HALF A CENTURY AGO AND TO-DAY. 



21 



after, I was most kindly received, and furnished with details- 

 extending over twenty-five years of observation, which com- 

 pletely verified my conclusions regarding the shrinkage, not 

 only of the Mer de Glace, but of all the glaciers of the Alps of 

 Savoy. 



Mons. J. Vallot's observations of the rate of rtiotion of the ice of 

 the Mer de Glace. — This may be the place to give some account 

 of the results arrived at by this authority from his observations, 

 conducted systematically for several years regarding the- 

 movement of the ice of the Mer de Glace.* These observations- 

 were conducted between the years 1891 and 1899 in an 

 elaborate manner by using the blocks of rock lying on the 

 surface of the ice or placed in position. Taking a straight line 

 across from side to side at four stations in the following order — 

 No. 1, Echelets, the highest of the stations, 



„ 2, Montanvert, about 1,000 metres lower, 



„ 3, Mauvais-Pas, next lower down, 



„ 4, Chapeau, near the lower end, 

 M. Vallot selected, or placed in position, a line of stones on 

 which to paint the numbers 1, 2, 3, etc., from side to side ; and 

 by visiting the glacier from time to time, and measuring the 

 positions of each stone as it had advanced from the starting 

 point marked on the plan, he was able to determine its rate of 

 motion downwards and its relative rate as regards those of its 

 neighbours. This laborious process was somewhat different 

 from that adopted by Professor James Forbes with the 

 assistance of his able assistant, Auguste Balmat, many years 

 previously. But the same general result regarding the rate of 

 motion of the glacier was arrived at in both cases ; that is to 

 say, the motion is similar to that of a river flowing down it& 

 bed, which is most rapid at the centre and least at the sides.f 

 Mons. Vallot holds that the difference in the rate of movement 

 at different points is caused by the difference in the form of 

 the bed of the glacier, also its breadth, depth and its inclination. 

 This is considerable when it was found that between two points 

 one kilometre^ distant from each other, namely, between 

 Mauvais-Pas and Chapeau, the rate varied from 34*2 to 43*4 

 metres during the year 1893. The following table gives the 

 results of the observations during nine years : — 



Annates de L Ohservatoire Meteor ologique dio Mont Blanc. By J. Vallot,. 

 tomes iv, v (Paris, 1900). 



t Similar results were arrived at by Agassiz from observations on the 

 ITnteraar Glacier. 



X 1,093-6 yards. 



