Column I contains the name of the place of observation, to which is prefixed the zone and serial number, by reference to which on the preceding pages the reader can find the average velocity of the wind from each point of the compass for each of the seasons. See, for example, Red River Settlement; near the foot of page 148 we find, 148 we find," Mean velocity in miles per hour, Spring, North 5.32, N. E. 2.71," etc. The places are also grouped-not as by the author, in strict sequence of latitude and longitude-but to conform as nearly as practicable to the divisions of the United States made in the "Discussion and Analysis of Winds."

Column II was computed as in all the tables of Series B, by having regard only to the number of observations, without any reference to velocity.

angle of 17° 32'; and southerly in one at an angle of 8° 38', making the average of the whole northerly by 15° 13′; while it increases the magnitude of the resultant in 5 of the districts by an average of 50 per cent., and diminishes it in 5 by an average of 15 per cent., making for the whole an average increase of 18 per cent.

"In 44 districts between the 40th and 45th parallels (exclusive of Great Salt Lake City where the results are too anomalous to be incorporated with the others), the resultant is thrown northerly in 36 at an average angle of 15° 49′, and southerly in 8 at an average angle of 4° 31', making the average for the whole northerly by 12° 8'. The influence on the direction seems generally to be much greater in the western than in the eastern States of this belt, and this accounts for my failure to detect it when I prepared my former publication. The magnitude of the resultant is increased in 36 by an average of 29 per cent., and diminished in 8 by an average of 14 per cent., making for the whole an average increase of 21 per cent. In 20 districts between the parallels of 3640 and 40° the resultant is thrown northerly in 17 at an average angle of 16° 36′, and southerly in 3 at an average angle of 4° 11', making the average for the whole northerly by 13° 29', while its magnitude is increased in 19 districts by an average of 43 per cent., and diminished in but one, and that only by 11 per cent., making for the whole an average increase of 36 per cent.

"The near coincidence of the results in these three belts authorizes us to combine them, and we thus find that the mean influence from the parallel of 50° down to that of 36° is to render the resultant more northerly by about 13°, and to increase its magnitude about 25 per cent. This dif ference is not great, but may affect the general principle.

"Through the States of Tennessee and North Carolina, from latitude 35° to 3620, the resultant is thrown northerly in 4 districts at an average angle of 18° 5', and southerly in one at an angle of 33° 57', the average for the whole being 7° 41' northerly. Most of the observations in the latter district were taken at Knoxville, Tenn., where there may be some local cause that renders the south and southwest winds so much stronger than those from the north and northwest. In each of the 5 districts the magnitude of the resultant is increased, the average increase for the whole being 40 per cent. Notice the accumulating increase of the magnitude of the resultants as we pass southerly through the 4 belts above described, viz., 18, 21, 36 and 40.

"The results in the next belt extending from latitude 30° to 35° seem perfectly chaotic. In 7 out of 16 districts the resultants are thrown northerly at angles ranging from 1° to 126°, and in 9 southerly with nearly as wide a range, the average for the whole being 3° 23′ northerly. The magnitude of the resultants is increased in 7 districts and diminished in 9, the average being an increase of 2 per cent. It is within this belt that the system of westerly winds breaks up and is replaced, as we go south, by the trade wind system, and the slight degree of prevalence of the wind in any direction allows it to be controlled very much by local influences.

"Still further south out of 6 districts represented, at 5 the resultant is thrown northerly at an average angle of 17° 48'. The remaining district is represented by the City of Mexico, where the general results are in some degree anomalous, and make a longer period of observation desirable In 5 of these districts the magnitude of the resultant is increased by an average of 25 per cent., while in one it is diminished by 8 per cent. The average increase for the whole being 19 per cent."

Column III is the laborious product obtained by computing the resultants from the number of miles travelled by the winds from each point of the compass for each season. As, for example, Red River Settlement, page 148, "Number of miles, Spring, North, 383, N. E. 38," etc. It therefore represents time multiplied by velocity.

The remaining columns IV, V, VI and VII, are taken from the sub-tables. (See, for instance, foot-note 2 on page 148.) Column IV containing the average velocity of all winds in miles per hour, though derived from the same source as the "Mean Velocity" for the separate points of the compass, is, of course, not the arithmetical average of the latter, but was separately computed. The numbers in column V show the velocity in miles per hour in the mean direction, on the supposition that the winds from every point of the compass move with the average velocity given in column IV. These figures are obtained by multiplying the numbers in column IV by the ratios in column II. Column VI exhibits the true velocity in the mean direction, giving to the winds from the several points of the compass each their own average velocity. The results are the product of the miles per hour in column IV multiplied by the corresponding ratios in column III. Column VII represents the excess of the velocities in column VI over those in column V, as expressed by the use of the plus sign, the minus sign being employed when the figures in column V are the greater. The "Mean Resultants" for the groups of stations in columns II and III were obtained mechanically by the use of a drafting instrument, and are given to the nearest whole degree, the fractions of a degree having been excluded after the computations were made.

A DRAFT OF THESE RESULTS is found in Plate 25, where the figures in column II are drawn as arrows, flying with the wind, the length of the shaft (without the barb) being proportioned to the ratios; those in column III are similarly noted, the barb being omitted, and the greater length of the shaft conforming to the increase in the ratios over those in column II. The average velocities given in column IV are found in the vertical series in the middle of the plate, a scale of miles being attached at the left. The vertical scries at the extreme right-hand of the plate contains delineations of the results in the remaining columns; column V being shown in a dotted line, column VI in a continuous line; and the intervening space, which is in most cases filled with the sign+, representing column VII. In the individual stations at the lower part of the page, the velocities were, in some cases, so great as to need changes in the scale employed, which is, therefore, recorded in the margin.

An inspection of the tables and plate shows clearly that, as a general thing, the difference in the velocity of the winds from different points of the compass affects the resultant but slightly either in direction or amount. In the United States, north of 32° N. latitude, the resultant had by noting the actual velocities (i. e., the dotted arrow) is found inclined more to the right hand, that is, it represents a direction more northerly than the unbroken arrow that represents the effect when the velocity is disregarded. The annual resultants in the former case averaging S. 89°+ W. with a ratio of .261, and in the latter S. 80°+ W. .227. The divergence of these

two classes of annual resultants is therefore about nine degrees (8° 48 by one mode of reckoning and 9° 38 by another), the divergence being greatest in winter. In passing into the adjacent geographical zones, it is significant that, within the limits of the Polar and Equatorial systems of winds, the places represented on the chart with like uniformity exhibit divergence, but in the contrary direction, i. e., the dotted arrow for velocity, is at the left hand of the continuous arrow for time.

The average velocity of all winds in the United States differs little from 7 miles an hour, being slightly in excess in the northeastern part of the Union, and less in the States nearer the centre of the continent. The anemometer gives greater figures than those obtained by estimation. The velocity in the mean direction on the hypothesis that the winds from every point of the compass move with an average velocity (given in column IV) is 1.7 miles per hour. But the true velocity in the mean direction, when each wind is allowed its own separate velocity, is nearly 2.0 miles per hour.

In the "Winds of the Northern Hemisphere" the average hourly velocity of all winds was given as 5.8 miles; and the mean resultant obtained from the actual distances was stated to be S. 87° 44′ W 1.74 miles per hour; and that obtained by disregarding velocity S. 85° 59′ W. 1.53 miles per hour.

81 July, 1875.