These numbers clearly shew that the atmospheric pressure varies with the direction of the wind; the barometer is every where very high when the wind blows between the east and the north, and very low when it comes from a point comprised between the south and the west; its height varies very regularly between these two extremes. In certain places, however, anomalies are found; thus, at Vienna and Buda, the pressure is very feeble with east winds; and, at St. Petersburg, the minimum almost coincides with the N.W. These anomalies have not yet been well explained, for they are not derived merely from the continental positions of these two towns, since the results obtained at Stockholm and Moscow agree with the laws which regulate western Europe. The only difference consists in that the oscillations are a little smaller in the interior of the continent than on the west coast.*

Analogous laws are found in other countries, only the wind that corresponds to the maximum barometric height varies according to the position of these points in relation to

* In one of the preceding notes, p. 161, I have given the mean temperatures corresponding to the different directions of the wind, as they were observed at the period of the winter solstice at Bosekop (Norway), latitude 69° 58′ north, by the French Commission sent into the north of Europe. The mean barometric pressures corresponding to the same epoch, and in the same place, were calculated by M. BRAVAIS. They are ranged in their turn within the following little table, which shews the barometric card of winds for this locality:

It is to be believed that the barometric height 753,2, which corresponds to the N.E. wind, is too high; this rests on only a few observations. But this table, when placed in contrast with the thermometric card (p. 161), proves that the coldest winds keep the barometer lower, and that the warm winds from the west and S.W. raise it several millimetres: this fact is a remarkable exception for Europe. According to WRANGEL, this is nearly the range of the barometer at New-Archangel (Dove, in SCHUMACHER'S Jahrbuch für 1841, p. 311). We should further observe the anomaly presented by these same facts, in another point of view: at Bosekop, the landbreezes depress the barometer; the column rises with the sea-breezes. An anomaly of the same kind exists at the mouth of the Rio de la Plata.-M.

Europe. Thus, in the United States, the barometer is highest with the N.W. winds, and lowest with the S.E.; it is the same at Pekin in China. On collecting these facts together, we conclude that the barometer attains its maximum when the winds blow from the north and from the interior of continents, its minimum when they come from the equator or the

sea.

After what we have said in respect to the influence of winds over temperature, we may easily explain these phenomena, the pressure is great with cold winds, feeble with warm winds. If the air is cooled with north winds, it contracts, the limits of the atmosphere fall, and the hot air flows in from all sides, and hence the rise of the barometer. If the air is heated by south winds, it ascends and flows away in all directions.**

INFLUENCE OF THE ROTATION OF THE WINDS ON THE HEIGHT OF THE BAROMETER.- In the researches, of which we have given the results in the preceding table, no attention has been paid to the hour of the day, except that for Paris and Halle I have chosen the hour of noon. However, on considering that in our climates the wind presents a regular and constant rotation, we ought to discover this regularity in the oscillations of the barometer, as we have formerly found it in those of the thermometer and the hygrometer. M. Dove arrived at this result by comparing the observations made at Paris at 9 A.M. and 9 P.M.; my own observations at Halle, when compared hourly, lead to the same results. I inquired what was the principal direction of the wind for each day, and I calculated the mean height of the barometer for each hour of the day; I then subtracted this mean from the general pressure observed at this hour with any particular wind. In the following table, the sign + means that the barometer was above the general mean; the sign - that it was below it. However, I should observe that the absolute

M. Dove, according to the small number of existing meteorological observations, inquired what might be the influence of the direction of the wind over the height of the barometer in the southern hemisphere, and over the temperature and the humidity of the air. The examination of the registers of the ship la Princesse Louise, and the accounts given by Captains FITZROY and WENDT, have led to the following conclusions:

1st. The barometer rises with west, S. W., and south winds; it attains its maximum height when the wind blows from the S.E., it then falls when the wind passes to the east, the N.E., and the north; its minimum height corresponds to the N.W.

2d. The temperature and the tension of aqueous vapour diminish with west, S. W., and south winds; they attain their minimum when they blow from the S.E.; they then augment with the east, the N.E., and the north, to attain their maximum when the wind is at N.W.- (SCHUMACHER'S Annuaire for 1841, p. 317.)

1838, but in this period there are likewise blanks of from eleven years of observations, namely, from 1827 to four years; the general mean, on the contrary, was deduced for the researches on the winds embrace a period of only value of these differences is not, perhaps, rigorously exact;

several months.

EXCESS OF THE MEAN HEIGHT OF THE BAROMETER, FOR A GIVEN WIND AND HOUR, OVER THE

HOURS.

MEAN HEIGHT OF THE COLUMN, AT THE SAME HOUR, WITH ANY WIND.

In this table we clearly recognise the influence of the rotation of the wind, it generally turns from the north to the N.E.; we may also remark that the barometer almost always rises during the days when the wind blows from the north, so that its height, after a deduction is made for the diurnal oscillation, is about two millimetres greater at 10 P.M. than at 6 A.M. As the pressure attains its maximum, when the wind is in the N.E., we find that the barometer changes but little during the day. However, long series of observations might permit us to appreciate its rise from morning till noon, and its fall till evening; for it frequently happens that the wind blows from the north during the morning, from the N.E. at noon, and from the east in the evening. I have placed my observations of this kind in the column N.E.; in the morning the barometer rose, it fell in the evening. The wind continuing to turn passes to the east, the S.E., and the south, and the pressure goes on diminishing; so that the barometer falls until it attains its minimum with the S.W. wind. The barometer then remains stationary throughout the day, only at noon it is a little lower than in the morning and evening., If it passes from the west to N.W. and the north, there is an increase in the pressure which may be appreciated in the course of the day.

The oscillations of the barometer depending on the direction of the wind explain to us the anomalies that we observe between the cards of barometric winds in places that are very near together. If we choose as the elements of the calculation the morning observations, the maximum approaches the N.E., the minimum the S.W.; if we take those of the evening, the maximum approaches the north, the minimum the south. The differences presented by the diurnal oscillations of the barometer in the same month, considered in different years, recognise the same cause. If in any month the west winds have been predominant, the minimum will take place a little earlier in the afternoon, the maximum a little later in the evening, than in the mean of observations comprising a great number of years. Moreover, the evening maximum exceeds that of the morning, whilst the contrary is the case with east winds. We must not forget that, in order to recognise the principal points of a barometric card, one year or even a few months are sufficient; but, to determine them rigorously, prolonged observations are required: for, if the S.W. winds predominate during a month, the barometer remains, for the few days

that the east winds blow, below the habitual mean that corresponds to these winds.

CORRESPONDING BAROMETRIC HEIGHTS FOR DIFFERENT PLACES.-Barometric oscillations in general describe curves that are sensibly parallel, when they are studied for places that are not very far distant from each other; but, at great distances, the barometer may rise in one place and fall in another. Neighbouring places also present differences that are easily appreciated, by calculating their differences of level by means of those of the barometric columns. I have taken the difference of level between Halle and Paris, and between Halle and Zurich, and I have arranged them according to the winds that prevail at a mean in North Germany. The years of observations furnish me with the following differences with regard to the general mean :

VARIATIONS OF THE DIFFERENCES OF LEVEL CALCULATED BY THE BAROMETER, according TO THE DIFFERENT WINDS.

Paris.+ 8,2 +22,0 +26,7 +35,5+23,8 6,6-25,0-24,3 Zurich.+25,7 +42,9 +36,1+27,3

6,221,424,0—13,8

(Vide Appendix, fig. 33.)

These quantities were obtained by comparison with the general mean. If we suppose all these points at a level with Halle, the sign+means that the place is situated above this level; the sign, that it is below. Or else, if we regard the height of the barometer, + signifies that the barometer, supposing it on a level with that at Halle, is lower than in the town, while the sign - indicates the reverse. From the preceding table, the following may be deduced:

DIFFERENCES OF MAXIMUM LEVEL OBTAINED WITH THE
BAROMETER ACCORDING TO THE DIFFERENT WINDS.