Q. W. Bulman — Revised Theory of Glaciation. 263 



of a heat unit during winter, and when that season is as its longest 

 068, which gives a difference of 0*07. Now each tenth of a unit 

 corresponds to a rise or fall of 30°, and hence 0-07 corresponds to 

 ^0- of 30° or 21°. 



Our present average winter temperature may be taken as 42°, and 

 hence during the long winter it would be 21°. This would give us 

 a climate milder than that of Greenland between the 10° and 0° 

 January isotherms, since its mean winter temperature is probably 

 not more than 6° above this. 



The climate represented by this winter average of 21° may 

 perhaps be fairly compared to that of America between the 20° and 

 10° January isotherms which include the southern part of the region 

 of the Great Lakes. That such a reduction in temperature would 

 produce glaciation is not then apparent. 



Using a different method of calculation, however, I have arrived 

 at a much lower temperature for the winter of 199 days. 



Assuming, as Sir K. Ball has done, that the direct heat of the sun 

 is expended in keeping the earth above — 300°, and taking our mean 

 January temperature of 36-9° for convenience of comparison with 

 the January isotherms, we have the following calculation : 



336'9°, the temperature maintained by the direct heat of the sun 

 at present, x ief = 303°, the same when that heat is spread over 

 199 instead of 179 days. 



This gives a mean Jauuary temperature of 3°, or a mean winter 

 temperature of 9°, if we suppose this latter 6° in excess as at 

 present. 



This would probably give us the winter climate of some part of 

 that strip of Greenland before alluded to, and lying between the 

 S.E. coast and a line drawn from about Clavering Islands on the 

 east to the point where the Arctic circle cuts the west Coast. This 

 would indicate a climate like that of the above glaciated region ; 

 but is it a necessary consequence that such a winter would produce 

 perpetual snow in our latitude ? 



We must remember that the heat received during summer would 

 be the same in quantity as at present, though concentrated into 

 fewer days ; and the question to be decided is, would this heat be 

 sufficient to melt the snow of the previous winter or not? It is not 

 quite obvious that it would be, and the point seems one for careful 

 consideration and calculation. 



What, for example, would be the effect on the ice of Greenland 

 if we could transfer our summer there for a few years without 

 altering its winter ? One is inclined to suggest that a gradual 

 clearing of the country from perpetual snow and ice would take 

 place. And a comparison of the part of Greenland under consider- 

 ation with the neighbourhood of Lake Superior and Quebec which 

 lies between the same January isotherms is instructive. For while 

 the former is glaciated, the latter is not ; nor are those portions of 

 Asia south of 60° N. lat., lying between the same isotherms. And 

 the reason of this is doubtless their much hotter summers. Hence, 

 although our summer heat supply may be less than that of the above 



