E. P. Culverwell — Theory of the Ice Age. 5 



heat, will be reduced by an amount which may be estimated 

 thus : — But for the sun-heat the earth would fall to nearly the 

 absolute zero of temperature — saj^ to be on the safe side, it would 

 fall to — 239° F. (Pouillet's temperature of space). Thus in mid- 

 winter the temperature of Great Britain (about 40° F.) is kept by 

 the sun-heat about 280° F. above what we may call its natural zero. 

 Hence, roughly speaking, the decrease of 16 per cent, in the mid- 

 winter intensity of sun-heat will lower the excess of midwinter 

 temperature above the temperature of space by a proportionate 

 amount, i.e. by 45° F. (pp. 35, 37, 323). 



(D) The effect of this lowering of temperature, combined with 

 the great length of the winter, will be to increase greatly the amount 

 of the snow-fall. In his " Discussions on Climate and Cosmology," 

 he says that "a simple lowering of temperature such as would 

 secure that snow instead of rain should fall for six or eight months 

 in the year would suffice," and adds that this would follow as a 

 direct result of the increase in eccentricity ("Climate and Time," 

 pp. 57, 58; "Cosmology," p. 53). 



(E) Although the summer sun-heat will be increased just as 

 much as the winter sun-heat is diminished, it will be unable to melt 

 the additional snow, and the summers will actually be colder, not- 

 withstanding the increased sun-heat. Thus from year to year there 

 will be an accumulation of ice, which will tend to produce on the 

 northern hemisphere a state of glaciation (pp. 58-66, 69, 324). On 

 p. 67, discussing Mr. Murphy's views, Croll says : " It is not correct 

 to say that the perihelion summers of the Glacial period must have 

 been hot. There are physical reasons, as we have just seen, which 

 go to prove, notwithstanding the nearness of the sun at that season, 

 the temperature would seldom, if ever, rise above the freezing-point." 

 The physical reasons he refers to will be given in full in the criticism 

 of this argument. 



(F) As the increase of eccentricity tends to produce a state of 

 glaciation in the hemisphere whose winters are in aphelion, so 

 " exactly opposite effects take place in the other hemisphere, which 

 has its winter in perihelion. There the shortness of the winters, 

 and the highness of the temperature, owing to the sun's nearness, 

 combine to prevent the accumulation of snow " (p. 69 ; repeated 

 on p. 402). 



This is a fair outline of the direct effects of the increased 

 eccentricity on climate, as urged by Croll. We must now give his 

 answer to the question, what indirect agency is set up by this direct 

 effect? 



His Answer to Question 2. 



(G). The direct tendency of the eccentricity when the northern 

 winters are in aphelion, and the southern in perihelion, being to 

 produce a state of glaciation in the northern hemisphere and a genial 

 state in the southern, the median line between the trade winds will 

 be shifted very much to the south, and the great equatorial currents 

 of the globe would be entirely changed. The Gulf Stream would 



