396 NOTES OF A NATURALIST, 



ing the climate of Europe and the adjacent parts of the arctic 

 zone, Mr. Croll agrees with many preceding writers ; but, so far 

 as I know, he was the first to suggest that in consequence of the 

 greater persistency of the south-east trade-winds, which ordinarily 

 extend up to, and, at some seasons, even north of, the equator, 

 the warm waters of the Northern Atlantic derive a large share of 

 the heat which is carried to the temperate and arctic zones from 

 the southern hemisphere. Applying the same reasoning to the 

 currents of the Pacific Ocean, Mr. Croll arrives at the general 

 conclusion (" Climate and Time," p. 94) that " the amount of 

 heat transferred from the southern hemisphere to the northern 

 is equal to all the heat falling within fifty-two miles on each side 

 of the equator." 



I do not beheve that the facts on which Mr. Croll bases this 

 essential portion of his theory are sufficiently established. With 

 regard to the Atlantic, I have expressed in the text (p. 344) an 

 opinion, derived from conversations with practical seamen, that 

 in the Atlantic the trade-winds of the northern are stronger 

 than those of the southern hemisphere. That opinion, I am 

 disposed, on further examination, to regard as incorrect. I 

 believe that the north-east trade-winds often blow with greater 

 force : but, taking the average of the entire year, I now think 

 there can be no doubt that the south-east trade-winds extend 

 over a wider area in the equatorial zone. However this may 

 be, our knowledge of the currents of the Atlantic does not, I 

 think, authorize us to conclude that the portion of heated water 

 carried from the southern to the northern hemisphere is nearly 

 so large as Mr. Croll has estimated. If the heat of the Gulf- 

 stream were mainly supplied, as Mr. Croll contends, from that 

 source, there should be a marked difference in the volume and 

 temperature of the current, between the season when the north- 

 east trade-winds approach the equator and that in which the 

 south-east trades prevail to the north of the line, for which there 

 is no evidence. 



As regards the currents and winds of the Pacific, in spite of 

 one considerable exception, to which I shall further allude, I 

 think that the balance of evidence points to a greater prevalence 

 of the south-east trade-winds, and to the probable transference 

 of some portion of the equatorial waters from the southern to 

 the northern hemisphere. 



