Dr. Croll's Theory of Glacial and Warm Periods. 8 1 



of the equatorial air in its circuit, and to greatly lessen the 

 course of the winds, which flow towards the equator, and 

 this is exactly what we find to be the case. The trade winds 

 do not blow from the polar or even from the temperate 

 zones, but they blow from latitudes even nearer the equator, 

 their limits being bounded towards the north and south by 

 the so-called calms of Cancer and Capricorn respectively. 



As we have seen, the column of equatorial air, on 

 reaching a certain height, spreads out and begins to flow to 

 the north-east and south-east, as the anti-trade winds. As 

 Mr. Scott says, this overflow takes place at a great height, 

 for the level of the counter current has never been reached 

 by the ascent of any of the peaks in the equatorial Andes ; 

 but that the air does flow away in the upper strata is 

 abundantly proved by the fact that clouds are often noticed 

 moving in a direction contrary to that of the trade wind 

 below. A proof even more striking is afforded by the fall of 

 ashes from the volcanoes in Central America in the Spanish 

 Main, and from those in the Dutch East Indies in the 

 Western Pacific. An instance of he former occurrence was 

 recorded in January, 1835, when ashes from Coseguina, on 

 the Bay of Fonseca, were borne in four days to Kingston 

 in Jamaica, in the teeth of the trade wind. The latter 

 phenomenon took place in 181 5, when the ashes from 

 Tomboro, in Sumbawa, were carried to Amboyna, a distance 

 of 800 miles, athwart the direction of the south-east trade. 



" When we reach the outer edge of the trade wind zone 

 we find the counter current gradually descending to the sea 

 level. On the Peak of Teneriffe (lat. 28 N.), and on Mauna 

 Loa, in the Sandwich Islands (lat. 20 N.), there are constant 

 south-west winds at the summit. . . . When these 

 upper currents reach the earth, about the latitude of the 

 tropics of Cancer and Capricorn, a great portion of the air 

 which goes to form them is caught in the under current and 

 drawn back to the equator ; but the remainder flows on ; 



F 



