Cadiz.-A time-ball is established at Cadiz, but we have no information of the time at which it is dropped.

Neuchâtel.-An extensive system of electrically controlled clocks and of time-signals radiates from this observatory, for the purpose of giving the true time to the chronometer and watch makers, and for the public convenience. Several towns participate in this.

AFRICA.

Cape of Good Hope.-Time-ball at 1a.

ASIA, ETC.

Madras.-A time-ball is dropped daily from the Customhouse at 8h 20m 57.3a Madras mean [civil] time=15h Greenwich mean time. The time of the flash of the evening gun is noted at the observatory, and published at the Master-Intendant's office the next morning.

Batavia (Java).-There is a time-ball dropped at Batavia mean noon, and also one at 1h 7m 12.58 Batavia mean time= 18h Greenwich mean time. Calcutta.-Daily time-gun.

Vladivostok.-There is a branch of the Russian Hydrographic Office established at Vladivostok, and a naval officer obtains the time daily with a transit instrument, and keeps his clock regulated for the benefit of navigators.

AUSTRALIA.

Melbourne.-A time-ball is dropped daily (Sundays excepted) at 14 m. s. t. The time is also given from the same place at 84 (P.M.) by the obscuration of a powerful light at two minutes before 8h: the instant of reappearance of the light is the true time. The errors of these two signals on any day are published on the next day in the newspapers. Sydney.-A time-ball is dropped daily.

Newcastle.-A time-ball is dropped daily by signals from Sydney.

SOUTH AMERICA.

Rio de Janeiro. We have no entirely satisfactory account of the details, but we are informed that a time-ball is dropped daily at noon.

Buenos Ayres.-The Observatory of Cordoba sends electric signals to Buenos Ayres for the regulation of clocks accessible to ship-masters.

NORTH AMERICA.

St. John's (New Brunswick).-Time-ball daily (except Sunday) at one o'clock, by a chronometer which is compared with a clock rated by a transit instrument.

Quebec.-A time-ball is dropped for the shipping at 14, and a time-gun fired in the city for public convenience at

noon.

Kingston (Canada).—Time is given to the city and to the shipping daily from the observatory.

Ontario. For the past four years the observatory has struck its time-signals on the fire-alarm bells.

Pittsburgh.-The City-hall clock is controlled from the Alleghany Observatory, and the fire-alarm bells are struck at noon and at every third hour. Time is furnished to the Pennsylvania Railway.

Cincinnati.-The clock on the City-hall is controlled by electric signals every two seconds, and the fire-alarm bells. are struck at noon.

Cambridge and Boston.-For some years the Harvard College Observatory has controlled clocks in Boston, and furnished standard time to some of the railways.

Albany. It is understood that the Dudley Observatory furnishes time to the city of Albany and to the Hudson River Railway.

Chicago.-Time is given to the city from the Dearborn Observatory.

Washington.-A time-ball is dropped daily (Sundays excepted) at noon. Clocks in the city are controlled (on Jones's system) at the Navy Department, State Department, Treasury Department, Signal-office, and one is proposed for erection at the Western Union Telegraph Office. Daily (except Sundays) at noon a signal is sent from the observatory to the Washington office of the Western Union Telegraph Company, and by them distributed over such of their wires as may be unemployed. Practically this signal always reaches Philadelphia and New York, and Chicago, Cincinnati, and St. Louis very often. The fire-alarm bells are struck at 7 A.M., 12 M., and 6 P.M.

GREAT BRITAIN.

Glasgow. The wire formerly owned by the observatory has been transferred to the government telegraphs, which distributes the time-signals to the public at very low rates: for example, £1 yearly is charged for a clock controlled within one third of a mile of the office, etc.

Liverpool.-A time-ball is dropped daily at 1 visible to the shipping, a time-gun is fired at the same hour at the Morpeth Dock pier-head; the clock in the Victoria Tower (six dials) is controlled, as well as several clocks in the city.

Edinburgh.-A time-ball, visible to the shipping in the Firth, is dropped daily from Nelson's Monument on the Calton Hill, a gun is fired from the Castle, and numerous clocks are electrically controlled, some of them being exposed for the convenience of the public. Time is sent daily to Dundee.

Dun Echt.-At Lord Lindsay's private observatory at Dun Echt, near Aberdeen, a time-gun is fired daily for the public convenience.

Dundee.-Signals are received daily from Edinburgh at an expense of £100 per year, and a time-gun is fired automatically.

Deal.-A time-ball is dropped at 1 from Greenwich.

Portsmouth and Start-Point.-Time-balls (at 1) are proposed.

Dublin.-Greenwich time-signal is received daily at 10h A.M., and distributed. We are not informed as to details.

Belfast.-Greenwich time-signal at 10 A.M.

Guernsey.

Newcastle.-Time-gun automatically fired at 1h Greenwich

time.

Devonport.-Time-balls are dropped on Mount Wise at 1 and at 1h 5m Greenwich mean time.

Greenwich.-A time-ball is dropped daily at 1 P.M.; a ball is automatically dropped at Deal. Time-balls are proposed for Portsmouth and Start-Point. Hourly currents are sent from the observatory to the Post-office, from which they are distributed to subscribers. Currents are sent automatically at 10 A.M. and 1 P.M., and widely distributed; and almost daily signals are sent directly to about 600 places, including railway termini, and from these places they are repeated to the lines radiating therefrom. The system is practically complete.

VISIBILITY OF STARS IN THE DAY-TIME.

Dr. Rudolf Wolf communicates to the Philosophical Society of Zurich (20th year, page 179) a note on the visibility of stars in the day-time from the bottom of deep wells. It appears that Mr. F. Carpentier, of Zurich, tried the experiment of looking for stars in the day-time from the bottom of a deep well (ninety feet), and that he was successful. It was done when the experimenter was but a lad, and although there is no doubt as to the fact, the names of the stars seen and the particulars of the observation can not be recovered.

MEASURE OF TIME BY HOUR-GLASSES.

Dr. Wolf, of Zurich, having occasion to use an hour-glass which was intended to mark half-hours, endeavored to deter mine the probable error of a measure made by means of this instrument. The ending of the flow of sand could be ob served quite exactly, i. e., to within one second of time; the mean of sixty trials gave him for the time of flow 28m 29.958

5.7. The probable error of a single observation was no less than 43.9 seconds. It thus appears that this instrument, which was extensively used by the ancients, is not a trustworthy one for exact determinations.

B. TERRESTRIAL PHYSICS AND METEOROLOGY. MECHANICAL THEORY OF OCEAN CURRENTS.

The application of mathematics and the laws of mechanics to the theoretical investigations of the currents of the atmosphere and the ocean, with which subject American students have become so familiar through the labors of Professor Ferrel, has of late years been taken up quite energetically in Europe; and to the labors of Colding, Peslin, Everett, Thomson, Hann, and others, we now have to add the somewhat elementary memoir of Professor Blazek on the elements of a mechanical theory of the ocean currents, which communication is, he implies, introductory to a more extended memoir that may be expected from him. He considers that every particle of water is actuated by two forces-that of gravity toward the centre of the earth, and the centrifugal force due to the daily rotation of the earth. The centrif ugal force in and of itself can produce no constant current, since it is in obedience to it that the earth owes its permanent ellipsoidal shape; but if on such an ellipsoid the temperature in general diminishes toward the equator and toward the two poles, there results a tendency toward a new distribution of the mass of the water, which therefore demands a new figure of equilibrium. The dense, cold waters of the two polar seas, therefore, flow toward the equator, while the lighter warm waters flow from the equator toward either pole. Less water flows from regions of low temperature toward the regions of high temperature, and the northern hemisphere sends to the equator less cold water than the southern hemisphere. Consequently, as he demonstrates, the centres of all the closed portions of the equatorial currents in all oceans are found between the 35th and 30th parallel of latitude. The centrifugal force drives the cold water toward the equator and the warm water toward the polar regions, and in consequence of the earth's rotation these latitudinal currents are turned aside-those from the poles to the west, and those from the equator to the east.-Sitzb. K. Böhm. Gesell., 1874, 195.