6 E. P. Culverwell — -Theory of the lee Age. 



be stopped, and the warm water of the tropics, instead of being 

 carried to northern latitudes, wonkl be sent southwards (pp. 69-71). 

 (II) Another effect which Croll seems to classify under the 

 indirect agencies is, that the great heat of the summer in the 

 tropical regions would give rise to great evaporation, which would 

 be carried up by the aerial currents, and at last fall in snow on the 

 ice-covered regions of the north, where, he says, the greatest snow- 

 fall would take place in summer. 



His Answer to Question 3. 



The answer to the third question is now easy. Dr. Croll has 

 been at much pains to show how greatly temperatures in northern 

 regions depend on the enormous amount of heat transferred by the 

 Gulf Stream and other ocean currents, so that the stoppage of these 

 currents completes the work begun by the previous agencies, and 

 thus accounts for the vast amount of glaciation observed. 



II. — CuiTioisM OF Croll. 



I now take each cause in detail and examine it. 



(A) This is undoubtedly the case. 



(B) Of course there is such an effect, but Croll does not seem to 

 have observed that at midwinter the effect of the greater distance 

 of the sun in diminishing the supply of heat is entirely confined 

 to iltose regions of the earth on which the sun shines, so that it is 

 scarcely felt in the Arctic regions, and it is chiefly felt in the southern 

 tropics, wliere, the heat received by solar radiation being greatest, 

 the percentage decrease is also greatest. In fact, the only difference 

 at the North Pole is, that while it is now only 179 days without 

 any sun-heat, it will in the time of greatest eccentricity be 199 days 

 in the same condition. But, since the lowest temperature appears 

 to occur in January, it seems unlikely that the slightly longer 

 absence of the sun would make much difference. 



(C) This is really the fundamental argument on which the whole 

 theory hinges. It is quite inconsistent with another statement of 

 Croll's, regarded by him as almost equally important, that the 

 influence of ocean streams in raising our winter temperature is 

 extremely great. For, if the winter temperature be so greatly due 

 to ocean currents and not to sun-heat, what can be more improper 

 than to treat the winter temperature as wholly due to winter sun- 

 heat when we are getting the reduction of winter temperature due 

 to reduction of winter sun-heat? Yet this is what Croll does. 

 He gets the enormous reduction of 45° in midwinter temperature 

 on the ground that the reduction of midwinter excess of temper- 

 ature over — 239° F. in Great Britain must be in proportion to 

 the reduction of sun-heat ; and then he tells us that so vast is 

 the effect of the Gulf Stream on the temperature of Great Britain 

 that a further great lowering of temperature must follow its 

 removal. Here Dr. Croll seems to have forgotten the homely 

 proverb that you cannot eat your cake and have it. Evidently 

 he should have estimated the proportion which the winter heat 



