fathom curve in lat. 22° 10' S., long. 37° 20′ W., after which the depth rapidly diminished to 50 fathoms at a distance of 70 miles from Cape Frio.

The opening address at Dublin, by Sir Wyville Thomson, President of the Section of Geography, after recounting in detail the numerous voyages made for the purpose of investigating ocean depths, currents, and temperatures, proceeds to give a review of his own most recent results with reference to the general circulation of the ocean.

K. Möbius, in the Deutsche Revue, gives a comprehensive summary of the principal results of the latest investigations into the ocean and its life. The first European who, by a drag-net, brought up animals from the depths of the sea was Otto F. Müller, of Denmark, 1788, and earlier. Since his day the oceanic investigations have extended so as to embrace the depth and topography, the bottom formations, the salts and gases contained in the water, the temperatures, the currents, and the living organisms. Of the results of investigations in these departments Möbius gives a short review.

DENSITY.

Negretti and Zambra have contrived a new deep-sea thermometer, described and figured in Nature. To a cylindrical bulb containing mercury a tube is fitted, which is contorted and constricted near the bulb, and is enlarged at the remote end, from which end it is graduated. When the bulb is held downward, the mercury expands as usual, but when it is reversed, the column breaks at the narrowed portion of the tube, flows to the other end of this, and is there read. Hence, if the thermometer be lowered with the bulb downward, and reversed on attaining the desired depth, the reading on coming to the surface will represent the temperature at the time of reversal. To prevent the errors caused by pressure, it is enclosed in a glass sheath.

A very remarkable series of papers, by C. Schmidt, of Dorpat, on hydrology, is being published by the St. Petersburg Academy. In the latest numbers are given many notes on the waters of American lakes, and a general summary of all known observations on density, etc., of oceanic waters. Lake Baikal and other European seas afford interesting results.

CURRENTS.

In the Canadian Naturalist, H. Y. Hind publishes a thoughtful article on the Mechanical Effect of Arctic Ice in producing. Ocean Currents.

The Labrador and Gulf Stream Currents and their Effects on American Fisheries are treated of in two memoirs by H. Y. Hind, published by the Fishery Commission at Halifax.

Dr. O. Krummel, in his Inaugural Dissertation at Göttengen, gives an analysis of our knowledge of the equatorial currents of the Atlantic Ocean, and an examination into the fundamental causes of the general oceanic circulation. In a note he calls attention to Aimé's Submarine Current Indicator, described in Ann. de Chemie, III., xiii., 1845, p. 461. His criticisms of most modern writers are very fair, although his conclusions seem to fall short of that which we are, perhaps, able to maintain with some certainty. He says: "The existence of a vertical circulation is undeniable, but the ascending current cannot alone account for the strong westerly equatorial current. Temperature differences do not suffice to explain the vertical circulation without taking account of the terrestrial centrifugal force. Two ascending currents, with the compensating Guinea current between them, suffice to explain the three equatorial currents of the Atlantic." This work is evidently well worthy of study by those specially devoted to this subject.

Zoppritz contributes to the Annalen and to the Philosophical Magazine a very important memoir on Hydrodynamic Problems in reference to the Theory of Ocean Currents. He has, namely, attempted to solve the analytical equation for the motion of a liquid ocean whose particles move over each other with appreciable friction-that is to say, if the wind blows steadily over the ocean, and the surface layer of water follows the lowest layer of air, what will be the resulting movements in the lower strata of water? The influence of the steady trade-wind must, he finds, extend to the bottom of the sea. By introducing Meyer's known value of the coefficient of friction for sea-water, he finds, for instance, that if the particles of the surface of the ocean begin to move forward with a constant velocity, in 239 years the stratum at a depth of 100 meters will be found moving with one half the surface

velocity; but at 10 meters depth the velocity will be the same in 2.39 years. Periodic changes in velocity are propagated very slowly. He shows that two layers moving in opposite directions can be sensibly in contact with each other without material disturbance. The mean motion of the sea as existing 10,000 years ago would to this day be the controlling factor in the present movements of the ocean.

In the Astronomische Nachrichten, No. 2226, Gyldén publishes a first paper on the Rotation of a Solid Body whose Surface is covered with a Fluid. He remarks that to definitely solve this problem we must have given the form of the solid and the quantity of the fluid. In the case of the earth we know not these data, although we can make approximate assumptions. After enumerating some of the uncertainties that surround the problem, and indicating the extreme limits of our knowledge and ignorance, Gyldén proceeds to develop the mechanical formulæ in the most general case practicable, assuming the only external force to be the mutual friction of water and earth.

An interesting paper on the Drifting Power of Tidal Currents appears in the last number which we have received of the Royal Irish Academy (January, 1876). The author, G. H. Kinaham, has studied the subject very carefully on a portion of the Irish coast, and submits the following conclusions: first, the driftage due to the incoming tidal current is during its progress always going on in deep water, and, more or less, in shallow water; second, the driftage due to windwaves only occurs during gales, and even then is only due to the waves that break on the shores; third, to prevent the tidal driftage groins or piers should be erected; and if the pier is to form a harbor, transverse groins should run out from it, to stop the back-wash generated by the pier; for otherwise this back-wash would carry the drift seaward, to be sucked around the pier into the harbor; fourth, as the wind-wave driftage occurs during gales, and then only on the shore-line, it might be prevented from filling up a harbor by placing a breakwater across the direction from which the prevailing storms come. If such a breakwater were fixed, it would probably help to fill up the harbor; but if it be a floating one, it will break the wind-waves in deep water and destroy their drifting powers, while not interfering with their tidal driftage.

EQUALITY OF THE SURFACE LEVELS OF THE ATLANTIC AND PACIFIC OCEANS.

Lines of levels run from sea to sea across the states of Nicaragua and Panama, during the recent inter-oceanic canal surveys, made under the direction of Commander E. P. Lull, U.S.N., confirm the fact that the surface levels of the Atlantic and Pacific oceans at mean tide are exactly the same. The Atlantic terminus of the Nicaragua line was at San Juan del Norte, which is practically at the leewardmost part of the Caribbean. The theory that the waters of that sea are banked up by the northeast trade-winds, forming a head for the Gulf Stream, seems thus to be disproved.

TIDAL CURRENTS IN THE GULF OF MAINE.

A very interesting and valuable series of observations on the Off-shore Tidal Currents in the Gulf of Maine, begun in 1877, have been completed during the present summer, under the direction of Dr. C. P. Patterson, Superintendent United States Coast Survey, by Master Robert Platt, U.S.N., commanding the Coast Survey schooner Drift. These observations show that the tidal currents of this locality are of sufficient strength to render their consideration in the reckoning, especially of sailing- vessels, highly important; and from them Professor Henry Mitchell, of the Coast Survey, has deduced rules and tables (part of which have already been published, with a chart of the Gulf of Maine, showing the positions of tide-stations and the localities of a number of remarkable tide-rips.-(Coast Survey Notice to Mariners, No. 15, 1877.) It is found that on the line between Nantucket Shoals and Cape Sable Bank (covered by the published tables) the ebb-current runs southwardly during the first four and a half hours, and the flood-current northwardly from the sixth to the eleventh hour after the moon's transit (northing or southing). Table I. gives for each of the localities named the times of turning from the flood-current to the ebb, and of the reverse, with the direction and rate of the flow-all referred to the times of the moon's transit. Table II. gives, for the same localities, the direction and rate of the current for each hour after the time of high-water at Bos

ton, Mass., as given for each civil day in the Coast Survey Tide-table for the Atlantic Coast. A discussion now being made by Professor Mitchell of the whole tidal phenomena of the Gulf of Maine will be of great interest, some hitherto unrecognized laws of tidal movement having been developed.

TIDES AND WAVES.

Of the tidal observations made by the English Arctic Expedition of 1876, the preliminary report has been published in Captain Nares's narrative.

Professor Haughton announces as the first result of the tidal observations made by the late British Polar Expedition the complete confirmation of the result obtained by Dr. Bessels on Hall's expedition-i. e., the meeting of two tidal waves from north and south in Smith Sound-and confirming the idea that Greenland is an island.

An important paper on the Tides of the Southern Hemisphere and the Mediterranean, by Captain Evans and Sir William Thomson, was read before the Dublin meeting of the British Association, and an abstract of it is printed in Nature.

A self-acting tide-computing machine has, according to Nature, been designed by Mr. E. Roberts, of the Nautical Almanac office, and is being constructed for the India Office.

The great ocean wave due to the Iquique earthquake of May 9 has been considered in a memoir, by Geinitz, in the December (1877) number of Petermann's Mittheilungen.

The accurate self-registering "limnimeter" on Lake Leman has afforded Forel the demonstration of the existence of temporary rhythmic changes in the level surface of the whole lake, due to a bodily vibration of the whole mass of water. He has now traced these vibrations up to their primary origin, which is occasionally, perhaps, to be found in an earthquake shock, but more usually in sudden changes of atmospheric pressure at some part of the lake. He finds that the formula for the vibration of water in a basin, given by Mérian, at Basle, in 1828, and its simplification given by William Thomson, apply well to the seiches of Lake Gene

va.

Similar oscillations are reported by Jansen to be recorded upon the self-recording tide-gauge (mèregraph) at Brest. Forel also has proposed a new theory of the variations in