1^4 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 Reo-ions of the Northern Hemisphere are likened to the Condenser of a Steam- 

 boiler 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, 222. — 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 

 io-norant. 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 w^as bringing to light. 



174. For instance, there was reason to suppose that there is a 

 crossino* of winds at the three calm belts ; that is, that the south- 

 east trade-winds, wdien 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- 



