272 DEPARTMEXT OF TEE XATAL SERVICE 



eliminating the first two columns of table 3, thefie being contained in table 1. 

 Cohmins 4 and 8 are left unaltered, column 5 is superfluous, and in columns 6, 7, 

 and 9, the last figure of each value should be discarded, partly as having no real 

 importance, and partly as rendering the values in question unnecessarily awkward 

 to handle in calculation. This done, the solenoids in these columns are expressed in 

 10 cgs. Column 9 may also be said to indicate cgs. solenoids per 10 km. Table 4 

 shows the simpler form given to table 3 by this process. Table 5 contains the 

 number of solenoids according to the scheme in table 4 for all pairs of stations in; 

 Dr. Hjort's sections. The heading above each pair of stations indicates the distance 

 between them, and the approximate mean depth of the intervening area. 



13.— INFLUEXCE OF THE EAKTH'S EOTATION UPON" CIRCULATION. 



The influence of the earth's rotation upon circulation makes itself apparent in a 

 very simple manner in the atmosphere. When the air at any point commences to 

 rise upwards, and the surrounding air in consequence pours in from all quarters to 

 replace that which has risen, then this indrawn air will, as it approaches the centre of 

 ascent, develop a marked cyclonic circulation. Thus in fig. 53, taking as the 

 centre of ascent, and ^1 as a closed curve composed of air particles about the same, 

 then, at the commencement of the movement, the velocity will be directed towards 

 the centre, and the curve will have no circulation. After a certain lapse of time, the 

 curve will, on account of the centripetal movement of the air, have contracted to 

 the position h, at the same time developing a cyclonic circulation. The circulation 

 increment per second is, according to Bjerknes: — 



¥ ~^'" dt ^'^ 



oj being here the angular velocity of the earth, and S the area of the closed curve's 

 projection upon the equatorial plane. And as S decreases, C is increased, vide fig. 53. 



Fig. 53. ^Cyclonic circulation pro- 

 duced by the earth's rotation. 



In the sea, the movement of the water is to a very high degree restricted and 

 deformed by the shape of the water basins. There is, therefore, in this case, no 

 regular concentric movement about the centre of descent. In spite of this, however, 

 we still find here a marked cyclonic circulation, which, in the Arctic ocean, where 

 the Gulf stream sinks doAvn, and in the waters south of Newfomidland, where the 

 Labrador current disappears, attains very considerable dimensions. 



The vertical velocities in the sea are insignificant in comparison with the 

 horizontal, and we may therefore, in calculating the circulation, neglect the former 



