172 Woeikqf- — CrolVs Hypotheses of Geological Climates. 



ence of the diathermancy of the atmosphere and its enormous 

 variations in time and place, another exceedingly important 

 consideration has been overlooked by Dr. Croll, viz : the very 

 great difference of continent and ocean in the matter of temper- 

 atures, the fact that an equal loss of heat expressed in calories 

 will have a very different influence on temperatures, both on 

 account of the great caloric capacity of water and of the mo- 

 bility of its particles. I must add that the latter condition is 

 too often lost sight of not only by Dr. Croll, but by many 

 other scientists in their speculations on the influence of a solid 

 or liquid substratum on the distribution of terrestrial tempera- 

 tures. Besides we have the formation of ice on the waters, 

 which also has a great influence on the temperatures. 



Thus it is easy to see, that the question how great will be 

 the temperature of the air at a given place, say in midwinter, 

 when the distance from the sun is greater or less than at present, 

 cannot be answered, even approximative^, especially in the 

 exceedingly crude way it is put by Dr. Croll, that is, without 

 distinguishing high and low latitudes, continent and ocean, etc. 

 One thing is certain, that such a change will certainly have a 

 greater influence on the temperatures in the interior of conti- 

 nents than on the oceans and their borders. The caloric capac- 

 ity of water is so great, and the mobility of its particles so 

 effectual in resisting a lowering of the surface temperature, by 

 the convection currents it causes, that I doubt very much if, 

 during a great excentricity and winter in aphelion, the surface 

 temperature of the oceans can be lower in winter than now : 

 the difference in the quantity of sun-heat is too small and too 

 short-continued to give an appreciable difference in winter; 

 and, as in the year there is no difference in the quantity of heat 

 received by the waters, I think there will be no difference in 

 the temperature of the waters, and thus no influence of great 

 excentricity with winter in aphelion on the ocean temperatures, 

 and also no greater snow-fall than now. As to the continents, 

 I admit that, though we are unable to calculate the rate of de- 

 crease of temperature of the winter months in these conditions, 

 there is no doubt that it will be appreciable, and be the greater the 

 less a given place is under the influence of the seas. 



But what has this to do with glaciation ? Even now, the 

 temperatures in the interior of large continents are low enough 

 in mid-winter to allow of the snow remaining on the ground 

 for some weeks, not only under 45° N., but even under 40° N. 

 And yet, we have no glaciers on the North American conti- 

 nent, which reaches to 71° N. and on the Asiatic, which reaches 

 to 78° N., except in high mountain regions, because the snow- 

 fall of winter is so small that it is melted in summer. Even 

 the mountains of Northeast Siberia have no glaciers. 



