Mr. J. Ball on a doubtful point in Climatology. 365 



account for the change of temperature in Greenland and in the 

 northern part of Baffin's Bay. 



But then comes the question, how it is possible to reconcile 

 this extension of ice and snow in certain regions with the 

 general constancy of the mean temperature of the earth, which 

 may be inferred from historical evidence proving that the limits 

 of cultivation of the best known vegetable products have not 

 perceptibly altered for the last 3000 years, or even a much 

 longer period. If no cosmical causes have interfered to alter 

 the annual supply of heat received by the earth, and if no im- 

 portant change has occurred in the distribution of land and sea, 

 it may be thought impossible that any reduction should occur in 

 the general ^nean temperature, such as would be implied in the 

 asserted cooling down of some districts, without a corresponding 

 increase of temperature elsewhere. To this I venture to reply, 

 that the increase of alpine glacier and polar ice does imply an 

 increase of mean temperature in those spots where the accumulation 

 originates. To return to the Alps from whence I started, I assert 

 that a reservoir wherein the annual deposit of snow exceeds the 

 annual melting and outflow, must have a mean temperature 

 below the freezing-point, that before the rock or soil was con- 

 stantly covered with snow or ice its mean temperature must 

 have been still lower, and that the result of the accumulation is 

 to raise that mean temperature. 



To illustrate this, let us suppose that, instead of the intense 

 dryness that prevails in the frigid regions of northern Siberia, 

 between the Lena and the Jenisei, the prevalence of moist winds 

 should determine a great annual fall of snow, we cannot doubt 

 but that an enormous accumulation of neve and ice would pro- 

 ceed for ages until a condition was produced similar to that of 

 the antarctic polar lands, the mean temperature of the region 

 itself would be considerably increased, while that of some neigh- 

 bouring districts would be diminished, the general mean for the 

 whole earth and for countries not within reach of the immediate 

 operating causes remaining unaltered. 



Not having seen this question anywhere satisfactorily discussed, 

 I have offered these somewhat crude considerations to the exa- 

 mination of those interested in its decision, and have the honour 

 to remain, Gentlemen, 



Your obedient Servant, 



John Ball. 



