276 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Icebergs, like islands, facilitate the formation of clouds and pro- 

 mote precipitation. 



514. Turn we now to the equatorial cloud-ring. Seafaring 

 The horse latitudes pGoplc havc, as If bj couimon conscnt, divided the 

 -the doldrums. occau oS" into regious, and characterized them ac- 

 cording to the winds; e. ^., there are the "trade-wind regions," 

 the "variables," the "horse latitudes," the "doldrums," etc. 

 The "horse latitudes" are the belts of calms and light airs 

 (§ 210) which border the polar edge of the northeast trades. 

 They were so called from the circumstance that vessels formerly 

 bound from New England to the West Indies, with a deck-load 

 of horses, were often so delayed in this calm belt of Cancer, that, 

 for the want of water for their animals, they were compelled to 

 throw a portion of them overboard. The " equatorial doldrums" 

 is another of these calm places (§ 212). Besides being a region 

 of calms and baffling winds, it is a region noted for its rains and 

 clouds, which make it one of the most oppressive and disagree- 

 able places at sea. The emigrant ships from Europe for Aus- 

 tralia have to cross it. They are often baffled in it for two or 

 three weeks ; then the children and the passengers who are of 

 delicate health suffer most. It is a frightful grave-yard on the 

 way-side to that golden land. A vessel bound into the southern 

 hemisphere from Europe or America, after clearing the region of 

 variable winds and crossing the "horse latitudes," enters the 

 northeast trades. Here the mariner finds the sky sometimes 

 mottled with clouds, but for the most part clear. Here, too, he 

 finds his barometer rising and falling under the ebb and flow of 

 a regular atmospherical tide, which gives a high and low barom- 

 eter every day with such regularity that the hour within a few 

 minutes may be told by it. The rise and fall of this tide, meas- 

 ured by the barometer, amounts to about one tenth (0.1) of an 

 inch, and it occurs daily and every where between the tropics: 

 the maximum about lOh. 80m. A.M., the minimum between 4h. 

 and 5h. P.M., with a second maximum and minimum about 10 

 P.M. and 5 A.M.* The diurnal variation of the needle (§ 344) 

 changes also with the turning of these invisible tides. Continu- 

 ing his course toward the equinoctial line, and entering the region 



* See paper on Meteorological Observations in India, by Colonel Sykes, Philosoph- 

 ical Transactions for 1850, part ii., page 2"J7. 



