60 E. P. CtikerweU — Theory of the Ice Age. 



37 — 25, or 38 and 12, for the summer and winter sun-lieats on 

 the portion of the hemisphere north of latitude 30°. This rough 

 and ready calculation is made merel}'^ to shoio hoiv far the numbers 

 63 and 37 are from any numbers ichich could be supposed to give 

 the ratios of the summer and winter sun-heats in those regions of 

 the earth with whose temperature during the long winter of great 

 eccentricity it is the business of the astronomical theory to deal. The 

 actual percentage of summer and winter sun-heat are — for lat. 50°, 

 73 and 27 (nearly 3 to 1); for lat. 60°, 82 and 18 (more than 

 4 to 1); and for lat. 70°, 91 and 9 (more than 10 to 1). How 

 greatly must the astronomical theory of the Ice Age, which is neither 

 more nor less than the theory of the temperature of these latitudes 

 during the long winter of great eccentricity, be weakened by sub- 

 stituting for these numbers the uniform ratio of 63 to 37 ! 



Again, the mode in which Sir Eobert uses these figures 63 and 37 

 to arouse in the untrained imagination the picture of a winter of 

 appalling severity is very unsafe. The argument is put on p. 135. 

 If in the period of great eccentricity " the [nearly] double supply 

 of heat [63 measures] be poured in like a torrent during the short 

 season [166 days], while the single supply of heat [37 measures] 

 is constrained to do duty over the long season [199 days], then an 

 intolerable climate is the result. The total quantity of heat received 

 on the hemisphere in the course of a year is no doubt the same in 

 each case ; but its unsuitable distribution bespeaks a climate of 

 appalling severity — an Ice Age, in fact." 



It will probably come as a surprise to most readers of this passage 

 to learn that they are even now suffering under a still more intoler- 

 able climate than this, one of far more "appalling severity." In the 

 latitude of Dublin, where the book was written, while 63 measures 

 of heat were poured in like a torrent during the 166 hottest days of 

 the year, not 37 but only 22 measures of heat are left to do duty 

 over the long period of the 199 coldest days ; that is, less than two- 

 thirds of the amount which is supposed to produce an Ice Age. In 

 fact, we have to go as far south as Madrid, Naples, or Constantinople, 

 in lat. 41°, to get the summer and winter distribution of sun-heat 

 during the 166 and 199 days in the appalling proportions of 63 

 and 37. 



Tliere are two other quantitative statements relative to alteration 

 in temperature made by Ball. The clearest is on pp. 130, 131, 

 where he deduces the result of a method of using the numbers 

 63 and 37 to obtain a numerical statement. He finds that in the 

 Ice Age the mean annual range of temperature of Great Britain 

 will be increased from its present value of 20° F. to 28° F. Surely 

 this is a reductio ad absurdum of the theory. There is hardly 

 a climate in the northern hemisphere where the range is not much 

 greater than 28° F. In latitudes 40°, 50°, and 60°, in America, the 

 ranges are 50° F., 65° F., and 75° F. respectively, but we have no 

 Ice Age there. Why should a range of 28° F. in Great Britain be 

 supposed to produce an Ice Age? The reason given is (p. 131) : 

 " It is to be observed that, generally speaking, the coldest places 



