E. P. CulvertceU — Theory of the Ice Age, 63 



bring in enough heat to pi'event freezing, if in 24 hours as much, 

 heat were radiated away, as, taken from 7-2 inches of water at zero, 

 would transform it to ice. This is no doubt much more than the 

 actual radiation would be if the water were 0°C. at the Pole and 

 7-1° at the Arctic circle." Add to this a south wind at 15 miles 

 per hour through 2300 feet above the surface, and also at 7-1° C. 

 (which would carry as much heat as 15 fathoms of the water), and 

 we have the agencies suggested by Lord Kelvin in 1877 for the 

 production of a genial period at the Pole. But suppose we grant 

 that they would keep the Arctic circle from frost, is there the least 

 probability of such agencies ever coming into play ? The Gulf 

 Stream flows at less than 4 miles per day, and we are asked ta 

 suppose a current flowing at 18 miles per day ! Where is the 

 impelling force to come from? Apparently Lord Kelvin suggested 

 that the diff'erence in specific gravity due to temperature might 

 be the motive power, but in view of the final abandonment of 

 temperature difi"erences as causes of ocean currents on a large 

 scale, this cannot be admitted as sufScient to produce a current of 

 anything like the required depth or velocity, and whether we assign 

 "winds or difference of specific gravity as the cause, we are met by 

 the difficulty that, as we have ultimately to depend on differences of 

 temperature in different latitudes. Lord Kelvin's result seems incon- 

 sistent with his cause, for he supposes the temperature differences to 

 be almost annihilated. Again, in January, we have to go far south 

 of the Arctic circle to get a temperature of 7'1° C. (nearly 45° F.). 

 Again, if the forest trees of Greenland, Grinnell Land, and Spitz- 

 bergen were only found at a height of 1000 feet above the present 

 sea-level, it might be rational enough to account for the high 

 temperature of which they are the evidences by supposing a sub- 

 mergence of the land to that extent, but, since this is not the case, 

 we cannot postulate such a submergence to explain the phenomena. 



As to an explanation of prehistoric glaciation, I am afraid I have 

 nothing very definite to offer. Of course an alteration of altitude 

 is sufficient, but the geological requirements do not seem to admit of 

 a very free use of this method of explanation. 



If, indeed, we could see any probability that at a former age 

 the south winds passed in the upper regions of the atmosphere in 

 summer, as they now do in winter when the surface wind is from 

 the north, so that there was a continuous and permanent north wind 

 blowing across the Arctic circle down to temperate latitudes, then 

 we might find a full explanation of an ice-age gradually spreading 

 southward over the land, especially as such winds would either 

 impede or reverse the Gulf Stream. I am not at present, however, 

 able to suggest any cause for such a difference from the present 

 distribution of the winds. 



It is not unlikely that there never was an Ice Age, but that there 

 have been at times various local glaciations such as we now see in* 

 Greenland. The present glaciation in Greenland is supposed to be 

 in great part due to the cold-water current which flows along its 

 shores from, the Polar regions, and this, in its turn, is in part due 



