PREFACE. This work has been prepared by the joint agency of the late Professor Coffin and the Smithsonian Institution, the former furnishing the general plan and oversight of the work, and such parts of the labor as could not be satisfactorily confided to others; while the latter contributed the greater part of the material, and defrayed the entire cost of making all the reductions and numerical computations, except what was done by Professor Coffin, or was found in other works. The resultants at the academies in the State of New York, computed by Dr. Franklin B. Hough, and those at numerous places in Russia, computed by Mr. Wesselowski, and some few others, have been made use of. This work may be considered an extension of Professor Coffin's former one on the “Winds of the Northern Hemisphere," so as to embrace the entire surface of the globe so far as it has been accessible to scientific observation. In the words of Professor Coffin, “the design is to show primarily “1st. The mean direction in which the lower currents of the atmosphere move over all parts of the surface of the earth, including in the term “lower currents' all that part of the atmosphere on which direct observations can be made, whether by means of a vane or by the motions of the clouds. “2d. The ratio that the progressive motion bears to the total distance travelled. “3d. The modifications that the mean current undergoes in the different seasons of the year. “4th. The directions in which the forces act that produce these modifications. 65th. The amount of their intensities, reckoned on the same scale as that which determines the mean annual direction. “6th. To show, by separate solutions for the surface winds and those indicated by the motion of the clouds, how the two differ, and how they differ according as we do, or do not take into account the difference in the velocity of the different winds; the discussion of this latter question being confined chiefly to the observations reported to the Smithsonian Institution from the year 1854 to 1857 inclusive. “The data used for elucidating these points consist of series of observations on 1 To avoid confusion the months of December, January and February are designated as winter in the southern as well as the northern hemisphere, March, April, May as spring, etc. · Monsoon influences. ( vii ) winds made at 3223 different stations on land, and during numerous voyages at sea, extending from the parallel of 83° 16' north latitude, to beyond the parallel of 75° south latitude (the extreme points ever reached by man) altogether embracing an aggregate period of over 18,500 years. - The stations on land are distributed over its surface as follows: Number of stations. . 2077 740 244 76 Aggregate number of years. 4,130 496 86 America Islands of the sea' “At sea, between the parallels of latitude 60° north and 60° south, the observations are mostly taken from the Wind and Current Charts prepared at the United States Naval Observatory, under the direction of Capt. M. F. Maury, which cover the entire Atlantic, Indian and South Pacific Oceans, and all of the North Pacific except a comparatively small portion, the completion of which is much to be desired, lying between the meridians of 150° east and 165° west from Greenwich; and nearly every square of 5° in latitude by 5° in longitude is more or less fully represented. For the Arctic and Antarctic Oceans, and the Mediterranean, Black and Red Seas, the material is derived mostly from other sources. The observations on the ocean embrace a total of a little more than one thousand years. “ The whole material is arranged in the form of tabular series, which require no explanation beyond what is given in the headings of the several columns; and for more ready reference to the data from any particular place, or group of places, as contained in the tables, as well as with a view to a more scientific arrangement of the whole, and for convenience in the discussion, the entire surface of the earth is conceived to be divided into 36 zones by parallels of latitude drawn 5° asunder, commencing at the north pole, and proceeding southerly; and in each zone the places of observation are arranged in the order of their longitudes, commencing at the 180th meridian from Greenwich, and proceeding easterly. “The method of reduction is the same throughout as in my former work. Instead of giving the prevailing direction, or that point or points of the compass from which the winds blow most frequently, and rejecting all the rest, the traverse of the whole is resolved, in the same manner as that of a ship at sea. The former method, which was once almost the universal one, and which still finds advocates, may be useful in pointing out local peculiarities in the winds at different places, as affected by the geographical features of the surrounding country, but can give us no enlarged ideas of the movement of the air as a whole. Suppose a particle of air to start from the point A, in the following diagram, and to move with a uniform velocity for 30 days as follows: From the northeast for an aggregate period of 3 days 4 2 southwest 6 9 west 5 northwest 66 7 66 66 5 the diagram represents its motions, and at the end of the 30 days the particle is found at B. The bearing of the point Fig. 1. A from it is now S. 70° 4' W., its distance in a direct line equivalent to 12 days' travel, and the ratio of this dis 7 tance to the whole distance travelled 9 40 per cent. “Or, to express the same by formulæ after the method of Lambert, or of Mr. Charles A. Schott, of the United States Coast Survey, or others, who have improved upon Lambert's method, let n represent the total number 3 of observations (corresponding to the sum of the sides of the foregoing polygon, except A B); 0, 01, 02, 0g..... the angles which the observed directions of the wind make with the meridian, reckoned round the compass from the north point eastward through 360°; S, S, S, Sg . . the number of observations recorded in these directions (corresponding to the foregoing sides taken separately); R the resulting distance A B, and othe angle S.70° 4'W. 12 A 1 The following is an extract from a letter of the author, in 1871, on this point: “The question as to the proper mode of discussing winds depends on what we wish to ascertain or point out. If it be to show their sanitary effect, or what winds one is likely to experience at any given place, Lambert's formula is manifestly inadequate, nor was it designed for that purpose. But, if the object be to ascertain in what direction the air, subject to observation, moves as a whole over a given place, it is equally obvious that the only proper method is to resolve its traverse; and to abandon this method would, in my view, put the science back a third of a century. It was the chaotic character of the results that came from the method formerly in vogue, that first drew my attention to the subject, and led me to conceive the idea of resolving the traverse of the winds : ignorant of Lambert's formula, as well as of the fact that Prof. Kaemtz was doing the same thing. The soundness of the principle seemed so obvious, and the results of its application so satisfactory, all over the globe, that I had not supposed it possible that it could ever be called in question.” ? See bis reduction of Dr. Kane's Arctic observations, published in the Smithsonian Contributions to Knowledge, Vol. XI. August, 1875. B a a a = which the direction of A B makes with the meridian at B, or (0+180°) the angle S sine 0+S sine 0,+S, sine 02+ Ssine 0, etc. 6 “The value of o, expressed in the ordinary method of reading bearings with reference to the four cardinal points, is given in the tables in the fifth column from the right, and as the numerical value of the tangent of p is the same for angles in each of the four quadrants, recourse must be had to the algebraic signs of the numerator and denominator. If both are t, the direction is in the northeast quadrant; if the numerator is + and the denominator –, it is in the southeast quadrant; if both are –, it is in the southwest quadrant; and if the numerator is — and the denominator +, it is in the northwest quadrant; thus: b. + Northwest R the last two forms being the most convenient for computation. the values of are given in the tables in the fourth column from the right. “Where the places of observation are isolated, resultants are computed for each separately; but where there are several in the same vicinity, they are often grouped together, and the resultants for the group only computed. The observations made at the different stations in a group are ordinarily combined by simply adding them together, in the same manner as if they had all been made at one station; but it did not seem best to adhere uniformly to this method. Suppose, for illustration, that the group consists of but two places, and that the number of observations made at them is very unequal, at each of which the number of observations is sufficient to determine the character of its winds; but that, owing to local influences, the results at the two differ widely. Now if the number of observations at the two places was nearly equal, their sum would afford a tolerable mean between the two; but if very unequal, the place which had the greater would have more weight than properly belonged to it, and a more reliable resultant could be obtained, either by equalizing the numbers representing the observations, or by computing a pew resultant from the separate ones of the two places. On the same principle, when in any group, or at any place, the number of observations in the different seasons of the year differ materially, the resultant for the year is computed, not from the sum of all the observations, but from the resultants for the separate seasons. “ The method of computing monsoon influences, or the forces which deflect the wind from its mean annual direction in the different months or seasons of the year, sine ♡ cos o n YEAR. N. 73° 13' W.: 30. N.69° 42'W.36. B is as follows: It is assumed that if no such forces existed, the mean direction and relative progress of the wind would be the same for each month of the year, and equal to one-twelfth of the mean annual progress. If, therefore, according to the usual method of applying the “parallelogram of forces,' we make the progress in any month the diagonal of a parallelogram, and one-twelfth of the mean annual progress one of the sides, either of the contiguous sides will represent the deflecting force, both in quantity and direction. Thus, for example, at Amherst, Massachusetts, Fig. 2, the resultant for January reads N. 69° 42' W..36, and for onetwelfth of the mean for the year, measured on the same scale, N. 73° 13' W..30. Draw A B in the direction N. 73° 13' W. and make its length .30. Also draw A D in the direction N. 69° 42 W. and make its length .36. Complete the parallelogram, and the side AC or B D will show the direction and amount of the de Fig. 2. flecting forces, viz., N. 52° 47' W., .0632; or a little more than one-fifth as great as the force which determines the mean annual resultant. This value is given in the tables in the second column from the right under the head of Force' of monsoon influences. “Figure 3 shows the same for seasons, where, as in the case of Easton, Pa., the resultant for the spring is represented by A B, which is S. 63° 23' W., length .230; and that for the entire year by A D, N. 74° 45' W., length .248; D B is Fig. 3. the monsoon influence, which is from AN S. 11° 18' E., length .172. For the most part the deflecting forces are approximations, determined, with tolerable accuracy, by mechanical construction upon a large drafting scale, though in a few cases they were com AK puted trigonometrically, as in the examples here adduced.” An inspection of Plate 26 will give a more full illustration of the mode of construction and delineation of D these forces, as well as show how S their computation afforded a ready test of the accuracy of the computations of the resultants from which they were derived, for these forces must be in equilibrio, however diverse their separate directions and amounts; were it not so, the particle of air at the end of the months and seasons that constitute its annual course would not be found at the same point that was indicated by the resultant for the year. B SPRINC S. 11° 18' E..172 YEAR; N.74° 45' W. 248 |