THE TEMPERATURE OF THE SEA.

Observations on the temperature of the sea have been made at Falmouth, England, continually since the autumn of 1871. It was at first proposed to make the observations about the time of high water in Falmouth harbor, it being thought that, owing to the great extent and depth of the harbor, the influence of the shore would not be felt when the water had freshly come in from the open sea. But it soon became ap parent that results obtained in the harbor and near the shore were worthless. Experiments proved that differences of sev eral degrees of temperature existed within very small limits of space; and Mr. Dymond, by whom the observations had been made, states that he has reason to think that observations on the temperature of the sea are, in general, of little or no value unless they are made from a vessel considerably outside of low-water mark. It was therefore determined, within a few months after the observations were begun, to make them in the open sea, at distances varying from half a mile to three or more miles from the nearest land. During the three years-1872, 3, and 4-observations were made on 747 days; and the mean of all these readings is 53.23°, while the mean of the 36 highest and 36 lowest monthly readings is 53.25°. The monthly range of the sea temperatures varied from 2o in March to 6.5° in July. The importance of making similar investigations at other stations where sea temperatures are systematically observed is forcibly suggested by this result of Mr. Dymond's studies, and it is evidently highly desirable that the light-ships stationed along our coasts should be utilized, whenever possible, for the purpose of observing sea temperatures.-Forty-second Annual Rep. Royal Cornwall Pol. Society, p. 105.

ORIGIN OF VOLCANIC ASHES.

Professor Von Roth communicates to the Berlin Academy of Sciences an investigation into the origin of the volcanic ashes that fell in Scandinavia on the 29th and 30th of March. He shows that these were the product of the great volcanic outbreak in the eastern half of Iceland at Vatua, as well as in the Dynqu Mountains.-Monatsber. Berlin Acad. der Wiss., 1875, 256.

ABNORMAL DEFLECTIONS OF THE PLUMB-LINE.

Lieutenant F. V. Greene, Engineer Corps, U. S. A., has recently discussed the station-errors of the 41 astronomical stations established on the 49th parallel of latitude by the joint commission of English and American engineer officers, for the purpose of marking the boundary-line between the United States and the British possessions. The 41 stations were all observed with the zenith telescope, and of them 19 were observed by the English alone, and the average probable error of the final latitude of a station was ±0.088"; 17 were observed by the Americans alone, and the probable error of a station established by them was ±0.059" (76 observations); and 5 were jointly observed by the two parties, their independent results differing by 0.28", 0.27", 0.07", 0.29′′, and 0.31" respectively. The various stations were connected geodetically by the method of tangents and offsets; and the difference between the astronomical and geodetic determinations was assumed to be due to abnormal variations in the local directions of gravity, and was called "stationerror."

Sufficiently accurate topographical work was done to enable 200-feet contours to be laid down on the maps. From these contours Lieutenant Greene has calculated A (see table), which is the deflection of the plumb-line produced by all masses above the ground within a radius of ten miles, and B, which is the deflection which would be produced by masses between ten and sixty miles distant. This has been done with reference to each of the 41 stations-a work of no little difficulty-and the results are given in the accompanying table. D is the observed deflection, and D-(A+B) is the outstanding residual and unexplained deflection. These quantities for 37 stations in the Ordnance Survey of Great Britain were D=2.05", and D-(A+B)=1.35′′. From this it appears that for 29 stations the abnormal phenomena are partially accounted for and in the right direction; for 12 stations the computed deflection is in the wrong direction. The quantity D-2.15" which is to be accounted for is about the same in magnitude as the mean error in latitude (2.64′′) found by Bessel from a discussion of all the great arcs previously measured, and goes to show that the mean hetero

geneity of large tracts of the earth's surface is about the same in every part of the earth itself:

Computed Deflections. 1 to 10 miles.

.21 -1.78

- .78

22.

+ .98

+1.50

23.

- .76

+1.90

.52 -2.66

-1.75 - .16

+ .70

The stations at which deflections, A, are not computed were situated in the midst of plains, where the deflection, A, would not amount to 0.4", the uncertainty of the determination of D.

+ Carried to 80 miles.

ON THE TEMPERATURE OF THE MEDITERRANEAN SEA NEAR THE COAST OF ALGERIA..

Messrs. Grad and Hagenmüller, in 1872, made a series of observations on the temperature of the water, on the occasion of a voyage along the shores of Algeria, and have continued them at three fixed stations since that year. The mean temperature of the surface through the year is found to vary from 18.3° Centigrade at Algiers, up to 19.5° at Oran ; the extremes between winter and summer being 11° and 18° respectively. Observations were made at different depths, down to four meters, at the fixed stations; and by comparison of the Algerine with the Adriatic measurements, it would seem that the isothermal lines on the surface of the Mediterranean bend toward the mouth of the Adriatic Sea, where the temperature is higher during the winter and spring time. -6 B, LXXXI, 292.

UNDERGROUND TEMPERATURES.

In some notes on the general facts relating to underground temperature, Mr. Schott states that the earth's solid crust being hotter than the mean temperature of the lower stratum of the atmosphere resting on its surface, heat is constantly and very slowly passing outward, and strata of equal depth would have very nearly uniform temperatures but for the influence of the irregular daily and annual variations of the atmospheric temperature received by conduction. The depth of the stratum of the so-called invariable temperature (viz., where the changes escape ordinary observation, or are less than 0.01 Centigrade) is found about six meters below the surface of the ground in the tropics, and about thirty meters below the surface in the middle latitudes. The depths at which the daily variations become imperceptible are, for these two regions of the globe, respectively 0.3 and 1.3 meters. These numbers, however, depend greatly upon the kind of soil or rock forming the surface, and differ considerably according to the porosity of the loose soil. The mean temperature of the earth's crust increases with increasing depth, and for moderate depths the increase is nearly uniform at the rate of 1° Centigrade for 28 meters. For greater depths, the descent necessary to produce an increase of 1° of temperature is greater

than this figure. The depths at which the daily and annual variations respectively disappear are in the proportion of 1 to 19; or as the square roots of the lengths of the periods. The amplitudes of the daily, annual, or other periodical changes diminish in a geometrical ratio as the depths increase arithmetically. The time required for the heat wave to reach a depth of 7.3 meters at Edinburgh is nearly six months. Therefore the maximum temperature at this depth is synchronous with the minimum temperature at the sur face. Mr. Schott computes, from the best data available, what should be the average invariable temperature at the depth of 229 meters underneath Chicago, corresponding to the depth from which water flows in a certain artesian well. The actual temperature observed is only 12.8°. The com puted temperature is 16.2°. The explanation of the discrep ancy can not be satisfactorily given, unless observations are made upon the influence of the lake water, and the actual rate of increase of temperature at that spot.-Report Sec. Smithsonian Institution, 1874, 249.

FORMATION OF BASALT COLUMNS.

Mr. Robert Mallet republishes in full his views on the origin and mechanism of the production of the prismatic or columnar structure of basalt. He states that our knowledge of the mechanism of the jointing of masses of rock is still very far from being complete, but less complete is our knowl edge of that which constitutes the complicated systems of joints shown in columnar basalt. The best-known writers are generally at variance on this subject, although the most philosophical views are those that have been defended by Professor James Thomson, now of the University of Glasgow. According to Mr. Mallet's investigations, the primary conditions for the production of straight prismatic structure in basalt are, first, general homogeneity of the material; second, a tolerable regularity in the general form of the mass; third, inequality in the rate of cooling in one or more direc tions. The more or less horizontal and tabular masses of basalt as they occur in nature are usually cooled most rapidly from their upper or lower faces; or, if the basalt be found filling a dike, then the rapid cooling has taken place on the two opposite surfaces of the dike. When, in conse