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We ■will here pause to take into our calculations another item. These winds (these 

 two north and south coining masses of meeting air, form the tradewinds, as they are 

 called. ' These winds, though starting to go from north and south towards the equator, 

 do not get there as north and south winds ; for the earth keeps turning round from west 

 to east, so that on the north the tradewind is a north-east wind, and on the south its 

 meeting tradewind is a south-east wind. These came, we remember, from the temperate 

 zones, leaving of course a space there which is instantly occupied by another mass of air 

 rushing in from the polar regions north and south. 



Now we will follow our meetiflg tradewinds upwards from the equator, rorced 

 upwards above the surrounding strata of air, beyond the levels of equilibrium, they flow 

 over to north and south towards their respective polar regions. These are the anti-trade- 

 winds, and they are acted upon by the earth's 'rotating movement as are the tradewinds 

 before mentioned, so that these returning currents blow from the south-west in our 

 northern hemisphere, and from the north-west in the southern hemisphere, always, how- 

 ever, towards the poles and from the equator. Near the poles, they approa«h the point 

 whence the polar air started to move towards the equator, to fill up the gap occasioned 

 by the rising equatorial air (or rather, there is no gap, but to prevent the gap which 

 would have been had they not pressed .in). Well, at this point near the poles they, as fast 

 as the polar air starts towards the equator, press into its place, follow it, go to the 

 equatorial regions in the tradewinds, rise up there and come back again to the poles in 

 the anti-tradewinds, and the current is complete. 



Now, at first the anti-tradewinds coming back towards the pole's keep high in the 

 air, so that they and the tradewinds below, going towards the equator, are quite separate ; 

 but once past the tropical circle they come down near the earth and blow towards the poles 

 ■on the same level as the tradewinds coming from the poles, ^hey are therefore upon the 

 same level, and kept asunder only by the rotating action of the earth. There are, to 

 quote Flammarion, " points at which these two currents come together, and their differ- 

 ent qualities cause numerous and sometimes disastrous atmospheric disturbances. Their 

 beds get shifted over the surface of the globe, and the succession of one after another in 

 the same place produces sudden variations in the state of the sky." To avoid confusion 

 they are, from the point at which they flow on the same level (where, I mean, the anti- 

 tradewind above flowing towards the poles, comes down to the same level as the trade- 

 wind below blowing from the poles), called no more trade or anti-tradewinds. The 

 anti-tradewind is from here to the poles called the equatorial current of air, and the 

 tradewind the polar current of air. 



you will remember that in our northern hemisphere the anti-tradewinds returning 

 from the equator blow from the south-west ; the tradewinds coming from the poles blow 

 from the north-east. We will remark, therefore, in passing that the equatorial current 

 must, as being laden with moisture risen from tho tropic seas, be humid, warm, and bring 

 much moisture with it, while the polar current, coming from the arctic regions, will be 

 cold and dry. But these two currents are varied in their moisture-bearing capacities by 

 many local and other circumstances ; great mountains condense their moisture ; the warm 

 Gulf Stream has much to do with evaporation in its course ; great stretches of prairie and 

 of woods cause differences. Here, for instance, in Toronto our Observatory records would 



