34 W. Ferrel on motions of Fluids and Solids 
called the tropical calm belts. Near the polar circles, where the 
polar and passage winds meet, there must also be calm belts, — 
which may be called polar calm belts. The motions of the at- — 
mosphere, therefore, at the earth’s surface, if they were not modi- — 
fied by the influence of continents, would be as represented in ~ 
the interior of the figure, in which the heavy lines represent the 
calm belts. On account of the influence of the continents, these 
belts are somewhat displaced and irregular, and on account of the 
varying position of the Sun, they change their positions a little 
in different seasons of the year. 
‘The southern limit of the polar winds in the northern hemi- 
sphere, and also the limit between the trade and _ passage winds, 
has been determined by Prof. J. H. Coffin, from the discussion 
of a great number of observations at different points, and given 
in a chart, in his treatise on the winds, published in the seventh 
volume of the Smithsonian Contributions, 
17. That the atmosphere is depressed at the equator and the 
_ poles, and has its maximum height near the tropics, as has been 
ics, and also a little less at the equator. Says Captain Wilkes: 
“The most remarkable phenomenon which our observations 
_ Says Sir James Ross:* “Our barometrical experiments ap- 
ig to prove that the atmospheric pressure is considerably 
the column of mercury between the 20th of November, 1839, 
and the 31st of July, 1843.” : 
Extract from Ross's Table. 
j___Latitude. Pressure. | Latitude. Pressure. | Latitude. Pressure. 
j atitude. soe titude. ee. ore {wateeed 2 or #09 
Eqvator, 29974 | 42° 53° 29950 | 55° 59r 
13° 0S. 30016 | 45 0 29664 | 60 9 
22 17 30085 | 49 8 29467 | 66 9 
84 48 30023 | 51 33 29497 | 74 9 
54 26 29°347 
* Voyage to the Southern Seas, vol. ii, p. 8383, ee: 
a 
