GEOLOGICAL CLIMATE IN HIGH LATITUDES. 355 



latitude regions, during the three middle months of the arctic day, is 

 greater than is received in the same time at the equator. 



In Dr. Kane's " Arctic Exploration," we read that the difference 

 between maximum and minimum (summer and winter) temperature, in 

 latitude 78 37', was 120 Fahr. At St. Michael's, latitude 63, the 

 thermometer ranged from -f 76 to 55, a variation of 131. It would, 

 I think, be a moderate estimate, should we attribute at Spitzbergen a 

 variation of 100 to the changes in the sun's declination, or, in other 

 words, to the obliquity of the earth's axis. 



The cold undoubtedly was greatly modified by the latent heat of 

 the surrounding ocean, and by the inflow of ocean-currents. But the 

 same capacity for giving off heat exists now, and the same currents 

 continue to flow ; yet in Spitzbergen a not large island, surrounded by 

 a broad expanse of water the cold is very intense. The specific heat 

 of water has undergone no change ; so far as that is concerned, the 

 surrounding ocean does as much now, as then, to make the Spitz- 

 bergen winters mild. 



Did the Gulf Stream, or the Japan Current, in those remote times, 

 have a greater flow than now ? Their effective cause is the difference 

 between polar and tropical temperature. If this was nothing, the flow 

 would be nothing. In geological times the difference of the tempera- 

 tures must have been small, since the same species of plants and ani- 

 mals extended from the tropics to as near the poles as has been ex- 

 plored. Hence the flow of these streams, to say the least, could not, 

 in those times, have been greater than it is at present. 



Whether 100 is an overestimate of the difference between the 

 summer and winter temperature at Spitzbergen, due to the long days 

 and nights, it is certain that the sun produces a great effect upon the 

 temperature in high latitudes. Whatever other thermal influences 

 may have existed in the Miocene, or in other and earlier periods of 

 geology, their effect was no greater in winter than in summer. Ad- 

 mitting it to have been the same a matter of great doubt the tem- 

 perature, as the nights grew longer, must have fallen until it reached 

 a point at which the loss of heat, by radiation into space, was just 

 equal to that brought in by the ocean-streams, and by such aerial cur- 

 rents as might blow from warmer regions.* In summer there were 

 the same sources of heat plus a sun shining not twelve nor fifteen 

 hours, but for months. Calling the winter heat A, and the increment 

 from the sun B, the heat during summer equaled A plus B. The dif- 

 ference at the present day between the temperature of arctic seasons 

 is enormous. It is difficult to see how it could have been so reduced 

 as to render life possible for plants whose fellows of the same species 

 were, at that very time, growing in regions thousands of miles nearer 

 the equator. 



* Stellar heat need not be considered, as it does not vary, and, besides, it is very 

 small. 



