17dt Woe-ikof — CrolVs Hypotheses of Geological Climates. 



is a tendency toward a higher pressure in the interior of conti- 

 nents in winter and on the oceans in summer, and to winds 

 from the first in winter, from the second in summer, that is, 

 there are what Coffin calls monsoon influences. A colder winter 

 in the interior of the continents, with an unchanged tempera- 

 ture on the oceans, would certainly strengthen the winter winds 

 from the interior, and thus bring more cold, dry weather than 

 is experienced now, and reduce the precipitation in winter. 

 Such conditions are certainly not favorable to a greater accum- 

 ulation of snow than the now prevailing. The Ural mountains 

 have, as well as those of Norway, prevailing west winds, and a 

 much colder winter, but on account of the smaller snowfall, no 

 permanent snow and no glaciers, while the west side of the 

 Scandinavian mountains has enormous glaciers. If a high 

 excentricity and winter in aphelion can have a considerable 

 influence on climates, it would give to Western Europe colder 

 winters with a greater proportion of dry east winds and warmer 

 summers, both conditions unfavorable to glaciation. It has 

 long seemed to me that those who have expressed an opinion 

 on the favorable influence of winter in aphelion on glaciation, 

 from Adhemar to Dr. Croll and his followers, have been influ- 

 enced by the present difference of the northern and southern 

 hemispheres. The glaciation is far more prevailing in the latter, 

 and this has been ascribed to winter in aphelion on the well- 

 known principle " post hoc, ergo propter hoc," as it gave a 

 ready explanation of the former glacial periods of the northern 

 hemisphere. I am quite sure that Dr. Croll was also influenced 

 by the present differences of both hemispheres. 



Dr. Croll has long been an advocate of the wind theory 

 of ocean currents and has proved that, at present, a considerable 

 quantity of warm waters is brought by these currents from the 

 southern to the northern hemisphere, serving to warm the lat- 

 ter. In these two questions he has rendered a good service to 

 science. The transport of warm waters from the southern to 

 the northern hemisphere is a fact, but what is the cause ? Dr. 

 Croll believes the cause to be, at least indirectly, winter in 

 aphelion, which brings, especially during high excentricity, but 

 to a certain degree even now, a host of other indirect results, by 

 which the given hemisphere is cooled, its trade-winds are 

 strengthened, and bring the more warm water into the other 

 hemisphere, the higher the excentricity. I have shown above 

 that the cause assigned by Dr. Croll is inadequate to cause any 

 considerable lowering of temperature on the ocean in winter, 

 and that even the small difference, perhaps possible, must be 

 regained in summer. Thus winter in aphelion can not bring 

 any change in the velocity of the trade-winds and their more 

 southerly extension when winter in aphelion exists in the 



