48 MR JOHN AITKEN ON DEW. 



surface ; whereas when there is no snow, the air rests on a warmer 

 one. 



Taking then these two things together, the bad absorbing power of snow 

 and its small conducting power for heat, we see that when snow has once got 

 possession of a land, the tendency to glacial conditions is greatly increased ; 

 and if it were not for the disturbing effects of heat in warmer climates, 

 it is hard to say how far glacial conditions might spread towards the 

 equator. 



Up to the time when the previous part of this paper was given in* I had 

 been unableto find records of any meteorolgical station at which the condition 

 of the ground with regard to snow had been recorded in addition to the usual 

 temperature observations ; even yet I have not succeeded in getting suitable 

 records for our climate, and one cannot help regretting that observations of 

 this kind are not more frequently kept in this country. 



My conclusions, however, with regard to the effect of snow on climate, I 

 now find are confirmed by the observations of Dr Woeikof, an abstract of 

 whose work in this direction has just appeared in Nature of 18th February 1886 

 (vol. xxxiii. p. 379). Dr Woeikof has approached the subject from the observa- 

 tional side, and as his results bear directly on ours, I shall quote the following- 

 paragraph from the abstract referred to : — 



"The year 1877 was a striking instance of how the absence of snow was 

 accompanied by a far less notable lowering of temperature during the preval- 

 ence of anticyclones, than would have been the case had the soil been covered 

 with snow. In 1877 there was no snow in Eastern Russia until Christmas, and 

 in November and December the anticyclones occurred, accompanied by no 

 wind, or only by feeble breezes. Quite bright weather lasted in December for 

 more than ten days ; and still, in the region which remained uncovered with 

 snow, no great cold was experienced, as usually happens in such circum- 

 stances; the minima were 8° to 9° above their average values. The same 

 conditions were noticed during the winters of 1879-80 and 1881-82 in West 

 Europe, as shown by Dr Billwiller in the Zeitschrift fur Meteorologie for 

 1882." 



In the next paragraph, the abstract states that, in the opinion of Dr 

 Woeikof, the higher temperature of November, as compared with March in 

 South-East Russia, is due to the ground not being usually covered with snow 

 in November. 



These observations of Dr Woeikof confirm the conclusions arrived at in this 

 paper from a consideration of the properties of snow. In the opinion of Dr 

 Woeikof, the low temperature accompanying the snow is to be attributed 

 to its bad conducting power. While we quite agree with the observer 



* Note added 26th February 188G. 



