APPENDIX. 403 



Iquitos, about 4° S. latitude, and 1600 miles from the mouth of 

 the river. 



In tropical Australia the rainy season falls during the pre- 

 valence of the north-west monsoon, and we cannot doubt that 

 this is mainly supplied by vapour carried from the northern 

 hemisphere. Another region wherein the same phenomenon is 

 exhibited on a large scale is the central portion of Polynesia, 

 extending from the Feejee to the Society Islands over a space 

 of at least twenty degrees of longitude. Over that wide area, 

 as far as about twenty degrees south of the line, the regular 

 south-east trade-wind prevails only in the winter of the southern 

 hemisphere, while during the rest of the year, especially in 

 summer, north and north-east winds have the predominance. 

 Taking the mean of three stations in the Feejee Islands, of 

 which the returns are given by Dr. Hann, I find in round 

 numbers the very large amount of 150 inches for the mean 

 annual rainfall, of which 105 fall during the seven months from 

 October to April, while the five colder months from May to 

 September supply only forty-five inches of rain. There can be 

 little doubt that the larger part of the 105 inches falling during 

 the warm season is derived from the northern hemisphere. 



I by no means seek to account fully for the apparent con- 

 tradiction between the results of theory, as developed by Dr. 

 CroU, and the actual distribution of heat over the earth as 

 proved by observation ; but I venture to think that I have 

 shown reason to doubt the possibility of drawing absolute 

 conclusions as to the results of astronomical changes until we 

 shall have fuller knowledge than we now possess of all the 

 agencies that regulate climates. 



Before concluding these remarks, I will notice one other 

 branch of the argument in regard to which I am unable to 

 concur with Mr. Croll. As we have seen, the essential point in 

 his theory as to the modus operandi of changes of eccentricity, 

 and the relative position of the poles, on the distribution of 

 temperature, is that the currents of the equatorial zone are 

 driven towards the pole which has the summer in aphelion, and 

 that the cause of this shifting of the currents depends on the 

 greater strength of the trade-winds in the hemisphere which 

 has the winter in aphelion ; the strength of the trade-winds in 

 turn depending on the amount of difference of temperature 



