338 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



mm mm 



respectively 791.46 and 761.12 ; but these again were preceded by two pen- 

 tads when the mean precipitation was also considerably above the average. 

 For convenience the figures are here introduced for each pentad from 1826 

 to 1875. 



Pentads. Precipitation. 



mm 



1826-30 818.02 



1831-35 724.10 



1830-40 791.48 



1841-45 945.40 



1846-50 848.74 



1851-55 848.92 



1856-60 791.46 



1861-65 761.12 



1866-70 815.62 



1871-75 814.40 



mm 



Mean 1826-75 815.93 



These fifty years begin, according to the best informed observers, just 

 about the time when the decrease of the glaciers of Switzerland began to be 

 noticed. " Le glacier des Bossons a commence a reculer en 1818, la Mer de 

 Glace en 1827, le glacier d'Argentiere en 1820; (?) et celui du Tour en 1821."* 

 This shrinking has gone on ever since with slight oscillations ; on the whole, 

 however, increasing in rapidity, if decrease in length of the glacial masses 

 is to be taken as a standard of diminishing force. But during this time 

 Switzerland has had several periods of dryness and several of increased 

 precipitation, the last two pentads — as before remarked — Avhen the recession 

 of the glaciers was certainly not diminishing in amount, exhibiting an average 

 almost exactly equal to that of the grand mean of the fifty years. 



Classing the years in four categories — namely, as '• very dry," "dry," 

 "wet," and "very wet" — Plantamour obtains the following results for the 

 order in which they have succeeded each other : — 



YEARS. 



Very dry. Dry. Wet. Veiy wet. 



12 years, 1826-37 5 3 4 



19 years, 1838-56 1 4 7 7 



9 years, 1857-65 5 1 2 1 



The last ten years, 1866-75, show no predominance either wa}', as they 



* Annuaire du Club Aljiiu Franyais, 1S76, p. 573. 



