350 ON MOUNTAINS AND MANKIND. 



required measurements of retreat or advance in the glacial snout, 

 when the glacier is situated in a remote and only casually visited 

 region. Still, with good will more might be d(me than has been. 

 The periods of ad\ance and retreat of glaciers appear to correspond 

 to a certain extent throughout the globe. The middle of the last 

 century was the culmination of the last great advance. The general 

 estimate of their duration appears to be half a century. The ice is 

 now retreating in the Alps, the Caucasus, and the Himalaya, and 

 I believe in North America. AYe live in a retrogressive period. The 

 minor oscillation of ad^'ance Avhich a few years ago gave hopes to 

 those who, like myself, had as children seen the glaciers of (irindel- 

 wald and Chamonix at their greatest, has not been carried on. 



Attempts are being made to connect the oscillations of glaciers Avith 

 periods of sun spots. They are, of course, connected with the rain or 

 snow fall in past seasons. But the difficulty of working out the con- 

 nection is obvious. 



The advance of the ice will not begin until the snows falling in its 

 upper basin have had time to descend as ice and become its snout. In 

 each glacier this period will vary according to its length, bulk, and 

 steepness, and the longer the glacier is the slower its lower extremity 

 will be to respond. Deficiency in snowfall wall take effect after the 

 same period. It wall be necessary, therefore, to ascertain (as has been 

 done in a tragic manner on Mont Blanc by the recovery in the lowest 

 portion of the Glacier des Bossons of the bodies of those lost in its 

 highest snows) the time each glacier takes to travel, and to apply 

 this interval to the date of the year with which the statistics of deposi- 

 tion t)f moisture are to be compared. If the glacier shows anything 

 about weather and climate, it is past not contemi)()rary Aveather it 

 indicates. 



Another point in which the Asiatic ranges, and particularly the 

 Himalaya, differ from the Alps is in the frequency of snow ava- 

 lanches, earth falls, and nnul slides. These are caused by the greater 

 deposition of snow^ and the more sudden and violent alternations of 

 heat and cold, which lead to the splitting of the hanging ice and 

 snows by the freezing of the water in their pores. T have noticed 

 at a bivouac that the moment of greatest cold — about the rising 

 of tlie morning star — is often hailed by the reports of a volley of 

 avalanches. 



The botanist nuiy find much to do in working out a comparison of 

 the flora of my four ranges. I am no botanist; I value flowers ac- 

 cording, not to their rarity, but to their abundance, from the artist's, 

 not the collector's, i)oint of view. But it is impossible not to take 

 interest in such matters as the variations of the gentian in different 

 regions, the behaxior of such a plant as the little edelweiss (once the 

 token of the Tyrolese lover, now the badge of every Alp trotter). 



