88 Mr. H. H. Howorth on 



impelled more to the southern than to the northern hemis- 

 phere ; and the warm water carried over in this manner 

 to the southern hemisphere would tend to increase the 

 difference of temperature between the two hemispheres. 

 This change, again, would in turn tend to increase the 

 difference of temperature between the two hemispheres. 

 This change, again, would in turn tend to strengthen the 

 north-east and to weaken the south-east trades, and would 

 thus induce a still greater flow of equatorial waters into the 

 southern hemisphere, a result which would still more increase 

 the difference in temperature between the northern and 

 southern hemisphere, and so on — the one cause reacting on 

 the other, so as to increase its effects." {Climate and Time, 

 227-229.) Having stated this principle in general terms, 

 Dr. Croll proceeds to test it by a critical example, and 

 says : — " We have in the present state of things a striking 

 example of the extent to which the median lines between 

 the two trades may be shifted, and the position of the great 

 equatorial currents of the ocean may be affected by a slight 

 difference in the relative strength of the two aerial currents. 

 The south-east trades are at present a little stronger than the 

 north-east, and the consequence is that they blow across the 

 equator into the northern hemisphere to a distance some- 

 times of 10 or 1 5 ; so that the mean position of the median 

 line lies at least six or seven degrees north of the equator. 

 And it is doubtless owing to the superior strength of the 

 south-east trades that so much warm water crosses the 

 equator from the South to the North Atlantic, etc., etc." 

 {id. 23^231). 



This reasoning seems to me to be eminently fallacious. 

 In the first place, I know of no adequate evidence for 

 the conclusion that the south-east trades are now stronger 

 than the north-east trades. It is quite true that the 

 belt of calms which separates the two trades is situated 

 very largely north of the equator. But this, I urge very 



