صور الصفحة
PDF
النشر الإلكتروني

this line, a third; and so on. In this manner I obtain a continuous line, which represents the course of the wind as long as it is continued. Such lines were drawn for February and March 1837; those for March are exhibited in Plate VII, which represents the curves for March, drawn for the stations, at the Society, at the Observatory and at Edinburgh. In all the cases the observations experienced interruptions, which make it difficult to draw any general conclusions from them. But we may remark that in February the wind blew almost constantly from a more westerly point at the Observatory than at the Society. It is not difficult to conceive this result to be occasioned by the peculiar circumstances of the Anemometer at the Observatory: but it is also possible that it may be a general fact that such differences obtain at neighbouring places, in consequence of the direction of valleys, &c. Further observation alone can clear up this and similar points.

It has been deemed an important point by Meteorologists to obtain the mean direction of the wind at a given place for a given time, for instance, a year. Kämtz in his Meteorologie, Vol. 11. p. 218, has collected several results of this kind. But in these researches the force of the wind has entirely been left out of the account, and each wind was reckoned according to the number of days which it blew. It is clear that such a procedure is entirely fallacious; for the high wind of one day may be greater, with regard to every possible effect, than the gentle breezes of a week. The mean annual direction is probably constant at each place within certain limits: and the mean directions at different places are perhaps connected by certain general relations, depending upon the quantity of fluid transferred, and upon other atmospherical conditions, which may hereafter be found to be important elements of meteorological speculation. But it is not at all likely that this will hold if the mean direction be taken without reference to the strength of the wind; and no mode of measurement can be good for this purpose which does not give the whole quantity of the aerial current, depending both upon velocity and upon time.

The Anemometer here referred to is, as I have said, the only one, so far as I know, which has been constructed with the view of thus

registering both the quantity and direction of the wind; and however imperfect its construction may yet be, it must give some approximation to the quantity which it is our object to measure, and must thus afford the means of a better estimate of the mean direction for a year (or for any other time) than has hitherto been possible.

It is obvious that the mode of obtaining the mean direction of the wind for any time would be to resolve each partial wind into its component parts E. and W. and N. and S. The sum of all the west components, subtracting the east elements, give the effective west wind; and the sum of all the south elements, subtracting the north elements, give the effective south wind. The magnitude and proportion of these two effective winds compounded will give the magnitude and direction of the effective wind, between west and south, which belongs to the whole time. And the same may be said of any other cardinal points.

The reduction of any wind to these cardinal directions is of course to be performed by considering it as the hypotenuse of a right-angled triangle, and here the multipliers by which the reduction is to be performed are easily found. We may take fractions which are sufficiently accurate, and yet simple enough to be easily used. Thus the intercardinal winds, NE, SE, SW, NW, are reduced to the cardinal direc7 tions N, S, E, W, by multiplying by The subordinate winds 10. NNE, ENE, ESE, SSE, SSW, wsw, WNW, NNW, are reduced 12 4 to the cardinal directions by the multipliers and ; thus a wind

13

10

NNE 65, is equivalent to N 60 and E 26. The oblique winds N by E, &c. might be reduced in the same manner by the multipliers

2

and

10

98 100

or 1

2 100°

But these last I have not used.

I annex calculations made in this manner for the months of January, February and March, 1837; in which I have resolved the days into periods during which a certain group of neighbouring winds were prevalent. Thus from January 1 to 14, the prevailing winds were SSW, SW and WSW; from January 26 to 30 they were NE, ENE and E..

It appears in this manner that on the scale of the Society's Anemometer the total wind for these three months was W. 321, S. 558.

It may be observed that the graphical method offers at once the mean direction of the wind, and the resolution of the winds into their cardinal parts. A straight line drawn from the beginning of the curve to its end is the direction and magnitude of the resulting wind; and if lines E and W and N and S be drawn from its extremities, they will give its component parts.

If we were to draw the graphical curve of the wind as registered by the Anemometer for a year, and were to do this for several years at the same place, beginning from the same point, we should probably have a set of curves in which a considerable resemblance might be traced; for there is a kind of annual cycle of the winds at each place. The mean of such curves for a sufficient time would be the mean annual type of the winds for that place. The mean annual type of the winds at different places would vary very much, as is clear from the materials which Kämtz has collected. Thus he finds (Vol. 11. p. 223) that the mean direction at Paris is S 68° W, at Montmorenci N 48° W, at Utrecht N 85° W, and Amsterdam S 61° W. And though, as we have seen, his method of obtaining these results is very insufficient, it still serves to show that they would probably be various by any method.

If Anemometers of the kind now described were fixed in various parts of the world, and the annual type, and other circumstances of the wind thus obtained, it cannot be doubted but that this portion of meteorology, and probably other portions which are connected with this, would soon make great progress.

TRINITY COLlege,

May 1, 1837..

W. W.

[subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small][merged small][graphic][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]
[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]
« السابقةمتابعة »