Imágenes de páginas
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small]

127 Southern Pennsylvania...... S. 87° W..63 N. 60° E. 1.01 S. 89° E. .06 S. 74° E. .03 N. 88° W..11 131 Northern Maryland.

N. 87 W..571 N. 66 E. .013 S. 62 E. .05 S. 69 E. .03 N. 70 W. .08 138 Dist. of Columbia and S. Md. S. 68 W..58' N. 75 E. 1.06' S. 64 E. .03 S. 261 W..05 N. 60 W..08 143 Southeastern Virginia....... S. 82 W..52 'N. 65 W..02 S. 25 E. .03 N. 6. E. .09 S. 82 W.;.07 145 Eastern North Carolina... N. 87 W..43 N. 801 W..09 S. 74 E. .08 S. 84' E. .12] N. 73} W..11 151 Southeastern Pennsylvania... N. 89 W..53 N. 78 E. .24 S. 2 E. .06 S. 32 w..06 N. 72, w..22 154 Southern New Jersey..... N. 88 W..39, N. 231 E. 1.035 S. 31 E. .13 N. 384 E. 1.03 N. 57 W..10

Zone 12. Lat. 30° to 35°N.

37 New Mexico, Southern Ceut. S. 6; W..27. N. 70 E. .07 S. 23 E. .13 S. 23 W.'.15 N. 10 W. .24 72 Texas, lat. 30-1°, long. 95-7° S. 3 W..27

W$.31.24N171226 81 Arkansas, lat. 34° to 35°. S. 75 W..59 S. 141 W..11 S. 56 E. 18 N. 69} W. .16 N. 11 W. 16 85 Northwestern Louisiana. S. 51 W..45 S. 4+1E. 28 S. 14 w..32 N. 11 w..30 N. 11 W..22 87 Northeastern Louisiana... S. 53 W..311 S. 45° w..16 S. 89 E 1.15 N. 16 E. .10 N. 69 W..06 94 Mississippi, lat. 34° to 35°. S. 57 W..324 N. 51 W..22 S. 17° E. .13 S. 43 E...10 N. 461 E. .08 96 Mississippi, lat. 32 to 34 S. 74 W..16° N. 85 W..16 N. 74 E. .21 N. 68 E. 1.05 S. 47 W..13 99 Mississippi, lat. 32 to 33 S. 43 W..25 S. 48 W.!.12 N. 661 E. .13 N. 56; E. 1.14 S. 72} W..15 102 Mississippi, lat. 31 to 32 S. 55 W..32; N. 57.1 W..25 N. 72 E. 315.05N863 108 Alabama, lat. 34 to 35 N. 37 E. 23 N. 36' w.1.07 S. 71 E. .26 N. 50 W..19 S. 32 W..12 138 S. Carolina, lat. 34 to 35 N. 80 W.,52 west4145878109 141 S. Carolina, lat. 33 to 34 S. 79 W..44, S. 83 W.,.08 N. 89 E. 1.06 N. 60 E. .16 S. 59 W..13

[blocks in formation]

29 Southeastern Louisiana........ S. 54 W..25 S. 49 W..23 N. 64 E. .28.1 N. 41 W..04 S. 86 E. .05 30 New Orleans, years 1851-57... S. 57 W..27 S. 55 W..29 N. 69 E. .27 N. 12 E. .08 S. 83 W..02

[blocks in formation]
[blocks in formation]


The aim of Prof. Coffin in this work on the “ Winds of the Globe," the reason why he did not write the text, and how I came to take charge of this part of it, has been already explained in the preface.

In what way the ideas of the deceased author would have been modified by the progress of theoretical meteorology in the last twenty years, as well as by the much more extended knowledge of facts we possess now, it is impossible to say. It is very likely, however, that he would have continued to rely principally on the inductive method, would have avoided hasty generalizations, and would have shown the same caution and candor as in his other works, omitting explanations of what our present knowledge did not give sufficient data, rather than mislead his readers.

Before drawing the conclusions which seem to follow from the tables and maps of this work, some explanations are necessary.

The object of this work is to ascertain the movement of the air over different parts of the earth's surface. For this purpose the mean direction and rate of progress of the wind were calculated according to the formula of Lambert. It is easy to see that to accomplish this with precision, we should know the velocity of the wind at all places at which calculations are to be made. Now we know the velocity of the winds in a somewhat accurate manner only for a very small number of stations. For many more the velocity of the wind was merely estimated, and for a majority of places, the direction of the wind alone is known. Now the progressive movement of the air over a certain place, even taking into account the direction only, without considering the number of miles travelled, can be ascertained from the number of observations alone if we make the supposition that all winds have the same velocity; but this is obviously not the case. In nearly all known instances where the velocity of the winds has been ascertained, it has been found to vary considerably; generally, the more accurate observations with self-registering anemometers give a greater difference between the velocities belonging to different directions of the winds than mere estimates have given, the difference being seldom less than 1 to 2, and sometimes even 1 to 4 or 1 to 5.

In considering attentively the observations for the stations where the number of observations, for hours, and the velocity are given, it is seen that generally the most frequent wind is also the strongest, or, comparing the mean direction of the wind calculated from the number of observations only, with that obtained by

( 659 )

taking into account the velocity of the winds, it will be found that in the last case the mean direction generally approaches nearer to the actual direction of the prevailing wind.

Besides it is seen that generally the ratio of resultant is greater in the second case than in the first.

Thus it follows that, when we have the mean direction of the wind at a given place, calculated from the number of observations only, we may infer that, if the velocity was known, it would modify the result in so far as to make the mean direction nearer to that of the prevailing wind, and the ratio of resultant greater.

Unfortunately most of the above deductions apply only to the United States, as it was the only country for which Prof. Coffin made his calculations from the original journals. As to printed meteorological journals, they were very scarce until within a late period, and many of these were not to be had in the United States. Therefore published means and abstracts had to be relied upon, and these gave only the number of observations for each wind. It might be thought that the results of the self-registering anemometers now in use in so many meteorological stations would give abundant material for the answer to this question, but, owing to the recent introduction of these instruments in some cases, and to discontinuity of record in others, comparatively few tabulated records of velocity of winds have been printed.

Yet it seems that the angle between the mean direction calculated, taking into account the number of observations only, and that in which the velocity is considered, seldom exceeds 15°. In case of a very small ratio of resultant it can be much greater, but this small ratio itself shows that the mean direction is not much to be relied upon.

All this leads to the conclusion that it is possible to calculate the mean direction of the wind from the number of observations only without incurring a large error. The

map, Plate 13, shows the resultant direction for the number of observations only, as also for velocity, in the United States. I must also explain in what sense I use the words “polar” and “equatorial” winds. Polar designates a wind blowing from a higher latitude towards a lower; and equatorial, a wind blowing from a lower towards a higher latitude. I use these terms in the way which is most generally admitted, to avoid confusion. This agrees also with the manner in which winds are generally designated, so far as we call north wind one that blows from the north towards the south, and not vice versa.

It will be remembered that in the “ Winds of the Northern Hemisphere” Prof. Coffin used the words “polar” and “ equatorial” in the opposite sense.

Another question, to my mind, more difficult to answer, is as to the value of the observations on the motion of clouds. They may serve two ends: 1, to ascertain the motion of an upper current of the air; 2, to observe the lower current, free from the irregularities often found immediately above the surface of the earth.

Naturally enough, in this case all depends on the height of the clouds observed. Very seldom, if ever, in discussing observations from a journal, can even the approximate height of the clouds observed be ascertained. This alone detracts very much from the value of such observations. Besides this, the cases must be taken into account when there were no clouds, or, the clouds being very high, no

« AnteriorContinuar »