Dr. Croll's Theory of Glacial and Warm Periods. 93 



the Narrows of Florida, its course, instead of being 

 from east to west, is from west to east, or rather from 

 south-west to north-east, so is that of the main northern 

 affluent of the equatorial current in the Pacific. That 

 is to say, both of them reverse their direction at a 

 certain part of their course and flow in a direction 

 contrary to that of " the trades." Dr. Croll points out 

 very clearly how this fact supports the theory of the 

 wind-origin of ocean currents. He shows that in spite of 

 the rotation of the earth, which would tend to give these 

 currents a north-westerly direction, they flow eastward, 

 because having reached the latitudes where the anti-trades 

 blow from west to east, they are dragged along by them. 

 {Climate and Time, 213.) This is quite true, but it seems 

 to me to be a very fatal argument for Dr. Croll to use. If 

 the Gulf Stream, and the corresponding Pacific current, owe 

 the larger part of their later motion, and their consequent 

 spread into far northern latitudes, to the anti-trades, and 

 if the present climate of the northern hemisphere depends 

 upon the extent of this spread, as Dr. Croll allows, then it 

 follows that a more important factor than the trade 

 winds which give the equatorial current its western 

 motion, are the anti-trades, which give the resulting 

 currents their north-eastern motion. The amount of 

 heat distributed in high latitudes by these currents will 

 depend not on the strength of the trade winds but on that 

 of the anti-trades. We can scarcely doubt that, as the 

 blowing of these winds is very uniform, and is limited to an 

 area where the parallels do not differ greatly in length, while 

 their distribution is very regular, the force of the anti- 

 trades is very nearly that of the trades. 



From this it follows that when the north-east trades are 

 strong the south-west anti-trades must be strong also. Dr. 

 Croll's main position is that during the so-called glacial 

 epoch the north-east trades were so strong as to force a 



