186 WINDS OF THE NORTHERN HEMISPHERE. 



single station is more or less subject, causing the velocity of winds from certain 

 points of compass to be greater or less than naturally belongs to them. The only 

 apparent exception is in North Carolina, and there it is only apparent, for twenty- 

 four out of the twenty-six months' observations reported came from one place. If 

 we combine all the places in the United States, at which the velocity has been 

 estimated by the use of the numbers 0, 1, 2, 3, &c., the mean resultant obtained 

 from the actual distances is S. 87° 44' W. 1.74 miles per hour; while, if we take 

 the same observations, and give the same mean velocity to each, it is S. 85° 59' W, 

 1.53 miles per hour — a difierence of only 1° 45' in direction, and 21 hundredths of 

 a mile in amount. . . . Nor is there any uniformity in the ojjeration of this 

 slight influence of velocity on the mean direction. If we look over the list, we 

 notice that in some cases it makes it more northerly, and in others more southerly ; 

 though it almost invariably increases the amount more or less ; showing that the mean 

 velocity of air moving in the same direction as the main current, is, on the whole, 

 a little greater than of that moving in the opposite direction. This is what we 

 should expect; for, in the case of any local disturbance or eddy in the atmosphere, 

 the velocity of those parts which move in the same direction as the main current 

 is equal to the 8xim of the two motions, while, in the opposite parts, it is equal 

 only to the difference. 



We can obtain light upon the remaining inquiry, viz. : the effect of difference in 

 the mean velocity of the loind in different countries or parts of tlve country, from the 

 general summary at the end of Series E. The only effect of this difference is, 

 as has already been remarked, to increase or diminish the amoiutt of the resultant, 

 without altering its direction. Other things being equal, the amount of the result- 

 ant must obviously be exactly proportional to the mean velocity of the wind ; so 

 that it is necessary only to compare the velocities, as given in the table just referred 

 to. Turning to it, we perceive that, while the mean velocity of the entire United 

 States is about six miles' per hour, there could hardly exist a greater diversity in 

 the geographical distribution of the parts of it where the velocity exceeds or falls 

 short of the mean. Is it not, therefore, more natural to refer the difierence to local 

 influences, or errors of observation, and to conclude that, on the whole, there is, 

 throughout the United States, no great difference of velocity? 



But if we now cross the Atlantic, and compare American with European obser- 

 vations, there seems to be a remarkable difference between the velocity there and 

 here. If the observations are to be relied on, and there is no apparent reason why 

 they are not, the velocity there is very much greater. We see it not only at those 

 places where the velocity was merely estimated; but at Greenwich and Devonport, 

 in England, as compared with Toronto and Girard College, in this country, at all of 

 which places it was accurately measured with instruments of the same construction. 

 Osier's anemometer being used at them all, and yet the records show the velocity to 

 be nearly three times greater at the former two places than at the latter two. 

 This difference of velocity, if it really exists, will more than compensate for the less 

 ratio that the progressive motion of the winds in Europe bears to the total motion, 

 ibrmerly adverted to, so as, on the whole, to make the progressive motion greater 

 there than in the United States. 



' More strictly 5.8 miles. 



