104 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
CHAPTER V. 
ON THE PROBABLE RELATION BETWEEN MAGNETISM AND THE 
CIRCULATION OF THE ATMOSPHERE. 
Reasons for supposing that the Air of the Northeast and of the Southeast Trades 
cross at the calm Belts, ^ 174. — What Observations have shown, 184. — Physical 
" Agencies not left to Chance, 188. — Conjectures, 192. — Reasons for supposing that 
there is a crossing of Trade-wind Air at the Equator, 194. — Why the extra-trop- 
ical Regions of the Northern Hemisphere are likened to the Condenser of a Steam- 
hoiler in the South, 199.— Illustration, 200.— A Coincidence, 202.— Proof, 203. — 
Nature affords nothing in contradiction to the supposed System of Circulation, 204. 
Objections answered, 205. — Why the Air brought to the Equator by the Northeast 
Trades will not readily mix with that brought by the Southeast, 207. — ^Additional 
Evidence, 209. — Rains for the Mississippi River are not supplied from the Atlan- 
tic, 210. — Traced to the South Pacific, 213. — ^Anticipation of Light from the Polar 
Regions, 216. — Received from the Microscope of Ehrenberg, 217, and the Exper- 
iments of Faraday, 219. — ^More Light, 221. — Why there should be a calm Place 
near each Pole, 223. — Why the Whirlwinds of the North should revolve against 
the Sun, 223. — Why certain Countries should have scanty Rains, 228. — Magnetism 
the Agent that causes the Atmospherical Crossings at the calm Places, 231. 
172. Oxygen, philosophers say, comprises one fifth part of the 
atmosphere, and Faraday has discovered that it is magnetic. 
This discovery presents itself to the mind as a great physical 
fact, which is perhaps to serve as the keystone for some of the 
grand and beautiful structures which philosophy is building up for 
monuments to the genius of the age. 
173. Certain facts and deductions elicited in the course of these 
investigations had directed my mind to the workings in the at- 
mosphere of some agent, as to whose character and nature I was 
ignorant. Heat, and the diurnal rotation of the earth on its axis, 
were not, it appeared to me, sufficient to account for all the cur- 
rents of both sea and air which investigation was bringing to light. 
174. For instance, there was reason to suppose that there is a 
crossing of winds at the three calm belts ; that is, that the south- 
east trade-winds, when they arrive at the belt of equatorial calms 
and ascend, cross over and continue their course as an upper cur- 
rent to the calms of Cancer, while the air that the northeast trade- 
