| 
d 
and the Velocity of the Wind. 355 
of 52° in the southern hemisphere the value of G=0-07 of an 
inch, and the tabular results from which this is obtained are 
regarded as being pretty accurate, and it is poner very nearly 
sensible velocity of the wind within that distance. The area 
of almost a perfect calm in some cyclones is said to be as 
much as 30 miles in diameter. 
_ The gyrations of the external part of a cyclone are necessar- 
ily in the contrary direction, and hence the component of gy- 
ratory motion vcos? must be negative, and consequently sec v 
in (1), and the sign of G becomes reversed. At some distance, 
therefore, from the center of a perfect cyclone between the 
center and the outer limit, the barometric pressure must be a 
maximum and G vanish. At this distance, therefore, by our 
law we have v=0, that is,a calm. Hence areas of high barom- 
eter must generally be areas of calms. 
18. If the isobars of a cyclone drawn to every tenth of an 
inch of the barometer reduced to sea level are 100 miles apart, 
we have G=0-1 of an inch. With this value of G, supposing 
the value of 7 to be so small that we can put seca=—1, we get 
from (1) at the distance of 400 miles from the center of the cy- 
clone, or center of curvature of the isobars, and on the parallel 
of 45°, v=29 miles for the velocity of the wind; and this 
would be very nearly the actual velocity at sea, where the 
* 4 rms = ae ca oe = by ce Wind na Cnrrenta n 47 
Physical Ureveptapily =— 2 Weir ites 
