644 Proceedings of the Royal Irish Academy. 



"We hence deduce the following where unity represents the mean 

 daily heat for the whole year on one hemisphere. 



Glaciax. 



Mean daily sun-heat in summer (short), , TSS 

 Mean daily sun-heat in winter (long), . . '68 



iNTEEaiACIAL, 



Mean daily sun-heat in summer (long), . 1-16 

 Mean daily sun-heat in winter (short), . '81 



Pkesent (Noetheen Hemisphere). 



Mean daily sun-heat in summer (186 days), 1*24 

 Mean daily sun-heat in winter (179 days), 0'75 



These figures exhibit a thermal force of great intensity. The unit 

 represents all the mean- daily heat received fi'om the sun by which the 

 earth is warmed up from the temperature of space. The heat unit in 

 fact maintains a temperature perhaps 300°, or even more, above what 

 the earth would have without that heat. Each tenth of a unit may 

 thus roughly be said to correspond to a rise or fall of mean tempera- 

 ture of 30° or more. The long winter of ] 99 days, when the average 

 heat is only two-thirds of a unit, leads to the accumulation of ice and 

 snow, which form the glacial epoch. The short winter of 166 days, 

 where the temperature is "06 of a unit above that of our present 

 winter, presents the condition necessary for the mild interglacial 

 epoch. 



