112 • On the Down ward Progress 



The glaciers we have mentioned, are situate at points wide- 

 ly remote from each other ; some form part of the group of 

 the Jungfrau, others of the group of Mont Rosa, the last of 

 the group of Mont Blanc. Some run from south to north, 

 others from north to south, others from east to west. All 

 are included within the parallels of 45° 45', and 46° 35' north. 

 Some are protected by superficial moraines, in others these 

 are insignificant. 



Must we conclude from these facts, that we are advancing 

 towards a slow and continuous sinking of the mean tempera- 

 ture of our hemisphere ? Tliis conclusion would be prema- 

 ture ; it would be opposed to the recent and skilful observa- 

 tions of MM. Dureau and Malle on the Comparative Glimatology 

 of Ancient and Modern Italy, — observations intended to prove, 

 that " since the age of Augustus up to the present period, 

 the climate of Italy has undergone no sensible modifications 

 in the annual, and even monthly, mean temperature."* MM. 

 Dureau and Malle having assured themselves, that " in re- 

 gard to the same places and the same altitudes, the periods 

 of sowing, flowering, mowing, harvest, ripening, and vintage, 

 were almost the same in ancient as tliey are in modern Italy, 

 we think we have it in our power to deduce the duration of 

 the cycle in which the complete work of annual vegetation 

 took place, and to obtain from it the proof of the constancy 

 of the climate of Italy during twenty centuries." -f- 



MM. Dureau and Malle have taken their examples from ve- 

 getation. It is indeed immediately dependent on meteorolo- 

 gical causes ; it may give valuable indications respecting cli- 

 matology, thermometrical means, and the secular changes 

 which take place in the ambient medium. 



But glaciers are not to be overlooked ; they ought to enter 

 as a considerable element into the solution of the question ; 

 their advancing or retrograde movements depend on the same 

 atmospheric causes. It has been said of glaciers, that they 

 may be compared to gigantic natural thermometers ; in cold 

 and moist years tl.ey descend into the valleys, in warm sea- 

 sons they ascend towards the snowy peaks. 



* Oomptes Ueiidus de I'Acad. des Sciences, t. xxvii., p. 356. t Ibid., p. 333. 



