Dr. Croll's Theory of Glacial and Warm Periods. 69 



which flow from the equator. And he argues with force 

 that since the winds flowing from the equator are the upper 

 anti-trade winds, which come from an altitude above the 

 snow line, and therefore below 3 2° in temperature, through 

 which they have to blow for some days, they cannot bring 

 much, if any, heat from thence (id., 27 and 28). • It is generally 

 admitted that the Gulf Stream causes the mean annual 

 temperature of our island to be 12 above the normal 

 temperature due to the latitude, but Dr. Croll shows that 

 this underrates the total effect of the Gulf Stream in these 

 latitudes, since the mean referred to is itself raised by other 

 tropical currents in the Pacific. He also shows that the 

 very great flexure of the isothermic lines in the North-east 

 Atlantic can be due to nothing else but the Gulf Stream, 

 and he adds : — " On no point of the earth's surface does the 

 mean annual temperature rise so high above the normal as 

 in the Northern Atlantic, just at the arctic circle, at a spot 

 believed to be in the middle of the Gulf Stream. This 

 place is no less than 22°5 above the normal, while in the 

 North Pacific the temperature nowhere rises more than 9 

 above the normal " (id., 46). 



With this reasoning I have no quarrel whatever, and 

 if such be the effects of the Gulf Stream we may well 

 ask with Dr. Croll, how enormous must be the quantity of 

 heat conveyed from the equatorial regions by all the ocean 

 currents together! 



Professor J. D. Forbes, putting aside the effect of 

 ■currents, calculated what would be the temperature of the 

 ■equator and poles were the earth all water or all land. 

 His result was that if it were all water yi°y would be the 

 temperature of the equator and I2° # 5 the temperature of the 

 poles, and were the surface all land io9° - 8 would be the 

 temperature of the equator, and 25° - 6 that of the poles. It 

 is therefore perfectly certain, argues Dr. Croll, that had he 

 added to his result the effect due to ocean currents, and 



