there are usually east winds, or, at least, an absence of west winds, and the sea level at this time is a little above the mean level. Very strong winds change the sea level in Boston Harbor a foot or more, ten such cases occurring in the course of one year.-Report of the U. S. Coast Survey, 1871, 94.

THE CHALLENGER OBSERVATIONS ON THE DEEP-SEA BOTTOM.

Professor Huxley, in a recent lecture at the Royal Institution upon the work of the Challenger expedition and its bearing upon geological problems, sums up the general results, in regard to the composition of the ocean bed, by showing that from the researches of Sabine, Ross, Penny, Ehren

D